ABCMdb

ABCC9 p.Val734Ile

ClinVar:	c.2200G>A , p.Val734Ile ? , Conflicting interpretations of pathogenicity
Predicted by SNAP2:	A: N (78%), C: N (87%), D: N (66%), E: N (72%), F: N (87%), G: N (82%), H: N (93%), I: N (97%), K: N (78%), L: N (97%), M: N (93%), N: N (78%), P: N (78%), Q: N (87%), R: N (82%), S: N (87%), T: N (93%), W: N (78%), Y: N (97%),
Predicted by PROVEAN:	A: N, C: N, D: N, E: N, F: N, G: N, H: N, I: N, K: N, L: N, M: N, N: N, P: N, Q: N, R: N, S: N, T: N, W: N, Y: N,

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[hide] The sulfonylurea receptor, an atypical ATP-binding... Circ Res. 2008 Feb 1;102(2):164-76. Burke MA, Mutharasan RK, Ardehali H
The sulfonylurea receptor, an atypical ATP-binding cassette protein, and its regulation of the KATP channel.
Circ Res. 2008 Feb 1;102(2):164-76., [PMID:18239147]

Abstract [show]
ATP-binding cassette (ABC) proteins are highly conserved and widely expressed throughout nature and found in all organisms, both prokaryotic and eukaryotic. They mediate myriad critical cellular processes, from nutrient import to toxin efflux using the energy derived from ATP hydrolysis. Most ABC proteins mediate transport of substances across lipid membranes. However, there are atypical ABC proteins that mediate other processes. These include, but are not limited to, DNA repair (bacterial MutS), ion transport (cystic fibrosis transmembrane receptor), and mRNA trafficking (yeast Elf1p). The sulfonylurea receptor (SUR) is another atypical ABC protein that regulates activity of the potassium ATP channel (K(ATP)). K(ATP) is widely expressed in nearly all tissues of higher organisms and couples cellular energy status to membrane potential. K(ATP) is particularly important in the regulation of insulin secretion from pancreatic beta-cells and in regulating action potential duration in muscle cells. SUR is indispensable for normal channel function, and mutations in genes encoding SURs increase the susceptibility to diabetes, myocardial infarction, and heart failure. Here, we review the structure and function of ABC proteins and discuss SUR, its regulation of the K(ATP) channel, and its role in cardiovascular disease.

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177 However, a rare mutation found in an Italian population encoding for a Val734Ile mutation in ABCC9 has been associated with a 6.4-fold increased risk of early myocardial infarction (defined as myocardial infarction before 60 years of age) compared with control patients.140 At present, the pathophysiological mechanism behind this increased risk is not known, but given the excessive vasospasm noted in the SUR2 KO, the authors posit that this mutation may increase the incidence of vasospasm, resulting in myocardial infarction. Login to comment

[hide] A novel Val734Ile variant in the ABCC9 gene associ... Clin Chim Acta. 2006 Aug;370(1-2):124-8. Epub 2006 Mar 6. Minoretti P, Falcone C, Aldeghi A, Olivieri V, Mori F, Emanuele E, Calcagnino M, Geroldi D
A novel Val734Ile variant in the ABCC9 gene associated with myocardial infarction.
Clin Chim Acta. 2006 Aug;370(1-2):124-8. Epub 2006 Mar 6., [PMID:16563363]

Abstract [show]
BACKGROUND: Alterations in coronary vasomotor tone are deemed to play an important role in myocardial infarction (MI), and the ATP-binding cassette transporter C9-ABCC9-may be involved in the regulation of coronary artery vasomotility. We sought to determine whether genetic variations in the coding sequence of ABCC9 gene could be associated with precocious MI (myocardial infarction before the age of 60 years) in humans. METHODS: In this study, we screened using PCR-SSCP analysis the entire coding region of the ABCC9 gene in 45 patients with precocious MI and 45 age- and gender-matched controls. RESULTS: A novel missense mutation, Val734Ile in exon 17, was detected in one MI patient. We therefore analyzed by PCR-RFLPs the frequency of this nonsynonymous change in a large Italian cohort of precocious MI patients (n=584) and healthy comparison subjects (n=873). After allowance for the potential confounding effects of age, gender, and established cardiovascular risk factors, multivariate logistic regression analysis revealed that carriers of the rare 734Ile allele would have a 6.40-fold risk of suffering MI before the age of 60 years as compared to controls (95% CI=1.58-25.90, P=0.009). CONCLUSIONS: Taken together, our results provide the first important evidence that the newly discovered 734Ile allele in ABCC9 might influence susceptibility to precocious MI in our population.

