Erbin as a negative regulator of Ras-Raf-Erk signaling

Abstract

The instant invention provides a method of inhibiting proliferation of maligant cells by administration of a Ras-activity inhibitory effective amount of DNA which encodes the protein Erbin into the maligant cells.

Description

[0001] This application takes priority from Provisional Patent Application No. 60/383,603 filed May 29, 2003.

BACKGROUND AND FIELD OF THE INVENTION

[0002] This invention relates to use of Erbin as a novel suppressor of Ras for inhibition of cell, particularly malignant cell, proliferation. Erbin has now been found to be a negative regulator of the Ras-Raf-Erk signaling pathway.

[0003] Extracellular signal regulated kinases (Erk) are a subfamily of mitogen-activated protein kinases (MAPK) that play important roles in a great array of cell programs, including proliferation, differentiation and apoptosis. As exemplified by binding to growth factors such as EGF, receptor typrosine kinases are activated and undergo autophophorylation on tyrosine residues. The phosphorylated tyrosine residues recruit adaptor proteins to plasma membrane by directly interacting with modules including Sre homology 2 (SH2) or phosphotyrosine binding domain (PTB). Grb2, one such adaptor, brings guanyl nucleotide exchange factor (SOS) to the plasma membrane in proximity with Ras and expedites exchange of GDP and GTP on Ras. The activated Ras (GTP-bound) then directly binds to Raf and allows the latter to be activated at the plasma membrane. Active Raf triggers sequential activation of MEK, a MAPK kinase, and Erk, leading to phosphorylation of various regulatory proteins, including nuclear transcription factors such as Erk-1 and Myc as well as many cytoplasmic proteins.

[0004] In the past, extensive efforts have been made to identify factors that participate in the regulation of Ras-Raf-Erk pathway. Several modulators have been identified that positively influence the pathway at different levels. For example, MEK partner 1 (MP1) was isolated as a binding protein that interacts with both MEK1 and Erk 1 to enhance the efficiency of Erk phosphorylation by MEK. A second protein is the Kinase Suppresor of Ras (KSR) that is believed to act as a scaffold for Raf-1, MEK and Erk instead of a Raf kinase although it contains a kinase domain. A third such regulator is the Connector Enhancer of KSR (CNK) with multiple functional domains that directly binds to Raf and is involved in activation of the Raf/MEK/Erk pathway. Another interesting protein is Sur-8 that contains multiple leucine-rich regions (LRR) and binds to both Ras and Raf-1. Although Ras can directly associate with Raf when it is activated by charging with GTP, the presence of Sur8 increases the interaction between Ras and Raf and the activation of downstream signaling events. These non-enzymatic factors are important regulators for normal cell proliferation and differentiation.

[0005] In addition, there are negative regulators of the Ras pathway in cells. Sprouty, a Ras suppressor in Drosophila and its mammalian homologue Spred (Sprouty-related EVH1 domain-containing protein) appear to serve as physiological negative feedback regulators of growth factor-mediated Erk pathway. The Ras effector RINI has been shown to inhibit Ras-induced activation of Raf by competitively binding to active Ras. Additionally, the Raf kinase inhibitory protein (RKIP), initially isolated as a phosphatidylethanolamine binding protein, binds directly to the kinase domains of both Raf and MEK and inhibits MEK phosphorylation. These negative regulators function to ensure that all programs are adequately executed through autonomous turn-on and turn-off mechanisms. They may also counterbalance over-amplified proliferative signals caused by active mutation of Ras frequently occurring in human cancers or mutation of upstream components leading to the increased activity of the wild-type Ras which is found as well in human cancers. Such an inhibitory mechanism is key to maintain normal cell growth rate.

[0006] Erbin belongs to the LAP (LRR and PDZ) protein family of PDZ domain-containing proteins. In addition to Erbin, the family members include LET-413 in C. elegans, Scribble, a Drosophila protein essential for epithelial integrity, Densin-180, and Lano in mammals. Genetic studies in non-vertebrate have demonstrated that LAP proteins play a role in cell polarity and cell morphology of epithelial cells. Erbin was initially identified as a binding partner for ErbB2 and delta-catenin and ARVCF. This 180-kDa protein contains two domains: LRR and PDZ. The sequence of Erbin has been deposited in GenBank and assigned No. AF 263744. The biological function of Erbin and its impact on ErbB2-mediated signaling have yet to be addressed.

SUMMARY OF THE INVENTION

[0007] The instant invention provides a method of inhibiting proliferation of maligant cells by administration of a Ras-activity inhibitory effective amount of DNA which encodes the protein Erbin into the maligant cells. The amount of DNA administered is sufficient to provide a blood concentration of 1 &mgr;M to 100 &mgr;M of DNA which encodes Erbin into the cells. The DNA encoding Erbin may be administered via viral vectors.

[0008] The invention also provides methods for evaluating proliferative properties and progression of proliferative activities in tumor cells by measurement of Erbin in tumor tissue.

