title: Characterization of the AB (AF-1) region in the muscle-specific retinoid X receptor-gamma: evidence that the AF-1 region functions in a cell-specific manner.
abstract: The retinoid X receptors alpha, beta and gamma (RXRs) share a highly conserved 'C' region or DNA binding domain (DBD). The conserved 'DE' region or ligand binding domain (LBD) of the RXRs is functionally complex, mediating dimerization and a ligand-dependent activation function (AF-2). The AB or N-terminal region of the RXRs is poorly conserved and encodes a ligand-independent activation function (AF-1). RXR gamma mRNA is preferentially expressed in skeletal and cardiac muscle, however, cell-specific steroid receptor-mediated trans-activation is a poorly understood phenomenon. We utilized the GAL4 hybrid assay system and have demonstrated that RXR gamma contains two functional domains in the AB and DE regions that activate transcription in a ligand-independent and -dependent manner respectively. The functions of the AB (AF-1) and DE (AF-2) domains were regulated by cAMP-dependent protein kinases, furthermore, the function of AF-2 in the LBD was activated by 8-Br-cAMP, independent of 9-cis-retinoic acid treatment. Deletion analysis demonstrated that the AF-1 of RXR gamma, is located between amino acids 1 and 103 and contained multiple motifs that were targets of cAMP-dependent protein kinases. Transfection analyses in non-muscle and myogenic cells clearly demonstrated that: (i) the AF-1 of RXR gamma functions in a muscle-specific manner and is required for optimal ligand-dependent trans-activation from an RXRE; (ii) RXR gamma trans-activates more efficiently in a myogenic background.
authors.affiliation: University of Queensland, Centre for Molecular and Cellular Biology, St Lucia, Australia.
authors.forename: D H
authors.initials: DH
authors.lastname: Dowhan
authors.forename: G E
authors.initials: GE
authors.lastname: Muscat
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology*; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002522:Chlorocebus aethiops; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004988:Ethers, Cyclic / Q000494:pharmacology; D005656:Fungal Proteins / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D009132:Muscles / Q000166:cytology / Q000378:metabolism / Q000502:physiology; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D018168:Receptors, Retinoic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology*; D014212:Tretinoin / Q000494:pharmacology
chemical_list: D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D004988:Ethers, Cyclic; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D019319:Okadaic Acid; D015124:8-Bromo Cyclic Adenosine Monophosphate; D014212:Tretinoin; D017868:Cyclic AMP-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases