title: CCAAT/enhancer-binding protein beta (nuclear factor for interleukin 6) transactivates the human MDR1 gene by interaction with an inverted CCAAT box in human cancer cells.
abstract: We investigated the mechanisms of MDR1 gene activation by CCAAT/enhancer binding protein beta (C/EBPbeta, or nuclear factor for interleukin 6) in human cancer cells. Transfection of the breast cancer cell line MCF-7 and its doxorubicin-selected variant MCF-7/ADR by either C/EBPbeta or C/EBPbeta-LIP (a dominant-negative form of C/EBPbeta) confirmed their roles in the activation or repression of the endogenous, chromosomally embedded MDR1 gene. Cotransfection experiments with promoter constructs revealed a C/EBPbeta interaction on the MDR1 promoter via the region within -128 to -75. Deletions within the putative AP-1 box (-123 to -111) increased MDR1 promoter activity when stimulated by C/EBPbeta, suggesting that the AP-1 site negatively regulates MDR1 activation by C/EBPbeta. Mutations within the inverted CCAAT box (Y box) (-82 to -73) abolished the C/EBPbeta-stimulated MDR1 promoter activity, indicating that the Y box is required for MDR1 activation by C/EBPbeta. Chromatin immunoprecipitation (ChIP) revealed that C/EBPbeta precipitates a transcription complex containing C/EBPbeta, the MDR1 promoter sequences (-250 to +54), and the hBrm protein. In conclusion, alteration of expression or function of C/EBPbeta plays an important role in MDR1 gene regulation. C/EBPbeta activates the endogenous MDR1 gene of MCF-7 cells, and this activation was associated with a novel C/EBPbeta interaction region within the proximal MDR1 promoter (-128 to -75). The mechanisms of MDR1 activation by C/EBPbeta include C/EBPbeta binding of the chromatin of the MDR1 gene and interactions of C/EBPbeta with the Y box and Y box-associated proteins.
authors.affiliation: Program in Cancer Biology, Division of Oncology, Stanford University Medical Center, Stanford, CA 94305-5151, USA.
authors.forename: Kevin G
authors.initials: KG
authors.lastname: Chen
authors.forename: Sanja
authors.initials: S
authors.lastname: Sale
authors.forename: Thomas
authors.initials: T
authors.lastname: Tan
authors.forename: Ralph P
authors.initials: RP
authors.lastname: Ermoian
authors.forename: Branimir I
authors.initials: BI
authors.lastname: Sikic
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism / Q000502:physiology*; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology; D020868:Gene Silencing; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D009154:Mutation; D051839:NFI Transcription Factors; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic / Q000502:physiology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000502:physiology; D014157:Transcription Factors; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D051840:Y-Box-Binding Protein 1
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; D015850:Interleukin-6; D051839:NFI Transcription Factors; D009687:Nuclear Proteins; D016760:Proto-Oncogene Proteins c-fos; D016329:Sp1 Transcription Factor; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D051840:Y-Box-Binding Protein 1; C070856:YBX1 protein, human