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0 A novel Val734Ile variant in the ABCC9 gene associated with myocardial infarction Piercarlo Minoretti a,b , Colomba Falcone b,c , Alessia Aldeghi b , Valentina Olivieri b , Francesca Mori c , Enzo Emanuele b , Margherita Calcagnino c , Diego Geroldi b,⁎ a Department of Cardiology, Alessandro Manzoni Hospital of Lecco, Lecco, Italy b Interdepartmental Center for Research in Molecular Medicine (CIRMC), University of Pavia, Viale Taramelli 24, I-27100, Pavia, Italy c Department of Cardiology, IRCCS San Matteo Hospital, University of Pavia, Pavia, Italy Received 11 January 2006; received in revised form 1 February 2006; accepted 1 February 2006 Available online 6 March 2006 Abstract Background: Alterations in coronary vasomotor tone are deemed to play an important role in myocardial infarction (MI), and the ATP-binding cassette transporter C9-ABCC9-may be involved in the regulation of coronary artery vasomotility. Login to comment
3 Results: A novel missense mutation, Val734Ile in exon 17, was detected in one MI patient. Login to comment
55 Genotyping of the missense variant Val734Ile by TspRI digestion PCR for ABCC9 exon 17 was performed with the upstream primer 5'-CCTGACGTGTATGCACATTG-3', and the downstream primer 5'-TCAGAGTAAGCAAAATGAGAT- TAAAGA-3', in a final volume of 50μL. PCR conditions were as follows: 95 °C for 90 s, 35 cycles of a 94 °C denaturing step for 30 s, a 58 °C annealing step for 45 s, and a 72 °C extension for 60 s, followed by a final extension at 72 °C for 5 min, resulting in a 197 bp fragment. Login to comment
83 Additionally, together with a 11bp deletion in the 5'UTR of exon 6, our analysis revealed three previously unidentified genetic variants: IVS21+44C>A, IVS26+8G>A, and a heterozygous missense mutation in exon 17, Val734Ile (Fig. 1). Login to comment
86 Of the detected genetic variants, we selected the missense Val734Ile mutation for subsequent genetic studies because of its potential functional relevance. Login to comment
88 Analysis of the Val734Ile variant The Val734Ile variant was typed in the large case-control cohort by using a PCR-RFLPs approach. Login to comment
92 Sequencing chromatogram of ABCC9 exon 17 (GenBank Accession: AF061304) showing a heterozygous G>A substitution (arrow) resulting in the missense Val734Ile mutation. Login to comment
101 Discussion In our initial screening of the entire coding region of the ABCC9 gene, we found a novel missense Val734Ile mutation in exon 17 from a patient with precocious myocardial infarction. Login to comment
106 In the next future, it would be important to know the functional significance of the missense Val734Ile variant in the ABCC9 gene. Login to comment
108 Given the high degree of conservation of the Val734 residue across different species, and the reduction in ATP sensitivity that results with the removal of exon 17 from ABCC9 [12], it would be tempting to speculate that the Val734Ile mutation would affect the risk of myocardial infarction by altering nucleotide responsiveness of ABCC9-containing KATP channels. Login to comment
112 Alternatively, another potential explanation for the association between the Val734Ile variant and MI may involve the role played by KATP channels against ischemia/reperfusion injury. Login to comment
116 Firstly, we are aware that the chief limitation of our study is the lack of a functional characterization of the Val734Ile mutation. Login to comment
124 Hence, because the Val734Ile mutation was found to be associated with precocious MI but not with arterial hypertension, it remains to be addressed whether alterations of vascular tone could actually represent the real pathophysiological link behind the identified association between the 734Ile allele and ischemic heart disease. Login to comment
125 Although the precise functional link between the Val734Ile mutation in ABCC9 and MI has yet to be elucidated, we believe that our present data provide novel important evidences that genetic defects in KATP channels could be associated with life-threatening cardiac diseases, possibly resulting from the inability of the channel complex to optimally fulfill their physiological role [17,18]. Login to comment
126 Table 2 Genotype and allele distribution of the Val734Ile variant of the ABCC9 gene in precocious MI patients and healthy comparison subjects Subject group n Genotype (%) Allele frequency (%) Val/Val Val/Ile Ile/Ile P Val Ile P Precocious MI 584 573 (98.1%) 11 (1.9%) 0 (0%) 0.0074 1157 (99.0%) 11 (1.0%) 0.0075 Control subjects 873 870 (99.7%) 3 (0.3%) 0 (0%) 1743 (99.8%) 3 (0.2%) P values are calculated by means of χ2 tests. Login to comment

[hide] Quaternary structure of KATP channel SUR2A nucleot... J Struct Biol. 2010 Feb;169(2):243-51. doi: 10.1016/j.jsb.2009.11.005. Epub 2009 Nov 15. Park S, Terzic A
Quaternary structure of KATP channel SUR2A nucleotide binding domains resolved by synchrotron radiation X-ray scattering.
J Struct Biol. 2010 Feb;169(2):243-51. doi: 10.1016/j.jsb.2009.11.005. Epub 2009 Nov 15., [PMID:19919849]

Abstract [show]
Heterodimeric nucleotide binding domains NBD1/NBD2 distinguish the ATP-binding cassette protein SUR2A, a recognized regulatory subunit of cardiac ATP-sensitive K(+) (K(ATP)) channels. The tandem function of these core domains ensures metabolism-dependent gating of the Kir6.2 channel pore, yet their structural arrangement has not been resolved. Here, purified monodisperse and interference-free recombinant particles were subjected to synchrotron radiation small-angle X-ray scattering (SAXS) in solution. Intensity function analysis of SAXS profiles resolved NBD1 and NBD2 as octamers. Implemented by ab initio simulated annealing, shape determination prioritized an oblong envelope wrapping NBD1 and NBD2 with respective dimensions of 168x80x37A(3) and 175x81x37A(3) based on symmetry constraints, validated by atomic force microscopy. Docking crystal structure homology models against SAXS data reconstructed the NBD ensemble surrounding an inner cleft suitable for Kir6.2 insertion. Human heart disease-associated mutations introduced in silico verified the criticality of the mapped protein-protein interface. The resolved quaternary structure delineates thereby a macromolecular arrangement of K(ATP) channel SUR2A regulatory domains.

