title: Production of P-glycoprotein from the MDR1 upstream promoter is insufficient to affect the response to first-line chemotherapy in advanced breast cancer.
abstract: Multidrug resistance, the phenomenon by which cells treated with a drug become resistant to the cytotoxic effect of a variety of other structurally and functionally unrelated drugs, is often associated with the expression of P-glycoprotein, an efflux membrane pump coded by the MDR1 (ABCB1) gene. Transcription from MDR1 can start at 2 promoters: a well-characterized downstream promoter and an as yet uncharacterized upstream promoter (USP). We have previously determined that the USP is activated in some drug-resistant cell lines, in primary breast tumors and in metastatic epithelial cells isolated from the lymph nodes of breast cancer patients. In this study, we report the cloning and characterization of the MDR1 USP and studied its association with chemotherapy response in breast cancer patients. Deletion analysis indicated that a nearby endogenous retroviral long terminal repeat is not responsible for promoter activation, and that the region within the first 400 nucleotides upstream from the transcription start point contained all the elements necessary for promoter activity in drug-resistant cells. We identified an element recognized by the transcription factor NF-IL6 (activated upon interleukin-6 exposure) which is necessary for promoter activity in drug-resistant cells and plays a role in the activation of the promoter in response to interleukin-6 in breast cancer MCF-7 cells. Although transcripts from this promoter are associated with translating polyribosomes, their low abundance makes the amount of synthesized P-glycoprotein insufficient to affect the response to first-line chemotherapy in patients with advanced breast cancer.
authors.affiliation: Medical Research Council Clinical Sciences Centre, Imperial College Faculty of Medicine, Hammersmith Hospital Campus, London, United Kingdom.
authors.forename: Selina
authors.initials: S
authors.lastname: Raguz
authors.forename: Rebecca A
authors.initials: RA
authors.lastname: Randle
authors.forename: Eva R
authors.initials: ER
authors.lastname: Sharpe
authors.forename: John A
authors.initials: JA
authors.lastname: Foekens
authors.forename: Anieta M
authors.initials: AM
authors.lastname: Sieuwerts
authors.forename: Marion E
authors.initials: ME
authors.lastname: Meijer-van Gelder
authors.forename: Junia V
authors.initials: JV
authors.lastname: Melo
authors.forename: Christopher F
authors.initials: CF
authors.lastname: Higgins
authors.forename: Ernesto
authors.initials: E
authors.lastname: Yagüe
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D000328:Adult; D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics*; D003001:Cloning, Molecular; D018432:Drug Resistance, Multiple / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D005260:Female; D019450:Genes, MDR; D006801:Humans; D008875:Middle Aged; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D012333:RNA, Messenger