Heat-induced inhibition of DNA synthesis in L5178Y-S cells is reversed by caffeine

Apurinic site induction in the DNA of cells heated at hyperthermic temperatures

The induction of DNA damage in cells heated at hyperthermic (43-48 degrees C) temperatures was determined by alkaline filter elution and alkaline sucrose gradient-sedimentation analysis of cell DNA denatured at pH 13.0. A class of DNA lesion which converted to strand breaks during denaturation of DNA at pH 13.0 was produced randomly throughout the cell DNA at temperatures as low as 43 degrees C. Induction of this lesion occurred with a T0 of 90 and 10 min at 45 and 48 degrees C, respectively. We estimate that these pH 13.0-detectable DNA lesions are produced in the cell DNA with a frequency of approximately 75 and 660 per min of heating at 45 and 48 degrees C, respectively. Since the lesions were quantitatively converted to DNA strand breaks at pH 13.0 with a half-time of 30 min, or less, we suggest that these pH 13.0-detectable DNA lesions are heat-induced, abasic DNA sites. The induction of these lesions does not appear to be directly involved in the initial heat-induced inhibition of DNA synthesis. The presence of these lesions cannot be excluded as an explanation for the long-term inhibition of replicon initiated in heated cells.