Induction of gadd153 gene in G0-specific ts mutant cells at nonpermissive temperature.

tsJT60 is a temperature-sensitive (ts) mutant of the cell cycle isolated from a rat cell line. It does not enter the cell cycle from the G0 phase at a nonpermissive temperature (40 degrees C) but proliferates normally in log phase at both permissive (34 degrees C) and nonpermissive temperatures (G0-specific ts mutant). Here we examined whether tsJT60 fails to downregulate growth arrest-specific genes after growth stimulation from G0 phase at 40 degrees C. Among growth arrest-specific genes examined, an expression of gadd153, which decreased after serum stimulation at 34 degrees C as expected, increased markedly at 40 degrees C. It is plausible to assume that induction of gadd153 at 40 degrees C is correlated with inability of tsJT60 to enter S phase from G0 phase at 40 degrees C, because it also occurred in tsJT366 (another ts mutant clone in the same complementation group) but did not occur in parental 3Y1 and in other ts mutant lines of different complementation groups. However, gadd153 was also induced after the temperature upshift in tsJT60 cells growing in log phase or progressing S phase.