IL-6 triggers malignant features in mammospheres from human ductal breast carcinoma and normal mammary gland

High serum levels of the pro-inflammatory cytokine Interleukin-6 (IL-6) correlate with poor outcome in breast cancer patients. No data are available on the relationship between IL-6 gene regulation and those cells which are currently considered at the origin of breast cancer, i.e. cancer stem cells. We here report that stem/progenitor cells of the mammary gland, isolated from node invasive breast carcinoma tissues and expanded in vitro as multicellular spheroids (mammospheres, MS), express higher IL-6 mRNA levels in respect to MS isolated from the same patient normal mammary gland. Moreover, IL-6 mRNA is detectable only in basal-like breast carcinoma tumor tissues, a type of aggressive cancer endowed with stem cell features. We then show that the stem cells regulatory gene Notch-3 is a crucial mediator of IL-6 activity. Indeed, IL-6 triggers a Notch-3 dependent up-regulation of the Notch ligand Jagged-1, whose interaction with Notch-3 promotes the growth of spheroids and MS. Moreover, IL-6 induces a Notch-3 dependent up-regulation of the hypoxia survival gene carbonic anhydrase IX, which is responsible for a hypoxia-resistant/invasive phenotype in breast cancer cells and MS. Finally, we convey that the autocrine IL-6 loop in breast cancer cells requires the presence of Notch-3 gene up-regulation. In conclusion, our data support the hypothesis that IL-6 triggers malignant features in Notch-3 expressing cells, such as putative stem cells of normal and tumor mammary gland.