c-Kit is required for growth and survival of the cells of origin of Brca1-mutation-associated breast cancer

摘要

BRCA1 mutation-associated breast cancer originates in oestrogen receptor-alpha-negative (ER~(鈭?/sup>) 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~(鈭?/sup> 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~(鈭?/sup> progenitors are c-Kit~(+), but also that most stem cells and the differentiated cell populations are c-Kit~(鈭?/sup>. 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~(鈭?/sup> 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.