The RhoA effector mDiaphanous regulates MyoD expression and cell cycle progression via SRF-dependent and SRF-independent pathways

Abstract

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 (mDiaΔN3), 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, β-catenin. TCF activity was suppressed by mDiaΔN3 and induced by silencing mDia. mDiaΔN3 disrupted the signal-dependent nuclear localization of β-catenin and suppressed MyoD expression. Co-expression of a degradation-resistant form of β-catenin with mDiaΔN3 restored MyoD expression, suggesting a mechanistic link between the two signaling proteins. We also implicate a region encompassing the FH1 domain of mDia1 in β-catenin-TCF regulation. Taken together, our results suggest that a balance between two pathways downstream of mDia regulates MyoD expression and cell cycle progression.

RhoA knockout fibroblasts lose tumor-inhibitory capacity in vitro and promote tumor growth in vivo

“…The lists of the genes in each group are given in Datasets S1-S6. The data on the SRF-mDia pathway are shown as described previously (24,25).…”

Mechanical signaling through the cytoskeleton regulates cell proliferation by coordinated focal adhesion and Rho GTPase signaling

“…In this case, a key target is 1-integrin, which is upregulated upon loss of SCA1 and induces invasion of breast carcinoma cells (Brandt et al, 2009). A number of MRTF and SRF targets are also found in skeletal and smooth muscle cells, and here Rho signaling to SRF induces both proliferation and expression of differentiation-specific genes that are involved in myogenesis (Gopinath et al, 2007;Kuwahara et al, 2005;Lockman et al, 2004).…”

“…In this case, a key target is 1-integrin, which is upregulated upon loss of SCA1 and induces invasion of breast carcinoma cells (Brandt et al, 2009). A number of MRTF and SRF targets are also found in skeletal and smooth muscle cells, and here Rho signaling to SRF induces both proliferation and expression of differentiation-specific genes that are involved in myogenesis (Gopinath et al, 2007; Kuwahara et al., 2005; Lockman et al, 2004).Rho GTPases also signal to phosphoinositide 3-kinase (PI 3-kinase), which activates proliferation through the Akt pathway. For example, both RhoA and RhoC are involved in promoting proliferation in gastric carcinoma that depends on PI 3-kinase and Akt (Sun et al, 2007).…”

The small chromatin-binding protein p8 coordinates the association of anti-proliferative and pro-myogenic proteins at the myogenin promoter

“…By contrast, exit of undifferentiated myoblasts into G0 is accompanied by loss of MyoD expression, lack of myogenin and p21 induction, and, consequently, absence of musclespecific gene induction (Milasincic et al, 1996;Kitzmann et al, 1998;Sachidanandan et al, 2002;Dhawan and Helfman, 2004). G0 is reversible, and the G0-G1 transition in myoblasts is accompanied by reactivation of MyoD expression (Gopinath et al, 2007) (reviewed by Dhawan and Rando, 2005). Thus, cell-cycle re-entry correlates with the re-emergence of the capacity to differentiate, but differentiation itself requires additional signals.…”

“…The molecular logic for this restriction is that MyoD expression is suppressed in G0 (Milasincic et al, 1996;Kitzmann et al, 1998). MyoD expression is regulated by multiple factors, including Pax3 and Pax7 (reviewed by Buckingham 2001), serum response factor (SRF) L'Honore et al, 2003;Gopinath et al, 2007), and the transcriptional co-activator p300 (also known as CBP), a histone acetyl transferase (HAT) (reviewed by McKinsey et al, 2001;McKinsey et al, 2002). Post-translational modifications of MyoD also modulate its ability to promote differentiation.…”