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Articles by T. Fushiki
Total Records ( 2 ) for T. Fushiki
  K Inouye , M Yasumoto , S Tsuzuki , S Mochida and T. Fushiki

Matriptase is a transmembrane serine protease that is strongly expressed in epithelial cells. The single-chain zymogen of matriptase is considered to have inherent activity, leading to its own activation (i.e. conversion to the disulphide-linked-two-chain form by cleavage after Thr–Lys–Gln–Ala–Arg614). Also, there is growing evidence that the activation of zymogen occurs at the cell surface and in relation to the acidification and lowering of ionic strength within cell-surface microenvironments. The present study aimed to provide evidence for the involvement of zymogen activity in its activation in physiologically relevant cellular contexts. For this purpose, the activity of a pseudozymogen form of recombinant matriptase (HL-matriptase zymogen) was examined using acetyl-l-Lys–l-Thr–l-Lys–l-Gln–l-Leu–l-Arg–4-methyl-coumaryl-7-amide as a substrate. HL-matriptase zymogen exhibited optimal activity toward the substrate pH ~6.0. The substrate hydrolysis at the pH value was hardly detected when NaCl was present at a concentration of 145 mM. In a buffer of pH 6.0 containing 5 mM NaCl, the activity of HL-matriptase zymogen was only ~30-times lower than that of the respective two-chain form. These findings suggest that the in vivo activation of matriptase zymogen occurs via a mechanism involving the zymogen activity.

  S Mochida , S Tsuzuki , K Inouye and T. Fushiki

Matriptase is a type-II transmembrane serine protease that is expressed strongly in the epithelial elements of various organs. In the small intestine, it is expressed prominently at the villus tip where aged epithelial cells undergo shedding and/or apoptosis. This observation, together with the ability of matriptase to cleave laminin (a basement membrane component critical for epithelial cell attachment), prompted us to hypothesize that it plays an important part in the removal of aged epithelial cells in the small intestine. We tested this hypothesis by determining whether a recombinant catalytic domain of rat matriptase (His6t-S-CD) causes detachment and/or apoptosis of small-intestinal epithelial IEC-6 cells. His6t-S-CD caused detachment of cells attached to laminin-coated plates but did not detach cells attached to fibronectin- or type-IV collagen-coated plates. Pre-treatment of laminin-coated plates with His6t-S-CD decreased the attachment of cells, suggesting that the recombinant matriptase caused detachment through a mechanism involving a direct effect on laminin. His6t-S-CD was also found to induce apoptosis in the cells cultured on laminin-coated plates, as assessed by annexin-V staining, DNA fragmentation and caspase-3 activity assays. These findings support our hypothesis regarding the role of matriptase in the small intestine.

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