title: Degradation of trafficking-defective long QT syndrome type II mutant channels by the ubiquitin-proteasome pathway.
abstract: Mutations in the human ether-a-go-go-related gene (hERG) cause chromosome 7-linked long QT syndrome type II (LQT2). We have shown previously that LQT2 mutations lead to endoplasmic reticulum (ER) retention and rapid degradation of mutant hERG proteins. In this study we examined the role of the ubiquitin-proteasome pathway in the degradation of the LQT2 mutation Y611H. We showed that proteasome inhibitors N-acetyl-L-leucyl-L-leucyl-L-norleucinal and lactacystin but not lysosome inhibitor leupeptin inhibited the degradation of Y611H mutant channels. In addition, ER mannosidase I inhibitor kifunensine and down-regulation of EDEM (ER degradation-enhancing alpha-mannosidase-like protein) also suppressed the degradation of Y611H mutant channels. Proteasome inhibition but not mannosidase inhibition led to the accumulation of full-length hERG protein in the cytosol. The hERG protein accumulated in the cytosol was deglycosylated. Proteasome inhibition also resulted in the accumulation of polyubiquitinated hERG channels. These results suggest that the degradation of LQT2 mutant channels is mediated by the cytosolic proteasome in a process that involves mannose trimming, polyubiquitination, and deglycosylation of mutant channels.
authors.affiliation: Division of Molecular Medicine, Department of Medicine, Oregon Health and Science University, Portland, Oregon 97239, USA.
authors.forename: Qiuming
authors.initials: Q
authors.lastname: Gong
authors.forename: David R
authors.initials: DR
authors.lastname: Keeney
authors.forename: Maurizio
authors.initials: M
authors.lastname: Molinari
authors.forename: Zhengfeng
authors.initials: Z
authors.lastname: Zhou
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000470:Alkaloids / Q000494:pharmacology; D015153:Blotting, Western; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006031:Glycosylation; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D007976:Leupeptins / Q000494:pharmacology; D008133:Long QT Syndrome / Q000235:genetics*; D009154:Mutation; D015221:Potassium Channels / Q000737:chemistry; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D012260:Ribonucleases / Q000737:chemistry / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors; D014162:Transfection; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000470:Alkaloids; D015853:Cysteine Proteinase Inhibitors; D004791:Enzyme Inhibitors; D007976:Leupeptins; D015221:Potassium Channels; D061988:Proteasome Inhibitors; D025801:Ubiquitin; C065629:kifunensine; C063261:acetylleucyl-leucyl-norleucinal; C067713:lactacystin; D049452:Green Fluorescent Proteins; D012260:Ribonucleases; D046988:Proteasome Endopeptidase Complex; C032854:leupeptin; D000111:Acetylcysteine