Integrin α5β1 facilitates cancer cell invasion through enhanced contractile forces

Cell migration through connective tissue, or cell invasion, is a fundamental biomechanical process during metastasis formation. Cell invasion usually requires cell adhesion to the extracellular matrix through integrins. In some tumors, increased integrin expression is associated with increased malignancy and metastasis formation. Here, we have studied the invasion of cancer cells with different alpha 5 beta 1 integrin expression levels into loose and dense 3D collagen fiber matrices. Using a cell sorter, we isolated from parental MDA-MB-231 breast cancer cells two subcell lines expressing either high or low amounts of alpha 5 beta 1 integrins (alpha 5 beta 1(high) or alpha 5 beta 1(low) cells, respectively). alpha 5 beta 1high cells showed threefold increased cell invasiveness compared to alpha 5 beta 1(low) cells. Similar results were obtained for 786-O kidney and T24 bladder carcinoma cells, and cells in which the alpha 5 integrin subunit was knocked down using specific siRNA. Knockdown of the collagen receptor integrin subunit alpha 2 also reduced invasiveness, but to a lesser degree than knockdown of integrin subunit alpha 5. Fourier transform traction microscopy revealed that the alpha 5 beta 1(high) cells generated sevenfold greater contractile forces than alpha 5 beta 1(low) cells. Cell invasiveness was reduced after addition of the myosin light chain kinase inhibitor ML-7 in alpha 5 beta 1(high) cells, but not in alpha 5 beta 1(low) cells, suggesting that alpha 5 beta 1 integrins enhance cell invasion through enhanced transmission and generation of contractile forces.