1
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Gomez-Lagunas F, Barriga-Montoya C, Pardo JP. State-independent inhibition of the oncogenic Kv10.1 channel by desethylamiodarone, a comparison with amiodarone. Pflugers Arch 2024; 476:323-335. [PMID: 38063872 PMCID: PMC10847070 DOI: 10.1007/s00424-023-02893-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 10/28/2023] [Accepted: 11/24/2023] [Indexed: 02/08/2024]
Abstract
Kv10.1 is a voltage-dependent K channel whose ectopic expression is associated with several human cancers. Additionally, Kv10.1 has structure-function properties which are not yet well understood. We are using drugs of clinical importance in an attempt to gain insight on the relationship between pharmacology and characteristic functional properties of this channel. Herein, we report the interaction of desethylamiodarone (desAd), the active metabolic product of the antiarrhythmic amiodarone with Kv10.1: desAd binds to both closed and open channels, with most inhibition taking place from the open state, with affinity ~ 5 times smaller than that of amiodarone. Current inhibition by desAd and amiodarone is not synergistic. Upon repolarization desAd becomes trapped in Kv10.1 and thereafter dissociates slowly from closed-and-blocked channels. The addition of the Cole-Moore shift plus desAd open-pore-block time courses yields an increasing phase on the steady-state inhibition curve (H∞) at hyperpolarized holding potentials. In contrast to amiodarone, desAd does not inhibit the Kv10.1 Cole-Moore shift, suggesting that a relevant hydrophobic interaction between amiodarone and Kv10.1 participates in the inhibition of the Cole-Moore shift, which is lost with desAd.
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Affiliation(s)
- F Gomez-Lagunas
- Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico City, México.
| | - C Barriga-Montoya
- Department of Physiology, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico City, México
| | - J P Pardo
- Department of Biochemistry, School of Medicine, Universidad Nacional Autónoma de México (UNAM), Mexico City, México
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2
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Intracellular hemin is a potent inhibitor of the voltage-gated potassium channel Kv10.1. Sci Rep 2022; 12:14645. [PMID: 36030326 PMCID: PMC9420133 DOI: 10.1038/s41598-022-18975-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 08/23/2022] [Indexed: 11/08/2022] Open
Abstract
Heme, an iron-protoporphyrin IX complex, is a cofactor bound to various hemoproteins and supports a broad range of functions, such as electron transfer, oxygen transport, signal transduction, and drug metabolism. In recent years, there has been a growing recognition of heme as a non-genomic modulator of ion channel functions. Here, we show that intracellular free heme and hemin modulate human ether à go-go (hEAG1, Kv10.1) voltage-gated potassium channels. Application of hemin to the intracellular side potently inhibits Kv10.1 channels with an IC50 of about 4 nM under ambient and 63 nM under reducing conditions in a weakly voltage-dependent manner, favoring inhibition at resting potential. Functional studies on channel mutants and biochemical analysis of synthetic and recombinant channel fragments identified a heme-binding motif CxHx8H in the C-linker region of the Kv10.1 C terminus, with cysteine 541 and histidines 543 and 552 being important for hemin binding. Binding of hemin to the C linker may induce a conformational constraint that interferes with channel gating. Our results demonstrate that heme and hemin are endogenous modulators of Kv10.1 channels and could be exploited to modulate Kv10.1-mediated cellular functions.
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Söğüt F, Çömelekoğlu Ü, Dervişoğlu H, Eroğlu P, Yalin S, Yilmaz NŞ. Effect of imipramine on ether à-go-go potassium channel (Kv1.10) expression in DU145 prostate cancer cells. Andrologia 2021; 54:e14291. [PMID: 34729805 DOI: 10.1111/and.14291] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2021] [Revised: 09/29/2021] [Accepted: 09/30/2021] [Indexed: 12/16/2022] Open
Abstract
In recent studies, it has been reported that ion channels play an important role in cancer formation. Therefore, it is possible that the use of pharmacological agents targeting ion channels will allow the development of new strategies for cancer treatment. In this study, we investigate the effect of imipramine on Eag1 channel expression in DU145 prostate cancer cells. Culture cells were divided into 4 groups as the control, 10, 50 and 75 µM imipramine. Eag1 channel currents and conductivity were determined by whole-cell patch-clamp technique and gene expression by real time-polymerase chain reaction (RT-PCR). Current records were taken before (at 0th minute, as control) and 10 min after imipramine administration to the cells. It was observed that all three doses of imipramine significantly reduced Eag1 currents and conductivity compared with the control. However, the differences between dose groups were not significant. Similarly, Eag1 channel protein expression was found to be significantly reduced for all three doses of imipramine compared with the control group, but there was no significant difference in gene expression between dose groups. Obtained results suggested that imipramine has the potential to be used as a pharmacological agent targeting the Eag1 channel in the treatment of prostate cancer.
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Affiliation(s)
- Fatma Söğüt
- Department of First Aid and Emergency, Vocational School of Medical Services, Mersin University, Mersin, Turkey
| | - Ülkü Çömelekoğlu
- Department of Biophysics, Faculty of Medicine, Mersin University, Mersin, Turkey
| | - Hülya Dervişoğlu
- Department of Histology and Embryology, Faculty of Medicine, Mersin University, Mersin, Turkey
| | - Pelin Eroğlu
- Department of Chemistry, Faculty of Science and Literature, Mersin University, Mersin, Turkey
| | - Serap Yalin
- Department of Biochemistry, Faculty of Pharmacy, Mersin University, Mersin, Turkey
| | - Necat Şakir Yilmaz
- Department of Histology and Embryology, Faculty of Medicine, Mersin University, Mersin, Turkey
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4
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Optimized Tuning of Auditory Inner Hair Cells to Encode Complex Sound through Synergistic Activity of Six Independent K + Current Entities. Cell Rep 2021; 32:107869. [PMID: 32640234 DOI: 10.1016/j.celrep.2020.107869] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 04/08/2020] [Accepted: 06/16/2020] [Indexed: 02/06/2023] Open
Abstract
Auditory inner hair cells (IHCs) convert sound vibrations into receptor potentials that drive synaptic transmission. For the precise encoding of sound qualities, receptor potentials are shaped by K+ conductances tuning the properties of the IHC membrane. Using patch-clamp and computational modeling, we unravel this membrane specialization showing that IHCs express an exclusive repertoire of six voltage-dependent K+ conductances mediated by Kv1.8, Kv7.4, Kv11.1, Kv12.1, and BKCa channels. All channels are active at rest but are triggered differentially during sound stimulation. This enables non-saturating tuning over a far larger potential range than in IHCs expressing fewer current entities. Each conductance contributes to optimizing responses, but the combined activity of all channels synergistically improves phase locking and the dynamic range of intensities that IHCs can encode. Conversely, hypothetical simpler IHCs appear limited to encode only certain aspects (frequency or intensity). The exclusive channel repertoire of IHCs thus constitutes an evolutionary adaptation to encode complex sound through multifaceted receptor potentials.
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5
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Hofschröer V, Najder K, Rugi M, Bouazzi R, Cozzolino M, Arcangeli A, Panyi G, Schwab A. Ion Channels Orchestrate Pancreatic Ductal Adenocarcinoma Progression and Therapy. Front Pharmacol 2021; 11:586599. [PMID: 33841132 PMCID: PMC8025202 DOI: 10.3389/fphar.2020.586599] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Accepted: 10/30/2020] [Indexed: 02/06/2023] Open
Abstract
Pancreatic ductal adenocarcinoma is a devastating disease with a dismal prognosis. Therapeutic interventions are largely ineffective. A better understanding of the pathophysiology is required. Ion channels contribute substantially to the "hallmarks of cancer." Their expression is dysregulated in cancer, and they are "misused" to drive cancer progression, but the underlying mechanisms are unclear. Ion channels are located in the cell membrane at the interface between the intracellular and extracellular space. They sense and modify the tumor microenvironment which in itself is a driver of PDAC aggressiveness. Ion channels detect, for example, locally altered proton and electrolyte concentrations or mechanical stimuli and transduce signals triggered by these microenvironmental cues through association with intracellular signaling cascades. While these concepts have been firmly established for other cancers, evidence has emerged only recently that ion channels are drivers of PDAC aggressiveness. Particularly, they appear to contribute to two of the characteristic PDAC features: the massive fibrosis of the tumor stroma (desmoplasia) and the efficient immune evasion. Our critical review of the literature clearly shows that there is still a remarkable lack of knowledge with respect to the contribution of ion channels to these two typical PDAC properties. Yet, we can draw parallels from ion channel research in other fibrotic and inflammatory diseases. Evidence is accumulating that pancreatic stellate cells express the same "profibrotic" ion channels. Similarly, it is at least in part known which major ion channels are expressed in those innate and adaptive immune cells that populate the PDAC microenvironment. We explore potential therapeutic avenues derived thereof. Since drugs targeting PDAC-relevant ion channels are already in clinical use, we propose to repurpose those in PDAC. The quest for ion channel targets is both motivated and complicated by the fact that some of the relevant channels, for example, KCa3.1, are functionally expressed in the cancer, stroma, and immune cells. Only in vivo studies will reveal which arm of the balance we should put our weights on when developing channel-targeting PDAC therapies. The time is up to explore the efficacy of ion channel targeting in (transgenic) murine PDAC models before launching clinical trials with repurposed drugs.
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Affiliation(s)
| | - Karolina Najder
- Institute of Physiology II, University of Münster, Münster, Germany
| | - Micol Rugi
- Institute of Physiology II, University of Münster, Münster, Germany
| | - Rayhana Bouazzi
- Department of Experimental and Clinical Medicine, Section of Internal Medicine, University of Florence, Florence, Italy
| | - Marco Cozzolino
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Annarosa Arcangeli
- Department of Experimental and Clinical Medicine, Section of Internal Medicine, University of Florence, Florence, Italy
| | - Gyorgy Panyi
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Albrecht Schwab
- Institute of Physiology II, University of Münster, Münster, Germany
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Şahin M, Öncü G, Yılmaz MA, Özkan D, Saybaşılı H. Transformation of SH-SY5Y cell line into neuron-like cells: Investigation of electrophysiological and biomechanical changes. Neurosci Lett 2021; 745:135628. [PMID: 33440235 DOI: 10.1016/j.neulet.2021.135628] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Revised: 12/14/2020] [Accepted: 01/04/2021] [Indexed: 02/07/2023]
Abstract
SH-SY5Y human neuroblastoma cells are commonly used as neuronal models. Here, we examined different aspects of SH-SY5Y cell differentiation. Various differentiation protocols have been proposed previously, including treatments with retinoic acid, brain-derived neurotrophic factor (BDNF), cholesterol and oestradiol. We examined undifferentiated SH-SY5Y cells (UNDIFF); cells differentiated by the treatment with retinoic acid (RA); retinoic acid + BDNF (RB); and retinoic acid + BDNF + cholesterol + oestradiol (RBCE). We performed whole-cell patch-clamp recordings from these cells and nanomechanically characterised them by using atomic force microscopy (AFM). Our results indicated that Na+ currents become most pronounced in the differentiated RB cells, whereas UNDIFF SH-SY5Y cells had significantly larger K+ currents, which is a characteristic feature of cancer cells. AFM observations of these two groups showed that Young's moduli of SH-SY5Y cells increased threefold with differentiation. Furthermore, we showed a direct relationship between Na+ channel activity and elasticity in these cells. We conclude that SH-SY5Y human neuroblastoma cells should be used as a neuronal model only when they are differentiated by the treatment with retinoic acid and BDNF.
