the signaling event that triggers c FLIP degradation has not been known. Our previous studies demonstrate that celecoxib and its analogue DMC downregulate c FLIP levels through facilitating ubiquitination and proteasome mediated degradation of c FLIP. In the present study, purchase VX-661 we found that the inhibition of GSK3 with SB216763 didn’t raise c FLIP mRNA levels, and that the existence of the proteasome inhibitor MG132 prevented SB216763 induced c FLIP downregulation. Moreover, SB216763 substantially improved h FLIP ubiquitination. Collectively, these show that GSK3 inhibitioninduced h FLIP down-regulation occurs at a post translational stage via promoting ubiquitin/ proteasome mediated protein degradation. Provided that celecoxib inhibits GSK3, as mentioned above, and decreases c FLIP levels through the same mechanism as we previously demonstrated, we suggest that celecoxib inhibits GSK3, ultimately causing facilitation of c FLIP destruction. The E3 ligase Itch has been suggested to be associated with TNF induced Papillary thyroid cancer d FLIP degradation. In our research, we found that silencing of Itch expression with Itch siRNAs neither elevated basal levels of c FLIP nor blocked c FLIP down-regulation induced by both SB216763 or celecoxib, suggesting that Itch is impossible to be concerned in GSK3 inhibition induced c FLIP degradation. Previous work has demonstrated that c FLIP downregulation plays a role in celecoxibinduced apoptosis and enhancement of TRAIL induced apoptosis. In agreement, we found in this research that siRNA mediated silencing of GSK3B enhanced the ability of celecoxib to down-regulate d FLIP. When cells were co addressed with celecoxib and a GSK3 Gemcitabine molecular weight inhibitor similar were also generated. Hence, our further support a significant part of c FLIP down-regulation, that is mediated by inhibition, in celecoxib induced apoptosis. We have previously found that celecoxib downregulates h FLIP independent of its COX 2 inhibitory activity by using DMC and COX 2 siRNA, which lacks COX 2 inhibitory activity. In this study, we further showed that DMC also increased p GSK3 levels, this effect could not be abrogated by LY294002. Ergo, celecoxib induced GSK3 phosphorylation and subsequent downregulation of c FLIP is unlikely to be secondary to COX 2 inhibition. In summary, the current research demonstrates a novel mechanism where celecoxib induces c FLIP degradation through Akt independent phosphorylation or inhibition of GSK3. Through this study, we are able to show, for the first time, that inhibition of GSK3 is related to induction of c FLIP degradation, hence giving an acceptable explanation for how GSK3 inhibits the extrinsic death receptor mediated apoptotic pathway.