Extracellular Matrix Density Regulates Extracellular Proteolysis via Modulation of Cellular Contractility

The Extracellular Matrix (ECM) undergoes changes in composition and organization during tumor progression. In breast cancer, increased deposition and cross linking-induced alignment of collagen I create a stiffer microenvironment that directly contributes to cancer invasion. While ECM stiffness-induced invasion has been documented, it remains unclear if ECM density also contributes to invasion independent of ECM stiffness. In this paper, using collagen I-coated glass coverslips of varying density, we sought to study the influence of ECM density on the invasiveness of human MDA-MB-231 breast cancer cells. We first showed that cell spreading and contractility increases with ECM density. Concomitant with increase in cell contractility, matrix degradation was seen to increase with ECM density and was associated with higher invadopodia activity. The density-dependent increase in degradation was associated with higher activity of MMP-2, MMP-9 and MT1-MMP. Treatment with either the MMP inhibitor GM6001 or the myosin II inhibitor blebbistatin, were found to inhibit cell contractility and suppress matrix degradation. Contractility was found to modulate the activity of MMP-2 and MMP-9, and the localization of MT1-MMP at invadopodia. Taken together, our results indicate that ECM density regulates ECM degradation through modulation of cell contractility.