D609, a specific PC-PLC inhibitor was seen to positively inhibit TRAIL, Fas and TNF+Cyclo-stimulated apoptosis, PC-PLC activity and DAG production in Jurkat I9.2 cells too. Combination treatment of D609 and Z-IETD (caspase 8 inhibitor) in HeLa cells could inhibit TRAIL, Fas and TNF+Cyclo-stimulated tBID formation more significantly comparing to treatment with Z-IETD merely. In the Jurkat I9.2 cells model, treatment of D609 could also inhibit TRAIL, Fas and TNF+Cyclo-stimulated tBID formation significantly. So based on the fact that TRAIL, Fas and TNF+Cyclo can induce apoptosis in Jurkat I9.2 cells and the tBID formation data, we suggested that besides caspase 8, there is other possibly second messenger that can mediate the apoptosis. Caspase 10, which is also bound with death domain, can be one of the possible candidates. Some reports had shown that caspase 10 has a possible same function like caspase 8. To our study on caspase 10, we found that D609 is potential to inhibit cleavage of caspase 10. In our apoptosis assay, it is also clearly shown that transfection of caspase 10 (Long or Short) to Jurkat I9.2 cells can make it more susceptible to TRAIL, Fas and TNF+Cyclo treatment. These data were emphasized by our data that Z-AEVD (caspase 10 inhibitor) could inhibit TRAIL, Fas and TNF+Cyclo-stimulated apoptosis in Jurkat I9.2 cells.
Combination of Z-AEVD with D609 could have more potential to inhibit TRAIL, Fas and TNF+Cyclo-stimulated apoptosis in Jurkat I9.2 cells. This is possible, because as in our previous report, it was shown that PC-PLC had possible direct signal to affect mitochondria membrane, such as cardiolipin.
To our conclusion in this study that besides caspase 8, caspase 10 also plays an important role in TRAIL, Fas and TNF+Cyclo-stimulated apoptosis pathway.