Temperature sensitive cells in the study of carcinogenic transformation.

Two temperature sensitive variants (ts13 and ts14) of an African green monkey tetraploid kidney cell line (epithelial), carrying temperature sensitive lesions in thymidine metabolism, were transformed by methylnitrosourea (MNU) at the permissive temperature of 33 degrees C, nor was there any transformation in the wild type parental cell line of BSC-1 at these temperatures under similar conditions. A comparative study of the cell cycle and metabolic efficiency in the 3 cell lines was performed in order to get an understanding of the physiology of the "target cells" in culture. Compared with the parental cell line of BSC-1, ts13 and ts14 cells were blocked in the G1 phase of the cell cycle during the time that the cell were in contact with the carcinogen (MNU); the variant cells also had higher mitotic indices at this time. The cells of ts13 which showed 50% more transformation than those of ts14 differed from the latter in having larger numbers of viable cells arrested in mitosis over the G1 period. The results were interpreted to indicate that there were other factors, besides cells arrested being in G1, which contributed to the difference in the frequency of transformation between the variant cell lines which had an otherwise similar physiology. Using gel electrophoresis a new protein was located in the nuclei of the transformed cells of ts13 and ts14 which was absent in the wild type cell line of BSC-1 or in the variants ts13 and ts14 at 39-5 degrees C.