DIFFERENTIAL P53 PHOSPHORYLATION AND ACTIVATION OF APOPTOSIS-PROMOTING GENES BAX AND FAS APO-1 BY IRRADIATION AND ARA-C TREATMENT/

In this study, we examined the effects of radiation and ara-C on induc tion of apoptosis and on the apoptosis-promoting genes p53, Bar and Fa s/APO-1, in BV173 human leukemia cells, which harbor the wild-type p53 gene. It has been reported that p53 upregulates Fas/APO-1 acid Bar ex pression. Both irradiation and ara-C treatment resulted in apoptosis a nd induction of p53 proteins within hours, The Bar gene was activated in irradiated and ara-C-treated BV173 cells, but Fas/APO-1 was induced only in irradiated BV173 cells, Radiation and ara-C treatment did not induce Bar or Fas/APO-1 protein expression in p53-null HL60 cells. Ra diation weakly induced Fas/APO-1 expression in KBM-7 cells, which harb or a partially defective p53 gene, Both HL60 and KBM-7 cells are more resistant to radiation- and ara C-induced apoptosis than BV173 cells, These results suggest that functional p53 is necessary for the activat ion of Bar and Fas/APO-1 expression. However, elevated p53 protein is not sufficient to activate Fas/APO-1 gene expression in ara-C-treated cells. Using two-dimensional gel electrophoresis, we found that the p5 3 proteins in irradiated and ara-C-treated BV173 cells have different isoelectric points; they converged to a single isoelectric point after in vitro treatment with phosphatase, These results suggest that diffe rent genotoxic treatments cause different phosphorylations of p53, whi ch may account for the different levels of activation of Fas/APO-1 exp ression.