Organizational diversity among distinct glycoprotein endoplasmic reticulum-associated degradation programs.
Protein folding and quality control in the early secretory pathway function as posttranslational checkpoints in eukaryote gene expression. Herein, an aberrant form of the hepatic secretory protein alpha1-antitrypsin was stably expressed in a human embryonic kidney cell line to elucidate the mechanisms by which glycoprotein endoplasmic reticulum-associated degradation (GERAD) is administered in cells from higher eukaryotes. After biosynthesis, genetic variant PI Z underwent alternative phases of secretion and degradation, the latter of which was mediated by the proteasome. Degradation required release from calnexin- and asparagine-linked oligosaccharide modification by endoplasmic reticulum mannosidase I, the latter of which occurred as PI Z was bound to the molecular chaperone grp78/BiP. That a distinct GERAD program operates in human embryonic kidney cells was supported by the extent of PI Z secretion, apparent lack of polymerization, inability of calnexin to participate in the degradation process, and sequestration of the glycoprotein folding sensor UDP-glucose:glycoprotein glucosyltransferase in the Golgi complex. Because UDP-glucose:glycoprotein glucosyltransferase sustains calnexin binding, its altered distribution is consistent with a GERAD program that hinders the reentry of substrates into the calnexin cycle, allowing grp78/BiP to partner with a lectin, other than calnexin, in the recognition of a two-component GERAD signal to facilitate substrate recruitment. How the processing of a mutant protein, rather than the mutation itself, can contribute to disease pathogenesis, is discussed.
Cabral
Christopher M
CM
Department of Pathology, Baylor College of Medicine, Houston, Texas 77030-3498, USA.
Liu
Yan
Y
Moremen
Kelley W
KW
Sifers
Richard N
RN
D000470:Alkaloids / Q000378:metabolism; D000818:Animals; D037281:Calnexin / Q000378:metabolism; D002240:Carbohydrate Sequence; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors / Q000378:metabolism; D005964:Glucosyltransferases / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism*; D006360:Heat-Shock Proteins; D006801:Humans; D018832:Molecular Chaperones / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism; D009842:Oligopeptides; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D020033:Protein Isoforms / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals; D021381:Protein Transport / Q000502:physiology*; D015842:Serine Proteinase Inhibitors / Q000378:metabolism; D014532:Uridine Diphosphate Glucose / Q000378:metabolism; D000515:alpha 1-Antitrypsin / Q000378:metabolism*
D000470:Alkaloids; D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; D006023:Glycoproteins; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009097:Multienzyme Complexes; D009842:Oligopeptides; D020033:Protein Isoforms; D021382:Protein Sorting Signals; D015842:Serine Proteinase Inhibitors; D000515:alpha 1-Antitrypsin; C065629:kifunensine; C073762:lysyl-aspartyl-glutamyl-leucine; D037281:Calnexin; D005964:Glucosyltransferases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D014532:Uridine Diphosphate Glucose