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 G(q)/G(11) and G(12)/G(13) are major upstream regulators of RhoA activity, and G(12)/G(13) 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 G(q)/G(11) 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 G(alpha12)/G(alpha13)-deficient as well as in Galpha(q)/Galpha(11)-deficient mouse embryonic fibroblasts (MEFs), in which coupling of receptors is restricted to G(q)/G(11) and G(12)/G(13), respectively, receptor activation results in Rho activation. Rho activation induced by receptor agonists via G(q)/G(11) occurs with lower potency than Rho activation via G(12)/G(13). Activation of RhoA via G(q)/G(11) 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 G(12)/G(13) as well as G(q)/G(11) alone can couple GPCRs to the rapid activation of RhoA. G(q)/G(11)-mediated RhoA activation occurs independently of phospholipase C-beta and appears to involve LARG.