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150 This includes the NBD1 V734I variant (Fig. 5A), associated with myocardial infarction, and the NBD2 A1513T and T1547I mutations implicated in dilated cardiomyopathy and stress-induced atrial fibrillation, respectively (Fig. 5B). Login to comment
153 While the monomeric structure could not decisively address the structural consequences of either V734I or T1547I mutations due to their remote positions from critical functional motifs (Fig. 5A and B), resolved heterodimer and Fig. 3. Login to comment
192 A case in point is the recently reported variant V734I, implicated in increased susceptibility towards myocardial infarction (Minoretti et al., 2006). Login to comment

[hide] Coronary spasm and acute myocardial infarction due... Int J Cardiol. 2013 Oct 9;168(4):3506-13. doi: 10.1016/j.ijcard.2013.04.210. Epub 2013 Jun 3. Smith KJ, Chadburn AJ, Adomaviciene A, Minoretti P, Vignali L, Emanuele E, Tammaro P
Coronary spasm and acute myocardial infarction due to a mutation (V734I) in the nucleotide binding domain 1 of ABCC9.
Int J Cardiol. 2013 Oct 9;168(4):3506-13. doi: 10.1016/j.ijcard.2013.04.210. Epub 2013 Jun 3., [PMID:23739550]

Abstract [show]
BACKGROUND: Alterations in coronary vasomotor tone may participate in the pathogenesis of acute myocardial infarction (AMI). Vascular ATP-sensitive K(+) (KATP) channels, formed by Kir6.x/SUR2B, are key regulators of coronary tone and mutations in cardiac (Kir6.2/SUR2A) KATP channels result in heart disease. Here we explore the pathophysiological mechanism of a rare mutation (V734I) found in exon 17 of the ABCC9 gene, estimated to cause a 6.4-fold higher risk of AMI before the age of 60. METHODS AND RESULTS: Eleven patients carrying the mutation were identified; they presented AMI of vasospastic origin associated with increased plasma levels of endothelin-1 and increased leukocyte ROCK activity. The effects of the mutation on the functional properties of the two splice variants of ABCC9 (SUR2A and SUR2B) were studied using patch-clamp electrophysiology. The mutation reduced the sensitivity to MgATP inhibition of Kir6.2/SUR2B channels but not of Kir6.2/SUR2A and Kir6.1/SUR2B channels. Furthermore, the stimulatory effects of MgNDP (MgADP, MgGDP and MgUDP) were unaltered in mutant Kir6.2/SUR2A and Kir6.1/SUR2B channels. In contrast, mutant channels composed of Kir6.2 and SUR2B were less sensitive to MgNDP activation, assessed in the presence of MgATP. The antianginal drug nicorandil activated Kir6.2/SUR2B-V734I channels, thus substituting for the loss of MgNDP stimulation, suggesting that this drug could be of therapeutic use in the treatment of AMI associated with V734I. CONCLUSIONS: The 734I allele in ABCC9 may influence susceptibility to AMI by impairing the response of vascular, but not cardiac, KATP channels to intracellular nucleotides. This is the first human mutation in an ion channel gene to be implicated in AMI.

