Laminin - myCAF interplay promotes α6-integrin-mediated breast cancer cell invasion.

It is well established that the tumor microenvironment (TME) plays a dynamic role in breast cancer progression. Stromal components of the TME, including fibroblasts and the extracellular matrix (ECM), provide biophysical and biochemical cues to drive tumor cell proliferation and invasion. However, how the interplay between activated fibroblast (CAF) subtypes and ECM composition impinges on breast cancer cell behavior is still not well understood. To address this gap, we leveraged microfluidic technologies to engineer a model of the breast TME that incorporates tumor cells, CAFs, and ECM components. Our model consists of a tubular duct filled with MDA-MB-231 or MCF-7 cells surrounded by a 3D collagen type I matrix with or without two human fibroblasts/CAFs. To further investigate how ECM composition affects the stromal compartment, we altered the matrix to include laminin-111 (LN) and thrombospondin-1 (TSP-1), which we previously found to be dysregulated in invasive ductal carcinoma compared to normal breast tissue. By incorporating LN or TSP-1 into the collagen matrix, we identified significant differences in collagen fiber metrics (fiber length, density, and width), matrix stiffness, and alterations in matrix remodeling by CAFs. Specifically, remodeling was more pronounced in LN- vs. TSP-1-enriched microenvironments populated by myofibroblast-like (myCAF-like) cells compared to inflammatory CAFs (iCAF-like). Notably, MDA-MB-231 cell proliferation and invasion were significantly enhanced under these same conditions, and invasion was dependent on the LN-binding receptor, α6-integrin.