WGA binding to the surface of two autologous human melanoma cell lines: Different expression of sialyl and N-acetylglucosaminyl residues

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Abstract
Two autologous human melanoma cell lines were studied to determine their capacities to bind wheat germ agglutinin (WGA). Both cell lines were divided from the same patient, the first, IGR 39, originated from the primary tumor, the second, IGR 37, was established from a metastatic lymph node. WGA binding sites on the surface of these cell lines were compared before and after sialidase and/or tunicamycin treatments. IGR 39 cells exhibited two classes of WGA binding sites with high and low affinities, whereas IGR 37 cells had only one class of high affinity binding sites. After tunicamycin treatment, the capacity of IGR 39 cells to bind WGA was markedly altered, since only one class of WGA binding sites with high affinity was observed under these conditions, whereas tunicamycin did not induce significant changes in the lectin binding of IGR 37 cells. The low affinity WGA binding sites, which were only found on IGR cells, corresponded to sialyl residues present in N-linked glycoproteins. The high affinty binding sites present on both cell lines probably involved sialyl and N-acetylglucosaminyl residues associated with O-linked glycoproteins and/or glycolipids. No direct correlation could be drawn between the number of WGA binding sites and the overall sialic acid levels exposed to sialidase treatment. The 3-fold increase in the amount of cell surface glycopeptides obtained after pronase digestion and specifically binding to WGA-Sepharose was in good agreement with the overall higher number of WGA binding sites on IGR 39 compared to IGR 37 cells. Thus, subtle carbohydrate change of cell surface glycoconjugates might account for the differences between the biological properties of human melanoma cell lines of low and high tumorigenicity.