Cytoplasmic sequestration of the RhoA effector mDiaphanous1 by Prohibitin2 promotes muscle differentiation
Adhesion and growth factor dependent signalling control muscle gene expression through common effectors, coupling cytoskeletal dynamics to transcriptional activation. Earlier, we showed that mDiaphanous1, an effector of adhesion-dependent RhoA-signalling promotes MyoD expression in myoblasts, linking contractility to lineage determination. Here, we report that paradoxically, mDia1 negatively regulates MyoD function in myotubes. Knockdown of endogenous mDia1 during differentiation enhances MyoD and Myogenin expression, while over-expression of mDia1{Delta}N3, a RhoA-independent mutant, suppresses Myogenin promoter activity and expression. We investigated mechanisms that may counteract mDia1 to promote Myogenin expression and timely differentiation by analysing mDia1-interacting proteins. We report that mDia1 has a stage-specific interactome, including Prohibitin2, MyoD, Akt2, and {beta}-Catenin, of which Prohibitin2 colocalises with mDia1 in cytoplasmic punctae and opposes mDia1 function in myotubes. Co-expression of mDia1-binding domains of Prohibitin2 reverses the anti-myogenic effects of mDia1{Delta}N3. Our results suggest that Prohibitin2 sequesters mDiaphanous1 to dampen its activity and finetune RhoA-mDiaphanous1 signalling to promote differentiation. Overall, we report that mDia1 is multi-functional signaling effector with opposing functions in different cellular stages, but is modulated by a differentiation-dependent interactome.\n\nSummary statementmDia1 has common and stage-specific functions in muscle cells. In myotubes, mDia1 is sequestered by an interacting protein Prohibitin2, which promotes Myogenin expression and mitigates mDia1s inhibitory effects on differentiation.\n\nGraphical abstract\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=119 SRC=\"FIGDIR/small/283044v1_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (28K):\norg.highwire.dtl.DTLVardef@1b1578eorg.highwire.dtl.DTLVardef@1eb6b13org.highwire.dtl.DTLVardef@c2c913org.highwire.dtl.DTLVardef@1f1f9c_HPS_FORMAT_FIGEXP M_FIG C_FIG