Studying neoplastic transformation of telomerase immortalized human fibroblasts (cen3tel), we found that the transition from normal to tumorigenic cells was associated with the loss of growth contact inhibition, the acquisition of an epithelial-like morphology and a change in actin organization, from stress fibers to cortical bundles. We show here that these variations were paralleled by an increase in N-cadherin expression and relocalization of different adhesion molecules, such as N-cadherin, α-catenin, p-120 and β-catenin. These proteins presented a clear membrane localization in tumorigenic cells compared to a more diffuse, cytoplasmic distribution in primary fibroblasts and non-tumorigenic immortalized cells, suggesting that tumorigenic cells could form strong cell-cell contacts and cell contacts did not induce growth inhibition. The epithelial-like appearance of tumorigenic cells did not reflect a mesenchymal-epithelial transition; in fact, cen3tel cells expressed vimentin and did not express cytokeratins at all transformation stages. Moreover, they did not express epithelial proteins such as occluding and claudin-1. In contrast, ZO-1 showed higher levels and a more defined membrane localization in tumorigenic cells compared to non-tumorigenic cells; this confirms its role in adherens junction formation in mesenchymal cells and is in agreement with the strong cell-cell contact formation by neoplastically transformed cells. Finally, we found α-catenin and ZO-1 nuclear localization in non-transformed cells, suggestive of possible additional roles of these proteins besides cell junction formation.

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