Retinoic acid receptor-alpha is stabilized in a repressive state by its C-terminal, isotype-specific F domain.
Retinoic acid receptors (RARs) are hormone-regulated transcription factors that play multiple roles in vertebrate development and differentiation. Three isotypes of RARs, alpha, beta, and gamma, are encoded by distinct genetic loci and possess distinct transcriptional properties. Typically, RARalpha represses target gene transcription in the absence of hormone, whereas RARbeta and gamma fail to repress under these conditions. This inability of RARbeta and RARgamma to repress transcription is due to intramolecular interactions between helix 3 and helix 12 of the hormone binding domains of these isotypes that inhibit corepressor binding while favoring coactivator binding. We report here that the converse ability of RARalpha to repress requires the integrity of the receptor F domain, a domain that maps C-terminal to helix 12, varies in sequence among different nuclear receptors, and is of poorly understood function. The F domain appears to help stabilize helix 12 of RARalpha in a more open position that enhances corepressor binding and inhibits coactivator binding in the absence of hormone. Intriguingly, the RARalpha F domain is isotype autonomous in its function. We speculate that the RARalpha F domain may dock elsewhere on the receptor surface, and this intramolecular interaction may maintain RARalpha helix 12 in an open, repression-competent conformation.
Section of Microbiology, Division of Biological Sciences, One Shields Avenue, University of California at Davis, Davis, California 95616, USA.
Behnom
B
Farboud
Martin L
ML
Privalsky
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D008969:Molecular Sequence Data; D056985:Nuclear Receptor Co-Repressor 2; D020033:Protein Isoforms / Q000235:genetics / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D018168:Receptors, Retinoic Acid / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D017384:Sequence Deletion / Q000235:genetics; D014158:Transcription, Genetic; D014212:Tretinoin / Q000494:pharmacology; D000097768:Retinoic Acid Receptor gamma
D004268:DNA-Binding Proteins; D056985:Nuclear Receptor Co-Repressor 2; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D012097:Repressor Proteins; D000072482:Retinoic Acid Receptor alpha; D014212:Tretinoin; D000097768:Retinoic Acid Receptor gamma; C082925:retinoic acid receptor beta