Metabolic Flux through the Sialic Acid Pathway Selectively controls the Sialylation and Activity of Adhesion Molecules involved in Metastasis

Sialic acids are located at the termini of mammalian cell-surface glycostructures and play pivotal rolesin nature. They are mostly found in eukaryote cells and because of their negative charge and locationat the cell surface, mediate cell recognition and adhesion. In many cancers, sialylated structures suchas the sialyl Lewis antigens are over expressed and are correlated with malignacy. In this work we demonstrate that a high flux non-natural sugar analog can modulate sialylation making a pancreatic cancer cell line more migratory when tested using in vitro environments that mimic certain steps of the metastatic process. We demonstrated that surface expression of cancer-associated sialyl carbohydrate determinants such as sialyl Lewis X and sialyl Lewis A increases with increased flux through the sialicacid pathway while other epitopes, including Lewis X and RCA-lectin ligands decrease, suggesting that the overall number of glycoconjugates remains unchanged and only the level of sialylation is affected by increased metabolic flux. Glycoproteomic experiments demonstrated that the increased flux through the sialic acid pathway, which increases the intracellular pool of this sugar, inturn modulates the sialylation of individual glycoconjugates. Functional studies demonstrated significant differences in the biophysical properties of analog-treated cells relative to untreated cells; specific examples include enhanced CD44-selectin binding under flow as well as increased migrationon integrin and fibronectin substrates. These results indicate that cancer cells may adopt a strategy ofincreasing early steps of sialylation to modulate cell adhesion molecules involved in metastasis to become more aggressively malignant.