COX-2 and cytosolic PLA₂mediate IL-1β-induced cAMP production in human vascular smooth muscle cells

Interleukin (IL)-1 is a potent vasodilator that causes prolonged induction of prostacyclin (PGI2) and cAMP synthesis in human vascular smooth muscle cells (HVSMC). The present study investigated IL-1 induction of PG synthetic enzymes in HVSMC and tested their respective roles in PGI2 and cAMP production. Cyclooxygenase (COX)-1 mRNA was not detectable in either control or IL-1-treated HVSMC, as assessed by RT-PCR. In contrast, COX-2 mRNA was detectable in control HVSMC, increased markedly (16-fold) after 1 h of IL-1 exposure, and increased further (52-fold) after 24 h. COX-2 protein levels, assessed by Western analysis, were increased concomitantly. HVSMC contained mRNA encoding both the secreted and cytosolic forms of phospholipase A2 (sPLA2 and cPLA2, respectively). IL-1 stimulation did not affect sPLA2 mRNA levels, but cPLA2 mRNA levels increased at 8 h, after the initial induction of PG synthesis. HVSMC constitutively expressed PGI2 synthase mRNA, and its levels were not affected by IL-1. A selective COX-2 inhibitor, NS-398, reversed IL-1-induced PGI2 and cAMP production, supporting a role of COX-2 in mediating increased PG synthesis. IL-1-induced cAMP was also reversed by a selective cPLA2 inhibitor, AACOCF3, but not by thioetheramide phosphorylcholine, which inhibits sPLA2 preferentially over cPLA2, supporting a requirement for cPLA2-derived arachidonic acid in IL-1-induced PG synthesis. The delayed induction of cPLA2 mRNA was also attenuated by NS-398, suggesting that it was secondary to the initial COX-2-induced PG synthesis. Together, the results support the hypothesis that IL-1 induces intracellular PG synthesis in HVSMC via rapid upregulation of COX-2, which utilizes cPLA2-derived arachidonic acid to generate PG metabolites that regulate adenylate cyclase.