Nuclear localization of beta-catenin in normal and carcinogenic endometrium.

We have previously shown that the connexin (Cx) 26 and 32 genes are expressed during the secretory phase of the human endometrium and that their expression is downregulated during the proliferative phase, suggesting a role for intercellular transduction in cell growth control in human endometrium. To further study the possible role of cell-to-cell interaction in growth regulation, we immunohistochemically analyzed 80 endometrial samples (30 of normal endometrium, 20 of endometrial hyperplasia, and 30 of endometrial cancer) for the expression of E-cadherin; alpha-, beta-, and gamma-catenin; adenomatous polyposis coli (APC) protein, and sex-steroid hormone receptors at three points in the cells: the cell-to-cell border, the cytoplasm, and the nucleus. In this study, moderate or strong staining of beta-catenin in the nuclei was observed in 60.0% of endometrial hyperplasia samples and 30.0% of endometrial cancer samples, although the beta-catenin gene was mutated in only two of the nine samples that showed the intensive nuclear staining. Western blotting analysis showed that the samples that had intense nuclear staining of beta-catenin had much higher expression of beta-catenin than the samples that did not have nuclear staining. Furthermore, normal endometrium showed nuclear localization, especially in the mid- and late-proliferative and early-secreting phases of the menstrual cycle. The results suggest that the nuclear localization of beta-catenin observed in endometrial hyperplasia and endometrial cancer, as in other tumors, implies that beta-catenin/Wnt-1 signal transduction is highly activated in carcinogenesis of the endometrium as well as in normal physiological conditions.