ROLE OF NITRIC-OXIDE IN POLY(I-C)-INDUCED ENDOTHELIAL-CELL EXPRESSIONOF LEUKOCYTE ADHESION MOLECULES

Polyinosinic-polycytidylic acid [poly(I-C)] is a synthetic double-stra nded RNA (dsRNA) that simulates a viral-infected state in cells. It ha s been shown that viral infection, as well as poly(I-C), stimulates le ukocyte adhesion to endothelial cell (EC) monolayers and that this is mediated through the surface expression of the adhesion molecules E-se lectin, vascular cell adhesion molecule 1 (VCAM-1), and intercellular adhesion molecule 1. We have tested the involvement of nitric oxide (N O) in poly(I-C)-induced monocytic cell adhesion to human vascular EC. Using primary cultured EC for these studies, we confirmed the results from previous reports that these cells have higher basal levels of NO production than passaged cells. Poly(I-C)-induced monocytic cell adhes ion to primary EC was concentration-dependently inhibited by 40-74% by the nitric oxide synthase (NOS) inhibitor NG-methyl-L-arginine (L-NMA ), as well as three other NOS inhibitors, without significantly affect ing interleukin-1 beta-induced adhesion. L-NMA inhibited poly(I-C)-ind uced surface expression of E-selectin and VCAM-1 by 25 and 45%, respec tively, and mRNA levels of E-selectin and VCAM-1 by 62 and 74%, respec tively. Primary EC transiently transfected with a plasmid containing a n E-selectin promoter-driven luciferase reporter gene showed that L-NM A treatment reduced poly(I-C)-induced E-selectin promoter activity to basal levels. Electrophoretic mobility shift analysis indicated that p oly(I-C)-induced nuclear factor-kappa B (NF-kappa B) binding to a radi olabeled oligonucleotide corresponding to the consensus NF-KB binding domain of the E-selectin promoter was decreased by L-NMA pretreatment. Hence, NO appears to augment E-selectin gene expression in response t o poly(I-C) at the transcriptional level in vascular EC. Collectively, these data support the hypothesis that NO augments poly(I-C)-induced EC activation. These data suggest a novel role for NO as a response me diator in dsRNA-induced leukocyte adhesion to EC.