G protein-coupled receptor kinases (GRKs) represent a class of proteins that classically phosphorylate agonist-activated G protein-coupled receptors, leading to uncoupling of the receptor from further G protein activation. Recently, we have reported that the heterotrimeric G protein α-subunit, Gαq/11, can mediate insulin-stimulated glucose transport. GRK2 contains a regulator of G protein signaling (RGS) domain with specificity for Gαq/11. Therefore, we postulated that GRK2 could be an inhibitor of the insulin signaling cascade leading to glucose transport in 3T3-L1 adipocytes. In this study, we demonstrate that microinjection of anti-GRK2 antibody or siRNA against GRK2 increased insulin-stimulated insulin-responsive glucose transporter 4 (GLUT4) translocation, while adenovirus-mediated overexpression of wild-type or kinase-deficient GRK2 inhibited insulin-stimulated GLUT4 translocation as well as 2-deoxyglucose uptake. Importantly, a mutant GRK2 lacking the RGS domain was without effect. Taken together, these results indicate that through its RGS domain endogenous GRK2 functions as a negative regulator of insulin-stimulated glucose transport by interfering with Gαq/11 signaling to GLUT4 translocation. Furthermore, inhibitors of GRK2 can lead to enhanced insulin sensitivity.
- GLUT4 translocation
- Insulin signal transduction
ASJC Scopus subject areas
- Molecular Biology
- Biochemistry, Genetics and Molecular Biology(all)
- Immunology and Microbiology(all)