The Role of Cdc42 and the Cross-talk with RhoA/RhoC during Invadopodia Formation and Invasion in Glioblastoma Multiforme

Abstract

Glioblastoma multiforme (GM) is a malignant grade IV tumor characterized by its ability to rapidly proliferate and infiltrate into the normal neighboring brain tissue. Tumor invasion and metastasis remain the major cause of death in patients with GM. The Rho family of GTPases is a key regulator of cell migration and invasion. Previous work in our lab has shown that the well characterized members of this family, Cdc42, RhoA and RhoC positively regulate 2D motility in GM. In this study, we sought to investigate the role of these three Rho GTPases in 3D migration, particularly in the formation of invadopodia which are the actin rich structures required for the degradation of the extracellular matrix. Our findings showed that Cdc42 and RhoA are essential for invadopodia formation. The depletion of RhoC did not affect the invadopodia number which implies that it might regulate invadopodia formation through a different mechanism. Our data also showed that Cdc42, but not RhoA and RhoC, localizes to the invadopodia structure. To better understand the signaling mechanism underlying Cdc42 positive regulation of invadopodia, we examined the effect of Cdc42 knockdown on the activation of RhoA. We found that Cdc42 depletion decreased RhoA activation which suggests that Cdc42 might be operating upstream of RhoA and regulating invadopodia formation through RhoA. We also investigated the effect of Cdc42 and RhoC on MMP2 and MMP9 expression. Our results showed that Cdc42 and RhoC knockdown decreased MMP9 expression levels while only RhoC depletion reduced MMP2 expression. Overall, our findings suggest that, in glioblastoma, Cdc42, RhoA and RhoC regulate the formation of invadopodia differently.