Myocardin enhances Smad3-mediated transforming growth factor- β1 signaling in a CArG box-independent manner: Smad-binding element is an important cis element for SM22α transcription in vivo

Ping Qiu, Raquel P. Ritchie, Zhiyao Fu, Dongsun Cao, Jerry Cumming, Joseph M. Miano, Da Zhi Wang, Hui J. Li, Li Li

Research output: Contribution to journalArticlepeer-review

118 Scopus citations


Transforming growth factor (TGF)-β1 is an important cytokine involved in various diseases. However, the molecular mechanism whereby TGF-β1 signaling modulates the regulatory network for smooth muscle gene transcription remains largely unknown. To address this question, we previously identified a Smad-binding element (SBE) in the SM22α promoter as one of the TGF-β1 response elements. Here, we show that mutation of the SBE reduces the activation potential of a SM22α promoter in transgenic mice during embryogenesis. Chromatin immunoprecipitation assays reveal that TGF-β1 induces Smad3 binding to the SM22α promoter in vivo. A multimerized SBE promoter responsive to TGF- β1 signaling is highly activated by Smad3 but not by the closely related Smad2. Intriguingly, myocardin (Myocd), a known CArG box-dependent serum response factor coactivator, participates in Smad3-mediated TGF-β1 signaling and synergistically stimulates Smad3-induced SBE promoter activity independent of the CArG box; no such synergy is seen with Smad2. Importantly, Myocd cooperates with Smad3 to activate the wild-type SM22α, SM myosin heavy chain, and SMα-actin promoters; they also activate the CArG box-mutated SM22α promoter as well as the CArG box-independent aortic carboxypeptidase-like protein promoter. Immunopreciptiation assays reveal that Myocd and Smad3 directly interact both in vitro and in vivo. Mutagenesis studies indicate that the C-terminal transactivation domains of Myocd and Smad3 are required for their functional synergy. These results reveal a novel regulatory mechanism whereby Myocd participates in TGF-β1 signal pathway through direct interaction with Smad3, which binds to the SBEs. This is the first demonstration that Myocd can act as a transcriptional coactivator of the smooth muscle regulatory network in a CArG box-independent manner.

Original languageEnglish (US)
Pages (from-to)983-991
Number of pages9
JournalCirculation research
Issue number10
StatePublished - Nov 2005
Externally publishedYes


  • Myocardin
  • SM22α or transgelin
  • Smad-binding site (SBE)
  • Smad3
  • Smooth muscle transcription
  • Transforming growth factor-β

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine


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