Mechanical Strain in Actin Networks Regulates FilGAP and Integrin Binding to Filamin A

Translational Medicine Division, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
Nature (Impact Factor: 41.46). 09/2011; 478(7368):260-3. DOI: 10.1038/nature10430
Source: PubMed


Mechanical stresses elicit cellular reactions mediated by chemical signals. Defective responses to forces underlie human medical disorders such as cardiac failure and pulmonary injury. The actin cytoskeleton's connectivity enables it to transmit forces rapidly over large distances, implicating it in these physiological and pathological responses. Despite detailed knowledge of the cytoskeletal structure, the specific molecular switches that convert mechanical stimuli into chemical signals have remained elusive. Here we identify the actin-binding protein filamin A (FLNA) as a central mechanotransduction element of the cytoskeleton. We reconstituted a minimal system consisting of actin filaments, FLNA and two FLNA-binding partners: the cytoplasmic tail of β-integrin, and FilGAP. Integrins form an essential mechanical linkage between extracellular and intracellular environments, with β-integrin tails connecting to the actin cytoskeleton by binding directly to filamin. FilGAP is an FLNA-binding GTPase-activating protein specific for RAC, which in vivo regulates cell spreading and bleb formation. Using fluorescence loss after photoconversion, a novel, high-speed alternative to fluorescence recovery after photobleaching, we demonstrate that both externally imposed bulk shear and myosin-II-driven forces differentially regulate the binding of these partners to FLNA. Consistent with structural predictions, strain increases β-integrin binding to FLNA, whereas it causes FilGAP to dissociate from FLNA, providing a direct and specific molecular basis for cellular mechanotransduction. These results identify a molecular mechanotransduction element within the actin cytoskeleton, revealing that mechanical strain of key proteins regulates the binding of signalling molecules.

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Available from: Thomas P Stossel, Oct 03, 2015
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    • "The internal tension of the fibers not only changes the basic mechanical properties of the filaments [12] [46], but is also crucial in maintaining the mechanical shape and integrity of the cell [47]. Furthermore, microfilament tension alters the affinities of binding proteins [48] [49], and can directly serve as a mechanism of mechanotransduction by exposing previously inaccessible cryptic binding sites [50]. Because of the dominant role of active processes in the cell, the incorporation of motors into reconstituted in vitro systems has received considerable attention over the past decade. "
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    ABSTRACT: The intracellular cytoskeleton is an active dynamic network of filaments and associated binding proteins that control key cellular properties, such as cell shape and mechanics. Due to the inherent complexity of the cell, reconstituted model systems have been successfully employed to gain an understanding of the fundamental physics governing cytoskeletal processes. Here, we review recent advances and key aspects of these reconstituted systems. We focus on the importance of assembly kinetics and dynamic arrest in determining network mechanics, and highlight novel emergent behavior occurring through interactions between cytoskeletal components in more complex networks incorporating multiple biopolymers and molecular motors. Copyright © 2015. Published by Elsevier B.V.
    Biochimica et Biophysica Acta 06/2015; DOI:10.1016/j.bbamcr.2015.06.013 · 4.66 Impact Factor
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    • "ightly associated and are turned over together by this exercise - stimulated pathway . Therefore exercise - stimulated autophagy might lead to a further increase in the exchange rate of aciculin to ensure stable protein amounts in Z - disc and to prevent damage during exercise . In this context , filamins have been shown to act as mechanosensors ( Ehrlicher et al . , 2011 ; Pentikäinen and Ylänne , 2009 ; Rognoni et al . , 2012 ; Ulbricht et al . , 2013 ) , and FLNc probably plays such a role in the Z - disc , at the sarcolemma and in cell – cell and cell – matrix contacts ( Ulbricht et al . , 2013 ) . FLNc – aciculin binding might be modulated by structural alterations in FLNc , suggesting that aciculin"
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    ABSTRACT: Filamin C (FLNc) and Xin actin-binding repeat-containing proteins (XIRPs) are multi-adapter proteins mainly expressed in cardiac and skeletal muscles that play important roles in the assembly and repair of myofibrils and their attachment to the membrane. We identified the dystrophin-binding protein aciculin (PGM5), as a novel interaction partner of FLNc and Xin. All three proteins colocalize at intercalated discs of cardiac muscle and myotendinous junctions of skeletal muscle, while FLNc and aciculin also colocalize in mature Z-discs. Bimolecular fluorescence complementation experiments in developing cultured mammalian skeletal muscle cells demonstrate that Xin and aciculin also interact in FLNc-containing immature myofibrils and areas of myofibrillar remodeling and repair induced by electrical pulse stimulation (EPS). FRAP experiments show that aciculin is a highly dynamic and mobile protein. Aciculin knockdown in myotubes leads to failure in myofibril assembly, alignment and membrane attachment, and massive reduction in myofibril number. A highly similar phenotype was found upon depletion of aciculin in zebrafish embryos. Our results point to a thus far unappreciated but essential function of aciculin in myofibril formation, maintenance and remodeling.
    Journal of Cell Science 06/2014; 127(16). DOI:10.1242/jcs.152157 · 5.43 Impact Factor
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    • "A mechanotransduction mechanism for maintaining homeostasis in mechanically stressed cells has recently been proposed involving tension-induced targeted degradation of the actin crosslinker protein filamin and its upregulation [43,44]. Filamin C is highly enriched at the myotendinous junction and its ability to crosslink makes it a suitable candidate to sense mechanical stress, as tension can induce the exposition of cryptic interaction sites [45] and changes in the rates of protein turnover [43]. Since the immunoglobulin- and fibronectin-like repeats present in filamin are also found in many other muscle proteins with filament and myofibril crosslinking roles [46,47], adaptations to specific mechanical strains could also be mediated by other globular repeat containing proteins. "
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    ABSTRACT: The myotendinous junction is a specialized structure of the muscle fibre enriched in mechanosensing complexes, including costameric proteins and core elements of the z-disc. Here, laser capture microdissection was applied to purify membrane regions from the myotendinous junctions of mouse skeletal muscles, which were then processed for proteomic analysis. Sarcolemma sections from the longitudinal axis of the muscle fibre were used as control for the specificity of the junctional preparation. Gene ontology term analysis of the combined lists indicated a statistically significant enrichment in membrane-associated proteins. The myotendinous junction preparation contained previously uncharacterized proteins, a number of z-disc costameric ligands (e.g., actinins, capZ, αB cristallin, filamin C, cypher, calsarcin, desmin, FHL1, telethonin, nebulin, titin and an enigma-like protein) and other proposed players of sarcomeric stretch sensing and signalling, such as myotilin and the three myomesin homologs. A subset were confirmed by immunofluorescence analysis as enriched at the myotendinous junction, suggesting that laser capture microdissection from muscle sections is a valid approach to identify novel myotendinous junction players potentially involved in mechanotransduction pathways.
    Proteome Science 05/2014; 12(25). DOI:10.1186/1477-5956-12-25 · 1.73 Impact Factor
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