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Affiliation(s)
- Meryem Şahin
- Institute of Biomedical Engineering, Boğaziçi University, Istanbul, Turkey
| | - Gül Öncü
- Institute of Biomedical Engineering, Boğaziçi University, Istanbul, Turkey
| | - Mustafa Alper Yılmaz
- Department of Mechanical Engineering, National Defense University, Naval Academy, Istanbul, Turkey
| | - Doğuş Özkan
- Department of Mechanical Engineering, National Defense University, Naval Academy, Istanbul, Turkey
| | - Hale Saybaşılı
- Institute of Biomedical Engineering, Boğaziçi University, Istanbul, Turkey.
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7
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Scorpion Toxins and Ion Channels: Potential Applications in Cancer Therapy. Toxins (Basel) 2020; 12:toxins12050326. [PMID: 32429050 PMCID: PMC7290751 DOI: 10.3390/toxins12050326] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 04/14/2020] [Accepted: 04/15/2020] [Indexed: 12/24/2022] Open
Abstract
Apoptosis, a genetically directed process of cell death, has been studied for many years, and the biochemical mechanisms that surround it are well known and described. There are at least three pathways by which apoptosis occurs, and each pathway depends on extra or intracellular processes for activation. Apoptosis is a vital process, but disturbances in proliferation and cell death rates can lead to the development of diseases like cancer. Several compounds, isolated from scorpion venoms, exhibit inhibitory effects on different cancer cells. Indeed, some of these compounds can differentiate between healthy and cancer cells within the same tissue. During the carcinogenic process, morphological, biochemical, and biological changes occur that enable these compounds to modulate cancer but not healthy cells. This review highlights cancer cell features that enable modulation by scorpion neurotoxins. The properties of the isolated scorpion neurotoxins in cancer cells and the potential uses of these compounds as alternative treatments for cancer are discussed.
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8
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Implication of Voltage-Gated Potassium Channels in Neoplastic Cell Proliferation. Cancers (Basel) 2019; 11:cancers11030287. [PMID: 30823672 PMCID: PMC6468671 DOI: 10.3390/cancers11030287] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2019] [Revised: 02/21/2019] [Accepted: 02/24/2019] [Indexed: 12/12/2022] Open
Abstract
Voltage-gated potassium channels (Kv) are the largest group of ion channels. Kv are involved in controlling the resting potential and action potential duration in the heart and brain. Additionally, these proteins participate in cell cycle progression as well as in several other important features in mammalian cell physiology, such as activation, differentiation, apoptosis, and cell volume control. Therefore, Kv remarkably participate in the cell function by balancing responses. The implication of Kv in physiological and pathophysiological cell growth is the subject of study, as Kv are proposed as therapeutic targets for tumor regression. Though it is widely accepted that Kv channels control proliferation by allowing cell cycle progression, their role is controversial. Kv expression is altered in many cancers, and their participation, as well as their use as tumor markers, is worthy of effort. There is an ever-growing list of Kv that remodel during tumorigenesis. This review focuses on the actual knowledge of Kv channel expression and their relationship with neoplastic proliferation. In this work, we provide an update of what is currently known about these proteins, thereby paving the way for a more precise understanding of the participation of Kv during cancer development.
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9
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Bai X, Li K, Yao L, Kang XL, Cai SQ. A forward genetic screen identifies chaperone CNX-1 as a conserved biogenesis regulator of ERG K + channels. J Gen Physiol 2018; 150:1189-1201. [PMID: 29941431 PMCID: PMC6080891 DOI: 10.1085/jgp.201812025] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 05/15/2018] [Indexed: 12/15/2022] Open
Abstract
The human ether-a-go-go-related gene (hERG) encodes a voltage-gated potassium channel that controls repolarization of cardiac action potentials. Accumulating evidence suggests that most disease-related hERG mutations reduce the function of the channel by disrupting protein biogenesis of the channel in the endoplasmic reticulum (ER). However, the molecular mechanism underlying the biogenesis of ERG K+ channels is largely unknown. By forward genetic screening, we identified an ER-located chaperone CNX-1, the worm homologue of mammalian chaperone Calnexin, as a critical regulator for the protein biogenesis of UNC-103, the ERG-type K+ channel in Caenorhabditis elegans Loss-of-function mutations of cnx-1 decreased the protein level and current density of the UNC-103 K+ channel and suppressed the behavioral defects caused by a gain-of-function mutation in unc-103 Moreover, CNX-1 facilitated tetrameric assembly of UNC-103 channel subunits in a liposome-assisted cell-free translation system. Further studies showed that CNX-1 act in parallel to DNJ-1, another ER-located chaperone known to regulate maturation of UNC-103 channels, on controlling the protein biogenesis of UNC-103. Importantly, Calnexin interacted with hERG proteins in the ER in HEK293T cells. Deletion of calnexin reduced the expression and current densities of endogenous hERG K+ channels in SH-SY5Y cells. Collectively, we reveal an evolutionarily conserved chaperone CNX-1/Calnexin controlling the biogenesis of ERG-type K+ channels.
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Affiliation(s)
- Xue Bai
- Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Kai Li
- Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China
| | - Li Yao
- Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Xin-Lei Kang
- Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China
| | - Shi-Qing Cai
- Institute of Neuroscience and State Key Laboratory of Neuroscience, CAS Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China
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10
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Yang XJ, Zhang K, Xu JJ, Chen HY. In Situ Visualization of hERG Potassium Channel via Dual Signal Amplification. Anal Chem 2018; 90:6199-6205. [DOI: 10.1021/acs.analchem.8b00725] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Xue-Jiao Yang
- State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Kai Zhang
- State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Jing-Juan Xu
- State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
- Key Laboratory of Sensor Analysis of Tumor Marker, Ministry of Education, College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China
| | - Hong-Yuan Chen
- State Key Laboratory of Analytical Chemistry for Life Science and Collaborative Innovation Center of Chemistry for Life Sciences, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
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11
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Dierich M, Evers S, Wilke BU, Leitner MG. Inverse Modulation of Neuronal K v12.1 and K v11.1 Channels by 4-Aminopyridine and NS1643. Front Mol Neurosci 2018; 11:11. [PMID: 29440988 PMCID: PMC5797642 DOI: 10.3389/fnmol.2018.00011] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Accepted: 01/09/2018] [Indexed: 01/24/2023] Open
Abstract
The three members of the ether-à-go-go-gene-like (Elk; Kv12.1-Kv12.3) family of voltage-gated K+ channels are predominantly expressed in neurons, but only little information is available on their physiological relevance. It was shown that Kv12.2 channels modulate excitability of hippocampal neurons, but no native current could be attributed to Kv12.1 and Kv12.3 subunits yet. This may appear somewhat surprising, given high expression of their mRNA transcripts in several brain areas. Native Kv12 currents may have been overlooked so far due to limited knowledge on their biophysical properties and lack of specific pharmacology. Except for Kv12.2, appropriate genetically modified mouse models have not been described; therefore, identification of Kv12-mediated currents in native cell types must rely on characterization of unique properties of the channels. We focused on recombinant human Kv12.1 to identify distinct properties of these channels. We found that Kv12.1 channels exhibited significant mode shift of activation, i.e., stabilization of the voltage sensor domain in a “relaxed” open state after prolonged channel activation. This mode shift manifested by a slowing of deactivation and, most prominently, a significant shift of voltage dependence to hyperpolarized potentials. In contrast to related Kv11.1, mode shift was not sensitive to extracellular Na+, which allowed for discrimination between these isoforms. Sensitivity of Kv12.1 and Kv11.1 to the broad-spectrum K+ antagonist 4-aminopyridine was similar. However, 4-AP strongly activated Kv12.1 channels, but it was an inhibitor of Kv11 channels. Interestingly, the agonist of Kv11 channels NS1643 also differentially modulated the activity of these channels, i.e., NS1643 activated Kv11.1, but strongly inhibited Kv12.1 channels. Thus, these closely related channels are distinguished by inverse pharmacological profiles. In summary, we identified unique biophysical and pharmacological properties of Kv12.1 channels and established straightforward experimental protocols to characterize Kv12.1-mediated currents. Identification of currents in native cell types with mode shift that are activated through 4-AP and inhibited by NS1643 can provide strong evidence for contribution of Kv12.1 to whole cell currents.
