KITS FOR DETECTING AND MONITORING ENDOCRINE DISRUPTING CHEMICALS (EDCs)
Described herein are compositions, methods, a system, and kits for detection of endocrine disruptor chemicals (EDCs) in environmental and other samples, such as samples of water including but not limited to waste water treatment plant effluent, using a live-cell fluorescence-based nuclear translocation reporter system. Upon binding of a ligand to a fluorescent-labeled reporter protein, the protein (and therefore the fluorescence) is translocated in a ligand level-dependent manner from the cytoplasm to the nucleus of live mammalian cells; this translocation is detectable as diffuse (cytoplasmic) fluorescence converting to localized, brightly fluorescent nuclei. The described methods, kits and system can be used to reliably detect very low levels of EDC contamination, including in high throughput analysis systems as described.
This application claims the benefit of the earlier filing date of U.S. Provisional Application No. 61/656,473, filed Jun. 6, 2012, which is incorporated herein in its entirety.
FIELDThis disclosure relates to methods, systems and kits for monitoring, detecting and/or measuring chemicals, such as endocrine disruptor chemicals, in environmental and other samples. This disclosure further relates to genetically engineered constructs that encode traceable fusion proteins that translocate from the cytoplasm to the nucleus in the presence of an endocrine disrupting chemical, and mammalian cells expressing one or more of such constructs.
BACKGROUNDAn endocrine disruptor chemical (EDC) is an exogenous substance that impacts at least one function of an animal's endocrine system and consequently causes adverse health effects in an intact organism, its progeny, or (sub)populations. EDCs can cause adverse biological effects in animals and humans (Diamanti-Kandarakis et al., Horm. Metab Res 42:543-552, 2010).
Contamination of the environment, particularly water sources, with EDCs is a major concern for human health and threatens the integrity of aquatic ecosystems (Diamanti-Kandarakis et al., Endocr. Rev. 30:293-342, 2009; Deblonde et al., Int. J Hyg. Environ. Health 214:442-448, 2011). Harmful effects of synthetic progestogens (Zeilinger et al., Environ. Toxicol. Chem. 28:2663-2670, 2009; Paulos et al., Aquat. Toxicol. 99:256-262, 2010) and especially of estrogenic water contaminants (Iwanowicz et al., Environ. Toxicol. Chem. 28:1072-1083, 2009; Alvarez et al., Environ. Toxicol. Chem. 28:1084-1095, 2009; Caldwell et al., Environ. Sci. Technol. 42:7046-7054, 2008; Lange et al., Environ. Toxicol. Chem. 20:1216-1227, 2001; Blazer et al., Environ. Monit. Assess. DOI 10.1007/s10661-011-2266-5, 2011) on fish reproduction are well documented. In addition, there is growing concern that environmental contamination with EDCs has deleterious effects on human reproduction, breast development and cancer, prostate cancer, neuroendocrinology, thyroid metabolism and obesity, and cardiovascular endocrinology (Diamanti-Kandarakis et al., Endocr. Rev. 30:293-342, 2009).
Glucocorticoids act through the glucocorticoid and mineralocorticoids receptors (GR and MR, respectively). Glucocorticoid deficiency is associated with a number of complex symptoms and is a life-threatening condition (Arlt & Allolio, Lancet 361:1881-1893, 2003). Naturally occurring glucocorticoids are released in mammalian organisms during the circadian cycle. However, excess exposure to glucocorticoids is associated with immune suppression and variety of other deleterious side effects (Schacke et al., Pharmacol. Ther. 96:23-43, 2002). Unoccupied glucocorticoid receptor resides in the cytoplasm and is bound to various heat-shock proteins and immunophilins in a large multi-protein complex (Pratt & Toft, Endocr. Rev. 18:306-360, 1997; Pratt et al., Handb. Exp. Pharmacol. 172:111-138, 2006). Upon hormone binding, GR dissociates from the chaperones and translocates to the cell nucleus, where it interacts with GR regulatory elements (GREs) and elicits GR-specific transcription regulation (John et al., Mol. Cell 29:611-624, 2008).
At present, nothing is known about the prevalence of GCs activity in US water sources. However, using chemical methods, a few reports on water contamination in the Netherlands and China have demonstrated detectable levels of glucocorticoids (Schriks et al., Environ. Sci. Technol. 44:4766-4774, 2010; Change et al., Environ. Sci. Technol. 41:3462-3468, 2007). Another recent study has demonstrated that environmentally relevant concentrations of synthetic GCs have deleterious effects on fish (Kugathas & Sumpter, Environ. Sci. Technol. 45:2377-2383, 2011). The anti-inflammatory properties of the glucocorticoids make them highly prescribed pharmaceuticals. They could readily enter water sources and there are few sparse reports on water contamination with glucocorticoids (Schriks et al., Environ. Sci. Technol. 44:4766-4774, 2010; Chang et al., Environ. Sci. Technol. 41:3462-3468, 2007). Moreover, waste water treatment plants (WWTP) are not capable of efficiently removing glucocorticoids; it is well documented that anti-inflammatory chemicals are among the most resistant to treatment (30-40% of removal rate).
In spite of their importance, the levels of EDCs, such as steroidal EDCs, in the environment currently are not efficiently monitored and/or regulated. One of the reasons is that no high-throughput, reliable, low-cost detection methods exist for monitoring of biologically active EDCs. Current EDC detection relies on chemical analysis techniques (e.g., mass spectrometry, HPLC, GC, and other purely chemical analytical procedures), in vitro biologically-based but cell-free analysis techniques (e.g., purified receptor binding assays and immunoaffinity chromatography), in vitro cell-based analyses (e.g., cell proliferation assays and receptor-dependent gene expression assays, in human cells, or engineered yeast or bacterial cells), and in vivo analyses (e.g., uterotrophic and other growth/development assays in live rats or other animals). It is crucial to develop and implement novel high-throughput and low-cost methods for detection of EDCs in the environment. The need of such methods is well recognized in the field (Roy et al., J. Exp. Biol. 43:975-992, 2005). Existing methods for EDC detection may be sensitive, and in some instances are specific for individual ligands, but in general they are expensive, time-consuming, and largely incompatible with a large-scale sample testing.
SUMMARYDescribed herein are methods, systems and kits for monitoring, detecting and/or measuring EDCs in environmental and other types of samples. These methods, systems and kits employ live mammalian (for instance, human) cells engineered to express at least one traceable fusion protein that changes its sub-cellular localization, for example translocates from the cytoplasm to the nucleus of the cell in the presence of an EDC. Specifically provided are cells and kits that detect more than one EDC, more than one class of EDC, and in some examples an array of EDCs simultaneously. Also provided are methods, systems and kits tailored for high throughput detection (and optionally quantification) of EDCs in environmental samples, such as water samples.
Provided herein in a first set of embodiments are systems for detecting or quantifying a ligand (e.g., an agonist or an antagonist) of a superfamily receptor protein in an environmental sample. In examples thereof, the system comprises a first mammalian cell expressing a first traceable fusion protein; a second mammalian cell expressing a second traceable fusion protein; and a detection system for the detection of the cytoplasm-to-nuclear translocation of the marker proteins, wherein the first and second traceable fusion proteins independently comprise either: (1) a superfamily receptor protein, and a marker protein domain; or (2) the cytoplasmic/nuclear translocation domain of glucocorticoid receptor, the ligand binding domain of a superfamily receptor protein, and a marker protein domain. Optionally, the mammalian cells are human cells.
Also described are systems for detecting or quantifying a ligand of a superfamily receptor protein in an environmental sample, wherein the ligand for the first or second traceable fusion protein is a natural ligand for the superfamily receptor protein of the traceable fusion protein, or a natural or synthetic compound that binds competitively therewith.
Also provided are systems for detecting or quantifying a ligand of a superfamily receptor protein in an environmental sample that additionally comprise one or more compounds and/or compositions that stably associate with a traceable fusion protein in the absence of a ligand for the ligand binding domain of the traceable fusion protein, and which dissociates from the fusion protein in the presence of a ligand for the ligand binding domain of the traceable fusion protein.
The systems described herein are optionally provided as kits.
Also described are methods for detecting or quantifying an endocrine disruptor chemical (EDC) ligand in an environmental sample, which methods involve contacting with the environmental sample a human cell expressing in its cytoplasm a fusion protein comprising: a receptor for the ligand, which receptor translocates from the cytoplasm to the nucleus upon ligand binding; and a marker protein domain; and then detecting cytoplasmic to nuclear translocation of the fusion protein in response to a ligand of the ligand binding domain in the water sample.
Additional described methods of determining the concentration of an endocrine disruptor chemical (EDC) ligand in an environmental sample involve contacting with the environmental sample a population of eukaryotic cells expressing in their cytoplasm a fusion protein comprising: a receptor for the ligand, which receptor translocates from the cytoplasm to the nucleus upon ligand binding; and a marker protein domain; and scanning one or more test cell(s) to obtain signal data from the marker of the fusion protein; converting the signal data to obtain the cellular location of the labeled protein in the test cell(s); and analyzing the signal data using an analysis system having an algorithm to calculate changes in distribution of the labeled fusion protein between the cytoplasm and the nucleus of the test cell(s), the analysis system having the capability of providing an accurate reading of the concentration of the ligand.
In any of the systems, kits, and methods described herein, the environmental sample can include a water sample, soil sample, or air sample. By way of example, where the environmental sample comprises a water sample, the sample includes in various embodiments one or more of surface water, sub-surface (ground) water, rain, run-off, well water, spring water, drinking water (processed or not), river water, estuary water, ocean water, effluent, treated sewage or untreated sewage.
Without limitation, the systems, methods and kits provided herein may use or include any cellular receptors including the following (generically termed) traceable fusion proteins: GFP-GR, GFP-AR, GFP-AhR, GFP-PR-B, GFP-GR-ER, GFP-GR-RAR, GFP-MR, and GFP-GR-TR, as well as fusion(s) in which the GFP is replaced with a different fluorescent domain that emits light at a different wavelength. By way of specific example, contemplated herein for use (singly or in combinations of two or more) in the described systems, methods and kits are the following traceable fusion proteins: eGFP-GR-ER310 (SEQ ID NOs: 1 & 2); eGFP-GR-TR216 (SEQ ID NOs: 3 & 4); pCI-nGFP-C656G (SEQ ID NOs: 5 & 6); eGFP-hAR (SEQ ID NOs: 7 & 8); pRefTRE-GFP-mAhR (SEQ ID NOs: 9 & 10); eGFP-ratMP (SEQ ID NO: 11 & 12); and/or eGFP-hPRB (SEQ ID NOs: 13 & 14).
The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.
