TY - JOUR
T1 - Myocardin enhances Smad3-mediated transforming growth factor- β1 signaling in a CArG box-independent manner
T2 - Smad-binding element is an important cis element for SM22α transcription in vivo
AU - Qiu, Ping
AU - Ritchie, Raquel P.
AU - Fu, Zhiyao
AU - Cao, Dongsun
AU - Cumming, Jerry
AU - Miano, Joseph M.
AU - Wang, Da Zhi
AU - Li, Hui J.
AU - Li, Li
PY - 2005/11
Y1 - 2005/11
N2 - 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.
AB - 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.
KW - Myocardin
KW - SM22α or transgelin
KW - Smad-binding site (SBE)
KW - Smad3
KW - Smooth muscle transcription
KW - Transforming growth factor-β
UR - http://www.scopus.com/inward/record.url?scp=27944445459&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=27944445459&partnerID=8YFLogxK
U2 - 10.1161/01.RES.0000190604.90049.71
DO - 10.1161/01.RES.0000190604.90049.71
M3 - Article
C2 - 16224064
AN - SCOPUS:27944445459
SN - 0009-7330
VL - 97
SP - 983
EP - 991
JO - Circulation research
JF - Circulation research
IS - 10
ER -