TUMOR-CELL SURFACE BETA-1-4-LINKED GALACTOSE BINDS TO LECTIN(S) ON MICROVASCULAR ENDOTHELIAL-CELLS AND CONTRIBUTES TO ORGAN COLONIZATION

Cell surface carbohydrate structures acting as ligands for tissue specific mammalian lectins have been implicated in cell-cell interactions during embryogenesis, lymphocyte homing, and tumor cell metastasis. In this report, we provide evidence that β1-4 linked galactose (Gal) residues in N-linked oligosaccharides on the surface of blood born tumor cells serve as a ligand for binding to microvascular endothelial cells. D36W25, a class 1 glycosylation mutant of the MDAY-D2 lymphoreticular tumor cell line, lacks sialic acid and Gal in cellular glycans due to a defect in the Golgi UDP-Gal transporter. Using UDP-Gal and bovine galactosyltransferase in vitro, β1-4 Gal was restored to the surface of the cells and 70% of the galactosylated glycans persisted for 8 h in vitro at 37°C. Compared to mock-treated D36W25 cells, galactosylated D36W25 cells showed an 80% increase in binding to microvascular endothelial cell monolayers in vitro. The enhanced binding of galactosylated D36W25 cells to endothelial cell was inhibited by the addition of lactosamine-conjugated albumin to the assay. Consistent with these observations, swainsonine and castinospermine, two inhibitors of N-linked processing that result in loss of lactosamine antennae inhibited the binding of wild-type MDAY-D2 cells to endothelial cells in vitro. Injection of radiolabeled tumor cells into the circulation of syngeneic mice, showed that galactosylation of D36W25 cells resulted in 2-3 more tumor cells retained in the lungs and livers. In addition, galactosylation of D36W25 cells increased by 30-fold the number of visible liver metastases on inspection 4 wk after tumor cell injection. These results suggest that β1-4Gal-binding lectins on microvascular endothelial cells can contribute to retention and secondary tumor formation of blood born tumor cells. With the increasing availability of purified glycosyl-transferases, reconstruction of a variety of carbohydrate sequences on the surface of class 1 mutants provides a controlled means of studying carbohydrate-lectin interactions on viable cells.