The Experts below are selected from a list of 75 Experts worldwide ranked by ideXlab platform
Jan Tytgat - One of the best experts on this subject based on the ideXlab platform.
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apetx4 a novel sea anemone toxin and a modulator of the cancer relevant Potassium Channel kv10 1
Marine Drugs, 2017Co-Authors: Lien Moreels, Loic Quinton, Lászlo Béress, Diogo T Galan, Steve Peigneur, Luis A Pardo, Etienne Waelkens, Edwin De Pauw, Jan TytgatAbstract:The human ether-a-go-go Channel (hEag1 or KV10.1) is a cancer-relevant voltage-gated Potassium Channel that is overexpressed in a majority of human tumors. Peptides that are able to selectively inhibit this Channel can be lead compounds in the search for new anticancer drugs. Here, we report the activity-guided purification and electrophysiological characterization of a novel KV10.1 inhibitor from the sea anemone Anthopleura elegantissima. Purified sea anemone fractions were screened for inhibitory activity on KV10.1 by measuring whole-cell currents as expressed in Xenopus laevis oocytes using the two-microelectrode voltage clamp technique. Fractions that showed activity on Kv10.1 were further purified by RP-HPLC. The amino acid sequence of the peptide was determined by a combination of MALDI- LIFT-TOF/TOF MS/MS and CID-ESI-FT-ICR MS/MS and showed a high similarity with APETx1 and APETx3 and was therefore named APETx4. Subsequently, the peptide was electrophysiologically characterized on KV10.1. The selectivity of the toxin was investigated on an array of voltage-gated ion Channels, including the cardiac human ether-a-go-go-related gene Potassium Channel (HERG or Kv11.1). The toxin inhibits KV10.1 with an IC50 value of 1.1 μM. In the presence of a similar toxin concentration, a shift of the activation curve towards more positive potentials was observed. Similar to the effect of the gating modifier toxin APETx1 on HERG, the inhibition of Kv10.1 by the isolated toxin is reduced at more positive voltages and the peptide seems to keep the Channel in a closed state. Although the peptide also induces inhibitory effects on other KV and NaV Channels, it exhibits no significant effect on HERG. Moreover, APETx4 induces a concentration-dependent cytotoxic and proapoptotic effect in various cancerous and noncancerous cell lines. This newly identified KV10.1 inhibitor can be used as a tool to further characterize the oncogenic Channel KV10.1 or as a scaffold for the design and synthesis of more potent and safer anticancer drugs.
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apetx4 a novel sea anemone toxin and a modulator of the cancer relevant Potassium Channel kv10 1
Marine Drugs, 2017Co-Authors: Lien Moreels, Loic Quinton, Lászlo Béress, Diogo T Galan, Steve Peigneur, Luis A Pardo, Etienne Waelkens, Edwin De Pauw, Jan TytgatAbstract:The human ether-a-go-go Channel (hEag1 or KV10.1) is a cancer-relevant voltage-gated Potassium Channel that is overexpressed in a majority of human tumors. Peptides that are able to selectively inhibit this Channel can be lead compounds in the search for new anticancer drugs. Here, we report the activity-guided purification and electrophysiological characterization of a novel KV10.1 inhibitor from the sea anemone Anthopleura elegantissima. Purified sea anemone fractions were screened for inhibitory activity on KV10.1 by measuring whole-cell currents as expressed in Xenopus laevis oocytes using the two-microelectrode voltage clamp technique. Fractions that showed activity on Kv10.1 were further purified by RP-HPLC. The amino acid sequence of the peptide was determined by a combination of MALDI- LIFT-TOF/TOF MS/MS and CID-ESI-FT-ICR MS/MS and showed a high similarity with APETx1 and APETx3 and was therefore named APETx4. Subsequently, the peptide was electrophysiologically characterized on KV10.1. The selectivity of the toxin was investigated on an array of voltage-gated ion Channels, including the cardiac human ether-a-go-go-related gene Potassium Channel (HERG or Kv11.1). The toxin inhibits KV10.1 with an IC50 value of 1.1 μM. In the presence of a similar toxin concentration, a shift of the activation curve towards more positive potentials was observed. Similar to the effect of the gating modifier toxin APETx1 on HERG, the inhibition of Kv10.1 by the isolated toxin is reduced at more positive voltages and the peptide seems to keep the Channel in a closed state. Although the peptide also induces inhibitory effects on other KV and NaV Channels, it exhibits no significant effect on HERG. Moreover, APETx4 induces a concentration-dependent cytotoxic and proapoptotic effect in various cancerous and noncancerous cell lines. This newly identified KV10.1 inhibitor can be used as a tool to further characterize the oncogenic Channel KV10.1 or as a scaffold for the design and synthesis of more potent and safer anticancer drugs.
