IONIZING-RADIATION ACTIVATES NUCLEAR FACTOR KAPPA-B BUT FAILS TO PRODUCE AN INCREASE IN HUMAN-IMMUNODEFICIENCY-VIRUS GENE-EXPRESSION IN STABLY TRANSFECTED HUMAN-CELLS

We have investigated the differential effects of ultraviolet light (UV ) and ionizing radiation (IR) on human immunodeficiency virus type 1 ( HIV) and c-jun expression in HIVcat/HeLa cells. This cell line harbors stably integrated copies of the chloramphenicol acetyltransferase (ca t) gene under control of the HIV promoter. Both UV and IR increased th e binding of nuclear proteins to an oligonucleotide spanning the HIV e nhancer region nuclear factor KB sites, but only UV increased HIVcat s teady-state mRNA and CAT activity. By comparison, transcription of the cellular c-jun gene increased after both types of radiation, but UV w as at least 5-fold more effective than IR despite the fact that protei n binding to an activator protein 1 oligonucleotide increased similarl y after both UV and IR. The lack of HIVcat transcriptional response af ter IR does not appear to be the result of a repressor binding to upst ream promoter elements since cells stably transfected with different H IV promoter deletions showed a lack of response to IR indistinguishabl e from that of the intact promoter. While our findings indicate no cor relation between increased binding of transcription factors to upstrea m promoter elements and increased expression of these genes after radi ation, we did observe major differences in how UV and IR affected chro matin structure. UV produced extensive global chromatin decondensation , whereas IR did not, as seen in the microscope and determined by the increased susceptibility of chromatin to micrococcal nuclease digestio n. Finally, although no effect of IR was detected by the CAT assay up to 24 h, a 2-3-fold increase was seen after several days, suggesting t hat HIVcat expression is regulated by both early and late effects afte r radiation; only UV produces the much more pronounced early effect. I n summary, our findings are in agreement with a mechanism whereby UV e xerts a positive effect on HIVcat transcription through extensive glob al changes in chromatin structure, perhaps associated with the DNA rep air process, while bypassing ''true'' transcriptional activation throu gh upstream promoter elements.