The nucleic and amino acid sequences listed in the accompanying sequence listing are shown using standard letter abbreviations for nucleotide bases, and three letter code for amino acids, as defined in 37 C.F.R. 1.822. Only one strand of each nucleic acid sequence is shown, but the complementary strand is understood as included by any reference to the displayed strand. The Sequence Listing is submitted as an ASCII text file named Sequences.txt, created on Jun. 5, 2013, ˜100 KB, which is incorporated by reference herein.
SEQ ID NO: 1 is the nucleic acid sequence which encodes traceable fusion protein eGFP-GR-ER310. The sequence includes the following features at the indicated nucleotide positions: EGFP (1-717), GA Linker (718-747), hGR (748-2400), and hER (2401-3261).
SEQ ID NO: 2 is the amino acid sequence of traceable fusion protein eGFP-GR-ER310. The sequence includes the following features at the indicated amino acid positions: EGFP (1-239), GA Linker (240-249), hGR (250-800), and hER (801-1086).
SEQ ID NO: 3 is the nucleic acid sequence which encodes traceable fusion protein eGFP-GR-TR216. The sequence includes the following features at the indicated nucleotide positions: EGFP (1-717), GA Linker (718-747), hGR (748-2400), and hTR (2401-3141).
SEQ ID NO: 4 is the amino acid sequence of traceable fusion protein eGFP-GR-TR216. The sequence includes the following features at the indicated amino acid positions: EGFP (1-290), GA Linker (240-249), hGR (250-800), and hTR (801-1046).
SEQ ID NO: 5 is the nucleic acid sequence which encodes traceable fusion protein pCI-nGFP-C656G. The sequence includes the following features at the indicated nucleotide positions: 6X His tag (8-24), HA Tag (28-59), GFP (60-780), GA Linker (781-810), and Rat
GR (829-3213), containing within it the C656G mutation (single point mutation T->G, codon changes from TGC->GGC) (2791; underlined & bold)
SEQ ID NO: 6 is the amino acid sequence of traceable fusion protein pCI-nGFP-C656G. The sequence includes the following features at the indicated amino acid positions: 6X His tag (3-8), HA Tag (10-18), GFP (23-260), GA Linker (261-270), and Rat GR (277-1070), containing within it the C656G mutation (Cysteine to Glycine) (931; underlined & bold).
SEQ ID NO: 7 is the nucleic acid sequence which encodes traceable fusion protein eGFP-hAR. The sequence includes the following features at the indicated nucleotide positions: EGFP (1-717), Vector polylinker (718-752), and hAR (753-3516).
SEQ ID NO: 8 is the amino acid sequence of traceable fusion protein eGFP-hAR. The sequence includes the following features at the indicated amino acid positions: EGFP (1-239), Vector polylinker (240-251), and hAR (252-1171).
SEQ ID NO: 9 is the nucleic acid sequence which encodes traceable fusion protein pRevTRE-GFP-mAhR. The sequence includes the following features at the indicated nucleotide positions: 6X His tag (8-27), HA Tag (28-58), GFP (59- 780), GA Linker (781- 810), and mouse AhR (829-3243).
SEQ ID NO: 10 is the amino acid sequence of traceable fusion protein pRevTRE-GFP-mAhR. The sequence includes the following features at the indicated nucleotide positions: 6X His tag (3-8), HA Tag (9-18), GFP (23-260), GA Linker (261-270), and Mouse AhR (277-1080).
SEQ ID NO: 11 is the nucleic acid sequence which encodes traceable fusion protein eGFP-ratMR. The sequence includes the following features at the indicated nucleotide positions: EGFP (1-717), Vector polylinker (718-732), and rat MR (733-368).
SEQ ID NO: 12 is the amino acid sequence of traceable fusion protein EGFP-rMR. The sequence includes the following features at the indicated nucleotide positions: EGFP (1-239), Vector polylinker (240-244), and rat MR (245-1225).
SEQ ID NO: 13 is the nucleic acid sequence which encodes traceable fusion protein eGFP-hPRB. The sequence includes the following features at the indicated nucleotide positions: eGFP (1-714), GA Linker (715-744), and hPRB (757-3555).
SEQ ID NO: 14 is the amino acid sequence of traceable fusion protein eGFP-hPRB. The sequence includes the following features at the indicated and nucleotide positions: EGFP (1-238), GA Linker (239-248), and hPRB (253-1184).
SEQ ID NOs: 15-28 are primer sequences used for Q-PCR analysis, as follows:
AhR aryl hydrocarbon receptor
AR androgen receptor
ATRA all-trans retinoic acid
CAR constitutive androstane receptor
cst corticosterone
dex dexamethasone
ER estrogen receptor protein (α, β)
ERR estrogen-related receptor (α, β, γ)
FP fluorescent protein
FXR farnesoid X receptor
GCNF germ cell nuclear factor
GFP green fluorescent protein
GFP-AhR chimera w/aryl hydrocarbon receptor and GFP
GFP-AR chimera w/androgen receptor and GFP
GFP-GR chimera w/GR (or GR*) and GFP (also, GR-GFP)
GFP-GR-ER chimera w/ GR translocation domain, estrogen receptor, and GFP
GFP-GR-RAR chimera w/GR translocation domain, retinoic acid receptor, and GFP
GFP-GR-TR chimera w/GR translocation domain, thyroid hormone receptor, and GFP
GFP-PR-B chimera w/GR translocation domain, progesterone B receptor, and GFP
GR glucocorticoid receptor
GR* modified GR with increased ligand binding affinity
HNF4 hepatocyte nuclear factor-4 (α, γ)
Hsp heat shock protein
LBD ligand binding domain (of a receptor protein)
LCA lithocholic acid
LRH-1 liver receptor homolog-1
LTR long terminal repeat
LXR liver X receptor (α, β)
MR mineralocorticoid receptor
MMTV mouse mammary tumor virus
NF1 nuclear factor 1
NHRs nuclear hormone receptors
OTF1 octomer transcription factor 1
POCIS polar organic chemical integrative samplers
PPAR peroxisome proliferator-activated receptor (α, β/δ, γ)
PR progesterone receptor
PXR pregnane X receptor
RAR retinoic acid receptor
ROR RAR-related orphan receptor (α, β, γ)
RXR retinoid-X receptor (α, β, γ)
SF1 steroidogenic factor 1
SHP small heterodimer partner
SRC1 steroid receptor coactivator 1
TR thyroid hormone receptor (α, β)
T3 triiodothyronine
T4 thyroxine
UDCA ursodeoxycholic acid
VDR vitamin D receptor
WWTP waste water treatment plant
Unless otherwise noted, technical terms are used according to conventional usage. In order to facilitate review of the various embodiments of the invention, the following explanations of specific terms are provided:
Cell-based System: A system based employing live cells derived, isolated, or otherwise acquired from a living organism. This term includes, for example, a cell culture.
Chimera/Chimeric: A recombinant nucleic acid molecule generated by cloning portion(s) of one or more nucleic acid sequence(s) in-frame to one or more other nucleic acid sequence(s) to produce a single nucleic acid sequence capable of being transcribed into a polypeptide. A polypeptide expressed from such a nucleic acid sequence chimera is referred to as a “chimeric protein” or “protein chimera”.
Contacting: To place in direct physical association, including in solid or in liquid form. Contacting can occur in vivo, for example by administering an agent to a subject, or in vitro for example with isolated cells or cell-cultures.
Control: Samples believed to be normal (e.g., representative of an activity or function in the absence of the variable being tested), as well as laboratory values, even though possibly arbitrarily set, keeping in mind that such values can vary from laboratory to laboratory. A control sample or group is practically identical to the test sample or group, except for the variable(s) of interest the effect of which is being tested, which is only applied to or found in the test group. A difference between a test sample and a control can be an increase or a decrease. The difference can be a qualitative difference or a quantitative difference, for example a statistically significant difference. In some examples, a difference is an increase or decrease, relative to a control, of at least about 10%, such as at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 100%, at least about 150%, at least about 200%, at least about 250%, at least about 300%, at least about 350%, at least about 400%, at least about 500%, or greater than 500%.
Detect: To determine if an agent (such as a bacterium) is present or absent. In some examples this can further include quantification. For example, use of the disclosed methods permits detection of one or more target bacterium, such as by flow cytometry or fluorescence microscopy. Detection can be in bulk, so that a macroscopic number of molecules can be observed contemporaneously or simultaneously. Detection can also include detection of single events, such as a single bacterium.
Emission or emission signal: The light of a particular wavelength generated from a source. In particular examples, an emission signal is emitted from a fluorophore, such as a fluorescent protein, after the fluorophore absorbs light at its excitation wavelength(s).
Environmental sample: A sample obtained from the environment, for instance a water sample (e.g., of surface, sub-surface (ground), rain, run-off, well, spring, drinking, river, estuary, ocean, effluent, treated or untreated sewage, etc. water), soil sample (including soil samples that contain water), air sample, or a sample of another substance.
Excitation or excitation signal: The light of a particular wavelength necessary and/or sufficient to excite an electron transition to a higher energy level. In particular examples, an excitation is the light of a particular wavelength necessary and/or sufficient to excite a fluorophore, such as a fluorescent protein, to a state such that the fluorophore will emit a different (such as a longer) wavelength of light then the wavelength of light from the excitation signal.
Fluorescent property: A characteristic of a fluorescent molecule, such as a fluorescent protein, for example green fluorescent protein, red fluorescent protein, yellow fluorescent protein, cyan fluorescent protein and the like. Examples of fluorescent properties include the molar extinction coefficient at an appropriate excitation wavelength, the fluorescence quantum efficiency, the shape of the excitation spectrum or emission spectrum (the “fluorescence spectrum,” the excitation wavelength maximum and emission wavelength maximum, the ratio of excitation amplitudes at two different wavelengths, the ratio of emission amplitudes at two different wavelengths, the excited state lifetime, or the fluorescence anisotropy. Quantifying fluorescence refers to the determination of the amount of fluorescence generated by a fluorophore, for example a fluorescent protein, which can be the quantity of photons emitted by a fluorophore. In some examples, fluorescence is quantified by measuring the intensity of a fluorescence signal at a particular wavelength, for example the wavelength of the emission maxima of a particular fluorophore, such as a fluorescent protein. Fluorescence intensity can also be quantified at a wavelength that is not the emission maxima of a particular fluorophore, for example to avoid emission spectra that overlap and thereby interfere with the emission maxima of a particular fluorophore, such as a particular fluorescent protein. In some examples, a fluorescence signal is emitted by a population of fluorescent proteins, for example fluorescent proteins present in a population of cells containing such fluorescent proteins. Such a signal can be quantified, for example to determine the number, or relative number of cells that emit such a fluorescent signal. Detecting a pattern of fluorescence refers to the correlation of a fluorescent signal to a specific location to determine the location where a fluorescence signal, such as a fluorescent signal of a particular wavelength, originates. In some examples, a pattern of fluorescence determines the location and or shape of the cells that emit a fluorescence signal, such as cells containing a fluorescent protein, including for example to sub-cellular localization of the fluorescent protein (e.g., cytoplasmic or nuclear) as well as the absolute or relative quantitative distribution between sub-cellular compartments and organelles.
