Alteration of ultraviolet light-induced HIV-LTR CAT activity by vitamin E and dimethylsulfoxide in stably transfected HeLa cells
Chauvin, Theodore R.
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It has been known for a number of years now that ultraviolet light (UVC, 220- 280 nm) can induce the long terminal repeat (LTR) of the human immunodeficiency virus type 1 (HIV). This phenomena has been studied by using a HeLa cell line that has been stably transfected with a plasmid that contains the HIV-LTR which has direct transcriptional control of the E. coli chloramphenicol acetyl transferase (CAT) reporter gene. By looking at CAT activity, one can measure the amount of induction by the LTR. HeLa cells containing the HIV-LTR CAT construct were exposed to UV light and immediately incubated with 0.012 mg/ml of vitamin E for at least 24 hours. While there was no effect of vitamin E on the constitutive level of CAT activity, there was a significant (between 20% and 40%) reduction in UV induced HIV-LTR CAT activity. Ethanol (the carrier for vitamin E) had no effect on the level of CAT activity in control or UV exposed cells. Vitamin E incubation for 24 hours has no effect on cell proliferation or cell viability, as measured by growth curves and colony forming assays. UVC at a fluence rate of 19 J/m2 induces the LTR to a greater extent than does UVB at a fluence rate of 270 J/m2 (280-315 nm). It was found that 1% DMSO can potentiate the CAT activity in cells that were exposed to UVC. The addition of 1% DMSO for 24 hours immediately following exposure to UVC gave a significant increase in the UV-induced CAT activity measured at 24,48, and 72 hours after exposure to UVC. There was no effect of DMSO on the constitutive level of CAT activity. In the case of UVB, a 24-hour post UV incubation or a 24-hour preincubation with 1% DMSO had no effect on CAT levels at 24, 48, and 72 hours post UV exposure between cells that were treated with DMSO and ones that were not. DMSO at a concentration of 1% had no effect on cell viability. The results with vitamin E suggest a role for nuclear factor kappa B (NFkB) activity is necessary for UV induction of the HIV-LTR, since vitamin E has previously been shown to reduce the amount of NFkB activity. DMSO appears to be acting directly on the HIV-LTR when cells are exposed only to UVC and not UVB.