MODULATION OF E-CADHERIN EXPRESSION IN TPA-INDUCED CELL MOTILITY - WELL-DIFFERENTIATED HUMAN ADENOCARCINOMA CELLS MOVE AS COHERENT SHEETS ASSOCIATED WITH PHOSPHORYLATION OF E-CADHERIN-CATENIN COMPLEX

We previously presented a two-dimensional cell motility assay using L- 10, a highly metastatic variant of the human rectal adenocarcinoma cel l line RCM-1, as a motility model of tumor cells of epithelial origin. In this model, L-10 cells moved outward from the cell islands mainly as a localized coherent sheet of cells when stimulated with 12-O-tetra decanoylphorbol-13-acetate (TPA). Electronmicroscopic Study of the mig rating cell sheets revealed that wide intercellular gaps had developed at the lower portion of the cells, allowing them to extend leading la mellae, whereas close cell-cell contacts remained at the upper portion of the cells. In the present study, the mechanism involved in this lo calized modulation of cell-cell adhesion at the lower portion of the c ells was investigated with special reference to E-cadherin expression. E-cadherin immunostaining, which was demonstrated using an anti-E-cad herin mAb, HECD-1, was decreased in migrating L-10 cell sheets, Appare ntly, however, E-cadherin was involved in the sheet formation of migra ting cells because simultaneous or sequential treatment with TPA and H ECD-1 inhibited sheet formation and caused scattering of migrating cel ls. With immunoelectron microscopic study, E-cadherin immunoreactivity was confined to the upper portion of migrating cells and lost at the lower portion. The level of E-cadherin and alpha-catenin expression wa s not altered by TPA treatment, although tyrosine phosphorylation of E -cadherin and catenins increased 1.6- to 1.9-fold. We propose that cel ls are released from cell-cell adhesion only at the lower portion of t he cells via phosphorylation of the E-cadherin-caterin complex when st imulated with TPA. This change allows the cells to extend leading lame lla and thus move together as coherent sheets (cohort migration).