The RhoA effector mDiaphanous regulates MyoD expression and cell cycle progression via SRF-dependent and SRF-independent pathways.
Expression of the key muscle transcription factor MyoD is regulated by RhoA GTPase, which is an important regulator of adhesion-dependent signaling. We show that mDiaphanous (mDia)--an adaptor protein that mediates the effects of RhoA on cell motility and the cytoskeleton--is an upstream regulator of MyoD in C2C12 mouse myoblasts. Knockdown of mDia1 reduced MyoD expression and proliferation via a serum-response factor (SRF)-dependent pathway. Surprisingly, overexpression of a Rho-independent form of mDia1 (mDiaDeltaN3), despite activating SRF, also suppressed MyoD and the cell cycle, suggesting the presence of a second pathway downstream of mDia1. We present evidence that the alternative pathway by which mDia1 regulates MyoD involves T-cell factor (TCF)/lymphoid enhancer factor (LEF) and its co-activator, beta-catenin. TCF activity was suppressed by mDiaDeltaN3 and induced by silencing mDia. mDiaDeltaN3 disrupted the signal-dependent nuclear localization of beta-catenin and suppressed MyoD expression. Co-expression of a degradation-resistant form of beta-catenin with mDiaDeltaN3 restored MyoD expression, suggesting a mechanistic link between the two signaling proteins. We also implicate a region encompassing the FH1 domain of mDia1 in beta-catenin-TCF regulation. Taken together, our results suggest that a balance between two pathways downstream of mDia regulates MyoD expression and cell cycle progression.
Center for Cellular and Molecular Biology, Uppal Road, Hyderabad, 500 007, India.
Suchitra Devi
SD
Gopinath
Shuh
S
Narumiya
Jyotsna
J
Dhawan
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology*; D002454:Cell Differentiation; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D000080865:Formins; D006801:Humans; D051379:Mice; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism*; D018008:Myogenin / Q000378:metabolism; D026362:Serum Response Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D051822:T Cell Transcription Factor 1 / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D051176:beta Catenin / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
D002352:Carrier Proteins; C491464:Diap1 protein, mouse; D000080865:Formins; D017570:MyoD Protein; C503801:Myog protein, mouse; D018008:Myogenin; D026362:Serum Response Factor; D051822:T Cell Transcription Factor 1; D051176:beta Catenin; D020742:rhoA GTP-Binding Protein