| Cell migration is a fundamental and essential biological process that requires the precise coordination of several molecular pathways and physical forces. Understanding how cells encounter a plethora of extracellular signals in their environment, and translate these signals into the component processes that dictate how and where they migrate is of great importance to biology as breakdown of this complex system contributes to the pathology of several diseases. For cells to move in a directed manner, they must send out protrusions to find pro-migratory cues, make adhesive contract with these cues, and then couple the contraction of their cell body with release of adhesion at the rear of the cell.;The GTPase RhoA is a central player in the regulation of cell migration. RhoA is the master regulator of cell contractility, and promotes the formation of focal adhesions and actomyosin stress fibers. Inhibition of Rho activity is essential for initial cell spreading, and localized cycling of Rho activity must be tightly regulated for coordinated cell migration. The Abl family non-receptor tyrosine kinase, Arg, mediates adhesion-dependent inhibition of Rho through phosphorylation and activation of the Rho inhibitor p190RhoGAP. In this dissertation, I describe the elucidation of the mechanism of integrin-mediated RhoA inhibition by Arg and its substrate p190RhoGAP.;Here I show that Arg interacts directly with the cytoplasmic tail of the beta1 integrin receptor, which leads to stimulation of Arg kinase activity. Upon integrin adhesion, Arg colocalizes to and cofractionates with the integrin alpha5beta1, where the two likely interact to activate Arg in cells. Following integrin-mediated activation, Arg phosphorylates and activates p190RhoGAP, which forms a phosphorylation-dependent complex with p120RasGAP. p190 requires its p120-binding domain to undergo Arg-dependent activation in vivo, but p120 binding does not stimulate p190 activity in vitro. Instead, Arg-mediated p190 phosphorylation is required for the p190-p120 complex to localize to the cell periphery, where p190 can inhibit active Rho. Overall, this mechanism serves as a brake on Rho-mediated contractility, and plays an essential role in cell migration. |
