A hERG mutation E1039X produced a synergistic lesion on IKs together with KCNQ1-R174C mutation in a LQTS family with three compound mutations

Jie Wu,Futoshi Toyoda,Takeru Makiyama,Andrew F James,Jules C Hancox,Hirohiko Kohjitani,Hideki Itoh,Qi Wang,Yuka Mizusawa,Hiroshi Matsuura,Seiko Ohno,Takashi Higaki,Wei-Guang Ding,Minoru Horie

doi:10.1038/s41598-018-21442-6

Abstract

Congenital long QT syndrome (LQTS) caused by compound mutations is usually associated with more severe clinical phenotypes. We identified a LQTS family harboring three compound mutations in different genes (KCNQ1-R174C, hERG-E1039X and SCN5A-E428K). KCNQ1-R174C, hERG-E1039X and SCN5A-E428K mutations and/or relevant wild-type (WT) cDNAs were respectively expressed in mammalian cells. IKs-like, IKr-like, INa-like currents and the functional interaction between KCNQ1-R174C and hERG-E1039X channels were studied using patch-clamp and immunocytochemistry techniques. (1) Expression of KCNQ1-R174C alone showed no IKs. Co-expression of KCNQ1-WT + KCNQ1-R174C caused a loss-of-function in IKs and blunted the activation of IKs in response to isoproterenol. (2) Expression of hERG-E1039X alone and co-expression of hERG-WT + hERG-E1039X negatively shifted inactivation curves and decelerated the recovery time from inactivation. (3) Expression of SCN5A-E428K increased peak INa, but had no effect on late INa. (4) IKs and IKr interact, and hERG-E1039X caused a loss-of-function in IKs. (5) Immunocytochemical studies indicated that KCNQ1-R174C is trafficking defective and hERG-E1039X is defective in biosynthesis/degradation, but the abnormities were rescued by co-expression with WT. Thus, KCNQ1-R174C and hERG-E1039X disrupted IKs and IKr functions, respectively. The synergistic lesion, caused by KCNQ1-R174C and hERG-E1039X in IKs, is very likely why patients showed more severe phenotypes in the compound mutation case.

Highlights

Congenital long QT syndrome (LQTS) is a life-threatening condition characterized by an abnormally prolonged QT interval on the electrocardiogram (ECG) and torsades de pointes (TdP)-triggered cardiac events such as syncope, cardiac arrest and sudden cardiac death[1,2]
LQTS caused by two compound mutations is relatively common, the arrhythmia associated with three different compound mutations is a rare case, which accounts for 0.2% of our LQTS cohort
The present study on the three-compound mutation case indicated that KCNQ1-R174C produced a mild inhibitory effect on IKs and hERG-E1039X caused an incomplete loss-of-function in IKr

Summary

Introduction

Congenital long QT syndrome (LQTS) is a life-threatening condition characterized by an abnormally prolonged QT interval on the electrocardiogram (ECG) and torsades de pointes (TdP)-triggered cardiac events such as syncope, cardiac arrest and sudden cardiac death[1,2]. Molecular genetic studies have revealed that congenital LQTS is linked to mutations in genes encoding for cardiac ion channels or their regulatory proteins. The KCNQ1 (Kv7.1) and KCNH2 (hERG or Kv11.1) genes respectively encode α-subunits of slow (IKs) and rapid (IKr) components of channels mediating delayed rectifier potassium (K+) currents. The SCN5A gene encodes the α-subunit of the predominant cardiac sodium channel (NaV1.5) that conducts the depolarizing sodium inward current and is mainly responsible for the initial depolarization in cardiomyocytes. Mutations in KCNQ1, hERG and SCN5A can cause LQTS through either a loss-of-function of potassium channels (IKs and IKr) or a gain-of-function of sodium channel leading to an increase in the late INa, lengthening the cardiac APD and manifesting as a prolonged QT interval[7].

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Results

Conclusion