Fibronectin fibrils regulate TGF-β1-induced Epithelial-Mesenchymal Transition

• Inhibition of FN fibril formation blocks Epithelial–Mesenchymal Transition (EMT)
• Increasing soluble FN or assembling FN fibrils without TGF–b1 doesn't induce EMT.
• Inhibiting the localization of TGF–b1 to assembled FN fibrils blocks EMT
• These suggest that FN fibrils facilitate EMT by clustering TGF–b1 at the cell surface.

Epithelial-Mesenchymal Transition (EMT) is a dynamic process through which epithelial cells transdifferentiate from an epithelial phenotype into a mesenchymal phenotype. Previous studies have demonstrated that both mechanical signaling and soluble growth factor signaling facilitate this process. One possible point of integration for mechanical and growth factor signaling is the extracellular matrix. Here we investigate the role of the extracellular matrix (ECM) protein fibronectin (FN) in this process. We demonstrate that inhibition of FN fibrillogenesis blocks activation of the Transforming Growth Factor-Beta (TGF-β) signaling pathway via Smad2 signaling, decreases cell migration and ultimately leads to inhibition of EMT. Results show that soluble FN, FN fibrils, or increased contractile forces are insufficient to independently induce EMT. We further demonstrate that inhibition of latent TGF-β1 binding to FN fibrils via either a monoclonal blocking antibody against the growth factor binding domain of FN or through use of a FN deletion mutant that lacks the growth factor binding domains of FN blocks EMT progression, indicating a novel role for FN in EMT in which the assembly of FN fibrils serves to localize TGF-β1 signaling to drive EMT.