Mechanical forces play a major role in the regulation of cell adhesion and cytoskeletal organization. In order to explore the molecular mechanism underlying this regulation, we have investigated the relationship between local force applied by the cell to the substrate and the assembly of focal adhesions. A novel approach was developed for real-time, high-resolution measurements of forces applied by cells at single adhesion sites. This method combines micropatterning of elastomer substrates and fluorescence imaging of focal adhesions in live cells expressing GFP-tagged vinculin. Local forces are correlated with the orientation, total fluorescence intensity and area of the focal adhesions, indicating a constant stress of 5.5 ± 2 nNμm-2. The dynamics of the force-dependent modulation of focal adhesions were characterized by blocking actomyosin contractility and were found to be on a time scale of seconds. The results put clear constraints on the possible molecular mechanisms for the mechanosensory response of focal adhesions to applied force.
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ACKNOWLEDGEMENTS We wish to thank E. Zamir and E. Moses for illuminating discussions and technical assistance. This study was supported by the Israel Science Foundation, administrated by the Israel Academy of Science and the Minerva Foundation. B.G. holds the E. Neter chair for Cell and Tumor Biology. L.A. is incumbent of the Dorothy and Patrick Gorman Professorial chair of Biological Ultrastructure. U.S.S. was supported by the Minerva Foundation. A. B. holds the J. Moss chair of Biomedical Research. Correspondence and requests for materials should be addressed to B.G. Supplementary Information is available on Nature Cell Biology’s website (http://cellbio.nature.com).