Entrance of SV40-transformed cells into G0 phase as revealed by a study using the G0-specific ts mutant tsJT60.
The purpose of this study is to distinguish two possibilities that the transformed cells are blocked to enter a resting state (G0) and that they enter but are persistently stimulated to return to a growing cycle, using SV40-transformed tsJT60 cells as a model system. tsJT60 is a temperature-sensitive (ts) mutant of a Fischer rat cell line (3Y1), which is classified as a G0 mutant; i.e., the ts defect is not expressed within the growing cell cycle but is expressed only between G0 and S phases. We assumed that if the former possibility were the case, the transformed cells would not show any ts phenotype; and if the latter case, they might be ts. All SV40-transformed tsJT60 clones grew at 34 degrees C as well as SV40-transformed 3Y1 cells did at both temperatures. At 39.5 degrees C, some SV40-transformed tsJT60 clones grew (not ts) but others did not (ts) under conditions adequate for growth of untransformed cells. When clones that grew at 39.5 degrees C were cultured under conditions inadequate for growth of untransformed cells such as serum restriction or high cell density, they were ts for growth or even cytocidal at 39.5 degrees C. These results indicate that all clones of SV40-transformed tsJT60 cells are ts and the latter possibility is the case.
Ninomiya-Tsuji
J
J
Department of Physiological Chemistry, Hiroshima University School of Medicine, Japan.
Ishibashi
S
S
Ide
T
T
D000818:Animals; D000957:Antigens, Viral, Tumor / Q000032:analysis*; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004622:Embryo, Mammalian; D005455:Fluorescent Antibody Technique; D007399:Interphase; D009154:Mutation; D051381:Rats; D011916:Rats, Inbred F344; D013539:Simian virus 40 / Q000235:genetics*
D000957:Antigens, Viral, Tumor