Microtubule disruption in keratinocytes induces cell-cell adhesion throughactivation of endogenous E-cadherin

The association of the cytoskeleton with the cadherin-catenin complex is es sential for strong cell-cell adhesion in epithelial cells. In this study, w e have investigated the effect of microtubule organization on cell-cell adh esion in differentiating keratinocytes. When microtubules of normal human e pidermal keratinocytes (NHEKs) grown in low calcium media (0.05 mM) were di srupted with nocodazole or colcemid, cell-cell adhesion was induced through relocalization of the E-cadherin-catenin-actin complex to the cell periphe ry. This was accompanied by actin polymerization. Also, it was found that m icrotubule disruption-induced cell-cell adhesion was significantly reduced in more advanced differentiated keratinocytes. For example, when NHEK cells cultured under high calcium (1.2 mM) for 8 d and then in low calcium for I d were treated with nocodazole, there was no induction of cell-cell adhesi on. Also long-term treatment of a phorbol ester for 48 h inhibited nocodazo le-induced cell-cell adhesion of NHEK. Furthermore, this nocodazole-induced cell-cell adhesion could be observed in squamous cancer cell lines (A431 a nd SCC-5, -9, and -25) under low calcium condition, but not in the keratino cyte cell lines derived from normal epidermis (HaCaT, RHEK). On the other h and, HaCaT cells continuously cultivated in low calcium media regained a le ss differentiated phenotype such as decreased expression of cytokeratin 10, and increased K5; these changes were accompanied with inducibility of cell -cell adhesion by nocodazole. Together, our results suggest that microtubul e disruption can induce the cell-cell adhesion via activation of endogenous E-cadherin in non- or early differentiating keratinocytes. However, this i s no longer possible in advanced terminally differentiating keratinocytes, possibly due to irreversible changes effected by cell envelope barrier form ation.