Subcellular localization of blood group Leb carbohydrate antigen (MSN-1-reactive antigen) in endometrial cancer cells.

MSN-1 is a monoclonal antibody, which was raised by immunizing mice with a human endometrial cancer cell line, SNG-II. The MSN-1 specifically recognizes a blood group carbohydrate antigen, Leb. We investigated the subcellular and suborganellar localization of the MSN-1-reactive carbohydrate antigens in the endometrial adenocarcinomas and the normal endometria using immunofluorescence microscopy, confocal laser scanning microscopy, and immunoelectron microscopy. In normal endometrium, the apical plasma membranes of endometrial glandular cells were weekly positive. In contrast, in endometrial adenocarcinoma specimens, the apical plasma membranes, the lateral plasma membranes, intracytoplasmic vesicular structures, and the Golgi apparatus were strongly positive. We also found that there are differences in the manner of the distribution of the MSN-1 antigen within the Golgi apparatus between the normal and tumor samples; namely, in the endometrial adenocarcinoma cells the antigens are found abundantly throughout the Golgi apparatus or tend to be located not only at the trans side but also close to the cis side, while the localization of this antigen in normal counterpart is restricted to the trans-Golgi cisternae. These findings imply that aberrant glycosylation occurs in endometrial adenocarcinomas, presumably as a result of abnormal expression of some glycosyltransferases involving the expression of the Leb carbohydrate antigen in the Golgi apparatus.