title: Ku70 acetylation and modulation of c-Myc/ATF4/CHOP signaling axis by SIRT1 inhibition lead to sensitization of HepG2 cells to TRAIL through induction of DR5 and down-regulation of c-FLIP.
abstract: In this study, we investigated the role of c-Myc/ATF4/CHOP signaling pathway in sensitization of human hepatoma HepG2 cells to TRAIL. Knockdown of SIRT1 or treatment with SIRT1 inhibitor caused the up-regulation of DR5 and down-regulation of c-FLIP through modulation of c-Myc/ATF4/CHOP pathway, and subsequently enhanced the cytotoxic and apoptotic effects of TRAIL on HepG2 cells. Interestingly, SIRT1 interacted directly with c-FLIP(L) and Ku70, and treatment with SIRT1 inhibitor enhanced acetylation of Ku70 and subsequently decreased its binding to c-FLIP. And this was followed by degradation of c-FLIP. Moreover, Ku70(-/-) MEF and Ku70-knockdown HepG2 cells showed the increased levels of c-Myc, ATF4, CHOP, and DR5 and decreased level of c-FLIP. These results were followed by increased sensitivity of Ku70(-/-) MEF cells and Ku70-knockdown HepG2 cells to TRAIL compared with their control cells. These findings reveal for the first time that SIRT1 inhibition increases Ku70 acetylation, and the acetylated Ku70 with a decreased function mediates the induction of DR5 and the down-regulation of c-FLIP by up-regulating c-Myc/ATF4/CHOP pathway, and consequently promotes the TRAIL-induced apoptosis of HepG2 cells. This study provides important mechanistic insight of the synergism exhibited by SIRT1 inhibition and TRAIL.
authors.affiliation: Department of Biochemistry and Medical Research Institute, Pusan National University School of Medicine, Yangsan 626-870, Republic of Korea.
authors.forename: Mi-Ju
authors.initials: MJ
authors.lastname: Kim
authors.forename: Kyung-Soo
authors.initials: KS
authors.lastname: Hong
authors.forename: Hak-Bong
authors.initials: HB
authors.lastname: Kim
authors.forename: Su-Hoon
authors.initials: SH
authors.lastname: Lee
authors.forename: Jae-Ho
authors.initials: JH
authors.lastname: Bae
authors.forename: Dong-Wan
authors.initials: DW
authors.lastname: Kim
authors.forename: Trong Tuan
authors.initials: TT
authors.lastname: Dao
authors.forename: Won Keun
authors.initials: WK
authors.lastname: Oh
authors.forename: Chi-Dug
authors.initials: CD
authors.lastname: Kang
authors.forename: Sun-Hee
authors.initials: SH
authors.lastname: Kim
mesh_terms: D000107:Acetylation; D051701:Activating Transcription Factor 4 / Q000378:metabolism; D000818:Animals; D034961:Antigens, Nuclear / Q000378:metabolism*; D017209:Apoptosis / Q000235:genetics*; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000378:metabolism*; D049109:Cell Proliferation; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015536:Down-Regulation; D056945:Hep G2 Cells; D006801:Humans; D000072200:Ku Autoantigen; D051379:Mice; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D015398:Signal Transduction; D056564:Sirtuin 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D051742:Transcription Factor CHOP / Q000378:metabolism
chemical_list: C497109:ATF4 protein, human; D034961:Antigens, Nuclear; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; C497249:DDIT3 protein, human; D004268:DNA-Binding Proteins; D016271:Proto-Oncogene Proteins c-myc; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053221:TNF-Related Apoptosis-Inducing Ligand; D051701:Activating Transcription Factor 4; D051742:Transcription Factor CHOP; C447939:SIRT1 protein, human; D056564:Sirtuin 1; C000606509:Xrcc6 protein, human; C000606510:Xrcc6 protein, mouse; D000072200:Ku Autoantigen