Assembly and Function of the Regulator of G protein Signaling 14 (RGS14)•H-Ras Signaling Complex in Live Cells Are Regulated by Gαi1 and Gαi-linked G Protein-coupled Receptors

Regulator of G protein signaling 14 (RGS14) is a multifunctional scaffolding protein that integrates heterotrimeric G protein and H-Ras signaling pathways. RGS14 possesses an RGS domain that binds active G alpha(i/o)-GTP subunits to promote GTP hydrolysis and a G protein regulatory (GPR) motif that selectively binds inactive G alpha(i1/3)-GDP subunits to form a stable heterodimer at cellular membranes. RGS14 also contains two tandem Ras/Rap binding domains (RBDs) that bind H-Ras. Here we show that RGS14 preferentially binds activated H-Ras-GTP in live cells to enhance H-Ras cellular actions and that this interaction is regulated by inactive G alpha(i1)-GDP and Gprotein-coupled receptors (GPCRs). Using bioluminescence resonance energy transfer (BRET) in live cells, we show that RGS14-Luciferase and active H-Ras(G/V)-Venus exhibit a robust BRET signal at the plasma membrane that is markedly enhanced in the presence of inactive G alpha(i1)-GDP but not active G alpha(i1)-GTP. Active H-Ras(G/V) interacts with a native RGS14.G alpha(i1) complex in brain lysates, and co-expression of RGS14 and G alpha(i1) in PC12 cells greatly enhances H-Ras(G/V) stimulatory effects on neurite outgrowth. Stimulation of the G alpha(i)-linked alpha(2A)-adrenergic receptor induces a conformational change in the G alpha(i1).RGS14.H-Ras(G/V) complex that may allow subsequent regulation of the complex by other binding partners. Together, these findings indicate that inactive G alpha(i1)-GDP enhances the affinity of RGS14 for H-Ras-GTP in live cells, resulting in a ternary signaling complex that is further regulated by GPCRs.