G-protein signaling modulator-3 regulates heterotrimeric G-protein dynamics through dual association with G? and G?i protein subunits.

ABSTRACT: Regulation of the assembly and function of G-protein heterotrimers (G?·GDP/G??) is a complex process involving the participation of many accessory proteins. One of these regulators, GPSM3, is a member of a family of proteins containing one or more copies of a small regulatory motif known as the GoLoco (or GPR) motif. Although GPSM3 is known to bind G?(i)·GDP subunits via its GoLoco motifs, here we report that GPSM3 also interacts with the G? subunits G?1 to G?4, independent of G? or G?·GDP subunit interactions. Bimolecular fluorescence complementation studies suggest that the G?-GPSM3 complex is formed at, and transits through, the Golgi apparatus and also exists as a soluble complex in the cytoplasm. GPSM3 and G? co-localize endogenously in THP-1 cells at the plasma membrane and in a juxtanuclear compartment. We provide evidence that GPSM3 increases G? stability until formation of the G?? dimer, including association of the G?-GPSM3 complex with phosducin-like protein PhLP and T-complex protein 1 subunit eta (CCT7), two known chaperones of neosynthesized G? subunits. The G? interaction site within GPSM3 was mapped to a leucine-rich region proximal to the N-terminal side of its first GoLoco motif. Both G? and G?(i)·GDP binding events are required for GPSM3 activity in inhibiting phospholipase-C? activation. GPSM3 is also shown in THP-1 cells to be important for Akt activation, a known G??-dependent pathway. Discovery of a G?/GPSM3 interaction, independent of G?·GDP and G? involvement, adds to the combinatorial complexity of the role of GPSM3 in heterotrimeric G-protein regulation.

SUBMITTER: Giguere PM 

PROVIDER: S-EPMC3281645 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature