1
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Kappel S, Melek K, Ross-Kaschitza D, Hauert B, Gerber CE, Lochner M, Peinelt C. CBA (4-chloro-2-(2-chlorophenoxy)acetamido) benzoic acid) inhibits TMEM206 mediated currents and TMEM206 does not contribute to acid-induced cell death in colorectal cancer cells. Front Pharmacol 2024; 15:1369513. [PMID: 38515848 PMCID: PMC10955468 DOI: 10.3389/fphar.2024.1369513] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Accepted: 02/08/2024] [Indexed: 03/23/2024] Open
Abstract
Introduction: Upon activation at low pH, TMEM206 conducts Cl- ions across plasma and vesicular membranes. In a (patho)physiological context, TMEM206 was reported to contribute to acid-induced cell death in neurons, kidney and cervical epithelial cells. We investigated the role of TMEM206 in acid-induced cell death in colorectal cancer cells. In addition, we studied CBA as a new small molecule inhibitor for TMEM206. Methods: The role of TMEM206 in acid-induced cell death was studied with CRISPR/Cas9-mediated knockout and FACS analysis. The pharmacology of TMEM206 was determined with the patch clamp technique. Results: In colorectal cancer cells, TMEM206 is not a critical mediator of acid-induced cell death. CBA is a small molecule inhibitor of TMEM206 (IC50 = 9.55 µM) at low pH, at pH 6.0 inhibition is limited. Conclusion: CBA demonstrates effective and specific inhibition of TMEM206; however, its inhibitory efficacy is limited at pH 6.0. Despite this limitation, CBA is a potent inhibitor for functional studies at pH 4.5 and may be a promising scaffold for the development of future TMEM206 inhibitors.
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Affiliation(s)
| | | | | | | | | | | | - Christine Peinelt
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
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2
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Kostritskaia Y, Klüssendorf M, Pan YE, Hassani Nia F, Kostova S, Stauber T. Physiological Functions of the Volume-Regulated Anion Channel VRAC/LRRC8 and the Proton-Activated Chloride Channel ASOR/TMEM206. Handb Exp Pharmacol 2024; 283:181-218. [PMID: 37468723 DOI: 10.1007/164_2023_673] [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] [Indexed: 07/21/2023]
Abstract
Volume-regulated anion channels (VRACs) and the acid-sensitive outwardly rectifying anion channel (ASOR) mediate flux of chloride and small organic anions. Although known for a long time, they were only recently identified at the molecular level. VRACs are heteromers consisting of LRRC8 proteins A to E. Combining the essential LRRC8A with different LRRC8 paralogues changes key properties of VRAC such as conductance or substrate selectivity, which is how VRACs are involved in multiple physiological functions including regulatory volume decrease, cell proliferation and migration, cell death, purinergic signalling, fat and glucose metabolism, insulin signalling, and spermiogenesis. VRACs are also involved in pathological conditions, such as the neurotoxic release of glutamate and aspartate. Certain VRACs are also permeable to larger, organic anions, including antibiotics and anti-cancer drugs, making them an interesting therapeutic target. ASOR, also named proton-activated chloride channel (PAC), is formed by TMEM206 homotrimers on the plasma membrane and on endosomal compartments where it mediates chloride flux in response to extracytosolic acidification and plays a role in the shrinking and maturation of macropinosomes. ASOR has been shown to underlie neuronal swelling which causes cell death after stroke as well as promoting the metastasis of certain cancers, making them intriguing therapeutic targets as well.
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Affiliation(s)
- Yulia Kostritskaia
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Malte Klüssendorf
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Yingzhou Edward Pan
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Fatemeh Hassani Nia
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Simona Kostova
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Tobias Stauber
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany.
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3
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Osei-Owusu J, Ruan Z, Mihaljević L, Matasic DS, Chen KH, Lü W, Qiu Z. Molecular mechanism underlying desensitization of the proton-activated chloride channel PAC. eLife 2022; 11:e82955. [PMID: 36547405 PMCID: PMC9779784 DOI: 10.7554/elife.82955] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Accepted: 12/12/2022] [Indexed: 12/24/2022] Open
Abstract
Desensitization is a common property of membrane receptors, including ion channels. The newly identified proton-activated chloride (PAC) channel plays an important role in regulating the pH and size of organelles in the endocytic pathway, and is also involved in acid-induced cell death. However, how the PAC channel desensitizes is largely unknown. Here, we show by patch-clamp electrophysiological studies that PAC (also known as TMEM206/ASOR) undergoes pH-dependent desensitization upon prolonged acid exposure. Through structure-guided and comprehensive mutagenesis, we identified several residues critical for PAC desensitization, including histidine (H) 98, glutamic acid (E) 94, and aspartic acid (D) 91 at the extracellular extension of the transmembrane helix 1 (TM1), as well as E107, D109, and E250 at the extracellular domain (ECD)-transmembrane domain (TMD) interface. Structural analysis and molecular dynamic simulations revealed extensive interactions between residues at the TM1 extension and those at the ECD-TMD interface. These interactions likely facilitate PAC desensitization by stabilizing the desensitized conformation of TM1, which undergoes a characteristic rotational movement from the resting and activated states to the desensitized state. Our studies establish a new paradigm of channel desensitization in this ubiquitously expressed ion channel and pave the way for future investigation of its relevance in cellular physiology and disease.
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Affiliation(s)
- James Osei-Owusu
- Department of Physiology, Johns Hopkins University School of MedicineBaltimoreUnited States
| | - Zheng Ruan
- Department of Structural Biology, Van Andel InstituteGrand RapidsUnited States
| | - Ljubica Mihaljević
- Department of Physiology, Johns Hopkins University School of MedicineBaltimoreUnited States
| | - Daniel S Matasic
- Department of Medicine, Johns Hopkins University School of MedicineBaltimoreUnited States
| | - Kevin Hong Chen
- Department of Physiology, Johns Hopkins University School of MedicineBaltimoreUnited States
| | - Wei Lü
- Department of Structural Biology, Van Andel InstituteGrand RapidsUnited States
| | - Zhaozhu Qiu
- Department of Physiology, Johns Hopkins University School of MedicineBaltimoreUnited States
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of MedicineBaltimoreUnited States
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4
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Osei-Owusu J, Kots E, Ruan Z, Mihaljević L, Chen KH, Tamhaney A, Ye X, Lü W, Weinstein H, Qiu Z. Molecular determinants of pH sensing in the proton-activated chloride channel. Proc Natl Acad Sci U S A 2022; 119:e2200727119. [PMID: 35878032 PMCID: PMC9351481 DOI: 10.1073/pnas.2200727119] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Accepted: 05/31/2022] [Indexed: 01/27/2023] Open
Abstract
In response to acidic pH, the widely expressed proton-activated chloride (PAC) channel opens and conducts anions across cellular membranes. By doing so, PAC plays an important role in both cellular physiology (endosome acidification) and diseases associated with tissue acidosis (acid-induced cell death). Despite the available structural information, how proton binding in the extracellular domain (ECD) leads to PAC channel opening remains largely unknown. Here, through comprehensive mutagenesis and electrophysiological studies, we identified several critical titratable residues, including two histidine residues (H130 and H131) and an aspartic acid residue (D269) at the distal end of the ECD, together with the previously characterized H98 at the transmembrane domain-ECD interface, as potential pH sensors for human PAC. Mutations of these residues resulted in significant changes in pH sensitivity. Some combined mutants also exhibited large basal PAC channel activities at neutral pH. By combining molecular dynamics simulations with structural and functional analysis, we further found that the β12 strand at the intersubunit interface and the associated "joint region" connecting the upper and lower ECDs allosterically regulate the proton-dependent PAC activation. Our studies suggest a distinct pH-sensing and gating mechanism of this new family of ion channels sensitive to acidic environment.
