Temperature‐sensitive DNA repair of ultraviolet damage in human cell lines

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Abstract
Following exposure to ultraviolet irradiation (UV), two of three human fibroblast strains and one of three melanoma cell lines showed lower rates of thymine dimer excision during 24 h at 40° C than at 36° C. All lines had lower rates at 32° C. Autoradiographic studies of three fibroblast strains and four melanoma lines incubated for four hours after irradiation revealed decreased unscheduled DNA synthesis at 42° C compared with 36° C. The rate of semiconservative DNA synthesis was decreased at the upper temperature in both series of experiments. All eight cell lines tested showed decreased repair at 42° C, as judged by slower sedimentation and increased heterogeneity of parental DNA in alkaline sucrose gradients. Experiments using the DNA synthesis inhibitor Actinomycin D suggested that these effects were due to temperature‐sensitive repair synthesis. In the two lines studied, preincubation of cells at 42° C apparently increased the extent of UV damage. Although by no means conclusive, these results are consistent with the possibility that temperaturesensitive DNA repair is a contributory factor in some cases of solar carcinogenesis.