Glycerol restores heat-induced p53-dependent apoptosis of human glioblastoma cells bearing mutant p53

BACKGROUND We have previously reported that glycerol acts as a chemical chaperone to restore the expression of WAF1 in some human cancer cell lines bearing mutant p53. Since the expression of WAF1 is up-regulated by activated wildtype p53, glycerol appears to restore wtp53 function. The aim of the present study is to examine the restoration of heat-induced p53-dependent apoptosis by glycerol in human glioblastoma cells (A-172) transfected with a vector carrying a mutant p53 gene (A-172/mp53 cells) or neo control vector (A-172/neo cells). RESULTS A-172/mp53 cells showed heat resistance compared with A-172/neo cells but A-172/mp53 cells in turn became heat sensitive when pre-treated with glycerol before heat treatment. The accumulation of Bax in the A-172/mp53 cells was induced by heating with glycerol pre-treatment, but not without it, whereas the accumulation in the A-172/neo cells was induced in both cases. Furthermore, mp53 extracted from heated cells came to bind to the sequence specific region after heating combined with glycerol pre-treatment. The phosphorylation of mp53 at serine15 was suppressed by an inhibitor of the phosphatidylinositol 3-kinase (PI3-K) family. CONCLUSION These results suggest that glycerol is effective in inducing conformational change of phosphorylated p53 and restoring mp53 to wtp53 function, leading to enhanced heat sensitivity through the induction of apoptosis. This novel tool for enhancement of heat sensitivity in cancer cells bearing mp53 may be applicable for p53-targeted hyperthermia, because mutation or inactivation of p53 is observed in approximately 50% of human cancers.