Vascular smooth muscle cells (VSMCs) that function as synthetic units play important roles in inflammatory diseases such as atherosclerosis and angiogenesis. As extracellular nucleotides such as ATP have been shown to act via activation of P₂ purinoceptors implicated in various inflammatory diseases, we hypothesized that extracellular nucleotides contribute to vascular diseases via upregulated expression of inflammatory proteins, such as cyclooxygenase (COX-2) and cytosolic phospholipase A₂ (cPLA₂) in VSMCs.

Western blotting, promoter assay, RT–PCR, and PGE₂ immunoassay revealed that ATPγS induced expression of COX-2 and prostaglandin (PGE₂) synthesis through the activation of p42/p44 MAPK (mitogen-activated protein kinase), p38 MAPK, and nuclear factor-κB (NF-κB). These responses were attenuated by inhibitors of MAPK/ERK kinase (MEK1/2; U0126), p38 MAPK (SB202190), and NF-κB (helenalin), or by tranfection with dominant negative mutants of p42, p38, IκB kinase (IKK)α, and IKKβ. Furthermore, the ATPγS-stimulated translocation of NF-κB into the nucleus and degradation of IκBα was blocked by U0126 and helenalin. In addition, the ATPγS-stimulated cPLA₂ expression was inhibited by U0126, SB202190, helenalin, celecoxib (a selective COX-2 inhibitor), and PGE₂ receptor antagonists (AH6809, GW627368X, and SC-19220). However, the inhibitory effect of celecoxib on cPLA₂ expression was reversed by addition of exogenous PGE₂.

Our results suggest that in VSMCs, activation of p42/p44 MAPK, p38 MAPK, and NF-κB is essential for ATPγS-induced COX-2 expression and PGE₂ synthesis. Newly synthesized PGE₂ was observed to act as an autocrine signal contributing to cPLA₂ expression, which may be implicated in inflammatory responses. Collectively, our findings provide insights into the correlation between COX-2 and cPLA₂ expression in ATPγS-stimulated VSMCs with similar molecular mechanisms and functional coupling to amplify the occurrence of vessel disease-related vascular inflammation.