Referenced in: none

Automatically associated channels: Kir2.3 , Kv11.1 , Kv7.1

Title: LQT2 nonsense mutations generate trafficking defective NH2-terminally truncated channels by the reinitiation of translation.

Authors: Matthew R Stump, Qiuming Gong, Zhengfeng Zhou

Journal, date & volume: Am. J. Physiol. Heart Circ. Physiol., 2013 Nov 1 , 305, H1397-404

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/23997099

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.