title: Induction of human MDR1 gene expression by 2-acetylaminofluorene is mediated by effectors of the phosphoinositide 3-kinase pathway that activate NF-kappaB signaling.
abstract: The expression of P-glycoprotein encoded by the multidrug resistance (MDR1) gene is associated with the emergence of the MDR phenotype in cancer cells. Human MDR1 and its rodent homolog mdr1a and mdr1b are frequently overexpressed in liver cancers. However, the underlying mechanisms are largely unknown. The hepatocarcinogen 2-acetylaminofluorene (2-AAF) efficiently activates rat mdr1b expression in cultured cells and in Fisher 344 rats. We recently reported that activation of rat mdr1b in cultured cells by 2-AAF involves a cis-activating element containing a NF-kappaB binding site located -167 to -158 of the rat mdr1b promoter. 2-AAF activates IkappaB kinase (IKK), resulting in degradation of IkappaBbeta and activation of NF-kappaB. In this study, we report that 2-AAF could also activate the human MDR1 gene in human hepatoma and embryonic fibroblast 293 cells. Induction of MDR1 by AAF was mediated by DNA sequence located at -6092 which contains a NF-kappaB binding site. Treating hepatoma cells with 2-AAF activated phosphoinositide 3-kinase (PI3K) and its downstream effectors Rac1, and NAD(P)H oxidase. Transient transfection assays demonstrated that constitutively activated PI3K and Rac1 enhanced the activation of the MDR1 promoter by 2-AAF. Treatment of hepatoma cells with 2-AAF also activated another PI3K downstream effector Akt. Transfection of recombinant encoding a dominant activated Akt also enhanced the activation of MDR1 promoter activation by 2-AAF. These results demonstrated that 2-AAF up-regulates MDR1 expression is mediated by the multiple effectors of the PI3K signaling pathway.
authors.affiliation: Department of Molecular Pathology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, TX 77030, USA. tkuo@mail.mdanderson.org
authors.forename: Macus Tien
authors.initials: MT
authors.lastname: Kuo
authors.forename: Zesheng
authors.initials: Z
authors.lastname: Liu
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Wei
authors.forename: Yen-chiu
authors.initials: YC
authors.lastname: Lin-Lee
authors.forename: Shigeru
authors.initials: S
authors.lastname: Tatebe
authors.forename: Gordon B
authors.initials: GB
authors.lastname: Mills
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Unate
mesh_terms: D015073:2-Acetylaminofluorene / Q000494:pharmacology*; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D000099:Acetoxyacetylaminofluorene / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular / Q000201:enzymology / Q000235:genetics; D002460:Cell Line; D018432:Drug Resistance, Multiple; D024202:Electrophoretic Mobility Shift Assay; D004789:Enzyme Activation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D051550:I-kappa B Kinase; D019255:NADPH Oxidases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013481:Superoxides / Q000378:metabolism; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects; D020744:rac GTP-Binding Proteins / Q000378:metabolism
chemical_list: D015073:2-Acetylaminofluorene; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000099:Acetoxyacetylaminofluorene; D051550:I-kappa B Kinase; D019255:NADPH Oxidases; D016328:NF-kappa B; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D013481:Superoxides; D020744:rac GTP-Binding Proteins; C494918:AKT1 protein, human; C496559:CHUK protein, human; C496560:IKBKB protein, human; C496565:IKBKE protein, human