The regulation of the serum response network by the RGS RHOGEFS is critical for YAP1 activity and cell fate decisions

Abstract

The growth of mammary epithelial cells is regulated by interactions with neighboring cells and by exposure to soluble factors including hormones and growth factors. These cues are integrated within the cell, perpetuating changes onto the organization of the actin cytoskeleton, resulting in altered transcriptional programs. Rho family GTPases regulates actin dynamics that facilitate transcriptional reprogramming. In particular, RhoA induces the formation of actin stress fibers to promote the transcriptional co-activator YAP1 to translocate from the cytosol into the nucleus. There, it co-activates TEAD family transcription factors to drive the expression of pro-growth and survival genes. Rho family members are activated by guanine exchange factors (GEF) and inhibited by GTPase activating proteins (GAP). Here, we determined the relative effects of expression of 67 RhoGEFs and RhoGAPs on the activation of TEAD. This revealed that regulator of G-protein signaling (RGS) domain containing ArhGEF1, ArhGEF11 and ArhGEF12 all promoted YAP1 dependent activation of TEAD. These RhoGEFs mediate signaling from heptahelical receptors that are stimulated by lipid mitogens to activate the heterotrimeric G-proteins Gα12 and Gα13. Consistently, loss of expression of ArhGEF12 and to a lesser degree ArhGEF11 prevented actin stress fiber accumulation and activation of YAP1 mediated signaling by serum. Conversely, several complementary experiments revealed that ArhGEF1 dominantly limits Gα13 selective activation of YAP1 and the mitogen activated protein kinase (MAPK) cascades. Furthermore excessive Gα13 activity results in both high levels of filamentous actin and arrest cells in the G1/0 phase of the cell cycle. This is likely due to the systemic inhibition of cell cycle promoting signaling and a loss of protein translation. Further, YAP1 was found to be essential for the survival of ArhGEF1 silenced cells. Together, these studies define a circuit whereby the rgRhoGEFs regulate Gα 12/13-RhoA signaling flux to regulate cellular growth that is promoted by serum factors.