RGS14 regulates the lifetime of Gα-GTP signaling but does not prolong Gβγ signaling following receptor activation in live cells

RGS14 is a multifunctional scaffolding protein possessing two distinct G protein interaction sites including a regulator of G protein signaling (RGS) domain that acts as a GTPase activating protein (GAP) to deactivate G alpha i/o-GTP proteins, and a G protein regulatory (GPR) motif that binds inactive G alpha i1/3-GDP proteins independent of G beta gamma. GPR interactions with G alpha i recruit RGS14 to the plasma membrane to interact with G alpha i-linked GPCRs and regulate G alpha i signaling. While RGS14 actions on G alpha proteins are well characterized, consequent effects on G beta gamma signaling remain unknown. Conventional RGS proteins act as dedicated GAPs to deactivate G alpha and G beta gamma signaling following receptor activation. RGS14 may do the same or, alternatively, may coordinate its actions to deactivate G alpha-GTP with the RGS domain and then capture the same G alpha-GDP via its GPR motif to prevent heterotrimer reassociation and prolong G beta gamma signaling. To test this idea, we compared the regulation of G protein activation and deactivation kinetics by a conventional RGS protein, RGS4, and RGS14 in response to GPCR agonist/antagonist treatment utilizing bioluminescence resonance energy transfer (BRET). Co-expression of either RGS4 or RGS14 inhibited the release of free G beta gamma after agonist stimulation and increased the deactivation rate of G alpha, consistent with their roles as GTPase activating proteins (GAPs). Overexpression of inactive G alpha i1 to recruit RGS14 to the plasma membrane did not alter RGS140s capacity to act as a GAP for a second G alpha o protein. These results demonstrate the role of RGS14 as a dedicated GAP and suggest that the G protein regulatory (GPR) motif functions independently of the RGS domain and is silent in regulating GAP activity in a cellular context.