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Affiliation(s)
- Marlen Dierich
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University of Marburg, Marburg, Germany
| | - Saskia Evers
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University of Marburg, Marburg, Germany
| | - Bettina U Wilke
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University of Marburg, Marburg, Germany
| | - Michael G Leitner
- Department of Neurophysiology, Institute of Physiology and Pathophysiology, Philipps University of Marburg, Marburg, Germany.,Division of Physiology, Department of Physiology and Medical Physics, Innsbruck Medical University, Innsbruck, Austria
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12
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Horst CH, Titze-de-Almeida R, Titze-de-Almeida SS. The involvement of Eag1 potassium channels and miR-34a in rotenone-induced death of dopaminergic SH-SY5Y cells. Mol Med Rep 2017; 15:1479-1488. [PMID: 28259991 PMCID: PMC5364983 DOI: 10.3892/mmr.2017.6191] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2015] [Accepted: 11/25/2016] [Indexed: 12/21/2022] Open
Abstract
The loss of dopaminergic neurons and the resultant motor impairment are hallmarks of Parkinson's disease. The SH‑SY5Y cell line is a model of dopaminergic neurons, and allows for the study of dopaminergic neuronal injury. Previous studies have revealed changes in Ether à go‑go 1 (Eag1) potassium channel expression during p53-induced SH‑SY5Y apoptosis, and the regulatory involvement of microRNA‑34a (miR‑34a) was demonstrated. In the present study, the involvement of Eag1 and miR‑34a in rotenone‑induced SH‑SY5Y cell injury was investigated. Rotenone is a neurotoxin, which is often used to generate models of Parkinson's disease, since it causes the death of nigrostriatal neurons by inducing intracellular aggregation of alpha synuclein and ubiquitin. In the present study, rotenone resulted in a dose‑dependent decrease in cell viability, as revealed by 3‑(4,5‑dimethylthiazol‑2‑yl)‑2,5‑diphenyltetrazolium bromide (MTT) and trypan blue cell counting assays. In addition, Eag1 was demonstrated to be constitutively expressed by SH‑SY5Y cells, and involved in cell viability. Suppression of Eag1 with astemizole resulted in a dose‑dependent decrease in cell viability, as revealed by MTT assay. Astemizole also enhanced the severity of rotenone‑induced injury in SH‑SY5Y cells. RNA interference against Eag1, using synthetic small interfering RNAs (siRNAs), corroborated this finding, as siRNAs potentiated rotenone‑induced injury. Eag1‑targeted siRNAs (kv10.1‑3 or EAG1hum_287) resulted in a statistically significant 16.4‑23.5% increase in vulnerability to rotenone. An increased number of apoptotic nuclei were observed in cells transfected with EAG1hum_287. Notably, this siRNA intensified rotenone‑induced apoptosis, as revealed by an increase in caspase 3/7 activity. Conversely, a miR‑34a inhibitor was demonstrated to exert neuroprotective effects. The viability of cells exposed to rotenone for 24 or 48 h and treated with miR‑34a inhibitor was restored by 8.4‑8.8%. In conclusion, Eag1 potassium channels and miR‑34a are involved in the response to rotenone-induced injury in SH‑SY5Y cells. The neuroprotective effect of mir‑34a inhibitors merits further investigations in animal models of Parkinson's disease.
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Affiliation(s)
- Camila Hillesheim Horst
- Technology for Gene Therapy Laboratory, Central Institute of Sciences, Faculty of Agronomy and Veterinary Medicine, University of Brasília, Brasília 70910‑900, Brazil
| | - Ricardo Titze-de-Almeida
- Technology for Gene Therapy Laboratory, Central Institute of Sciences, Faculty of Agronomy and Veterinary Medicine, University of Brasília, Brasília 70910‑900, Brazil
| | - Simoneide Souza Titze-de-Almeida
- Technology for Gene Therapy Laboratory, Central Institute of Sciences, Faculty of Agronomy and Veterinary Medicine, University of Brasília, Brasília 70910‑900, Brazil
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13
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Zhao Y, Goldschen-Ohm MP, Morais-Cabral JH, Chanda B, Robertson GA. The intrinsically liganded cyclic nucleotide-binding homology domain promotes KCNH channel activation. J Gen Physiol 2017; 149:249-260. [PMID: 28122815 PMCID: PMC5299623 DOI: 10.1085/jgp.201611701] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2016] [Revised: 11/29/2016] [Accepted: 12/21/2016] [Indexed: 12/17/2022] Open
Abstract
hEAG1 is a member of the KCNH family of ion channels, which are characterized by C-terminal regions with homology to cyclic nucleotide–binding domains (CNBhDs). Zhao et al. show that an “intrinsic ligand” occupying the CNBhD binding pocket promotes the activated and open state of the channel. Channels in the ether-à-go-go or KCNH family of potassium channels are characterized by a conserved, C-terminal domain with homology to cyclic nucleotide–binding homology domains (CNBhDs). Instead of cyclic nucleotides, two amino acid residues, Y699 and L701, occupy the binding pocket, forming an “intrinsic ligand.” The role of the CNBhD in KCNH channel gating is still unclear, however, and a detailed characterization of the intrinsic ligand is lacking. In this study, we show that mutating both Y699 and L701 to alanine, serine, aspartate, or glycine impairs human EAG1 channel function. These mutants slow channel activation and shift the conductance–voltage (G–V) relation to more depolarized potentials. The mutations affect activation and the G-V relation progressively, indicating that the gating machinery is sensitive to multiple conformations of the CNBhD. Substitution with glycine at both sites (GG), which eliminates the side chains that interact with the binding pocket, also reduces the ability of voltage prepulses to populate more preactivated states along the activation pathway (i.e., the Cole–Moore effect), as if stabilizing the voltage sensor in deep resting states. Notably, deletion of the entire CNBhD (577–708, ΔCNBhD) phenocopies the GG mutant, suggesting that GG is a loss-of-function mutation and the CNBhD requires an intrinsic ligand to exert its functional effects. We developed a kinetic model for both wild-type and ΔCNBhD mutant channels that describes all our observations on activation kinetics, the Cole–Moore shift, and G-V relations. These findings support a model in which the CNBhD both promotes voltage sensor activation and stabilizes the open pore. The intrinsic ligand is critical for these functional effects.
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Affiliation(s)
- Yaxian Zhao
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705.,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Marcel P Goldschen-Ohm
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705.,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - João H Morais-Cabral
- Instituto de Biologia Molecular e Celular, Universidade do Porto, 4150 Porto, Portugal.,Instituto de Investigação e Inovação em Saúde, Universidade do Porto, 4150 Porto, Portugal
| | - Baron Chanda
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705.,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
| | - Gail A Robertson
- Department of Neuroscience, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705 .,Cardiovascular Research Center, University of Wisconsin School of Medicine and Public Health, Madison, WI 53705
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14
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Gómez-Lagunas F, Carrillo E, Pardo LA, Stühmer W. Gating Modulation of the Tumor-Related Kv10.1 Channel by Mibefradil. J Cell Physiol 2017; 232:2019-2032. [DOI: 10.1002/jcp.25448] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2015] [Accepted: 06/02/2016] [Indexed: 01/24/2023]
Affiliation(s)
- Froylán Gómez-Lagunas
- Department of Physiology, School of Medicine. National Autonomous University of Mexico, UNAM; Ciudad Universitaria; México City México DF
| | - Elisa Carrillo
- Department of Physiology, School of Medicine. National Autonomous University of Mexico, UNAM; Ciudad Universitaria; México City México DF
| | - Luis A. Pardo
- Max-Planck Institute for Experimental Medicine; Göttingen Germany
| | - Walter Stühmer
- Max-Planck Institute for Experimental Medicine; Göttingen Germany
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15
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Li Z, Zhu K, Gong X, Vasilescu S, Sun Y, Hong K, Li H, Li L, Shan Y. Inducing Polyclonal Eag1-Specific Antibodies by Vaccination with a Linear Epitope Immunogen and Its Relation to Breast Tumorigenesis. Pathol Oncol Res 2017; 23:761-767. [DOI: 10.1007/s12253-016-0158-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Accepted: 12/08/2016] [Indexed: 11/30/2022]
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16
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Lörinczi E, Helliwell M, Finch A, Stansfeld PJ, Davies NW, Mahaut-Smith M, Muskett FW, Mitcheson JS. Calmodulin Regulates Human Ether à Go-Go 1 (hEAG1) Potassium Channels through Interactions of the Eag Domain with the Cyclic Nucleotide Binding Homology Domain. J Biol Chem 2016; 291:17907-18. [PMID: 27325704 PMCID: PMC5016179 DOI: 10.1074/jbc.m116.733576] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Indexed: 11/24/2022] Open
Abstract
The ether à go-go family of voltage-gated potassium channels is structurally distinct. The N terminus contains an eag domain (eagD) that contains a Per-Arnt-Sim (PAS) domain that is preceded by a conserved sequence of 25–27 amino acids known as the PAS-cap. The C terminus contains a region with homology to cyclic nucleotide binding domains (cNBHD), which is directly linked to the channel pore. The human EAG1 (hEAG1) channel is remarkably sensitive to inhibition by intracellular calcium (Ca2+i) through binding of Ca2+-calmodulin to three sites adjacent to the eagD and cNBHD. Here, we show that the eagD and cNBHD interact to modulate Ca2+-calmodulin as well as voltage-dependent gating. Sustained elevation of Ca2+i resulted in an initial profound inhibition of hEAG1 currents, which was followed by a phase when current amplitudes partially recovered, but activation gating was slowed and shifted to depolarized potentials. Deletion of either the eagD or cNBHD abolished the inhibition by Ca2+i. However, deletion of just the PAS-cap resulted in a >15-fold potentiation in response to elevated Ca2+i. Mutations of residues at the interface between the eagD and cNBHD have been linked to human cancer. Glu-600 on the cNBHD, when substituted with residues with a larger volume, resulted in hEAG1 currents that were profoundly potentiated by Ca2+i in a manner similar to the ΔPAS-cap mutant. These findings provide the first evidence that eagD and cNBHD interactions are regulating Ca2+-dependent gating and indicate that the binding of the PAS-cap with the cNBHD is required for the closure of the channels upon CaM binding.
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Affiliation(s)
- Eva Lörinczi
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Matthew Helliwell
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN, the School of Physiology and Pharmacology, University of Bristol, Bristol BS5 1TD, and
| | - Alina Finch
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Phillip J Stansfeld
- the Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom
| | - Noel W Davies
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Martyn Mahaut-Smith
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - Frederick W Muskett
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN
| | - John S Mitcheson
- From the Department of Molecular and Cell Biology, University of Leicester, Leicester LE1 9HN,
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17
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Acuña-Macías I, Vera E, Vázquez-Sánchez AY, Mendoza-Garrido ME, Camacho J. Differential regulation of human Eag1 channel expression by serum and epidermal growth factor in lung and breast cancer cells. Onco Targets Ther 2015; 8:2959-65. [PMID: 26527881 PMCID: PMC4621197 DOI: 10.2147/ott.s85504] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Oncogenic ether à-go-go-1 (Eag1) potassium channels are overexpressed in most primary human solid tumors. Low oxygen and nutrient/growth factor concentrations play critical roles in tumorigenesis. However, the mechanisms by which tumor cells survive and proliferate under growth factor-depleted conditions remain elusive. Here, we investigated whether serum-deprived conditions and epidermal growth factor (EGF) regulate Eag1 expression in human lung and breast cancer cells. The human cancer cell lines A549 and MCF-7 (from the lungs and breast, respectively) were obtained from the American Type Culture Collection and cultured following the manufacturer’s recommendations. Eag1 gene and protein expression were studied by real-time PCR and immunocytochemistry, respectively. Cell proliferation was evaluated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and ERK1/2 phosphorylation was investigated by Western blot. Serum-deprived conditions increased Eag1 mRNA and protein expression in both cell lines. This Eag1 upregulation was prevented by EGF and the ERK1/2 inhibitor U0126 in only lung cancer cells; vascular endothelial growth factor did not prevent Eag1 upregulation. Our results suggest that Eag1 may act as a survival and mitogenic factor under low-serum and nutrient conditions and may be a clinical target during the early stages of tumor development.
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Affiliation(s)
- Isabel Acuña-Macías
- Department of Pharmacology, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico
| | - Eunice Vera
- Department of Pharmacology, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico
| | - Alma Yolanda Vázquez-Sánchez
- Department of Pharmacology, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico
| | - María Eugenia Mendoza-Garrido
- Department of Physiology, Biophysics and Neurosciences, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico
| | - Javier Camacho
- Department of Pharmacology, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico
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18
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Involvement of potassium channels in the progression of cancer to a more malignant phenotype. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:2477-92. [PMID: 25517985 DOI: 10.1016/j.bbamem.2014.12.008] [Citation(s) in RCA: 95] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 12/01/2014] [Accepted: 12/08/2014] [Indexed: 12/22/2022]
Abstract
Potassium channels are a diverse group of pore-forming transmembrane proteins that selectively facilitate potassium flow through an electrochemical gradient. They participate in the control of the membrane potential and cell excitability in addition to different cell functions such as cell volume regulation, proliferation, cell migration, angiogenesis as well as apoptosis. Because these physiological processes are essential for the correct cell function, K+ channels have been associated with a growing number of diseases including cancer. In fact, different K+ channel families such as the voltage-gated K+ channels, the ether à-go-go K+ channels, the two pore domain K+ channels and the Ca2+-activated K+ channels have been associated to tumor biology. Potassium channels have a role in neoplastic cell-cycle progression and their expression has been found abnormal in many types of tumors and cancer cells. In addition, the expression and activity of specific K+ channels have shown a significant correlation with the tumor malignancy grade. The aim of this overview is to summarize published data on K+ channels that exhibit oncogenic properties and have been linked to a more malignant cancer phenotype. This article is part of a Special Issue entitled: Membrane channels and transporters in cancers.
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19
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Abstract
Ion channels and transporters are expressed in every living cell, where they participate in controlling a plethora of biological processes and physiological functions, such as excitation of cells in response to stimulation, electrical activities of cells, excitation-contraction coupling, cellular osmolarity, and even cell growth and death. Alterations of ion channels/transporters can have profound impacts on the cellular physiology associated with these proteins. Expression of ion channels/transporters is tightly regulated and expression deregulation can trigger abnormal processes, leading to pathogenesis, the channelopathies. While transcription factors play a critical role in controlling the transcriptome of ion channels/transporters at the transcriptional level by acting on the 5'-flanking region of the genes, microribonucleic acids (miRNAs), a newly discovered class of regulators in the gene network, are also crucial for expression regulation at the posttranscriptional level through binding to the 3'untranslated region of the genes. These small noncoding RNAs fine tune expression of genes involved in a wide variety of cellular processes. Recent studies revealed the role of miRNAs in regulating expression of ion channels/transporters and the associated physiological functions. miRNAs can target ion channel genes to alter cardiac excitability (conduction, repolarization, and automaticity) and affect arrhythmogenic potential of heart. They can modulate circadian rhythm, pain threshold, neuroadaptation to alcohol, brain edema, etc., through targeting ion channel genes in the neuronal systems. miRNAs can also control cell growth and tumorigenesis by acting on the relevant ion channel genes. Future studies are expected to rapidly increase to unravel a new repertoire of ion channels/transporters for miRNA regulation.
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Affiliation(s)
- Zhiguo Wang
- Harbin Medical University, Harbin, Heilongjiang, People's Republic of China.
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20
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Yang M, Brackenbury WJ. Membrane potential and cancer progression. Front Physiol 2013; 4:185. [PMID: 23882223 PMCID: PMC3713347 DOI: 10.3389/fphys.2013.00185] [Citation(s) in RCA: 362] [Impact Index Per Article: 32.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Accepted: 06/28/2013] [Indexed: 12/27/2022] Open
Abstract
Membrane potential (Vm), the voltage across the plasma membrane, arises because of the presence of different ion channels/transporters with specific ion selectivity and permeability. Vm is a key biophysical signal in non-excitable cells, modulating important cellular activities, such as proliferation and differentiation. Therefore, the multiplicities of various ion channels/transporters expressed on different cells are finely tuned in order to regulate the Vm. It is well-established that cancer cells possess distinct bioelectrical properties. Notably, electrophysiological analyses in many cancer cell types have revealed a depolarized Vm that favors cell proliferation. Ion channels/transporters control cell volume and migration, and emerging data also suggest that the level of Vm has functional roles in cancer cell migration. In addition, hyperpolarization is necessary for stem cell differentiation. For example, both osteogenesis and adipogenesis are hindered in human mesenchymal stem cells (hMSCs) under depolarizing conditions. Therefore, in the context of cancer, membrane depolarization might be important for the emergence and maintenance of cancer stem cells (CSCs), giving rise to sustained tumor growth. This review aims to provide a broad understanding of the Vm as a bioelectrical signal in cancer cells by examining several key types of ion channels that contribute to its regulation. The mechanisms by which Vm regulates cancer cell proliferation, migration, and differentiation will be discussed. In the long term, Vm might be a valuable clinical marker for tumor detection with prognostic value, and could even be artificially modified in order to inhibit tumor growth and metastasis.
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Affiliation(s)
- Ming Yang
- Department of Biology, University of York York, UK
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21
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Frolov RV, Bagati A, Casino B, Singh S. Potassium channels in Drosophila: historical breakthroughs, significance, and perspectives. J Neurogenet 2013. [PMID: 23181728 DOI: 10.3109/01677063.2012.744990] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Drosophila has enabled important breakthroughs in K(+) channel research, including identification and fi rst cloning of a voltage-activated K(+) channel, Shaker, a founding member of the K(V)1 family. Drosophila has also helped in discovering other K(+) channels, such as Shab, Shaw, Shal, Eag, Sei, Elk, and also Slo, a Ca(2+) - and voltage-dependent K(+) channel. These findings have contributed significantly to our understanding of ion channels and their role in physiology. Drosophila continues to play an important role in ion channel studies, benefiting from an unparalleled arsenal of genetic tools and availability of tens of thousands of genetically modified strains. These tools allow deletion, expression, or misexpression of almost any gene in question with temporal and spatial control. The combination of these tools and resources with the use of forward genetic approach in Drosophila further enhances its strength as a model system. There are many areas in which Drosophila can further help our understanding of ion channels and their function. These include signaling pathways involved in regulating and modulating ion channels, basic information on channels and currents where very little is currently known, and the role of ion channels in physiology and pathology.
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Affiliation(s)
- Roman V Frolov
- Department of Pharmacology and Toxicology, State University of New York at Buffalo, Buffalo, New York 14214-3000, USA
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22
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Huang X, Dubuc AM, Hashizume R, Berg J, He Y, Wang J, Chiang C, Cooper MK, Northcott PA, Taylor MD, Barnes MJ, Tihan T, Chen J, Hackett CS, Weiss WA, James CD, Rowitch DH, Shuman MA, Jan YN, Jan LY. Voltage-gated potassium channel EAG2 controls mitotic entry and tumor growth in medulloblastoma via regulating cell volume dynamics. Genes Dev 2012; 26:1780-96. [PMID: 22855790 DOI: 10.1101/gad.193789.112] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Medulloblastoma (MB) is the most common pediatric CNS malignancy. We identify EAG2 as an overexpressed potassium channel in MBs across different molecular and histological subgroups. EAG2 knockdown not only impairs MB cell growth in vitro, but also reduces tumor burden in vivo and enhances survival in xenograft studies. Mechanistically, we demonstrate that EAG2 protein is confined intracellularly during interphase but is enriched in the plasma membrane during late G2 phase and mitosis. Disruption of EAG2 expression results in G2 arrest and mitotic catastrophe associated with failure of premitotic cytoplasmic condensation. While the tumor suppression function of EAG2 knockdown is independent of p53 activation, DNA damage checkpoint activation, or changes in the AKT pathway, this defective cell volume control is specifically associated with hyperactivation of the p38 MAPK pathway. Inhibition of the p38 pathway significantly rescues the growth defect and G2 arrest. Strikingly, ectopic membrane expression of EAG2 in cells at interphase results in cell volume reduction and mitotic-like morphology. Our study establishes the functional significance of EAG2 in promoting MB tumor progression via regulating cell volume dynamics, the perturbation of which activates the tumor suppressor p38 MAPK pathway, and provides clinical relevance for targeting this ion channel in human MBs.
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Affiliation(s)
- Xi Huang
- Howard Hughes Medical Institute, San Francisco, CA 94158, USA
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23
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Ninkovic M, Mitkovski M, Kohl T, Stühmer W, Pardo LA. Physical and functional interaction of KV10.1 with Rabaptin-5 impacts ion channel trafficking. FEBS Lett 2012; 586:3077-84. [PMID: 22841712 DOI: 10.1016/j.febslet.2012.07.055] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2012] [Revised: 07/04/2012] [Accepted: 07/06/2012] [Indexed: 10/28/2022]
Abstract
K(V)10.1 is a potassium channel expressed in brain and implicated in tumor progression. We have searched for proteins interacting with K(V)10.1 and identified Rabaptin-5, an effector of the Rab5 GTPase. Both proteins co-localize on large early endosomes induced by Rab5 hyperactivity. Silencing of Rabaptin-5 induces down-regulation of recycling of K(V)10.1 channel in transfected cells and reduction of K(V)10.1 current density in cells natively expressing K(V)10.1, indicating a role of Rabaptin-5 in channel trafficking. K(V)10.1 co-localizes, but does not physically interact, with Rab7 and Rab11. Our data highlights the complex control of the amount of K(V)10.1 channels on the cell surface.