Fluorescent protein: A protein capable of emission of a detectable (and therefore traceable) fluorescent signal. Fluorescent proteins can be characterized by the wavelength of their emission spectrum. For example, wildtype green fluorescent protein (GFP) has a fluorescent emission spectrum in the green part of the visible spectrum. In addition to green-fluorescent proteins, fluorescent proteins are well known that fluoresce in other regions of the visible spectrum, for example blue-fluorescent proteins, cyan-fluorescent proteins. yellow-fluorescent proteins, orange-fluorescent proteins. red-fluorescent proteins, and far-red fluorescent proteins. Non-limiting examples of fluorescent proteins can be found in the following patent documents: U.S. Pat. Nos. 5,804,387; 6,090,919; 6,096,865; 6,054,321; 5,625,048; 5,874,304; 5,777,079; 5,968,750; 6,020,192; 6,146,826; 6,969,597; 7,150,979; 7,157,565; and 7,166,444; and published international patent applications WO 07/085923; WO 07/052102, WO 04/058973, WO 04/044203, WO 03/062270; and WO 99/64592. Additional examples of fluorescent proteins are available from Clontech, Laboratories, Inc. (Mountain View, Calif.) under the trade name Living Colors®. Nucleic acids encoding such fluorescent proteins can be incorporated into mammalian expression vectors for use in producing the disclosed fluorescent traceable proteins and fluorescent cell-lines.
Fusion protein: Proteins that have at least two domains fused together, at least one domain comprising traceable (marker) feature (such as a fluorescent protein domain) and another domain or set of domains that provides translocation of the fusion protein from one cellular compartment or organelle to another in a cell in which it is expressed upon the specific binding of a ligand (EDC) to the fusion protein. Optionally the translocation and ligand binding features may be provided from the same source protein (e.g., in a GFP-GR traceable translocation fusion protein). In other embodiments, the translocation and ligand binding features are provided from two different source proteins (thus making a “chimeric receptor” portion of the fusion protein), such that the resultant traceable translocating fusion protein contains domains or subdomains from at least three different source proteins. An example of such a three-component fusion protein is the GFP-GR-ER protein which contains GFP, translocating features of or derived from GR, and the ligand binding domain of an estrogen receptor.
In general, the domains of the disclosed fusions are genetically fused together, in that nucleic acid molecules that encode each protein domain (or subdomain) are functionally linked together, for instance directly or through the use of a linker oligonucleotide, thereby producing a single fusion-encoding (chimeric) nucleic acid molecule. The translated product of such a fusion-encoding (chimeric) nucleic acid molecule is the traceable translocating fusion protein.
High throughput technique: A fast, automated or semi-automated analysis process, for instance to analyze many samples at once in order to detect or measure the presence (or absence) of a substance. In certain examples, combining modern robotics, data processing and control software, liquid handling devices, and sensitive detectors, high throughput techniques allows the rapid screening of many (e.g., hundreds or thousands) samples in a short period of time and often in a highly parallel manner.
Traceable marker protein domain: A protein domain that is detectable based on its inherent structural or functional characteristics, such as fluorescence.
Nuclear hormone receptor family: Nuclear hormone receptors (NHRs) function as ligand-activated transcription factors and have roles in diverse cellular processes ranging from mammalian development and differentiation to metabolic homeostasis (Mangelsdorf et al., Cell, 83(6):835-839, 1995; Adams et al., Science, 287:2185-2195, 2000). NHRs bind to sequence-specific DNA response elements on target gene promoters as homodimers, heterodimers, or monomers. Structural and functional analyses of the NHR family have demonstrated that the receptors are comprised of functional modular domains. The DNA binding domain (DBD) consists of a well characterized zinc finger motif which recognizes a degenerate six to eight nucleotide sequence on the target DNA. The ligand binding domain (LBD) resides in the C-terminal portion of the protein and shares a common, predominantly alpha helical fold (Mangelsdorf et al., Cell, 83(6):835-839, 1995). As implied, this domain of the receptor is where cognate ligands of the receptors interact and induce conformational changes associated with transcriptional activation. Many of the known ligands for these receptors are essential metabolic products including retinoids, thyroid hormone, vitamin D3, bile acids, oxysterols, and prostenoids that act through their cognate receptors to control metabolic homeostasis in the body (Gudas, J. Biol. Chem., 269(22):15399-15402, 1994). In addition, NHRs are also instrumental in the ability of the body to respond to and adapt to complex environmental cues.
Nucleic acid: A polymer composed of nucleotide units (ribonucleotides, deoxyribonucleotides, related naturally occurring structural variants, and synthetic non-naturally occurring analogs thereof) linked via phosphodiester bonds, related naturally occurring structural variants, and synthetic non-naturally occurring analogs thereof. Non-naturally occurring synthetic analogs include, for example and without limitation, phosphorothioates, phosphoramidates, methyl phosphonates, chiral-methyl phosphonates, 2-O-methyl ribonucleotides, peptide-nucleic acids (PNAs), and the like. Such polynucleotides can be synthesized, for example, using an automated DNA synthesizer. The term “oligonucleotide” typically refers to short polynucleotides, generally no greater than about 50 nucleotides. It will be understood that when a nucleotide sequence is represented by a DNA sequence (i.e., A, T, G, C), this also includes an RNA sequence (i.e., A, U, G, C) in which “U” replaces “T.”
Conventional notation is used herein to describe nucleotide sequences: the left-hand end of a single-stranded nucleotide sequence is the 5′-end; the left-hand direction of a double-stranded nucleotide sequence is referred to as the 5′-direction. The direction of 5′ to 3′ addition of nucleotides to nascent RNA transcripts is referred to as the transcription direction. The DNA strand having the same sequence as an mRNA is referred to as the “coding strand;” sequences on the DNA strand having the same sequence as an mRNA transcribed from that DNA and which are located 5′ to the 5′-end of the RNA transcript are referred to as “upstream sequences;” sequences on the DNA strand having the same sequence as the RNA and which are 3′ to the 3′ end of the coding RNA transcript are referred to as “downstream sequences.”
“cDNA” refers to a DNA that is complementary or identical to an mRNA, in either single stranded or double stranded form.
“Encoding” refers to the inherent property of specific sequences of nucleotides in a polynucleotide, such as a gene, a cDNA, or an mRNA, to serve as templates for synthesis of other polymers and macromolecules in biological processes having either a defined sequence of nucleotides (i.e., rRNA, tRNA and mRNA) or a defined sequence of amino acids and the biological properties resulting therefrom. Thus, a gene encodes a protein if transcription and translation of mRNA produced by that gene produces the protein in a cell or other biological system. Both the coding strand (the nucleotide sequence of which is identical to the mRNA sequence and is usually provided in sequence listings) and non-coding strand (used as the template for transcription) of a gene or cDNA can be referred to as encoding the protein or other product of that gene or cDNA. Unless otherwise specified, a “nucleotide sequence encoding an amino acid sequence” includes all nucleotide sequences that are degenerate versions of each other and that encode the same amino acid sequence. Nucleotide sequences that encode proteins and RNA may include introns.
A first sequence is an “antisense” with respect to a second sequence if a polynucleotide whose sequence is the first sequence specifically hybridizes with a polynucleotide whose sequence is the second sequence.
Terms used to describe sequence relationships between two or more nucleotide sequences or amino acid sequences include “reference sequence,” “selected from,” “comparison window,” “identical,” “percentage of sequence identity,” “substantially identical,” “complementary,” and “substantially complementary.”
Operably linked: A first nucleic acid sequence is operably linked with a second nucleic acid sequence when the first nucleic acid sequence is placed in a functional relationship with the second nucleic acid sequence. For instance, a promoter is operably linked to a coding sequence (for example a coding sequence of an antibody or fragment therefore herein disclosed) if the promoter affects the transcription or expression of the coding sequence. Generally, operably linked DNA sequences are contiguous and, where necessary to join two protein-coding regions, in the same reading frame.
ORF (open reading frame): A series of nucleotide triplets (codons) coding for amino acids without any termination codons. These sequences are usually translatable into a peptide. In some examples an open reading frame encodes an antibody or antibody fragment, such as those disclosed herein.
Polypeptide: A polymer in which the monomers are amino acid residues that are joined together through amide bonds, for example γ amide bonds (for example from the γ position of a glutamic acid side chain) or α amide bonds. When the amino acids are alpha-amino acids, either the L-optical isomer or the D-optical isomer can be used. The terms “polypeptide” or “protein” as used herein is intended to encompass any amino acid sequence and include modified sequences such as glycoproteins. The term “polypeptide” is specifically intended to cover naturally occurring proteins, as well as those that are recombinantly or synthetically produced.
The term “polypeptide fragment” refers to a portion of a polypeptide which exhibits at least one useful epitope. The term “functional fragments of a polypeptide” refers to all fragments of a polypeptide that retain an activity of the polypeptide. Biologically functional fragments, for example, can vary in size from a polypeptide fragment as small as an epitope capable of binding an antibody molecule to a large polypeptide capable of participating in the characteristic induction or programming of phenotypic changes within a cell.
Sample: A material to be analyzed, for example to determine if it contains one or more target molecule such as an EDC. The term includes but is not limited to biological samples (e.g., obtained from a human or veterinary subject); food samples (e.g., vegetable, dairy, fruit or meat sample); environmental samples (e.g., soil, air, water, surfaces); industrial and construction samples; and the like. Specifically contemplated are samples of material known to or that potentially may leach (e.g., into the environment or surroundings) one or more compounds (molecules) with at least one potentially endocrine disrupting property, for instance upon degradation or aging of the material upon exposure to actual or simulated environmental or climactic conditions.
Sewage: Water-based fluid containing organic matter and solutes. Sewage may include feces and urine from human and non-human animals. Sewage may include waste from human activities, for example, blackwater (e.g., toilet and dishwasher waste) and grey water (e.g. waste water generated from washing activities). Residential, institutional, commercial and industrial establishments may produce sewage, including waste from toilets, baths, showers, kitchens, sinks, etc. Typically, sewage is waste intended to be carried away from the source of the waste, for example, carried to a sewage treatment facility.
Receptor Superfamily: Family of steroid, nuclear, and orphan receptor proteins having an identifiable ligand binding domain. The term as used herein is intended to encompass the known classic nuclear receptors, hormone receptors, and orphan receptors, as well as proteins having an identifiable ligand binding domain which may be discovered in the future.
Unless otherwise explained, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The word “or” is intended to include “and” unless the context clearly indicates otherwise. Hence “comprising A or B” means including A, or B, or A and B. It is further to be understood that all base sizes or amino acid sizes, and all molecular weight or molecular mass values, given for nucleic acids or polypeptides are approximate, and are provided for description. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, sequences defined by accession number, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including explanations of terms, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
III. Introduction and Overview of Several EmbodimentsThere is a growing interest in the possible health risks posed by endocrine-disrupting chemicals (EDCs) in the environment, water, food, and consumer products. Steroidal EDCs interfere with the normal function of the endocrine system and have been associated with developmental defects, metabolic disorders and cancer. Previous systems for the detection and monitoring of water sources for steroidal contamination relied on laborious analysis of their chemical structures.
Steroid hormones, such as estrogens, have been detected in water sources, and their deleterious effects are well documented. Considering that many natural steroids are rapidly metabolized, their derivatives are frequently not present in the currently existing libraries and thus cannot be identified. In addition, it is unclear whether EDCs detected by chemical methods can elicit specific biological responses in mammalian systems.
Described herein is are high-throughput assays (including automated assays) for biological testing of EDCs using mammalian cells that express GFP-tagged nuclear steroid receptor constructs. See also Stavreva et al. (Sci Rep. 2012;2:937. doi: 10.1038/srep00937. Epub Dec. 6, 2012). These assays re based on translocation of fluorescent marker(s) from the cytoplasm to the nucleus in the presence of a ligand that interacts with a specific receptor. Using this assay and studies of transcriptional activation, as described herein, water samples collected from 14 states in the U.S. have been screened; androgen activity was found in 35% of samples, and a previously unrecognized glucocorticoid (GC) activity in 27% of the samples. Androst-4-en-3,6-dione was identified in one of the samples. Androgen receptor (AR)-dependent nuclear translocation and transcriptional activation was confirmed for two AR-responsive genes, NKX3.1 and RHOU. NKX3.1 is a homeobox gene frequently deleted in prostate cancers, and RHOU is implicated in epidermal growth factor receptor signaling and cell migration. Glucocorticoid receptor (GR)-dependent transcriptional activation was detected using several targets. Induction of a circadian rhythm gene, Perl, was confirmed at concentrations equal to those present in one water sample. This water site was positive in a sample obtained by extraction of a filter (POCIS membranes), as well as a grab water sample obtained several years later. Widespread contamination with EDCs (including these two classes of steroid EDCs) is a possible health hazard not only for the aquatic ecosystems, but also humans. Testing for biological activity of glucocorticoids and many other steroid EDCs has not been previously performed. The herein described automated, highly reproducible, and low cost assays detect biologically active steroidal EDCs and is suitable for wide application in testing water samples, for instance for the analysis and monitoring of water contamination with steroidal EDCs.
Provided herein in a first set of embodiments are systems for detecting or quantifying a ligand (e.g., an agonist or an antagonist) of a superfamily receptor protein in an environmental sample. In examples thereof, the system comprises a first mammalian cell expressing a first traceable fusion protein; a second mammalian cell expressing a second traceable fusion protein; and a detection system for the detection of the cytoplasm-to-nuclear translocation of the marker proteins, wherein the first and second traceable fusion proteins independently comprise either: (1) a superfamily receptor protein, and a marker protein domain; or (2) the cytoplasmic/nuclear translocation domain of glucocorticoid receptor, the ligand binding domain of a superfamily receptor protein, and a marker protein domain. Optionally, the mammalian cells are human cells.
In examples of the described system for detecting or quantifying a ligand of a superfamily receptor protein in an environmental sample, the first traceable fusion protein binds a different ligand than the second traceable fusion protein.
In examples of the described system for detecting or quantifying a ligand of a superfamily receptor protein in an environmental sample, the marker protein domain is different in the first and second traceable fusion proteins. This enables differential detection of the two fusion proteins, for instance in the same analysis system or sample.
In any of the described system for detecting or quantifying a ligand of a superfamily receptor protein in an environmental sample, the marker protein domain may optionally be a fluorescent protein domain.
Without limitation, the systems provided herein may employ any cellular receptor including the following (generically termed) traceable fusion proteins: GFP-GR, GFP-AR, GFP-AhR, GFP-PR-B, GFP-GR-ER, GFP-GR-RAR, GFP-MR, and GFP-GR-TR, as well as fusion(s) in which the GFP is replaced with a different fluorescent domain that emits light at a different wavelength. By way of specific example, contemplated herein for use (singly or in combinations of two or more) in the described systems are the following traceable fusion proteins: eGFP-GR-ER310 (SEQ ID NOs: 1 & 2); eGFP-GR-TR216 (SEQ ID NOs: 3 & 4); pCI-nGFP-C656G (SEQ ID NOs: 5 & 6); eGFP-hAR (SEQ ID NOs: 7 & 8); pRefTRE-GFP-mAhR (SEQ ID NOs: 9 & 10); eGFP-ratMP (SEQ ID NO: 11 & 12); and/or eGFP-hPRB (SEQ ID NOs: 13 & 14).
Also described are systems for detecting or quantifying a ligand of a superfamily receptor protein in an environmental sample, wherein the ligand for the first or second traceable fusion protein is a natural ligand for the superfamily receptor protein of the traceable fusion protein, or a natural or synthetic compound that binds competitively therewith.
Also provided are systems for detecting or quantifying a ligand of a superfamily receptor protein in an environmental sample that additionally comprise one or more compounds and/or compositions that stably associate with a traceable fusion protein in the absence of a ligand for the ligand binding domain of the traceable fusion protein, and which dissociates from the fusion protein in the presence of a ligand for the ligand binding domain of the traceable fusion protein.
Yet another embodiment provides a system for detecting or quantifying a ligand of a superfamily receptor protein in an environmental sample, which system includes at least four mammalian cell lines each expressing a different traceable fusion protein, wherein at least one traceable fusion protein binds a glucocorticoid, at least one traceable fusion protein binds an androgen, at least one traceable fusion protein binds a progestin, and at least one traceable fusion protein binds an aryl hydrocarbon.
The systems described herein are optionally provided as kits.
Also described are methods for detecting or quantifying an endocrine disruptor chemical (EDC) ligand in an environmental sample, which methods involve contacting with the environmental sample a mammalian, optionally human, cell expressing in its cytoplasm a fusion protein comprising: a receptor for the ligand, which receptor translocates from the cytoplasm to the nucleus upon ligand binding; and a marker protein domain; and then detecting cytoplasmic to nuclear translocation of the fusion protein in response to a ligand of the ligand binding domain in the water sample.
Also described are methods of determining the concentration of an endocrine disruptor chemical (EDC) ligand in an environmental sample, which methods involve contacting with the environmental sample a population of eukaryotic cells expressing in their cytoplasm a fusion protein comprising: a receptor for the ligand, which receptor translocates from the cytoplasm to the nucleus upon ligand binding; and a marker protein domain; and scanning one or more test cell(s) to obtain signal data from the marker of the fusion protein; converting the signal data to obtain the cellular location of the labeled protein in the test cell(s); and analyzing the signal data using an analysis system having an algorithm to calculate changes in distribution of the labeled fusion protein between the cytoplasm and the nucleus of the test cell(s), the analysis system having the capability of providing an accurate reading of the concentration of the ligand.
Without limitation, the methods provided herein may employ any cellular receptor including the following (generically termed) traceable fusion proteins: GFP-GR, GFP-AR, GFP-AhR, GFP-PR-B, GFP-GR-ER, GFP-GR-RAR, GFP-MR, and GFP-GR-TR, as well as fusion(s) in which the GFP is replaced with a different fluorescent domain that emits light at a different wavelength. By way of specific example, contemplated herein for use (singly or in combinations of two or more) in the described methods are the following traceable fusion proteins: eGFP-GR-ER310 (SEQ ID NOs: 1 & 2); eGFP-GR-TR216 (SEQ ID NOs: 3 & 4);
pCI-nGFP-C656G (SEQ ID NOs: 5 & 6); eGFP-hAR (SEQ ID NOs: 7 & 8); pRefTRE-GFP-mAhR (SEQ ID NOs: 9 & 10); eGFP-ratMP (SEQ ID NO: 11 & 12); and/or eGFP-hPRB (SEQ ID NOs: 13 & 14).
In any of the provided systems, kits, and methods, the environmental sample can include a water sample, soil sample, or air sample. By way of example, where the environmental sample comprises a water sample, the sample includes in various embodiments one or more of surface water, sub-surface (ground) water, rain, run-off, well water, spring water, drinking water (processed or not), river water, estuary water, ocean water, effluent, treated sewage or untreated sewage.
Yet further embodiments are described herein.
IV. Systems and Kits for Detection of EDCsDisclosed herein is use of a highly sensitive cytoplasm-to-nucleus translocation assay to monitor one or more EDC level or activity, for instance in water samples. A high throughput screen of water samples is described, using in one example a cell line expressing GFP-tagged glucocorticoid receptor (GR) (GFP-GR); the detected output that signals presence of EDC/ligand (such as glucocorticoid) in the sample is accumulation of fluorescence in the cell nucleus (that is, migration of the fluorescent fusion protein from the cytoplasm into the nucleus). By way of example, an automated imaging system (such as the PerkinElmer Opera® High Content Imaging system) can be used to image the change in fluorescence localization in individual cells; also contemplated are non-automated, direct microscopic examination embodiments.
Though the high-throughput, low cost, high sensitivity EDC detection system is described in detail with regard to a few exemplary traceable cytoplasm-to-nuclear marker proteins, it will be apparent to one of ordinary skill based on the teachings herein that the provided principles can be applied to the detection of other EDC compounds though use of different receptor fusions. Thus, specifically contemplated herein are methods and kits that employ cell lines expressing one or more (such as at least one two, three, four, five, six, seven, eight, or all nine) of the following detector (traceable) fusions: GFP-GR, GFP-AR, GFP-AhR, GFP-PR-B, GFP-GR-ER, GFP-GR-RAR, GFP-MR, GFP-hAR, and GFP-GR-TR, as well as fusion(s) in which the GFP is replaced with a different fluorescent domain that emits light at a different wavelength. Specifically contemplated are kits that include cell lines expressing two or more traceable fusion, where each is responsive to a different EDC and contains a differentially fluorescing traceable domain. Kits containing multiple cell lines, each of which expresses a different cytoplasm-to-nuclear traceable fusion protein are also contemplated. Also envisioned are GFP fusions to mutant, variant, or modified forms of nuclear receptors that manifest detectable subcellular relocalization in response to ligand.
