Transformation by viral oncogenes increased sensitivity to heat in rat 3Y1 fibroblasts

Sensitivity to the lethal effect of hyperthermia was compared using the rat 3Y1 fibroblastic cell line and its seven sublines transformed by various agents in vitro. The cell lines examined were those transformed by simian virus 40 (SV3Y1), mouse polyoma virus (Py3Y1), adenovirus type 12 (Ad3Y1), the E1A region of adenovirus type 12 (E1A3Y1), Rous sarcoma virus (SR3Y1), v-Harvey ras oncogene (HR3Y1) and N-methyl-N-nitro-N-nitrosoguanidine (NG3Y1). We also examined the intracellular amount and distribution of 70-kilodalton heat shock protein which has previously been shown to be associated with thermal tolerance in several experimental systems. There was a striking difference in heat sensitivity, as defined by a clonogenic assay, depending on the transforming agents. The parental untransformed 3Y1 cells were most resistant to heat, whereas the Ad-, E1A- or NG3Y1 cell lines were most susceptible to heat. The other 4 lines showed intermediate sensitivity. We detected translocation of hsp70 from cytoplasm to nucleoli shortly after the heat shock in all cell lines, as detected by indirect immunofluorescence. Western blotting experiment failed to show any difference in amount of hsp70 among the cell lines. We conclude that transformed cells were more susceptible to heat than untransformed cells, and that a mechanism other than hsp70 synthesis may operate on the heat sensitivity, at least in our system.