title: Involvement of c-FLIP and survivin down-regulation in flexible heteroarotinoid-induced apoptosis and enhancement of TRAIL-initiated apoptosis in lung cancer cells.
abstract: The flexible heteroarotinoid, SHetA2, is a novel compound with apoptosis-inducing and anticancer activities in vitro and in vivo. Our previous research showed that up-regulation of death receptor 5 plays a critical role in the mechanism of SHetA2-induced apoptosis in human lung cancer cells. The hypothesis of this study was that the mechanism of SHetA2-induced apoptosis requires modulation of additional proteins critical for regulation of apoptosis, including cellular FLICE-inhibitory protein (c-FLIP), survivin, X-linked inhibitor of apoptosis, Bcl-2, Bcl-X(L), Bax, and Bim. Western blot analysis showed that c-FLIP and survivin were substantially reduced in all of the tested cell lines exposed to SHetA2 compared with other proteins that were reduced only in a subset of the cell lines tested. Strikingly, overexpression of c-FLIP, but not survivin, protected cells from SHetA2-induced apoptosis and enhancement of TRAIL-initiated apoptosis, although knockdown of endogenous survivin did slightly sensitize cells to SHetA2-induced apoptosis. Consistent with these results, small interfering RNA-mediated reduction of c-FLIP was more effective than survivin down-regulation in triggering apoptosis in these cell lines. SHetA2 increased ubiquitination of c-FLIP and the consequent degradation was abrogated by the proteasome inhibitor MG132. Although SHetA2 treatment led to increased c-Jun phosphorylation, the JNK inhibitor SP600125 did not prevent c-FLIP down-regulation by SHetA2. Thus, it appears that SHetA2 down-regulates c-FLIP levels by facilitating its ubiquitin/proteasome-mediated degradation independent of JNK activation. Collectively, the present study indicates that, in addition to death receptor 5 up-regulation, c-FLIP down-regulation is another important component of flexible heteroarotinoid (SHetA2)-induced apoptosis as well as enhancement of TRAIL-induced apoptosis.
authors.affiliation: Department of Hematology and Medical Oncology, Winship Cancer Institute, Emory University School of Medicine, 1365-C Clifton Road Northeast, Atlanta, GA 30322, USA.
authors.forename: Yidan
authors.initials: Y
authors.lastname: Lin
authors.forename: Xiangguo
authors.initials: X
authors.lastname: Liu
authors.forename: Ping
authors.initials: P
authors.lastname: Yue
authors.forename: Doris M
authors.initials: DM
authors.lastname: Benbrook
authors.forename: K Darrell
authors.initials: KD
authors.lastname: Berlin
authors.forename: Fadlo R
authors.initials: FR
authors.lastname: Khuri
authors.forename: Shi-Yong
authors.initials: SY
authors.lastname: Sun
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000235:genetics* / Q000378:metabolism; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002839:Chromans / Q000494:pharmacology*; D015536:Down-Regulation; D020868:Gene Silencing; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000235:genetics* / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D000077022:Survivin; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D013871:Thiones / Q000494:pharmacology*
chemical_list: C476105:(((4-nitrophenyl)amino)(2,2,4,4-tetramethyl thiochroman-6-yl)amino) methane-1-thione; D000970:Antineoplastic Agents; C107489:BIRC5 protein, human; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; D002839:Chromans; D051034:Inhibitor of Apoptosis Proteins; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D034741:RNA, Small Interfering; D000077022:Survivin; D053221:TNF-Related Apoptosis-Inducing Ligand; D013871:Thiones