Long QT Syndrome-Associated Mutations in KCNQ1 and KCNE1 Subunits Disrupt Normal Endosomal Recycling of IKs Channels

Department of Physiology I, University of Tuebingen, Germany.
Circulation Research (Impact Factor: 11.02). 12/2008; 103(12):1451-7. DOI: 10.1161/CIRCRESAHA.108.177360
Source: PubMed


Physical and emotional stress is accompanied by release of stress hormones such as the glucocorticoid cortisol. This hormone upregulates the serum- and glucocorticoid-inducible kinase (SGK)1, which in turn stimulates I(Ks), a slow delayed rectifier potassium current that mediates cardiac action potential repolarization. Mutations in I(Ks) channel alpha (KCNQ1, KvLQT1, Kv7.1) or beta (KCNE1, IsK, minK) subunits cause long QT syndrome (LQTS), an inherited cardiac arrhythmia associated with increased risk of sudden death. Together with the GTPases RAB5 and RAB11, SGK1 facilitates membrane recycling of KCNQ1 channels. Here, we show altered SGK1-dependent regulation of LQTS-associated mutant I(Ks) channels. Whereas some mutant KCNQ1 channels had reduced basal activity but were still activated by SGK1, currents mediated by KCNQ1(Y111C) or KCNQ1(L114P) were paradoxically reduced by SGK1. Heteromeric channels coassembled of wild-type KCNQ1 and the LQTS-associated KCNE1(D76N) mutant were similarly downregulated by SGK1 because of a disrupted RAB11-dependent recycling. Mutagenesis experiments indicate that stimulation of I(Ks) channels by SGK1 depends on residues H73, N75, D76, and P77 in KCNE1. Identification of the I(Ks) recycling pathway and its modulation by stress-stimulated SGK1 provides novel mechanistic insight into potentially fatal cardiac arrhythmias triggered by physical or psychological stress.

