Caspase-8 in apoptosis of hepatoma cell induced by 5-fluorouracil.

OBJECTIVE: To explore the relationship between the changes in the activity of caspase-8 and apoptosis of HepG2 cells induced by 5-fluorouracil (5-Fu). METHODS: Human hepatoma HepG2 cells were treated with 5-Fu at the concentrations of 1X10(-1), 1X10(-2), 1X10(-3), 1X10(-4), 1X10(-5) mol/L and for 1, 2, 4, 8, 16, 24 hours, respectively. The caspase-8 activity was detected using caspase-8 fluorescent assay kit. The apoptotic rate of HepG2 cells induced by 5-Fu with or without the caspase-8 inhibitor IETD-FMK was measured by flow cytometry. RESULTS: After the HepG2 cells were treated with 10(-2) mol/L 5-Fu, the caspase-8 activity increased gradually and reached the peak level (313.9+/-6.9) at 16 hours, then fell down. Compared with the control group, the activity was still significantly higher (274.2+/-3.9 vs 68.3+/-3.6, P<0.01). With the increasing concentration of 5-Fu, the caspase-8 activity was also increased; the activity in high concentration 5-Fu was significantly higher than that in low concentration 5-Fu (370.5+/-4.7 vs 313.7+/-6.9; 225.7+/-5.4 vs 183.3+/-4.8; 183.3+/-4.8 vs 124.0+/-6.2, P<0.01). The caspase-8 activity was the highest at 1X10(-1) mol/L 5-Fu (370.5+/-4.7). The caspase-8 activity in low concentration 5-Fu was higher than in the blank control group and inhibitor group (124.0+/-6.2 vs 68.5+/-3.4; 124.0+/-6.2 vs 41.0+/-2.1, P<0.01). IETD-FMK could block the activation of caspase-8 and reduce the apoptosis of HepG2 cells induced by 5-Fu. The apoptotic rate of HepG2 cells in the 5-Fu group was significantly different from that in the inhibitor group (P<0.01). CONCLUSIONS: 5-Fu can induce apoptosis of HepG2 cells via caspase-8 signal transduction pathway, which can be blocked by IETD-FMK. 5-Fu promotes the increase of caspase-8 activity in a time- or concentration-dependent manner.