Human ovarian surface epithelium (OSE), regarded as the precursor cell of epithelial ovarian adenocarcinoma, is not a fully developed epithelium when situated on the ovarian surface. It lacks epithelial characteristics such as the cell-cell adhesion factor epithelial (E)-cadherin, but as we have shown earlier, this OSE can form functional tight junctions (TJs) in culture. Recent gene-expression data on ovarian adenocarcinoma has pointed out a family of TJ proteins, the claudins, to be highly expressed in malignant compared to benign ovarian tumours. The purpose of this study was to investigate the distribution of claudin 1-5 proteins in cultured OSE (n=4), normal ovarian (n=11), benign (n=8), borderline (n=7) and ovarian cancer (n=22) tissues. We found that a weak or absence of expression of claudin 3 and claudin 4 in surface OSE changed to typical cell-border localisation in OSE of inclusion cysts in the normal ovarian stroma. Semiquantitative estimations of immunoblots showed that claudin 3 was significantly increased in ovarian adenocarcinomas compared to benign and borderline-type tumours. Claudin 4 was significantly increased in both borderline-type and ovarian adenocarcinomas compared to benign tumours, whereas no changes were found for claudin 1 or 5. Concerning relation to Federation for International Gynaecology and Obstetrics (FIGO) grade, claudin 3, but not claudin 4, was significantly increased in moderately, poorly and undifferentiated adenocarcinomas compared to well-differentiated and borderline-type tumours. No significant changes were noticed for any claudin with regard to FIGO stages. We conclude that both claudin 3 and 4, even though they differ in expression during ovarian malignant transformation, might be used as novel markers for ovarian tumours. The observations of lack of claudin 4 and low expression of claudin 3 in OSE strengthen our current knowledge about the biological nature of these cells as an undeveloped epithelium.
Copyright (c) 2005 Wiley-Liss, Inc.