MAP kinase kinase 6-p38 MAP kinase signaling cascade regulates cyclooxygenase-2 expression in cardiac myocytes in vitro and in vivo

Cyclooxygenase-2 (COX-2) catalyzes the rate-limiting step in delayed prostaglandin biosynthesis. The purpose of this study was to evaluate the role of the MAP kinase kinase 6 (MKK6)-p38 MAPK signaling cascade in the regulation of myocardial COX-2 gene expression, in vitro and in vivo. RT-PCR analysis identified p38α and p38β2 MAPK mRNA in rat cardiac myocytes. Interleukin-1β induced the phosphorylation of p38α and p38β2 MAPK in cardiomyocytes and stimulated RNA polymerase II binding to the COX-2 promoter, COX-2 transcription, COX-2 protein synthesis, and prostaglandin E₂ (PGE₂) release. Infecting cardiomyocytes with adenoviruses that encode mutant, phosphorylation-resistant MKK6 or p38β2 MAPK inhibited interleukin-1β-induced p38 MAPK activation, COX-2 gene expression, and PGE₂ release. Treatment with the p38α and p38β2 MAPK inhibitor, SB202190, attenuated interleukin-1β-induced COX-2 transcription and accelerated the degradation of COX-2 mRNA. Cells infected with adenoviruses encoding wild-type or constitutively activated MKK6 or p38β2 MAPK, in the absence of interleukin-1β, exhibited increased cellular p38 MAPK activity, COX-2 mRNA expression, and COX-2 protein synthesis, which was blocked by SB202190. In addition, elevated levels of COX-2 protein were identified in the hearts of transgenic mice with cardiac-restricted expression of wild-type or constitutively activated MKK6, in comparison with nontransgenic littermates. These results provide direct evidence that MKK6 mediated p38 MAPK activation is necessary for interleukin-1β-induced cardiac myocyte COX-2 gene expression and PGE2 biosynthesis in vitro and is sufficient for COX-2 gene expression by cardiac myocytes in vitro and in vivo.