Socius, a novel binding partner of Gα12/13, promotes the Gα12-induced RhoA activation

Heterotrimeric G proteins act as a molecular switch that conveys signals from G protein-coupled receptors in the cell membrane to intracellular downstream effectors. The Gα subunits of the G12 family of heterotrimeric G proteins, defined by Gα12 and Gα13, have many cellular functions through their specific downstream effectors. On the other hand, regulatory systems of the activity of Gα12 and Gα13 have not been fully clear. Here, we show that Socius, a previously identified Rho family small GTPase Rnd1 interacting protein, binds directly to Gα12 and Gα13 through its NH2-terminal region. Socius increased the amounts of GTP-bound active form of Gα12 in 293T cells. Furthermore, Socius promotes the Gα12-induced RhoA activation in 293T cells. These results demonstrate that Socius is a novel activator of the Gα12 family.