Enhanced reactivation and mutagenesis of UV-irradiated adenovirus in normal human fibroblasts

UV-enhanced reactivation (UVER) and UV-enhanced mutagenesis (UVEM) for two adenovirus temperature-sensitive mutants (Ad5ts35 and Ad5ts125) were examined following the infection of normal human fibroblasts. Fibroblast monolayers were either UV-irradiated or left non-irradiated and subsequently infected with either non-irradiated or UV-irradiated virus. After incubation of the infected cultures at the permissive temperature, the induction of wild-type revertants in the viral progeny was determined by plaquing at the permissive (33 degrees C) and the non-permissive (39 degrees C) temperatures on human HeLa or KB cells. UV-irradiation of the virus alone resulted in a dose-dependent increase in the UV-induced reversion frequency (RF) of viral progeny and a dose-dependent exponential decrease in progeny survival, when infecting non-irradiated cells. Analysis of the slopes of the UV-induced reversion curves suggested that 2.5 +/- 0.3 and 2.4 +/- 0.5 'hits' were required to produce a targeted reversion event among the viral progeny of Ad5ts36 and Ad5ts125 respectively. UV-irradiation of cells 24 h prior to infection resulted in a significant increase in progeny survival for UV-irradiated virus (UVER factor = 3.4 +/- 0.8) concomitant with a significant increase in RF for UV-irradiated virus (targeted increase = 1.9 +/- 0.3). The UV-induced RF per lethal hit to the virus was also significantly greater in UV-irradiated compared with non-irradiated cells. These results are consistent with the existence of a UV-inducible error-prone DNA repair mechanism in normal human cells.