title: YB-1 regulates Sox2 to coordinately sustain stemness and tumorigenic properties in a phenotypically distinct subset of breast cancer cells.
abstract: BACKGROUND
  Sox2, a transcription factor and an embryonic stem cell marker, has been implicated in the pathogenesis of breast cancer (BC). YB-1 is another transcription factor that has been shown to promote stemness in BC cells.
  
  
  METHODS
  Western blotting, quantitative PCR, and siRNAs were used to query the regulatory relationships between YB-1, Sox2, and their downstream targets. Chromatin immunoprecipitation was used to detect YB-1 interactions at the Sox2 promoter. Mammosphere and soft agar assays were used to assess the phenotypic consequences of YB-1 knockdown.
  
  
  RESULTS
  Here, we report that YB-1 regulates Sox2. YB-1 was found to bind to the SOX2 promoter and down-regulate its expression in MCF7 and ZR751. The regulatory interaction between YB-1 and Sox2 was drastically different between the two phenotypically distinct cell subsets, purified based on their differential response to a Sox2 reporter. They are referred to as the reporter unresponsive (RU) cells and the reporter responsive (RR) cells. Upon siRNA knockdown of YB-1, RU cells showed an increase in Sox2 expression but no change in Sox2 reporter activity; in contrast, RR cells exhibited increased expression and reporter activity of Sox2. Correlating with these findings, YB-1 knockdown induced a differential response in the expression of genes known to be regulated by both Sox2 and YB-1 (e.g. CCND1 and ITGA6). For instance, in response to YB-1 knockdown, CCND1 and ITGA6 expression were decreased or unchanged in RU cells but paradoxically increased in RR cells. Compared to RU cells, RR cells were significantly more resistant to the suppression of mammosphere formation due to YB-1 knockdown. Importantly, mammospheres derived from parental MCF7 cells treated with YB-1 siRNA knockdown exhibited higher expression levels of SOX2 and its downstream targets.
  
  
  CONCLUSIONS
  To conclude, in a subset of BC cells, namely RR cells, YB-1 regulates Sox2 to coordinately maintain stemness and tumorigenic properties.
authors.forename: Karen
authors.initials: K
authors.lastname: Jung
authors.forename: Fang
authors.initials: F
authors.lastname: Wu
authors.forename: Peng
authors.initials: P
authors.lastname: Wang
authors.forename: Xiaoxia
authors.initials: X
authors.lastname: Ye
authors.forename: Bassam S
authors.initials: BS
authors.lastname: Abdulkarim
authors.affiliation: Departments of Oncology, Edmonton, AB, Canada. rlai@ualberta.ca.
authors.forename: Raymond
authors.initials: R
authors.lastname: Lai
mesh_terms: D001665:Binding Sites; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D017930:Genes, Reporter; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D039503:Integrin alpha6 / Q000235:genetics / Q000378:metabolism; D061986:MCF-7 Cells; D000071317:Nanog Homeobox Protein; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000473:pathology; D010641:Phenotype; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D055748:SOXB1 Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D051840:Y-Box-Binding Protein 1 / Q000235:genetics / Q000378:metabolism*
chemical_list: C530104:CCND1 protein, human; D018398:Homeodomain Proteins; C588002:ITGA6 protein, human; D039503:Integrin alpha6; C486780:NANOG protein, human; D000071317:Nanog Homeobox Protein; C527782:SOX2 protein, human; D055748:SOXB1 Transcription Factors; D051840:Y-Box-Binding Protein 1; C070856:YBX1 protein, human; D019938:Cyclin D1