title: Alternative mRNA splicing of SMRT creates functional diversity by generating corepressor isoforms with different affinities for different nuclear receptors.
abstract: Many eukaryotic transcription factors are bimodal in their regulatory properties and can both repress and activate expression of their target genes. These divergent transcriptional properties are conferred through recruitment of auxiliary proteins, denoted coactivators and corepressors. Repression plays a particularly critical role in the functions of the nuclear receptors, a large family of ligand-regulated transcription factors involved in metazoan development, differentiation, reproduction, and homeostasis. The SMRT corepressor interacts directly with nuclear receptors and serves, in turn, as a platform for the assembly of a larger corepressor complex. We report here that SMRT is expressed in cells by alternative mRNA splicing to yield two distinct variants or isoforms. We designate these isoforms SMRTalpha and SMRTtau and demonstrate that these isoforms have significantly different affinities for different nuclear receptors. These isoforms are evolutionarily conserved and are expressed in a tissue-specific manner. Our results suggest that differential mRNA splicing serves to customize corepressor function in different cells, allowing the transcriptional properties of nuclear receptors to be adapted to different contexts.
authors.affiliation: Section of Microbiology, University of California, Davis, California 95616, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Goodson
authors.forename: Brian A
authors.initials: BA
authors.lastname: Jonas
authors.forename: Martin L
authors.initials: ML
authors.lastname: Privalsky
mesh_terms: D017398:Alternative Splicing; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics*; D019992:Databases as Topic; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D020224:Expressed Sequence Tags; D005799:Genes, Dominant; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D009113:Muramidase / Q000737:chemistry; D056985:Nuclear Receptor Co-Repressor 2; D016366:Open Reading Frames; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism*; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012984:Software; D014018:Tissue Distribution; D014158:Transcription, Genetic
chemical_list: D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C539130:NCOR2 protein, human; C539131:Ncor2 protein, mouse; D056985:Nuclear Receptor Co-Repressor 2; D020033:Protein Isoforms; D012333:RNA, Messenger; D012097:Repressor Proteins; D004247:DNA; D009113:Muramidase