Heterotrimeric G protein βγ subunits stimulate FLJ00018, a guanine nucleotide exchange factor for Rac1 and Cdc42

We previously reported that G beta gamma signaling regulates cell spreading or cell shape change through activation of a Rho family small GTPase, suggesting the existence of a G beta gamma-regulated Rho guanine-nucleotide exchange factor ( RhoGEF). In this study we examined various RhoGEF clones, found FLJ00018 to be a G beta gamma-activated RhoGEF, and investigated the molecular mechanism of G beta gamma-induced activation of Rho family GTPases. Co-expression of the genes for FLJ00018 and G beta gamma enhanced serum response element-mediated gene transcription in HEK-293 cells. Combined expression of G beta gamma and FLJ00018 significantly induced activation of Rac and Cdc42 but not RhoA. FLJ00018 also enhanced gene transcription induced by carbachol-stimulated m2 muscarinic acetylcholine receptor, and this enhancement was blocked by pertussis toxin. Furthermore, we demonstrated G beta gamma to interact directly with the N-terminal region of FLJ00018 and the N-terminal fragment of this molecule to inhibit serum response element-dependent transcription induced by G beta gamma/FLJ00018 and carbachol. In NIH3T3 cells, FLJ00018 enhanced lysophosphatidic acid-induced cell spreading, which was also blocked by the N-terminal fragment of FLJ00018. These results provide evidence for a signaling pathway by which G(i)-coupled receptor specifically induces Rac and Cdc42 activation through direct interaction of G beta gamma with FLJ00018.