ENHANCEMENT OF ADHESIVE PROPERTY OF EPITHELIAL-CELL LINE MM2T BY CULTURE IN THE PRESENCE OF METHYLATED VITAMIN-B-12

A thymic epithelial cell line Mm2T was cultured in a medium containing a high concentration (100 mu g/ml) of methylated vitamin B-12 (CH3-B- 12). After 19 days, cells were found to have a flat phenotype, to have lost the floating cells which were observed in the control cells at t he confluent stage, and to have acquired a resistance to trypsin. Howe ver, treatment of the CH3-B-12-treated cells with EDTA resulted in a d issociation of cell-to-cell contact and reaggregation was achieved by addition of Ca2+, indicating the involvement of Ca2+ ion in cell-to-ce ll contact. Electron microscopic analyses revealed that the CH3-B-12-t reated cells were nearly square in their vertical section, which was i n contrast to the dome-shaped feature of the control cells, and their cell-to-cell contact area was significantly widespread, as compared to those of the control, indicating that Mm2T cells acquires an adhesive property by treatment with CH3-B-12 Biochemical analyses of both cell s indicated that the concentration of glucosylceramide in the CH3-B-12 -treated cells was higher than that of the control. Free glucose chara cteristically inhibited the reattachment of cells dissociated with EDT A, suggesting the involvement of glucose in the cell-to-cell adhesion of CH3-B-12-treated cells. In addition, WGA-binding glycoconjugates we re intensely observed in the boundary region of CH3-B-12-treated cells by immunohistochemical staining, but not in that of the control cells . It is suggested that CH3-B-12 may affect the morphological alteratio n of Mm2T by enhancing cell adhesion through elevated expression of th e C-type lectin.