title: Sensitization of human K562 leukemic cells to TRAIL-induced apoptosis by inhibiting the DNA-PKcs/Akt-mediated cell survival pathway.
abstract: Despite the fact that many cancer cells are sensitive to TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, human K562 leukemic cells showed resistance to TRAIL-induced apoptosis. Interestingly, K562/R3 cells, a stable TRAIL-sensitive variant isolated from K562 cells, showed down-regulation of DNA-PK/Akt pathway and a high responsiveness to TRAIL-mediated growth inhibition and apoptosis. We revealed that siRNA-mediated suppression of DNA-PKcs led to decreased phosphorylation of Akt and Bad, a target molecule of Akt, and increased expression of DR4/DR5. Also, we found that suppression of DNA-PKcs using siRNA down-regulated c-FLIP and sensitized K562 cells to TRAIL-induced apoptosis through activation of caspase-8, -9 and -3. In addition, we revealed that treatment with DMNB, a specific inhibitor of DNA-PK, resulted in an increase of DR4/DR5 mRNA levels and their surface expression and a decrease of c-FLIP mRNA levels in K562 cells. DMNB potentiated TRAIL-induced cytotoxicity and apoptosis through inhibition of DNA-PK/Akt pathway and activation of caspase-8, -9 and -3 in K562 cells. This study is the first to show that a protective role of DNA-PK/Akt pathway against TRAIL-induced apoptosis and thus TRAIL in combination with agents that inhibit DNA-PK/Akt pathway would have clinical applicability in treating TRAIL-insensitive human leukemic cells. This model may provide a novel framework for overcoming TRAIL resistance of other cancer cells with agents that inhibit DNA-PK/Akt pathway.
authors.affiliation: Department of Biochemistry, Pusan National University School of Medicine, Yangsan, South Korea.
authors.forename: Mi-Ju
authors.initials: MJ
authors.lastname: Kim
authors.forename: Hak-Bong
authors.initials: HB
authors.lastname: Kim
authors.forename: Jae-Ho
authors.initials: JH
authors.lastname: Bae
authors.forename: Jae-Won
authors.initials: JW
authors.lastname: Lee
authors.forename: Soo-Jung
authors.initials: SJ
authors.lastname: Park
authors.forename: Dong-Wan
authors.initials: DW
authors.lastname: Kim
authors.forename: Sang-Ick
authors.initials: SI
authors.lastname: Park
authors.forename: Chi-Dug
authors.initials: CD
authors.lastname: Kang
authors.forename: Sun-Hee
authors.initials: SH
authors.lastname: Kim
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D020169:Caspases / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D020868:Gene Silencing; D006801:Humans; D020014:K562 Cells; D008297:Male; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors*; D034741:RNA, Small Interfering / Q000494:pharmacology*; D053218:Receptors, Death Domain / Q000037:antagonists & inhibitors / Q000235:genetics; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D034741:RNA, Small Interfering; D053218:Receptors, Death Domain; D053221:TNF-Related Apoptosis-Inducing Ligand; D051057:Proto-Oncogene Proteins c-akt; D020169:Caspases