p53/p21(CIP1) cooperate in enforcing rapamycin-induced G(1) arrest and determine the cellular response to rapamycin.

The relationship between G(1) checkpoint function and rapamycininduced apoptosis was examined using two human rhabdomyosarcoma cell lines, Rh1 and Rh30, that express mutated p53 alleles. Serum-starved tumor cells became apoptotic when exposed to rapamycin, but were completely protected by expression of a rapamycin-resistant mutant mTOR. Exposure to rapamycin (100 ng/ml) for 24 h significantly increased the proportion of Rh1 and Rh30 cells in...