Long QT syndrome is a disease associated with delayed cardiac repolarization and prolonged QT intervals on the electrocardiogram, which can lead to ventricular arrhythmias and sudden death. The chromosome 7- linked inherited long QT syndrome (LQT2) is caused by mutations in the human ether-a-go-go-related gene (hERG). hERG encodes the pore-forming subunit of the rapidly activating delayed rectifier potassium channel in the heart. More than 200 hERG mutations have been identified in patients with LQT2. These LQT2 mutations result in decreased hERG channel function, which leads to action potential prolongation and cardiac arrhythmias. Most of the previous studies were focused on the analysis of mutant proteins and channel function. More than 30% of LQT2 mutations are nonsense, frameshift, or splice site mutations, which may affect hERG mRNA splicing and stability. However, the effect of LQT2 mutations on hERG mRNA splicing and stability are largely unexplored. In addition, most of the previous studies involved expressing disease-causing mutations in Xenopus oocytes or mammalian cell lines, but little is known about how LQT2 mutations function when expressed in cardiac myocytes.
The specific aims of this application are: 1) To study abnormal splicing of hERG mRNA caused by splice site mutations, 2) To study whether LQT2 mutations that carry premature termination codons cause a decrease in the level of hERG mRNA transcripts by nonsense mediated mRNA decay, and 3) To study pre-mRNA splicing, mRNA stability, protein trafficking, subcellular distribution, and pharmacological rescue of LQT2 mutants expressed in cardiac myocytes. We will use molecular biology, biochemical, and electrophysiological approaches to study LQT2 mutations expressed in HEK 293 cells and in neonatal and adult rat cardiac myocytes. We will also analyze the splicing patterns and stability of endogenously expressed hERG mRNA isolated from lymphocytes of patients carrying LQT2 mutations. The results from these studies will increase our knowledge of how LQT2 mutations lead to hERG channel dysfunction at both the mRNA and protein levels. Elucidating these mechanisms will not only strengthen our understanding of the pathogenesis of hERG mutations in human long QT syndrome, but will also provide invaluable information directed towards the development of new therapeutic strategies for long QT syndrome.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL068854-09
Application #
7844826
Study Section
Electrical Signaling, Ion Transport, and Arrhythmias Study Section (ESTA)
Program Officer
Wang, Lan-Hsiang
Project Start
2001-12-05
Project End
2011-07-14
Budget Start
2010-06-01
Budget End
2011-07-14
Support Year
9
Fiscal Year
2010
Total Cost
$336,452
Indirect Cost
Name
Oregon Health and Science University
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
096997515
City
Portland
State
OR
Country
United States
Zip Code
97239
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Gong, Qiuming; Stump, Matthew R; Zhou, Zhengfeng (2014) Position of premature termination codons determines susceptibility of hERG mutations to nonsense-mediated mRNA decay in long QT syndrome. Gene 539:190-7
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Stump, Matthew R; Gong, Qiuming; Zhou, Zhengfeng (2012) Isoform-specific dominant-negative effects associated with hERG1 G628S mutation in long QT syndrome. PLoS One 7:e42552
Zarraga, Ignatius Gerardo; Zhang, Li; Stump, Matthew R et al. (2011) Nonsense-mediated mRNA decay caused by a frameshift mutation in a large kindred of type 2 long QT syndrome. Heart Rhythm 8:1200-6
Gong, Qiuming; Stump, Matthew R; Zhou, Zhengfeng (2011) Inhibition of nonsense-mediated mRNA decay by antisense morpholino oligonucleotides restores functional expression of hERG nonsense and frameshift mutations in long-QT syndrome. J Mol Cell Cardiol 50:223-9
Stump, Matthew R; Gong, Qiuming; Zhou, Zhengfeng (2011) Multiple splicing defects caused by hERG splice site mutation 2592+1G>A associated with long QT syndrome. Am J Physiol Heart Circ Physiol 300:H312-8

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