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Affiliation(s)
- James Osei-Owusu
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Ekaterina Kots
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065
| | - Zheng Ruan
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI 49503
| | - Ljubica Mihaljević
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Kevin Hong Chen
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Ami Tamhaney
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Xinyu Ye
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI 49503
| | - Wei Lü
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI 49503
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medicine, New York, NY 10065
| | - Zhaozhu Qiu
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205
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5
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Cai R, Tang J, Chen XZ. Ion permeation controlled by hydrophobic residues and proton binding in the proton-activated chloride channel. iScience 2021; 24:103395. [PMID: 34825147 PMCID: PMC8605177 DOI: 10.1016/j.isci.2021.103395] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 07/13/2021] [Accepted: 10/28/2021] [Indexed: 01/17/2023] Open
Abstract
Recently identified proton-activated chloride channel (PAC) contains two transmembrane helices (S1–S2) and is involved in lysosome function, hypoxia adaption, stroke, and carcinogenesis. Although a PAC structure was recently resolved, its gating and activation mechanisms remained largely unknown. By the two-electrode voltage clamp electrophysiology in Xenopus oocytes, we found that the hydrophobicity of site 304 at fenestrations, but not that of neighbor sites, is important for maintaining PAC at a closed state at pH 7.5. When activated at acidic pH, PAC activity significantly increased with the hydrophilicity of site 307 within S2, but not with that of neighbor sites, suggesting that 307 acts as an activation gate. We identified six conserved protonatable residues critical for proton-induced activation, consistent with structural studies. Our study depicted a scheme in which proton binding induces conformational changes from the W304-controlled closed state at fenestrations to an activated state controlled by activation gate I307 in helix S2. The hydrophobicity of site 304 is critical for maintaining PAC at a closed state The function of activated PAC is modulated by the hydrophilicity of site 307 Six protonatable amino acids are involved in proton-induced PAC activation H+ binding seem to change PAC from W304-controlled closed to I307-gated open state
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Affiliation(s)
- Ruiqi Cai
- Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Jingfeng Tang
- National "111" Center for Cellular Regulation and Molecular Pharmaceutics, Hubei University of Technology, Wuhan, Hubei 430086, China
- Corresponding author
| | - Xing-Zhen Chen
- Department of Physiology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
- Corresponding author
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6
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Okada Y, Sato-Numata K, Sabirov RZ, Numata T. Cell Death Induction and Protection by Activation of Ubiquitously Expressed Anion/Cation Channels. Part 2: Functional and Molecular Properties of ASOR/PAC Channels and Their Roles in Cell Volume Dysregulation and Acidotoxic Cell Death. Front Cell Dev Biol 2021; 9:702317. [PMID: 34307382 PMCID: PMC8299559 DOI: 10.3389/fcell.2021.702317] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 06/18/2021] [Indexed: 12/18/2022] Open
Abstract
For survival and functions of animal cells, cell volume regulation (CVR) is essential. Major hallmarks of necrotic and apoptotic cell death are persistent cell swelling and shrinkage, and thus they are termed the necrotic volume increase (NVI) and the apoptotic volume decrease (AVD), respectively. A number of ubiquitously expressed anion and cation channels play essential roles not only in CVR but also in cell death induction. This series of review articles address the question how cell death is induced or protected with using ubiquitously expressed ion channels such as swelling-activated anion channels, acid-activated anion channels, and several types of TRP cation channels including TRPM2 and TRPM7. In the Part 1, we described the roles of swelling-activated VSOR/VRAC anion channels. Here, the Part 2 focuses on the roles of the acid-sensitive outwardly rectifying (ASOR) anion channel, also called the proton-activated chloride (PAC) anion channel, which is activated by extracellular protons in a manner sharply dependent on ambient temperature. First, we summarize phenotypical properties, the molecular identity, and the three-dimensional structure of ASOR/PAC. Second, we highlight the unique roles of ASOR/PAC in CVR dysfunction and in the induction of or protection from acidotoxic cell death under acidosis and ischemic conditions.
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Affiliation(s)
- Yasunobu Okada
- National Institute for Physiological Sciences (NIPS), Okazaki, Japan.,Department of Physiology, School of Medicine, Aichi Medical University, Nagakute, Japan.,Department of Physiology, Kyoto Prefectural University of Medicine, Kyoto, Japan
| | - Kaori Sato-Numata
- Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan.,Japan Society for the Promotion of Science, Tokyo, Japan
| | - Ravshan Z Sabirov
- Laboratory of Molecular Physiology, Institute of Biophysics and Biochemistry, National University of Uzbekistan, Tashkent, Uzbekistan
| | - Tomohiro Numata
- Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan
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7
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Deng Z, Zhao Y, Feng J, Zhang J, Zhao H, Rau MJ, Fitzpatrick JAJ, Hu H, Yuan P. Cryo-EM structure of a proton-activated chloride channel TMEM206. SCIENCE ADVANCES 2021; 7:7/9/eabe5983. [PMID: 33627432 PMCID: PMC7904269 DOI: 10.1126/sciadv.abe5983] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Accepted: 01/08/2021] [Indexed: 05/12/2023]
Abstract
TMEM206 has been recently identified as an evolutionarily conserved chloride channel that underlies ubiquitously expressed, proton-activated, outwardly rectifying anion currents. Here, we report the cryo-electron microscopy structure of pufferfish TMEM206, which forms a trimeric channel, with each subunit comprising two transmembrane segments and a large extracellular domain. An ample vestibule in the extracellular region is accessible laterally from the three side portals. The central pore contains multiple constrictions. A conserved lysine residue near the cytoplasmic end of the inner helix forms the presumed chloride ion selectivity filter. Unprecedentedly, the core structure and assembly closely resemble those of the epithelial sodium channel/degenerin family of sodium channels that are unrelated in amino acid sequence and conduct cations instead of anions. Together with electrophysiology, this work provides insights into ion conduction and gating for a new class of chloride channels that is architecturally distinct from previously characterized chloride channel families.
