title: Dynamic regulation of CD24 and the invasive, CD44posCD24neg phenotype in breast cancer cell lines.
abstract: BACKGROUND
  The invasive, mesenchymal phenotype of CD44posCD24neg breast cancer cells has made them a promising target for eliminating the metastatic capacity of primary tumors. It has been previously demonstrated that CD44neg/lowCD24pos breast cancer cells lack the ability to give rise to their invasive CD44posCD24neg counterpart. Here we demonstrate that noninvasive, epithelial-like CD44posCD24pos cells readily give rise to invasive, mesenchymal CD44posCD24neg progeny in vivo and in vitro. This interconversion was found to be dependent upon Activin/Nodal signaling.
  
  
  METHODS
  Breast cancer cell lines were sorted into CD44posCD24pos and CD44posCD24neg populations to evaluate their progeny for the expression of CD44, CD24, and markers of a mesenchymal phenotype. The populations, separated by fluorescence activated cell sorting (FACS) were injected into immunocompromised mice to evaluate their tumorigenicity and invasiveness of the resulting xenografts.
  
  
  RESULTS
  CD24 expression was dynamically regulated in vitro in all evaluated breast cancer cell lines. Furthermore, a single noninvasive, epithelial-like CD44posCD24pos cell had the ability to give rise to invasive, mesenchymal CD44posCD24neg progeny. Importantly, this interconversion occurred in vivo as CD44posCD24pos cells gave rise to xenografts with locally invasive borders as seen in xenografts initiated with CD44posCD24neg cells. Lastly, the ability of CD44posCD24pos cells to give rise to mesenchymal progeny, and vice versa, was blocked upon ablation of Activin/Nodal signaling.
  
  
  CONCLUSIONS
  Our data demonstrate that the invasive, mesenchymal CD44posCD24neg phenotype is under dynamic control in breast cancer cell lines both in vitro and in vivo. Furthermore, our observations suggest that therapies targeting CD44posCD24neg tumor cells may have limited success in preventing primary tumor metastasis unless Activin/Nodal signaling is arrested.
authors.affiliation: Mammary Biology and Tumorigenesis Laboratory, Center for Cancer Research, National Cancer Institute, National Institutes of Health, 37 Convent Drive, Building 37, Room 1106, Bethesda, Maryland 20892-4254, USA. meyerm@mail.nih.gov
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Meyer
authors.forename: Jodie M
authors.initials: JM
authors.lastname: Fleming
authors.forename: Mustapha A
authors.initials: MA
authors.lastname: Ali
authors.forename: Mitchell W
authors.initials: MW
authors.lastname: Pesesky
authors.forename: Erika
authors.initials: E
authors.lastname: Ginsburg
authors.forename: Barbara K
authors.initials: BK
authors.lastname: Vonderhaar
mesh_terms: D028341:Activins / Q000378:metabolism; D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051927:CD24 Antigen / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D018960:Hyaluronan Receptors / Q000096:biosynthesis* / Q000378:metabolism; D008648:Mesoderm / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D009361:Neoplasm Invasiveness; D055457:Nodal Protein / Q000378:metabolism; D034741:RNA, Small Interfering / Q000008:administration & dosage / Q000235:genetics; D015398:Signal Transduction; D014183:Transplantation, Heterologous
chemical_list: D051927:CD24 Antigen; C497889:CD24 protein, human; C497483:CD44 protein, human; D018960:Hyaluronan Receptors; C526007:NODAL protein, human; D055457:Nodal Protein; D034741:RNA, Small Interfering; D028341:Activins