Researchers are exploring whether these ubiquitous fluorinated molecules might worsen infections or hamper vaccine effectiveness.
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Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved August 21, 2017 (received for review January 20, 2017)
Significance
Integrins are adhesion receptors linking cells to their environment, which function as sensors of physical and chemical information to regulate development, immune response, and vascular function. How integrins receive and transduce directional forces including flow or tissue tension has remained elusive. We used polarization-based microscopy techniques to discover that activated αVβ3 integrins are aligned with one another in focal adhesions in migrating fibroblasts. Integrin coalignment is sensitive to mechanical resistance of its ligand and coupling to a dynamic F-actin cytoskeleton, consistent with the “cytoskeleton force model” for integrin activation. Our work suggests that activated integrins are actively ordered at the molecular scale by cellular forces, which may underlie their ability to sense directional forces in their environment to mediate critical functions.
Abstract
Integrins are transmembrane receptors that, upon activation, bind extracellular ligands and link them to the actin filament (F-actin) cytoskeleton to mediate cell adhesion and migration. Cytoskeletal forces in migrating cells generated by polymerization- or contractility-driven “retrograde flow” of F-actin from the cell leading edge have been hypothesized to mediate integrin activation for ligand binding. This predicts that these forces should align and orient activated, ligand-bound integrins at the leading edge. Here, polarization-sensitive fluorescence microscopy of GFP-αVβ3 integrins in fibroblasts shows that integrins are coaligned in a specific orientation within focal adhesions (FAs) in a manner dependent on binding immobilized ligand and a talin-mediated linkage to the F-actin cytoskeleton. These findings, together with Rosetta modeling, suggest that integrins in FA are coaligned and may be highly tilted by cytoskeletal forces. Thus, the F-actin cytoskeleton sculpts an anisotropic molecular scaffold in FAs, and this feature may underlie the ability of migrating cells to sense directional extracellular cues.
Footnotes
↵1V.S., J.M.K., and S.B.M. contributed equally to this work.
↵2S.M., T.A.S., and C.M.W. contributed equally to this work.
- ↵3To whom correspondence should be addressed. Email: watermancm{at}nhlbi.nih.gov.
Author contributions: S.M., T.A.S., and C.M.W. designed research; V.S., J.M.K., S.B.M., and N.K. performed research; J.M.K., S.B.M., P.N., T.I.M., N.K., D.A.B., R.O., T.T., and T.A.S. contributed new reagents/analytic tools; V.S., J.M.K., S.B.M., P.N., and T.A.S. analyzed data; and V.S. and C.M.W. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1701136114/-/DCSupplemental.
Freely available online through the PNAS open access option.
Integrin coalignment in focal adhesions
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