Tumor-associated mammary fibroblast matrices contain O-glycosylated oncofetal fibronectin

Oncofetal fibronectin (oFN) is a known biomarker of cancer progression and is involved in events such as epithelial mesenchymal transition and multidrug resistance. It is also understood that fibronectin (FN) and its splice variants are differentially arranged by cancer associated fibroblasts (CAFs) to support cancer cell proliferation and migration. Contrastingly, little is understood about the mechanobiology of oFN, a post-translationally modified FN isoform defined by O-glycosylation of a specific threonine residue. To investigate the architectural features of the oFN matrix, CAFs were simulated by culturing human mammary fibroblasts (HMFs) on stiff polyacrylamide gels (20 kPa) in media collected from HCC-1937 (primary site breast adenocarcinoma) and MDA-MB-231 (metastatic breast adenocarcinoma) cells. As a control, HMFs were also cultured on softer gels representing healthy adipose tissue (2 kPa) in media not exposed to cancer cells. After immunocytochemical analysis, tumor conditioned HMFs displayed an expected CAF-like phenotype that was most prominent with MDA-MB-231 conditioned media. Matrices produced by tumor-conditioned HMFs contained more oFN with structural features mostly following that of the overall dense, aligned FN matrix. Cancer cells reseeded on their corresponding decellularized tumor-associated matrices had greater F-actin/oFN colocalization than control matrix. The lack of distinct oFN topographical cues may indicate that oFN O-glycosylation is more directly involved in biochemical signaling than mechanosignaling through matrix architecture. Together, this study established a platform for investigating stromal oFN which revealed that tumor-conditioned media sourced from cancer cells with different metastatic potential influences HMF activation, leading to distinct total FN and thus oFN matrix microarchitecture features.