CHOP down‐regulates cFLIPL expression by promoting ubiquitin/proteasome‐mediated cFLIPL degradation

The transcription factor CHOP/GADD153 is induced during the unfolded protein response and is related to the induction of ER stress‐mediated apoptosis. However, how CHOP is organized between the pro‐survival and pro‐apoptotic roles of ER stress remains largely undefined. In this study, we identified the apoptosis regulating protein suppressed by CHOP. We found that treatment of Caki cells with CHOP‐inducing drugs including withaferin A, thapsigargin, brefeldin A, and silybin led to a strong reduction in cFLIP_L protein levels together with a concomitant increase in the CHOP protein. Interestingly, Wit A down‐regulated cFLIP_L expression via both suppressing mRNA transcription and increasing cFLIPL protein instability. We also found that forced expression of CHOP dose‐dependently led to a decrease of cFLIP_L protein expression but did not alter cFLIP_L mRNA levels. Additionally, we observed that siRNA‐mediated CHOP silencing recovered the cFLIP_L expression decreased by CHOP‐inducing agents in Caki cells. Finally, we showed that CHOP facilitates ubiquitin/proteasome‐mediated cFLIP_L degradation, leading to down‐regulation of cFLIP_L. Finally, cFLIP_L over‐expression reduced cell death induced by treatment with brefeldin A, thapsigargin, and silybin. Taken together, our results provide novel evidence that cFLIP_L is a CHOP control target and that CHOP‐induced down‐regulation of cFLIP_L is due to activation of the ubiquitin/proteasome pathways. J. Cell. Biochem. 113: 3692–3700, 2012. © 2012 Wiley Periodicals, Inc.