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Affiliation(s)
- Zengqin Deng
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Yonghui Zhao
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Center for the Study of Itch and Sensory Disorders, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Jing Feng
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Center for the Study of Itch and Sensory Disorders, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Jingying Zhang
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Haiyan Zhao
- Department of Pathology and Immunology, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Michael J Rau
- Washington University Center for Cellular Imaging, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - James A J Fitzpatrick
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Washington University Center for Cellular Imaging, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Department of Neuroscience, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Department of Biomedical Engineering, Washington University in Saint Louis, Saint Louis, MO 63130, USA
| | - Hongzhen Hu
- Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
- Center for the Study of Itch and Sensory Disorders, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Peng Yuan
- Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO 63110, USA.
- Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, Saint Louis, MO 63110, USA
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8
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Ullrich F, Blin S, Lazarow K, Daubitz T, von Kries JP, Jentsch TJ. Identification of TMEM206 proteins as pore of PAORAC/ASOR acid-sensitive chloride channels. eLife 2019; 8:49187. [PMID: 31318332 PMCID: PMC6663466 DOI: 10.7554/elife.49187] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2019] [Accepted: 07/17/2019] [Indexed: 01/09/2023] Open
Abstract
Acid-sensing ion channels have important functions in physiology and pathology, but the molecular composition of acid-activated chloride channels had remained unclear. We now used a genome-wide siRNA screen to molecularly identify the widely expressed acid-sensitive outwardly-rectifying anion channel PAORAC/ASOR. ASOR is formed by TMEM206 proteins which display two transmembrane domains (TMs) and are expressed at the plasma membrane. Ion permeation-changing mutations along the length of TM2 and at the end of TM1 suggest that these segments line ASOR’s pore. While not belonging to a gene family, TMEM206 has orthologs in probably all vertebrates. Currents from evolutionarily distant orthologs share activation by protons, a feature essential for ASOR’s role in acid-induced cell death. TMEM206 defines a novel class of ion channels. Its identification will help to understand its physiological roles and the diverse ways by which anion-selective pores can be formed.
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Affiliation(s)
- Florian Ullrich
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany.,Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany
| | - Sandy Blin
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany.,Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany
| | - Katina Lazarow
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Tony Daubitz
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany.,Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany
| | | | - Thomas J Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany.,Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany.,NeuroCure Cluster of Excellence, Charité Universitätsmedizin, Berlin, Germany
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9
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Capurro V, Gianotti A, Caci E, Ravazzolo R, Galietta LJ, Zegarra-Moran O. Functional analysis of acid-activated Cl− channels: Properties and mechanisms of regulation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:105-14. [DOI: 10.1016/j.bbamem.2014.10.008] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Revised: 09/26/2014] [Accepted: 10/02/2014] [Indexed: 01/10/2023]
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10
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Ma Z, Qi J, Fu Z, Ling M, Li L, Zhang Y. Protective role of acidic pH-activated chloride channel in severe acidosis-induced contraction from the aorta of spontaneously hypertensive rats. PLoS One 2013; 8:e61018. [PMID: 23580361 PMCID: PMC3620281 DOI: 10.1371/journal.pone.0061018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 03/05/2013] [Indexed: 11/19/2022] Open
Abstract
Severe acidic pH-activated chloride channel (ICl,acid) has been found in various mammalian cells. In the present study, we investigate whether this channel participates in reactions of the thoracic aorta to severe acidosis and whether it plays a role in hypertension. We measured isometric contraction in thoracic aorta rings from spontaneously hypertensive rats (SHRs) and normotensive Wistar rats. Severe acidosis induced contractions of both endothelium-intact and -denuded thoracic aorta rings. In Wistar rats, contractions did not differ at pH 6.4, 5.4 and 4.4. However, in SHRs, contractions were higher at pH 5.4 or 4.4 than pH 6.4, with no difference between contractions at pH 5.4 and 4.4. Nifedipine, ICl,acid blockers 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and 4,4′-diisothiocyanatostilbene-2, 2′-disulfonic acid (DIDS) inhibited severe acidosis-induced contraction of aortas at different pH levels. When blocking ICl,acid, the remnant contraction was greater at pH 4.4 than pH 5.4 and 6.4 for both SHRs and Wistar rats. With nifedipine, the remnant contraction was greatly reduced at pH 4.4 as compared with at pH 6.4 and 5.4. With NPPB or DIDS, the ratio of remnant contractions at pH 4.4 and 5.4 (R4.4/5.4) was lower for SHRs than Wistar rats (all <1). However, with nifedipine, the R4.4/5.4 was higher for SHRs than Wistar rats (both >1). Furthermore, patch clamp recordings of ICl,acid and intracellular Ca2+ measurements in smooth muscle cells confirmed these findings. ICl,acid may protect arteries against excess vasoconstriction under extremely acidic extracellular conditions. This protective effect may be decreased in hypertension.
