Focal adhesion complexes components

The structural integrity of microfilaments has been shown to be necessary for signal transduction within osteoblasts. Examination of the effects of mechanical strain on the expression of major structural elements of the cytoskeleton indicated that the amount of tubulin decreased by 75% and the amount of vinculin, a major component of focal adhesion complexes, increased by about 250%. Immunofluorescence microscopy demonstrated that mechanical strain led to increased formation and thickening of actin stress fibers, with dissociation of the microtubules and a clear increase in levels of vinculin at the peripheral edges of the cell. This suggests that mechanical strain leads to a coordinated change in both the cytoskeleton and in ECM proteins that facilitate tighter adhesion of osteoblasts and their ECM. 

Westendorf et al, 2004, Giancotti and Ruoslahti, 1999). FAK is one of the main components of the integrin mechanotransduction pathway (Rubin et al, 2006, Shakibaei et al., 2008). Once associated with the focal adhesion complex (FAC), FAK is subsequently activated, autophosphorylates and then binds with sarcoma (Src) to form a Src-homology-2 binding domain (Millward-Sadler and Salter, 2004, Yoon and Fisher, 2007). As an SFIC-2 it is able to phosphorylate other proteins such as paxillin and tensin (Millward-Sadler and Salter, 2004, Giancotti and Ruoslahti, 1999). 

Fig. 4.4 Integrins are transmembrane receptors. They are activated by components of the extracellular matnx, such as fibronectin and collagen. These interactions lead to clustering of integrin receptors and the formation of focal adhesions, intracellular cytoskeletal complexes, and formation of actin bundles.30 Activation of integrins is part of the celi-ceil adhesion process, integrins also bind to adhesion moiecules on adjacent celis.

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