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Affiliation(s)
- Milena Ninkovic
- Department of Molecular Biology of Neuronal Signals, Max-Planck-Institute of Experimental Medicine, Göttingen, Germany
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24
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Sahoo N, Schönherr R, Hoshi T, Heinemann SH. Cysteines control the N- and C-linker-dependent gating of KCNH1 potassium channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:1187-95. [PMID: 22310694 DOI: 10.1016/j.bbamem.2012.01.021] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Revised: 01/23/2012] [Accepted: 01/24/2012] [Indexed: 12/30/2022]
Abstract
KCNH1 (EAG1) is a member of the Kv family of voltage-gated potassium channels. However, KCNH1 channels also show some amino-acid sequence similarity to cyclic-nucleotide-regulated channels: they harbor an N-terminal PAS domain, a C-terminal cyclic nucleotide binding homology domain (cNBHD), and N- and C-terminal binding sites for calmodulin. Another notable feature is the channels' high sensitivity toward oxidative modification. Using human KCNH1 expressed in Xenopus oocytes and HEK 293 cells we investigated how oxidative modification alters channel function. Intracellular application of H(2)O(2) or cysteine-specific modifiers potently inhibited KCNH1 channels in two phases. Our systematic cysteine mutagenesis study showed that the rapid and dominant phase was attributed to a right-shift in the voltage dependence of activation, caused by chemical modification of residues C145 and C214. The slow component depended on the C-terminal residues C532 and C562. The cysteine pairs are situated at structural elements linking the transmembrane S1 segment with the PAS domain (N-linker) and the transmembrane channel gate S6 with the cNBH domain (C-linker), respectively. The functional state of KCNH1 channels is determined by the oxidative status of these linkers that provide an additional dimension of channel regulation.
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Affiliation(s)
- Nirakar Sahoo
- Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena & Jena University Hospital, Hans-Knöll-Str. 2, D-07745 Jena, Germany
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25
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Kohl T, Lörinczi E, Pardo LA, Stühmer W. Rapid internalization of the oncogenic K+ channel K(V)10.1. PLoS One 2011; 6:e26329. [PMID: 22022602 PMCID: PMC3192180 DOI: 10.1371/journal.pone.0026329] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Accepted: 09/24/2011] [Indexed: 11/18/2022] Open
Abstract
K(V)10.1 is a mammalian brain voltage-gated potassium channel whose ectopic expression outside of the brain has been proven relevant for tumor biology. Promotion of cancer cell proliferation by K(V)10.1 depends largely on ion flow, but some oncogenic properties remain in the absence of ion permeation. Additionally, K(V)10.1 surface populations are small compared to large intracellular pools. Control of protein turnover within cells is key to both cellular plasticity and homeostasis, and therefore we set out to analyze how endocytic trafficking participates in controlling K(V)10.1 intracellular distribution and life cycle. To follow plasma membrane K(V)10.1 selectively, we generated a modified channel of displaying an extracellular affinity tag for surface labeling by α-bungarotoxin. This modification only minimally affected K(V)10.1 electrophysiological properties. Using a combination of microscopy and biochemistry techniques, we show that K(V)10.1 is constitutively internalized involving at least two distinct pathways of endocytosis and mainly sorted to lysosomes. This occurs at a relatively fast rate. Simultaneously, recycling seems to contribute to maintain basal K(V)10.1 surface levels. Brief K(V)10.1 surface half-life and rapid lysosomal targeting is a relevant factor to be taken into account for potential drug delivery and targeting strategies directed against K(V)10.1 on tumor cells.
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Affiliation(s)
- Tobias Kohl
- Max-Planck-Institute of Experimental Medicine, Department of Molecular Biology of Neuronal Signals, Göttingen, Germany
| | - Eva Lörinczi
- Max-Planck-Institute of Experimental Medicine, Department of Molecular Biology of Neuronal Signals, Göttingen, Germany
| | - Luis A. Pardo
- Max-Planck-Institute of Experimental Medicine, Department of Molecular Biology of Neuronal Signals, Göttingen, Germany
| | - Walter Stühmer
- Max-Planck-Institute of Experimental Medicine, Department of Molecular Biology of Neuronal Signals, Göttingen, Germany
- DFG Research Center for Molecular Physiology of the Brain (CMPB), Göttingen, Germany
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26
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Lin H, Li Z, Chen C, Luo X, Xiao J, Dong D, Lu Y, Yang B, Wang Z. Transcriptional and post-transcriptional mechanisms for oncogenic overexpression of ether à go-go K+ channel. PLoS One 2011; 6:e20362. [PMID: 21655246 PMCID: PMC3105031 DOI: 10.1371/journal.pone.0020362] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2011] [Accepted: 04/30/2011] [Indexed: 11/23/2022] Open
Abstract
The human ether-à-go-go-1 (h-eag1) K+ channel is expressed in a variety of cell lines derived from human malignant tumors and in clinical samples of several different cancers, but is otherwise absent in normal tissues. It was found to be necessary for cell cycle progression and tumorigenesis. Specific inhibition of h-eag1 expression leads to inhibition of tumor cell proliferation. We report here that h-eag1 expression is controlled by the p53−miR-34−E2F1 pathway through a negative feed-forward mechanism. We first established E2F1 as a transactivator of h-eag1 gene through characterizing its promoter region. We then revealed that miR-34, a known transcriptional target of p53, is an important negative regulator of h-eag1 through dual mechanisms by directly repressing h-eag1 at the post-transcriptional level and indirectly silencing h-eag1 at the transcriptional level via repressing E2F1. There is a strong inverse relationship between the expression levels of miR-34 and h-eag1 protein. H-eag1antisense antagonized the growth-stimulating effects and the upregulation of h-eag1 expression in SHSY5Y cells, induced by knockdown of miR-34, E2F1 overexpression, or inhibition of p53 activity. Therefore, p53 negatively regulates h-eag1 expression by a negative feed-forward mechanism through the p53−miR-34−E2F1 pathway. Inactivation of p53 activity, as is the case in many cancers, can thus cause oncogenic overexpression of h-eag1 by relieving the negative feed-forward regulation. These findings not only help us understand the molecular mechanisms for oncogenic overexpression of h-eag1 in tumorigenesis but also uncover the cell-cycle regulation through the p53−miR-34−E2F1−h-eag1 pathway. Moreover, these findings place h-eag1 in the p53−miR-34−E2F1−h-eag1 pathway with h-eag as a terminal effecter component and with miR-34 (and E2F1) as a linker between p53 and h-eag1. Our study therefore fills the gap between p53 pathway and its cellular function mediated by h-eag1.
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Affiliation(s)
- Huixian Lin
- Research Center, Montreal Heart Institute, Montreal, Quebec, Canada
| | - Zhe Li
- Department of Pharmacology (State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Chang Chen
- Department of Pharmacology (State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Xiaobin Luo
- Research Center, Montreal Heart Institute, Montreal, Quebec, Canada
- Department of Medicine, Universite de Montreal, Montreal, Quebec, Canada
- Cardiovascular Research Institute (Key Laboratory of Cardiovascular Research, Ministry of Education of China), Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Jiening Xiao
- Research Center, Montreal Heart Institute, Montreal, Quebec, Canada
| | - Deli Dong
- Department of Pharmacology (State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Yanjie Lu
- Department of Pharmacology (State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
- Cardiovascular Research Institute (Key Laboratory of Cardiovascular Research, Ministry of Education of China), Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Baofeng Yang
- Department of Pharmacology (State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
- Cardiovascular Research Institute (Key Laboratory of Cardiovascular Research, Ministry of Education of China), Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
- * E-mail: (ZW); (BY)
| | - Zhiguo Wang
- Research Center, Montreal Heart Institute, Montreal, Quebec, Canada
- Department of Medicine, Universite de Montreal, Montreal, Quebec, Canada
- Cardiovascular Research Institute (Key Laboratory of Cardiovascular Research, Ministry of Education of China), Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
- * E-mail: (ZW); (BY)
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27
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Wang Y, Zhang Y, Yang L, Cai B, Li J, Zhou Y, Yin L, Yang L, Yang BF, Lu YJ. Arsenic trioxide induces the apoptosis of human breast cancer MCF-7 cells through activation of caspase-3 and inhibition of HERG channels. Exp Ther Med 2011; 2:481-486. [PMID: 22977528 DOI: 10.3892/etm.2011.224] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Accepted: 02/28/2011] [Indexed: 01/27/2023] Open
Abstract
Arsenic trioxide (As(2)O(3)) has been widely used to treat patients with acute promyelocytic leukemia and has also been shown to exhibit therapeutic effects on various types of solid tumors, including gastric cancer and lung carcinoma. Breast cancer is a type of solid tumor whose incidence has been increasing for many years. The present study was designed to investigate the effects of As(2)O(3) on the human breast cancer cell line MCF-7, and to explore its potential mechanisms. The MTT assay demonstrated that As(2)O(3) decreased the cellular viability of MCF-7 cells in a concentration-dependent manner. Morphological observation, the TUNEL assay and flow cytometric analysis revealed that apoptosis was involved in the process. An assay for caspase-3 activity suggested that the apoptosis was mediated through caspase-3 activation. Further investigation indicated that protein levels of the human ether-a-go-go-related gene (HERG) were markedly downregulated by As(2)O(3). Taken together, the results indicate that arsenic trioxide induces the apoptosis of human breast cancer MCF-7 cells at least in part through the activation of caspase-3 and the decrease in HERG expression.
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Affiliation(s)
- Ying Wang
- Department of Pharmacology, State-Province Key Laboratories of Biomedicine and Pharmaceutics, and
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Asher V, Sowter H, Shaw R, Bali A, Khan R. Eag and HERG potassium channels as novel therapeutic targets in cancer. World J Surg Oncol 2010; 8:113. [PMID: 21190577 PMCID: PMC3022597 DOI: 10.1186/1477-7819-8-113] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2010] [Accepted: 12/29/2010] [Indexed: 12/03/2022] Open
Abstract
Voltage gated potassium channels have been extensively studied in relation to cancer. In this review, we will focus on the role of two potassium channels, Ether à-go-go (Eag), Human ether à-go-go related gene (HERG), in cancer and their potential therapeutic utility in the treatment of cancer. Eag and HERG are expressed in cancers of various organs and have been implicated in cell cycle progression and proliferation of cancer cells. Inhibition of these channels has been shown to reduce proliferation both in vitro and vivo studies identifying potassium channel modulators as putative inhibitors of tumour progression. Eag channels in view of their restricted expression in normal tissue may emerge as novel tumour biomarkers.
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Affiliation(s)
- Viren Asher
- Department of Obstetrics and Gynaecology, School of Graduate Medicine and Health, Royal Derby Hospital, Uttoxeter road, Derby DE22 3DT, UK.
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Current inhibition of human EAG1 potassium channels by the Ca2+ binding protein S100B. FEBS Lett 2010; 584:3896-900. [PMID: 20708613 DOI: 10.1016/j.febslet.2010.07.063] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2010] [Revised: 07/16/2010] [Accepted: 07/30/2010] [Indexed: 12/13/2022]
Abstract
Voltage-dependent human ether à go-go (hEAG1) potassium channels are implicated in neuronal signaling as well as in cancer cell proliferation. Unique sensitivity of the channel to intracellular Ca(2+) is mediated by calmodulin (CaM) binding to the intracellular N- and C-termini of the channel. Here we show that application of the acidic calcium-binding protein S100B to inside-out patches of Xenopus oocytes causes Ca(2+)-dependent inhibition of expressed hEAG1 channels. Protein pull-down assays and fluorescence correlation spectroscopy (FCS) revealed that S100B binds to hEAG1 and shares the same binding sites with CaM. Thus, S100B is a potential alternative calcium sensor for hEAG1 potassium channels.
