Mechanistic Basis for Type 2 Long QT Syndrome Caused by KCNH2 Mutations that Disrupt Conserved Arginine Residues in the Voltage Sensor

Abstract

KCNH2 encodes the Kv11.1 channel, which conducts the rapidly activating delayed rectifier K+ current (IKr) in the heart. KCNH2 mutations cause type 2 long QT syndrome (LQT2), which increases the risk for life-threatening ventricular arrhythmias. LQT2 mutations are predicted to prolong the cardiac action potential (AP) by reducing IKr during repolarization. Kv11.1 contains several conserved basic amino acids in the fourth transmembrane segment (S4) of the voltage sensor that are important for normal channel trafficking and gating. This study sought to determine the mechanism(s) by which LQT2 mutations at conserved arginine residues in S4 (R531Q, R531W or R534L) alter Kv11.1 function. Western blot analyses of HEK293 cells transiently expressing R531Q, R531W or R534L suggested that only R534L inhibited Kv11.1 trafficking. Voltage-clamping experiments showed that R531Q or R531W dramatically altered Kv11.1 current (IKv11.1) activation, inactivation, recovery from inactivation and deactivation. Coexpression of wild type (to mimic the patients’ genotypes) mostly corrected the changes in IKv11.1 activation and inactivation, but deactivation kinetics were still faster. Computational simulations using a human ventricular AP model showed that accelerating deactivation rates was sufficient to prolong the AP, but these effects were minimal compared to simply reducing IKr. These are the first data to demonstrate that coexpressing wild type can correct activation and inactivation dysfunction caused by mutations at a critical voltage-sensing residue in Kv11.1. We conclude that some Kv11.1 mutations might accelerate deactivation to cause LQT2 but that the ventricular AP duration is much more sensitive to mutations that decrease IKr. This likely explains why most LQT2 mutations are nonsense or trafficking-deficient.

Large-scale mutational analysis of Kv11.1 reveals molecular insights into type 2 long QT syndrome

“…Since co-expression of WT can improve mutant Kv11.1 channel dysfunction 66 , functional studies of co-expressed channels are needed. For example, Kv11.1 G657R appears to behave similar to a Shaker channel mutation that converts it from a K + channel passing outward current to a K + channel passing inward current at negative voltages 67 What loss-of-function mechanism(s), if any, underlie the other Kv11.1 structural regions like the VSD 68 or the linker regions? Interestingly, as shown in Fig 1 , all reported SNPs lie in linker regions of the Kv11.1 protein lacking highly ordered structure except for the CCD, thus these areas may be more tolerant of amino acid substitutions.…”

R534C mutation in hERG causes a trafficking defect in iPSC-derived cardiomyocytes from patients with type 2 long QT syndrome

“…LQTS2 has been modeled in vitro using Xenopus oocytes or HEK293 cells to dissect the underlying genetic causes of hERG dysfunction 20–23 . However, these exogenous expression systems do not recapitulate the complex interactions between the various types of ion channels present in a human cardiomyocyte.…”

Kcnh2 and Kcnj8 interactively regulate skin wound healing and regeneration

“…In addition, kcnh2 protein transports potassium ions out of cells and mutations in this gene can cause long QT syndrome type 2. 32,33 Interestingly, another member of the potassium channel family, the kcnj8 protein, an integral membrane protein and inward-rectifier type potassium channel, has a greater tendency to allow potassium to flow into a cell rather than out of a cell. 34 In this study, using the mouse embryo skin wound as a model system, we show that Kcnh2 and Kcnj8 are differentially expressed between the regenerative (prior to embryonic day 14.5, E14.5) and nonregenerative state (after embryonic day 14.5, E14.5) of a mouse skin wound.…”

“…It encodes a voltage‐activated potassium channel and it shares sequence similarity with the Drosophila ether‐a‐go‐go (eag) gene. In addition, kcnh2 protein transports potassium ions out of cells and mutations in this gene can cause long QT syndrome type 2 . Interestingly, another member of the potassium channel family, the kcnj8 protein, an integral membrane protein and inward‐rectifier type potassium channel, has a greater tendency to allow potassium to flow into a cell rather than out of a cell …”