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In cell biology, focal adhesions (also cell–matrix adhesions or FAs) are large macromolecular assemblies through which mechanical force and regulatory signals are transmitted between the extracellular matrix (ECM) and an interacting cell. More precisely, focal adhesions are the sub-cellular structures that mediate the regulatory effects (i.e., signaling events) of a cell in response to ECM adhesion.〔Chen CS, Alonso JL, Ostuni E, Whitesides GM and Ingber DE, 2003. Cell shape provides global control of focal adhesion assembly. ''Biochemical and Biophysical Research Communications'', 307(2):355–61.〕 Focal adhesions serve as the mechanical linkages to the ECM, and as a biochemical signaling hub to concentrate and direct numerous signaling proteins at sites of integrin binding and clustering. ==Structure and function== Focal adhesions are integrin-containing, multi-protein structures that form mechanical links between intracellular actin bundles and the extracellular substrate in many cell types. Focal adhesions are large, dynamic protein complexes through which the cytoskeleton of a cell connects to the ECM. They are limited to clearly defined ranges of the cell, at which the plasma membrane closes to within 15 nm of the ECM substrate.〔Zaidel-Bar R, Cohen M, Addadi L and Geiger B, 2004. Hierarchical assembly of cell matrix adhesion complexes. ''Biochemical Society Transactions'', 32(3):416–20.〕 Focal adhesions are in a state of constant flux: proteins associate and disassociate with it continually as signals are transmitted to other parts of the cell, relating to anything from cell motility to cell cycle. Focal adhesions can contain over 100 different proteins, which suggests a considerable functional diversity.〔Zamir E and Geiger B, 2001. Molecular complexity and dynamics of cell–matrix adhesions. ''Journal of Cell Science'', 114(20):3583–90.〕 More than anchoring the cell, they function as signal carriers (sensors), which inform the cell about the condition of the ECM and thus affect their behavior.〔Riveline D, Zamir E, Balaban NQ, Schwarz US, Ishizaki T, Narumiya S, Kam Z, Geiger B and Bershadsky AD, 2001. Focal contacts as mechanosensors: externally applied local mechanical force induces growth of focal contacts by an mDia1-dependent and ROCK-independent mechanism. ''Journal of Cell Biology'', 153(6):1175–86〕 In sessile cells, focal adhesions are quite stable under normal conditions, while in moving cells their stability is diminished: this is because in motile cells, focal adhesions are being constantly assembled and disassembled as the cell establishes new contacts at the leading edge, and breaks old contacts at the trailing edge of the cell. One example of their important role is in the immune system, in which white blood cells migrate along the connective endothelium following cellular signals to damaged biological tissue. ==Morphology== Connection between focal adhesions and proteins of the extracellular matrix generally involves integrins. Integrins bind to extra-cellular proteins via short amino acid sequences, such as the R-G-D sequence motif (found in proteins such as fibronectin, laminin, or vitronectin), or the DGEA and GFOGER motifs found in collagen. Integrins are heterodimers which are formed from one beta and one alpha subunit. These subunits are present in different forms, which differ in their specificity and affinity to the different ECM proteins. Within the cell, the intracellular domain of integrin binds to the cytoskeleton via adapter proteins such as talin, α-actinin, filamin, vinculin and tensin. Many other intracellular signalling proteins, such as focal adhesion kinase, bind to and associate with this integrin-adapter protein–cytoskeleton complex, and this forms the basis of a focal adhesion. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「focal adhesion」の詳細全文を読む スポンサード リンク
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