A Novel Role for the Extracellular Matrix in Regulation of Hepcidin in Breast Cancer Spheroids

Iron is an essential nutrient for breast cancer cell growth and proliferation. Our laboratory has demonstrated that ferroportin (Fpn), an iron efflux pump, plays a critical role in maintenance of intracellular iron levels. Fpn is controlled by hepcidin, a secreted peptide hormone that binds to Fpn and triggers its degradation. We have observed that Fpn expression is down‐regulated and hepcidin expression is up‐regulated in breast cancer cells, promoting increased accumulation of iron in cancer cells to fuel their proliferative demands. Since expression of Fpn/hepcidin predicts outcome in breast cancer patients, we explored pathways that control these proteins. We used a 3D spheroid culture system to model in vivo breast tumor architecture, microenvironment and metabolism. We found that hepcidin expression is significantly up‐regulated from 2D to 3D culture of MCF‐7 and patient‐derived breast cancer cells, suggesting that hepcidin may be regulated by processes that exceed the realm of 2D culture. Culturing MCF‐7 cells as spheroids in the presence of Matrigel repressed the induction of hepcidin, suggesting that exogenous extracellular matrix (ECM) proteins present in Matrigel may negatively regulate hepcidin. Further analysis of the effect of exogenous ECM on hepcidin expression revealed that collagen IV, one of the most abundant basement membrane (BM) proteins in Matrigel, negatively regulates hepcidin expression in MCF‐7 spheroids. On the other hand, endogenous production of ECM components, such as collagen I and collagen II, matrix components frequently up‐regulated in breast cancer, was increased in MCF‐7 spheroids compared to monolayer culture. It is known that there is a modified microenvironement during breast tumorigenesis that includes breakdown of the structural BM proteins and deregulation of matrix components, including those that support tumor progression and promote metastatic spread. Together, our data suggest that components of the ECM play a dynamic role in both positive and negative regulation of hepcidin expression in breast cancer spheroids. This finding suggests that the ECM is an integral component in regulation of hepcidin within the tumor microenvironment. Understanding mechanisms of hepcidin regulation by ECM components will provide a greater understanding of the crosstalk between the ECM and iron metabolism in breast cancer. Support or Funding Information This research is supported by NIH R01 CA171101 and NIH R01 CA188025.