title: ABCG2, a novel antigen to sort luminal progenitors of BRCA1- breast cancer cells.
abstract: BACKGROUND
  Tumor-initiating cells (TICs), aka "cancer stem cells", are believed to fuel tumors and to sustain therapy resistance and systemic metastasis. Breast cancer is the first human carcinoma in which a subpopulation of cells displaying a specific CD44+/CD24-/low/ESA+ antigenic phenotype was found to have TIC properties. However, CD44+/CD24-/low/ESA+ is not a universal marker phenotype of TICs in all breast cancer subtypes. The aim of this study was to identify novel antigens with which to isolate the TIC population of the basal-A/basal-like breast cancer cell lines.
  
  
  METHODS
  We used polychromatic flow-cytometry to characterize the cell surface of several breast cancer cell lines that may represent different tumor molecular subtypes. We next used fluorescence-activated cell sorting to isolate the cell subpopulations of interest from the cell lines. Finally, we explored the stem-like and tumorigenic properties of the sorted cell subpopulations using complementary in vitro and in vivo approaches: mammosphere formation assays, soft-agar colony assays, and tumorigenic assays in NOD/SCID mice.
  
  
  RESULTS
  The CD44+/CD24+ subpopulation of the BRCA1-mutated basal-A/basal-like cell line HCC1937 is enriched in several stemness markers, including the ABCG2 transporter (i.e., the CD338 antigen). Consistently, CD338-expressing cells were also enriched in CD24 expression, suggesting that coexpression of these two antigenic markers may segregate TICs in this cell line. In support of ABCG2 expression in TICs, culturing of HCC1937 cells in ultra-low adherent conditions to enrich them in precursor/stem-cells resulted in an increase in CD338-expressing cells. Furthermore, CD338-expressing cells, unlike their CD338-negative counterparts, displayed stemness and transformation potential, as assessed in mammosphere and colony formation assays. Lastly, CD338-expressing cells cultured in ultra-low adherent conditions maintained the expression of CD326/EpCAM and CD49f/α6-integrin, which is a combination of antigens previously assigned to luminal progenitors.
  
  
  CONCLUSIONS
  Collectively, our data suggest that CD338 expression is specific to the tumor-initiating luminal progenitor subpopulation of BRCA1-mutated cells and is a novel antigen with which to sort this subpopulation.
authors.affiliation: CEINGE-Biotecnologie Avanzate, via Gaetano Salvatore 486, 80145 Naples, Italy. felicia.leccia@univ-bpclermont.fr.
authors.forename: Felicia
authors.initials: F
authors.lastname: Leccia
authors.forename: Luigi
authors.initials: L
authors.lastname: Del Vecchio
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Mariotti
authors.forename: Rosa
authors.initials: R
authors.lastname: Di Noto
authors.forename: Anne-Pierre
authors.initials: AP
authors.lastname: Morel
authors.forename: Alain
authors.initials: A
authors.lastname: Puisieux
authors.forename: Francesco
authors.initials: F
authors.lastname: Salvatore
authors.forename: Stéphane
authors.initials: S
authors.lastname: Ansieau
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000818:Animals; D019313:BRCA1 Protein / Q000378:metabolism*; D001943:Breast Neoplasms / Q000473:pathology*; D051927:CD24 Antigen / Q000378:metabolism; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000378:metabolism / Q000473:pathology; D005260:Female; D005434:Flow Cytometry; D055785:Gene Knockdown Techniques; D006801:Humans; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D009363:Neoplasm Proteins / Q000378:metabolism*; D014411:Neoplastic Stem Cells / Q000473:pathology*; D018874:Spheroids, Cellular / Q000473:pathology
chemical_list: C116614:ABCG2 protein, human; D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D019313:BRCA1 Protein; D051927:CD24 Antigen; D009363:Neoplasm Proteins