Enhancement of SV40 transformation by treatment of C3H2K cells with uv light and caffeine

Abstract

Abstract The transformation frequency of C3H2K cells infected with SV40 was enhanced by treatment of cells with uv light and/or caffeine. This enhancement depended upon: (a) multiplicity of infection (m.o.i.) of the virus; (b) cell phase at time of infection; and (c) length of exposure to caffeine. The transformation frequency of C3H2K cells was proportional to the viral dose between an m.o.i. of 103 and 104 (one-hit response). Treatment of cells with uv (75 ergs/mm2) or caffeine (1 mM) enhanced the transformation frequency without affecting the linearity of the reaction. When irradiated cells were infected with virus and incubated with caffeine, the transformation frequency was not proportional to the virus dose, and far exceeded the expected response if uv and caffeine act additively. The maximum transformation frequency obtained was 45%. Experiments with partially synchronized cultures indicated that cells passing through the late S period was highly susceptible to the transformation. However, the enhancement of transformation by uv and/or caffeine did not appear to depend upon a particular period in the cell cycle. The transformation frequency of unirradiated cells increased progressively during a 4-day incubation with 1 mM caffeine, after which time it leveled off. In contrast, when cells were uv-irradiated prior to virus infection and then incubated in the presence of caffeine, the enhancement of transformation appeared in the early period of incubation, reaching a maximum within 24 hr. The latter time course was coincident with that of the repair process of uv-damaged DNA, as judged from unscheduled DNA synthesis.