title: A polarized epithelial cell mutant deficient in translocation of UDP-galactose into the Golgi complex.
abstract: Two lectin-resistant mutants derived from a polarized epithelial cell line have been described (Meiss, H.K., Green, R.F., and Rodriguez-Boulan, E.J. (1982) Mol. Cell. Biol. 2, 1287-1294). One of these mutants, the Madin-Darby canine kidney strain II cell line resistant to Ricinus communis agglutinin (MDCKII-RCAr), has been further characterized, and the biochemical defect leading to its altered phenotype has been determined. MDCKII-RCAr cells are shown to be enriched in cell-surface glycoconjugates bearing terminal N-acetylglucosamine residues by in vitro exogalactosylation and by labeling with fluorescent lectins. Binding assays with a sialic acid-specific lectin reveal a 70-75% reduction in sialylation of cell-surface glycoconjugates. The defect is pleiotropic in nature, affecting glycoproteins as well as glycosphingolipids. Analysis of glycosphingolipids shows a strong reduction of galactose-containing glycosphingolipids. Almost 90% of the glycosphingolipids are identified as glucosyl-ceramide. The mutant is not deficient in galactosyl- and sialytransferase activities. However, Golgi vesicles isolated from MDCKII-RCAr cells translocate UDP-galactose at only 2% of the rate observed for vesicles from wild-type MDCKII cells. The deficiency is specific, because translocation rates of UDP-N-acetylglucosamine and CMP-sialic acid are comparable for vesicles isolated from MDCKII-RCAr cells and wild-type cells. Despite the inability to translocate UDP-galactose into the lumen of the Golgi apparatus, MDCKII-RCAr cells are able to form monolayers with normal apical and basolateral polarity as shown by plasma membrane domain-restricted exogalactosylation.
mesh_terms: D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D005700:Galactosyltransferases / Q000235:genetics* / Q000378:metabolism; D006028:Glycosphingolipids / Q000235:genetics* / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism*; D007700:Kinetics; D037102:Lectins; D009154:Mutation; D012799:Sialyltransferases / Q000235:genetics* / Q000378:metabolism; D014531:Uridine Diphosphate Galactose / Q000378:metabolism*; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000378:metabolism; D014539:Uridine Diphosphate Sugars / Q000378:metabolism*
chemical_list: D006028:Glycosphingolipids; D037102:Lectins; D014539:Uridine Diphosphate Sugars; D014531:Uridine Diphosphate Galactose; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid; D014537:Uridine Diphosphate N-Acetylglucosamine; D005700:Galactosyltransferases; D012799:Sialyltransferases