Subcellular localization of galactosyltransferase associated with tumors in endometrial and ovarian cancer cells

Frozen or resin sections of normal human endometrium, endometrial adenocarcinoma, and ovarian adenocarcinoma were examined with two monoclonal antibodies for galactosyltransferase associated with tumor (GAT) by immunofluorescence and immunoelectron microscopy. One antibody (MAb8628) stained the trans-cisternae of the Golgi apparatus, the trans-Golgi network, and the intracytoplasmic vesicles more intensely in cancer cells than in normal endometrial glandular cells. The other antibody (MAb8513) stained intracytoplasmic vesicles more intensely in cancer cells than in normal cells. MAb8513 also showed moderate staining of the trans-cisternae of the Golgi apparatus and trans-Golgi network in cancer cells, but only faint staining of these structures in normal glandular cells, indicating that GAT was overexpressed in the cancer cells. An immunofluorescence study using serial semithin cryosections (1 μm) demonstrated that the staining pattern of each antibody was different inside a single cancer cell, conforming to the two patterns mentioned above. The reason for this difference in staining remains unclear. GAT is a soluble form of β1,4-galactosyltransferase, so a difference in the cleavage site of the membrane-bound peptide may cause changes in immunoreactivity after its conversion to the soluble form (i.e., GAT) in endometrial or ovarian adenocarcinoma cells.