Presence of erythroglycan on human K-562 chronic myelogenous leukemia-derived cells
Abstract
Total glycopeptides from human K-562 cells, labeled metabolically with [3H]glucosamine or [3H]mannose, were prepared by extracting the cells with organic solvents to remove lipids and by digesting the residue with pronase. 3H-labeled glycopeptides were fractionated on Sephadex G-50 revealing a high molecular weight fraction (M(r) = 7,000 to 11,000), comprising approximately 10% of the [3H]glucosamine and 25% of the [3H]mannose label. Digestion of this glycopeptide fraction with endo-β-galactosidase from Escherichia freundii, specific for a repeating structure of Gal(β1 → 4)GlcNAc(β1→3), results in the following four products as resolved by Bio-Gel P-2 gel filtration: 1) a disaccharide with the structure β-2-deoxy-2-acetamidoglucosyl → β-galactose; 2) a trisaccharide with the structure β-galactosyl → β-2-deoxy-2-acetamidoglucosyl → β-galactose; 3) a tetrasaccharide with the sequence α-N-acetylneuraminyl → β-galactosyl → β-2-deoxy-2-acetamidoglucosyl → β-galactose; and 4) a larger, complex fragment which contains mannose and β-2-deoxy-2-acetamidoglucose and which is probably the protein linkage region. In addition, visualization of radiolabeled glycoproteins by fluorography on polyacrylamide gels revealed a 105,000-dalton 'Band 3'-like glycoprotein and other bands that were sensitive to endo-β-galactosidase. These results indicate that the K-562 cell line bears a glycopeptide, erythroglycan, which has been found on erythrocytes, and that this polymer is expressed mainly in the fetal form as a linear chain.