Angiotensin II inhibits insulin signaling in aortic smooth muscle cells at multiple levels. A potential role for serine phosphorylation in insulin/angiotensin II crosstalk.
To investigate potential interactions between angiotensin II (AII) and the insulin signaling system in the vasculature, insulin and AII regulation of insulin receptor substrate-1 (IRS-1) phosphorylation and phosphatidylinositol (PI) 3-kinase activation were examined in rat aortic smooth muscle cells. Pretreatment of cells with AII inhibited insulin-stimulated PI 3-kinase activity associated with IRS-1 by 60%. While AII did not impair insulin-stimulated tyrosine phosphorylation of the insulin receptor (IR) beta-subunit, it decreased insulin-stimulated tyrosine phosphorylation of IRS-1 by 50%. AII inhibited the insulin-stimulated association between IRS-1 and the p85 subunit of PI 3-kinase by 30-50% in a dose-dependent manner. This inhibitory effect of AII on IRS-1/PI 3-kinase association was blocked by the AII receptor antagonist saralasin, but not by AT1 antagonist losartan or AT2 antagonist PD123319. AII increased the serine phosphorylation of both the IR beta-subunit and IRS-1. In vitro binding experiments showed that autophosphorylation increased IR binding to IRS-1 from control cells by 2.5-fold versus 1.2-fold for IRS-1 from AII-stimulated cells, suggesting that AII stimulation reduces IRS-1's ability to associate with activated IR. In addition, AII increased p85 serine phosphorylation, inhibited the total pool of p85 associated PI 3-kinase activity, and decreased levels of the p50/p55 regulatory subunit of PI 3-kinase. These results suggest that activation of the renin-angiotensin system may lead to insulin resistance in the vasculature.
Folli
F
F
Department of Medicine I, I.R.C.C.S.H. San Raffaele, Milano, Italy.
Kahn
C R
CR
Hansen
H
H
Bouchie
J L
JL
Feener
E P
EP
D000804:Angiotensin II / Q000502:physiology*; D000818:Animals; D001011:Aorta / Q000502:physiology; D002478:Cells, Cultured; D007328:Insulin / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010768:Phosphoserine / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011972:Receptor, Insulin / Q000378:metabolism; D011945:Receptors, Angiotensin / Q000502:physiology; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D011945:Receptors, Angiotensin; D000804:Angiotensin II; D010768:Phosphoserine; D019000:Phosphotyrosine; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D017479:Receptors, Platelet-Derived Growth Factor; D013755:Tetradecanoylphorbol Acetate