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2 Here we explore the pathophysiological mechanism of a rare mutation (V734I) found in exon 17 of the ABCC9 gene, estimated to cause a 6.4-fold higher risk of AMI before the age of 60. Methods and results: Eleven patients carrying the mutation were identified; they presented AMI of vasospastic origin associated with increased plasma levels of endothelin-1 and increased leukocyte ROCK activity. Login to comment
7 The antianginal drug nicorandil activated Kir6.2/SUR2B-V734I channels, thus substituting for the loss of MgNDP stimulation, suggesting that this drug could be of therapeutic use in the treatment of AMI associated with V734I. Login to comment
38 The mutation is a non-synonymous substitution of valine 734 with isoleucine (V734I). Login to comment
42 In this study, we identified a total of 11 patients with early-onset AMI who carried the V734I mutation. Login to comment
49 In contrast, mutant Kir6.2/SUR2B channels (Kir6.2/SUR2B-V734I) presented reduced sensitivity to i) MgATP inhibition and ii) MgNDP activation assessed in the presence of MgATP. Login to comment
50 We investigated the molecular basis of the impaired regulation by nucleotides of Kir6.2/SUR2B-V734I channels and propose that this may involve a change in the stimulatory effect of MgATP at the NBD1 of SUR2B. Login to comment
57 Carriers of the V734I mutation in ABCC9 identified by genetic screening (n = 11) were enrolled in this study as cases. Login to comment
58 For control purposes, AMI patients without the V734I mutation were considered. Login to comment
65 Molecular genetic analysis All 1123 patients considered in this study were screened for the V734I mutation. Login to comment
79 Patient characteristics We identified a heterozygous mutation in ABCC9 (V734I) in 11 of the 1123 patients (0.98%) with precocious AMI who underwent genetic screening. Login to comment
80 The characteristics of the carriers of the mutation were compared with those of 33 age-and gender-matched AMI individuals who did not possess the V734I variant. Login to comment
81 Patients were aged between 40 and 59 years (V734I carriers) and between 41 and 59 years (control group). Login to comment
82 As Table 1 shows, heterozygous carriers of the V734I mutation did not differ from non-carriers in terms of body mass index, smoking, diabetes mellitus, hypertension, family history of ischemic heart disease, lipid parameters, and left ventricular ejection fraction. Login to comment
84 However, carriers of the V734I mutation showed increased surrogate markers of endothelial dysfunction such as raised plasma endothelin levels and increased leukocyte ROCK activity. Login to comment
85 Interestingly, the number of stenosed coronary arteries was significantly lower in the 11 patients presenting the V734I mutation: 7 of them demonstrated unstenosed coronary arteries while the remaining 4 presented only one stenosed artery (Table 1). Login to comment
87 However, none of the carriers of the V734I mutation had evidence of left ventricular apical aneurysm, left ventricular ballooning syndrome, or hypertrophic cardiomyopathy. Login to comment
93 Functional analysis of the V734I mutation To gain insights into the molecular mechanisms by which the V734I mutation causes AMI, we began by constructing a structural model of the human NBD1 of SUR2B harbouring the V734I mutation (Fig. 2). Login to comment
98 To examine the possibility that the V734I mutation affects the channel's regulation by nucleotides, we assessed the sensitivity of wild-type and mutant channels to MgATP in inside-out membrane patches. Login to comment
99 Fig. 3A shows that Kir6.2/SUR2A-V734I presented unaltered sensitivity to MgATP compared to Kir6.2/ SUR2A (Suppl. Table 1A). Login to comment
100 In contrast, Kir6.2/SUR2B-V734I channels were less sensitive to MgATP inhibition than Kir6.2/SUR2B channels: the concentration causing half-maximal block (IC50) was 214 bc;M and 96 bc;M, for mutant and wild-type channels, respectively (Fig. 3B, Suppl. Table 1B). Login to comment
106 Coronary angiogram carried out on a male AMI patient with the V734I mutation in the ABCC9 gene showing a focal narrowing of the right coronary artery (panel A, red arrow). Login to comment
112 The V734I mutation within NBD1 is represented as a magenta star. Login to comment
119 The V734I mutation is shown in magenta. Login to comment
122 A and B. i, Currents recorded in inside-out patches excised from HEK-293T cells expressing Kir6.2 and either SUR2x or SUR2x-V734I as indicated. The membrane potential was held at -80 mV. Login to comment
124 The dashed lines indicate the zero current level. ii, Mean relationship between [MgATP] and KATP current (I), expressed relative to the current in the absence of nucleotide (I0) for KATP channels composed of Kir6.2 and either SUR2x or SUR2x-V734I subunits as indicated. The continuous lines are the best fit of suppl. Eq. (1) to the data. The number of experiments was 8-11 (A) and 18 (B) in each case. C. i Currents recorded in inside-out patches excised from HEK-293T cells expressing Kir6.1 and either SUR2B or SUR2B-V734I as indicated. The membrane potential was held at -80 mV. Login to comment
127 The dashed lines indicate the zero current level. ii, Mean relationship between [MgATP] and KATP current (I), expressed relative to the current in the absence of nucleotide (I0) for KATP channels composed of Kir6.1 and either SUR2B or SUR2B-V734I. Login to comment
131 In the presence of concentrations of MgATP lower than ~30 bc;M, MgATP had a stimulatory effect on Kir6.1/SUR2B and Kir6.1/ SUR2B-V734I channels (EC50 values were 1.9 &#b1; 0.7 bc;M (n = 7) and 2.2 &#b1; 0.8 bc;M (n = 10), respectively) while at higher doses, MgATP inhibited the activity of these channels (Fig. 3C). Login to comment
132 Importantly, the response of wild-type (Kir6.1/SUR2B) and mutant (Kir6.1/SUR2B-V734I) channels to MgATP were unaltered (Suppl. Table 1C). Login to comment
135 We therefore assessed the sensitivity of Kir6.2/SUR2B and Kir6.2/SUR2B-V734I channels to ATP in the absence of Mg2+ . Login to comment
136 Under these conditions, ATP does not interact with SUR2 to stimulate channel activity [43]; this enables the effects of the V734I mutation on ATP inhibition at Kir6.2 to be analysed in isolation from MgATP activation at SUR2. Login to comment
138 Suppl. Fig. 1 shows that V734I does not affect the sensitivity of Kir6.2/ SUR2B channels to ATP inhibition; the IC50 and h being 13 &#b1; 3 bc;M and 1.1 &#b1; 0.1 (n = 13) (Kir6.2/SUR2B) and 10 &#b1; 2 bc;M and 1.3 &#b1; 0.1 (n = 9) (Kir6.2/SUR2B-V734I). Login to comment
139 Furthermore, single-channel recordings demonstrated that the mutation did not affect either the single channel current (i) or the open probability in the absence of ligands (Po), which were 4.9 &#b1; 0.1 pA and 0.34 &#b1; 0.04 (n = 11) and 4.9 &#b1; 0.2 pA and 0.42 &#b1; 0.05 (n = 11) for Kir6.2/SUR2B and Kir6.2/SUR2B-V734I, respectively (Fig. 4). Login to comment
141 We therefore investigated if V734I enhances the Kir6.2/ SUR2B response to MgADP, as well as the response to other MgNDPs (MgUDP and MgGDP), studied in the absence of MgATP. Login to comment
145 These analyses indicate that the V734I mutation had no or only a small effect on the time course of the channel response to MgNDPs. Login to comment
146 Another possible explanation for the rightward shift of the ATP dose-response curve for Kir6.2/SUR2B-V734I channels is that the mutation results in a conformational change in the NBD1 of SUR2B that allows MgATP to act directly as a channel activator (rather than via hydrolysis to MgADP). Login to comment
148 Suppl. Fig. 3 shows that Kir6.2/SUR2B and Kir6.2/SUR2B-V734I channels were inhibited to the same extent by this compound, the IC50 being 56.3 &#b1; 14.6 bc;M (n = 6) and 42.2 &#b1; 2.3 bc;M (n = 7) and h being 1.29 &#b1; 0.09 (n = 6) and 1.84 &#b1; 0.17 (n = 7), respectively. Login to comment
