title: LQT2 nonsense mutations generate trafficking defective NH2-terminally truncated channels by the reinitiation of translation.
abstract: The human ether-a-go-go-related gene (hERG) encodes a voltage-activated K(+) channel that contributes to the repolarization of the cardiac action potential. Long QT syndrome type 2 (LQT2) is an autosomal dominant disorder caused by mutations in hERG, and patients with LQT2 are susceptible to severe ventricular arrhythmias. We have previously shown that nonsense and frameshift LQT2 mutations caused a decrease in mutant mRNA by the nonsense-mediated mRNA decay (NMD) pathway. The Q81X nonsense mutation was recently found to be resistant to NMD. Translation of Q81X is reinitiated at Met(124), resulting in the generation of NH2-terminally truncated hERG channels with altered gating properties. In the present study, we identified two additional NMD-resistant LQT2 nonsense mutations, C39X and C44X, in which translation is reinitiated at Met(60). Deletion of the first 59 residues of the channel truncated nearly one-third of the highly structured Per-Arnt-Sim domain and resulted in the generation of trafficking-defective proteins and a complete loss of hERG current. Partial deletion of the Per-Arnt-Sim domain also resulted in the accelerated degradation of the mutant channel proteins. The coexpression of mutant and wild-type channels did not significantly disrupt the function and trafficking properties of wild-type hERG. Our present findings indicate that translation reinitiation may generate trafficking-defective as well as dysfunctional channels in patients with LQT2 premature termination codon mutations that occur early in the coding sequence.
authors.affiliation: Knight Cardiovascular Institute, Oregon Health and Science University, Portland, Oregon.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Stump
authors.forename: Qiuming
authors.initials: Q
authors.lastname: Gong
authors.forename: Zhengfeng
authors.initials: Z
authors.lastname: Zhou
mesh_terms: D018389:Codon, Nonsense; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics / Q000378:metabolism*; D010442:Peptide Chain Initiation, Translational; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D059748:Proteolysis; D013997:Time Factors; D014162:Transfection
chemical_list: D018389:Codon, Nonsense; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human
keywords: Per-Arnt-Sim domain; human ether-a-go-go-related gene; long QT syndrome; potassium channels; protein trafficking