RhoGDIβ Inhibits Bone Morphogenetic Protein 4 (BMP4)-induced Adipocyte Lineage Commitment and Favors Smooth Muscle-like Cell Differentiation

The integration of signals involved in deciding the fate of mesenchymal stem cells is largely unknown. We used proteomics profiling to identify RhoGDI beta, an inhibitor of the small G-protein Rho family, as a component that regulates commitment of C3H10T1/2 mesenchymal stem cells to the adipocyte or smooth muscle cell lineage in response to bone morphogenetic protein 4 (BMP4). RhoGDI beta is notably down-regulated during BMP4-induced adipocytic lineage commitment of C3H10T1/2 mesenchymal stem cells, and this involves the cytoskeleton-associated protein lysyl oxidase. Excess RhoGDI beta completely prevents BMP4-induced commitment to the adipocyte lineage and simultaneously stimulates smooth muscle cell commitment by suppressing the activation of Rac1. Overexpression of RhoGDI beta induces stress fibers of F-actin by a process involving phosphomyosin light chain, indicating that cytoskeletal tension regulated by RhoGDI beta contributes to determining adipocyte versus myocyte commitment. Furthermore, the overexpression of RacV12 (constitutively active form of Rac1) totally rescues the inhibition of adipocyte commitment by RhoGDI beta, simultaneously preventing formation of the smooth muscle-like phenotype and disrupting the stress fibers in cells overexpressing RhoGDI beta. Collectively, these results indicate that RhoGDI beta functions as a novel BMP4 signaling target that regulates adipogenesis and myogensis.