The ability of breast cancer cells to interconvert between epithelial and mesenchymal states contributes to their metastatic potential. As opposed to cell autonomous effects, the impact of epithelial-mesenchymal plasticity (EMP) on primary and metastatic tumor microenvironments remains poorly characterized. Herein we utilize global gene expression analyses to characterize a metastatic model of EMP as compared to their non-metastatic counterparts. Using this approach we demonstrate that upregulation of the extracellular matrix crosslinking enzyme tissue transglutaminase-2 (TGM2) is part of novel gene signature that only emerges in metastatic cells that have undergone induction and reversion of epithelial-mesenchymal transition (EMT). Consistent with our model system patient survival is diminished when primary tumors demonstrate enhanced levels of TGM2 in conjunction with its substrate, fibronectin. Targeted depletion of TGM2 inhibits metastasis, while overexpression of TGM2 is sufficient to enhance this process. In addition to being present within cells, we demonstrate a robust increase in the amount of TGM2 and crosslinked fibronectin present within extracellular vesicle (EV) fractions derived from metastatic breast cancer cells. Confocal microscopy of these EVs suggests that FN becomes fibrillated on their surface via a TGM2 and Tesin1-dependent process. Upon in vivo administration, the ability of tumor-derived EVs to induce metastatic niche formation and enhance subsequent pulmonary tumor growth requires the presence and activity of TGM2. Finally, we develop a novel 3D model of the metastatic niche to demonstrate that education of pulmonary fibroblasts via pretreatment with tumor-derived EVs promotes subsequent growth of breast cancer cells in a TGM2-dependent fashion. Overall, our studies illustrate a novel mechanism through which EMP contributes to metastatic niche development and distant metastasis via tumor-derived EVs containing abberent levels of TGM2 and fibular FN.
