Effect of claudin expression on paracellular permeability, migration and invasion of colonic cancer cells

Alteration in the expression of claudins, consisting of tight junctions (TJs), has been reported in various clinically isolated tumors. Claudins play an important role not only in the intercellular barrier function of TJs but also in migration and invasiveness of cancer cells. However, the use of different types of cells and different claudins in these studies has complicated the picture. In this study, we systematically examined the effect of claudin (claudin-1, -2, -3, -4 and -15) overexpression on the paracellular permeability, migration and invasiveness of Caco-2 colonic cancer cells. Overexpression of claudin-4 or claudin-2 increased or decreased, respectively, paracellular permeability. Overexpression of claudin-4 specifically stimulated the invasive activity of the Caco-2 cells. Furthermore, activation of matrix metalloproteinase (MMP)-2 and MMP-9 were observed in the claudin-4- overexpressing cells, suggesting that the invasive activity was stimulated through an increase in MMP activity. Overexpression of claudin-2 or claudin-3 and -4 stimulated or inhibited, respectively, the migration activity of the Caco-2 cells. Immunostaining analysis revealed that each of the overexpressed claudins localized at TJs under the conditions used to evaluate paracellular permeability. In contrast, they localized mainly in intracellu- lar compartments under experimental conditions designed to assess cell invasion and migration. Overall, the results of this study show that the effect exerted by the claudins on the intercellular barrier function of TJs, as well as on cell migration and invasive activity, differs depending on the particular claudin species. Furthermore, the subcellular localization of the claudins varies according to the culture conditions.