Expression of cyclooxygenase-2 in rat vascular smooth muscle cells is unrelated to nuclear factor-κB activation

The promoter region of cyclooxygenase-2 (COX-2) gene contains binding sites for a number of important transcription factors including cyclic AMP response element, nuclear factor-IL6, nuclear factor-kB (NF-kB) and TGF-beta response element. Several reports have documented that the activation of NF-kB triggers the expression of COX-2 gene. In the present study, NF-kB was activated by TNF-alpha in rat aortic smooth muscle cells as demonstrated by electrophoretic mobility shift assay. The activity of NF-kB induced by TNF-alpha was blocked by calpain inhibitor I, a potent NF-kB inhibitor. However, the activation of NF-kB was not related to the expression of COX-2 induced by TNF-alpha since calpain inhibitor I blocked the activation of NF-kB but not the expression of COX-2 mRNA or protein. Mutation of rat COX-2 NF-kB-like sites in the promoter region did not significantly reduce the promoter activity. These results suggest that the transcriptional regulation of COX-2 expression by NF-kB depends upon the types of cells studied and that activation of this transcription factor alone does not play an important role in the expression of COX-2 in rat smooth muscle cells.