Angiotensin II Impairs the Insulin Signaling Pathway Promoting Production of Nitric Oxide by Inducing Phosphorylation of Insulin Receptor Substrate-1 on Ser ³¹² and Ser ⁶¹⁶ in Human Umbilical Vein Endothelial Cells

Abstract

Abstract-It has been suggested that serine (Ser) phosphorylation of insulin receptor substrate-1 (IRS-1) decreases the ability of IRS-1 to be phosphorylated on tyrosine, thereby attenuating insulin signaling. There is evidence that angiotensin II (AII) may impair insulin signaling to the IRS-1/phosphatydilinositol 3-kinase (PI 3-kinase) pathway by enhancing Ser phosphorylation. Insulin stimulates NO production by a pathway involving IRS-1/PI3-kinase/Akt/endothelial NO synthase (eNOS). We addressed the question of whether AII affects insulin signaling involved in NO production in human umbilical vein endothelial cells and tested the hypothesis that the inhibitory effect of AII on insulin signaling was caused by increased site-specific Ser phosphorylation in IRS-1. Exposure of human umbilical vein endothelial cells to AII resulted in inhibition of insulin-stimulated production of NO. This event was associated with impaired IRS-1 phosphorylation at Tyr 612 and Tyr 632 , two sites essential for engaging the p85 subunit of PI3-kinase, resulting in defective activation of PI 3-kinase, Akt, and eNOS. This inhibitory effect of AII was reversed by the type 1 receptor antagonist losartan. AII increased c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) 1/2 activity, which was associated with a concomitant increase in IRS-1 phosphorylation at Ser 312 and Ser 616 , respectively. Inhibition of JNK and ERK1/2 activity reversed the negative effects of AII on insulin-stimulated NO production. Our data suggest that AII, acting via the type 1 receptor, increases IRS-1 phosphorylation at Ser 312 and Ser 616 via JNK and ERK1/2, respectively, thus impairing the vasodilator effects of insulin mediated by the IRS-1/PI 3-kinase/Akt/eNOS pathway. Key Words: endothelium Ⅲ angiotensin II Ⅲ nitric oxide Ⅲ insulin E ndothelial dysfunction is an early event in the pathogenesis of atherosclerosis and a feature of insulin-resistant conditions, including type 2 diabetes, obesity, and hypertension. 1-4 Several preclinical and clinical studies have established the involvement of angiotensin II (AII) and its type 1 receptor (AT 1 ) in endothelial dysfunction. [5][6][7] Insulin promotes vasodilatation by activation of the signaling pathway involving the insulin receptor/insulin receptor substrate-1 (IRS-1)/ phosphatidylinositol 3-kinase (PI 3-kinase)/Akt that leads to activation of endothelial NO synthase (eNOS) in endothelium. 8 Cross-talk between the renin-angiotensin system (RAS) and insulin signaling has been demonstrated. 9 Inhibition of RAS by angiotensin-converting enzyme inhibitors or AT 1 antagonists has been shown to both increase insulin sensitivity and improve endothelial function. 10 -12 Evidence has been provided that AII interferes with insulin signaling in vascular cells mainly by affecting insulin-induced tyrosine phosphorylation of IRS-1 and impairing its interaction with the p85 regulatory subunit of PI 3-kinase. 9 However, it is still unclear whether AII adversely affects the downstream signaling path...

The multi‐faceted cross‐talk between the insulin and angiotensin II signaling systems

“…Furthermore, okadaic acid, a serine/threonine phosphatase inhibitor, as well as phorbol ester, mimicked Ang II effects on PI 3-kinase and IRS-1 [36]. It has been recently shown that Ang II impairs the insulin signaling pathway towards the production of NO by inducing serine phosphorylation of IRS-1 on Ser 312 and Ser 616 , via JNK and ERK1-2 respectively, thus impairing the vasodilator effects of insulin mediated by the IRS-1/PI 3-kinase/Akt/eNOS pathway [42].…”

“…Alternatively, Ang II may decrease IRS-1/PI 3-kinase association by rapidly inducing the tyrosine dephosphorylation of IRS-1 via the activation or up regulation of a protein-tyrosine phosphatase [42]. Results from this study suggest that Ang II and other agents that are able to induce serine phosphorylation of the IR, IRS-1, and/or PI 3-kinase, can contribute to insulin resistance in the blood vessels [42]. Thus, we believe that Ang II negatively modulates insulin signaling by stimulating multiple serine phosphorylation events in the early components of the insulin-signaling cascade.…”

“…Pre-treatment of vascular endothelial cells with Ang II promotes the activation of ERK1/2 and JNK by an AT 1 dependent mechanism [84,85]. Once activated, these kinases promote the phosphorylation of IRS-1 in serine residues, impairing the transduction of the insulin signal towards eNOS [42]. Thus, in this tissue, Ang II is able to impair insulin signal transduction by a cross-talk between the ERK/JNK and IRS-1 signaling systems.…”

Cross-talk das vias de sinalização de insulina e angiotensina II: implicações com a associação entre diabetes mellitus e hipertensão arterial e doença cardiovascular

“…Além disso, a utilização de inibidores de fosfatases de serina/treonina mimetizaram os efeitos da angiotensina II sobre IRS-1 e PI-3 quinase (30). Recentemente, foi demonstrado que a angiotensina II é capaz de bloquear os efeitos vasodilatadores da insulina através da fosforilação em serina do IRS-1 nos resíduos Ser 312 e Ser 616 , através da ativação das serina-quinase JNK e ERK1-2, o que leva à modulação negativa da via IRS-1/PI-3 quinase/Akt/ eNOS, diminuindo a produção de NO induzida por insulina (36 (38,40,43). Além disso, a SOCS-3 é capaz de ligar-se ao IRS-1/2, provocando sua degradação proteossômica, através de um mecanismo dependente de ubiquitinação (44) (figura 4).…”

“…O pré-tratamento destas células com angiotensina II leva à ativação da ERK 1/2 e da Jnk por um mecanismo molecular dependente da ativação do AT1. Estas serina-quinases, uma vez ativadas, promovem a fosforilação em serina do IRS-1, impedindo a ativação da eNOS mediada pela insulina (36). Portanto, nesse tecido, a angiotensina II é capaz de induzir resistência à insulina pela via do IRS-1 por um mecanismo dependente de Jnk e ERK 1/2.…”