Therefore, we can summarize that TNFRSF10B and CFLARL are involved in PTL induced extrinsic apoptosis. PMAIP1 and MCL1 contribute to parthenolide induced intrinsic apoptosis We wonder if PTL could also activate intrinsic apoptotic pathway in lung cancer cells. Since PMAIP1 and MCL1 are both important proteins in intrinsic signaling pathway, we detected their expression after PTL treatment. Western blot analysis revealed that MCL1 was decreased in both concentration and time dependent manners after PTL exposure, while PMAIP1 was up regulated. Gene silencing experiment presented that when PMAIP1 was knocked down, the expression of MCL1 was partially increased and the cleavage of pro caspases and PARP1 in duced by PTL were reduced. Annexin V stain ing analysis showed that apoptosis induced by PTL was weakened after knocking down of PMAIP1.

It could be concluded that the intrinsic apoptosis process induced by PTL is through PMAIP1 and MCL1 axis. Parthenolide induces apoptosis through activation of ER stress response DDIT3, which is a target protein of ATF4, is reported to regulate the expression of TNFRSF10B and PMAIP1 by binding to their promoter sites. Therefore, we wonder BAPTA-AM clinical trial if PTL induces TNFRSF10B and PMAIP1 through ATF4 DDIT3 axis. We examined expression of ATF4 and DDIT3 after PTL treatment. Western blot revealed that PTL could up regulate ATF4 and DDIT3 in both concentration and time dependent manner. When ATF4 was knocked down, DDIT3 was decreased, and activation of pro caspases was weakened at the same time compared with control knockdown cells.

In addition, apoptosis was suppressed when selleck SB-480848 DDIT3 was knocked down, while the expression of TNFRSF10B and PMAIP1 were de creased simultaneously. Since ATF4 and DDIT3 are important hallmarks involved in ER stress pathway, we examined the expression of other molecules in ER stress signaling such as ERN1, HSPA5 and p EIF2A as well. We found that they were both increased after PTL treat ment. All these data indicated that PTL in duces apoptosis through activation of ER stress response. Parthenolide selectively eradicates lung cancer stem like cells Weinberg et al. has demonstrated that knocking down of CDH1 E cadherin with shRNA could make the cells have stem like properties. We had demonstrated that A549 shCDH1 cells in which CDH1 E cadherin expression is inhibited had stronger capacity of proliferation, migration and invasiveness. Furthermore, we found that the expression of SOX2 and POU5F1 which were considered to be the makers of stem cells were up regulated in A549 shCDH1 cells. So in order to determine why PTL could selectively eradicate cancer stem like cells, A549 shCDH1 cell line was used to mimic cancer stem cells and the A549 shCtrl cell line served as control.