Cell Biology

Pulling Harder, Standing Firm

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Science  22 Jun 2001:
Vol. 292, Issue 5525, pp. 2219
DOI: 10.1126/science.292.5525.2219b

Cells grab onto the extracellular matrix (ECM) via the transmembrane protein integrin; inside the cell, integrin is linked to cytoskeletal components, such as vinculin and paxillin, and thus indirectly to actin filaments, whereas the external part of integrin binds to the ECM. Initial dot-like adhesions, known as focal complexes (1 micrometer in size), can convert into the stronger, streak-like focal contacts (3 to 10 mm).

By following fluorescently tagged vinculin or paxillin in living cells and by interference reflection microscopy, Riveline et al. were able to monitor the development of focal contacts. This process was dependent on the GTPase Rho, which was known from previous work to activate two downstream targets: the Rho-associated kinase (ROCK) and a profilin ligand called formin or mDia1. Although the direct application of force with a micropipette obviated the need to activate ROCK (and its downstream myosin II target), formin still was required for focal contact formation. Balaban et al. have examined the adhesion of cells to micropatterned grids and find a relation between applied force and the size of the contacts. It appears that the dot-like complexes may serve as micromechanosensors that initiate directional assembly of focal contact components in response to locally applied force. — SMH

J. Cell Biol.153, 1175 (2001); Nature Cell Biol.3, 466 (2001).

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