title: Selected contribution: insulin utilizes NO/cGMP pathway to activate myosin phosphatase via Rho inhibition in vascular smooth muscle.
abstract: Our laboratory has recently demonstrated that insulin induces relaxation of vascular smooth muscle cells (VSMCs) by activating myosin-bound phosphatase (MBP) and by inhibiting Rho kinase (Begum N, Duddy N, Sandu OA, Reinzie J, and Ragolia L. Mol Endocrinol 14: 1365-1376, 2000). In this study, we tested the hypothesis that insulin via the nitric oxide (NO)/cGMP pathway may inactivate Rho, resulting in a decrease in phosphorylation of the myosin-bound subunit (MBS(Thr695)) of MBP and in its activation. Treatment of confluent serum-starved VSMCs with insulin prevented thrombin-induced increases in membrane-associated RhoA, Rho kinase activation, and site-specific phosphorylation of MBS(Thr695) of MBP and caused MBP activation. Preexposure to N(G)-monomethyl-L-arginine, a NO synthase inhibitor, and R-p-8-(4-chlorophenylthio)cGMP, a cGMP antagonist, attenuated insulin's inhibitory effect on Rho translocation and restored thrombin-mediated Rho kinase activation and site-specific MBS(Thr695) phosphorylation, resulting in MBP inactivation. In contrast, 8-bromo-cGMP, a cGMP agonist, mimicked insulin's inhibitory effects by abolishing thrombin-mediated Rho signaling and promoted dephosphorylation of MBS(Thr695). Furthermore, expression of a dominant-negative RhoA decreased basal as well as thrombin-induced MBS(Thr695) phosphorylation and caused insulin activation of MBP. Collectively, these results indicate that insulin inhibits Rho signaling by decreasing RhoA translocation via the NO/cGMP signaling pathway to cause MBP activation via site-specific dephosphorylation of its regulatory subunit MBS.
authors.affiliation: The Diabetes Research Laboratory, Winthrop University Hospital, Mineola, New York 11501, USA.
authors.forename: O A
authors.initials: OA
authors.lastname: Sandu
authors.forename: M
authors.initials: M
authors.lastname: Ito
authors.forename: N
authors.initials: N
authors.lastname: Begum
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D006973:Hypertension / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000201:enzymology*; D043263:Myosin-Light-Chain Phosphatase; D009218:Myosins / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011921:Rats, Inbred WKY; D015398:Signal Transduction / Q000502:physiology*; D013912:Threonine / Q000378:metabolism; D014664:Vasodilation / Q000502:physiology; D054460:rho-Associated Kinases
chemical_list: D007004:Hypoglycemic Agents; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D013912:Threonine; D009569:Nitric Oxide; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D010749:Phosphoprotein Phosphatases; D043263:Myosin-Light-Chain Phosphatase; D009218:Myosins; D006152:Cyclic GMP