doi: 10.1161/CIRCULATIONAHA.105.570200
(Circulation. 2006;113:365-373.)
© 2006 American Heart Association, Inc.
Arrhythmia/Electrophysiology |
Most LQT2 Mutations Reduce Kv11.1 (hERG) Current by a Class 2 (Trafficking-Deficient) Mechanism
From the Departments of Medicine and Physiology (C.L.A., B.P.D., B.D.A., J.A.K., C.T.J.), University of Wisconsin-Madison, Madison, Wis; Departments of Medicine, Pediatrics and Molecular Pharmacology (M.L.W., D.J.T., M.J.A.), Mayo Clinic College of Medicine, Rochester, Minn; and Division of Cardiovascular Medicine (Q.G., Z.Z.), Department of Medicine, Oregon Health and Science University, Portland, Ore.
Correspondence to Craig T. January, MD, PhD, University of Wisconsin Hospital and Clinics, Section of Cardiology, H6/354 CSC, Box 3248, 600 Highland Ave, Madison, WI 53792. E-mail ctj{at}medicine.wisc.edu
Received June 20, 2005; revision received October 20, 2005; accepted November 11, 2005.
Background— The KCNH2 or human ether-a-go-go related gene (hERG) encodes the Kv11.1 
-subunit of the rapidly activating delayed rectifier K+ current (IKr) in the heart. Type 2 congenital long-QT syndrome (LQT2) results from KCNH2 mutations that cause loss of Kv11.1 channel function. Several mechanisms have been identified, including disruption of Kv11.1 channel synthesis (class 1), protein trafficking (class 2), gating (class 3), or permeation (class 4). For a few class 2 LQT2-Kv11.1 channels, it is possible to increase surface membrane expression of Kv11.1 current (IKv11.1). We tested the hypotheses that (1) most LQT2 missense mutations generate trafficking-deficient Kv11.1 channels, and (2) their trafficking-deficient phenotype can be corrected.
Methods and Results— Wild-type (WT)-Kv11.1 channels and 34 missense LQT2-Kv11.1 channels were expressed in HEK293 cells. With Western blot analyses, 28 LQT2-Kv11.1 channels had a trafficking-deficient (class 2) phenotype. For the majority of these mutations, the class 2 phenotype could be corrected when cells were incubated for 24 hours at reduced temperature (27°C) or in the drugs E4031 or thapsigargin. Four of the 6 LQT2-Kv11.1 channels that had a wild-type–like trafficking phenotype did not cause loss of Kv11.1 function, which suggests that these channels are uncommon sequence variants.
Conclusions— This is the first study to identify a dominant mechanism, class 2, for the loss of Kv11.1 channel function in LQT2 and to report that the class 2 phenotype for many of these mutant channels can be corrected. This suggests that if therapeutic strategies to correct protein trafficking abnormalities can be developed, it may offer clinical benefits for LQT2 patients.
CLINICAL PERSPECTIVE
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