Arthur M Brown - One of the best experts on this subject based on the ideXlab platform.
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role of the cytosolic chaperones hsp70 and hsp90 in maturation of the cardiac Potassium Channel HERG
Circulation Research, 2003Co-Authors: Eckhard Ficker, Adrienne T Dennis, Lu Wang, Arthur M BrownAbstract:The human ether-a-gogo-related gene (HERG) encodes the alpha subunit of the cardiac Potassium current IKr. Several mutations in HERG produce trafficking-deficient Channels that may cause hereditary long-QT syndrome and sudden cardiac death. Although HERG currents have been studied extensively, little is known about the proteins involved in maturation and trafficking of HERG. Using immunoprecipitations, we show that the cytosolic chaperones heat shock protein (Hsp) 70 and Hsp90, but not Grp94, interact with HERG wild type (WT) during maturation. The specific Hsp90 inhibitor geldanamycin prevents maturation and increases proteasomal degradation of HERG WT, while reducing HERG currents in heterologous expression systems. In ventricular myocytes, inhibition of Hsp90 also decreases IKr, whereas geldanamycin had no effect on IKs or heterologously expressed Kv2.1 and Kv1.5 currents. Both Hsp90 and Hsp70 interact directly with the core-glycosylated form of HERG WT present in the endoplasmic reticulum but not the fully glycosylated, cell-surface form. For the trafficking-deficient LQT2 mutants, HERG R752W and HERG G601S, interactions with Hsp90 and Hsp70 are increased as both mutants remained tightly associated with Hsp90 and Hsp70 in the endoplasmic reticulum. Incubation at lower temperature for R752W or with the HERG blocker astemizole for G601S dissociates Channel-chaperone complexes and restores trafficking. In contrast, nonfunctional but trafficking-competent HERG G628S is released from chaperone complexes during maturation comparable to WT. We conclude that Hsp90 and Hsp70 are crucial for the maturation of HERG WT as well as the retention of trafficking-deficient LQT2 mutants. The full text of this article is available online at http://www.circresaha.org.
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retention in the endoplasmic reticulum as a mechanism of dominant negative current suppression in human long qt syndrome
Journal of Molecular and Cellular Cardiology, 2000Co-Authors: Eckhard Ficker, Adrienne T Dennis, Carlos A Obejeropaz, Pasqualina Castaldo, Maurizio Taglialatela, Arthur M BrownAbstract:Mutations in the cardiac Potassium Channel HERG (KCNH2) cause chromosome 7-linked long QT syndrome (LQT2) characterized by a prolonged QT interval, recurrent syncope and sudden cardiac death. Most mutations in HERG exhibit "loss of function" phenotypes with defective Channels either inserted into the plasma membrane or retained in the endoplasmic reticulum. "Loss of function" mutations reduce I(Kr), the cardiac delayed rectifier current encoded by HERG, due to haploinsufficiency or suppression of wild-type function by a dominant-negative mechanism. One explanation for dominant-negative current suppression is that mutant subunits render tetrameric Channel complexes non-conducting on co-assembly. In the present paper we describe an alternative mechanism for this phenomenon. We show (1) that the dominant-negative HERG mutation A561V is retained in the endoplasmic reticulum and (2) that wild-type Channels are tagged for retention in the ER by co-assembly with trafficking deficient A561V subunits. Thus, in HERG A561V dominant-negative suppression of wild-type function is the result of an acquired trafficking defect.
