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Heart Rhythm. 2016 May;13(5):1121-30. doi: 10.1016/j.hrthm.2016.01.012. Epub 2016 Jan 13.

hERG 1a LQT2 C-terminus truncation mutants display hERG 1b-dependent dominant negative mechanisms.

Author information

1
Department of Physiology & Cellular Biophysics, Columbia University, New York, New York.
2
Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, New York.
3
Cardiovascular Research Program, VA New York Harbor Healthcare System, Brooklyn, New York; Departments of Medicine, Cell Biology and Pharmacology, State University of New York Downstate Medical Center, Brooklyn, New York,; Department of Medicine, New York University School of Medicine, New York, New York.
4
Department of Physiology & Cellular Biophysics, Columbia University, New York, New York. Electronic address: aa3000@cumc.columbia.edu.

Abstract

BACKGROUND:

The human ether-à-go-go-related gene (hERG 1a) potassium channel is critical for cardiac repolarization. hERG 1b, another variant subunit, co-assembles with hERG 1a, modulates channel biophysical properties and plays an important role in repolarization. Mutations of hERG 1a lead to type 2 long QT syndrome (LQT2), and increased risk for fatal arrhythmias. The functional consequences of these mutations in the presence of hERG 1b are not known.

OBJECTIVE:

To investigate whether hERG 1a mutants exert dominant negative gating and trafficking defects when co-expressed with hERG 1b.

METHODS:

Electrophysiology, co-immunoprecipitation, and fluorescence resonance energy transfer (FRET) experiments in HEK293 cells and guinea pig cardiomyocytes were used to assess the mutants on gating and trafficking. Mutations of 1a-G965X and 1a-R1014X, relevant to gating and trafficking were introduced in the C-terminus region.

RESULTS:

The hERG 1a mutants when expressed alone did not result in decreased current amplitude. Compared to wild-type hERG 1a currents, 1a-G965X currents were significantly larger, whereas those produced by the 1a-R1014X mutant were similar in magnitude. Only when co-expressed with wild-type hERG 1a and 1b did a mutant phenotype emerge, with a marked reduction in surface expression, current amplitude, and a corresponding positive shift in the V1/2 of the activation curve. Co-immunoprecipitation and FRET assays confirmed association of mutant and wild-type subunits.

CONCLUSION:

Heterologously expressed hERG 1a C-terminus truncation mutants, exert a dominant negative gating and trafficking effect only when co-expressed with hERG 1b. These findings may have potentially profound implications for LQT2 therapy.

KEYWORDS:

Cardiomyocytes; Guinea pig; HEK293; I(Kr); KCNH2; LQT2; Potassium channel; Truncation mutants; hERG 1a; hERG 1b

PMID:
26775140
DOI:
10.1016/j.hrthm.2016.01.012
[Indexed for MEDLINE]

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