Akt-dependent phosphorylation of serine 1179 and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 cooperatively mediate activation of the endothelial nitric-oxide synthase by hydrogen peroxide.

Hydrogen peroxide mediates vasodilation, but the mechanisms responsible for this process remain undefined. We examined the effect of H(2)O(2) on nitric oxide (NO*) production and the signaling events involved. NO* release from bovine aortic endothelial cells was detected with an NO*-specific microelectrode. The addition of H(2)O(2) caused a potent dose-dependent increase in NO* production. This was partially Ca(2+)-dependent because BAPTA/AM reduced NO* production at low (<50 microM) but not high (>100 microM) concentrations of H(2)O(2). Phosphatidylinositol (PI) 3-kinase inhibition [with wortmannin or 2-(4-morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride], infection with a dominant-negative mutant of Akt, or mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 (MEK/ERK1/2) inhibition (with PD98059 or U0126) partially attenuated, whereas inhibition of both PI 3-kinase and MEK1/2 abolished H(2)O(2)-dependent NO* production. ERK1/2 seemed necessary for NO* production early (<5 min) after H(2)O(2) addition, whereas PI 3-kinase/Akt was more important at later time points. Phosphorylation of endothelial nitric-oxide synthase (eNOS) at serine 1179 was observed >10 min after the addition of H(2)O(2), and this was prevented by wortmannin but not by PD98059. c-Src family tyrosine kinase(s) was found to be upstream of H(2)O(2)-dependent Akt and eNOS serine 1179 phosphorylation and subsequent NO* production. In summary, H(2)O(2) causes endothelial NO* release mediated by cooperative effects between PI 3-kinase/Akt-dependent eNOS serine 1179 phosphorylation and activation of MEK/ERK1/2. This may represent an acute cellular adaptation to an increase in oxidant stress.