Published online before print June 18, 2007, doi: 10.1161/CIRCULATIONAHA.107.708818
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(Circulation. 2007;116:17-24.)
© 2007 American Heart Association, Inc.
Arrhythmia/Electrophysiology |
Nonsense Mutations in hERG Cause a Decrease in Mutant mRNA Transcripts by Nonsense-Mediated mRNA Decay in Human Long-QT Syndrome
From the Division of Cardiovascular Medicine, Department of Medicine, Oregon Health and Science University, Portland (Q.G., Z.Z.); and Departments of Medicine and Cardiology (L.Z., G.M.V.) and Genetic Epidemiology Division (B.D.H.), LDS Hospital, Intermountain Healthcare and University of Utah, Salt Lake City.
Correspondence to Dr Zhengfeng Zhou, Division of Cardiovascular Medicine, Oregon Health and Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239. E-mail zhouzh{at}ohsu.edu
Received October 26, 2006; accepted May 8, 2007.
Background— Long-QT syndrome type 2 (LQT2) is caused by mutations in the human ether-a-go-go-related gene (hERG). More than 30% of the LQT2 mutations result in premature termination codons. Degradation of premature termination codon–containing mRNA transcripts by nonsense-mediated mRNA decay is increasingly recognized as a mechanism for reducing mRNA levels in a variety of human diseases. However, the role of nonsense-mediated mRNA decay in LQT2 mutations has not been explored.
Methods and Results— We examined the expression of hERG mRNA in lymphocytes from patients carrying the R1014X mutation using a technique of allele-specific transcript quantification. The R1014X mutation led to a reduced level of mutant mRNA compared with that of the wild-type allele. The decrease in mutant mRNA also was observed in the LQT2 nonsense mutations W1001X and R1014X using hERG minigenes expressed in HEK293 cells or neonatal rat ventricular myocytes. Treatment with the protein synthesis inhibitor cycloheximide or RNA interference–mediated knockdown of the Upf1 protein resulted in the restoration of mutant mRNA to levels comparable to that of the wild-type minigene, suggesting that hERG nonsense mutations are subject to nonsense-mediated mRNA decay.
Conclusions— These results indicate that LQT2 nonsense mutations cause a decrease in mutant mRNA levels by nonsense-mediated mRNA decay rather than production of truncated proteins. Our findings suggest that the degradation of hERG mutant mRNA by nonsense-mediated mRNA decay is an important mechanism in LQT2 patients with nonsense or frameshift mutations.