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a mechanism for the proarrhythmic effects of cisapride propulsid high affinity blockade of the human cardiac Potassium Channel HERG
FEBS Letters, 1997Co-Authors: David Rampe, Marylouise Roy, Adrienne T Dennis, Arthur M BrownAbstract:Cisapride (Propulsid) is a gastrointestinal prokinetic agent commonly used to treat nocturnal heartburn as well as a variety of other gastrointestinal disorders. The use of cisapride has been associated with acquired long QT syndrome and ventricular arrhythmias such as torsades de pointes which produces sudden cardiac death. These cardiotoxic effects can be due to blockade of one or more types of K+ Channel currents in the human heart. For this reason we compared the effects of cisapride on two cloned human cardiac K+ Channels, Kv1.5 and the human ether-a-go-go-related gene (HERG) stably transfected into mammalian cells. Using patch clamp electrophysiology, we found that cisapride was a potent inhibitor of HERG displaying an IC50 value of 44.5 nmol/l when tail currents at −40 mV were measured following a 2 s test depolarization to +20 mV. When HERG currents were measured at the end of prolonged (20 s) depolarizing steps to +20 mV, the apparent affinity of cisapride was increased and measured 6.70 nmol/l. The main effect of cisapride was to enhance the rate of HERG current decay thereby reducing current at the end of the voltage clamp pulse. Furthermore, the potency of cisapride for the HERG Channel was similar to that observed for the class III antiarrhythmic agent dofetilide (IC50=15.3 nmol/l) and the nonsedating antihistamine terfenadine (IC50=56.0 nmol/l). In contrast to its effects on HERG, cisapride inhibited Kv1.5 Channel currents weakly displaying an IC50 value of 21.2 μmol/l. It is concluded that cisapride displays specific, high affinity block of the human cardiac K+ Channel HERG. It is likely that this interaction underlies the proarrhythmic effects of the drug observed under certain clinical settings.
Lien Moreels - One of the best experts on this subject based on the ideXlab platform.
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apetx4 a novel sea anemone toxin and a modulator of the cancer relevant Potassium Channel kv10 1
Marine Drugs, 2017Co-Authors: Lien Moreels, Loic Quinton, Lászlo Béress, Diogo T Galan, Steve Peigneur, Luis A Pardo, Etienne Waelkens, Edwin De Pauw, Jan TytgatAbstract:The human ether-a-go-go Channel (hEag1 or KV10.1) is a cancer-relevant voltage-gated Potassium Channel that is overexpressed in a majority of human tumors. Peptides that are able to selectively inhibit this Channel can be lead compounds in the search for new anticancer drugs. Here, we report the activity-guided purification and electrophysiological characterization of a novel KV10.1 inhibitor from the sea anemone Anthopleura elegantissima. Purified sea anemone fractions were screened for inhibitory activity on KV10.1 by measuring whole-cell currents as expressed in Xenopus laevis oocytes using the two-microelectrode voltage clamp technique. Fractions that showed activity on Kv10.1 were further purified by RP-HPLC. The amino acid sequence of the peptide was determined by a combination of MALDI- LIFT-TOF/TOF MS/MS and CID-ESI-FT-ICR MS/MS and showed a high similarity with APETx1 and APETx3 and was therefore named APETx4. Subsequently, the peptide was electrophysiologically characterized on KV10.1. The selectivity of the toxin was investigated on an array of voltage-gated ion Channels, including the cardiac human ether-a-go-go-related gene Potassium Channel (HERG or Kv11.1). The toxin inhibits KV10.1 with an IC50 value of 1.1 μM. In the presence of a similar toxin concentration, a shift of the activation curve towards more positive potentials was observed. Similar to the effect of the gating modifier toxin APETx1 on HERG, the inhibition of Kv10.1 by the isolated toxin is reduced at more positive voltages and the peptide seems to keep the Channel in a closed state. Although the peptide also induces inhibitory effects on other KV and NaV Channels, it exhibits no significant effect on HERG. Moreover, APETx4 induces a concentration-dependent cytotoxic and proapoptotic effect in various cancerous and noncancerous cell lines. This newly identified KV10.1 inhibitor can be used as a tool to further characterize the oncogenic Channel KV10.1 or as a scaffold for the design and synthesis of more potent and safer anticancer drugs.
