β1- and αv-class integrins cooperate to regulate myosin II during rigidity sensing of fibronectin-based microenvironments

How different integrins that bind to the same type of extracellular matrix protein mediate specific functions is unclear. We report the functional analysis of β 1 - and α v -class integrins expressed in pan-integrin-null fibroblasts seeded on fibronectin. Reconstitution with β 1 -class integrins promotes myosin-II-independent formation of small peripheral adhesions and cell protrusions, whereas expression of α v -class integrins induces the formation of large focal adhesions. Co-expression of both integrin classes leads to full myosin activation and traction-force development on stiff fibronectin-coated substrates, with α v -class integrins accumulating in adhesion areas exposed to high traction forces. Quantitative proteomics linked α v -class integrins to a GEF-H1–RhoA pathway coupled to the formin mDia1 but not myosin II, and α 5 β 1 integrins to a RhoA–Rock–myosin II pathway. Our study assigns specific functions to distinct fibronectin-binding integrins, demonstrating that α 5 β 1 integrins accomplish force generation, whereas α v -class integrins mediate the structural adaptations to forces, which cooperatively enable cells to sense the rigidity of fibronectin-based microenvironments. Faessler and colleagues analyse the distinct properties of β 1 and α v integrin subclasses, and provide insight into the different protein compositions, signalling activities and contributions to rigidity sensing of adhesion sites anchored by each integrin subtype.