Structural characterization of intermediates in the biosynthetic pathway of neolacto glycosphingolipids: differential expression in human leukaemia cells.

The biosynthesis of neolacto glycosphingolipids is thought to proceed via reactions catalysed by the two enzymes beta 1-3-N-acetylglucosaminyltransferase (beta 1,3GlcNAcT) and beta 1-4 galactosyltransferase (beta 1,4GalT). In general, only the products of the latter enzyme have been isolated from tissues and structurally characterized. Among the GlcNAc beta 1-3-R glycosphingolipids, only lactotrioasylceramide (Lc3Cer, the initial product in the biosynthesis of neolacto glycosphingolipids) has been isolated and structurally characterized. Longer-chain glycosphingolipids with a terminal GlcNAc-beta 1-3-R structure are considered to be intermediates in the synthesis of complex neolacto glycosphingolipids. We have detected a series of GlcNAc beta 1-3-R glycosphingolipids in extracts obtained from human leukocytes isolated from patients with leukaemia using a monoclonal antibody (TE5) which specifically recognizes these compounds. The structures of three of these compounds purified from chronic myelocytic leukaemia (CML) cells have been determined using a combination of enzymatic, immunostaining and chemical methods. The compounds were found to have the following structures: GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (Lc3Cer) GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (nLc5Cer) GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc beta 1-1Cer (nLc7Cer) A longer-chain compound, apparently nLc9Cer, was also detected. TLC immunostaining analysis of glycosphingolipids isolated from cells obtained from patients with various leukaemias demonstrated that GlcNAc beta 1-3-R glycosphingolipids have a distribution that depends on the stage of differentiation and lineage of the cell population.(ABSTRACT TRUNCATED AT 250 WORDS)