Further studies on cell adhesion based on Lex-Lex interaction, with new approaches: embryoglycan aggregation of F9 teratocarcinoma cells, and adhesion of various tumour cells based on Lex expression

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Abstract
We previously proposed specific interaction of Lex (Galβ1 → 4[Fucα1 → 3]-GlcNAcβ1 → 3Gal) with Lex as a basis of cell adhesion in pre-implantation embryos and in aggregation of F9 teratocarcinoma cells, based on several lines of evidence (Eggenset al., J Biol Chem (1989)264:9476–9484). We now present additional evidence for this concept, based on autoaggregation studies of plastic beads coated with glycosphingolipids (GSLs) bearing Lex or other epitopes, and affinity chromatography on Lex-columns of multivalent lactofucopentaose III (Lex oligosaccharide) conjugated with lysyllysine. Comparative adhesion studies of Lex-expressing tumour cellsvs their Lex-non-expressing variants showed that only Lex-expressing cells adhere to Lex-coated plates and are involved in tumour cell aggregation, in analogy to F9 cell aggregation. The major carrier of Lex determinant in F9 cells is not GSL but rather polylactosaminoglycan (‘embryoglycan’), and we demonstrated autoaggregation of purified embryoglycan in the presence of Ca2+, and reversible dissociation in the absence of Ca2+ (addition of EDTA). Defucosylated embryoglycan did not show autoaggregation under the same conditions. Thus, Lex-Lex interaction has been demonstrated on a lactosaminoglycan basis as well as a GSL basis. A molecular model of Lex-Lex interaction based on minimum energy conformation with involvement of Ca2+ is presented.