RECONSTITUTION OF WILD-TYPE P53 EXPRESSION TRIGGERS APOPTOSIS IN A P53-NEGATIVE V-MYC RETROVIRUS-INDUCED T-CELL LYMPHOMA LINE

Inactivation or mutation of the p53 tumor suppressor gene has been observed in a wide variety of human and murine tumors. We have found that a v-myc retrovirus (J3)-induced T-cell lymphoma line (J3D) has lost one of its p53 alleles, whereas the other has become inactivated due to the insertion of a Moloney murine leukemia provirus in intron 4 with an opposite transcriptional orientation. No p53 protein could be detected by immunoprecipitation with monoclonal anti-p53 antibodies. We have transfected this line with the temperature-sensitive murine Val135 construct that is expressed as mutant p53 at 37-degree-C and largely wild-type p53 at 32-degree-C. There was no difference in the number of viable cells among the p53 transfectants, the parental cells, and neomycin vector-transfected control cells at 37-degrees-C. Following a temperature shift to 32-degrees-C, the p53 transfectants rapidly lost viability, and 95-100% of the cells were dead by 3 days, whereas the control cells remained unaffected. Examination of DNA isolated from p53-transfected cells grown at 32-degrees-C revealed nucleosomal fragmentation, indicating cell death by apoptosis. It is suggested that apoptosis is triggered by contradictory signaling. Constitutively expressed v-myc can stimulate cell proliferation, whereas expression of wild-type p53 in cells that have lost endogenous p53 expression in the course of their neoplastic development may suppress growth.