Nuclear localization of G protein β5 and regulator of G protein signaling 7 in neurons and brain

The role that G beta (5) regulator of G protein signaling (RGS) complexes play in signal transduction in brain remains unknown. The subcellular localization of G beta (5) and RGS7 was examined in rat PC12 pheochromocytoma cells and mouse brain. Both nuclear and cytosolic localization of G beta (5) and RGS7 was evident in PC12 cells by immunocytochemical staining. Subcellular fractionation of PC12 cells demonstrated G beta (5) immunoreactivity in the membrane, cytosolic, and nuclear fractions. Analysis by limited proteolysis confirmed the identity of G beta (5) in the nuclear fraction, Subcellular fractionation of mouse brain demonstrated G beta (5) and RGS7 but not G gamma (2/3) immunoreactivity in the nuclear fraction. RGS7 and G beta (5) were tightly complexed in the brain nuclear extract as evidenced by their coimmunoprecipitation with anti-RGS7 antibodies. Chimeric protein constructs containing green fluorescent protein fused to wild-type G beta (5) but not green fluorescent fusion proteins with G beta (1) or a mutant G beta (5) impaired in its ability to bind to RGS7 demonstrated nuclear localization in transfected PC12 cells, These findings suggest that G beta (5) undergoes nuclear translocation in neurons via an RGS-dependent mechanism. The novel intracellular distribution of G beta (5). RGS protein complexes suggests a potential role in neurons communicating between classical heterotrimeric G protein subunits and/or their effecters at the plasma membrane and the cell nucleus.