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Agarwal JR, Griesinger F, Stühmer W, Pardo LA. The potassium channel Ether à go-go is a novel prognostic factor with functional relevance in acute myeloid leukemia. Mol Cancer 2010; 9:18. [PMID: 20105281 PMCID: PMC2835655 DOI: 10.1186/1476-4598-9-18] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2009] [Accepted: 01/27/2010] [Indexed: 11/16/2022] Open
Abstract
Background The voltage-gated potassium channel hEag1 (KV10.1) has been related to cancer biology. The physiological expression of the human channel is restricted to the brain but it is frequently and abundantly expressed in many solid tumors, thereby making it a promising target for a specific diagnosis and therapy. Because chronic lymphatic leukemia has been described not to express hEag1, it has been assumed that the channel is not expressed in hematopoietic neoplasms in general. Results Here we show that this assumption is not correct, because the channel is up-regulated in myelodysplastic syndromes, chronic myeloid leukemia and almost half of the tested acute myeloid leukemias in a subtype-dependent fashion. Most interestingly, channel expression strongly correlated with increasing age, higher relapse rates and a significantly shorter overall survival. Multivariate Cox regression analysis revealed hEag1 expression levels in AML as an independent predictive factor for reduced disease-free and overall survival; such an association had not been reported before. As a functional correlate, specific hEag1 blockade inhibited the proliferation and migration of several AML cell lines and primary cultured AML cells in vitro. Conclusion Our observations implicate hEag1 as novel target for diagnostic, prognostic and/or therapeutic approaches in AML.
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Affiliation(s)
- Jasmin R Agarwal
- Max-Planck-Institute of Experimental Medicine, Hermann-Rein-Str, 3, 37075 Göttingen, Germany
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Brelidze TI, Carlson AE, Zagotta WN. Absence of direct cyclic nucleotide modulation of mEAG1 and hERG1 channels revealed with fluorescence and electrophysiological methods. J Biol Chem 2009; 284:27989-27997. [PMID: 19671703 DOI: 10.1074/jbc.m109.016337] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Similar to CNG and HCN channels, EAG and ERG channels contain a cyclic nucleotide binding domain (CNBD) in their C terminus. While cyclic nucleotides have been shown to facilitate opening of CNG and HCN channels, their effect on EAG and ERG channels is less clear. Here we explored cyclic nucleotide binding and modulation of mEAG1 and hERG1 channels with fluorescence and electrophysiology. Binding of cyclic nucleotides to the isolated CNBD of mEAG1 and hERG1 channels was examined with two independent fluorescence-based methods: changes in tryptophan fluorescence and fluorescence of an analog of cAMP, 8-NBD-cAMP. As a positive control for cyclic nucleotide binding we used changes in the fluorescence of the isolated CNBD of mHCN2 channels. Our results indicated that cyclic nucleotides do not bind to the isolated CNBD domain of mEAG1 channels and bind with low affinity (K(d) > or = 51 microm) to the isolated CNBD of hERG1 channels. Consistent with the results on the isolated CNBD, application of cyclic nucleotides to inside-out patches did not affect currents recorded from mEAG1 channels. Surprisingly, despite its low affinity binding to the isolated CNBD, cAMP also had no effect on currents from hERG1 channels even at high concentrations. Our results indicate that cyclic nucleotides do not directly modulate mEAG1 and hERG1 channels. Further studies are necessary to determine if the CNBD in the EAG family of K(+) channels might harbor a binding site for a ligand yet to be uncovered.
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Affiliation(s)
- Tinatin I Brelidze
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195; Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195
| | - Anne E Carlson
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195
| | - William N Zagotta
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195; Howard Hughes Medical Institute, University of Washington, Seattle, Washington 98195.
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Downie BR, Sánchez A, Knötgen H, Contreras-Jurado C, Gymnopoulos M, Weber C, Stühmer W, Pardo LA. Eag1 expression interferes with hypoxia homeostasis and induces angiogenesis in tumors. J Biol Chem 2008; 283:36234-40. [PMID: 18927085 PMCID: PMC2606018 DOI: 10.1074/jbc.m801830200] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2008] [Revised: 09/19/2008] [Indexed: 01/07/2023] Open
Abstract
Ether-á-go-go-1 (Eag1) is a CNS-localized voltage-gated potassium channel that is found ectopically expressed in a majority of extracranial solid tumors. While circumstantial evidence linking Eag1 to tumor biology has been well established, the mechanisms by which the channel contributes to tumor progression remain elusive. In this study, we have used in vivo and in vitro techniques to identify a candidate mechanism. A mutation that eliminates ion permeation fails to completely abolish xenograft tumor formation by transfected cells, indicating that Eag1 contributes to tumor progression independently of its primary function as an ion channel. Our data suggest that Eag1 interferes with the cellular mechanism for maintaining oxygen homeostasis, increasing HIF-1 activity, and thereby VEGF secretion and tumor vascularization.
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Affiliation(s)
- Bryan R Downie
- Max-Planck Institute of Experimental Medicine, Hermann-Rein Str. 3, 37075 Göttingen, Germany
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Wadhwa S, Wadhwa P, Dinda AK, Gupta NP. Differential expression of potassium ion channels in human renal cell carcinoma. Int Urol Nephrol 2008; 41:251-7. [PMID: 18777199 DOI: 10.1007/s11255-008-9459-z] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2008] [Accepted: 08/11/2008] [Indexed: 11/29/2022]
Abstract
PURPOSE Ether-a-go-go (EAG) or EAG-related (ERG) voltage-gated potassium ion channels are involved in tumor generation and progression. Their over- and/or misexpression has been demonstrated in various tumors, and inhibition of these channels has suppressed proliferation of various cancer cells. We investigate and compare the pattern of expression of EAG and human ERG (HERG) channels in renal cell carcinoma and "normal" renal tissue. METHOD Tissue samples, obtained at the time of radical nephrectomy from the tumor-bearing areas, and uninvolved renal tissue were preserved in 4% paraformaldehyde and cryosectioned at 20 mum. Immunohistochemical and Western blot analysis was performed on the tumor and uninvolved kidney parenchyma by incubating with polyclonal anti-HERG 1b (Alomone Lab, Israel), anti-EAG1, and anti-EAG2. Pattern of expression of EAG/HERG channels in normal renal tissue and carcinoma were noted and compared. RESULTS The study was performed on 16 radical and four partial nephrectomy specimens (n = 20). All tumors in the cohort were clear cell renal carcinoma. Normal renal tissue was found to exhibit heterogeneous cytoplasmic positivity for EAG1 and focal HERG immunoreactivity (IR) in the proximal (PCT) and distal convoluted tubules (DCT). EAG2 IR was absent in the normal renal tissue. Clear cell RCC demonstrated a loss of HERG expression while diffuse overexpression of EAG1 and EAG2 was noted. Western blot analysis corroborated the immunohistochemical observations. CONCLUSIONS In our study both EAG1 and EAG2 potassium channels were overexpressed in clear cell renal cancer. In contrast to other adenocarcinomas, there is loss of HERG expression in clear cell RCC, which may possibly explain its chemoresistance. These ion channels may provide a potential for targeted therapy.
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Affiliation(s)
- Surbhi Wadhwa
- Department of Anatomy, All India Institute of Medical Sciences, New Delhi, India
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Expression and prognostic roles of Eag1 in resected esophageal squamous cell carcinomas. Dig Dis Sci 2008; 53:2039-44. [PMID: 18080766 DOI: 10.1007/s10620-007-0116-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2007] [Accepted: 11/05/2007] [Indexed: 12/22/2022]
Abstract
Expression of Eag1 was detected in resected esophageal squamous cell carcinomas tissues and matched tissues by immunohistochemistry and RT-PCR. Positive expression of Eag1 protein was 75% (51/68), and mRNA was 73% (8/11) in primary cancer tissues. Eag1 protein positively stained in all 10 metastatic lymph nodes. Eag1 protein and mRNA were negatively expressed in all non-cancerous matched tissues. Eag1 protein was associated with depth of penetration (P = 0.023), but not associated with other clinicopathological factors. Eag1 protein positive group had a significantly shorter survival time than the negative group (P = 0.005). Survival rates at each time-point for the positive group were lower than that for the negative group (P = 0.006), and Eag1 was identified as an independent prognostic factor of long-term survival (P = 0.016). In conclusion, Eag1 was aberrantly expressed in ESCC and correlated with poor prognosis after surgery.
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Abstract
Emerging evidence indicates that ion channels act in a variety of physiologic and pathologic processes beyond electronic signal transmission, including in cancer. We recently found that the potassium channel Eag1 can mediate cancer progression and that a monoclonal antibody, which inhibits Eag1 action, can effectively restrict cancer cell proliferation. We discuss how Eag1 targeting may be useful in diagnostic or therapeutic settings.
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Affiliation(s)
- Luis A Pardo
- Max-Planck Institute of Experimental Medicine, Göttingen, Germany.
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Raschi E, Vasina V, Poluzzi E, De Ponti F. The hERG K+ channel: target and antitarget strategies in drug development. Pharmacol Res 2008; 57:181-95. [PMID: 18329284 DOI: 10.1016/j.phrs.2008.01.009] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 01/21/2008] [Accepted: 01/22/2008] [Indexed: 12/16/2022]
Abstract
The human ether-à-go-go related gene (hERG) K+ channel is of great interest for both basic researchers and clinicians because its blockade by drugs can lead to QT prolongation, which is a risk factor for torsades de pointes, a potentially life-threatening arrhythmia. A growing list of agents with "QT liability" have been withdrawn from the market or restricted in their use, whereas others did not even receive regulatory approval for this reason. Thus, hERG K+ channels have become a primary antitarget (i.e. an unwanted target) in drug development because their blockade causes potentially serious side effects. On the other hand, the recent identification and functional characterization of hERG K+ channels not only in the heart, but also in several other tissues (e.g. neurons, smooth muscle and cancer cells) may have far reaching implications for drug development for a possible exploitation of hERG as a target, especially in oncology and cardiology.
