title: TRAIL sensitize MDR cells to MDR-related drugs by down-regulation of P-glycoprotein through inhibition of DNA-PKcs/Akt/GSK-3beta pathway and activation of caspases.
abstract: BACKGROUND
  The development of new modulator possessing high efficacy, low toxicity and high selectivity is a pivotal approach to overcome P-glycoprotein (P-gp) mediated multidrug resistance (MDR) in cancer treatment. In this study, we suggest a new molecular mechanism that TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) down-regulates P-glycoprotein (P-gp) through inhibition of DNA-PKcs/Akt/GSK-3beta pathway and activation of caspases and thereby sensitize MDR cells to MDR-related drugs.
  
  
  RESULTS
  MDR variants, CEM/VLB10-2, CEM/VLB55-8 and CEM/VLB100 cells, with gradually increased levels of P-gp derived from human lymphoblastic leukemia CEM cells, were gradually more susceptible to TRAIL-induced apoptosis and cytotoxicity than parental CEM cells. The P-gp level of MDR variants was positively correlated with the levels of DNA-PKcs, pAkt, pGSK-3beta and c-Myc as well as DR5 and negatively correlated with the level of c-FLIPs. Hypersensitivity of CEM/VLB100 cells to TRAIL was accompanied by the activation of mitochondrial apoptotic pathway as well as the activation of initiator caspases. In addition, TRAIL-induced down-regulation of DNA-PKcs/Akt/GSK-3beta pathway and c-FLIP and up-regulation of cell surface expression of death receptors were associated with the increased susceptibility to TRAIL of MDR cells. Moreover, TRAIL inhibited P-gp efflux function via caspase-3-dependent degradation of P-gp as well as DNA-PKcs and subsequently sensitized MDR cells to MDR-related drugs such as vinblastine and doxorubicin. We also found that suppression of DNA-PKcs by siRNA enhanced the susceptibility of MDR cells to vincristine as well as TRAIL via down-regulation of c-FLIP and P-gp expression and up-regulation of DR5.
  
  
  CONCLUSIONS
  This study showed for the first time that the MDR variant of CEM cells was hypersensitive to TRAIL due to up-regulation of DR5 and concomitant down-regulation of c-FLIP, and degradation of P-gp and DNA-PKcs by activation of caspase-3 might be important determinants of TRAIL-induced sensitization of MDR cells to MDR-related drugs. Therefore, combination of TRAIL and chemotherapeutic drugs may be a good strategy for treatment of cancer with multidrug resistance.
authors.affiliation: Department of Biochemistry, Pusan National University School of Medicine, Yangsan, South Korea.
authors.forename: Suk-Bin
authors.initials: SB
authors.lastname: Seo
authors.forename: Jung-Gu
authors.initials: JG
authors.lastname: Hur
authors.forename: Mi-Ju
authors.initials: MJ
authors.lastname: Kim
authors.forename: Jae-Won
authors.initials: JW
authors.lastname: Lee
authors.forename: Hak-Bong
authors.initials: HB
authors.lastname: Kim
authors.forename: Jae-Ho
authors.initials: JH
authors.lastname: Bae
authors.forename: Dong-Wan
authors.initials: DW
authors.lastname: Kim
authors.forename: Chi-Dug
authors.initials: CD
authors.lastname: Kang
authors.forename: Sun-Hee
authors.initials: SH
authors.lastname: Kim
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000502:physiology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D020169:Caspases