Modulation of the Trafficking Efficiency and Functional Properties of ATP-sensitive Potassium Channels through a Single Amino Acid in the Sulfonylurea Receptor

Cartier, Etienne; Shen, Shu Hua; Show-Ling, Shyng,

doi:10.1074/jbc.m211395200

Cited by 25 publications

(22 citation statements)

References 58 publications

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“…B, surface mutant channels rescued by tolbutamide displayed normal response to MgADP and diazoxide after tolbutamide washout. The MgADP or diazoxide response was quantified as described previously (38). First, the response was calculated as the current in a K-INT solution plus 0.1 mM ATP, 0.5 mM ADP or 0.25 mM diazoxide, and 1 mM free Mg 2ϩ , relative to that in plain K-INT solution (see C and D below).…”

Section: Discussionmentioning

confidence: 99%

“…Drug treatment was initiated 32-40 h post-transfection and lasted for 4 -24 h. The cells were then processed for chemiluminescence assays as described previously (36,38). Briefly, the cells were fixed with 2% paraformaldehyde for 30 min at 4°C, preblocked in PBS with 0.1% BSA for 30 min, incubated in M2 anti-FLAG antibody (10 g/ml) for an hour, washed four times for 30 min in PBS with 0.1% BSA, incubated in horseradish peroxidase-conjugated anti-mouse (Jackson, 1:1000 dilution) for 20 min, and washed again four times for 30 35 S-Label, 150 -250 Ci/ml) for 30 min.…”

Section: Methodsmentioning

confidence: 99%

“…To address this possibility, we used a heterotandem dimer construct in which the C terminus of the mutant fSUR1 has been fused to the N terminus of Kir6.2 (referred to as A116P-or V187D-fSUR1/Kir6.2 fusion) to achieve obligatory physical association between the two subunits; similar SUR1/ Kir6.2 fusion constructs have been used previously by a number of groups for structure-function and trafficking studies (7,9,10,28,34). Surface expression of the fusion protein was quantified using chemiluminescence assays as described previously (36,38). Although WT fSUR1/Kir6.2 fusion protein was expressed at a level comparable with that observed in cells transfected with WT-fSUR1 and Kir6.2 as individual subunits, fusion proteins carrying the A116P-or V187D-SUR1 mutation had poor surface expression, ϳ10 and 20% that of WT fSUR1/ Kir6.2 fusion, respectively (Fig.…”

Section: Both the A116p And V187d Mutations In Sur1 Preventmentioning

confidence: 99%

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Sulfonylureas Correct Trafficking Defects of ATP-sensitive Potassium Channels Caused by Mutations in the Sulfonylurea Receptor

Yan

Lin

Weisiger

et al. 2004

Journal of Biological Chemistry

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101

144

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The pancreatic ATP-sensitive potassium (K ATP ) channel, a complex of four sulfonylurea receptor 1 (SUR1) and four potassium channel Kir6.2 subunits, regulates insulin secretion by linking metabolic changes to ␤-cell membrane potential. Sulfonylureas inhibit K ATP channel activities by binding to SUR1 and are widely used to treat type II diabetes. We report here that sulfonylureas also function as chemical chaperones to rescue K ATP channel trafficking defects caused by two SUR1 mutations, A116P and V187D, identified in patients with congenital hyperinsulinism. Sulfonylureas markedly increased cell surface expression of the A116P and V187D mutants by stabilizing the mutant SUR1 proteins and promoting their maturation. By contrast, diazoxide, a potassium channel opener that also binds SUR1, had no effect on surface expression of either mutant. Importantly, both mutant channels rescued to the cell surface have normal ATP, MgADP, and diazoxide sensitivities, demonstrating that SUR1 harboring either the A116P or the V187D mutation is capable of associating with Kir6.2 to form functional K ATP channels. Thus, sulfonylureas may be used to treat congenital hyperinsulinism caused by certain K ATP channel trafficking mutations. ATP-sensitive potassium (K ATP )1 channels present in the plasma membrane of pancreatic ␤-cells play a central role in mediating glucose-induced insulin secretion (1-4). The activity of K ATP channels, which regulates ␤-cell membrane potential, is determined by the relative concentrations of intracellular ATP and ADP. When the blood glucose level rises, the increased intracellular [ATP/ADP] ratio favors K ATP channel closure, resulting in membrane depolarization, Ca 2ϩ influx, and insulin secretion. When the blood glucose level falls, the above molecular events reverse, and insulin release is stopped. In the event where K ATP channels fail to open during glucose starvation, ␤-cell membrane potential remains depolarized, and insulin secretion persists, leading to severe hypoglycemia. These symptoms are found in patients suffering from congenital hyperinsulinism (5), also known as persistent hyperinsulinemia hypoglycemia of infancy (PHHI) (6). Indeed, mutations in the K ATP channel genes, sulfonylurea receptor 1 (SUR1) and the inward rectifier potassium channel Kir6.2, that lead to a loss of channel function have been shown to be major causes of PHHI (4, 6).The pancreatic K ATP channel complex consists of four poreforming Kir6.2 subunits and four regulatory SUR1 subunits (7-10). Gating of K ATP channels occurs as a result of the interplay between both channel subunits and intracellular ATP and ADP. Binding of ATP to the Kir6.2 subunit inhibits channel activity, whereas binding of Mg 2ϩ -complexed ATP or ADP to the SUR1 subunit stimulates channel activity (11)(12)(13)(14). SUR1 is a member of the ATP-binding cassette transporter family; it has three transmembrane domains: TM0, TM1, and TM2, and two large cytoplasmic nucleotide binding domains: NBD1 and NBD2 (15,16). Structure-function studies sugges...

