The signaling protein Rho is necessary for vascular smooth muscle migration and survival but not for proliferation.

BACKGROUND: The small GTPase Rho has been implicated in a variety of cellular processes. Vascular smooth muscle cell (SMC) migration, proliferation, and apoptosis are important events that contribute to the formation of intimal hyperplasia. To better understand the importance of Rho in intimal hyperplasia, we evaluated the necessity of Rho for these 3 cellular processes.
METHODS: We used for these studies a recombinant C3 exoenzyme (C3), which selectively adenosine diphosphate-ribosylates and, thus, functionally inactivates Rho. SMC migration was determined by scratch and modified Boyden chamber assays, proliferation by tritiated-thymidine incorporation, and apoptosis by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling.
RESULTS: Pretreatment of human SMC with C3 overnight resulted in adenosine diphosphate-ribosylation and inactivation of Rho. Inactivation of Rho completely eliminated SMC migration in response to platelet-derived growth factor (PDGF)-AB. Furthermore, C3 blocked phosphorylation of focal adhesion kinase, tensin, and paxillin, which are essential for cellular migration. In contrast, C3 did not significantly affect DNA synthesis in response to PDGF-AB or activation of mitogen-activated protein kinase, a signaling mediator of PDGF-stimulated proliferation. However, prolonged inactivation of Rho by C3 induced apoptosis of SMC.
CONCLUSIONS: The small GTPase Rho is necessary for vascular SMC migration and cell survival but not for proliferation. Manipulation of Rho might have therapeutic value in modulating intimal hyperplasia.