The Role of Constitutive Nitric-oxide Synthase in Ultraviolet B Light-induced Nuclear Factor κB Activity

NF-kappa B is a transcription factor involved in many signaling pathways that also plays an important role in UV-induced skin tumorigenesis. LTV radiation can activate NF-kappa B, but the detailed mechanism remains unclear. In this study, we provided evidence that the activation of constitutive nitric-oxide synthase plays a role in regulation of I kappa B reduction and NF-kappa B activation in human keratinocyte HaCa'E cells in early phase (within 6 h) post-UVB. Treating the cells with L-NAME, a selective inhibitor of constitutive nitric-oxide synthase (cNOS), can partially reverse the I kappa B reduction and inhibit the DNA binding activity as well as nuclear translocation of NF-kappa B after UVB radiation. A luciferase reporter assay indicates that UVB-induced NF-kappa B activation is totally diminished in cNOS null cells. The cNOSmediated reduction of I kappa B is likely due to the imbalance of nitric oxide/peroxynitrite because treating the cells with lower (50 mu M), but not higher (100-500 mu m), concentration of S-nitrosoN-acetylpenicillamine (SNAP) can reverse the effect of L-NAME in partial restore I kappa B level post-LTVB. Our data also showed that NF-kappa B activity was required for maintaining a stable I kappa B kinase subunit (IKK alpha) level because treating the cells with NF-kappa B or cNOS inhibitors could reduce IKK alpha level upon UVB radiation. In addition, our data demonstrated that although NF-kappa B protects cells from UVB-induced death, its pro-survival activity was likely neutralized by the pro-death activity of peroxynitrite after UVB radiation.