DETAILED DESCRIPTION OF THE INVENTION

[0009] This invention relates to use of Erbin, a known protein whose sequence is known and a DNA sequence encoding Erbin is deposited in GenBank as No. AF 263744, which is: 1 aaagatcttt tttttttttt tttctttttt tttcggcgga gatcctcgtt (SEQ ID. No. 1) ggggctggga aactcctgca aaactcgaga ccaggaagcc agcccgcacc ccaaccccca ccaaagccac ctactcttct tctgtgggag gccagtccac atccgctctc acccgagaga gatattcagc tggatccaaa gtgactgatg aagggaagga aatcatgtca agcgaagcct tgaaaaagct gccctgagac ggtgtcccgc cgaaagaatg ttggctcaat taagaaacat cagggagata aattcaaccc agtgtgtcta aaaatgacta caaaacgaag tttgtttgtg cggttggtac catgtcgctg tctacgaggg gaagaggaga ctgtcactac tcttgattat tctcattgca gcttagaaca agttccgaaa gagattttta cttttgaaaa aaccttggag gaactctatt tagatgctaa tcagattgaa gagcttccaa agcaactttt taactgtcag tctttacaca agctgagttt gccagacaat gatttaacaa cgttaccagc atccattgca aaccttatta atctcaggga actggatgtc agcaagaatg gaatacagga gtttccagaa aatataaaaa attgtaaagt tttgacaatt gtggaggcca gtgtaaaccc tatttccaag ctccctgatg gattttctca gctgttaaac ctaacccagt tgtatctgaa tgatgctttt cttgagttct tgccagcaaa ttttggcaga ttaactaaac tccaaatatt agagcttaga gaaaaccagt taaaaatgtt gcctaaaact atgaatagac tgacccagct ggaaagattg gatttgggaa gtaacgaatt cacggaagtg cctgaagtac ttgagcaact aagtggattg aaagagtttt ggatggatgc taatagactg acttttattc cagggtttat tggtagtttg aaacagctca catatttgga tgtttctaaa aataatattg aaatggttga agaaggaatt tcaacatgtg aaaaccttca agacctccta ttatcaagca attcacttca gcagcttcct gagactattg gttcgttgaa gaatataaca acgcttaaaa tagatgaaaa ccagttaatg tatctgccag actctatagg agggttaata tcagtagaag aactggattg tagtttcaat gaggttgaag ctttgccttc atctattggg cagcttacta acttaagaac ttttgctgct gatcataatt acttacagca gttgccccca gagattggaa gctggaaaaa tataactgtg ctgtttctcc attccaataa acttgagaca cttccagagg aaatgggtga tatgcaaaaa ttaaaagtca ttaatttaag tgataataga ttaaagaatt taccctttag ctttacaaag ctacagcaat tgacagctat gtggctctca gataatcagt ccaaacccct gatacctctt caaaaagaaa ctgattcaga gacccagaaa atggtgctta ccaactacat gttccctcaa cagccaagga ctgaggatgt tatgtttata tcagataatg aaagttttaa cccttcattg tgggaggaac agaggaaaca gcgggctcaa gttgcatttg aatgtgatga agacaaagat gaaagggagg cacctcccag ggagggaaat ttaaaaagat atccaacacc atacccagat gagcttaaga atatggtcaa aactgttcaa accattgtac atagattaaa agatgaagag accaatgaag actcaggaag agatttgaaa ccacatgaag atcaacaaga tataaataaa gatgtgggtg tgaagacctc agaaagtact actacagtaa aaagcaaagt tgatgaaaga gaaaaatata tgataggaaa ctctgtacag aagatcagtg aacctgaagc tgagattagt cctgggagtt taccagtgac tgcaaatatg aaagcctctg agaacttgaa gcatattgtt aaccatgatg atgtttttga ggaatctgaa gaactttctt ctgatgaaga gatgaaaatg gcggagatgc gaccaccatt aattgaaacc tctattaacc agccaaaagt cgtagcactt agtaataaca aaaaagatga tacaaaggaa acagattctt tatcagatga agttacacac aatagcaatc agaataacag caattgttct tctccatctc ggatgtctga ttcagtttct cttaatactg atagtagtca agacacctca ctctgctctc cagtgaaaca aactcatatt gatattaatt ccaaaatcag gcaagaagat gaaaatttta acagcctttt acaaaatgga gatattttaa acagttcaac agaggaaaag ttcaaagctc atgataaaaa agattttaac ttacctgaat atgatttgaa tgttgaagag cgattagttc taattgagaa aagtgttgac tcaacagcca cagctgatga cactcacaaa ttagatcata tcaatatgaa tcttaataaa cttataacta atgatacatt tcaaccagag atcatggaaa gatcaaaaac acaggatatt gtgcttggaa caagcttttt aagcattaat tctaaagagg aaactgagca cttggaaaat ggaaacaagt atcctaattt ggaatccgta aataaggtaa atggacattc tgaggaaact tcccagtctc ctaataggac tgaaccacat gacagtgatt gttctgttga cttaggtatt tccaaaagca ctgaagatct ctcccctcag aaaagtggtc cagttggatc tgttgtgaaa tctcatagca taactaatat ggagattgga gggctaaaaa tctatgatat tcttagtgat aatggacctc agcagccaag tacaaccgtt aaaatcacat ctgctgttga tggaaaaaat atagtcagga gcaagtctgc cacactgttg tatgatcaac cattgcaggt atttactggt tcttcctcat cttctgattt aatatcagga acaaaggcaa ttttcaagtt tgattcaaat cataatcccg aagagccaaa tataataaga ggccccacaa gtggcccaca atctgcacct caaatatatg gtcctccaca gtataatatc caatacagta gcagtgctgc agtcaaagac actttgtggc actccaaaca aaatccccaa atagaccatg ccagttttcc tcctcagctc cttcctagat cagagagcac agaaaatcaa agttatgcta aacattctgc caatatgaat ttctctaatc ataacaatgt tcgagctaat actgcatacc atttacatca gagacttggc ccagcaagac atggggaaat gtgggccatc tcaccaaacg accgacttat tcctgcagta actcgaagta caatccagcg acaaagtagt gtgtcctcca cagcctctgt aaatcttggt gatccaggct ctacaaggcg ggctcagatt cctgaaggag attatttatc atacagagag ttccactcag cgggaagaac tcctccaatg atgccaggat cacagagacc cctttctgca cgaacataca gcatagatgg tccaaatgca tcaagacctc agagtgctcg accctctatt aatgaaatac cagagagaac tatgtcagtt agtgatttca attattcacg gactagtcct tcaaaaagac caaatgcaag ggttggttct gagcattctt tattagatcc tccaggaaaa agtaaagttc ctcgtgactg gagagaacaa gtacttcgac atattgaagc caaaaagtta gaaaagatgc ctttgagtaa tggacagatg ggccagcctc tcaggcctca ggcaaattat agtcaaatac atcacccccc tcaggcatct gtggcaaggc atccctctag agaacaacta attgattact tgatgctgaa agtggcccac cagcctccat atacacagcc ccattgttct cctagacaag gccatgaact ggcaaaacaa gagattcgag tgagggttga aaaggatcca gaacttggat ttagcatatc aggtggtgtc gggggtagag gaaacccatt cagacctgat gatgatggta tatttgtaac aagggtacaa cctgaaggac cagcatcaaa attactgcag ccaggtgata aaattattca ggctaatggc tacagtttta taaatattga acatggacaa gcagtgtcct tgctaaaaac tttccagaat acagttgaac tcatcattgt acgagaagtt tcctcataag cactgtggac aaaaaaagcg gggaagacag caagatttat tggaagatac ttacagggga aattaatatt ttgactattt ttatatataa agaagaactc aaaaaattat gttcaaattt gtacattaat gaaataatgg ataaaggaga ctgttgaatt cataccatat aaaacttgtt aggtttttaa acatagcaat caaggctaca aaaacaaacc tgtgttgttt ttgtatagat tgtaggttta tttttggatt tcatatacat gactgaactg tgtgcaaggc aatagttagc cttgatttta gcccagagac agatggcaga gctatctctc tcatagcttt tatgccctta tttttattca actggtatta atgtttttct cctgaaacta ctttttttga tgtgggcaag agatttgaag tgttggcttt tgctatgtgc atattgaatt gaagagtgag taggtgaagg tggtgctggt gggttcactt tccaaggcca gactaaaaca gttattttct ataaaaatct ggaagcaaag aatggggatg gggagagcta cgtggtagta tgtttttatt aggagaataa tgcaataaaa tatgtaatgt cttttttata aagcaaaaaa gacaataatt gcatttatga gctcggcagg atctgttctt gtcatagcca ttgactatac atttgctact ggtgattcag tttttaattt tttagtcaca ggaaattttt aactctactg tagatgcatg tccatgcatt ttctgtgtta tggaaatcca ctgatttttt tttttttttc aaatggtggt acttgcaatc tgttttataa ttagtgctcc atttaaatct aatttataat ttttatttta agcagcaaat gaaacaaaaa tggccagttt taagattgtg ttgcctgtaa cacaaaatgt tacgaaggtt taggaaagcc tctttgattt ttgtttggcc ttgcattggc ccttggtaaa gtaaaaggaa acagtacact tggagctagg aaaccaaagc aagctttgtg aaactggcac agtgatagag aattgctgtg gagagttata gagcaaaggg atgggtcctt gaggcctgcc agtgtgtaaa ggtgttcaaa taaagggctg tttctacagg taacattaaa tgtgaactca acacttccag agtctttaaa gggtttctat gtgtatcagt gtaatagtgt tttaccacca actgcctttc tttgttccta gttactgtaa caaatatttg atgatagagg tttattaatt ttgtttatcc agaccattaa ttttatttgt ttttgtctat gtaatcaaat aaaatttgag taacatgtaa tggtaaggat taatgcatgg ttatttggac cagaaaaaag tgccatagaa gaccaataac tgtttagttg aggctagtct ggaacctttc attagagcaa tatttggtta ttgcacttca tttttattta ctaagaaatg caatttggga atttttaatc tgttatgctt tgtttatcaa ccttgatttt aattaagact tttataagac tagcttaaaa caccaaccaa cattattttt gcaaaagtga gttggactca ctttccattc ttgctagtca gagtaagtag gcagcacttt taaaaatatg tgaactcaaa tattgcactt ctttcaagat gttatcaatt ggttattgta ctgtatagtt ttaataattt tgattgaaac cctttaacaa ctctttgtaa attttaactc attttagttg attttcagta ctatttacat aggaattgat ttttatggat atagtagaag aaatgtgctg tattttgata aaattcactt attgtatgtg tgttgtaatc taaaaaaaaa aagaatgaca aacagcttct ttaagacaaa aaaaaaaaaa aaaaaaaaa

