Analysis of physiological function of a focal adhesion protein vinexin

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Vinexin is a focal adhesion protein belonging to vinexin family (vinexin, CAP (c-cbl associated protein), ArgBP2 (Arg-binding protein 2). Proteins in this family share a sorbin homology (SoHo) domain at their N-terminal half. Functions of SoHo domain are not well known, although it is seemed to be involved in the regulation of actin cytoskeleton. Here we screened the SoHo-binding protein to clarify the function of SoHo domains and found that the fragment of alpha actin could bound to vinexin SoHo domain in two-hybrid system. The interaction of SoHo domain with alpha actin was confirmed by pull down assay and co-immunoprecipitation. Furthermore, the SoHo domain of vinexin was co-precipitated with filamentous actin. Interestingly, SoHo domains of other proteins were also associated. with fliamentous actin. Together, these findings suggest that SoHo domain functions as an actin binding domain.To elucidate the function of vinexin in detail, we analyzed the vinexin knockout mice. Vinexin knockout mice were born, matured and bred as wild type mice. To examine the function in cultured cell, we isolated primary fibroblast from embryo. Unlike to the overexpression of vinexin, knockout of vinexin gene did not affect the activation of ERK or anchorage-dependence of ERK signaling. However, it affected the cell motility. Together these finding suggested that vinexin is involved in cell migration.