A. Traceable Translocating Fusion Proteins with Non-chimeric Receptors
Embodiments provided herein employ cells that express a traceable fusion protein, which changes its sub-cellular localization (for example, translocates from the cytoplasm into the nucleus) upon binding of an EDC ligand compound. Examples of such traceable translocating fusion proteins comprise a traceable marker domain (exemplified by a fluorescent protein domain, such as GFP) functionally fused to a nuclear superfamily receptor domain that is sufficient for both recognition of the EDC ligand and for consequent translocation of the fusion protein from the cytoplasm into the nucleus.
Cell lines expressing other “non-chimeric” receptors (that is, not needing to be fused to the translocation domain of GR) such as GFP-AR (Klokk, et al., Mol. Cell Biol. 27:1823-1843, 2007), GFP-AhR (Elbi et al., Proc Natl Acad Sci USA 101(9):2876-2881, 2004), GFP-PR-B (Rayasam et al., Mol Cell Biol 25(6):2406-2418, 2005) have been generated previously in our laboratory. In addition to the GFP-GR, which could detect biologically active glucocorticoids in water samples, GFP-AR was used for the detection of androgen activity and positive results were obtained for many of the tested water samples.
A fluorescent protein (or protein domain) is a protein (or portion of a protein) that fluoresces in cells without adding exogenous cofactors. That is, it is a protein that can be expressed in cells and detected in these cells simply by exciting the protein with light and visualizing the resultant fluorescence. An example of such a fluorescent protein is the green fluorescent protein (GFP) originally isolated from the jellyfish Aequorea victoria. Another example of a fluorescent protein as defined herein is the green fluorescent protein originally isolated from Renilla reniforms, which exhibits a single absorption peak at 498 nm and an emission peak at 509 nm (Cubitt et al. TIBS 20: 448-455, 1995). It is also contemplated that modifications may be made to a fluorescent protein, as long as the resulting protein fluoresces when expressed in cells. The art recognizes many modifications that can be (and have been) made to existing fluorescent proteins, for instance to provide different excitation and emission peaks, to increase stability, that speed up the rate of the oxidation step of chromophore formation, that increase brightness at longer wavelengths, and that reduce pohotoisomerization and/or photobleaching.
Optionally, the fusion protein can include a linking peptide sequence between the traceable (e.g., fluorescent protein) domain and the steroid or other receptor domain. For example, a sequence of the amino acids glycine and alanine, or a sequence of alanine alone can be used; however, any sequence of amino acids and any length can be used that does not interfere with the binding of the receptor domain to its response element and that does not prevent fluorescence of the fluorescent protein. Typically, a linker peptide will range from two to about ten amino acids but maybe shorter or longer. Of course, certain linker peptides maybe preferred over others, e.g., the presence of four basic amino acids in a string of six might suffice as a nuclear localization signal so as to mislocate the uninduced state of the factor. A linker peptide can be used to separate the fluorescent protein structurally from the response element and can function to allow the fluorescent protein independently of the remaining portion of the chimeric protein. Typically, the traceable protein domain (e.g., fluorescent protein) can be fused to either the C-terminus or the N-terminus of the ligand receptor domain; however, the preferable construction for any specific fusion protein can readily be determined. Linker peptides can readily be introduced between the two protein domains in the fusion protein by producing a nucleic acid that encodes the fusion protein having the linker sequence between the detectable protein component and ligand responsive/translocation component.
The ligand binding domain (e.g., transcription factor component) of the traceable fusion protein can be derived from any selected mammal. Additionally, fusion proteins utilizing a transcription factor from one mammal can often be used in a cell from another mammal. For example, the glucocorticoid receptor amino acid sequence is highly conserved, particularly in the binding region among rat, human and mouse, and, for example, the rat glucocorticoid receptor binds with high affinity to the human glucocorticoid response element. However, in various embodiments provided herein, the ligand-binding and/or translocation component(s) of the traceable fusion proteins are based on human proteins.
Additional information regarding the construction of traceable translocating fusion proteins useful in the described methods and kits is provided in WO 97/20931 and U.S. Pat. Nos. 6,455,300, 7,312,032 and 8,058,395, each of which is incorporated by reference herein.
B. Traceable Translocating Fusion Proteins with Chimeric Receptors
Also contemplated are cell lines, methods, systems and kits that employ traceable chimeric receptors, that is traceable receptors that include a portion of a nuclear receptor for example responsible for cytoplasmic/nuclear translocation activity functionally fused to the ligand-binding portion of another superfamily receptor. A representative example is the GR-ER chimera (Martinez et al., J. Ster. Biochem Mol. Biol. 97:307-321, 2005), which contains the rat GR (rGR) N-terminus, DNA binding domain (DBD) and hinge regions upstream of a hybrid ligand binding domain (LBD) composed of GR helix 1 and partial loop 1-3 sequences linked to human ER alpha (hERa) LBD sequences starting with the C-terminus of loop 1-3.
The construction of examples of such chimeric traceable receptors is described in U.S. Patent Publication No. 2003/0077645, Mackem et al. (J. Biol. Chem. 276(49):45501-45504, 2001), and Martinez et al. (J. Ster. Biochem Mol. Biol. 97:307-321, 2005), each of which is incorporated herein by reference. These references describe production of fluorescently tagged fusion proteins that contain a chimera between the translocation features of glucocorticoid receptor and another nuclear superfamily receptor, such as the estrogen receptor, a retinoic acid receptor, and so forth. In each case, the labeled chimera is found in the cytoplasm in the absence of its cognate ligand), and is rapidly translocated to the nucleus in a dose-dependent manner upon exposure of the cell to ligand.
C. Additional Chimeric ReceptorsGFP-GR (pCI-nGFP-C656G) and GFP-AR (eGFP-hAR) fusion proteins have been published ((Walker et al., Methods (Comp. to Meth. Enzym.) 19:386-393, 1999; Klokk et al., Mol. Cell Biol. 27:1823-1843, 2007) and have proven useful in detecting biologically active glucocorticoid and androgens in water samples, as described below in Example 1. Additional chimeras (eGFP-GR-ER310 and eGFP-GR-TR216) have been constructed. Mammalian cell lines can be readily prepared which express each of these chimeras under tetracycline regulation. The nucleotide sequences of eGFP-GR-ER310 (SEQ ID NO: 1), eGFP-GR-TR216 (SEQ ID NO: 2), pCI-nGFP-C656G (SEQ ID NO: 5), eGFP-hAR (SEQ ID NO: 7), pRevTRE-GFP-mAhR (SEQ ID NO: 9), eGFP-ratMR (SEQ ID NO: 11), and eGFP-hPRB (SEQ ID NO: 13) are provided. The encoded proteins are also provided herein (SEQ ID NOs: 2, 4, 6, 8, 10, 12, and 14, respectively).
D. Detection Cell LinesThe methods and kits described herein employ cell lines that express at least one traceable translocating fusion protein as described herein. For detection of the translocation of the labeled fusion protein from one sub-cellular compartment or organelle to another, any eukaryotic cell can be utilized, though mammalian cells and particularly human cells are contemplated. Representative methods for the construction of cell lines useful in the described methods and kits, as well as examples of such cell lines, are provided in WO 97/20931, U.S. Pat. Nos. 6,455,300, 7,312,032 and 8,058,395; U.S. Patent Publication No. 2003/0077645, Mackem et al. (J. Biol. Chem. 276(49):45501-45504, 2001), and Martinez et al. (J. Ster. Biochem Mol. Biol. 97:307-321, 2005), each of which is incorporated by reference herein.
In addition to steroid receptors, there are other ligand-dependent receptors (such as thyroid hormone receptor, retinoic acid receptor, retinoid X receptor, TCCD (dioxin) receptor
(AhR), fatty acid activatable receptors, etc.) and stimulus-dependent receptors (such as peroxisome proliferator activated receptor, growth factor-dependent receptors such as epidermal growth factor, nerve growth factor, etc.), and factors (such as CREB, NFAT, NFkB/IkB, etc.), and other receptors whose ligand remains to be defined (such as mammalian homologs of the Drosophila tailless, knirps, sevenup, FTZF1 genes, etc.). Many of these receptors or factors can be found listed in Parker, Steroid Hormone Action (Oxford University Press, New York, pp. 210, 1993), in Tsai & O'Malley (Annu. Rev. Biochem. 63:451-486, 1994), and in GenBank and other publicly available sequence databases, which contain additional receptors as well as the complete nucleotide sequences of the genes and cDNAs.
E. Methods for Detecting and/or Quantifying EDC(s) in Environmental Samples and Other Types of Samples
The present disclosure provides methods of detecting in an environmental sample the presence of an agonist or antagonist of a nuclear superfamily receptor comprising contacting the sample with a cell expressing at least one traceable translocating fusion protein and directly detecting the sub-cellular location of fluorescence (or other appropriate label) within the cell, the location of fluorescence aggregated in the nucleus indicating the presence in the environmental sample of at least one agonist or antagonist of the ligand-binding EDC receptor domain of the traceable translocation fusion protein. In addition to the exemplary methods described herein, methods generally applicable for detecting or quantifying a ligand using a traceable translocation fusion protein can be found in WO 97/20931, U.S. Pat. No. 6,455,300, 7,312,032 and 8,058,395; U.S. Patent Publication No. 2003/0077645, Mackem et al. (J. Biol. Chem. 276(49):45501-45504, 2001), and Martinez et al. (J. Ster. Biochem Mol. Biol. 97:307-321, 2005), each of which is incorporated by reference herein.
Direct detection means detection of the fluorescence emitted from the site in the cells when excited by (ultraviolet or visible) light, without the need for any additional chemical reactions or treatment of the cells. The fluorescence is directly detected by any device capable of detecting fluorescence, such as a fluorescent microscope, as visualized by the eye of the operator of the microscope at the time or as recorded from the microscope such as by photography of the field of view or through the use of photosensitive detectors. A fluorescent microscope, such as a confocal laser scanning microscope or an epifluorescent microscope, can be used, as is known in the art.
There is no requirement that cells be, e.g., fixed or stained or contacted by any additional reagents, in order to detect the translocation. Thus living cells can be assayed, and results obtained, shortly (for instance, about 30 minutes) after being contacted with a test sample. Furthermore, screening nuclear localization of fluorescence (translocation) can readily be adapted to high throughput computerized image analysis. Thus, the analysis of large numbers of samples can be automated, for instance for the repetitive examination of multiple environmental samples (for instance, from multiple sources or locations) as well as for the large-scale screening of sets of samples for multiple EDC contaminants.
