title: Trafficking-deficient hERG K⁺ channels linked to long QT syndrome are regulated by a microtubule-dependent quality control compartment in the ER.
abstract: The human ether-a-go-go related gene (hERG) encodes the voltage-gated K(+) channel that underlies the rapidly activating delayed-rectifier current in cardiac myocytes. hERG is synthesized in the endoplasmic reticulum (ER) as an "immature" N-linked glycoprotein and is terminally glycosylated in the Golgi apparatus. Most hERG missense mutations linked to long QT syndrome type 2 (LQT2) reduce the terminal glycosylation and functional expression. We tested the hypothesis that a distinct pre-Golgi compartment negatively regulates the trafficking of some LQT2 mutations to the Golgi apparatus. We found that treating cells in nocodazole, a microtubule depolymerizing agent, altered the subcellular localization, functional expression, and glycosylation of the LQT2 mutation G601S-hERG differently from wild-type hERG (WT-hERG). G601S-hERG quickly redistributed to peripheral compartments that partially colocalized with KDEL (Lys-Asp-Glu-Leu) chaperones but not calnexin, Sec31, or the ER golgi intermediate compartment (ERGIC). Treating cells in E-4031, a drug that increases the functional expression of G601S-hERG, prevented the accumulation of G601S-hERG to the peripheral compartments and increased G601S-hERG colocalization with the ERGIC. Coexpressing the temperature-sensitive mutant G protein from vesicular stomatitis virus, a mutant N-linked glycoprotein that is retained in the ER, showed it was not restricted to the same peripheral compartments as G601S-hERG at nonpermissive temperatures. We conclude that the trafficking of G601S-hERG is negatively regulated by a microtubule-dependent compartment within the ER. Identifying mechanisms that prevent the sorting or promote the release of LQT2 channels from this compartment may represent a novel therapeutic strategy for LQT2.
authors.affiliation: Department of Physiology, University of Kentucky, Lexington, Kentucky, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Smith
authors.forename: Christie M
authors.initials: CM
authors.lastname: McBride
authors.forename: Parvathi S
authors.initials: PS
authors.lastname: Nataraj
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Bartos
authors.forename: Craig T
authors.initials: CT
authors.lastname: January
authors.forename: Brian P
authors.initials: BP
authors.lastname: Delisle
mesh_terms: D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D015153:Blotting, Western; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D051638:Ether-A-Go-Go Potassium Channels / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins; D057809:HEK293 Cells; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D009154:Mutation; D032383:Myocytes, Cardiac / Q000378:metabolism; D015739:Nocodazole / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010880:Piperidines / Q000494:pharmacology; D021381:Protein Transport; D011725:Pyridines / Q000494:pharmacology; D050257:Tubulin Modulators / Q000494:pharmacology
chemical_list: D000889:Anti-Arrhythmia Agents; D051638:Ether-A-Go-Go Potassium Channels; D010880:Piperidines; D011725:Pyridines; D050257:Tubulin Modulators; C063968:E 4031; D049452:Green Fluorescent Proteins; D015739:Nocodazole