One critical step of
metastasis formation is the extravasation of
circulating tumor cells from the bloodstream. This process requires the dynamic interaction of
cell adhesion molecules like
E-selectin on endothelial cells with
carbohydrate ligands on
tumor cells. To characterize these
glycans in a comprehensible approach, the rolling, tethering, and firm adhesion of nine human tumor cell lines on human umbilical vein endothelial cells was analyzed using laminar flow adhesion assays. The tumor cell lines were grouped into three subsets by their canonical
E-selectin ligand status (
sialyl-Lewis A and X +/+, -/+, -/-) and their adhesiveness was compared after enzymatic, pharmacologic, chemical treatment or antibody blockade of the
tumor cells or endothelial cells, respectively.
Tumor cells were also screened regarding their
glycosyltransferase expression profile. We found that although
E-selectin and terminal α2,3-sialic
acid largely determined firm adhesion, adhesive events did not exclusively depend on the presence of
sialyl-Lewis A and/or
sialyl-Lewis X. Nevertheless, two of the three
sialyl-Lewis A/X-/-
tumor cells additionally or fully depended on
vascular cell adhesion molecule-1 for firm adhesion. The significance of O-GalNAc- and N-
glycans for adhesion varied remarkably among the
tumor cells. The
sialyl-Lewis A/X+/+ subset showed
glycoprotein-independent adhesion, suggesting a role of
glycolipids as well. All
sialyl-Lewis A/X-/-
tumor cells lacked FUT3 and FUT7 expression as opposed to
sialyl-Lewis A/X+/+ or -/+ cell lines. In summary, the
glycans on
tumor cells mediating endothelial adhesion are not as much restricted to
sialyl-Lewis A /X as previously assumed. The present study specifically suggests α2,3-linked
sialic acid, O-GalNAc
glycans,
glycosphingolipids, and FUT3/FUT7 products as promising targets for future studies.