A KCNQ1 mutation contributes to the concealed type 1 long QT phenotype by limiting the Kv7.1 channel conformational changes associated with protein kinase A phosphorylation

Abstract

BACKGROUND Type 1 long QT syndrome (LQT1) is caused by loss-of-function mutations in the KCNQ1-encoded Kv7.1 channel that conducts the slowly activating component of the delayed rectifier K+ current (IKs). Clinically, the diagnosis of LQT1 is complicated by variable phenotypic expressivity, whereby approximately 25% of genotype-positive individuals present with concealed LQT1 (resting corrected QT [QTc] interval ≤ 460 ms). OBJECTIVE To determine whether a specific molecular mechanism contributes to concealed LQT1. METHODS We identified a multigenerational LQT1 family whereby 79% of the patients genotype-positive for p.Ile235Asn-KCNQ1 (I235N-Kv7.1) have concealed LQT1. We assessed the effect I235N-Kv7.1 has on IKs and the ventricular action potential (AP) by using in vitro analysis and computational simulations. RESULTS Clinical data showed that all 10 patients with I235N-Kv7.1 have normal resting QTc intervals but abnormal QTc interval prolongation during the recovery phase of an electrocardiographic treadmill stress test. Voltage-clamping HEK293 cells coexpressing wild-type Kv7.1 and I235N-Kv7.1 (to mimic the patients’ genotypes) showed that I235N-Kv7.1 generated relatively normal functioning Kv7.1 channels but were insensitive to protein kinase A (PKA) activation. Phosphomimetic and quinidine sensitivity studies suggest that I235N-Kv7.1 limits the conformational changes in Kv7.1 channels, which are necessary to upregulate IKs after PKA phosphorylation. Computational ventricular AP simulations predicted that the PKA insensitivity of I235N-Kv7.1 is primarily responsible for prolonging the AP with β-adrenergic stimulation, especially at slower cycle lengths. CONCLUSIONS KCNQ1 mutations that generate relatively normal Kv7.1 channels, but limit the upregulation of IKs by PKA activation, likely contribute to concealed LQT1.

Quantitative analysis of the Ca2+‐dependent regulation of delayed rectifier K+ current IKs in rabbit ventricular myocytes

“…, ; Bartos et al . ). The ISO‐ and Ca 2+ ‐dependent changes in I Ks biophysical properties are similar, and these effects may influence the voltage‐sensing and pore domains in a comparable fashion.…”

“…We conclude that β-adrenergic activation is able to stimulate I Ks in a manner independent of [Ca 2+ ] i ; however, the similar (and additive) effects might imply a common molecular shift. Specifically, several studies showed how PKA phosphorylation at S27 on the N-terminus of Kv7.1 leads to a reduction in drug sensitivity suggesting that PKA phosphorylation restricts allosteric drug binding because of changes in the molecular conformation of Kv7.1 (Yang et al 2009(Yang et al , 2013Bartos et al 2014). The ISO-and Ca 2+ -dependent changes in I Ks biophysical properties are similar, and these effects J Physiol 595.7 may influence the voltage-sensing and pore domains in a comparable fashion.…”

“…During β-adrenergic stimulation, Kv7.1 is phosphorylated by protein kinase A (PKA) on the amino terminus and causes an increase of I Ks that is important for normal AP shortening (Walsh & Kass, 1988;Marx et al 2002). Mutations that disrupt the β-adrenergic upregulation of I Ks are also linked to LQT1, further emphasizing the importance of this process (Heijman et al 2012;Bartos et al 2014). Interestingly, [Ca 2+ ] i can also influence I K (sum of I Kr and I Ks ), and β-adrenergic stimulation increases Ca 2+ transients (CaTs) in myocytes (Tohse, 1990;Bers, 2002).…”

Role of the Autonomic Nervous System in Atrial Fibrillation

“…59 The most important of these are I CaL , already discussed, the slow delayed-rectifier K + -current I Ks , and the inward-rectifier I K1 . I Ks is strongly enhanced by adrenergically-induced PKA-phosphorylation, 60 allowing it to offset the increased inward current resulting from adrenergic enhancement of I CaL and prevent EADs. 61 I K1 is important in setting the resting potential, contributing to repolarization reserve 62 and governing AF-dynamics.…”

Arrhythmogenic Cardiomyopathy in a Patient With a Rare Loss‐of‐Function KCNQ1 Mutation

“…Functionally, IKs is regulated by a number of interacting proteins and posttranslational modifications. [12][13][14][15][16] The IKs currents and the channel subunits KCNQ1 and KCNE1 proteins are regulated by the b-adrenergic-mediated protein kinase A-dependent phosphorylation, a process that might be pathogenic in heart failure. 14,[17][18][19][20] Likewise, IKs are calcium-responsive currents, partly because of interaction of the KCNQ1 with calmodulin, which is a constitutive component of the K + channels.…”