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Both the A116p And V187d Mutations In Sur1 Preventmentioning

confidence: 99%

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Sulfonylureas Correct Trafficking Defects of ATP-sensitive Potassium Channels Caused by Mutations in the Sulfonylurea Receptor

Yan

Lin

Weisiger

et al. 2004

Journal of Biological Chemistry

Self Cite

101

144

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“…Indeed, opener binding to SUR1 is detectable, although binding assays showed a 1000-to 10,000-fold difference in dissociation constants for pinacidil, P1075, or levcromakakim between SUR1 and SUR2 isoforms (Schwanstecher et al, 1998). Functional evidence of a low-affinity SUR1 site for nondiazoxide openers has also been presented by Cartier et al (2003) who observed activation of SUR1-based channels by high concentrations of pinacidil after SUR1 had been mutated (F1388L) in NBD2, a region not thought to be directly involved in opener binding.…”

mentioning

confidence: 94%

The Size of a Single Residue of the Sulfonylurea Receptor Dictates the Effectiveness of K_ATP Channel Openers

Moreau

Gally²,

Jacquet-Bouix³

et al. 2004

Mol Pharmacol

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K ATP channel openers are a diverse group of molecules able to activate ATP-sensitive K ϩ channels in a tissue-dependent manner by binding to the channel regulatory subunit, the sulfonylurea receptor (SUR), an ATP-binding cassette protein. Residues crucial to this action were previously identified in the last transmembrane helix of SUR, transmembrane helix 17. This study examined the residue at the most important position, 1253 in the muscle isoform SUR2A and the matching 1290 in the pancreatic/neuronal isoform SUR1 (rat numbering). At this position in either isoform, a threonine enables action of openers, whereas a methionine prohibits it. Using single-point mutagenesis, we have examined the physicochemical basis of this phenomenon and discovered that it relied uniquely on side chain volume and not on shape, polarity, or hydrogen-bonding capacity of the residue. Moreover, the aromatic nature of neighboring residues conserved in SUR1 and SUR2A was found necessary for SUR2A to sustain the wild-type levels of channel activation by the openers tested, the cromakalim analog SR47063 [4-(2-cyanimino-1,2-dihydro-1-pyridyl)-2,2-dimethyl-6-nitrochromene] and the pinacidil analog P1075 [N-cyano-NЈ-(1,1-dimethylpropyl)-NЈ-3-pyridylguanidine]. These observations suggest that these residues can interact with openers via nonspecific stacking interactions provided that the adjacent 1253/1290 residue does not obstruct access. The smaller Thr1253 of SUR2A would permit activation, whereas the bulky Met1290 of SUR1 would not. This hypothesis is discussed in the context of a simple molecular model of transmembrane helix 17.

