title: Nonsense mutations in hERG cause a decrease in mutant mRNA transcripts by nonsense-mediated mRNA decay in human long-QT syndrome.
abstract: 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.
  
  
  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.
authors.affiliation: Division of Cardiovascular Medicine, Oregon Health and Science University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA.
authors.forename: Qiuming
authors.initials: Q
authors.lastname: Gong
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.forename: G Michael
authors.initials: GM
authors.lastname: Vincent
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Horne
authors.forename: Zhengfeng
authors.initials: Z
authors.lastname: Zhou
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000328:Adult; D000368:Aged; D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured / Q000378:metabolism; D018389:Codon, Nonsense; D003513:Cycloheximide / Q000494:pharmacology; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels / Q000172:deficiency / Q000235:genetics*; D005260:Female; D016368:Frameshift Mutation; D005813:Genes, Synthetic; D006801:Humans; D007668:Kidney; D008133:Long QT Syndrome / Q000151:congenital / Q000235:genetics* / Q000378:metabolism; D008214:Lymphocytes / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D032383:Myocytes, Cardiac / Q000378:metabolism; D010375:Pedigree; D017354:Point Mutation; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D020365:RNA Helicases; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015534:Trans-Activators / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology; D014162:Transfection
chemical_list: D018389:Codon, Nonsense; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D015534:Trans-Activators; D003513:Cycloheximide; D020365:RNA Helicases; C101828:UPF1 protein, human