Signal transduction and HIV transcriptional activation after exposure to ultraviolet light and other DNA-damaging agents.

Short wavelength (254 nm) ultraviolet light (UVC) radiation was much more potent in activating transcription of human immunodeficiency virus 1 (HIV) reporter genes stably integrated into the genomes of human and monkey cells than ionizing radiation (IR) from a 137Cs source at similarly cytotoxic doses. A similar differential was also observed when c-jun transcription levels were examined. However, these transcription 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 radiation produce similar increases in NF-kappa B and AP-1 activity, suggesting existence of additional levels of regulation during these responses. Because of the well-established involvement of cytoplasmic signaling 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 cell system. We demonstrate that UVC and TNF-alpha activate HIV gene expression 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 resulted in one order of magnitude lower levels of HIV expression than that observed after UVC exposure. We also observed an additive effect of UVC and TNF-alpha on c-jun steady-state mRNA levels, suggestive of a partial overlap in activation mechanism of c-jun by UVC and TNF-alpha; yet these responses are distinct to some extent. Our results indicate that the HIV, and to some extent also the c-jun, transcriptional responses to UVC are not the result of TNF-alpha stimulation and subsequent downstream cytoplasmic signaling events in HeLa cells. Additional levels of regulation that do not directly involve the NF-kappa B and AP-1 transcription factors, such as changes in chromatin structure associated with the UV repair process, may also be important for a full transcriptional response of HIV and c-jun to UVC. In addition to the new data, this report also summarizes our current views regarding UVC-induced activations of HIV gene expression in stably transfected cells.