title: Mithramycin A sensitizes cancer cells to TRAIL-mediated apoptosis by down-regulation of XIAP gene promoter through Sp1 sites.
abstract: Mithramycin A is a DNA-binding antitumor agent, which has been clinically used in the therapies of several types of cancer and Paget's disease. In this study, we investigated the combined effect of mithramycin A and tumor necrosis factor-alpha-related apoptosis-inducing ligand (TRAIL) on apoptosis of cancer cells. In Caki renal cancer cells, which are resistant to TRAIL, cotreatment with subtoxic doses of mithramycin A and TRAIL resulted in a marked increase in apoptosis. This combined treatment was also cytotoxic to Caki cells overexpressing Bcl-2 but not to normal mesengial cells. Moreover, apoptosis by the combined treatment with mithramycin A and TRAIL was dramatically induced in various cancer cell types, thus offering an attractive strategy for safely treating malignant tumors. Mithramycin A-stimulated TRAIL-induced apoptosis was blocked by pretreatment with the broad caspase inhibitor zVAD-fmk or Crm-A overexpression, showing its dependence on caspases. We found that mithramycin A selectively down-regulated XIAP protein levels in various cancer cells. Luciferase reporter assay and the chromatin immunoprecipitation assay using the XIAP promoter constructs show that mithramycin A down-regulates the transcription of XIAP gene through inhibition of Sp1 binding to its promoter. Although XIAP overexpression significantly attenuated apoptosis induced by mithramycin A plus TRAIL, suppression of XIAP expression by transfection with its small interfering RNA prominently enhanced TRAIL-induced apoptosis. We present here for the first time that mithramycin A-induced suppression of XIAP transcription plays a critical role in the recovery of TRAIL sensitivity in various cancer cells.
authors.affiliation: Department of Immunology, School of Medicine, Keimyung University, 194 DongSan-Dong Jung-Gu, Taegu 700-712, South Korea.
authors.forename: Tae-Jin
authors.initials: TJ
authors.lastname: Lee
authors.forename: Eun Mi
authors.initials: EM
authors.lastname: Jung
authors.forename: Jung Tae
authors.initials: JT
authors.lastname: Lee
authors.forename: Shin
authors.initials: S
authors.lastname: Kim
authors.forename: Jong-Wook
authors.initials: JW
authors.lastname: Park
authors.forename: Kyeong Sook
authors.initials: KS
authors.lastname: Choi
authors.forename: Taeg Kyu
authors.initials: TK
authors.lastname: Kwon
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001665:Binding Sites; D001943:Breast Neoplasms / Q000378:metabolism; D002292:Carcinoma, Renal Cell / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D003110:Colonic Neoplasms / Q000378:metabolism; D015536:Down-Regulation; D005260:Female; D019073:HT29 Cells; D006801:Humans; D008297:Male; D008926:Plicamycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000187:drug effects*; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000235:genetics* / Q000378:metabolism
chemical_list: D016329:Sp1 Transcription Factor; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D051636:X-Linked Inhibitor of Apoptosis Protein; C066851:mithramycin A; D020169:Caspases; D008926:Plicamycin