149 This supports the idea that impaired MgATP hydrolysis underlies the stimulatory effects of the V734I mutation. Login to comment
153 In these experiments, for both Kir6.2/SUR2A and Kir6.2/SUR2A-V734I channels, IC50 was ~140 bc;M, ~170 bc;M and ~250 bc;M, in the presence of MgADP, MgUDP and MgGDP, respectively (Suppl. Table 1A). Login to comment
154 However, Kir6.2/ SUR2B-V734I channels were almost insensitive to MgNDP activation, the IC50 for MgATP inhibition being ~200-400 bc;M when measured in either the absence or in the presence of intracellular MgNDPs (Suppl. Table 1B). Login to comment
156 Finally, for Kir6.1/SUR2B and Kir6.1/SUR2B-V734I channels, the sensitivity to MgATP was assessed in the presence of 500 bc;M MgGDP and 300 bc;M pinacidil. Login to comment
159 Response of Kir6.2/SUR2B-V734I channels to nicorandil Finally, we asked if nicorandil, an efficacious antianginal drug that acts on KATP channels [45,46], could be used to augment the sensitivity of Kir6.2/SUR2B-V734I channels to stimulatory MgNDPs in the presence of MgATP. Login to comment
160 The response of Kir6.2/SUR2B-V734I channels to MgATP was tested in the presence of 500 bc;M MgGDP and 30 bc;M nicorandil. Login to comment
161 Suppl. Fig. 4 shows that for Kir6.2/SUR2B-V734I channels IC50 values were 1364 &#b1; 350 bc;M (n = 6) and h was 1.2 &#b1; 0.1 (n = 5), respectively. Login to comment
162 Thus, low doses of nicorandil potently activate Kir6.2/SUR2B-V734I channels. Login to comment
164 Discussion The key finding of this paper is the observation that a variant of human ABCC9 (V734I), which influences susceptibility to AMI during adulthood [32], results in an altered responsiveness of KATP channels to intracellular nucleotides. Login to comment
166 We found that KATP channels composed of Kir6.2 and SUR2B-V734I presented a reduced sensitivity to MgATP inhibition compared to wild-type. Login to comment
169 Nicorandil activated Kir6.2/SUR2B-V734I channels, effectively substituting for the loss of MgNDP stimulation, suggesting that this drug could be efficacious in the treatment of AMI associated with V734I. Login to comment
173 Representative single KATP channel currents recorded at -80 mV from inside-out patches excised from HEK-293 T cells expressing Kir6.2 and either SUR2B or SUR2B-V734I, as indicated. The dashed line indicates the zero current level. Login to comment
176 All carriers of the V734I mutation presented with levels of inflammatory markers, such as interleukin-6, hs-CRP, TNF-b1; and adiponectin, which did not differ from those of the control group. Login to comment
178 Four out of the 11 carriers of the V734I mutation presented with one stenosed coronary artery. Login to comment
186 However, none of the carriers of the V734I mutation in our study presented with ventricular ballooning. Login to comment
189 Functional implication of mutation V734I The IC50 for MgATP inhibition of Kir6.2/SUR2B-V734I was decreased relative to that of wild-type channels. Login to comment
190 In the physiological range of cytoplasmic MgATP concentrations (i.e. >~0.5 mM) [53,54], however, there was only a small difference between the residual Kir6.2/SUR2B and Kir6.2/SUR2B-V734I channel currents. Login to comment
191 The addition of physiological MgNDPs altered the MgATP response of wild-type, but not that of Kir6.2/SUR2B-V734I channels. Login to comment
192 For instance, in the presence of 1 mM MgATP, the addition of 0.5 mM MgADP did not produce a significant change in Kir6.2/SUR2B-V734I current whereas the Kir6.2/SUR2B current showed a two-fold increase in amplitude. Login to comment
193 In the absence of human or animal samples of coronary arteries carrying the SUR2B-V734I mutation, it is only possible to speculate on the exact cellular consequences of the V734I mutation. Login to comment
194 It could be envisaged that in intact endothelial cells, where Kir6.2/SUR2B channels are expressed, mutant Kir6.2/SUR2B-V734I channels would fail to respond in the normal way to MgNDP activation under metabolic stress (Fig. 6). Login to comment
199 Mean relationship between [MgATP] and KATP current (I), expressed relative to the current in the absence of nucleotide (I0) for experiments conducted in the presence of 500 bc;M of individual MgNDP, as indicated, for Kir6.2/SUR2x (i) and Kir6.2/SUR2x-V734I channels (ii). Login to comment
202 Mean relationship between [MgATP] and KATP current (I), expressed relative to the current in the absence of nucleotide (I0) for experiments conducted in the presence of 500 bc;M MgGDP, as indicated, for Kir6.1/SUR2B (i) and Kir6.1/SUR2B-V734I channels (ii). Login to comment
209 The increase in circulating levels of endothelin-1 in patients carrying V734I seen here is consistent with the observation that blockage of KATP channels increased endothelin-1 secretion from isolated human coronary endothelial cells [31]. Login to comment
210 In contrast, under conditions of high metabolism, when the ratio between MgATP and MgADP is high, the small decrease in MgATP inhibition presented by Kir6.2/SUR2B-V734I channels might have a protective effect. Login to comment
211 This is consistent with the fact that patients carrying the V734I mutation suffer AMI only in adulthood. Login to comment
212 Another possible mechanism by which the V734I mutation may promote AMI is via a loss of Kir6.2/SUR2B current in neuronal cells. Login to comment
218 The observation that the responses of Kir6.2/SUR2A to MgATP and MgNDP are unaltered by the mutation excludes the possibility that V734I causes AMI by altering the protective role of cardiac KATP channels in ischemia/reperfusion injury. Login to comment
219 The exact molecular mechanism of the SUR2B-V734I mutation in vivo will be more thoroughly understood when animal models carrying this mutation become available, thus enabling cardiovascular changes in conditions of high and low metabolism to be assessed. Login to comment
221 Molecular mechanism The V734I mutation caused a decrease in sensitivity to MgATP inhibition. Login to comment
222 This effect appeared to be Mg2+ -dependent as Kir6.2/SUR2B and Kir6.2/SUR2B-V734I channels presented identical sensitivities to ATP in the absence of Mg2+ . Login to comment
224 Thus, it can be inferred that the V734I mutation did not alter the affinity/efficacy of ATP binding at the inhibitory site of Kir6.2. Login to comment
225 Furthermore, the reduction in MgATP sensitivity of Kir6.2/SUR2B-V734I channels was not secondary to a change in the intrinsic Po of the channel [61]. Login to comment
227 However, the observation that the non-hydrolysable ATP analogue AMP-PNP was equally potent on Kir6.2/SUR2B and Kir6.2/SUR2B-V734I channels argues against this hypothesis. Login to comment
229 A plausible scenario is that the V734I mutation results in channels with an enhanced rate of MgATP hydrolysis which would account for the greater residual current in the presence of MgATP for Kir6.2/SUR2B-V734I channels. Login to comment
233 Structural considerations A recent study indicated that the region to which V734I maps is a site potentially critical for the interaction between NBD1 of adjacent SUR2 subunits [62]. Login to comment
235 The mutation acts only on SUR2B- and not SUR2A-containing KATP channels: our findings indicate a possible functional interaction between the region where V734I lies and the 42 amino-acid C-terminal region that differs between SUR2A and SUR2B. Login to comment
238 We have shown that low doses (30 bc;M) of nicorandil promoted activation of Kir6.2/SUR2B-V734I channels. Login to comment
239 It can be extrapolated that the circulating plasma levels of nicorandil, which are likely to be in the nanomolar range [64], may be sufficient to activate Kir6.2/SUR2B-V734I channels to near normal levels. Login to comment
240 These observations point out nicorandil as a possible therapeutic drug in the treatment of AMI associated with the V734I mutation. Login to comment

