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
✍ Scribed by Tetsuya Mitsudomi; Genki Kimura
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- English
- Weight
- 761 KB
- Volume
- 123
- Category
- Article
- ISSN
- 0021-9541
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✦ Synopsis
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 (39.8OC)(temperature arrest) or at the permissive temperature (33.8OC) at a confluent cell density (density arrest) (Ohno et al., 1984). We studied the temperature-or the densityarrested 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 39.8OC of entry into S phase and cellular proliferation. Three mutants, 3YltsD123, 3YltsF121 and 3YltsGl25, expressed T antigen and entered S phase at 39.8OC 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 3YltsH203, expression of T antigen and entry into S phase were inefficient and ts. Following the WT-SV40 induced entry into S phase, t h e temperaturearrested 3YltsD123 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. 3YltsF121 and 3YltsG125 in the both arrested states proliferated through more than one generation. 3YltsF121 and 3YltsC125 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 tsAmutated 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.
Untransformed fibroblasts in culture cease to proliferate under suboptimal environmental conditions such as at a confluent cell density, at a low concentration of serum or growth factors in the medium, and in the presence of nutrient insufficiency (for review, see Yanishevsky and Stein, 1981). Simian virus 40 (SV40) stim-