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    • "This being stated, KCNE1 effects could also involve other pathways for internalization, such as caveolae in lipid rafts, which also utilize dynamin, or ubiquitylation. The aspartate residue in the DPFNVY motif, D76, has been found by Seebohm et al. (2008) to be important for Rab 5 mediated internalization of KCNQ1-KCNE1 complexes in Xenopus oocytes. This residue is also the site of a LQTS mutation, D76N, which has a strong dominant-negative effect on IKs currents, significantly decreasing IKs current density (Splawski et al., 1997; Hoppe et al., 2001). "
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    ABSTRACT: Voltage-gated potassium (Kv) channels shape the action potentials of excitable cells and regulate membrane potential and ion homeostasis in excitable and non-excitable cells. With 40 known members in the human genome and a variety of homomeric and heteromeric pore-forming α subunit interactions, post-translational modifications, cellular locations, and expression patterns, the functional repertoire of the Kv α subunit family is monumental. This versatility is amplified by a host of interacting proteins, including the single membrane-spanning KCNE ancillary subunits. Here, examining both the secretory and the endocytic pathways, we review recent findings illustrating the surprising virtuosity of the KCNE proteins in orchestrating not just the function, but also the composition, diaspora and retrieval of channels formed by their Kv α subunit partners.
    Frontiers in Physiology 06/2012; 3:231. DOI:10.3389/fphys.2012.00231 · 3.53 Impact Factor
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    • "The ß-catenin protein generated by translation from the injected mRNA could, in theory, enter the nucleus of the oocytes and modulate expression of endogenous genes as transcription factor. For instance, ß-catenin could stimulate I Ks by upregulating the expression of SGK1 (Naishiro et al. 2005, Dehner et al. 2008) and subsequent stimulation of KCNE1/KCNQ1 by SGK1 (Busjahn et al. 2004, Seebohm et al. 2008, Strutz-Seebohm et al. 2009). Xenopus oocytes do express an endogenous SGK1 (Sopjani et al. 2010b). "
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    ABSTRACT: β-catenin, a multifunctional protein expressed in all tissues including the heart stimulates the expression of several genes important for cell proliferation. Signaling involving ß-catenin participates in directing cardiac development and in the pathophysiology of cardiac hypertrophy. Nothing is known, however, on the role of β-catenin in the regulation of cardiac ion channels. The present study explored the functional interaction of β-catenin and KCNE1/KCNQ1, the K⁺ channel complex underlying the slowly activating outwardly rectifying K⁺ current. To this end, KCNE1/KCNQ1 was expressed in Xenopus oocytes with and without β-catenin and the depolarization (up to + 80 mV) induced current (I(Ks)) was determined using the two-electrode voltage clamp. As a result, β-catenin enhanced I(Ks) by 30%. The effect of β-catenin on I(Ks) was not affected by actinomycin D (10 μM), an inhibitor of transcription, indicating that β-catenin was not effective as transcription factor. Confocal microscopy revealed that β-catenin enhanced the KCNE1/KCNQ1 protein abundance in the cell membrane. Exposure of the oocytes to brefeldin A (5 μM), an inhibitor of vesicle insertion, was followed by a decline of I(Ks), which was then similar in oocytes expressing KCNE1/KCNQ1 together with β-catenin and in oocytes expressing KCNE1/KCNQ1 alone. In conclusion, β-catenin enhances I(Ks) by increasing the KCNE1/KCNQ1 protein abundance in the cell membrane, an effect requiring vesicle insertion into the cell membrane.
    Molecular Membrane Biology 05/2012; 29(3-4):87-94. DOI:10.3109/09687688.2012.678017 · 1.69 Impact Factor
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    • "In the heart the KCNQ1–E1 complex conducts the delayed rectifier current I KS (Barhanin et al. 1996). KCNE-mediated current (I KS ) plays a critical role in repolarisation of cardiac myocytes, and mutations in Q1 or E1 cause some forms of long QT syndrome, a disease associated with prolonged cardiac action potentials and an increased risk of sudden death (Seebohm et al. 2008). KCNQ1–E1-mediated forms of long QT syndrome are also associated with deafness, as the channel complex also plays a critical role in the formation of the K + -rich endolymph in the ear (Casimiro et al. 2001). "
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    ABSTRACT: KCNE1 is a protein of low molecular mass that is known to regulate the chromanol 293B and clofilium-sensitive K+ channel, KCNQ1, in a number of tissues. Previous work on the kidney of KCNE1 and KCNQ1 knockout mice has revealed that these animals have different renal phenotypes, suggesting that KCNE1 may not regulate KCNQ1 in the renal system. In the current study, in vivo clearance approaches and whole cell voltage-clamp recordings from isolated renal proximal tubules were used to examine the physiological role of KCNE1. Data from wild-type mice were compared to those from KCNE1 knockout mice. In clearance studies the KCNE1 knockout mice had an increased fractional excretion of Na+, Cl−, HCO3(−) and water. This profile was mimicked in wild-type mice by infusion of chromanol 293B, while chromanol was without effect in KCNE1 knockout animals. Clofilium also increased the fractional excretion of Na+, Cl− and water, but this was observed in both wild-type and knockout mice, suggesting that KCNE1 was regulating a chromanol-sensitive but clofilium-insensitive pathway. In whole cell voltage clamp recordings from proximal tubules, a chromanol-sensitive, K+-selective conductance was identified that was absent in tubules from knockout animals. The properties of this conductance were not consistent with its being mediated by KCNQ1, suggesting that KCNE1 regulates another K+ channel in the renal proximal tubule. Taken together these data suggest that KCNE1 regulates a K+-selective conductance in the renal proximal tubule that plays a relatively minor role in driving the transport of Na+, Cl− and HCO3(−).
    The Journal of Physiology 05/2011; 589(Pt 14):3595-609. DOI:10.1113/jphysiol.2011.209155 · 5.04 Impact Factor
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