Paulussen Aimée D C, Raes Adam, Jongbloed Roselie J, Gilissen Ron A H J, Wilde Arthur A M, Snyders Dirk J, Smeets Hubert J M, Aerssens Jeroen
Department of Genetics and Cell Biology (CARIM/NUTRIM), University of Maastricht, P.O. Box 616 (#16), 6200 MD Maastricht, The Netherlands.
Cardiovasc Res. 2005 Aug 15;67(3):467-75. doi: 10.1016/j.cardiores.2005.05.017.
Mutations in the KCNH2 (hERG, human ether-à-go-go related gene) gene may cause a reduction of the delayed rectifier current I(Kr), thereby leading to the long QT syndrome (LQTS). The reduced I(Kr) delays the repolarisation of cardiac cells and renders patients vulnerable to ventricular arrhythmias and sudden death. We identified a novel mutation in a LQTS family and investigated its functional consequences using molecular and microscopic techniques.
Genetic screening in the LQTS family revealed a heterozygous frameshift mutation p.Pro872fs located in the C-terminus of the KCNH2 gene. The mutation leads to a premature truncation of the C-terminus of the hERG protein. p.Pro872fs channels lack 282 amino acids at the C-terminus and possess an extra 4-amino acid tail. Both the kinetic and biochemical properties of the p.Pro872fs and p.Pro872fs/WT channels were studied in HEK293 cells and resulted in a novel proof of concept for heterozygous LQTS mutations: homotetrameric p.Pro872fs channels displayed near-normal expression, trafficking, and channel kinetics. Unexpectedly, upon co-expression of p.Pro872fs and WT channels, the repolarising power (the proportion of hERG current contributing to the action potential as the percentage of the total current available) was substantially higher during action potential clamp experiments as compared to WT channels alone. This would lead to a shorter rather than a prolonged QT interval. However, at the same time, heterotetramerisation of p.Pro872fs and WT channels also caused a dominant negative effect on trafficking by an increase in ER retention of these heterotetrameric channels, which surpassed the former gain in repolarising power.
The LQTS phenotype in the studied family is caused by a mutation with novel properties. We demonstrate that a KCNH2 mutation that clinically leads to long QT syndrome causes at the cellular level both a "gain" and a "loss" of HERG channel function due to a kinetic increase in repolarising power and a decrease in trafficking efficiency of heteromultimeric channels.
KCNH2（hERG，人类醚 - 去极化相关基因）基因的突变可能导致延迟整流电流I(Kr)降低，从而引发长QT综合征（LQTS）。I(Kr)降低会延迟心肌细胞的复极化，使患者易患室性心律失常和猝死。我们在一个LQTS家族中鉴定出一种新的突变，并使用分子和显微镜技术研究其功能后果。
对该LQTS家族进行基因筛查发现，KCNH2基因的C末端存在一个杂合移码突变p.Pro872fs。该突变导致hERG蛋白C末端过早截断。p.Pro872fs通道在C末端缺少282个氨基酸，并具有一个额外的4个氨基酸的尾巴。在HEK293细胞中研究了p.Pro872fs和p.Pro872fs/WT通道的动力学和生化特性，得出了杂合LQTS突变的一个新的概念验证：同四聚体p.Pro872fs通道表现出接近正常的表达、转运和通道动力学。出乎意料的是，在共表达p.Pro872fs和WT通道时，与单独的WT通道相比，在动作电位钳实验中，复极化能力（hERG电流对动作电位的贡献占总可用电流的百分比）显著更高。这将导致QT间期缩短而非延长。然而，与此同时，p.Pro872fs和WT通道的异四聚化也通过增加这些异四聚体通道在内质网的滞留对转运产生显性负效应，这超过了之前复极化能力的增加。
所研究家族中的LQTS表型是由具有新特性的突变引起的。我们证明，临床上导致长QT综合征的KCNH2突变在细胞水平上由于复极化能力的动力学增加和异源多聚体通道转运效率的降低，导致HERG通道功能既有“增益”又有“损失”。
