RhoJ interacts with the GIT-PIX complex and regulates focal adhesion disassembly

Abstract

RhoJ is a RhoGTPase expressed in endothelial cells and tumour cells which regulates cell motility, invasion, endothelial tube formation and focal adhesion numbers. This study aimed to further delineate the molecular function of RhoJ. Using timelapse microscopy RhoJ was found to regulate focal adhesion disassembly; siRNA-mediated knockdown of RhoJ increased focal adhesion disassembly time, while expression of an active mutant (daRhoJ) decreased it. Further, daRhoJ co-precipitated with the GIT-PIX complex, a regulator of focal adhesion disassembly. An interaction between daRhoJ and GIT1 was confirmed using yeast-2-hybrid, which depended on the Spa homology domain of GIT1. GIT1, GIT2, β-PIX and RhoJ all co-localised in focal adhesions and depended on each other for their recruitment to focal adhesions. Functionally, the GIT-PIX complex regulated endothelial tube formation, with knockdown of GIT1/2 or β-PIX phenocopying RhoJ knockdown. RhoJ knockout mice showed reduced tumour growth and diminished tumour vessel density, identifying a role for RhoJ in mediating tumour angiogenesis. These studies give novel insight into the molecular function of RhoJ in regulating cell motility and tumour vessel formation.