[hide] ABCC9 is a novel Brugada and early repolarization ... Int J Cardiol. 2014 Feb 15;171(3):431-42. doi: 10.1016/j.ijcard.2013.12.084. Epub 2014 Jan 4. Hu D, Barajas-Martinez H, Terzic A, Park S, Pfeiffer R, Burashnikov E, Wu Y, Borggrefe M, Veltmann C, Schimpf R, Cai JJ, Nam GB, Deshmukh P, Scheinman M, Preminger M, Steinberg J, Lopez-Izquierdo A, Ponce-Balbuena D, Wolpert C, Haissaguerre M, Sanchez-Chapula JA, Antzelevitch C
ABCC9 is a novel Brugada and early repolarization syndrome susceptibility gene.
Int J Cardiol. 2014 Feb 15;171(3):431-42. doi: 10.1016/j.ijcard.2013.12.084. Epub 2014 Jan 4., [PMID:24439875]

Abstract [show]
BACKGROUND: Genetic defects in KCNJ8, encoding the Kir6.1 subunit of the ATP-sensitive K(+) channel (I(K-ATP)), have previously been associated with early repolarization (ERS) and Brugada (BrS) syndromes. Here we test the hypothesis that genetic variants in ABCC9, encoding the ATP-binding cassette transporter of IK-ATP (SUR2A), are also associated with both BrS and ERS. METHODS AND RESULTS: Direct sequencing of all ERS/BrS susceptibility genes was performed on 150 probands and family members. Whole-cell and inside-out patch-clamp methods were used to characterize mutant channels expressed in TSA201-cells. Eight ABCC9 mutations were uncovered in 11 male BrS probands. Four probands, diagnosed with ERS, carried a highly-conserved mutation, V734I-ABCC9. Functional expression of the V734I variant yielded a Mg-ATP IC(5)(0) that was 5-fold that of wild-type (WT). An 18-y/o male with global ERS inherited an SCN5A-E1784K mutation from his mother, who displayed long QT intervals, and S1402C-ABCC9 mutation from his father, who displayed an ER pattern. ABCC9-S1402C likewise caused a gain of function of IK-ATP with a shift of ATP IC(5)(0) from 8.5 +/- 2 mM to 13.4 +/- 5 muM (p<0.05). The SCN5A mutation reduced peak INa to 39% of WT (p<0.01), shifted steady-state inactivation by -18.0 mV (p<0.01) and increased late I(Na) from 0.14% to 2.01% of peak I(Na) (p<0.01). CONCLUSION: Our study is the first to identify ABCC9 as a susceptibility gene for ERS and BrS. Our findings also suggest that a gain-of-function in I(K-ATP) when coupled with a loss-of-function in SCN5A may underlie type 3 ERS, which is associated with a severe arrhythmic phenotype.

