The organization of adherens junctions in mouse osteoblast-like cells (MC3T3-E1) and their modulation by triiodothyronine and 1,25-dihydroxyvitamin D3.

Cadherin-mediated cell-cell adhesion is essential for the development and survival of multicellular tissues. Thus it is hypothesized that these molecules also play a fundamental role for the development and maintenance of bone by mediating cellular crosstalk between osteogenic cells and by providing targets for the sorting and migration of osteogenic precursors toward the bone surface. We describe the localization of cadherin-11 and N-cadherin along the cell margins of mouse osteoblast-like cells, the colocalization of "pancadherin" with alpha-catenin, beta-catenin, p120, and vinculin, and the association of these complexes with the actin microfilaments. Furthermore, we measured the influence of cell confluency and the effects of the osteogenic hormones triiodothyronine (T3) and 1,25-dihydroxyvitamin D3 (D3) on these parameters. By mRNA studies we found the abundantly expressed cadherin-11 being unaffected during T3- and D3-induced osteoblastic differentiation. However, protein levels of N-cadherin and "pancadherin" were strongly suppressed by D3. We also observed a clear distinction in cadherin immunolocalization when comparing confluent control and confluent hormone-treated cultures. Immunoprecipitation experiments indicated that vinculin is part of the junctional complex, and that the association of "pancadherin"/beta-catenin is strongly increased after treatment with T3 which might influence the functional competence of cell-cell contacts. Thus, this study demonstrates the molecular organization of adherens junctions in mouse osteoblastic MC3T3-E1 cells and their sensitivity to the osteogenic factors T3 and D3 in confluent cultures.