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apetx4 a novel sea anemone toxin and a modulator of the cancer relevant Potassium Channel kv10 1
Marine Drugs, 2017Co-Authors: Lien Moreels, Loic Quinton, Lászlo Béress, Diogo T Galan, Steve Peigneur, Luis A Pardo, Etienne Waelkens, Edwin De Pauw, Jan TytgatAbstract:The human ether-a-go-go Channel (hEag1 or KV10.1) is a cancer-relevant voltage-gated Potassium Channel that is overexpressed in a majority of human tumors. Peptides that are able to selectively inhibit this Channel can be lead compounds in the search for new anticancer drugs. Here, we report the activity-guided purification and electrophysiological characterization of a novel KV10.1 inhibitor from the sea anemone Anthopleura elegantissima. Purified sea anemone fractions were screened for inhibitory activity on KV10.1 by measuring whole-cell currents as expressed in Xenopus laevis oocytes using the two-microelectrode voltage clamp technique. Fractions that showed activity on Kv10.1 were further purified by RP-HPLC. The amino acid sequence of the peptide was determined by a combination of MALDI- LIFT-TOF/TOF MS/MS and CID-ESI-FT-ICR MS/MS and showed a high similarity with APETx1 and APETx3 and was therefore named APETx4. Subsequently, the peptide was electrophysiologically characterized on KV10.1. The selectivity of the toxin was investigated on an array of voltage-gated ion Channels, including the cardiac human ether-a-go-go-related gene Potassium Channel (HERG or Kv11.1). The toxin inhibits KV10.1 with an IC50 value of 1.1 μM. In the presence of a similar toxin concentration, a shift of the activation curve towards more positive potentials was observed. Similar to the effect of the gating modifier toxin APETx1 on HERG, the inhibition of Kv10.1 by the isolated toxin is reduced at more positive voltages and the peptide seems to keep the Channel in a closed state. Although the peptide also induces inhibitory effects on other KV and NaV Channels, it exhibits no significant effect on HERG. Moreover, APETx4 induces a concentration-dependent cytotoxic and proapoptotic effect in various cancerous and noncancerous cell lines. This newly identified KV10.1 inhibitor can be used as a tool to further characterize the oncogenic Channel KV10.1 or as a scaffold for the design and synthesis of more potent and safer anticancer drugs.
Adrienne T Dennis - One of the best experts on this subject based on the ideXlab platform.
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antidepressant induced ubiquitination and degradation of the cardiac Potassium Channel HERG
Journal of Biological Chemistry, 2011Co-Authors: Adrienne T Dennis, Dierk Thomas, Drew M Nassal, Isabelle Deschenes, Eckhard FickerAbstract:The most common cause for adverse cardiac events by antidepressants is acquired long QT syndrome (acLQTS), which produces electrocardiographic abnormalities that have been associated with syncope, torsade de pointes arrhythmias, and sudden cardiac death. acLQTS is often caused by direct block of the cardiac Potassium current IKr/HERG, which is crucial for terminal repolarization in human heart. Importantly, desipramine belongs to a group of tricyclic antidepressant compounds that can simultaneously block HERG and inhibit its surface expression. Although up to 40% of all HERG blockers exert combined HERG block and trafficking inhibition, few of these compounds have been fully characterized at the cellular level. Here, we have studied in detail how desipramine inhibits HERG surface expression. We find a previously unrecognized combination of two entirely different mechanisms; desipramine increases HERG endocytosis and degradation as a consequence of drug-induced Channel ubiquitination and simultaneously inhibits HERG forward trafficking from the endoplasmic reticulum. This unique combination of cellular effects in conjunction with acute Channel block may explain why tricyclic antidepressants as a compound class are notorious for their association with arrhythmias and sudden cardiac death. Taken together, we describe the first example of drug-induced Channel ubiquitination and degradation. Our data are directly relevant to the cardiac safety of not only tricyclic antidepressants but also other therapeutic compounds that exert multiple effects on HERG, as HERG trafficking and degradation phenotypes may go undetected in most preclinical safety assays designed to screen for acLQTS.
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role of the cytosolic chaperones hsp70 and hsp90 in maturation of the cardiac Potassium Channel HERG
Circulation Research, 2003Co-Authors: Eckhard Ficker, Adrienne T Dennis, Lu Wang, Arthur M BrownAbstract:The human ether-a-gogo-related gene (HERG) encodes the alpha subunit of the cardiac Potassium current IKr. Several mutations in HERG produce trafficking-deficient Channels that may cause hereditary long-QT syndrome and sudden cardiac death. Although HERG currents have been studied extensively, little is known about the proteins involved in maturation and trafficking of HERG. Using immunoprecipitations, we show that the cytosolic chaperones heat shock protein (Hsp) 70 and Hsp90, but not Grp94, interact with HERG wild type (WT) during maturation. The specific Hsp90 inhibitor geldanamycin prevents maturation and increases proteasomal degradation of HERG WT, while reducing HERG currents in heterologous expression systems. In ventricular myocytes, inhibition of Hsp90 also decreases IKr, whereas geldanamycin had no effect on IKs or heterologously expressed Kv2.1 and Kv1.5 currents. Both Hsp90 and Hsp70 interact directly with the core-glycosylated form of HERG WT present in the endoplasmic reticulum but not the fully glycosylated, cell-surface form. For the trafficking-deficient LQT2 mutants, HERG R752W and HERG G601S, interactions with Hsp90 and Hsp70 are increased as both mutants remained tightly associated with Hsp90 and Hsp70 in the endoplasmic reticulum. Incubation at lower temperature for R752W or with the HERG blocker astemizole for G601S dissociates Channel-chaperone complexes and restores trafficking. In contrast, nonfunctional but trafficking-competent HERG G628S is released from chaperone complexes during maturation comparable to WT. We conclude that Hsp90 and Hsp70 are crucial for the maturation of HERG WT as well as the retention of trafficking-deficient LQT2 mutants. The full text of this article is available online at http://www.circresaha.org.
