STRUCTURAL DIFFERENCES BETWEEN COMPLEX-TYPE ASN-LINKED GLYCAN CHAINS OF GLYCOPROTEINS IN RAT HEPATOCYTES AND ZAJDELA HEPATOMA-CELLS

Using serial lectin-affinity chromatography, glycosidase digestion, and NMR and methylation analysis, the structures of complex N-linked glycan chains (M(r) range 2000-3500) of rat hepatocytes and poorly differentiated chemically transformed Zajdela ascites hepatoma cells were determined and compared. The results revealed considerable differences between the two cell types: (i) hepatoma cells only expressed tri- and/or tetra-antennary complex N-linked glycan chains, whereas hepatocytes displayed large amounts of bi-antennary N-linked structures and smaller amounts of tri-/tetra-antennary structures; (ii) 20% of the glycan chains in hepatoma cells contained a bisecting GlcNAc residue which was beta(1,4)-linked to the beta-mannosyl residue of the core and was not detected in the hepatocytes; (iii) hepatoma cells expressed a high proportion of the fucosylated or not GlcNAc beta(1,6) Man alpha 1 --> branch, whereas hepatocytes only contained a little of this branch; (iv) hepatoma cells, but not hepatocytes, exhibited a repeating (Gal beta(1,4) GlcNAc beta(1,3)) sequence characteristic of poly-N-acetyllactosaminoglycans. These glycans were capped by both alpha-galactosyl and sialyl residues; (v) The alpha(2,3)/alpha(2,6)-linkage ratio of sialic acid was significantly higher in hepatoma cells (4/1 vs. 2/1 in hepatocytes); (vi) Only hepatocytes expressed an unusual structure in which a sialyl residue was alpha(2,6)-linked to a GlcNAc residue located within a NeuAc alpha(2,3) Gal beta(1,3) GlcNAc branch which was beta(1,4)-linked to Man alpha 1,3 -->. The differences between these complex N-linked glycan chains in hepatocytes and hepatoma cells seem to be both quantitative and qualitative, since some glycan structures were only present in one cell type.