c-FLIP downregulation contributes to apoptosis induction by the novel synthetic triterpenoid methyl-2-cyano-3, 12-dioxooleana-1, 9-dien-28-oate (CDDO-Me) in human lung cancer cells.
The novel synthetic triterpenoid methyl-2-cyano-3, 12-dioxooleana-1, 9-dien-28-oate (CDDO-Me) induces apoptosis of cancer cells, enhances tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, and exhibits potent anticancer activity in animal models with a favorable pharmacokinetic profile. Thus, CDDO-Me is being tested in Phase I clinical trials. In an effort to understand the mechanism by which CDDO-Me induces apoptosis, particularly in human lung cancer cells, we previously demonstrated that CDDO-Me induces apoptosis involving c-Jun N-terminal kinase (JNK)-dependent upregulation of death receptor 5 (DR5) expression. In the current work, we determined the modulatory effects of CDDO-Me on the levels of c-FLIP, a major inhibitor of death receptor-mediated caspase-8 activation, and its impact on CDDO-Me-induced apoptosis and enhancement of TRAIL-induced apoptosis in human lung cancer cells. CDDO-Me rapidly and potently decreased c-FLIP levels including both long (FLIP(L)) and short (FLIP(S)) forms of c-FLIP in multiple human lung cancer cell lines. The presence of the proteasome inhibitor MG132, but not the JNK inhibitor SP600125, prevented CDDO-Me-induced c-FLIP reduction. Moreover, CDDO-Me increased ubiquitination of c-FLIP. Thus, CDDO-Me induces ubiquitin/proteasome-dependent c-FLIP degradation independently of JNK activation. Importantly, overexpression of c-FLIP (e.g., FLIP(L)) protected cells not only from CDDO-Me-induced apoptosis, but also from induction of apoptosis by the combination of CDDO-Me and TRAIL. Accordingly, silencing of c-FLIP with c-FLIP siRNA sensitized cancer cells to CDDO-Me. Collectively, these results indicate that c-FLIP downregulation contributes to CDDO-Me-initiated apoptosis and also to enhancement of TRAIL-induced apoptosis by CDDO-Me.
Zou
Wei
W
Winship Cancer Institute, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Chen
Shuzhen
S
Liu
Xiangguo
X
Yue
Ping
P
Sporn
Michael B
MB
Khuri
Fadlo R
FR
Sun
Shi-Yong
SY
D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000037:antagonists & inhibitors*; D002289:Carcinoma, Non-Small-Cell Lung / Q000378:metabolism*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D006801:Humans; D008175:Lung Neoplasms / Q000378:metabolism*; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D009828:Oleanolic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology; D013729:Terpenes / Q000494:pharmacology*; D025801:Ubiquitin / Q000378:metabolism
D000970:Antineoplastic Agents; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D053221:TNF-Related Apoptosis-Inducing Ligand; D013729:Terpenes; D025801:Ubiquitin; D009828:Oleanolic Acid; C445068:bardoxolone methyl; D048670:MAP Kinase Kinase 4; D046988:Proteasome Endopeptidase Complex