Abstract
Specific regulation and activation of focal adhesion kinase (FAK) are thought to be important for focal adhesion formation, and activation of Rho-kinase has been suggested to play a role in determining the effects of FAK on the formation of stress fibers and focal adhesions. To clarify the role of FAK in stress fiber formation and focal adhesion organization, the author examined the formation of new stress fibers and focal adhesions by activation of Rho-kinase in FAK knockout (FAK–/–) fibroblasts. FAK–/– cells were elliptical in shape, and showed reduced numbers of stress fibers and focal adhesions in the central part of the cells along with large focal adhesions in the peripheral regions. Activation of Rho-kinase in FAK–/– cells transiently increased the actin filaments in the cell center, but these did not form typical thick stress fibers. Moreover, only plaque-like structures as the origins of newly formed focal adhesions were observed in the center of the cell. Furthermore, introduction of an exogenous GFP-labeled FAK gene into FAK–/– cells resulted in increased numbers of stress fibers and focal adhesions in the center of the cells, which showed typical fibroblast morphology. These results indicated that FAK plays an important role in the formation of stress fibers and focal adhesions as well as in regulation of cell shape and morphology with the activation of Rho-kinase.
Highlights
Actin filaments are the major components of the actomyosin contractile systems in eukaryotic cells, and function as regulators of cell movement
When GFP-FAK-related non-kinase (FRNK) was introduced into focal adhesion kinase (FAK)−/− cells, the quantitative analysis was excluded, because there were no significant changes in the cell morphology or in the formation of stress fibers and focal adhesions. ± represents standard error of the mean
On the other hand, when GFP-FRNK was introduced into FAK−/− cells, there were no changes in the cell morphology or in the formation of stress fibers and focal adhesions at the center of the cell. These results indicated that FAK and c-Src play important roles in the formation of novel stress fibers and focal adhesions accompanying the activation of Rho-kinase and in the maintenance of cell morphology
Summary
Actin filaments are the major components of the actomyosin contractile systems in eukaryotic cells, and function as regulators of cell movement. Activation of the Rho family of small G proteins and their downstream effector molecules (WASP/WAVE family protein and Arp2/3 complex) is accompanied by marked changes in polymerization and depolymerization of actin molecules (Uruno et al, 2001). These changes result in dynamic alterations in stress fibers, lamellipodia, and filopodia, which control cell morphology and movement. A web-like structure is formed when the cell moving in the front portion of the cell Such dynamic changes in the membrane structure and organelles within cells associated with cell motility require changes in cytoskeletal proteins, such as actin filaments and microtubules, which are involved in the control of membrane transport
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