title: A functional N-terminal domain in C/EBPβ-LAP* is required for interacting with SWI/SNF and to repress Ric-8B gene transcription in osteoblasts.
abstract: The chromatin remodeling complex SWI/SNF and the transcription factor C/EBPβ play critical roles in osteoblastic cells as they jointly control transcription of a number of bone-related target genes. The largest C/EBPβ isoform, LAP*, possesses a short additional N-terminal domain that has been proposed to mediate the interaction of this factor with SWI/SNF in myeloid cells. Here we examine the requirement of a functional N-terminus in C/EBPβ-LAP* for binding SWI/SNF and for recruiting this complex to the Ric-8B gene to mediate transcriptional repression. We find that both C/EBPβ-LAP* and SWI/SNF simultaneously bind to the Ric-8B promoter in differentiating osteoblasts that repress Ric-8B expression. This decreased expression of Ric-8B is not accompanied by significant changes in histone acetylation at the Ric-8B gene promoter sequence. A single aminoacid change at the C/EBPβ-LAP* N-terminus (R3L) that inhibits C/EBPβ-LAP*-SWI/SNF interaction, also prevents SWI/SNF recruitment to the Ric-8B promoter as well as C/EBPβ-LAP*-dependent repression of the Ric-8B gene. Inducible expression of the C/EBPβ-LAP*R3L protein in stably transfected osteoblastic cells demonstrates that this mutant protein binds to C/EBPβ-LAP*-target promoters and competes with the endogenous C/EBPβ factor. Together our results indicate that a functional N-terminus in C/EBPβ-LAP* is required for interacting with SWI/SNF and for Ric-8B gene repression in osteoblasts.
authors.affiliation: Center for Biomedical Research and FONDAP Center for Genome Regulation, Faculty of Biological Sciences and Faculty of Medicine, Universidad Andres Bello, Santiago, Chile.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Aguilar
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Grandy
authors.forename: Daniel
authors.initials: D
authors.lastname: Meza
authors.forename: Hugo
authors.initials: H
authors.lastname: Sepulveda
authors.forename: Philippe
authors.initials: P
authors.lastname: Pihan
authors.forename: Andre J
authors.initials: AJ
authors.lastname: van Wijnen
authors.forename: Jane B
authors.initials: JB
authors.lastname: Lian
authors.forename: Gary S
authors.initials: GS
authors.lastname: Stein
authors.forename: Janet L
authors.initials: JL
authors.lastname: Stein
authors.forename: Martin
authors.initials: M
authors.lastname: Montecino
mesh_terms: D016475:3T3 Cells; D000107:Acetylation; D000818:Animals; D001665:Binding Sites; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D042002:Chromatin Assembly and Disassembly; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D015536:Down-Regulation; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D051379:Mice; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010006:Osteoblasts / Q000378:metabolism*; D015675:Osteocalcin / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D020033:Protein Isoforms; D051381:Rats; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D002868:Chromosomal Proteins, Non-Histone; D020662:Guanine Nucleotide Exchange Factors; D006657:Histones; D009687:Nuclear Proteins; D020033:Protein Isoforms; C559967:Ric8b protein, mouse; C485886:Ric8b protein, rat; C445179:SWI-SNF-B chromatin-remodeling complex; D014157:Transcription Factors; D015675:Osteocalcin