Transforming growth factor beta-mediated transcriptional repression of c-myc is dependent on direct binding of Smad3 to a novel repressive Smad binding element

Mol Cell Biol. 2004 Mar;24(6):2546-59. doi: 10.1128/mcb.24.6.2546-2559.2004.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • Binding Sites / genetics
  • Cell Cycle Proteins*
  • Cell Line
  • DNA / genetics
  • DNA / metabolism
  • DNA-Binding Proteins / deficiency
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • E2F Transcription Factors
  • E2F4 Transcription Factor
  • Genes, myc / drug effects*
  • Humans
  • Mice
  • Mice, Knockout
  • Mutagenesis
  • Promoter Regions, Genetic
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Recombinant Proteins / pharmacology
  • Smad3 Protein
  • Trans-Activators / deficiency
  • Trans-Activators / genetics
  • Trans-Activators / metabolism*
  • Transcription Factors / metabolism
  • Transforming Growth Factor beta / pharmacology*

Substances

  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • E2F Transcription Factors
  • E2F4 Transcription Factor
  • E2F4 protein, human
  • E2f4 protein, mouse
  • RNA, Messenger
  • Recombinant Proteins
  • SMAD3 protein, human
  • Smad3 Protein
  • Smad3 protein, mouse
  • Trans-Activators
  • Transcription Factors
  • Transforming Growth Factor beta
  • DNA