RhoA GTPase Regulates M-Cadherin Activity and Myoblast Fusion

Abstract

The Rho family of GTP-binding proteins plays critical roles during myogenesis induction. To elucidate their role later during myogenesis, we have analyzed RhoA function during myoblast fusion into myotubes. We find that RhoA activity is rapidly and transiently increased when cells are shifted into differentiation medium and then is decreased until myoblast fusion. RhoA activity must be down-regulated to allow fusion, because expression of a constitutively active form of RhoA (RhoAV14) inhibits this process. RhoAV14 perturbs the expression and localization of M-cadherin, a member of the Ca 2؉ -dependent cell-cell adhesion molecule family that has an essential role in skeletal muscle cell differentiation. This mutant does not affect N-cadherin and other proteins involved in myoblast fusion, ␤1-integrin and ADAM12. Active RhoA induces the entry of M-cadherin into a degradative pathway and thus decreases its stability in correlation with the monoubiquitination of M-cadherin. Moreover, p120 catenin association with M-cadherin is decreased in RhoAV14-expressing cells, which is partially reverted by the inhibition of the RhoA effector Rho-associated kinase ROCK. ROCK inhibition also restores M-cadherin accumulation at the cell-cell contact sites. We propose that the sustained activation of the RhoA pathway inhibits myoblast fusion through the regulation of p120 activity, which controls cadherin internalization and degradation.

Fam65b Is a New Transcriptional Target of FOXO1 That Regulates RhoA Signaling for T Lymphocyte Migration

“…Interestingly, we show that this particularly well-conserved region related to PKN and predicted to display a coiled-coil structure is necessary to bind RhoA, suggesting that the effect of Fam65b on myoblast fusion may depend on its ability to interact with RhoA and to inhibit its activity. Consistent with this model, other investigators showed that a decrease in RhoA-GTP content was indispensable to allow myoblast fusion (32). Therefore, we consider it very likely that Fam65b behaves as an inducible repressor of RhoA activity to allow cellcell fusion during muscle or placenta formation.…”

Convergence ofIgf2expression and adhesion signalling via RhoA and p38 MAPK enhances myogenic differentiation

“…We demonstrate a transient but substantial and celldensity-dependent increase in RhoA activity 12-24 hours after initiation of differentiation -a period not investigated by Nishiyama et al (Nishiyama et al, 2004). Charrasse et al (Charrasse et al, 2006) suggest that RhoA is only upregulated after the initiation of myoblast fusion, which is not necessarily compatible with the observation that RhoA is required for upregulation of specific pro-myogenic genes (Carnac et al, 1998;Takano et al, 1998;Wei et al, 1998). Activation of RhoA, by inhibition of p190RhoGAP, enhances myogenesis and directs adipogenesis or myogenesis cell fate decisions towards the myogenic lineage (Sordella et al, 2003).…”

Tuning Collective Cell Migration by Cell–Cell Junction Regulation

“…Myoblast interactions engage multiple receptor systems in parallel, including focalized highdensity accumulation of M-and N-cadherin, neural cell adhesion molecule (NCAM), vascular cell adhesion molecule (VCAM-1), meltrin, and integrins (Fig. 1A) (Charrasse et al 2006;Abmayr and Pavlath 2012;Ozawa 2015). Once myoblasts connect with each other, individual mobility is largely disabled, whereas collective contractility and force transmission across cell-cell junctions are gained, particularly through the actomyosin cytoskeleton, which develops prominent stress fibers under the control of RhoA and bridges multiple cell bodies for coordinated rhythmic contractility of the multicellular ensemble (Charrasse et al 2006).…”

“…1A) (Charrasse et al 2006;Abmayr and Pavlath 2012;Ozawa 2015). Once myoblasts connect with each other, individual mobility is largely disabled, whereas collective contractility and force transmission across cell-cell junctions are gained, particularly through the actomyosin cytoskeleton, which develops prominent stress fibers under the control of RhoA and bridges multiple cell bodies for coordinated rhythmic contractility of the multicellular ensemble (Charrasse et al 2006). Thus, in fusing myoblasts high junction stability mediated through overlapping adhesion systems and cytoskeletal linkages support mechanically very stable junctions, which mediate collective contractility and eventually cell fusion, but discourage position change of the group as a whole and individual cells within the group.…”