Calnexin-dependent enhancement of nicotinic acetylcholine receptor assembly and surface expression.
The muscle-type nicotinic acetylcholine receptor (AChR)2 is a pentameric membrane ion channel assembled in the endoplasmic reticulum from four homologous subunits by mechanisms that are insufficiently understood. Nascent AChR subunits were recently found to form complexes with the endoplasmic reticulum-resident molecular chaperone calnexin. To determine the contribution of this interaction to AChR assembly and surface expression, we have now used transient transfection of mouse AChR subunits and calnexin into non-muscle cells. Co-transfection of calnexin along with AChR subunits into COS and HEK 293 cells was found to enhance AChR subunit folding and assembly, and to decrease degradation rates of newly synthesized AChR alpha-subunits, resulting in elevated surface expression of assembled AChR. Moreover, inhibition of the interaction between endogenous calnexin and AChR by castanospermine resulted in decreased AChR subunit folding, assembly, and surface expression in muscle and HEK 293 cells. Together, these findings provide evidence that calnexin directly contributes to AChR biogenesis by promoting subunit folding and assembly.
Chang
W
W
Department of Pharmacological Sciences, State University of New York at Stony Brook, Stony Brook, New York 11794, USA.
Gelman
M S
MS
Prives
J M
JM
D000818:Animals; D019556:COS Cells; D002135:Calcium-Binding Proteins / Q000502:physiology*; D037281:Calnexin; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D007212:Indolizines / Q000494:pharmacology; D051379:Mice; D017510:Protein Folding; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014162:Transfection; D054836:Indolizidines
D002135:Calcium-Binding Proteins; D037281:Calnexin; D007212:Indolizines; D011978:Receptors, Nicotinic; C037806:castanospermine; D054836:Indolizidines