Effect of hyperthermia on thymidine salvage as related to DNA synthesis.
The effect of increasing temperature up to 43 degrees C on thymidine (TdR) salvage, i.e. uptake of TdR, thymidine kinase (TK) activity, intracellular amount of thymidinetriphosphate (dTTP) and specific activity of 3H-dTTP and incorporation of dTTP into DNA, was studied in ascites tumour cells in vitro. While the uptake of [3H]TdR was almost unchanged up to 40.5 degrees C and 2.4 h followed by a decrease at later times and higher temperatures, TK activity declined already after 30 min in a temperature-dependent way, leading to a decrease in cellular amount of dTTP reaching almost undetectable values at 43 degrees C and 6.0 h. The specific activity of [3H]dTTP in the cell was elevated at 39 degrees C and 43 degrees C, but somewhat reduced at 40.5 degrees C. Incorporation into DNA of [3H]TdR decreased in a temperature-dependent way with increasing incubation time. After correction for specific activity of [3H]dTTP, however, the incorporation of [3H]TdR into DNA at 39 degrees C and 40.5 degrees C was unchanged up to 2.4 h and for 40.5 degrees C up to 6.0 h, while incorporation into DNA at 43 degrees C was still reduced. The overall protein synthesis was also reduced in a temperature-dependent way. We concluded that phosphorylation of TdR to dTMP was more sensitive to moderately elevated temperatures than uptake of TdR and DNA synthesis per se, caused by a reduced TK activity. The decline in TK activity was probably due to a decrease in TK polypeptide synthesis.
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Department of Medical Radiobiology, Karolinska Institutet, Stockholm, Sweden.
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D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism / Q000628:therapy; D004273:DNA, Neoplasm / Q000096:biosynthesis*; D006979:Hyperthermia, Induced; D007700:Kinetics; D007930:Leucine / Q000378:metabolism; D051379:Mice; D009363:Neoplasm Proteins / Q000096:biosynthesis; D013936:Thymidine / Q000378:metabolism*; D013937:Thymidine Kinase / Q000378:metabolism; D013942:Thymine Nucleotides / Q000378:metabolism
D004273:DNA, Neoplasm; D009363:Neoplasm Proteins; D013942:Thymine Nucleotides; D013937:Thymidine Kinase; D007930:Leucine; C024157:thymidine 5'-triphosphate; D013936:Thymidine