Also provided is a method of detecting or monitoring the level of agonists and antagonists of a steroid receptor in an environmental sample, comprising obtaining periodic samples from a source or location over time (e.g., on a daily, weekly, monthly, bi-annually, annually, or longer basis), contacting the samples with cell(s) expressing one or more of the herein-described traceable translocating fusion proteins, and detecting the location of fluorescence within the cells. Optionally, the cells each or collectively express a set of two or more different traceable translocating fusion proteins that are responsive to different ligands (e.g., different EDCs known to or suspected of being contaminants in the environment being sampled). The amount or magnitude of fluorescence migration from the cytoplasm to the nucleus can be compared between the periodic samples, in order to monitor trends (upwards or downwards) in the levels of EDC contamination at a single location or set of locations over time. Decrease in the nuclear translocation in a later-obtained sample relative to an earlier-obtained sample indicating a decrease in level of the EDC agonist or antagonist of the receptor in the sample, while an increase in translocation into the nucleus in a later-obtained sample relative to an earlier-obtained sample indicates an increase in level of the EDC agonist or antagonist of the steroid receptor in the sample.
F. Automated High Throughput Analysis Systems and Image Analysis SoftwareDescribed herein is one embodiment of automated high throughput analysis of the presence of EDCs in environmental samples, using the PerkinElmer Opera® High Content Image Screening System and accompanying software package. With this teaching, additional high throughput applications of the herein described EDC detection and measuring methods are now enabled.
Contemplated herein is the use of “arrays” of cells that express one or more traceable translocating fusion protein, which cells are placed into an array such as a microchannel array, microtiter plate or other array system that permits separate cell samples to be contacted separately with different test samples (e.g., environmental samples, such as water samples, to be analyzed for the presence or level of one or more EDCs).
Arrays, as the term is used herein, are arrangements of addressable locations on a substrate; each address may contain a sample of one or more cells or cell lines. A “microarray” is an array that is miniaturized so as to require microscopic examination for evaluation of hybridization or other detection signals. “Macroarrays” are somewhat larger, such that at least the spot at each address is recognizable by the naked human eye. Primary examination for the presence and location of cellular fluorescence (or other traceable signals) in cells of the array is usually carried out using a microscope or other magnifying device.
Within an array, each arrayed cell sample is addressable, in that its location can be reliably and consistently determined within the at least the two dimensions of the array surface. Thus, in ordered arrays the location of each cell sample is assigned to the sample at the time when it is applied to the array and usually a key is provided in order to correlate each location with the appropriate “target” cell sample. Often, ordered arrays are arranged in a symmetrical grid pattern, but samples could be arranged in other patterns (e.g., in radially distributed lines or ordered clusters).
The data generated using an array according to this invention (e.g., subcellular localization of one or more traceable translocating fusion proteins) can be analyzed using computerized systems. For instance, the array can be read by a computerized “reader” or scanner and the quantification of the location traceable signal to individual cells and/or subcellular compartments within cells on the array carried out using computer algorithms. Such analysis of the array can be referred to as “automated detection” in that the data is being gathered by an automated reader system.
In the case of labels that emit detectable electromagnetic waves or particles, the emitted light (e.g., fluorescence or luminescence) or radioactivity can be detected by sensitive cameras, confocal scanners, image analysis devices, radioactive film or a Phosphoimager, which capture the signals (such as a color image or artificial color image) from the array. A computer with image analysis software then detects this image, and analyzes the intensity and/or pattern of the signal for each cell sample location (address), and optionally individual cells within a location, in the array. Signals can be compared between locations on a single array, or between arrays (such as a single array that is sequentially analyzed at different wavelengths in order to detect the localization of different traceable fusion proteins).
Computer algorithms can also be used for comparison between spots on a single array or on multiple arrays. In addition, the data from an array can be stored in a computer readable form.
Certain examples of automated array readers (scanners) will be controlled by a computer and software programmed to direct the individual components of the reader (e.g., mechanical components such as motors, analysis components such as signal interpretation and background subtraction). Optionally software may also be provided reader to control a graphic user interface and one or more systems for sorting, categorizing, storing, analyzing, or otherwise processing the data output of the reader.
By way of example, to “read” an array that contains cells expressing a traceably labeled translocating protein (e.g., a fusion protein that contains a GFP or other fluorescent protein domain), the array can be placed into (or onto, or below, etc., depending on the location of the detector system) the reader and a traceable signal detected by the reader. These detectable signals could be associated with an address identifier signal. The reader gathers information from each of the addresses, associates it with the address identifier signal, and recognizes addresses with a detectable signal (including a particular type of signal, such as relatively intense fluorescence localized to the nucleus of the cell) as distinct from those not producing such a signal (or producing a different kind of signal, such as diffuse fluorescence in the cytoplasm of cells). Certain readers are also capable of detecting intermediate levels of signal, between no signal at all and a high signal, such that quantification of signals at individual addresses is enabled. In particularly beneficial embodiments, the reader is equipped with software that enables it to map individual cells and cell nuclei in order to determine and measure the subcellular localization of the traceable signal.
Certain readers that can be used to collect data from the arrays used with the described methods, especially those that use a fluorescently tagged fusion protein, will include a light source for optical radiation emission. The wavelength of the excitation light will usually be in the UV or visible range, but in some situations may be extended into the infra-red range. A beam splitter can direct the reader-emitted excitation beam into the object lens, which for instance may be mounted such that it can move in the x, y and z directions in relation to the surface of the array substrate. The objective lens focuses the excitation light onto the array, and more particularly onto the (microbial cell) targets on the array. Light at longer wavelengths than the excitation light is emitted from addresses on the array that contain fluorescently-labeled probe molecules (i.e., those addresses containing a cell to which the probe binds).
In certain embodiments of the invention, the array may be movably disposed within the reader as it is being read, such that the array itself moves (for instance, rotates) while the reader detects information from each address. Alternatively, the array may be stationary within the reader while the reader detection system moves across or above or around the array to detect information from the addresses of the array. Specific movable-format array readers are known and described, for instance in U.S. Pat. No. 5,922,617, hereby incorporated in its entirety by reference. Examples of methods for generating optical data storage focusing and tracking signals are also known (see, for example, U.S. Pat. No. 5,461,599).
G. Kits for Screening an Environmental Sample, and Methods of Use ThereofIt is contemplated that the fusion proteins and cells described herein can be used to screen environmental samples for the presence and/or level of one or more EDCs, which methods optionally may be carried out using kits.
In one specific contemplated example, the kits are very simple—comprising one or more water-tight container(s) in which water or other environmental samples are collected (one sample per container). In examples of this embodiment, the containers are substantially non-reactive and contain no chemicals that might be transferred into the collected sample (e.g., by leaching) and thereby detected during subsequent sample analysis. By way of example only, containers may be 500 ml (or smaller) pre-cleaned glass bottles. Optionally, such kits may include system(s) for holding the sample containers (e.g., a rack or other device, including for instance providing the containers as part of a single unit such that two or more containers are joined to each other), including for instance for holding the containers during shipping or other transportation. Sample collection containers may be joined to each other, for instance in a plate or sheet configuration. In some instances, the kits include an acidifying agent that is used to acidify the environmental samples (e.g., to pH ˜3); an example of such acidifying agent is 6N hydrochloric acid (though one of ordinary skill in the art will recognize that other acidifying agents can be used). The kits may also be formatted to permit chilling of samples once they are collected, for instance chilling to about 4° C.
Capture kits of this relatively simple variety may be used in a remote-analysis system, where the samples are obtained from the environment at one location and then transported (e.g., by shipping the collected samples) to a remote location for analysis. Optionally, such kits are formatted so that the samples are shipped cold (e.g., under ice) so as to maintain a temperature of ˜4° C. from soon after collection until the samples are processed for analysis at the remote location (e.g., a centralized analysis center, such as a mail-order analysis site). Kits intended for shipping to a remote analysis site optionally may be provided with mailers, such as pre-paid mailers, and/or instructions for how to ship the samples to the analysis site after collection. It is contemplated that regular sample analysis systems may be employed, for instance where a site is (or set of sites are) sampled on a regular basis and the samples returned to the same analysis site on a daily, weekly, bi-weekly, monthly, quarterly, yearly, or other regular basis. In such instances, for instance where a water processing plant or other utility or agency is taking samples, a shipping system or pick-up/delivery system can be used for transporting the samples from the collection site(s). This may enable highly reliable sample movement, while helping to keep costs down for repeat sample analysis.
Also contemplated are analysis kits, which contemplate and enable the analysis of the sample(s) without needing to engage a remote analysis site. Such kits can be used with the methods described herein to detect (and optionally quantify) one or more EDCs from samples, such as environmental samples. Such analysis kits include (for instance, in addition to one or more components of the capture kits described above—such as sample collection containers) components of a herein described system used to analyze the environmental sample, including for instance one or more (e.g., two, three, four or more) mammalian cell line(s), each of which expresses at least one traceable fusion protein. In one embodiment, the kit implements a system for detecting or quantifying a ligand of a superfamily receptor protein in a water sample, the system comprising a first mammalian cell expressing a first traceable fusion protein, a second mammalian cell expressing a second traceable fusion protein; and (optionally) a detection system for detection of the cytoplasm-to-nuclear translocation of the marker proteins (for instance, detection of the sub-cellular localization of each marker protein), wherein the first and second traceable fusion proteins independently comprise either: (1) a superfamily receptor protein, and a marker protein domain; or (2) the cytoplasmic/nuclear translocation domain of glucocorticoid receptor, the ligand binding domain of a superfamily receptor protein, and a marker protein domain. Optionally, the analysis kit comprises one or more compounds and/or compositions that stably associate with a traceable fusion protein of the kit in the absence of a ligand for the ligand binding domain of the traceable fusion protein, and which compound/composition dissociates from the fusion protein in the presence of a ligand for the ligand binding domain of the traceable fusion protein.
Specifically contemplated are kits that comprise at least four mammalian cell lines each expressing a different traceable fusion protein, wherein at least one traceable fusion protein of the kit binds a glucocorticoid, at least one traceable fusion protein of the kit binds an androgen, at least one traceable fusion protein of the kit binds a progestin, and at least one traceable fusion protein of the kit binds an aryl hydrocarbon.
Optionally, analysis kits provided herein include a portable fluorescence reader programmed to detect and monitor translocation of one or more traceable translocating fusion proteins described herein. Portable in this context may refer to a device that can readily be carried by a person into the field. However, in additional embodiments, the portable fluorescence reader is of a size that requires a transport vehicle, for instance a portable analysis van that can be moved from location to location to provide analysis of environmental samples.
Kits may be provided with instructions, for instance instructions for the collection of environmental samples, instructions for after-collection processing of the samples, for analysis of the samples to detect one or more EDCs using the systems and cells and methods described herein, and so forth. The instructions can provide calibration curves or charts to compare with the determined (e.g., experimentally measured) values.
