RADIATION-INDUCED APOPTOSIS OF HUMAN PROSTATE-CANCER CELLS IS INDEPENDENT OF MUTANT P53 OVEREXPRESSION

Background: Previous studies have demonstrated that androgen-independe nt prostate cancer cells undergo apoptosis in response to ionizing irr adiation. The p53 protein controls cell cycle nn est and apoptosis by acting as a checkpoint control that halts the cell cycle in G1, while DNA damage is present, in this study the effect of overexpression of m utant p53 protein, on radiation-induced apoptotic cell death of human prosrate cancer cells PC-3 was investigated. Materials and Methods: PC -3 cells were transfected with the plasmid encoding the mutant p53 seq uence, and the neomycin resistance gene. Selected transfectant clones, were characterized at the molecular level (gene integration, and leve l of mRNA and protein expression) and cloned transfectants expressing high levels of p53 protein were treated with increasing doses of ioniz ing ii-radiation. The cellular response to radiation was determined on the basis of: a) clonogenic survival (colony forming ability of irrad iated cells); b) induction of apoptosis as determined by the terminal transferase assay; c) apoptotic DNA fragmentation; and d) induction of expression of genes associated with prostate-apoptosis. Results: Both mutant p53 transfectant and parental PC-3 cells underwent apoptosis i n response to ionizing irradiation following similar kinetics of induc tion of DNA fragmentation. In addition the magnitude of induction of e xpression of prostate apoptosis associated genes, SGP-2 and TGF-beta, was similar in the mutant p53 overexpressing and parental PC-3 cells a nd coincidental with DNA fragmentation. Conclusions: These findings se riously challenge the involvement of p53 in radiation-induced apoptosi s in human prostate cancel cells and suggest that p53 mutations provid e no selective advantage in the development of radioresistance of pros tate tumor cells within the context of p53-independent apoptotic pathw ay.