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Affiliation(s)
- Emanuel Raschi
- Department of Pharmacology, University of Bologna, Via Irnerio, 48, I-40126 Bologna BO, Bologna, Italy
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Schwarzer S, Kolacna L, Lichtenberg-Fraté H, Sychrova H, Ludwig J. Functional expression of the voltage-gated neuronal mammalian potassium channel rat ether à go-go1 in yeast. FEMS Yeast Res 2008; 8:405-13. [DOI: 10.1111/j.1567-1364.2007.00351.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Ding XW, Luo HS, Jin X, Yan JJ, Ai YW. Aberrant expression of Eag1 potassium channels in gastric cancer patients and cell lines. Med Oncol 2008; 24:345-50. [PMID: 17873312 DOI: 10.1007/s12032-007-0015-y] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2006] [Revised: 11/30/1999] [Accepted: 12/24/2006] [Indexed: 01/22/2023]
Abstract
Recently, an interesting relationship between potassium channels and cancer has evolved. The aim of this study is to investigate expression of Eag1 potassium channel in gastric cancer and its role in cancer cells growth. The expression of Eag1 for gasric cancer patients and cell lines as well as gastric adenoma was investigated by immunohistochemistry and reverse transcription polymerase chain reaction. In addition, imipramine was used to identify the involvement of Eag1 in the growth of SGC-7901 and BGC-823 cells. Frequency of positive expression of Eag1 protein was 70.5% (67/95) and Eag1 mRNA was 68.2% (15/22) in gastric cancer primary tissues. Eag1 mRNA was positively expressed in two gastric cell lines. Eag1 protein and mRNA were negatively expressed in paired non-cancerous matched tissues and 5 cases of adenoma tissues. The expression level of Eag1 protein was associated with lymph node metastasis (P = 0.049) and stage (P = 0.039), but had no correlation with sex, age, differentiation grades, and other organs metastases. Imipramine significantly inhibited the proliferation of SGC-7901 and BGC-823 cells at 12 h and 24 h detected by cells number counting and MTT assay (P < 0.01). The study indicates Eag1 is aberrantly expressed in gastric cancer tissues and cell lines and associated with cancer lymph node metastasis and stage and play an important role in the proliferation of gastric cancer cells.
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Affiliation(s)
- Xiang-Wu Ding
- Department of Gastroenterology, Renmin Hospital, Wuhan University, Wuhan 430060, P.R., China.
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Ding XW, Luo HS. Ether à go-go potassium channel and malignant tumors. Shijie Huaren Xiaohua Zazhi 2007; 15:2772-2779. [DOI: 10.11569/wcjd.v15.i26.2772] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Recently, increasing evidence from cell biology and pharmacology demonstrates that cancer cells exhibit ion channel expression patterns, ion conductances and electric properties that are very different from those of resting cells. These peculiar properties are functionally involved in cancer pathogenesis. In particular, because of its oncogenic properties, distribution, modulation and pharmacology, human ether à go-go potassium channel (Eag1, Kv10.1, KCNH1) is considered a critical ion channel-encoding gene involved in the establishment and maintenance of neoplastic growth. This review summarizes most of the findings regarding Eag1 channels and malignant tumors, focusing on cellular mechanisms, mRNA and protein expression in tissues, oncogenic properties, modulation and pharmacology.
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Gómez-Varela D, Zwick-Wallasch E, Knötgen H, Sánchez A, Hettmann T, Ossipov D, Weseloh R, Contreras-Jurado C, Rothe M, Stühmer W, Pardo LA. Monoclonal antibody blockade of the human Eag1 potassium channel function exerts antitumor activity. Cancer Res 2007; 67:7343-9. [PMID: 17671204 DOI: 10.1158/0008-5472.can-07-0107] [Citation(s) in RCA: 161] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The potassium channel ether à go-go has been directly linked to cellular proliferation and transformation, although its physiologic role(s) are as of yet unknown. The specific blockade of human Eag1 (hEag1) may not only allow the dissection of the role of the channel in distinct physiologic processes, but because of the implication of hEag1 in tumor biology, it may also offer an opportunity for the treatment of cancer. However, members of the potassium channel superfamily are structurally very similar to one another, and it has been notoriously difficult to obtain specific blockers for any given channel. Here, we describe and validate the first rational design of a monoclonal antibody that selectively inhibits a potassium current in intact cells. Specifically blocking hEag1 function using this antibody inhibits tumor cell growth both in vitro and in vivo. Our data provide a proof of concept that enables the generation of functional antagonistic monoclonal antibodies against ion channels with therapeutic potential. The particular antibody described here, as well as the technique developed to make additional functional antibodies to Eag1, makes it possible to evaluate the potential of the channel as a target for cancer therapy.
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Toral C, Mendoza-Garrido ME, Azorín E, Hernández-Gallegos E, Gomora JC, Delgadillo DM, Solano-Agama C, Camacho J. Effect of extracellular matrix on adhesion, viability, actin cytoskeleton and K+ currents of cells expressing human ether à go-go channels. Life Sci 2007; 81:255-65. [PMID: 17586530 DOI: 10.1016/j.lfs.2007.05.014] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2006] [Revised: 05/12/2007] [Accepted: 05/18/2007] [Indexed: 10/23/2022]
Abstract
Ether à go-go (EAG) potassium channels possess oncogenic properties and have gained great interest as research tools for cancer detection and therapy. Besides, EAG electrophysiological properties are regulated through the cell cycle and determined by cytoskeletal interactions. Thus, because of the pivotal role of extracellular matrix (ECM) and cytoskeleton in cancer progression, we studied the effect of ECM components on adhesion, viability, actin organization and EAG currents in wild-type CHO cells (CHO-wt) and cells expressing human EAG channels (CHO-hEAG). At short incubation times, adhesion and viability of CHO-hEAG cells grown on collagen, heparin or poly-lysine were lower than CHO-wt cells, however, only CHO-hEAG sustained growing under total serum starvation. CHO-hEAG cells grown on poly-lysine did not organize their cytoskeleton but when grown on collagen or fibronectin displayed lamellipodia and stress fibers, respectively. Interestingly, EAG expressing cells displayed special actin structures suggesting a dynamic actin cytoskeleton, such structures were not exhibited by wild-type cells. EAG current density was significantly lower in cells grown on collagen at short incubation times. Finally, we studied potential associations between hEAG channels and integrins or actin filaments by confocal microscopy. No association between beta1-integrins and hEAG channels was found, however, a very strong co-localization was observed between hEAG channels and actin filaments, supported by immunoblot experiments in which hEAG channels were found in the insoluble fraction (associated to cytoskeleton). Our results suggest ECM components as potential modulators of oncogenic human-EAG expressing cells and emphasize the relationship between potassium channels, cytoskeleton, ECM and cancer.
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Affiliation(s)
- Claudia Toral
- Pharmacology Section, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico City, Mexico
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Ding XW, Yan JJ, An P, Lü P, Luo HS. Aberrant expression of ether à go-go potassium channel in colorectal cancer patients and cell lines. World J Gastroenterol 2007; 13:1257-61. [PMID: 17451210 PMCID: PMC4147004 DOI: 10.3748/wjg.v13.i8.1257] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To study the expression of ether à go-go (Eag1) potassium channel in colorectal cancer and the relation-ship between their expression and clinico-pathological features.
METHODS: The expression levels of Eag1 protein were determined in 76 cancer tissues with paired non-cancerous matched tissues as well as 9 colorectal adenoma tissues by immunohistochemistry. Eag1 mRNA expression was detected in 13 colorectal cancer tissues with paired non-cancerous matched tissues and 4 colorectal adenoma tissues as well as two colorectal cancer cell lines (LoVo and HT-29) by reverse transcription PCR.
RESULTS: The frequency of positive expression of Eag1 protein was 76.3% (58/76) and Eag1 mRNA was 76.9% (10/13) in colorectal cancer tissue. Expression level of Eag1 protein was dependent on the tumor size, lymphatic node metastasis, other organ metastases and Dukes’ stage (P < 0.05), while not dependent on age, sex, site and degree of differentiation. Eag1 protein and mRNA were negative in normal colorectal tissue, and absolutely negative in colorectal adenomas except that one case was positively stained for Eag1 protein.
CONCLUSION: Eag1 protein and mRNA are aberrantly expressed in colorectal cancer and occasionally expressed in colorectal adenoma. The high frequency of expression of Eag1 in tumors and the restriction of normal expression to the brain suggest the potential of this protein for diagnostic, prognostic and therapeutic purposes.
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Affiliation(s)
- Xiang-Wu Ding
- Department of Gastroenterology, Renmin Hospital of Wuhan University, Wuhan 430060, Hubei Province, China
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Lin H, Xiao J, Luo X, Wang H, Gao H, Yang B, Wang Z. Retracted: Overexpression HERG K+ channel gene mediates cell-growth signals on activation of oncoproteins SP1 and NF-κB and inactivation of tumor suppressor Nkx3.1. J Cell Physiol 2007; 212:137-47. [PMID: 17311278 DOI: 10.1002/jcp.21015] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The long QT syndrome gene human ether-a-go-go related gene (HERG) encodes a K(+) channel critical to cardiac repolarization. It peculiarly overexpresses in cancer cells of different histogenesis and promotes tumorigenesis. To decipher the molecular mechanisms for HERG overexpression, we identified and characterized the promoter region of the HERG gene, which contains cis-elements for multiple oncoproteins and tumor suppressors. Oncoprotein Sp1 was found to be essential to driving the HERG promoter thereby transcription. Another oncoprotein NF-kappaB transactivated, while tumor suppressor Nkx3.1 repressed HERG promoter activity and endogenous HERG transcription. Loss-of-function mutations in the corresponding cis-elements rendered a loss of the ability of the oncoproteins Sp1 and NF-kappaB to transactivate, and of the tumor repressor Nkx3.1 to repress, HERG transcription. Either activation of Sp1 and NF-kappaB or silencing of Nkx3.1 promoted tumor cell growth, and the effects were abrogated by HERG inhibition or knockdown, but facilitated by overexpression of HERG, indicating that HERG mediates the cell growth signals generated by activation of oncoproteins or inactivation of tumor suppressors. Binding of Sp1, NF-kappaB, and Nkx3.1 to their respective cis-elements in the HERG promoter in vitro and their presence on the HERG promoter in vivo were confirmed. Therefore, the HERG promoter region is characterized by multiple Sp1 binding sites that are responsible for transcription initiation of the HERG gene and by binding sites for multiple other oncogenes and tumor suppressor genes being important for regulating HERG expression. The HERG K(+) channel is likely a mediator of growth-promoting processes induced by oncoproteins and/or by silencing of tumor suppressors.
