RGS16 inhibits signalling through the Gα13–Rho axis

Gα13 stimulates the guanine nucleotide exchange factors (GEFs) for Rho, such as p115Rho-GEF1. Activated Rho induces numerous cellular responses, including actin polymerization, serum response element (SRE)-dependent gene transcription and transformation2. p115Rho-GEF contains a Regulator of G protein Signalling domain (RGS box) that confers GTPase activating protein (GAP) activity towards Gα12 and Gα13 (ref. 3). In contrast, classical RGS proteins (such as RGS16 and RGS4) exhibit RGS domain-dependent GAP activity on Gαi and Gαq, but not Gα12 or Gα13 (ref 4). Here, we show that RGS16 inhibits Gα13-mediated, RhoA-dependent reversal of stellation and SRE activation. The RGS16 amino terminus binds Gα13 directly, resulting in translocation of Gα13 to detergent-resistant membranes (DRMs) and reduced p115Rho-GEF binding. RGS4 does not bind Gα13 or attenuate Gα13-dependent responses, and neither RGS16 nor RGS4 affects Gα12-mediated signalling. These results elucidate a new mechanism whereby a classical RGS protein regulates Gα13-mediated signal transduction independently of the RGS box.