Gγ subunit-selective G protein β5 mutant defines regulators of G protein signaling protein binding requirement for nuclear localization

The signal transducing function of Gbeta(5) in brain is unknown. When studied in vitro Gbeta(5) is the only heterotrimeric Gbeta subunit known to interact with both Ggamma subunits and regulators of G protein signaling (RGS) proteins. When tested with Ggamma, Gbeta(5) interacts with other classical components of heterotrimeric G protein signaling pathways such as Galpha and phospholipase C-beta. We recently demonstrated nuclear expression of Gbeta(5) in neurons and brain (Zhang, J. H., Barr, V. A., Mo, Y., Rojkova, A M., Liu, S., and Simonds, W. F. (2001) J. Biol. Chem. 276, 10284-10289). To gain further insight into the mechanism of Gbeta(5) nuclear localization, we generated a Gbeta(5) mutant deficient in its ability to interact with RGS7 while retaining its ability to bind Ggamma, and we compared its properties to the wild-type Gbeta(5). In HEK-293 cells co-transfection of RGS7 but not Ggamma(2) supported expression in the nuclear fraction of transfected wild-type Gbeta(5). In contrast the Ggamma-preferring Gbeta(5), mutant was not expressed in the HEK-293 cell nuclear fraction with either co-transfectant. The Ggamma-selective Gbeta(5) mutant was also excluded from the cell nucleus of transfected PC12 cells analyzed by laser confocal microscopy. These results define a requirement for RGS protein binding for Gbeta(5) nuclear expression.