[0010] Erbin is a negative regulator of the Ras-Raf-Erk signaling pathway. Expression of Erbin decreases neuregulin-induced transcription of AChR &egr;-subunit gene, an event that requires Erk activation. Although it interacts with the ErbB2 C-terminus through the PDZ domain, Erbin has no effect on ErbB2 tyrosine phosphorylation and binding to adaptor proteins Shc or Grb2. In contrast, expression of Erbin greatly impairs Erk activation by ligands that activate receptor tyrosine kinases, without causing a significant change in AKT activity. It is now shown herein that Erbin diminishes the ability of Ras but not Raf-1 to activate Erk. Consistently, Erbin binds only to active Ras, as opposed to inactive Ras or Raf, resulting in inhibition of the interaction between Ras and Raf both in vivo and in vitro. As a suppressor of the Ras by disrupting Raf binding to active Ras, Erbin acts to suppress tumorigenesis of cancer cells, especially breast and prostate cancer cells. The control of tumorigenesis by increasing level of Erbin in malignant tissue by various means, especially through gene therapy, to obtain a blood or target tissue cell concentration of about 1 &mgr;M to 100 &mgr;M concentration would be appropriate for control of malignancies.

[0011] Materials and Methods:

[0012] Plasmid Construction—The human Erbin N-terminal domain (aa 1-391) consisting of 16 LRRs was generated by PCR amplification using sense primer containing BamHI and antisense primer containing XhoI. The resulting 1.2 kb-fragment was digested with BamHI and XhoI, and subcloned in the BamHI-SalI sites of yeast vector pGBT9 downstream of the Gal4 DNA binding domain (Clontech). Myc-Erbin LRR, Myc-ErbinD965 and Myc-DPDZ were generated by introducing a stop codon after the LRR domain following aa 965 or aa 1279 in pRK5-Myc-Erbin. The N-terminal deletion mutant (pRK5-Erbin965) was described previously (Huang, Y. Z., Wang, Q., Xiong, W. C., and Mei, L. (2001) J Biol Chem 276, 19318-19326); and Borg, J. P., Marchetto, S., Le Bivic, A., Ollendorff, V., Jaulin-Bastard, F., Saito, H., Fournier, E., Adelaide, J., Margolis, B., and Birnbaum, D. (2000) Nat Cell Biol 2, 407-414). A fragment encoding the full-length Akt cDNA generated by PCR using sense primer containing EcoRI and antisense primer containing XhoI. The resulting 1.6 kb-fragment was digested with EcoRI and XhoI, and subcloned into EcoRI-XhoI sites of the mammalian expression vector pCS2+MT (for the Myc tag at the amino terminus). Wild type-ErbB2 and constitutive active form of ErbB2 (NeuT) (generously provided by Dr. M. C. Hung, University of Texas M. D. Anderson Cancer Center) were subcloned downstream of the Flag-tag and an artificial signal peptide in pCMV. pCMV-Flag-Erk1 was generously provided by Dr. Mike Weber (University of Virginia). Flag-Ras, Flag-RasV12, Flag-RasN17, GST-Raf-C4, and GST-Raf-BXB were described as previously (Zang, M., Hayne, C., and Luo, Z. (2002) J Biol Chem 277, 4395-4405).

[0013] Cell Culture and Transfection—HEK 293 cells and COS-7 cells were cultured as described previously (Huang, supra). The C2C2 cells were maintained as undifferentiated myoblasts in DMEM with high glucose supplemented with 20% fetal bovine serum, and 0.5% chicken embryo extract. Fusing of myoblasts into myotubes was induced by culturing myoblasts for 48 hours in differentiation medium DM (DMEM plus 4% horse serum). Mouse lung epithelial Mv1Lu cells were maintained in DMEM plus 10% fetal bovine serum (FBS). Rat pheochromocytoma-derived PC12 cells were grown in DMEM supplemented with 10% FBS and 5% horse serum. HEK 293, COS-1 and C2C12 cells were transfected with the standard calcium phosphate technique. PC12 cells and Mv1Lu cells were transfected with SuperFect regents (Qiagen). Two days after transfection, cells were washed with PBS and lysed in the modified RIPA buffer containing 20 mM sodium phosphate, pH 7.4, 50 mM sodium fluoride, 40 mM sodium pyrophosphate, 1% Triton X-100, 2 mM sodium vanadate, 10 mM p-nitrophenyl phosphate, and protease inhibitors. Lysed cells were incubated on ice for 20 min and centrifuged at 13,000×g for 10 min at 4 C. The clear supernatant was designated as cell lysates.

