GENETIC STATUS OF P53 AND INDUCTION OF APOPTOSIS BY RADIATION OR ISOFLAVONES IN HUMAN GASTRIC-CARCINOMA CELL-LINES

We have shown previously that various human cancer cell lines undergo morphological changes and internucleosomal DNA fragmentation character istic of apoptosis after exposure to ionizing radiation or isoflavones . Here, we assessed the role of p53 gene in cell cycle and apoptosis f ollowing treatment of 11 gastric carcinoma cell lines with gamma-rays, genistein, biochanin A, or daidzein. Cell survival was measured by tr ypan blue staining, and apoptosis was assessed by fluorochrome stainin g. The rate of cell survival and apoptosis of the cells by gamma-irrad iation or isoflavones did not correlate with p53 gene abnormalities. F low cytometric measurement of DNA content demonstrated that while gamm a-irradiation and genistein induced G(2) arrest, biochanin A and daidz ein blocked the cell cycle of all carcinoma cells at G(1) phase. At mu ltiple time points following irradiation, G(2) arrest was observed at 12-16 h in the wild-type and mutant p53 cell lines. Induction of p53 a nd p21 proteins was not observed in wild-type p53 lines after exposure to gamma-irradiation or isoflavones by Western blotting. Moreover, tr ansfection of the wild-type p53 gene into MKN-1 cells failed to induce G(1) arrest by gamma-irradiation and genistein. Based on these result s, we hypothesize that gastric cancer cells may possess a signal pathw ay which is different from the usual mechanisms of the p53-mediated DN A damage response in normal or hematopoietic tumor cells.