Negative modulation of eNOS by laminin involving post-translational phosphorylation

Nitric oxide (NO) regulates the vascular tone, and influences survival and apoptosis of endothelial cells (ECs). NO is produced by nitric oxide synthase (NOS) and eNOS is the constitutive enzyme in the endothelium. Though the extracellular matrix (ECM) has been reported to regulate various EC functions, the role of ECM in the regulation of eNOS is not clear. The present study was designed to analyze if laminin-1 (Ln-1), the major glycoprotein of the basement membrane, can regulate eNOS. The activity of eNOS was significantly low in ECs maintained on Ln-1 as compared to those on Col I and polylysine. Reversal of the effect of Ln-1 on treatment with inhibitor of p38 MAPK and changes in Thr and Ser phosphorylation in purified eNOS suggested that eNOS activity in cells maintained on Ln-1 is negatively regulated by post-translational phosphorylation at Ser and Thr residues by recruiting p38 MAPK pathway. Increase in eNOS activity and induction of apoptosis upon inhibition of p38 MAPK and reversal of this on inhibition of NOS by L-NAME suggested that increased NO induced apoptosis in ECs maintained on Ln-1 when p38 MAPK was inhibited. These results suggest that Ln contributes to survival of ECs by negatively modulating eNOS in a p38 MAPK dependent pathway.