TNF-alpha enhances cardiac myocyte NO production through MAP kinase-mediated NF-kappaB activation.

We have previously reported that interleukin-1beta (IL-1beta) alone induced nitric oxide (NO) production by neonatal rat cardiac myocytes (CM). The effects of tumor necrosis factor-alpha (TNF-alpha) on inducible NO synthase (iNOS) were not characterized. Unlike IL-1beta, TNF-alpha alone failed to enhance NO production in CM. However, the addition of TNF-alpha to IL-1beta significantly enhanced iNOS mRNA expression, iNOS protein synthesis, and NO production (NO(-)(2)). TNF-alpha enhancement of IL-1beta-induced NO(-)(2) production was blocked by PD-98059, a selective mitogen-activated protein (MAP) kinase kinase inhibitor, but not calphostin C (Cal C), a protein kinase C inhibitor. TNF-alpha-enhanced MAP kinase activity was associated with an increase in IL-1beta-stimulated NF-kappaB activity. PD-98059, but not Cal C, inhibited both TNF-alpha-enhanced MAP kinase and NF-kappaB activities. Thus TNF-alpha enhancement of IL-1beta-induced NO production is associated with MAP kinase-mediated activation of NF-kappaB.