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G Protein-Coupled Receptor Kinase 2 Mediates Endothelin-1-Induced Insulin Resistance via the Inhibition of Both Gq/11 and Insulin Receptor Substrate-1 Pathways in 3T3-L1 Adipocytes

The Department of Medicine (I.U., T.I., J.L.B., H.S., J.-C.L., C.J.H., J.M.O.), Division of Endocrinology and Metabolism, and the Biological Sciences Graduate Program (J.L.B.), University of California, San Diego, La Jolla, California 92093-0673

Address all correspondence and requests for reprints to: Jerrold M. Olefsky, MD., Department of Medicine (0673), University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0673. E-mail: jolefsky{at}ucsd.edu.

G protein-coupled receptor kinases (GRKs) regulate seven-transmembrane receptors (7TMRs) by phosphorylating agonist-activated 7TMRs. Recently, we have reported that GRK2 can function as a negative regulator of insulin action by interfering with G protein-q/11 -subunit (Gq/11) signaling, causing decreased glucose transporter 4 (GLUT4) translocation. We have also reported that chronic endothelin-1 (ET-1) treatment leads to heterologous desensitization of insulin signaling with decreased tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and Gq/11, and decreased insulin-stimulated glucose transport in 3T3-L1 adipocytes. In the current study, we have investigated the role of GRK2 in chronic ET-1-induced insulin resistance. Insulin-induced GLUT4 translocation was inhibited by pretreatment with ET-1 for 24 h, and we found that this inhibitory effect was rescued by microinjection of anti-GRK2 antibody or GRK2 short interfering RNA. We further found that GRK2 mediates the inhibitory effects of ET-1 by two distinct mechanisms. Firstly, adenovirus-mediated overexpression of either wild-type (WT)- or kinase-deficient (KD)-GRK2 inhibited Gq/11 signaling, including tyrosine phosphorylation of Gq/11 and cdc42-associated phosphatidylinositol 3-kinase activity. Secondly, ET-1 treatment caused Ser/Thr phosphorylation of IRS-1 and IRS-1 protein degradation. Overexpression of KD-GRK2, but not WT-GRK2, inhibited ET-1-induced serine 612 phosphorylation of IRS-1 and restored activation of this pathway. Taken together, these results suggest that GRK2 mediates ET-1-induced insulin resistance by 1) inhibition of Gq/11 activation, and this effect is independent of GRK2 kinase activity, and 2) GRK2 kinase activity-mediated IRS-1 serine phosphorylation and degradation.

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