A truncated form of RGS3 negatively regulates G protein-coupled receptor stimulation of adenylyl cyclase and phosphoinositide phospholipase C

Identification of a new family of proteins (RGS proteins) that function as negative regulators of (G) under bar protein Signaling has sparked new understanding of desensitization of this signaling process, Recent studies with several mammalian RGS proteins has delineated their ability to interact with and function as GTPase activating proteins specifically for G proteins in the G(i) family, Here, we investigated the functional activity of RGS3 and a truncated form of RGS3 on G protein-coupled receptor-mediated activation of adenylyl cyclase, phosphoinositide phospholipase C, and mitogen-activated protein kinase in intact cells, Polymerase chain reaction and 5'-rapid amplification of cDNA ends analyses revealed the tissue specific expression of a short form of the RGS3 transcript that encodes the approximate carboxyl terminal half of RGS3. This truncated form of RGS3 (RGS3T) was shown recently to function as a negative regulator of pheromone signaling in yeast (Druey, K, M,, Blumer, K, J,, Rang, V, R,, and Kehrl, J, H, (1996) Nature 379, 742-746), Baby hamster kidney cells transiently transfected with RGS3T cDNA exhibited a pronounced impairment in platelet-activating factor receptor-stimulated inositol phosphate production, a pertussis toxin insensitive response, Similarly, calcitonin gene-related peptide receptor-stimulated increases in intracellular cAMP and pituitary adenylate-cyclase activating polypeptide receptor stimulated increases in both cAMP and inositol phosphates were reduced significantly in RGS3T transfectants compared with vector-transfected control cells, In contrast, baby hamster kidney cells transfected with the full length RGS3 cDNA showed no impairment in cAMP and inositol phosphate production mediated by these G; protein-coupled receptors, However, lysophosphatidic acid receptor-stimulated phosphorylation of endogenous ERK1 and ERK2 was impaired markedly in both RGS3 and RGS3T transfectants, demonstrating the functional ability of both RGS forms to modulate G(i)-mediated signaling, These results provide the first evidence for regulatory effects of an RGS protein on G(s)- and G(q)-mediated signaling in intact cells and document that the carboxyl-terminal region of RGS3 comprises the structural domain for this activity.