Receptor-dependent RhoA activation in G12/G13-deficient cells: genetic evidence for an involvement of Gq/G11.

The small GTPase RhoA is involved in the regulation of various cellular functions like the remodeling of the actin cytoskeleton and the induction of transcriptional activity. G-protein-coupled receptors (GPCRs), which are able to activate Gq/G11 and G12/G13 are major upstream regulators of RhoA activity, and G12/G13 have been shown to couple GPCRs to the activation of Rho by regulating the activity of a subfamily of RhoGEF proteins. However, the possible contribution of Gq/G11 to the regulation of RhoA activity via GPCRs is controversial. We have used a genetic approach to study the role of heterotrimeric G-proteins in the activation of RhoA via endogenous GPCRs. In pertussis toxin-treated Galpha12/Galpha13-deficient as well as in Galphaq/Galpha11-deficient mouse embryonic fibroblasts (MEFs), in which coupling of receptors is restricted to Gq/G11 and G12/G13, respectively, receptor activation results in Rho activation. Rho activation induced by receptor agonists via Gq/G11 occurs with lower potency than Rho activation via G12/G13. Activation of RhoA via Gq/G11 is not affected by the phospholipase-C blocker U73122 or the Ca2+-chelator BAPTA, but can be blocked by a dominant-negative mutant of the RhoGEF protein LARG. Our data clearly show that G12/G13 as well as Gq/G11 alone can couple GPCRs to the rapid activation of RhoA. Gq/G11-mediated RhoA activation occurs independently of phospholipase C-beta and appears to involve LARG.