This study describes the colocalized distribution and dimeric complex formation between RGS7, a GTPase-activating protein for several heterotrimeric Galpha protein families, and the Gbeta5 subunit in the adult rat brain. Confocal dual immunofluorescence labeling studies indicated a broad regional specificity in the cellular coexpression between RGS7 and Gbeta5 within the cerebral cortical layers I and V-VI, hippocampal formation, caudate-putamen, medial habenula, most thalamic nuclei, and cerebellar molecular and granular layers. In all instances, Gbeta1-beta4 immunoreactivities exhibited no observable colocalization with RGS7, despite their widespread codistribution throughout similar neuronal networks. Coimmunoprecipitation studies confirmed the selective protein-protein interaction between RGS7 and Gbeta5 within brain regions that displayed immunohistochemical colocalization. The influence of RGS7 to modulate Gbeta5gamma2-mediated phosphatidyl inositol (PI) production was examined in COS-7-cotransfected cells. In the presence of Gbeta5gamma2 only, intracellular PI accumulation was increased by 25% above basal levels; addition of RGS7 produced no significant alteration in Gbeta5gamma2-mediated PI accumulation. A similar trend was exhibited when full-length RGS7 was substituted with an RGS7 construct lacking the Gbeta5-interacting region (G protein gamma-like domain; GGL domain) or with RGS4. In conclusion, RGS7/Gbeta5 dimers occurred within most brain regions in which both proteins were cellularly coexpressed. However, an influence of RGS7 on Gbeta5gamma2-mediated PLCbeta signaling activity was not apparent, athough this was in COS-7 cell transfection studies.
Copyright 2000 Wiley-Liss, Inc.