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Affiliation(s)
- Huixian Lin
- Research Center, Montreal Heart Institute, Montreal, Canada
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Hemmerlein B, Weseloh RM, Mello de Queiroz F, Knötgen H, Sánchez A, Rubio ME, Martin S, Schliephacke T, Jenke M, Stühmer W, Pardo LA. Overexpression of Eag1 potassium channels in clinical tumours. Mol Cancer 2006; 5:41. [PMID: 17022810 PMCID: PMC1621079 DOI: 10.1186/1476-4598-5-41] [Citation(s) in RCA: 205] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2006] [Accepted: 10/05/2006] [Indexed: 01/12/2023] Open
Abstract
Background Certain types of potassium channels (known as Eag1, KCNH1, Kv10.1) are associated with the production of tumours in patients and in animals. We have now studied the expression pattern of the Eag1 channel in a large range of normal and tumour tissues from different collections utilising molecular biological and immunohistochemical techniques. Results The use of reverse transcription real-time PCR and specifically generated monoclonal anti-Eag1 antibodies showed that expression of the channel is normally limited to specific areas of the brain and to restricted cell populations throughout the body. Tumour samples, however, showed a significant overexpression of the channel with high frequency (up to 80% depending on the tissue source) regardless of the detection method (staining with either one of the antibodies, or detection of Eag1 RNA). Conclusion Inhibition of Eag1 expression in tumour cell lines reduced cell proliferation. Eag1 may therefore represent a promising target for the tailored treatment of human tumours. Furthermore, as normal cells expressing Eag1 are either protected by the blood-brain barrier or represent the terminal stage of normal differentiation, Eag1 based therapies could produce only minor side effects.
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Affiliation(s)
- Bernhard Hemmerlein
- Department of Pathology, Georg-August University, Robert-Koch-Str. 40, 37075 Göttingen, Germany
| | - Rüdiger M Weseloh
- Max-Planck Institute of Experimental Medicine, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
| | - Fernanda Mello de Queiroz
- Max-Planck Institute of Experimental Medicine, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
- Divisão de Farmacologia, Coordenação de Pesquisa, Instituto Nacional do Câncer, Rua André Cavalcanti 37/3° andar, Rio de Janeiro, Brasil
| | | | - Araceli Sánchez
- Max-Planck Institute of Experimental Medicine, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
| | - María E Rubio
- Max-Planck Institute of Experimental Medicine, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
| | - Sabine Martin
- Max-Planck Institute of Experimental Medicine, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
- DFG Research Center for the Molecular Physiology of the Brain (CMPB), Göttingen, Germany
| | | | - Marc Jenke
- Max-Planck Institute of Experimental Medicine, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
- iOnGen AG, Stiegbreite 13, 37077 Göttingen, Germany
| | - Walter Stühmer
- Max-Planck Institute of Experimental Medicine, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
| | - Luis A Pardo
- Max-Planck Institute of Experimental Medicine, Hermann-Rein-Str. 3, 37075 Göttingen, Germany
- iOnGen AG, Stiegbreite 13, 37077 Göttingen, Germany
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Potassium channels: new targets in cancer therapy. ACTA ACUST UNITED AC 2006; 30:375-85. [PMID: 16971052 DOI: 10.1016/j.cdp.2006.06.002] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/26/2006] [Indexed: 01/01/2023]
Abstract
BACKGROUND Potassium channels (KCh) are the most diverse and ubiquitous class of ion channels. KCh control membrane potential and contribute to nerve and cardiac action potentials and neurotransmitter release. KCh are also involved in insulin release, differentiation, activation, proliferation, apoptosis, and several other physiological functions. The aim of this review is to provide an updated overview of the KCh role during the cell growth. Their potential use as pharmacological targets in cancer therapies is also discussed. METHODS We searched PubMed (up to 2005) and identified relevant articles. Reprints were mainly obtained by on line subscription. Additional sources were identified through cross-referencing and obtained from Library services. RESULTS KCh are responsible for some neurological and cardiovascular diseases and for a new medical discipline, channelopathies. Their role in congenital deafness, multiple sclerosis, episodic ataxia, LQT syndrome and diabetes has been proven. Furthermore, a large body of information suggests that KCh play a role in the cell cycle progression, and it is now accepted that cells require KCh to proliferate. Thus, KCh expression has been studied in a number of tumours and cancer cells. CONCLUSIONS Cancer is far from being considered a channelopathy. However, it seems appropriate to take into account the involvement of KCh in cancer progression and pathology when developing new strategies for cancer therapy.
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Abstract
Cancer is the second most common cause of death in western countries. It is therefore of fundamental importance to improve the treatment of patients with malignant tumors. This goal can only be achieved if we get closer insight in the various mechanisms leading to tumor formation. Significant progress in the understanding of carcinogenesis has been made during the last couple of years. Ion channels contribute to the regulation of cell proliferation which has initially been shown for K+ channels. Meanwhile, other ion channels such as Cl-, Na+ and Ca2+ channels seem to influence cellular function like growth, migration and invasion. In addition, cation channels of the transient receptor potential (TRP) superfamily are implicated in cancer formation. Most recent data concerning TRP vanilloid (TRPV) type 6, TRP melastatin (TRPM) type 1 and 8 channels and their relevance for common human cancer types will be highlighted in this review. Furthermore, TRP channel structure and function will be discussed in the light of their possible importance as prognostic markers and targets for drug discovery.
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Affiliation(s)
- Matthias Bödding
- Experimentelle und Klinische Pharmakologie und Toxikologie, Universität des Saarlandes, D-66421 Homburg, Germany.
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Camacho J. Ether à go-go potassium channels and cancer. Cancer Lett 2006; 233:1-9. [PMID: 16473665 DOI: 10.1016/j.canlet.2005.02.016] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2005] [Accepted: 02/14/2005] [Indexed: 12/28/2022]
Abstract
Ion channels play important roles in health and disease. In the last few years, an interesting relationship between potassium channels and cancer has evolved. Especially, members of the ether à go-go (EAG) potassium channels family have gained interest as research tools for detection and therapy of different cancers. This review will summarize most of the findings relating EAG channels and cancer, focusing on mRNA expression in tissues, oncogenic properties, modulation and pharmacology. Plausible scenarios on the cellular mechanisms of EAG oncogenicity will be discussed.
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Affiliation(s)
- Javier Camacho
- Pharmacology Section, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Avenida Instituto Politécnico Nacional 2508, México, DF 07360, México.
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Ziechner U, Schönherr R, Born AK, Gavrilova-Ruch O, Glaser RW, Malesevic M, Küllertz G, Heinemann SH. Inhibition of human ether à go-go potassium channels by Ca2+/calmodulin binding to the cytosolic N- and C-termini. FEBS J 2006; 273:1074-86. [PMID: 16478480 DOI: 10.1111/j.1742-4658.2006.05134.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Human ether à go-go potassium channels (hEAG1) open in response to membrane depolarization and they are inhibited by Ca2+/calmodulin (CaM), presumably binding to the C-terminal domain of the channel subunits. Deletion of the cytosolic N-terminal domain resulted in complete abolition of Ca2+/CaM sensitivity suggesting the existence of further CaM binding sites. A peptide array-based screen of the entire cytosolic protein of hEAG1 identified three putative CaM-binding domains, two in the C-terminus (BD-C1: 674-683, BD-C2: 711-721) and one in the N-terminus (BD-N: 151-165). Binding of GST-fusion proteins to Ca2+/CaM was assayed with fluorescence correlation spectroscopy, surface plasmon resonance spectroscopy and precipitation assays. In the presence of Ca2+, BD-N and BD-C2 provided dissociation constants in the nanomolar range, BD-C1 bound with lower affinity. Mutations in the binding domains reduced inhibition of the functional channels by Ca2+/CaM. Employment of CaM-EF-hand mutants showed that CaM binding to the N- and C-terminus are primarily dependent on EF-hand motifs 3 and 4. Hence, closure of EAG channels presumably requires the binding of multiple CaM molecules in a manner more complex than previously assumed.
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Affiliation(s)
- Ulrike Ziechner
- Institute of Molecular Cell Biology, Research Unit Molecular and Cellular Biophysics, Friedrich Schiller University Jena, Germany
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Clarke CE, Hill AP, Zhao J, Kondo M, Subbiah RN, Campbell TJ, Vandenberg JI. Effect of S5P alpha-helix charge mutants on inactivation of hERG K+ channels. J Physiol 2006; 573:291-304. [PMID: 16556651 PMCID: PMC1779719 DOI: 10.1113/jphysiol.2006.108332] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The ether-à-go-go (EAG) family of voltage-gated K(+) channels contains three subfamilies, EAG, ether-à-go-go related (ERG) and ether-à-go-go like (ELK). The human ether-à-go-go related gene (hERG) K(+) channel has been of significant interest because loss of function in the hERG channel is associated with a markedly increased risk of cardiac arrhythmias. The hERG channel has unusual kinetics with slow activation and deactivation but very rapid and voltage-dependent inactivation. The outer pore region of the hERG K(+) channel is predicted to be different from that of other members of the voltage-gated K(+) channel family. HERG has a much longer linker between the fifth transmembrane domain (SS) and the pore helix (S5P linker) compared to other families of voltage-gated K(+) channels (43 amino acids compared to 14-23 amino acids). Further, the S5P linker contains an amphipathic alpha-helix that in hERG channels probably interacts with the mouth of the pore to modulate inactivation. The human EAG and rat ELK2 channels (hEAG and rELK2) show reduced or no inactivation in comparison to hERG channels, yet both channels are predicted to contain a similarly long S5P linker to that of hERG. In this study, we have constructed a series of chimaeric channels consisting of the S1-S6 of hERG but with the S5P alpha-helical region of either hEAG or rELK2, and one consisting of the S1-S6 of rELK2 but with the S5P alpha-helical region of hERG to investigate the role of the S5P linker in inactivation. Our studies show that charged residues on the alpha-helix of the S5P linker contribute significantly to the differences in inactivation characteristics of the EAG family channels. Further, individually mutating each of the hydrophilic residues on the S5P alpha-helix of hERG to a charged residue had significant effects on the voltage dependence of inactivation and the two residues with the greatest affect when mutated to a lysine, N588 and Q592, both lie on the same face of the S5P alpha -helix. We suggest that inactivation of hERG involves the interaction of this face of the S5P alpha-helix with a charged residue on the remainder of the outer pore domain of the channel.
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Affiliation(s)
- C E Clarke
- Department of Medicine, University of New South Wales, St. Vincent's Clinical School, Darlinghurst, NSW 2010, Australia
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