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retention in the endoplasmic reticulum as a mechanism of dominant negative current suppression in human long qt syndrome
Journal of Molecular and Cellular Cardiology, 2000Co-Authors: Eckhard Ficker, Adrienne T Dennis, Carlos A Obejeropaz, Pasqualina Castaldo, Maurizio Taglialatela, Arthur M BrownAbstract:Mutations in the cardiac Potassium Channel HERG (KCNH2) cause chromosome 7-linked long QT syndrome (LQT2) characterized by a prolonged QT interval, recurrent syncope and sudden cardiac death. Most mutations in HERG exhibit "loss of function" phenotypes with defective Channels either inserted into the plasma membrane or retained in the endoplasmic reticulum. "Loss of function" mutations reduce I(Kr), the cardiac delayed rectifier current encoded by HERG, due to haploinsufficiency or suppression of wild-type function by a dominant-negative mechanism. One explanation for dominant-negative current suppression is that mutant subunits render tetrameric Channel complexes non-conducting on co-assembly. In the present paper we describe an alternative mechanism for this phenomenon. We show (1) that the dominant-negative HERG mutation A561V is retained in the endoplasmic reticulum and (2) that wild-type Channels are tagged for retention in the ER by co-assembly with trafficking deficient A561V subunits. Thus, in HERG A561V dominant-negative suppression of wild-type function is the result of an acquired trafficking defect.
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a mechanism for the proarrhythmic effects of cisapride propulsid high affinity blockade of the human cardiac Potassium Channel HERG
FEBS Letters, 1997Co-Authors: David Rampe, Marylouise Roy, Adrienne T Dennis, Arthur M BrownAbstract:Cisapride (Propulsid) is a gastrointestinal prokinetic agent commonly used to treat nocturnal heartburn as well as a variety of other gastrointestinal disorders. The use of cisapride has been associated with acquired long QT syndrome and ventricular arrhythmias such as torsades de pointes which produces sudden cardiac death. These cardiotoxic effects can be due to blockade of one or more types of K+ Channel currents in the human heart. For this reason we compared the effects of cisapride on two cloned human cardiac K+ Channels, Kv1.5 and the human ether-a-go-go-related gene (HERG) stably transfected into mammalian cells. Using patch clamp electrophysiology, we found that cisapride was a potent inhibitor of HERG displaying an IC50 value of 44.5 nmol/l when tail currents at −40 mV were measured following a 2 s test depolarization to +20 mV. When HERG currents were measured at the end of prolonged (20 s) depolarizing steps to +20 mV, the apparent affinity of cisapride was increased and measured 6.70 nmol/l. The main effect of cisapride was to enhance the rate of HERG current decay thereby reducing current at the end of the voltage clamp pulse. Furthermore, the potency of cisapride for the HERG Channel was similar to that observed for the class III antiarrhythmic agent dofetilide (IC50=15.3 nmol/l) and the nonsedating antihistamine terfenadine (IC50=56.0 nmol/l). In contrast to its effects on HERG, cisapride inhibited Kv1.5 Channel currents weakly displaying an IC50 value of 21.2 μmol/l. It is concluded that cisapride displays specific, high affinity block of the human cardiac K+ Channel HERG. It is likely that this interaction underlies the proarrhythmic effects of the drug observed under certain clinical settings.
Eckhard Ficker - One of the best experts on this subject based on the ideXlab platform.