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5 Four probands, diagnosed with ERS, carried a highly-conserved mutation, V734I-ABCC9. Login to comment
6 Functional expression of the V734I variant yielded a Mg-ATP IC50 that was 5-fold that of wild-type (WT). Login to comment
50 Mutagenesis, cell transfection and electrophysiological recordings Variations (S1402C and V734I) in the regulatory ABCC9 subunit (human) were introduced in pECE plasmid by PCR amplification of both DNA strands with complementary primers containing the desired amino acid changes (QuickChange, Stratagene, Agilent Technologies, Inc., Santa Clara, CA, USA). Login to comment
102 Clinical characteristics and genetic analysis of probands with ABCC9-V734I mutation Four probands were found to carry an ABCC9-V734I mutation. Login to comment
119 Age for Dx (y/o) Gender Dx VT/VF FH a Syncope SCD Other b Name SIFT score Polyphen score Exon Change in amino acid Global MAF (1000 genome) Global MAF (ESP) 1 27 M ERS3 Y Y Y - Y - - R663C 0.02 0.99 14 c.1987C N T 0 0.000154 2 38 M ERS3 - - Y Y - - - A665T 0.57 0.002 14 c.1993G N A 0.001 N/A 3 63 M BrS + CAD - Y - Y Y ICD - N733D 0.05 0.069 16 c.2197A N G 0 0 4 20 M ERS3 + bradycardia - Y Y - Y - - V734I 0.43 0.002 17 c.2200G N A 0.005 0.009236 5 20 M ERS3 + bradycardia Y Y Y Y Y ICD, quinidine - 6 40 M ERS3 + AVB + bradycardia Y - Y Y - ICD SCN5A 7 20 M ERS2 + bradycardia - - Y - - - CACNA1C 8 25 M ERS2 - - - Y - - SCN10A V1137I 0.76 0.005 27 c.3409G N A 0.0041 0.0082 9 65 M BrS + SQTS Y - Y Y - ICD SCN10A, CACNA1C R1197C 0.05 0.999 29 c.3589C N T 0 0 10 18 M BrS + SAB - Y Y - Y - SCN5A S1402C 0 0.996 34 c.4205C N G 0 0.000077 11 39 M BrS Y - Y Y Y ICD - L1524K fs*5 N/A N/A 38 4570-4572 delTTA InsAAAT 0 0 -: No; Dx: diagnosis; VT/VF: ventricular tachycardia/ventricular fibrillation; SCD: sudden cardiac death; MAF: the minor-allele frequency; 1000 genome: the 1000 Human Genome Project Database; ESP: exome sequencing project; ERS3: early repolarization syndrome type 3; BrS: Brugada syndrome; CAD: coronary artery disease; ICD: implantable cardioverter defibrillator; AVB: atrioventricular block; ERS2: ERS type 2; SQTS: short QT syndrome; SAB: sinoatrial block. Login to comment
126 Genetic screening revealed that all four cases had a c.2200G N A transition in exon 17 predicting substitution of an isoleucine for a valine at position 734 of ABBCC9 (V734I, Fig. 2B). Login to comment
131 Functional expression of ABCC9-V734I mutation Expression studies using inside-out patch clamp techniques to evaluate the effect of the mutation were performed with ABCC9-V734I coexpressed with KCNJ11-WT. Login to comment
133 The IC50 value of Mg-ATP for the mutant KCNJ11-WT/ABCC9-V734I was 5 fold that of WT (97 &#b1; 22 bc;M for WT, n = 5; 510 &#b1; 29 bc;M for V734I, n = 5; Fig. 2D & E). Login to comment
141 Electrocardiograms (ECGs) of ABCC9-V734I variant carriers (Probands 4, 5 and 6 in Table 2). Login to comment
177 ABCC9-V734I mutation causes a gain of function in ATP-sensitive potassium channel (KATP) activity by reducing sensitivity of KATP channels to ATP. Login to comment
179 B: Chromatogram showing a heterozygous G-to-A transition at nucleotide 2200 (exon 17) in ABCC9, predicting a substitution of Isoleucine (I) for Valine (V) at residue 734 (V734I). Login to comment
181 D: Sensitivity to ATP of KCNJ11-WT/ABCC9-WT and KCNJ11-WT/ABCC9-V734I channels measured using an excised inside-out patch. Login to comment
182 E: Graph depicting IC50 for Mg-ATP inhibition of IK-ATP for ABCC9-WT and V734I channels. Login to comment
220 Thus, mutations that alter nucleotide binding or compromise the cooperative nucleotide-dependent NBD interaction within the regulatory channel subunit, such as S1402C and V734I described in this study, are primary candidates for metabolic sensing deficits underlying cardiac channelopathies. Login to comment
221 Using synchrotron radiation X-ray scattering, we also demonstrated that V734I can disrupt protein-protein interaction critical for the structural integrity of the KATP channel complex [20]. Login to comment
227 Mutations that alter nucleotide binding or compromise the cooperative nucleotide-dependent NBD interaction within the regulatory channel subunit, such as the S1402C and V734I described in this study, are primary candidates for metabolic sensing deficits underlying cardiac. Login to comment
234 scattering, we recently demonstrated that V734I of SUR2A can disrupt protein-protein interaction critical for the structural integrity of the KATP channel complex [20]. Login to comment
236 In a cohort of patients with MI at an early age, a rare missense variant V734I in the ABCC9 gene was found to be over-represented [34]. Login to comment
257 A gain of function in IK-ATP secondary to a mutation in ABCC9, V734I, was also found to be associated with an ERS phenotype in Probands 4 to 7 in Table 2. Login to comment
258 With this finding, our study expands the spectrum of ABCC9-V734I variant beyond MI-related arrhythmogenesis, demonstrating its association with ERS-mediated ventricular arrhythmias. Login to comment
262 Interestingly, a recent study reported that V734I reduced the sensitivity of Kir6.2/SUR2B channels but not of Kir6.2/SUR2A or Kir6.1/ SUR2B channels, to MgATP inhibition [36]. Login to comment
299 An ABCC9-S1402C missense mutation, highly conserved among species and absent in N200 ethnically-matched controls, and a previously reported MI-related ABCC9-V734I mutation, are shown to cause a significant gain of function in KATP current when co-expressed in a heterologous expression system and evaluated using inside-out patch clamp experiments. Login to comment
315 R1197C was identified as a newly-identified mutation and V734I was the most frequently encountered variant. Login to comment

