Coordinated regulation of endothelial nitric oxide synthase activity by phosphorylation and subcellular localization

Endothelial nitric oxide synthase (eNOS) is regulated by multiple mechanisms including Ca²⁺/calmodulin binding, protein-protein interactions, phosphorylation, and subcellular locations. Emerging evidence suggests that these seemingly independent mechanisms may be closely correlated. In the present study, the interplay between membrane targeting and phosphorylation of eNOS was investigated by using various mutants designed to target specific subcellular locations or to mimic different phospho states. Phospho-mimicking mutations of wild-type eNOS at S635 and S1179 synergistically activated the enzyme. The targeted eNOS mutants to plasma membrane and Golgi complex exhibited higher NO production activities than that of a myristoylation-deficient cytosolic mutant. Phospho-mimicking mutations at S635 and S1179 rescued the activity of the cytosolic mutant and increased those of the plasma membrane- and Golgi-targeted mutants. In contrast, phospho-deficient mutations at these sites led to inactivation of eNOS. Unlike the other targeted mutants, the cytosolic eNOS mutant was unresponsive to cAMP, indicating that membrane association and phosphorylation are required for eNOS activation. These findings suggest that the coordinated interplay between phosphorylation and subcellular localization of eNOS plays an important role in regulating NO production in endothelial cells.