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

We previously reported that Gbetagamma signaling regulates cell spreading or cell shape change through activation of a Rho family small GTPase, suggesting the existence of a Gbetagamma-regulated Rho guanine-nucleotide exchange factor (RhoGEF). In this study we examined various RhoGEF clones, found FLJ00018 to beaGbetagamma-activated RhoGEF, and investigated the molecular mechanism of Gbetagamma-induced activation of Rho family GTPases. Co-expression of the genes for FLJ00018 and Gbetagamma enhanced serum response element-mediated gene transcription in HEK-293 cells. Combined expression of Gbetagamma 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 Gbetagamma 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 Gbetagamma/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 Gbetagamma with FLJ00018.