Smads orchestrate specific histone modifications and chromatin remodeling to activate transcription.
Smads are intracellular transducers for TGF-beta superfamily ligands, but little is known about the mechanism by which complexes of receptor-phosphorylated Smad2 and Smad4 regulate transcription. Using an in vitro transcription system, we have discovered that, unlike most transcription factors that are sufficient to recruit the basal transcription machinery and therefore activate transcription on both naked DNA and chromatin templates, the Smads only activate transcription from chromatin templates. We demonstrate that Smad2-mediated transcription requires the histone acetyltransferase, p300. Smad2-recruited p300 exhibits an altered substrate specificity, specifically acetylating nucleosomal histone H3 at lysines 9 and 18, and these modifications are also detected on an endogenous Smad2-dependent promoter in a ligand-induced manner. Furthermore, we show that endogenous Smad2 interacts with the SWI/SNF ATPase, Brg1, in a TGF-beta-dependent manner, and demonstrate that Brg1 is recruited to Smad2-dependent promoters and is specifically required for TGF-beta-induced expression of endogenous Smad2 target genes. Our data indicate that the Smads define a new class of transcription factors that absolutely require chromatin to assemble the basal transcription machinery and activate transcription.
Ross
Sarah
S
Laboratory of Developmental Signalling, Cancer Research UK London Research Institute, London, UK.
Cheung
Edwin
E
Petrakis
Thodoris G
TG
Howell
Michael
M
Kraus
W Lee
WL
Hill
Caroline S
CS
D000107:Acetylation; D000818:Animals; D002478:Cells, Cultured; D002843:Chromatin / Q000378:metabolism; D042002:Chromatin Assembly and Disassembly / Q000187:drug effects; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D006367:HeLa Cells; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008957:Models, Genetic; D041681:NIH 3T3 Cells; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D051899:Smad2 Protein / Q000378:metabolism*; D051901:Smad4 Protein / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D050880:p300-CBP Transcription Factors / Q000378:metabolism
D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D006657:Histones; D009687:Nuclear Proteins; C445179:SWI-SNF-B chromatin-remodeling complex; D051899:Smad2 Protein; D051901:Smad4 Protein; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D050880:p300-CBP Transcription Factors