Expression of L-PHA-binding proteins in breast cancer: Reconstitution and molecular characterization of β1-6 branched oligosaccharides in three-dimensional cell culture

Expression of β1-6 branched oligosaccharides in human breast cancer cells was investigated in vivo and in vitro. Lectin histochemical and lectin blotting analyses of surgically resected specimens were performed using L-PHA (phaseolus vulgaris leukoagglutinin) lectin, which binds to β1-6 oligosaccharides. The glycoproteins bearing β1-6 oligosaccharides of breast cancer tissues were found to be 170 kD and 120 kD in molecular weight, and the former appeared to be an epitope of carcinoembryonic antigen (CEA). The β1-6 oligosaccharides were expressed in both cancer cell lines at the outer layer of the colonies when cultured in type I collagen, but not in agarose gel. No correlation was observed between β1-6 expression and cell cycle. The β1-6 oligosaccharides did not coincide with breast cancer-associated antigens, such as CEA, MUC1, and cathepsin D. The β1-6 oligosaccharides of these cell lines were markedly inhibited when swainsonine, a mannosidase II inhibitor, was added to the culture medium. The 120 kD molecule, which was obtained from MCF-7 cells cultured in type I collagen gel, was consistent with that of breast cancer tissues and was similar to lysosome-associated membrane glycoproteins (LAMPs). The results suggest that the glycoproteins bearing β1-6 branched oligosaccharides in human breast cancer incorporate an epitope of CEA and human LAMPs and that the expression of LAMPs may depend on their surrounding matrices and may play an important role in cancer invasion or metastasis.