Abstract: A method of easily measuring whether or not an LXR ligand has the function of effecting, e.g., increasing, plasma triglyceride concentration and/or LDL cholesterol concentration in a mammal by using the binding activity between LXR and a coactivator, and a method of identifying LXR ligands that do not have the function of effecting, e.g., increasing, plasma triglyceride concentration and/or LDL cholesterol concentration by using the binding activity between LXR and a coactivator.

Abstract: A method of easily measuring whether or not an LXR ligand has the function of effecting, e.g., increasing, plasma triglyceride concentration and/or LDL cholesterol concentration in a mammal by using the binding activity between LXR and a coactivator, and a method of identifying LXR ligands that do not have the function of effecting, e.g., increasing, plasma triglyceride concentration and/or LDL cholesterol concentration by using the binding activity between LXR and a coactivator.

Abstract: Regulators of the activation of the 20S proteasome for hydrolysis of peptide and protein substrates. Proteasome activating factors PA28 and PA700 are described and a carboxy-terminal fragment of a protein activator PA28 is described that is an effective inhibitor of the activation of the proteasome. The carboxy-terminal fragment binds to the proteasome and prevents the binding of PA28 and PA700 thereby preventing activation of the proteasome. Methods of treatment for muscle wasting are described wherein compositions of the present invention are administered to prevent unwanted protein degradation. Conversely, compositions of the present invention may be used to activate protein breakdown in situations where unwanted proteins accumulate in, for example, aging and Alzheimer's Disease.

Abstract: The characterization of LXR.alpha., an orphan member of the nuclear hormone receptor superfamily that can function as a tissue-specific mediator of 9-cis retinoic acid (9cRA) is described herein. When expressed in cells, LXR.alpha. activates transcription in response to 9cRA on a distinct response element, termed an LXRE. Significantly, neither RXR homodimers nor RXR/RAR heterodimers are able to substitute for LXR.alpha. in mediating this retinoid response. The LXR.alpha. response to retinoids is due to its unique interaction with endogenous RXR. This interaction shifts RXR from its previously described role as a silent, heterodimer partner to an active ligand binding partner, thus defining a novel retinoid response pathway.