Mechanisms of disease pathogenesis in long QT syndrome type 5

Harmer, Stephen C.; Wilson, Andrew J.; Aldridge, Robert W; Tinker, Andrew

doi:10.1152/ajpcell.00308.2009

Cited by 41 publications

(34 citation statements)

References 33 publications

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“…In the present study, A341V trafficked normally, and this agrees with other previous reports [29,30]. We had wondered whether P127T could act to increase retention of the channel complex in the ER as some LQT5 mutations can perturb the trafficking of KCNQ1 [31,32]. However, P127T did not increase ER retention of KCNQ1-GFP or A341V-GFP.…”

Section: Channelsupporting

confidence: 93%

Cellular mechanisms underlying the increased disease severity seen for patients with long QT syndrome caused by compound mutations in KCNQ1

Harmer

Mohal

Royal

et al. 2014

Biochemical Journal

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The KCNQ1 (potassium voltage-gated channel, KQT-like subfamily, member 1) gene encodes the Kv7.1 potassium channel which forms a complex with KCNE1 (potassium voltage-gated channel Isk-related family member 1) in the human heart to produce the repolarizing IKs (slow delayed rectifier potassium current). Mutations in KCNQ1 can perturb IKs function and cause LQT1 (long QT syndrome type 1). In LQT1, compound mutations are relatively common and are associated with increased disease severity. LQT1 compound mutations have been shown to increase channel dysfunction, but whether other disease mechanisms, such as defective channel trafficking, contribute to the increase in arrhythmic risk has not been determined. Using an imaging-based assay we investigated the effects of four compound heterozygous mutations (V310I/R594Q, A341V/P127T, T391I/Q530X and A525T/R518X), one homozygous mutation (W248F) and one novel compound heterozygous mutation (A178T/K422fs39X) (where fs denotes frameshift) on channel trafficking. By analysing the effects in the equivalent of a homozygous, heterozygous and compound heterozygous condition, we identify three different types of behaviour. A341V/P127T and W248F/W248F had no effect, whereas V310I/R594Q had a moderate, but not compound, effect on channel trafficking. In contrast, T391I/Q530X, A525T/R518X and A178T/K422fs39X severely disrupted channel trafficking when expressed in compound form. In conclusion, we have characterized the disease mechanisms for six LQT1 compound mutations and report that, for four of these, defective channel trafficking underlies the severe clinical phenotype.

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Section: Channelsupporting

confidence: 93%

Cellular mechanisms underlying the increased disease severity seen for patients with long QT syndrome caused by compound mutations in KCNQ1

Harmer

Mohal

Royal

et al. 2014

Biochemical Journal

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“…F193L does not alter the G ( V ), but speeds up K V 7.1+KCNE1 channel closing by a factor of 2 (Supplementary file 1). These results are consistent with previous reported findings for some of these mutants (Bianchi et al, 2000; Yamaguchi et al, 2003; Eldstrom et al, 2010; Henrion et al, 2009; Yang et al, 2013; Yang et al, 2002; Harmer et al, 2010). …”

Section: Resultssupporting

confidence: 94%

“…To avoid mutants with severe trafficking defects, we therefore selected mutants that have previously been shown to localize abundantly enough to the cell membrane to generate detectable K + currents. Several of the selected mutants have been shown to traffic well in mammalian systems (K V 7.1/V215M and KCNE1/S74L [Eldstrom et al, 2010; Harmer et al, 2010]) or generate clearly detectable currents in mammalian cells (K V 7.1/R583C [Yang et al, 2002]). Our Xenopus oocyte experiments that compare mutant current amplitudes with wild-type current amplitudes (Figure 1—figure supplement 4) suggest that the reduced ability of the selected mutants to generate currents in Xenopus oocytes may largely be explained by the shifted G ( V ) of mutants.…”

