The novel C-terminal KCNQ1 mutation M520R alters protein trafficking
Section snippets
Materials and methods
Molecular biology. For DNA diagnosis, informed consent according to the ethics committee of the University of Münster was obtained from all family members. DNA was isolated from venous EDTA blood and direct sequencing of the complete coding sequences of the LQT1 (KCNQ1) and the LQT2 (KCNH2) genes were performed. The mutation M520R of human Kv7.1 (NM_000218) was constructed using site-directed PCR mutagenesis and subsequently cloned into the pcDNA3 and pGEM-HE vectors for expression in mammalian
Case presentation
A family of 7 living members was referred for clinical and genetic consultation (Fig. 1); the 34-year-old female proband (III-1) was asymptomatic but had a prolongation of the heart-rate corrected QT-interval (QTc: 460–490 ms1/2). At a heart-rate of 54 bpm, the T-wave was small-based and tall, together with an isoelectric ST-segment. Transthoracic echocardiography revealed a discrete mitral valve prolaps. Other examinations including routine physical examination, exercise ECG, EEG, programmed
Discussion
We identified the novel KCNQ1 M520R mutation that co-segregates in a patient diagnosed with LQT1-syndrome. Analysis of family members showed that the heterozygous mutation carriers are characterized by a mild QTc prolongation, an isoelectric ST-segment together with a heart-rate in the lower normal range and a mitral valve prolaps indicating an intermediate probability for familial LQT-syndrome. Our heterologous ion channel expression data show that homomeric mutant channels failed to conduct
Acknowledgments
E.S.-B was funded by German Research Foundation, Germany (DFG Schu 1082/3-1) and the Ernst und Berta Grimmke-Stiftung, Germany. N.S. and K.C. were supported by The John and Birthe Meyer Foundation, the Velux foundation, and the Danish National Research Foundation, Denmark. N.H.N. received a research fellowship from the Danish Cardiovascular Research Academy (DaCRA).
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Cardiac Delayed Rectifier Potassium Channels in Health and Disease
2016, Cardiac Electrophysiology ClinicsA phosphoinositide 3-Kinase (PI3K)-serum- and glucocorticoid-inducible Kinase 1 (SGK1) pathway promotes Kv7.1 channel surface expression by inhibiting Nedd4-2 protein
2013, Journal of Biological ChemistryCitation Excerpt :In its recessive form, the Jervell and Lange-Nielsen syndrome (13), the disease additionally leads to hearing loss due to disturbances in the flow of potassium in the inner ear. The mechanism underlying the LQT syndrome is reflected in a loss of Kv7.1 function, frequently originating from trafficking disorders, and hence a decrease in number of channels in the plasma membrane (14–16). Nevertheless, the molecular and cellular mechanisms controlling the cell surface expression of Kv7.1 in cardiomyocytes and epithelial cells are still largely unknown.
Structure of a Ca<sup>2 +</sup>/CaM:Kv7.4 (KCNQ4) B-helix complex provides insight into M current modulation
2013, Journal of Molecular BiologyCitation Excerpt :The Kv7.1 mutant M520R51 corresponds to anchor position (14) in the 1–14 motif, Leu540 in Kv7.4 (Fig. 4b and d). In accordance with the buried nature of this position, the M520R change has been reported to disrupt both channel function and CaM binding.51 Two Kv7.2 mutations, R533Q26,52 and K562N,53 correspond to Kv7.4 positions Arg547 and Lys548 (Fig. 4b) that make electrostatic interactions with Ca2 +/N-lobe residues Glu54 and Asp50, respectively (Fig. 4e), and would disrupt these electrostatic contacts.
The rate-dependent biophysical properties of the LQT1 H258R mutant are counteracted by a dominant negative effect on channel trafficking
2010, Journal of Molecular and Cellular CardiologyCitation Excerpt :This indicates that the reduced current level is due to an impaired translocation to the plasma membrane of channel complexes carrying a mutant H258R subunit and that the H258R mutation has a dominant negative effect on the trafficking efficiency of the resulting mutant IKs channel complex. Reduced ion channel trafficking by itself can indeed lead to cardiac arrhythmias and is a well-known mechanism for LQT2 [46] but has recently also been described for the LQT1 isoform [47–54]. While the current density at + 60 mV is a convenient measure for functional expression, the cardiac action potential reaches this voltage for less than a millisecond during the initial peak and the subsequent plateau is situated between + 10 mV and − 30/− 40 mV depending on the size of the early repolarization (notch).
Novel mechanisms of trafficking defect caused by KCNQ1 mutations found in long QT syndrome
2009, Journal of Biological ChemistryCitation Excerpt :There are several other mutations not affecting the pore structure but causing functional impairment, most of which were identified in the C-terminal cytoplasmic region. Although the cytoplasmic region contained several functional domains (9–12), molecular mechanisms of KCNQ1 mutations in the cytoplasmic domain have not been fully elucidated. On the other hand, more information is available about the functional alterations caused by mutations in KCNH2 that encodes pore-forming α-subunits of another voltage-gated cardiac potassium channel, HERG.
Trafficking-deficient long QT syndrome mutation KCNQ1-T587M confers severe clinical phenotype by impairment of KCNH2 membrane localization: Evidence for clinically significant I<inf>Kr</inf>-I<inf>Ks</inf> α-subunit interaction
2009, Heart RhythmCitation Excerpt :Cellular processing and membrane trafficking is also a crucial determinant of KCNQ1 function. A variety of KCNQ1 mutations induce LQTS by preventing effective membrane trafficking.7,18–22 Critical domains for KCNQ1 trafficking have been identified in both the N- and C-terminal regions.18,21
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These authors joint first authorship.