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“…Mutations in both of these genes are associated with disorders of insulin secretion including congenital hyperinsulinism and neonatal diabetes (4, 7). Studies have shown that although some mutations affect the nucleotide regulation of the channel (12-14), others alter the density of the channels at the cell surface by affecting trafficking (15)(16)(17)(18)(19). Recent large scale genome-wide studies have established a strong link between the KCNJ11 gene and type 2 diabetes (20); however, the underlying mechanisms are unknown.…”

mentioning

confidence: 99%

Constitutive Endocytic Recycling and Protein Kinase C-mediated Lysosomal Degradation Control KATP Channel Surface Density

Manna¹,

Smith²,

Taneja

et al. 2010

Journal of Biological Chemistry

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Pancreatic ATP-sensitive potassium (K ATP ) channels control insulin secretion by coupling the excitability of the pancreatic ␤-cell to glucose metabolism. Little is currently known about how the plasma membrane density of these channels is regulated. We therefore set out to examine in detail the endocytosis and recycling of these channels and how these processes are regulated. To achieve this goal, we expressed K ATP channels bearing an extracellular hemagglutinin epitope in human embryonic kidney cells and followed their fate along the endocytic pathway. Our results show that K ATP channels undergo multiple rounds of endocytosis and recycling. Further, activation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate significantly decreases K ATP channel surface density by reducing channel recycling and diverting the channel to lysosomal degradation. These findings were recapitulated in the model pancreatic ␤-cell line INS1e, where activation of PKC leads to a decrease in the surface density of native K ATP channels. Because sorting of internalized channels between lysosomal and recycling pathways could have opposite effects on the excitability of pancreatic ␤-cells, we propose that PKC-regulated K ATP channel trafficking may play a role in the regulation of insulin secretion.The ATP-sensitive potassium (K ATP ) channel plays a key role in the regulation of glucose-induced insulin secretion by the pancreatic ␤-cells (1-3). Central to this role is its unique ability to couple changes in the metabolism of glucose to changes in membrane potential. A rise in blood glucose levels increases the uptake and metabolism of glucose, resulting in an increase in the intracellular [ATP]/[ADP] ratio and inhibition of K ATP channels. This leads to depolarization of the ␤-cell membrane (caused by inhibition of K ϩ efflux), stimulating opening of voltage-activated calcium channels, Ca 2ϩ influx, and insulin release (4). Regulation of K ATP channel function by products of metabolism (e.g. nucleotides) as well as other cellular signals (e.g. protein kinases, lipids) has been extensively studied (1,5,6). By comparison, little is known about how the number of channels at the plasma membrane of the cell is controlled, although there is growing evidence that changes in the membrane density of the channel underlie disease states (7,8).Structurally, K ATP channels exist as octamers formed from four subunits of the inwardly rectifying potassium channel Kir6.1 or Kir6.2, together with four sulfonylurea receptor (SUR1, SUR2A, or SUR2B) subunits (5, 9 -11). The pancreatic K ATP channel comprises Kir6.2 and SUR1 subunits, which are encoded by the genes KCNJ11 and ABCC8, respectively (5, 6, 10, 11). Mutations in both of these genes are associated with disorders of insulin secretion including congenital hyperinsulinism and neonatal diabetes (4, 7). Studies have shown that although some mutations affect the nucleotide regulation of the channel (12-14), others alter the density of the channels at the cell surface by affecting traffickin...

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Modulation of the Trafficking Efficiency and Functional Properties of ATP-sensitive Potassium Channels through a Single Amino Acid in the Sulfonylurea Receptor

Cited by 25 publications

References 58 publications

Sulfonylureas Correct Trafficking Defects of ATP-sensitive Potassium Channels Caused by Mutations in the Sulfonylurea Receptor

Sulfonylureas Correct Trafficking Defects of ATP-sensitive Potassium Channels Caused by Mutations in the Sulfonylurea Receptor

The Size of a Single Residue of the Sulfonylurea Receptor Dictates the Effectiveness of K_ATP Channel Openers

Constitutive Endocytic Recycling and Protein Kinase C-mediated Lysosomal Degradation Control KATP Channel Surface Density

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Modulation of the Trafficking Efficiency and Functional Properties of ATP-sensitive Potassium Channels through a Single Amino Acid in the Sulfonylurea Receptor

Cited by 25 publications

References 58 publications

Sulfonylureas Correct Trafficking Defects of ATP-sensitive Potassium Channels Caused by Mutations in the Sulfonylurea Receptor

Sulfonylureas Correct Trafficking Defects of ATP-sensitive Potassium Channels Caused by Mutations in the Sulfonylurea Receptor

The Size of a Single Residue of the Sulfonylurea Receptor Dictates the Effectiveness of KATP Channel Openers

Constitutive Endocytic Recycling and Protein Kinase C-mediated Lysosomal Degradation Control KATP Channel Surface Density

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Product

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The Size of a Single Residue of the Sulfonylurea Receptor Dictates the Effectiveness of K_ATP Channel Openers