[0014] Immunoprecipitation and Immunoblottina—Cell lysates (˜400 &mgr;g of protein) were incubated without or with indicated antibodies one hour at 40° C. and subsequently with protein A- or protein G-agarose beads overnight at 4° C. on a rotating platform. After centrifugation, beads were washed five times with the modified RIPA buffer. Bound proteins were eluted with the SDS sample buffer, resolved by SDS-PAGE and transferred onto nitrocellulose membranes (Schleicher and Schuell). Nitrocellulose membranes were incubated at room temperature for one hour in the blocking buffer containing Tris-buffered saline with 0.1% Tween (TBS-T) containing 5% milk or 5% BSA followed by an incubation with indicated antibodies in the blocking buffer. After washing 3 times for 5 min each with TBS-T, the membrane was incubated with horseradish peroxidase-conjugated donkey anti-mouse or anti-rabbit IgG (Amersham Pharmacia Biotech) followed by washing. Immunoreactive bands were visualized with enhanced chemiluminescence substrate (Pierce). In some experiments, the nitrocellulose filter was incubated in a buffer containing 62.5 mM Tris/HCl, pH 6.7, 100 mM &bgr;-mer-captoenthanol, and 2% SDS at 50° C. for 30 min, and washed with 0.1% Tween 20 in 50 mM TBS at room temperature for 1 hr, and reblotted with different antibodies. The following antibodies were used: Flag (M2, Sigma), Myc (9E10, Santa Cruz), phospho-MAPK (Promega), phospho-Akt (Ser473, New England Biolab) and Erbin.

[0015] Luciferase Assay—Myoblasts were co-transfected with or without Myc-Erbin, plus the &egr;-subunit promoter-luciferase transgene that contains 416 nucleotides of the 5′UTR of the &egr;-subunit gene (25) and a control plasmid pRL-SV40 (Promega). Twenty four hours after transfection, the myoblasts were incubated in DM to induce myotube formation. Myotube formation was complete 48 hours after switch to DM. The C2C12 myotubes were stimulated with neuregulin at a final concentration of 10 Nm at 37° C. for 24 hours. Mv1Lu cells were transiently transfected with the promoter reporter construct p3TP-Lux, which promoter contains three AP-1 sites and the plasminogen activator inhibitor-1 (PAI-1) promoter and firefly luciferase. pRL-SV40 that express Renilla luciferase under the control of SV40 promoter was cotransfected as a control to monitor the transfection efficiency. Fourty eight hours after transfection, cells were lysed and activities of the two different luciferases were assayed with respective substrates with a dual luciferase assay kit (Promega).

[0016] Differentiation of PC12 cells—PC12 cells were cotransfected pEGFP with empty vector pRK5-Myc, Myc-Erbin or its mutants, or Erbin RNAi duplex. Forty eight hours after transfection, PC12 cells were stimulated by 100 ng/ml or 20 &eegr;g/ml NGF for 2 days. Cells were examined by fluorescence microscopy. Cells with processes 1.5 times longer than the diameter of the cell body were considered to be differentiated.

[0017] Inhibition of Erbin expression by RNAi—The target region of siRNA was 100 nt downstream of the start codon, which contained approximately 50% G/C content. The nucleotide sequence was 5′ UAG ACU GAC CCA GCU GGA A dTdT 3′ (nt 866-884) (Borg, J. P., Marchetto, S., Le Bivic, A., Ollendorff, V., Jaulin-Bastard, F., Saito, H., Fournier, E., Adelaide, J., Margolis, B., and Birnbaum, D. (2000) Nat Cell Biol 2, 407-414). The NCBI sequence bank was searched against this segment Cof DNA using the blast program, which revealed no match, suggesting of the specificity of target recognition by siRNA. The 21-nucleotide RNAs were chemically synthesized by Dharmacon Research Inc. Synthetic oligonucleotides were deprotected and gel-purified. To demonstrate the silencing effect of endogenous Erbin expression by siRNA, cells in 60 mm-culture dish were co-transfected with empty vector pEGFP and with siRNA duplex using the SuperFect kit (Qiagen). Briefly, 2 mg of pEGFP and 30 ml of 20 mM RNAi duplex were mixed with 300 ml of Opti-MEM (GIBCO-BRL). After incubating 10 min at room temperature, Opti-MEM was added to obtain a final volume of 1 ml. Cells were incubated with the mixture for 2-3 hours at 37° C. and 5% CO before the addition of 5 ml of growth medium. Seventy two hours after transfection, cells were resuspended in PBS buffer. GFP-positive cells were collected by fluorescence-activated cell sorting (FACS) analysis. Cells were lysed in modified RIPA buffer and lysates were subjected to immunoblotting for expression of Erbin. In parallel experiments, GFP-positive PC12 cells were scored for differentiation.

