Selectin ligands on human melanoma cells

Twelve established human melanoma lines were screened for surface expression of the carbohydrate antigens Lewis^a (Le^a), sialyl Lewis^a (SLe^a), dimeric sialyl Lewis^a (diSLe^a), sialyl Lewis(X) (SLe(X)) and dimeric sialyl Lewis(X) (diSLe(X)). None of the lines expressed SLe(X), but 11/12 were positive for diSLe(X)) and 7/12 were positive for SLe^a. Although both diSLe(X)) and SLe^a have been reported to bind to E-selectin, none of the melanoma lines exhibited E-selectin-dependent adhesion to activated human umbilical vein endothelial cells (HUVECs). Three melanoma lines infected with a retroviral vector carrying the cDNA for the human Lewis fucosyltransferase (FucT-III) subsequently expressed SLe(X) at their cell surface and exhibited E-selectin-dependent adhesion to activated HUVECs. Treatment of these transduced cells with inhibitors of O-linked or N-linked protein glycosylation significantly inhibited E-selectin -mediated adhesion, though fluorescence-activated cell sorter analysis indicated no decrease in cell surface expression of SLe(X), SLe^a or diSLe(X). This suggests that the majority of SLe(X)/SLe^a-type glycans endogenously produced by human melanoma cells are not protein-associated and do not mediate E-selectin-dependent adhesion. These results support the hypothesis that E-selectin-dependent adhesion requires presentation of SLe(X)-type moieties on appropriate glycoproteins.