UV-induced expression of GADD45 is mediated by an oxidant sensitive pathway in cultured human keratinocytes and in human skin in vivo.

The expression of GADD45 was examined in cultured skin keratinocytes and in human skin in vivo following UV irradiation. Northern blot analysis revealed that UV-induced the expression of GADD45 (alpha, beta, gamma) in a time- and dose-dependent manner. Messenger RNA of GADD45 (alpha, beta, gamma) increased within 30 min, peaked at 4 h and remained elevated for at least 8 h following UV irradiation in vitro and in vivo. Maximal induction of GADD45alpha was approximately 5-fold compared to the level in sham-irradiated controls. Similarly H2O2 and IL-1 also induced GADD45alpha expression in cultured human keratinocytes. The kinetics of induction of GADD45alpha by H2O2, IL-1beta and UV were very similar. Interestingly, UV-induced GADD45alpha expression was inhibited by diphenylene iodonium (DPI), an inhibitor of NADPH oxidase, and antioxidant, N-acetyl-L-cysteine (NAC), indicating the involvement of reactive oxygen species in UV signaling. Previously we have shown that EGF receptor activation by UV is prerequisite for subsequent activation of NADPH oxidase and generation of reactive oxygen species. We therefore examined the effect of EGF receptor inhibitor on UV-induced GADD45alpha expression. Our results showed that PD168393, a potent EGF receptor inhibitor, blocked UV-induced GADD45alpha expression. Collectively, our data suggest that UV-induced GADD45alpha expression occur via an EGF receptor-mediated oxidative pathway sensitive to antioxidant regulation.