[0018] Protein Assay—Protein was assayed with Coomassie Protein Assay Regent (Pierce) using bovine serum albumin as a standard.

[0019] Erbin inhibits neuregulin-induced transcription of the AChR &egr;-subunit gene and Erk activation—It was found that transcription of AChR subunit genes is increased by neuregulin, a ligand that activates the ErbB2 receptor tyrosine kinase. Previous studies in this laboratory and by others have demonstrated that neuregulin-induced AChR expression requires ErbB2 tyrosine phosphorylation and activation of the Ras-Raf-Erk signaling pathway. It now is seen that Erbin, interacting with ErbB2, plays a role in regulating neuregulin signaling. To test this hypothesis, it was useful to examine the effect of Erbin on the promoter activity of &egr;416-Luc, a transgene reporter that contains 416 nucleotides of the 5′UTR of the -subunit gene. Expression of this transgene is up-regulated by neuregulin or Ras- or Raf-activation and requires Erk activation. Unexpectedly, it was found that co-expression of Erbin inhibited neuregulin-activated expression of the &egr;416-Luc transgene, suggesting that Erbin may regulate the Erk activation.

[0020] To test this hypothesis, it was useful to characterize effects of Erbin on Erk1 activation in COS-7 cells. Flag-Erk1 was activated in response to the growth factor NRG in cells cotransfected with ErbB4. Coexpression of Erbin caused a significant decrease in the level of phopho-Erk, indicating that Erbin negatively regulate the Ras-Raf-MEKErk pathway. The inhibitory effect of Erbin featured the following: (1) it was dose-dependent; (2) Erbin did not seem to delay the peak Erk activation that usually occurred within 5 min of stimulation; (3) the inhibition was not growth factor-specific. In addition, expression of Erbin inhibited EGF- and NGF-induced Erk activation and (4) it was Erk activation-specific, since expression of Erbin had no apparent effect on NRG activation of Akt. Thus, the results demonstrate that Erbin specifically inhibits Erk activation with little effect on the PI3 kinase pathway.

[0021] To identify the domain that inhibits the Erk activation, we examined the effect of a series of Erbin mutations. The results revealed that the inhibition of Erk did not require PDZ domain, which interacts with ErbB2 or the region between the LRR domain and the PDZ domain. In contrast, deletion of the LRR domain disabled Erbin to inhibit Erk activation. Furthermore, it was demonstrated that the LRR domain was sufficient to mediate the inhibitory effect. These results are in agreement with the differentiation assay and thus indicates that Erbin plays an important role in regulating the Ras-Raf-MEK-Erk pathway.

[0022] Erbin inhibits Erk activation by Ras—An attempt was made to dissect the position for Erbin action by walking upstream of Erk. Since ErbB2 directly interacts with the cytoplasmic domain of tyrosine kinase receptors, it is possible that Erbin interferes with the tyrosine kinase activation and/or subsequent binding to adaptor proteins. To test these hypotheses, it was decided to take the advantage of NeuT, an active form of ErbB2 (Bargmann, C. I., Hung, M. C., and Weinberg, R. A. (1986) Cell 45, 649-657). When expressed in COS1 cells, NeuT was tyrosine-phosphorylated, resulting in an increase in the promoter activity of p3TP-Lux. When NeuT was immunoprecipitated, association of Shc and Grb2 could be easily detected. Coexpression of Erbin had no effect on either tyrosine phosphorylation of NeuT or its association with Shc and Grb2. However, the NeuT-induced promoter activity of 3TP was greatly inhibited by Erbin, indicating that the site of Erbin action is downstream of the adapter proteins. Further examination was conducted to determine whether Erbin inhibits Erk activation by Raf or Ras. Since expression of the active mutant of Raf bypasses the requirement of upstream components for the MEK/Erk activation, Erbin would attenuate the Erk activation by active Raf, if it acted downstream of Raf. The results showed that coexpression of Erbin with active Raf was essentially without an effect on the Erk activation. Conversely, inhibition of Erk activation by active Ras was evidently observed. These results indicate that Erbin acts above Raf, likely at the level of Ras.

[0023] Erbin disrupts the Ras-Raf interaction—In considering the mechanism of the Erbin-induced inhibition of the Erk pathway, it was postulated that Erbin inhibits the interaction between active Ras and Raf by competitive binding to either of them, or diminishing the GTP-bound form of Ras. To test this, an active mutant of Ras (Flag-RasV12) was coexpressed with GST-Raf1 into HEK293 cell. Flag-RasV12 was found to copurify with GST-Raf1. In a reciprocal study, Raf1 was detected in the immunoprecipitates of active Ras. Remarkably, coexpression of Erbin decreased the interaction between active Ras and Raf. In an alternative study, the Ras pull-down assay developed by Rooij and Bos in which they exploited the nature of high affinity of GTP-Ras for the Ras-binding domain (RBD) of Raf-1, as compared with GDP-Ras was employed. The RBD (aa 50-150) was expressed as a GST-fusion protein and used to pull down GTP-Ras that had been activated inside cells cotransfected with or without Erbin. In cells transfected with Flag-Ras, GTP-Ras was recovered by the GST-Raf-RBD beads. Expression of Erbin inhibited the interaction of Raf with growth factor-activated Ras, accompanied by a decrease in phospho-Erk1. These results indicate that Erbin inhibits the Erk pathway by disrupting the interaction between active Ras and Raf.

