Cells can sense the density and distribution of extracellular matrix (ECM) molecules by means of individual integrin proteins and larger, integrin-containing adhesion complexes within the cell membrane. This spatial sensing drives cellular activity in a variety of normal and pathological contexts1,2. Previous studies of cells on rigid glass surfaces have shown that spatial sensing of ECM ligands takes place at the nanometre scale, with integrin clustering and subsequent formation of focal adhesions impaired when single integrin–ligand bonds are separated by more than a few tens of nanometres3,4,5,6. It has thus been suggested that a crosslinking ‘adaptor’ protein of this size might connect integrins to the actin cytoskeleton, acting as a molecular ruler that senses ligand spacing directly3,7,8,9. Here, we develop gels whose rigidity and nanometre-scale distribution of ECM ligands can be controlled and altered. We find that increasing the spacing between ligands promotes the growth of focal adhesions on low-rigidity substrates, but leads to adhesion collapse on more-rigid substrates. Furthermore, disordering the ligand distribution drastically increases adhesion growth, but reduces the rigidity threshold for adhesion collapse. The growth and collapse of focal adhesions are mirrored by, respectively, the nuclear or cytosolic localization of the transcriptional regulator protein YAP. We explain these findings not through direct sensing of ligand spacing, but by using an expanded computational molecular-clutch model10,11, in which individual integrin–ECM bonds—the molecular clutches—respond to force loading by recruiting extra integrins, up to a maximum value. This generates more clutches, redistributing the overall force among them, and reducing the force loading per clutch. At high rigidity and high ligand spacing, maximum recruitment is reached, preventing further force redistribution and leading to adhesion collapse. Measurements of cellular traction forces and actin flow speeds support our model. Our results provide a general framework for how cells sense spatial and physical information at the nanoscale, precisely tuning the range of conditions at which they form adhesions and activate transcriptional regulation.
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This work was supported by the Spanish Ministry of Economy and Competitiveness (grants BFU2016-79916-P and BFU2014-52586-REDT to P.R.-C.; BFU2015-65074-P to X.T.; DPI2015-64221-C2-1-R to J.M.G.-A.; PI14/00280 to D.N.; SAF2016-75241-R (MINECO-FEDER) to L.A.), the European Commission (grant agreement SEP-210342844 to X.T. and P.R.-C.), the Generalitat de Catalunya (grant 2014-SGR-927), the European Research Council (CoG-616480 to X.T. and StG 306571 to J.M.G.-A.), Obra Social ‘La Caixa’, Fundació la Marató de TV3 (project 20133330 to P.R.-C.), the German Science Foundation (DFG SFB1129 P15 to E.A.C.-A.), and the EMBO Young Investigator Programme. A.E.-A., R.O., and L.A. were supported respectively by a Juan de la Cierva Fellowship (Spanish Ministry of Economy and Competitiveness, fellowship number IJCI-2014-19156), an FI fellowship (Generalitat de Catalunya), and a Ramon y Cajal Fellowship (Spanish Ministry of Economy and Competitiveness). The support of the Max Planck Society and the Alexander von Humboldt foundation (to I.P.) is acknowledged. We thank P. Oakes, J. Spatz, J. L. Jones, M. D. Allen and the members of the P.R.-C. and X.T. laboratories for technical assistance and discussions.