title: Endoplasmic reticulum chaperones stabilize nicotinic receptor subunits and regulate receptor assembly.
abstract: We examined interactions between the endoplasmic reticulum (ER) chaperones calnexin (CN), ERp57, and immunological heavy chain-binding protein (BiP) and nicotinic acetylcholine receptor (nAChR) subunits. The three chaperones rapidly associate with newly synthesized nAChR subunits. Interactions between nAChR subunits and ERp57 occur via transient intermolecular disulfide bonds and do not require subunit N-linked glycosylation. The associations of ERp57 or CN with AChR subunits are long lived and prolong subunit lifetime approximately 10-fold. Coexpression of CN or ERp57 alone does not affect nAChR assembly or trafficking, but together they cause a significant decrease in nAChR expression and assembly. In contrast, associations with BiP are shorter lived and do not alter nAChR expression and assembly. However, a mutated BiP that slows its dissociation significantly increases its associations and decreases nAChR expression and assembly. Our results suggest that interactions with the chaperones regulate the levels of nAChRs assembled in the ER by stabilizing and sequestering subunits during assembly.
authors.affiliation: Department of Neurobiology and Committee on Neurobiology, University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Christian P
authors.initials: CP
authors.lastname: Wanamaker
authors.forename: William N
authors.initials: WN
authors.lastname: Green
mesh_terms: D000818:Animals; D015153:Blotting, Western; D037281:Calnexin / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002458:Cell Fractionation; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D000939:Epitopes; D050485:GABA Plasma Membrane Transport Proteins; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007457:Iodine Radioisotopes / Q000378:metabolism; D007668:Kidney / Q000166:cytology; D008954:Models, Biological; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011233:Precipitin Tests; D011485:Protein Binding; D019704:Protein Disulfide-Isomerases / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000096:biosynthesis* / Q000737:chemistry*; D012995:Solubility; D013347:Subcellular Fractions / Q000378:metabolism; D014101:Torpedo / Q000378:metabolism; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D000939:Epitopes; D050485:GABA Plasma Membrane Transport Proteins; D006360:Heat-Shock Proteins; D007457:Iodine Radioisotopes; D018832:Molecular Chaperones; D011978:Receptors, Nicotinic; D037281:Calnexin; C072207:betaine plasma membrane transport proteins; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human