Transforming growth factor beta-mediated transcriptional repression of c-myc is dependent on direct binding of Smad3 to a novel repressive Smad binding element.
Smad proteins are the most well-characterized intracellular effectors of the transforming growth factor beta (TGF-beta) signal. The ability of the Smads to act as transcriptional activators via TGF-beta-induced recruitment to Smad binding elements (SBE) within the promoters of TGF-beta target genes has been firmly established. However, the elucidation of the molecular mechanisms involved in TGF-beta-mediated transcriptional repression are only recently being uncovered. The proto-oncogene c-myc is repressed by TGF-beta, and this repression is required for the manifestation of the TGF-beta cytostatic program in specific cell types. We have shown that Smad3 is required for both TGF-beta-induced repression of c-myc and subsequent growth arrest in keratinocytes. The transcriptional repression of c-myc is dependent on direct Smad3 binding to a novel Smad binding site, termed a repressive Smad binding element (RSBE), within the TGF-beta inhibitory element (TIE) of the c-myc promoter. The c-myc TIE is a composite element, comprised of an overlapping RSBE and a consensus E2F site, that is capable of binding at least Smad3, Smad4, E2F-4, and p107. The RSBE is distinct from the previously defined SBE and may partially dictate, in conjunction with the promoter context of the overlapping E2F site, whether the Smad3-containing complex actively represses, as opposed to transactivates, the c-myc promoter.
Frederick
Joshua P
JP
Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina 27710, USA.
Liberati
Nicole T
NT
Waddell
David S
DS
Shi
Yigong
Y
Wang
Xiao-Fan
XF
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D018797:Cell Cycle Proteins; D002460:Cell Line; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D050684:E2F Transcription Factors; D050704:E2F4 Transcription Factor; D016259:Genes, myc / Q000187:drug effects*; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D016296:Mutagenesis; D011401:Promoter Regions, Genetic; D000090063:Proto-Oncogene Mas; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D051900:Smad3 Protein; D015534:Trans-Activators / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; C493763:E2f4 protein, mouse; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D012333:RNA, Messenger; D011994:Recombinant Proteins; C497790:SMAD3 protein, human; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D004247:DNA