title: Nuclear localization and increased levels of transcription factor YB-1 in primary human breast cancers are associated with intrinsic MDR1 gene expression.
abstract: Breast cancers are either primarily resistant to chemotherapy (intrinsic resistance), or respond to chemotherapy but later recur with a multidrug-resistant phenotype because of overexpression of the multidrug transporter P-glycoprotein. The MDR1 gene encoding P-glycoprotein may be transcriptionally regulated by a Y-box transcription factor. We now report that, in multidrug-resistant MCF-7 breast cancer cells, nuclear localization of YB-1 is associated with MDR-1 gene expression. In drug-sensitive MCF-7 cells, however, YB-1 was localized to the cytoplasm. Regulated overexpression of YB-1 in drug-sensitive diploid breast epithelial cells induced MDR-1 gene expression and multidrug resistance. In 27 out of 27 untreated primary breast cancers, YB-1 protein was expressed in the cytoplasm although it was undetectable in normal breast tissue of these patients. In a subgroup of tumors (9/27), however, YB-1 was also localized to the nucleus and, in these cases, high levels of P-glycoprotein were present. These results show that in a subset of untreated primary breast cancers, nuclear localization of YB-1 protein is associated with intrinsic multidrug resistance. Our data show that YB-1 has an important role in controlling MDR1 gene transcription and this finding provides a basis for the analysis of molecular mechanisms responsible for intrinsic multidrug resistance in human breast cancer.
authors.affiliation: Humboldt Universität zu Berlin, Universitätsklinikum Rudolf Virchow, Robert-Rössle Klinik, Germany.
authors.forename: R C
authors.initials: RC
authors.lastname: Bargou
authors.forename: K
authors.initials: K
authors.lastname: Jürchott
authors.forename: C
authors.initials: C
authors.lastname: Wagener
authors.forename: S
authors.initials: S
authors.lastname: Bergmann
authors.forename: S
authors.initials: S
authors.lastname: Metzner
authors.forename: K
authors.initials: K
authors.lastname: Bommert
authors.forename: M Y
authors.initials: MY
authors.lastname: Mapara
authors.forename: K J
authors.initials: KJ
authors.lastname: Winzer
authors.forename: M
authors.initials: M
authors.lastname: Dietel
authors.forename: B
authors.initials: B
authors.lastname: Dörken
authors.forename: H D
authors.initials: HD
authors.lastname: Royer
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D022762:CCAAT-Enhancer-Binding Proteins; D002451:Cell Compartmentation; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D018432:Drug Resistance, Multiple / Q000235:genetics*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008875:Middle Aged; D051839:NFI Transcription Factors; D009687:Nuclear Proteins; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D051840:Y-Box-Binding Protein 1
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D051839:NFI Transcription Factors; D009687:Nuclear Proteins; D014157:Transcription Factors; D051840:Y-Box-Binding Protein 1; C070856:YBX1 protein, human