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antidepressant induced ubiquitination and degradation of the cardiac Potassium Channel HERG
Journal of Biological Chemistry, 2011Co-Authors: Adrienne T Dennis, Dierk Thomas, Drew M Nassal, Isabelle Deschenes, Eckhard FickerAbstract:The most common cause for adverse cardiac events by antidepressants is acquired long QT syndrome (acLQTS), which produces electrocardiographic abnormalities that have been associated with syncope, torsade de pointes arrhythmias, and sudden cardiac death. acLQTS is often caused by direct block of the cardiac Potassium current IKr/HERG, which is crucial for terminal repolarization in human heart. Importantly, desipramine belongs to a group of tricyclic antidepressant compounds that can simultaneously block HERG and inhibit its surface expression. Although up to 40% of all HERG blockers exert combined HERG block and trafficking inhibition, few of these compounds have been fully characterized at the cellular level. Here, we have studied in detail how desipramine inhibits HERG surface expression. We find a previously unrecognized combination of two entirely different mechanisms; desipramine increases HERG endocytosis and degradation as a consequence of drug-induced Channel ubiquitination and simultaneously inhibits HERG forward trafficking from the endoplasmic reticulum. This unique combination of cellular effects in conjunction with acute Channel block may explain why tricyclic antidepressants as a compound class are notorious for their association with arrhythmias and sudden cardiac death. Taken together, we describe the first example of drug-induced Channel ubiquitination and degradation. Our data are directly relevant to the cardiac safety of not only tricyclic antidepressants but also other therapeutic compounds that exert multiple effects on HERG, as HERG trafficking and degradation phenotypes may go undetected in most preclinical safety assays designed to screen for acLQTS.
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role of the cytosolic chaperones hsp70 and hsp90 in maturation of the cardiac Potassium Channel HERG
Circulation Research, 2003Co-Authors: Eckhard Ficker, Adrienne T Dennis, Lu Wang, Arthur M BrownAbstract:The human ether-a-gogo-related gene (HERG) encodes the alpha subunit of the cardiac Potassium current IKr. Several mutations in HERG produce trafficking-deficient Channels that may cause hereditary long-QT syndrome and sudden cardiac death. Although HERG currents have been studied extensively, little is known about the proteins involved in maturation and trafficking of HERG. Using immunoprecipitations, we show that the cytosolic chaperones heat shock protein (Hsp) 70 and Hsp90, but not Grp94, interact with HERG wild type (WT) during maturation. The specific Hsp90 inhibitor geldanamycin prevents maturation and increases proteasomal degradation of HERG WT, while reducing HERG currents in heterologous expression systems. In ventricular myocytes, inhibition of Hsp90 also decreases IKr, whereas geldanamycin had no effect on IKs or heterologously expressed Kv2.1 and Kv1.5 currents. Both Hsp90 and Hsp70 interact directly with the core-glycosylated form of HERG WT present in the endoplasmic reticulum but not the fully glycosylated, cell-surface form. For the trafficking-deficient LQT2 mutants, HERG R752W and HERG G601S, interactions with Hsp90 and Hsp70 are increased as both mutants remained tightly associated with Hsp90 and Hsp70 in the endoplasmic reticulum. Incubation at lower temperature for R752W or with the HERG blocker astemizole for G601S dissociates Channel-chaperone complexes and restores trafficking. In contrast, nonfunctional but trafficking-competent HERG G628S is released from chaperone complexes during maturation comparable to WT. We conclude that Hsp90 and Hsp70 are crucial for the maturation of HERG WT as well as the retention of trafficking-deficient LQT2 mutants. The full text of this article is available online at http://www.circresaha.org.
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retention in the endoplasmic reticulum as a mechanism of dominant negative current suppression in human long qt syndrome
Journal of Molecular and Cellular Cardiology, 2000Co-Authors: Eckhard Ficker, Adrienne T Dennis, Carlos A Obejeropaz, Pasqualina Castaldo, Maurizio Taglialatela, Arthur M BrownAbstract:Mutations in the cardiac Potassium Channel HERG (KCNH2) cause chromosome 7-linked long QT syndrome (LQT2) characterized by a prolonged QT interval, recurrent syncope and sudden cardiac death. Most mutations in HERG exhibit "loss of function" phenotypes with defective Channels either inserted into the plasma membrane or retained in the endoplasmic reticulum. "Loss of function" mutations reduce I(Kr), the cardiac delayed rectifier current encoded by HERG, due to haploinsufficiency or suppression of wild-type function by a dominant-negative mechanism. One explanation for dominant-negative current suppression is that mutant subunits render tetrameric Channel complexes non-conducting on co-assembly. In the present paper we describe an alternative mechanism for this phenomenon. We show (1) that the dominant-negative HERG mutation A561V is retained in the endoplasmic reticulum and (2) that wild-type Channels are tagged for retention in the ER by co-assembly with trafficking deficient A561V subunits. Thus, in HERG A561V dominant-negative suppression of wild-type function is the result of an acquired trafficking defect.