Mouse mammary epithelial cells expressing a fusion protein of c-Fos and the estrogen receptor (FosER) formed highly polarized epithelial cell sheets in the absence of estradiol. β-Catenin and p120ctn were exclusively located at the lateral plasma membrane in a tight complex with the adherens junction protein, E-cadherin. Upon activation of FosER by estradiol addition, cells lost epithelial polarity within two days, giving rise to a uniform distribution of junctional proteins along the entire plasma membrane. Most of the β-catenin and p120ctn remained in a complex with E-cadherin at the membrane, but a minor fraction of uncomplexed cytoplasmic β-catenin increased significantly. The epithelial–mesenchymal cell conversion induced by prolonged estradiol treatment was accompanied by a complete loss of E-cadherin expression, a 70% reduction in β-catenin protein level, and a change in the expression pattern of p120ctn isoforms. In these mesenchymal cells, β-catenin and p120ctn were localized in the cytoplasm and in defined intranuclear structures. Furthermore, β-catenin colocalized with transcription factor LEF-1 in the nucleus, and coprecipitated with LEF-1–related proteins from cell extracts. Accordingly, β-catenin– dependent reporter activity was upregulated in mesenchymal cells and could be reduced by transient expression of exogenous E-cadherin. Thus, epithelial mesenchymal conversion in FosER cells may involve β-catenin signaling.

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Many previous reports have demonstrated that systemic administration of endostatin (ES), a proteolytic cleavage product of collagen type XVIII and an endogenous angiogenesis inhibitor, represses tumor angiogenesis in different preclinical tumor models with varying efficacy. For example, systemic delivery of recombinant ES to rat insulin promoter 1 (Rip1)T-antigen 2 (Tag2)-transgenic mice, a mouse model of pancreatic beta-cell carcinogenesis, has repressed tumor angiogenesis efficiently and with it, tumor growth. Here, we report that the transgenic expression of ES in Rip1ES-transgenic mice only interferes moderately with tumor growth in Rip1Tag2;Rip1ES double-transgenic mice. Tumor incidence is not reduced by the local expression of ES, and tumor outgrowth and progression to tumor malignancy are only retarded slightly. A significant effect of local ES expression on tumor angiogenesis is only apparent during the early stages of tumor development, where less angiogenic hyperplastic lesions are observed. Although efficiently produced and secreted by transgenic beta cells, locally expressed ES appears to be sequestered in the microenvironment, and its systemic levels are not increased. The results indicate that the antiangiogenic functions of ES critically depend on the mode of delivery and the site of expression: although its systemic application represses tumor angiogenesis and tumor growth efficiently, locally expressed ES appears to be less effective, and hence, additional mechanisms of solubilization or activation of latent ES seem to be required. These results have important implications about the modes of delivery used in antiangiogenic, therapeutic strategies, which are based on the antiangiogenic activities of ES.