Chen J, Weber M, Um SY, Walsh CA, Tang Y, McDonald TV. A dual mechanism for I(Ks) current reduction by the pathogenic mutation KCNQ1-S277L.
PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2011;
34:1652-64. [PMID:
21895724 DOI:
10.1111/j.1540-8159.2011.03190.x]
[Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND
The hereditary long QT syndrome is characterized by prolonged ventricular repolarization that can be caused by mutations to the KCNQ1 gene, which encodes the α subunits of the cardiac potassium channel complex that carries the I(Ks) current (the β subunits are encoded by KCNE1). In this study, we characterized a deleterious variant, KCNQ1-S277L, found in a patient who presented with sudden cardiac death in the presence of cocaine use.
METHODS
The KCNQ1-S277L mutation was analyzed via whole-cell patch clamp, confocal imaging, surface biotinylation assays, and computer modeling.
RESULTS
Homomeric mutant KCNQ1-S277L channels were unable to carry current, either alone or with KCNE1. When co-expressed in a 50/50 ratio with WT KCNQ1, current density was reduced in a dominant-negative manner, with the residual current predominantly wild type. There was no change in the activation rate and minimal changes to voltage-dependent activation for both KCNQ1 current and I(Ks) current. Immunofluorescence confocal imaging revealed reduced surface expression of mutant KCNQ1-S277L, which was biochemically confirmed by surface biotinylation showing a 44% decrease in mutant surface expression. Expression of KCNQ1-S277L with human ether-a-go-go-related gene (HERG) did not significantly affect HERG protein or current density compared to KCNQ1-WT co-expression.
CONCLUSION
The KCNQ1-S277L mutation causes biophysical defects that result in dominant-negative reduction in KCNQ1 and I(Ks) current density, and a trafficking defect that results in reduced surface expression, both without affecting HERG/I(Kr) . KCNQ1-S277L mutation in the proband resulted in defective channels that compromised repolarization reserve, thereby enhancing the arrhythmic susceptibility to pharmacological blockage of I(Kr) current.
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