Selected Contribution: Insulin utilizes NO/cGMP pathway to activate myosin
phosphatase via Rho inhibition in vascular smooth muscle.
Sandu, Oana A., Masaaki Ito, and Najma Begum.
1The Diabetes Research Laboratory, Winthrop University Hospital, Mineola 11501;
3School of Medicine, State University of New York, Stony Brook, New York 11794; and
2First Department of Internal Medicine, Mie University School of Medicine, Mie,
Japan
APStracts 8:0320A, 2001.
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 (MBSThr695) 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 MBSThr695 of MBP and caused MBP activation.
Preexposure to «lgnmma», 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
MBSThr695 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 MBSThr695. Furthermore,
expression of a dominant-negative RhoA decreased basal as well as thrombin-induced
MBSThr695 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.
Received 19 April 2001; accepted in final form 5 June 2001
APS Manuscript Number A363-1.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001