Without limitation, the kits provided herein may include any cellular receptor or receptor subdomain tagged florescent protein, including but not limited to the following (generically termed) traceable fusion proteins: GFP-GR, GFP-AR, GFP-AhR, GFP-PR-B, GFP-GR-ER, GFP-GR-RAR, GFP-MR, and GFP-GR-TR, as well as fusion(s) in which the GFP is replaced with a different fluorescent domain that emits light at a different wavelength. By way of specific example, contemplated herein for inclusion (singly or in combinations of two or more) in the described kits are the following traceable fusion proteins: eGFP-GR-ER310 (SEQ ID NOs: 1 & 2); eGFP-GR-TR216 (SEQ ID NOs: 3 & 4); pCI-nGFP-C656G (SEQ ID NOs: 5 & 6); eGFP-hAR (SEQ ID NOs: 7 & 8); pRefTRE-GFP-mAhR (SEQ ID NOs: 9 & 10); eGFP-ratMP (SEQ ID NO: 11 & 12); and/or eGFP-hPRB (SEQ ID NOs: 13 & 14).
The following example is provided to illustrate certain particular features and/or embodiments. The example should not be construed to limit the invention to the particular features or embodiments described.
EXAMPLE 1 Prevalent Glucocorticoid and Androgen Activity in U.S. Water SourcesContamination of the environment with various endocrine disrupting chemicals (EDCs) is a major health concern. The presence of estrogenic compounds in water and their deleterious effects are well documented. However, effective detection and monitoring of EDCs, including corticosteroids and androgens, is lacking.
Described in this example (and in Stavreva et al., Sci Rep. 2012;2:937. doi: 10.1038/srep00937. Epub Dec. 6, 2012, incorporated herein by reference in its entirety) is use of a highly sensitive live cell assay based on sub-cellular relocalization of green fluorescent protein (GFP)-tagged nuclear receptors, exemplified by the glucocorticoid receptor (GR) and androgen receptor (AR) to test samples from US water sources for hormonal activity. This assay is based on the fact that unoccupied GR resides in the cytoplasm bound to various heat-shock proteins and immunophilins in a large multi-protein complex (Pratt & Tort, Endocr. Rev. 18:306-360, 1997; Pratt et al., Exp. Pharmacol. 111-138, 2006). Upon hormone binding, GR dissociates from the chaperones and translocates to the cell nucleus (
The levels of steroidal EDCs in the environment are not efficiently monitored and/or regulated at present. One of the reasons is that a high-throughput, reliable, and low-cost detection methods for monitoring of biologically active steroidal EDCs, including corticosteroids, have not been developed and are in demand (Roy & Pereira, Indian J Exp. Biol 43:975-992, 2005).
Chemical methods for detection of EDCs reveal the presence of several classes of steroid hormones in water sources in China (Chang et al., Environ. Sci. Technol. 43:7691-7698, 2009).
Mass spectrometry data from wastewaters in the Netherlands (Schriks et al., Environ. Sci. Technol. 44:4766-4774, 2010) and also China (Chang et al., Environ. Sci. Technol. 41:3462-3468, 2007) suggest possible contamination with glucocorticoids and a recent study demonstrated that environmentally relevant concentrations of synthetic glucocorticoids have deleterious effects on fish (Kugathas & Sumpter, Environ. Sci. Technol. 45:2377-2383, 2011). However, it is unclear whether in U.S. water sources are also contaminated by EDCs and to what extent. It is also unclear whether the EDCs detected in water sources could elicit steroid-specific biological response(s) in mammalian systems.
Chemical methods for EDCs detection, although sensitive, are expensive, time-consuming, and largely incompatible with a large-scale sample testing. Therefore, it is crucial to develop, test, and implement methods for high-speed, reliable, and low-cost detection of biologically active EDCs in contaminated water and other environmental sources. Here we utilize a highly sensitive cellular assay based on cytoplasm to nucleus translocation to detect glucocorticoid activity in U.S. water sources.
Materials and Methods Samples CollectionEnvironmental water samples were collected as part of ongoing U.S. Geological Survey (USGS) projects that were implemented to monitor the presence and effects of endocrine-disruptors and other contaminants of emerging concern. They were collected between 2005 and 2010 from different geographic locations in the United States (
POCIS samples: The POCIS membranes were shipped to the USGS, Columbia Environmental Research Center for analyte recovery. The procedures used for preparing the POCIS samples for analysis were described earlier (Alvarez et al., Environ. Toxicol. Chem. 28:1084-1095, 2009). Briefly, chemicals of interest were recovered from the POCIS sorbent using 50 mL of 1:1:8 (V:V:V) methanol:toluene:dichloromethane followed by 20 mL of ethyl acetate. The extracts were reduced by rotary evaporation, filtered, and composited into 2-POCIS equivalent samples thereby concentrating the amount of chemical present in each sample to aid in the detection.
Grab Water samples: Grab water samples were collected in 500 ml pre-cleaned amber glass bottles (I-Chem, Rockwood, Tenn.). Water was acidified to pH 3 using 6N hydrochloric acid, held on ice, and stored at 4° C. Within one week of collection, the preserved water samples were filtered through a GF/F filter (0.7 μm) using a solvent rinsed all-glass apparatus. Filters were rinsed with 1 ml of methanol to liberate soluble compounds from the retained suspended solids. Filtered samples and blanks were subjected to solid phase extraction (SPE) using OASIS® HLB (200 mg) glass cartridges (Waters Corporation, Milford, Mass.), following an existing protocol (Ciparis et al., Sci. Total Environ. 414:268-276, 2012). In short, cartridges were sequentially pre-conditioned and 400 ml of filtered samples were loaded onto the cartridge at a flow rate of 5-6 ml/minute (continuous vacuum). Analytes were eluted from the cartridge with 100% methanol and concentrated by rotary evaporation.
For biological testing, samples prepared as above were reconstituted in DMSO and diluted in growth media to a final 1,000× concentration from the original water volume while maintaining DMSO at <0.2%. Samples were added to cells for 30 minutes at 100 x concentration or as indicated in the text.
Cell Lines and Translocation AssayThe 3617 and 3108 cell lines are derivatives of 3134 mouse mammary adenocarcinoma cell line that express green fluorescent protein (GFP)-tagged GR (GFP-GR) and AR (GFP-AR), respectively from a chromosomal locus under control of the tetracycline-repressible promoter (Walker et al., Methods (Comp. to Meth. Enzym.) 19:386-393, 1999; Klokk et al., Mol. Cell Biol. 27:1823-1843, 2007). Prior to imaging, cells were grown overnight on 22-mm2 coverslips in DMEM medium containing 10% charcoal stripped serum (Hyclone, Logan, Utah) without tetracycline (to allow the expression of the GFP-GR or GFP-AR, respectively) at a density of 2×105 per 6-well plate. For the automated experiments conducted in 96 or 384 well plates, cell density was 10, 000 or 2,500 cells per well, respectively. Cells were treated with vehicle control, hormones (100 nM) or water samples for 30 min at 37° C. at a final concentration of 100×for water samples (unless otherwise specified). Additional negative controls contained samples that tested the activity of the POCIS membranes themselves.
Upon treatment, cells were fixed with 4% paraformaldehyde in PBS for 15 minutes and washed three times with PBS. Cells on the 22-mm2 coverslips were mounted in VECTASHIELD® mounting media with DAPI (Vector Laboratories, Inc.) and examined on a Leica DMRA microscope with Leica 100× 1.3-N.A. oil immersion objective. Images were acquired in green (GFP-GR and GFP-AR) and UV (DAPI) channel with SenSys (Photometrics) camera with KAF1400 chip configured to collect 0.067-μm-diameter pixels. For the automated experiments conducted in 96 or 384 well plates, cells were stained with DRAQ5 (BioStatus Limited) at a dilution of 1:5000 for 15 minutes and after three final washes with PBS were imaged either immediately on the Perkin Elmer Opera Image Screening System or kept in PBS at 4° C. for later imaging.
Automated Imaging and Analysis by Perkin Elmer Opera Image Screening SystemA Perkin Elmer Opera Image Screening System was used for fully automated collection of fluorescence images of cells. This system employed a 40×water immersion objective lens, laser illuminated Nipkow disk, and cooled CCD cameras to digitally capture high resolution confocal fluorescence micrographs (300 nm pixel size with 2×2 camera pixel binning). An algorithm was customized using the Acapella image analysis software development kit (Perkin Elmer) to automatically segment both the nucleus and cytoplasm of each cell in the digital micrographs. The algorithm also measured the mean GFP-GR or GFP-AR intensity in both compartments, and translocation was calculated as a ratio of these intensities. Each value was further normalized to the value for the control (DMSO) sample.
Gene Transcription AnalysisFor gene transcription studies, 3134 cells or LNCaP cells (expressing endogenous GR and AR, respectively) were plated in 24-well dishes 24 hours before each experiment in DMEM (3134 cells) or RPMI (LNCaP cells) media supplemented with charcoal stripped fetal bovine serum (Hyclone, Logan, Utah). Cells were treated with water samples, vehicle control (DMSO), or GR and AR specific hormones for 30 minutes. To reduce cell stress, these experiments were performed under conditions of stable CO2 and temperature levels throughout the duration of an experiment (though this is not essential for the assay). Cells were lysed in 600 μl of RLT buffer (with β-mercaptoethanol added) followed by syringe/needle shearing. Total RNA was extracted using the RNeasy Mini Kit (Qiagen), including a DNaseI digestion step (RNase free DNase Set, Qiagen). One microgram (μg) of RNA was reverse transcribed (iScript cDNA Synthesis Kit, BioRad) in 20 μl reaction volume and 0.5 μl was used per Q-PCR reaction using SyBr green and Bio-Rad IQ system (BioRad, Hercules, Calif.). Primer sequences were designed to amplify nascent RNA (amplicons that cross an exon/intron boundary). The primer sequences are shown below. PCR was performed as recommended by a manufacturer. Standard curves were created by 10-fold serial dilution of template. The expression data from three or more independent experiments were normalized to the expression of a control gene β-Actin (3134 cells) and GAPDH (LNCaP cells), the mean values and SEM were calculated and displayed as a fold change in relation to the control (DMSO treated) sample.
Data were analyzed using the statistical functions of IBM SPSS Statistics 19 and SigmaPlot 11 (SPSS Inc., Chicago, Ill.). From the repeated experiments, the mean value was calculated for each sample. The mean values were used in a one-way analysis of variance test. If a significant F-value of P<0.05 was obtained, a Dunnett's multiple comparison versus the control group analysis was conducted.
Table 5A-5B contains information about additional samples tested for GFP-GR and GFP-AR translocation efficiency.