[hide] ABCC9/SUR2 in the brain: Implications for hippocam... Ageing Res Rev. 2015 Nov;24(Pt B):111-25. doi: 10.1016/j.arr.2015.07.007. Epub 2015 Jul 28. Nelson PT, Jicha GA, Wang WX, Ighodaro E, Artiushin S, Nichols CG, Fardo DW
ABCC9/SUR2 in the brain: Implications for hippocampal sclerosis of aging and a potential therapeutic target.
Ageing Res Rev. 2015 Nov;24(Pt B):111-25. doi: 10.1016/j.arr.2015.07.007. Epub 2015 Jul 28., [PMID:26226329]

Abstract [show]
The ABCC9 gene and its polypeptide product, SUR2, are increasingly implicated in human neurologic disease, including prevalent diseases of the aged brain. SUR2 proteins are a component of the ATP-sensitive potassium ("KATP") channel, a metabolic sensor for stress and/or hypoxia that has been shown to change in aging. The KATP channel also helps regulate the neurovascular unit. Most brain cell types express SUR2, including neurons, astrocytes, oligodendrocytes, microglia, vascular smooth muscle, pericytes, and endothelial cells. Thus it is not surprising that ABCC9 gene variants are associated with risk for human brain diseases. For example, Cantu syndrome is a result of ABCC9 mutations; we discuss neurologic manifestations of this genetic syndrome. More common brain disorders linked to ABCC9 gene variants include hippocampal sclerosis of aging (HS-Aging), sleep disorders, and depression. HS-Aging is a prevalent neurological disease with pathologic features of both neurodegenerative (aberrant TDP-43) and cerebrovascular (arteriolosclerosis) disease. As to potential therapeutic intervention, the human pharmacopeia features both SUR2 agonists and antagonists, so ABCC9/SUR2 may provide a "druggable target", relevant perhaps to both HS-Aging and Alzheimer's disease. We conclude that more work is required to better understand the roles of ABCC9/SUR2 in the human brain during health and disease conditions.

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1219 Clinical condition/ endophenotype Mutation Type* Notes (Refs) Cantu syndrome E, I Apparent autosomal dominant inheritance of functional gain of toxic function; many mutations identified, mostly in exons coding transmembrane domains of SUR2 protein Harakalova et al. (2012); van Bon et al. (2012) Atrial fibrillation E Case of mutation [Thr1547Ile] associated with atrial fibrillation originating in the vein of Marshal Olson, et al. (2007) Dilated cardiomyopathy E Two cases with distinct mutations [frameshift1524, A1513T] associated with dilated cardiomyopathy Bienengraeber et al. (2004) Myocardial infarction, early repolarization syndrome (ERS), and Brugada syndrome (BrS) E Coronary arterial vasospam and myocardial infarction linked to V734I mutation. Login to comment
1220 Severe cardiac arhythmias associated with 8 ABCC9 mutations from 11 BrS probands and 4 ERS probands, the latter with V734I mutations. Login to comment