title: Defects in N-glycosylation induce apoptosis in yeast.
abstract: N-glycosylation in the endoplasmic reticulum is an essential protein modification and highly conserved in evolution from yeast to man. Defects of N-glycosylation in humans lead to congenital disorders. The pivotal step of this pathway is the transfer of the evolutionarily conserved lipid-linked core-oligosaccharide to the nascent polypeptide chain, catalysed by the oligosaccharyltransferase. One of its nine subunits, Ost2, has homology to DAD1, originally characterized in hamster cells as a defender against apoptotic death. Here we show that ost mutants, such as ost2 and wbp1-1, display morphological and biochemical features of apoptosis upon induction of the glycosylation defect. We observe nuclear condensation, DNA fragmentation as well as externalization of phosphatidylserine. We also demonstrate induction of caspase-like activity, both determined by flow cytometric analysis and in cell-free extracts. Similarly, the N-glycosylation inhibitor tunicamycin in combination with elevated temperature is able to challenge the apoptotic cascade. Heterologous expression of anti-apoptotic human Bcl-2 diminishes caspase activation, improves survival of cells and suppresses the temperature-sensitive growth defect of wbp1-1. Furthermore, accumulation of reactive oxygen species occurs in response to defective glycosylation. As deletion of the metacaspase YCA1 does not seem to abrogate glycosylation-induced apoptosis, we postulate a different proteolytic process to be involved in this death pathway.
authors.affiliation: Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universität Regensburg, Regensburg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Hauptmann
authors.forename: Constanze
authors.initials: C
authors.lastname: Riel
authors.forename: Leoni A
authors.initials: LA
authors.lastname: Kunz-Schughart
authors.forename: Kai-Uwe
authors.initials: KU
authors.lastname: Fröhlich
authors.forename: Frank
authors.initials: F
authors.lastname: Madeo
authors.forename: Ludwig
authors.initials: L
authors.lastname: Lehle
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017209:Apoptosis / Q000235:genetics; D020169:Caspases / Q000378:metabolism; D002467:Cell Nucleus / Q000648:ultrastructure; D053938:DNA Fragmentation; D005816:Genetic Complementation Test; D006031:Glycosylation / Q000187:drug effects; D006602:Hexosyltransferases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D017382:Reactive Oxygen Species / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D008565:Membrane Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D014415:Tunicamycin; D006602:Hexosyltransferases; C025620:dolichyl-diphosphooligosaccharide - protein glycotransferase; D020169:Caspases