mTORc1 activity is necessary and sufficient for phosphorylation of eNOSS1177

Nitric oxide, produced by eNOS, plays critical roles in the regulation of vascular function and maintenance. Chronic PI3K signaling has recently been associated with vascular malformations. A well described substrate downstream of PI3K signaling is eNOS. Another critical downstream target of PI3K is the metabolic regulator, mTORc1. The relationship between mTORc1 and eNOS regulation, has not been determined. We generated cells with manipulated PI3K signaling by expressing the activating mutation, PIK3CA(H1047R), or knocking down PTEN expression. We investigated eNOS(S1177) phosphorylation, a major activating regulatory site, following mTORC1 inhibition. We also tested the sufficiency of mTORc1 activation to stimulate eNOS(S1177) phosphorylation. Our data indicate mTORc1 activity is required for the phosphorylation of eNOS(S1177), even in the presence of robust AKT activation. Moreover, we found that expression of RHEB, which functions in the absence of AKT activation to activate mTORc1, is sufficient to phosphorylate this site. Our data indicate that mTORc1, rather than AKT, may be the critical determinant of eNOS(S1177) phosphorylation. As mTORc1 is a central regulator of cellular metabolism, the finding that this regulatory complex can directly participate in the regulation of eNOS provides new insights into metabolic uncoupling and vascular disease that often accompanies diabetes, high fat diets, and aging.