5-FLUOROURACIL (5-FU) INDUCED APOPTOSIS IN GASTRIC-CANCER CELL-LINES - ROLE OF THE P53 GENE

We examined chemosensitivity to 5-fluorouracil (5-FU) in four human ga stric cancer cell lines, by analyzing the expression of p53 and its re lated genes. Treatment with 1 mM 5-FU induced variable degrees of apop tosis in the cultured cells. The apoptotic indices 72 h after treatmen t were approximately 14% in MKN-74 (wild-type p53 gene), 12% in MKN-45 (wild-type), 3% in MKN-28 (mutated) and 0.5% in KATO-III cells (delet ed), respectively. On the other hand, 50 mu M 5-FU had little effect o n the induction of apoptosis in MKN-74 cells, the value being approxim ately 2% after 72 h, Induction of P53 expression was noted 3 h after i nitiating the treatment, followed by the induction of P21/Waf1 after 6 h in both MKN-74 and MKN-45 cells. The same expression mode was noted in MKN-74 treated with 50 mu M 5-FU, Conversely, the level of P53 exp ression was constant in MKN-28 cells and absent in KATO-III cells, in which P21/Waf1 had never been induced, The Bax/Bcl-2 expression ratio was gradually elevated for up to 72 h in MKN-74 and MKN-45 cells treat ed with 1 mM 5-FU; in contrast, it was unchanged in MKN-28 and KATO-II I cells, and MKN-74 treated with 50 mu M 5-FU, These results might ind icate that (1) 1 mM 5-FU induces apoptosis in cultured gastric cancer cells carrying the wild-type p53 gene, but not those carrying the muta ted type or a gene deletion, and (2) the elevated Bax/Bcl-2 expression ratio plays a more crucial role than the higher expression of P21/Waf 1 in the induction of p53-gene dependent apoptosis.