Activation of HIV Type 1 Long Terminal Repeat by Ultraviolet Light Is Serum and Strain Specific

We have studied the UV responsiveness of xeroderma pigmentosum (XP) and HeLa cell lines transfected with a CAT reporter gene under the control of the HIV-1 LTR promoter. XP fibroblasts grown in 10% newborn bovine serum (NBS) were three times more responsive to UV radiation than cells grown in 10% fetal calf serum (FCS). Moreover, cocultivation of UV-irradiated XP cells with XP cells containing stable integrants of HIV-LTR CAT was found to be more than four times more effective in inducing the CAT activity when cells were maintained in 10% NBS than in 10% FCS. The level of induction was also dependent on the serum concentration. These data indicate that a serum component, possibly a cytokine(s), can enhance the UV response of both irradiated cells and unirradiated cells cocultivated with irradiated cells. The magnitude of UV responsiveness seemed also to be strain dependent. CAT activity for the HIV LTR promoter from the HTLV-III_B (HIV-III_B) strain was induced more than 30-fold by UV irradiation whereas activity from the LAV-1_BRU strain was less than 2-fold. In contrast, both constructs were strongly induced by Tat expression. This indicates that there are differences in the induction mechanism for these two stimuli, even though UV radiation has been previously reported to induce a cellular Tat-like factor (Valerie K, et al., Nature [London] 1988;333:78–81).