title: c-Kit is required for growth and survival of the cells of origin of Brca1-mutation-associated breast cancer.
abstract: BRCA1 mutation-associated breast cancer originates in oestrogen receptor-alpha-negative (ER(-)) progenitors in the mammary luminal epithelium. These cells also express high levels of the Kit gene and a recent study demonstrated a correlation between Brca1 loss and Kit over-expression in the mammary epithelium. However, the functional significance of c-Kit expression in the mammary gland is unknown. To address this, c-Kit(-) and c-Kit(+) mammary epithelial subsets were isolated by flow cytometry, characterised for expression of lineage-specific cell markers and functionally analysed by in vitro colony forming and in vivo transplantation assays. The results confirm that the majority of luminal ER(-) progenitors are c-Kit(+), but also that most stem cells and the differentiated cell populations are c-Kit(-). A subset of c-Kit(+) cells with high proliferative potential was found in the luminal ER(+) population, however, suggesting the existence of a distinct luminal ER(+) progenitor cell type. Analysis of mouse Brca1 mammary tumours demonstrated that they expressed Kit and its downstream effector Lyn at levels comparable to the most strongly c-Kit(+) luminal ER(-) progenitors. Consistent with c-Kit being a progenitor cell marker, in vitro three-dimensional differentiation of c-Kit(+) cells resulted in a loss of c-Kit expression, whereas c-Kit over-expression prevented normal differentiation in vivo. Furthermore, c-Kit was a functional marker of proliferative potential, as c-Kit inhibition by short hairpin knockdown prevented normal epithelial growth and caused cells to undergo apoptosis. Therefore, c-Kit defines distinct progenitor populations in the mammary epithelium and is critical for mammary progenitor survival and proliferation. Importantly, c-Kit is only the second mammary epithelial stem/progenitor marker to be shown to have a functional role in the mammary epithelium and the first marker to be shown to be required for progenitor cell function. The c-Kit signalling network has potential as a target for therapy and/or prevention in BRCA1-associated breast cancer.
authors.affiliation: Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK.
authors.forename: J L
authors.initials: JL
authors.lastname: Regan
authors.forename: H
authors.initials: H
authors.lastname: Kendrick
authors.forename: F-A
authors.initials: FA
authors.lastname: Magnay
authors.forename: V
authors.initials: V
authors.lastname: Vafaizadeh
authors.forename: B
authors.initials: B
authors.lastname: Groner
authors.forename: M J
authors.initials: MJ
authors.lastname: Smalley
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000235:genetics; D019313:BRCA1 Protein / Q000235:genetics* / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002454:Cell Differentiation / Q000235:genetics; D049109:Cell Proliferation; D002470:Cell Survival / Q000235:genetics; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism; D005260:Female; D020869:Gene Expression Profiling; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008321:Mammary Glands, Animal / Q000166:cytology / Q000378:metabolism; D008325:Mammary Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D019009:Proto-Oncogene Proteins c-kit / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000235:genetics; D013234:Stem Cells / Q000378:metabolism
chemical_list: D019313:BRCA1 Protein; D047628:Estrogen Receptor alpha; D019009:Proto-Oncogene Proteins c-kit