Tumor cell surface carbohydrate and the metastatic phenotype

The synthesis and expression of cell surface carbohydrates is a developmentally regulated process that appears to affect a number of cell-cell interactions. To determine whether specific oligosaccharide structures present on highly malignant cells are required for expression of the metastatic phenotype, we have isolated lectin resistant tumor cell mutants with defects in the biosynthesis of oligosaccharides. The mutants selected from the highly aggressive lymphoreticular-like tumor line MDAY-D2 were grouped into genetic complementation classes, compared for metastatic ability and for changes in cell surface glycoconjugates. The Asn-linked oligosaccharides and glycolipids of class 1 mutants were deficient in both sialic acid and galactose and the cells showed a greatly attenuated metastatic phenotype compared to the parental cells. A revertant of the class 1 mutation selected in vitro regained the wild type glycoconjugate profile and the highly metastatic phenotype indicating a direct association between the mutation and the loss of metastatic potential. Class 2 mutants remained highly metastatic and had Asn-linked oligosaccharide structures very similar to those found in the wild type cells with N-glycolylneuraminic acid rather than the N-acetylneuraminic acid. Swainsonine, an inhibitor of golgi alpha-mannosidase II, blocks the synthesis of complex-type Asn-linked oligosaccharides resulting in the expression of hybrid-type oligosaccharides at the cell surface and the cells display a lectin resistant phenotype. Although swainsonine inhibited neither tumor cell growth in vitro nor solid tumor growth in situ, the drug dramatically reduced the incidence of lung colonies after i.v. inoculation of both MDAY-D2 and B16F10 melanoma cells. These results, taken together, indicate that certain sialylated Asn-linked oligosaccharides found on metastatic tumor cells are required for expression of the metastatic phenotype.