Sialosyl Le^a-carrying gangliosides present on the surface of colon carcinoma cells are not directly involved in adhesion to E-selectin

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• 作者：Anna Laskowska ; Barbara Doliń ; ska-Krajewska ; Maciej Zabel ; Maciej Ugorski
• 关键词：Cancer ; adhesion ; sialosyl Lewis ^a antigen ; gangliosides ; mucins ; E selectin
• 刊名：European Journal of Cell Biology
• 出版年：2001
• 出版时间：December 2001
• 年：2001
• 卷：80
• 期：12
• 页码：784-791
• 全文大小：281 K

文摘

We have shown previously that human colon cancer CX-1 cells contain lipid- and protein-bound sialosyl Lewis ^a structures that support the adhesion of these cells to E-selectin. Treatment of cancer cells with O-sialoglycoprotease did not decrease either the binding of anti-sialosyl Le^a antibodies or binding to E-selectin-expressing CHO cells. This suggested that cleavage of sialomucins uncovered cryptic sialosyl Le^a gangliosides that support such interactions. In the present study, inhibitors of glycolipid and O-glycan biosynthesis, d, l-threo-PPPP and GalNAc-α-O-benzyl, respectively, were used to study whether the binding of anti-sialosyl Le^a antibody and adhesion of CX-1 cells to E-selectin can be mediated by sialosyl Le^a gangliosides. Treatment of cancer cells with each of the inhibitors decreased the expression of the respective glycoconjugates as shown by TLC-binding assay and immunoblotting with anti-sialosyl Le^a antibody. However, only slight differences in binding of anti-sialosyl Le^a antibody to the surfaces of control and inhibitor-treated CX-1 cells were found by flow cytometry, as well no differences were observed in binding of control and inhibitor-treated CX-1 cells to E-selectin-expressing CHO cells, supporting the earlier hypothesis on the involvement of gangliosides in binding of anti-sialosyl Lewis ^a in the partial absence of mucin O-glycans. This hypothesis was further proven by electron microscopy data. Both native CX-1 and d, l-threo-PPPP-treated cells were labelled with anti-sialosyl Lewis ^a antibody mostly at a distance 70 – 90 nm from cell surface, suggesting interaction with protein-bound carbohydrate structures only. In contrast, the cancer cells treated with GalNAc-α-O-benzyl showed most of the staining around 20 nm distance from the plasmalemma, implying that the antibody interacts with lipid-bound sialosyl Lewis ^a instead. The electron microscopy data in conjunction with other results described in this report strongly support the hypothesis that sialosyl Le^a gangliosides are not involved in the adhesion of CX-1 cells to E-selectin when mucins are present on the cell surface, but they may be involved in binding to E-selectin in their absence.