SIGNAL-TRANSDUCTION AND HIV TRANSCRIPTIONAL ACTIVATION AFTER EXPOSURETO ULTRAVIOLET-LIGHT AND OTHER DNA-DAMAGING AGENTS

Short wavelength (254 nm) ultraviolet light (UVC)dagger radiation was much more potent in activating transcription of human immunodeficiency virus 1 (HIV) reporter genes stably integrated into the genomes of hu man and monkey cells than ionizing radiation (IR) from a Cs-137 source at similarly cytotoxic doses, A similar differential was also observe d when c-jun transcription levels were examined, However, these transc ription levels do not correlate with activation of nuclear factor (NF) -kappa B and AP-1 measured by band-shift assays, i.e. both types of ra diation produce similar increases in NF-kappa B and AP-1 activity, sug gesting existence of additional levels of regulation during these resp onses, Because of the well-established involvement of cytoplasmic sign aling pathways in the cellular response to tumor necrosis factor-alpha (TNF-alpha), UVC, and IR using other types of assays, the role of TNF -alpha in the UVC response of HIV and c-jun was investigated in our ce ll system, We demonstrate that UVC and TNF-alpha activate HIV gene exp ression in a synergistic fashion, suggesting that it is unlikely that TNF-alpha is involved in UVC activation of HIV transcription in stably transfected HeLa cells, Moreover, maximum TNF-alpha stimulation resul ted in one order of magnitude lower levels of HIV expression than that observed after UVC exposure, We also observed an additive effect of U VC and TNF-alpha on c-jun steady-state mRNA levels, suggestive of a pa rtial overlap in activation mechanism of c-jun by UVC and TNF-alpha; y et these responses are distinct to some extent, Our results indicate t hat the HIV, and to some extent also the c-jun, transcriptional respon ses to UVC are not the result of TNF-alpha stimulation and subsequent downstream cytoplasmic signaling events in HeLa cells, Additional Leve ls of regulation that do not directly involve the NF-kappa B and AP-1 transcription factors, such as changes in chromatin structure associat ed with the UV repair process, may also be important for a full transc riptional response of HIV and c-jun to UVC, In addition to the new dat a, this report also summarizes our current views regarding UVC-induced activations of HIV gene expression in stably transfected cells.