[0024] Studies were conducted to determine whether Erbin directly bound to active Ras or Raf in a manner to prevent them from forming a complex. When recombinant Erbin was isolated from HEK293 cells contransfected with Raf-1, no association was found between these two proteins. A parallel experiment was performed with Erbin and Ras. Only the active RasV12 was co-immunoprecipitated with Erbin, as opposed to the dominant negative mutant Ras. These clearly indicate that Erbin competes with Raf1 by binding to active Ras.

[0025] Inhibition of NGF-induced PC12 cell differentiation by Erbin—To further study the physiological importance of the Ras inhibition by Erbin, the effect of its overexpression on neuronal differentiation of rat pheochromocytoma (PC12) cells was examined. By chronic incubation with NGF, these cells differentiated developed sympathetic neuron-like phenotypes. The NGF-treated cells stopped to divide and in turns developed long, sometimes branched processes. The signaling events have been well characterized during NRG-induced differentiation of PC12 cells in which the Ras-Raf-Erk pathway plays an essential role. The inhibition of Erk activation by Erbin prompted an extended study to more broadly examine its effect on NRG-induced differentiation of PC12 cells. Expression of enhanced green fluorescent protein (EGFP) and the pRK5-Myc empty vector (control) had no apparent effect on the differentiation, whereas Erbin-transfected PC12 cells exhibited altered morphology. The neurites became shorter and were less branched. Under the control condition, cells bearing neurites 1.5 times longer than the cell body accounted for 60±5% of the total cell population, whereas the number of differentiated cells are significantly reduced after Erbin transfection. Ectopic expression of the LRR domain showed similar effect on differentiation, suggesting the inhibitory activity was contained in this domain. In contrast, cells transfected with &Dgr;965 encoding C-terminal domain of Erbin appeared to have normal differentiation.

[0026] To verify the inhibitory effect of Erbin on PC12 cell differentiation, the effect of suppressed Erbin expression in PC12 cells was examined. RNA interference (RNAi) techniques were used for this purpose. As an emerging new technique to diminish expression of specific genes at a cellular level, sequence-specific double-stranded RNA are first employed in evolutionarily diverse organisms including plants, fungi, and metazoans (Hammond, S. M., Caudy, A. A., and Hannon, G. J. (2001) Nat Rev Genet 2, 110-119). Recently, RNAi has been shown to specifically suppress the expression of endogenous and heterologous genes in mammalian cell lines. Thus, 21 nucleotide RNAi duplexes directed against Erbin (nucleotides 866-884) were synthesized and transfected in PC12 cells to suppress the expression of endogenous Erbin. Two days after transfection, cells expressing co-transfected EGFP were sorted out and analyzed for Erbin expression by Western blot. Expression of Erbin in RNAi-transfected cells was significantly decreased in comparison with missense RNAi-transfected cells (control). The suppressing effect by Erbin RNAi appeared to be specific since it had no effect on expression of endogenous Erk1. Moreover, expression of cotransfected EGFP was unaffected. Having demonstrated that sense RNAi inhibits expression of endogenous Erbin, RNAi-transfected PC12 cells were challenged with 20 ng/ml NGF to induce differentiation. To capture the maximal effect of Erbin RNAi, a sub-maximal effective concentration of NGF was used, as at this concentration, NGF caused differentiation of only 25±2% PC12 cells. Remarkably, suppressing Erbin expression by sense RNAi enhanced NGF-mediated cell differentiation (52±2%), while missense RNAi had no significant effect (18±2%). These data reinforce the conclusion that Erbin inhibits NGF-induced differentiation of PC12 cells.

[0027] Preparation and administration of viral vectors. The costruction of adenovirus is carried out according to established protocols (Proc. Natl. Acad. Sci. USA (1998) 95: 2509-2514) using a set of commercially available plasmids. Briefly, DNA encolding the full length of Erbin or the LRR domain (Erbin-LRR) is coded into pAdTrack-CMV. Ad-Erbin or Erbin-LRR and control AdGFP adenoviruses are generated in BJ5183 (available from American Type Culture Collection (ATCC) as deposit JHU-18) bacterial cells by homologous recimbination of the viral pAdEasy-1 and pAdTrack CMV-Erbin or Erbin-LRR and pAdTrack-CMV, respectively. Cells available from ATCC under deposit number CRL-1573 known as 293 cells are used as hosts for viral productions by known methods. (See Neuron. (2002), 35:489-505)

[0028] The adenoviruses expressing Erbin or Erbin-LRR are injected into the tumor tissue to infect cancer cells, particularly breast or prostate cancer cells.

