Establishment of Ryudocan Null Mouse and ELISA for Blood Levels of Ryudocan

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Focal adhesion formation on fibronectin requires two signals, i.e. one from the cell-binding domain of fibronectin and one from the heparin-binding domain. While the cell-binding domain is recognized by integrins, the cell surface molecules that recognize the heparin-binding domain have not been identified. Previous reports have demonstrated that ryudocan (syndecan-4), a heparan sulfate proteoglycan, is a component of focal adhesions and that anti-syndecan-4 antibody can promote focal adhesion formation. Thus, ryudocan is a candidate that recognizes the heparin-binding domain. To study the role of syndecan-4 in focal adhesion formation, we generated ryudocan null mice. Even in ryudocan (-/-) fibroblasts, focal adhesions were formed and actin fibers terminated normally at focal adhesions. However, neither the fibronectin heparin-binding fragment in a soluble form nor anti-ryudocan antibody promoted focal adhesion formation in ryudocan (-/-) fibroblasts cultured on the cell-binding fragment, promoted focal adhesion formation. Thus, the present study has revealed that the heparin-binding fragment in a soluble form requires ryudocan for focal adhesion formation, whereas one in a solid form could utilize not only ryudocan but also some unidentified cell surface molecules.