title: Biosynthesis of the cancer-associated sialyl-Lea antigen.
abstract: A cancer-associated glycolipid antigen defined by monoclonal antibody 19-9 has the structure NeuAc alpha 2-3Gal Gal beta 1-3GlcNAc beta 1-3Gal beta 1-4Glc beta 1-Cer. We have (formula; see text) studied its biosynthesis by testing the capacity of a crude microsomal fraction of SW 1116 cells to catalyze the addition of fucosyl or sialyl residues from GDP-fucose or CMP-sialic acid to glycolipid or oligosaccharide precursors. When the tetrasaccharide NeuAc alpha 2-3Gal beta 1-3GlcNAc beta 1-3Gal beta 1-4Glc (LSTa) is incubated with GDP-[14C]fucose and SW 1116 microsomes, a 14C-labeled oligosaccharide is formed that can be separated from the incubation mixture on an affinity column containing antibody 19-9 bound to protein A-Sepharose. The product migrates slower than LSTa when analyzed by paper or thin-layer chromatography. After treatment with neuraminidase, it co-migrates with the pentasaccharide Gal beta 1-3GlcNAc beta 1-3Gal beta 1-4Glc (formula; see text) (LNF II) in both chromatographic systems. Similar experiments demonstrate that SW 1116 microsomes catalyze the addition of a sialyl residue to the tetrasaccharide Gal beta 1-3GlcNAc beta 1-3Gal beta 1-4Glc to form LSTa. However, when LNF II is incubated with CMP-[14C]sialic acid and SW 1116 microsomes, no 19-9-active product is detected by affinity chromatography or by paper or thin-layer chromatography. Results using glycolipid precursors are consistent with these findings and also demonstrate the presence of the Lewis fucosyltransferase in SW 1116 cells. Thus, the biosynthesis of the sialyl-Lea antigen proceeds by addition of sialic acid to a type 1 precursor chain by a sialyltransferase, followed by addition of fucose by the Lewis fucosyltransferase.
mesh_terms: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm / Q000032:analysis*; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002460:Cell Line; D005647:Fucosyltransferases / Q000378:metabolism; D005732:Gangliosides / Q000378:metabolism; D006017:Glycolipids / Q000378:metabolism; D006026:Glycoside Hydrolases; D006028:Glycosphingolipids / Q000032:analysis* / Q000302:isolation & purification; D006801:Humans; D008861:Microsomes / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D000951:Antigens, Neoplasm; D005732:Gangliosides; D006017:Glycolipids; D006028:Glycosphingolipids; C045461:ceramide heptassaccharide; D005647:Fucosyltransferases; D006026:Glycoside Hydrolases