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 1×10-1, 1×10-2, 1×10-3, 1×10-4, 1×10-5 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 1×10-1 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.