[0029] Administration of Erbin DNA into tumors. Mice are anesthetized with phenobarbital sodium. Tumor tissues are injected with 100 &mgr;g of closed circular DNA (pcDNA3-Erbin or Erbin-LRR) at concentration of 1.0 &mgr;g/&mgr;l in saline using a syringe with a 27-gauge needle. To enhance the transfection efficiency, injected tumor tissues are subjected to electroporation with a pair of tungsten needles inserted into the tumor encompassing DNA injection sites. Electric pulses are delivered using an electric pulse generator.

[0030] Monitoring Erbin expression. Erbin expression in tumor tissues and cells may be monitored by two methods: Western blot and immunohitochemical analysis, both using anti-Erbin antibody.

[0031] Western blot: Tumor tissue or cell lysates (about 400 &mgr;g of protein) from the suspect tissue and from control, normal tissue are resolved by SDS-PAGE, and transferred into nitrocellulose membranes. Nitrocellulose membranes are incubated at room temperature for one hour in the blocking buffer containing Tris-buffered saline with 0.1% Tween (TBS-T) containing 5% milk followed by incubation with anti-Erbin antibody in the blocking buffer. After washing three times for 5 minutes each with TBS-T, the membrane is incubated with horseradish peroxidase-conjugated donkey anti-rabbit IgG (Amersham Biosciences) followed by washing. Immunoreactive bands are visualized with enhanced chemiluminescence substrate (Pierce).

[0032] Immunohistochemical analysis. Tumor tissues are rapidly dissected and frozen in isopentane cooled with dry ice. Ten &mgr;M sections are prepared using a cryostat, thaw mounted on gelatin-coated slides and stored at −80°C. Sections of tumor tissue sections are incubated with 2% normal goat serum (Vector Laboratories, Burlingame, Calif.) in PBS for 1 hour at room temperature to reduce background staining and then incubated with the affinity-purified and anti-Erbin antibody in 2% normal goat serum in PBS overnight at 4° C. After wiashing the sections five times with PBS, each for 30 minutes, the sections are incubated with a flourescein istothiocyanate-conjugated anti-rabbit antibody (Zymed Laboratories Inc., San Francisco, Calif.) or visualized by the established DAB method. Fluorescent images are captured on Sony CCD camera mounted on a Nikon E600 microsope using Photoshop imaging software. The amount of Erbin is then determined.

[0033] In each instance, the amount of Erbin as measured is measured against standards and against the amount of Erbin in normal tissues. It is also possible to evaluate progression of disease by measuring the amount of Erbin in samples from target tissue repeatedly.

[0034] Identification of Erbin mutants. Tumor tissue samples are collected from patients with breast or prostate cancer and from health controls, matched for geographical origin. DNA is isolated and collected in tripotassium EDTA strile tubes and immediately stored at −70° C. Genomic DNA extraction is performed on the tissue. The DNA sequence encoding the LRR domain is subjected to analysis of the Erbin gene. The polymorphism is identified using ARMS-PCR as previously described (Genes Immunity (2002) 3:30-33).

[0035] It appears that following Raf activation, Erbin functions to kick Raf off the plasma membrane by competing with Raf in binding to active Ras. Thus, overexpression of Erbin diminishes the accessibility of Ras-GTP to Raf-1. Alternatively, Erbin may compete with Sur-8 for binding to Ras and then dissociate the Sur 8/Ras/Raf ternary complex, resulting in down-regulation of the Erk pathway. It is conceivable that Erbin may act more quickly and efficiently than Sur 8, as it is enriched at the plasma membrane. Active mutations of the Ras gene renders it the most frequent oncogene found in human cancers and even more, many other oncogenes exploit Ras and its downstream cohorts to execute their functions. Thus, the use of Erbin for inhibitory mechanisms and blockers for this pathway is indicted as a means of inhibiting growth of malignant cells. The method involved administration of a proliferation inhibiting effective amount of Erbin or the administration of a vector which gives rise to production of a proliferation inhibiting effective amount of Erbin.

Claims

1. A method of inhibiting proliferation of maligant cells by administration of a Ras-activity inhibitory effective amount of DNA which encodes the protein Erbin into the maligant cells.

2. The method of claim 1 wherein the amount of Erbin administered is sufficient to provide an intracellular concentration of 1 &mgr;M to 100 &mgr;M of DNA which encodes Erbin into the cells.

3. The method of claim 1 wherein the DNA encoding Erbin is administered via viral vectors.

4. A method of evaluating proliferative properties and progression of proliferative activities in tumor cells by measurement of Erbin in tumor tissue comprising:

1) obtaining tumor tissue or cell lysates and

2) measuring the amount of Erbin in the sample obtained in step 1.

5. The method of claim 4 wherein the amount of Erbin is evaluated by Western blot.

6. The method of claim 4 wherein the amount of Erbin is evaluated by immunohistochemical analysis.