Comparing nitrosative versus oxidative stress toward zinc ringer-dependent transcription.: Unique role for NO.

During inflammatory reactions, cells are under nitrosative and/or oxidative stress. The zinc finger transcription factors vitamin D receptor (VDR) and retinoid X receptor (RXR) were used as a model system to characterize effects of NO. and/or reactive oxygen species on zinc finger-dependent gene expression. Nitric oxide (NO.) as well as H2O2, singlet oxygen (O-1(2)), peroxyl radicals (ROO.), and peroxynitrite (ONOO-), respectively, were shown to inhibit VDR/RXR-DNA complex formation in vitro in a dose-dependent manner. While NO-induced inhibition of VDR/RXR-DNA complex formation could be restored nearly completely by subsequent treatment with dithiothreitol, inhibition by H2O2 proved to be only partially reversible, and inhibition by O-1(2), ROO. or ONOO- was found to be irreversible. In cells transiently transfected with VDR and RXR, subtoxic concentrations of NO. or hydroperoxides and intracellular generation of superoxide anion radicals inhibited VDR/RXR-dependent reporter gene activity in a dose-dependent manner. Interestingly, cells can repair the zinc fingers of VDR and RXR after nitrosative stress but not after oxidative stress. The results indicate that, among the reactive species investigated, only NO. may act sufficiently gentle to be considered as a regulator and not only as an inhibitor of gene expression via zinc finger transcription factors.