Abortive transformation of temperature-sensitive mutants of rat 3Y1 cells by simian virus 40: Effect of cellular arrest states on entry into S phase and cellular proliferation

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Abstract
Four temperature‐sensitive (ts) mutants of rat 3Y1 fibroblasts, representing independent complementation groups, cease to proliferate predominantly with a 2n DNA content, at the restrictive temperature (39.8°C)(temperature arrest) or at the permissive temperature (33.8°C) at a confluent cell density (density arrest) (Ohno et al., 1984). We studied the temperature‐ or the density‐arrested cells of these mutants infected with simian virus 40 (SV40) or its mutants affecting large T or small t antigen with respect to kinetics at 39.8°C of entry into S phase and cellular proliferation. Three mutants, 3Y1tsD123, 3Y1tsF121 and 3Y1tsG125, expressed T antigen and entered S phase at 39.8°C from both the arrested states after infection with either wild‐type, tsA mutants, or a .54/.59 deletion mutant of SV40, whereas in the density‐arrested 3Y1tsH203, expression of T antigen and entry into S phase were inefficient and ts. Following the WT‐SV40 induced entry into S phase, the temperature‐arrested 3Y1tsD123 detached from the substratum with no detectable increase in cell number, whereas the density‐arrested ones completed a round of the cell cycle and then detached. 3Y1tsF121 and 3Y1tsG125 in the both arrested states proliferated through more than one generation. 3Y1tsF121 and 3Y1tsG125 in the density‐arrested state infected with tsA mutants once proliferated and then ceased to increase in number as the percentage of T‐antigen positive population decreased. These results suggest that wild‐type and tsA‐mutated large T antigens are able to overcome the cellular ts blocks of entry into S phase in the 3 ts mutants of 3Y1 cells in both the arrested states, and that small t antigen is not required to overcome the blocks. It is also suggested that cellular behaviors subsequent to S phase (viability, mitosis, and proliferation in the following generations) depend on cellular arrest states, on traits of cellular ts defects, and on the duration of large T antigen expression.