Glossary Term: Fibrillar Adhesions (FBs)
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Fibrillar adhesions are a type of Cell-Matrix Adhesion; Fibrillar adhesions originate from Focal adhesions (FAs);
See also Common components of Cell-matrix adhesions and the Functional Modules: Activators and Integrin in matrix binding and signaling and Myosin-II in Filament Retraction
Basic Description
Fibrillar adhesions (FBs) are cell-matrix adhesion structures, that are located towards the center of a cell and are believed to evolve from mature focal adhesions. They are bound specifically to fibronectin via α5β1–integrins [1] and appear as long streaks or array of dots [2, 3]. FBs are mainly composed of thin actin cables that are crosslinked by the actin binding protein, tensin, and lack linkage to stress fibres [4, 5].
Read Further…
Fibrillar adhesions are a type of Cell-Matrix Adhesion; Fibrillar adhesions originate from Focal adhesions (FAs);
See also Common components of Cell-matrix adhesions and the Functional Modules: Activators and Integrin in matrix binding and signaling and Myosin-II in Filament Retraction
Steps in Formation
FBs arise from the medial ends of growing focal adhesions at sites where α5β1-integrins translocated out of these complexes centripetally along the underlying fibronectin fibres [6]. The amount of tensin that is bound to the FBs increases as they are translocated [1, 7]. This directional movement towards the cell center causes stretching of the bound fibronectin dimers fibrils in the extracellular matrix (ECM) and promotes its reorganization into fibrils, driven by Rho GTPase activation of actomyosin contractility [7, 8](reviewed in [9]).The physical state of the extracellular matrix also influences the formation of FBs [4] in the same way as on focal adhesions (see Factors affecting FA formation). The translocation of pliant matrix components (such as fibronectin) and increased cellular tension from the actin cables to the translocating integrins and associated fibronectin molecules is suggested to initiate fibronectin fibrillogenesis and FB assembly [1].
FBs are distinguished from FAs by the high levels of tensin and low levels or absence of phosphotyrosine [4, 5, 10]. They also lack attachment to stress fibres and do not diassemble when the force is relaxed [7]. Integrin linked kinase (ILK) and the complex it forms with cytoskeleton adaptor proteins, PINCH1 and parvin, are thought to be essential for the transition from early FAs to FBs [11]. This IPP complex functions to reinforce α5β1-actin linkage and provide a platform for tensin and zyxin recruitment.
Controversial evidences exist for the role of FAK-Src signaling pathway in regulating FBs and fibrillogenesis. Some studies report that loss of Src family kinases or FAK activity increases tensin recruitment [12], while in others, similar mutants show reduced efficiency in assembling fibronectin into fibrils [13, 14].