Accumulated data hint at an unacknowledged and potentially wide spread contamination with glucocorticoids (GCs) at biologically-relevant concentrations. To directly examine this possibility, 10 water samples collected from different locations (
In an attempt to determine the active constituent(s) in sample SS97, known corticosteroids (dexamethasone and corticosterone) were tested by high performance liquid chromatography/mass spectrometry (HPLC/MS) analysis to establish chromatographic retention times on a C18 HPLC column using published techniques (Chang et al., Environ. Sci. Technol. 43, 7691-7698, 2009). In addition, 20 other synthetic GCs were surveyed by monitoring the mass spectrometric data for the presence of the corresponding molecular ions (Table 3). Under these assay conditions, sample SS97 showed no evidence of any known compounds tested. Next, sample SS97 was subjected to HPLC fractionation followed by biological testing. Four of the eleven HPLC fractions showed activity in the nuclear translocation assay (
Visual comparison of the mass spectra of chromatographic peaks 1-3 (
Androgens are the original anabolic steroids and the precursor of all estrogens, the female sex hormones. Through their binding to androgen receptor (AR), they control the development and maintenance of male characteristics in vertebrates (Gottlieb et al., Reprod. Biomed. Online. 10:42-48, 2005). Similarly to the GR, AR is largely cytoplasmic in the absence of its ligand, and rapidly translocates to the nucleus in response to testosterone (Klokk et al., Mol. Cell Biol. 27:1823-1843, 2007) (
We conclude that environmental degradation and metabolic processes alter the structure of the glucocorticoid(s) in water samples, producing bioactive chemical structures which are not contained in the existing databases. Rapid transformation of hormonal steroids by aquatic microorganisms has been reported previously (Yin et al., Environ. Int. 28:545-551, 2002). We also conclude that, in contrast to the traditional chemical analysis, the translocation assay described herein is faster, cheaper, and also detects biologically relevant hormonal activity which cannot readily be discerned by chemical methods. Translocation assay allows unbiased “non-candidate” approach for detection of EDCs and could be used in a powerful combination with fractionation methods and “forensic chemistry” in the discovery of novel bioactive ligands.
Next, the search was expanded to screen over 100 additional samples from water sources throughout 14 states in the US (Table 5A) for both, glucocorticoid and androgen activities. To accomplish this screening, the GFP-GR- and GFP-AR-expressing cell lines (Walker et al., Methods (Comp. to Meth. Enzym.) 19:386-393, 1999; Klokk et al., Mol. Cell Biol. 27:1823-1843, 2007) were implemented in an automated imaging analysis system (Perkin Elmer Opera Image Screening System) and an algorithm for cytoplasm and nuclear segmentation was used to calculate translocation efficiency (
Considering that the tested samples were collected over a span of several years (Tables 2 and 5A), we sought to determine whether the observed contaminations persist over time. Two of the previously identified contaminated sites (SS97 and GL2W) were revisited and new grab water samples were collected. As shown in
Interestingly, 100× concentration of samples SS97 (
In conclusion, mammalian cell lines expressing GFP-tagged nuclear receptor constructs were utilized in an automated, highly reproducible, and low cost assay for detection of biologically active glucocorticoids and androgens in water sources. Using this high-throughput screening, combined with studies on transcriptional activation, glucocorticoid and androgen activities were discovered in water sources from 8 of 14 states in the US. This level of wide-spread contamination with steroids of both classes is a possible health hazard not only for the aquatic ecosystems, but may also negatively impact the human population. Largely unrestricted human activity with respect to many potential endocrine disruptors is of concern, and represents one of the main reasons for these wide-spread contaminations. Considering the largely unrestricted human activity in respect to many potential endocrine disruptors and limited methods (Roy & Pereira, Indian J Exp. Biol 43:975-992, 2005) for their detection in the environment, there is an urgent need of better assays for EDC screening. The results discussed here not only highlight the prevalence of contamination of water sources with glucocorticoid and androgen activities, but also introduce a novel approach for monitoring the quality of water. This approach can be readily extended to other nuclear receptors and applied to detection of various classes of EDCs in the environment.
EXAMPLE 2 Additional Traceable Fusion ProteinsThis example provides additional traceable fusion proteins that can be used in the methods and kits described herein.
Using molecular cloning methods essentially similar to those employed in Example 1, the following additional traceable fusion proteins have been constructed: an aryl hydrocarbon (e.g., dioxin) sensitive fusion protein, pRevTRE-GFP-mAhR (SEQ ID NOs: 9/10); a mineralocorticoid (e.g., aldosterone) sensitive fusion protein, eGFP-ratMR (SEQ ID NOs: 11/12); and a progestin-sensitive fusion protein, eGFP-hPRB (SEQ ID NOs: 13/14). All three proteins were expressed in mammalian cells and exhibited the expected translocation in response to the corresponding ligand (dioxin, aldosterone, and progesterone—see Example 3) such as those described in Example 1.
EXAMPLE 3 Translocation in GFP-PR-B Construct-Expressing Cell Line ClonesThis example demonstrates translocation response of four clonal lines expressing the traceable fusion protein GFP-PR-B upon exposure to defined amounts of progesterone.
Five mammalian clonal lines expressing the same traceable fusion protein, GFP-PR-B (eGFP-hPRB; SEQ ID NO: 14) were contacted with the indicated levels of progesterone, then assayed essentially as in Example 1 for translocation of the fusion protein into the nucleus from the cytoplasm. Four of the five clones tested (clones 8122, 8124, 8127, 8130) were positive for translocation in response to progesterone.
In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.
Claims
1. A system for detecting or quantifying a ligand of a superfamily receptor protein in a sample, the system comprising: wherein the first and second traceable fusion proteins independently comprise either: wherein at least one of the traceable fusion proteins is GFP-mAhR, GFP-MR, or GFP-PRB.
- a first mammalian cell expressing a first traceable fusion protein;
- a second mammalian cell expressing a second traceable fusion protein; and
- a detection system for the detection of the cytoplasm-to-nuclear translocation of the marker proteins,
- (1) a superfamily receptor protein, and
- a marker protein domain; or
- (2) the cytoplasmic/nuclear translocation domain of glucocorticoid receptor, the ligand binding domain of a superfamily receptor protein, and
- a marker protein domain
2. The system of claim 1, wherein the ligand is an agonist or an antagonist.
3. The system of claim 1, wherein the first traceable fusion protein binds a different ligand than the second traceable fusion protein.
4. The system of claim 3, wherein the marker protein domain is different in the first and second traceable fusion proteins.
5. The system of claim 1, wherein the marker protein domain is a fluorescent protein domain.
6. The system of claim of claim 1, wherein the ligand for the first or second traceable fusion protein is a natural ligand for the superfamily receptor protein of the traceable fusion protein, or a natural or synthetic compound that binds competitively therewith.
7. The system of claim 1, additionally comprising:
- one or more compounds and/or compositions that stably associate with a traceable fusion protein of the system in the absence of a ligand for the ligand binding domain of the traceable fusion protein, and which dissociates from the fusion protein in the presence of a ligand for the ligand binding domain of the traceable fusion protein.
8. The system of claim 1, wherein the mammalian cells are human cells.
9. The system of claim 1, comprising at least four mammalian cell lines each expressing a different traceable fusion protein, wherein at least one traceable fusion protein binds a glucocorticoid, at least one traceable fusion protein binds an androgen, at least one traceable fusion protein binds a progestin, and at least one traceable fusion protein binds an aryl hydrocarbon.
10. The system of claim 1, comprising at least four mammalian cell lines each expressing a different traceable fusion protein, wherein the traceable fusion proteins each bind one of a glucocorticoid, an androgen, a progestin, an aryl hydrocarbon, a thyroid hormone, or a mineralocorticoid.
11. The system of claim 1, provided as a kit.
12. A method for detecting or quantifying an endocrine disruptor chemical (EDC) ligand in a sample, the method comprising: wherein the fusion protein is GFP-mAhR, GFP-MR, or GFP-PRB.
- contacting with the environmental sample a human cell expressing in its cytoplasm a fusion protein comprising: a receptor for the ligand, which receptor translocates from the cytoplasm to the nucleus upon ligand binding; and a marker protein domain; and
- detecting cytoplasmic to nuclear translocation of the fusion protein in response to binding a ligand of the ligand binding domain in the environmental sample,
13. A method of determining the concentration of an endocrine disruptor chemical (EDC) ligand in a sample, the method comprising: wherein the fusion protein is GFP-mAhR, GFP-MR, or GFP-PRB.
- contacting with the environmental sample a population of eukaryotic cells expressing in their cytoplasm a fusion protein comprising: a receptor for the ligand, which receptor translocates from the cytoplasm to the nucleus upon ligand binding; and a marker protein domain; and
- scanning one or more test cell(s) to obtain signal data from the marker of the fusion protein;
- converting the signal data to obtain the cellular location of the labeled protein in the test cell(s); and
- analyzing the signal data using an analysis system having an algorithm to calculate changes in distribution of the labeled fusion protein between the cytoplasm and the nucleus of the test cell(s), the analysis system having the capability of providing an accurate reading of the concentration of the ligand,
14. The system of claim 19, wherein the environmental sample comprises a water sample, soil sample, or air sample.
15. The system of claim 14, wherein the sample comprises a water sample comprising surface water, sub-surface (ground) water, rain, run-off, well water, spring water, drinking water (processed or not), river water, estuary water, ocean water, effluent, treated sewage or untreated sewage.
16-18. (canceled)
19. The system of claim 1, wherein the sample is an environmental sample.
20. The method of claim 12, wherein the sample is an environmental sample.
21. The method of claim 13, wherein the sample is an environmental sample.
22. A traceable fusion protein capable of binding an endocrine disruptor chemical (EDC) ligand in a sample, comprising: wherein the ligand is an aryl hydrocarbon, a mineralocorticoid, or a progestin.
- a receptor for the ligand, which receptor translocates from the cytoplasm to the nucleus upon ligand binding; and
- a marker protein domain;
23. The traceable fusion protein of claim 22,
- comprising the polypeptide sequence shown in one of: SEQ ID NO: 10 (pRevTRE-GFP-mAhR); SEQ ID NO: 12 (eGFP-ratMR); or SEQ ID NO: 14 (eGFP-hPRB);
- or, encoded by the nucleic acid sequence shown in one of: SEQ ID NO: 9 (pRevTRE-GFP-mAhR); SEQ ID NO: 11 (eGFP-ratMR); or SEQ ID NO: 13 (eGFP-hPRB).
Type: Application
Filed: Jun 6, 2013
Publication Date: Jun 18, 2015
Inventors: Gordon L. Hager (Garrett Park, MD), Diana A. Stavreva (Washington, DC)
Application Number: 14/405,696