Section: Discussionmentioning

confidence: 99%

“…We selected eight mutations of residues mutated in patients with LQTS located in different segments of the K V 7.1+KCNE1 channel and that were previously shown to form active channels (Bianchi et al, 2000; Yamaguchi et al, 2003; Eldstrom et al, 2010; Henrion et al, 2009; Yang et al, 2013; Yang et al, 2002; Harmer et al, 2010; Splawski et al, 1997). We measure the movement of the S4 voltage sensor in selected mutants using voltage clamp fluorometry to further our understanding of the molecular mechanisms underlying the defects caused by the diverse mutations.…”

Section: Introductionmentioning

confidence: 99%

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Fatty acid analogue N-arachidonoyl taurine restores function of IKs channels with diverse long QT mutations

Liin

Larsson

Barro-Soria

et al. 2016

eLife

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About 300 loss-of-function mutations in the IKs channel have been identified in patients with Long QT syndrome and cardiac arrhythmia. How specific mutations cause arrhythmia is largely unknown and there are no approved IKs channel activators for treatment of these arrhythmias. We find that several Long QT syndrome-associated IKs channel mutations shift channel voltage dependence and accelerate channel closing. Voltage-clamp fluorometry experiments and kinetic modeling suggest that similar mutation-induced alterations in IKs channel currents may be caused by different molecular mechanisms. Finally, we find that the fatty acid analogue N-arachidonoyl taurine restores channel gating of many different mutant channels, even though the mutations are in different domains of the IKs channel and affect the channel by different molecular mechanisms. N-arachidonoyl taurine is therefore an interesting prototype compound that may inspire development of future IKs channel activators to treat Long QT syndrome caused by diverse IKs channel mutations.DOI: http://dx.doi.org/10.7554/eLife.20272.001

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“…500 ng of each vector was transfected using Lipofectamine (Invitrogen) as per the manufacturer's instructions. CHO-K1 cells and CHO-hM 1 cells were cultured as previously described (15,29). Whole cell voltage-clamp recording was carried out at room temperature using an Axopatch 200B amplifier (Axon Instruments).…”

Section: Methodsmentioning

confidence: 99%

Characterization of a Binding Site for Anionic Phospholipids on KCNQ1

Thomas¹,

Harmer²,

Khambra

et al. 2011

Journal of Biological Chemistry

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The KCNQ family of potassium channels underlie a repolarizing K ؉ current in the heart and the M-current in neurones.The assembly of KCNQ1 with KCNE1 generates the delayed rectifier current I Ks in the heart. Characteristically these channels are regulated via G q/11 -coupled receptors and the inhibition seen after phospholipase C activation is now thought to occur from membrane phosphatidylinositol (4,5)-bisphosphate (PIP 2 ) depletion. It is not clear how KCNQ1 recognizes PIP 2 and specifically which residues in the channel complex are important. Using biochemical techniques we identify a cluster of basic residues namely, Lys-354, Lys-358, Arg-360, and Lys-362, in the proximal C terminus as being involved in binding anionic phospholipids. The mutation of specific residues in combination, to alanine leads to the loss of binding to phosphoinositides. Functionally, the introduction of these mutations into KCNQ1 leads to shifts in the voltage dependence of channel activation toward depolarized potentials and reductions in current density. Additionally, the biophysical effects of the charge neutralizing mutations, which disrupt phosphoinositide binding, mirror the effects we see on channel function when we deplete cellular PIP 2 levels through activation of a G q/11 -coupled receptor. Conversely, the addition of diC8-PIP 2 to the wild-type channel, but not a PIP 2 binding-deficient mutant, acts to shift the voltage dependence of channel activation toward hyperpolarized potentials and increase current density.In conclusion, we use a combined biochemical and functional approach to identify a cluster of basic residues important for the binding and action of anionic phospholipids on the KCNQ1/KCNE1 complex.

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Mechanisms of disease pathogenesis in long QT syndrome type 5

Cited by 41 publications

References 33 publications

Cellular mechanisms underlying the increased disease severity seen for patients with long QT syndrome caused by compound mutations in KCNQ1

Cellular mechanisms underlying the increased disease severity seen for patients with long QT syndrome caused by compound mutations in KCNQ1

Fatty acid analogue N-arachidonoyl taurine restores function of IKs channels with diverse long QT mutations

Characterization of a Binding Site for Anionic Phospholipids on KCNQ1

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