Integrin connections to the cytoskeleton through talin and vinculin.
ABSTRACT Integrins are alphabeta heterodimeric receptors that mediate attachment of cells to the extracellular matrix and therefore play important roles in cell adhesion, migration, proliferation and survival. Among the cytoskeletal proteins that interact directly with the beta-chain cytoplasmic domain, talin has emerged as playing a critical role in integrin activation and linkage to the actin cytoskeleton. Talin (2541 amino acids) is an elongated (60 nm) flexible antiparallel dimer, with a small globular head connected to an extended rod. The talin head contains a FERM (4.1/ezrin/radixin/moesin) domain (residues 86-400) with binding sites for several beta integrin cytodomains and the talin rod contains a second lower-affinity integrin-binding site, a highly conserved C-terminal actin-binding site and also several binding sites for vinculin. We have determined previously the crystal structures of two domains from the talin rod, spanning residues 482-789. Talin-(482-655), which contains a VBS (vinculin-binding site), folds into a five-helix bundle whereas talin-(656-789) is a four-helix bundle. We have also reported the crystal structure of the N-terminal vinculin head domain in complex with an activated form of talin. In the present paper, we consider how binding sites buried within the folded helical bundles of talin and alpha-actinin form interactions with vinculin.
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ABSTRACT: External forces play complex roles in cell organization, fate, and homeostasis. Changes in these forces, or how cells respond to them, can result in abnormal embryonic development and diseases in adults. How cells sense and respond to these mechanical stimuli requires an understanding of the biophysical principles that underlie changes in protein conformation and result in alterations in the organization and function of cells and tissues. Here, we discuss mechano-transduction as it applies to protein conformation, cellular organization, and multi-cell (tissue) function.PLoS Biology 11/2014; 12(11):e1001996. DOI:10.1371/journal.pbio.1001996 · 11.77 Impact Factor
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ABSTRACT: Without Focal Adhesion Kinase (FAK), developing murine Schwann cells (SCs) proliferate poorly, sort axons inefficiently, and cannot myelinate peripheral nerves. Here we show that FAK is required for the development of SCs when their basal lamina (BL) is fragmentary, but not when it is mature in vivo. Mutant SCs fail to spread on fragmentary BL during development in vivo, and this is phenocopied by SCs lacking functional FAK on low laminin (LN) in vitro. Furthermore, SCs without functional FAK initiate differentiation prematurely, both in vivo and in vitro. In contrast to their behavior on high levels of LN, SCs lacking functional FAK grown on low LN display reduced spreading, proliferation, and indicators of contractility (i.e., stress fibers, arcs, and focal adhesions) and are primed to differentiate. Growth of SCs lacking functional FAK on increasing LN concentrations in vitro revealed that differentiation is not regulated by G1 arrest but rather by cell spreading and the level of contractile actomyosin. The importance of FAK as a critical regulator of the specific response of developing SCs to fragmentary BL was supported by the ability of adult FAK mutant SCs to remyelinate demyelinated adult nerves on mature BL in vivo. We conclude that FAK promotes the spreading and actomyosin contractility of immature SCs on fragmentary BL, thus maintaining their proliferation, and preventing differentiation until they reach high density, thereby promoting radial sorting. Hence, FAK has a critical role in the response of SCs to limiting BL by promoting proliferation and preventing premature SC differentiation.The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 10/2014; 34(40):13422-34. DOI:10.1523/JNEUROSCI.1764-14.2014 · 6.75 Impact Factor
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ABSTRACT: Purpose: To identify plasma protein biomarkers for age-related macular degeneration (AMD) using a large-scale quantitative proteomic discovery procedure. Methods: Plasma proteomes from 20 exudative AMD patients and 20 healthy control patients were comparatively profiled by 4-dimensional liquid chromatography-tandem mass spectrometry (LC-MS/MS). Proteins existing at statistically different levels were validated by enzyme-linked immunosorbent assay (ELISA) and western blotting in 233 case-controlled samples. Newly discovered plasma biomarkers were further confirmed using in vivo and in vitro experiments. Results: Out of 320 proteins identified, vinculin, protein S100A9, triosephosphateisomerase, protein S100A8, protein z-dependent protease inhibitor, C-X-C motif chemokine 7, and tenascin X showed significantly differential expression in AMD patient plasma compared to control plasma. Among them, the AUC for vinculin was 0.871 for discriminating between exudative AMD and controls (N = 201) and 0.879 for discriminating between AMD and controls (N = 233). A proteo-genomic combination model using vinculin and two known risk genotypes in ARMS2 and CFH genes additionally provided excellent discrimination of AMD from controls (AUC = 0.916). The plasma level of vinculin was not associated with any confounding clinical variables, such as age, smoking, and other comorbidities. Additionally, vinculin was strongly expressed in retinal pigment epithelial cells of human eyes, and its expression was elevated when exposed to oxidative stress in vitro. Conclusions: Vinculin was identified as a potential plasma biomarker for AMD. The early detection of AMD using novel plasma biomarkers with genetic modeling may enable timely treatment and vision preservation in the elderly.Investigative Ophthalmology & Visual Science 10/2014; DOI:10.1167/iovs.14-15168 · 3.66 Impact Factor