Substrate stiffness modulates lung cancer cell migration but not epithelial to mesenchymal transition

Biomechanical properties of the tumor microenvironment, including matrix/substrate stiffness, play a significant role in tumor evolution and metastasis. Epithelial to Mesenchymal Transition (EMT) is a fundamental biological process that is associated with increased cancer cell migration and invasion. The goal of this study was to investigate (1) how substrate stiffness modulates the migration behaviors of lung adenocarcinoma cells (A549) and (2) if stiffness-induced changes in cell migration correlate with biochemical markers of EMT. Collagen-coated polydimethylsiloxane (PDMS) substrates and an Ibidi migration assay were used to investigate how substrate stiffness alters the migration patterns of A549 cells. RT-PCR, western blotting and immunofluorescence were used to investigate how substrate stiffness alters biochemical markers of EMT, that is, E-cadherin and N-cadherin, and the phosphorylation of focal adhesion proteins. Increases in substrate stiffness led to slower, more directional migration but did not alter the biochemical markers of EMT. Interestingly, growth factor (i.e., Transforming Growth Factor-β) stimulation resulted in similar levels of EMT regardless of substrate stiffness. We also observed decreased levels of phosphorylated focal adhesion kinase (FAK) and paxillin on stiffer substrates which correlated with slower cell migration. These results indicate that substrate stiffness modulates lung cancer cell migration via focal adhesion signaling as opposed to EMT signaling.