The RhoA-specific guanine nucleotide exchange factor p63RhoGEF binds to activated Gα 16 and inhibits the canonical phospholipase Cβ pathway

Abstract

Heterotrimeric G proteins regulate diverse physiological processes by modulating the activities of intracellular effectors. Members of the Gα q family link G protein-coupled receptor activation to phospholipase Cβ (PLCβ) activity and intracellular calcium signaling cascades. However, they differ markedly in biochemical properties as well as tissue distribution. Recent findings have shown that some of the cellular activities of Gα q family members are independent of PLCβ activation. A guanine nucleotide exchange factor, p63RhoGEF, has been shown to interact with Gα q proteins and thus provides linkage to RhoA activation. However, it is not known if p63RhoGEF can associate with other Gα q family members such as Gα 16. In the present study, we employed co-immunoprecipitation studies in HEK293 cells to demonstrate that p63RhoGEF can form a stable complex with the constitutively active mutant of Gα 16 (Gα 16QL). Interestingly, overexpression of p63RhoGEF inhibited Gα 16QL-induced IP 3 production in a concentration-dependent manner. The binding of PLCβ 2 to Gα 16QL could be displaced by p63RhoGEF. Similarly, p63RhoGEF inhibited the binding of tetratricopeptide repeat 1 to Gα 16QL, leading to a suppression of Gα 16QL-induced Ras activation. In the presence of p63RhoGEF, Gα 16QL-induced STAT3 phosphorylation was significantly reduced and Gα 16QL-mediated SRE transcriptional activation was attenuated. Taken together, these results suggest that p63RhoGEF binds to activated Gα 16 and inhibits its signaling pathways.