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Affiliation(s)
- Zhiyong Ma
- Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Public Health; Department of Cardiology, Qilu Hospital, Shandong University, Jinan, China
| | - Jia Qi
- Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Public Health; Department of Cardiology, Qilu Hospital, Shandong University, Jinan, China
| | - Zhijie Fu
- Department of Otorhinolaryngology, Shandong Provincial Qianfoshan Hospital, Clinical Medical College of Shandong University, Jinan, China
| | - Mingying Ling
- Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Public Health; Department of Cardiology, Qilu Hospital, Shandong University, Jinan, China
| | - Li Li
- Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Public Health; Department of Cardiology, Qilu Hospital, Shandong University, Jinan, China
| | - Yun Zhang
- Key Laboratory of Cardiovascular Remodeling and Function Research, Chinese Ministry of Education and Chinese Ministry of Public Health; Department of Cardiology, Qilu Hospital, Shandong University, Jinan, China
- * E-mail:
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11
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Fu ZJ, Li XZ, Wang QR, Shi L, Zhang LQ, Pan XL. Extracellular acidic pH-activated, outward rectifying chloride currents can be regulated by reactive oxygen species in human THP-1 monocytes. Biochem Biophys Res Commun 2013; 432:701-6. [PMID: 23376719 DOI: 10.1016/j.bbrc.2013.01.090] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Accepted: 01/25/2013] [Indexed: 12/01/2022]
Abstract
Extracellular acidic pH-activated chloride channels (ICl,acid) have been found in a variety of mammalian cells. In the present study, the expression and regulation of ICl,acid were investigated in THP-1 cells. Patch clamp recordings demonstrated that an extracellular acidic solution induced an outward rectified current, which could be blocked by the Cl(-) channel blocker. The currents exhibited time-dependent facilitation and inactivation. The relative anion permeability of this current followed the sequence Cl(-)>Br(-)>I(-)>gluconate. NADPH oxidase inhibitors did not decrease pH 4.4-induced currents. However, reactive oxygen species (ROS) scavengers and mitochondrial inhibitors inhibited pH 4.4-induced currents. Fluorescence imaging of intracellular ROS and mitochondrial activity confirmed these findings. We conclude that ICl,acid occurs in human THP-1 cells and that ICl,acid may be regulated by intracellular ROS mainly originating from mitochondria.
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Affiliation(s)
- Zhi-jie Fu
- Department of Otorhinolaryngology, QiLu Hospital, Shandong University, Jinan, China
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12
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Wang HL, Cheng X, Sine SM. Intramembrane proton binding site linked to activation of bacterial pentameric ion channel. J Biol Chem 2011; 287:6482-9. [PMID: 22084238 DOI: 10.1074/jbc.m111.305839] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Prokaryotic orthologs of eukaryotic Cys-loop receptor channels recently emerged as structural and mechanistic surrogates to investigate this superfamily of intercellular signaling proteins. Here, we examine proton activation of the prokaryotic ortholog GLIC using patch clamp electrophysiology, mutagenesis, and molecular dynamics (MD) simulations. Whole-cell current recordings from human embryonic kidney (HEK) 293 cells expressing GLIC show half-maximal activation at pH 6, close to the pK(a) of histidine, implicating the three native His residues in proton sensing linked to activation. The mutation H235F abolishes proton activation, H277Y is without effect, and all nine mutations of His-127 prevent expression on the cell surface. In the GLIC crystal structure, His-235 on transmembrane (TM) α-helix 2, hydrogen bonds to the main chain carbonyl oxygen of Ile-259 on TM α-helix 3. MD simulations show that when His-235 is protonated, the hydrogen bond persists, and the channel remains in the open conformation, whereas when His-235 is deprotonated, the hydrogen bond dissociates, and the channel closes. Mutations of the proximal Tyr-263, which also links TM α-helices 2 and 3 via a hydrogen bond, alter proton sensitivity over a 1.5 pH unit range. MD simulations show that mutations of Tyr-263 alter the hydrogen bonding capacity of His-235. The overall findings show that His-235 in the TM region of GLIC is a novel proton binding site linked to channel activation.
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Affiliation(s)
- Hai-Long Wang
- Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota 55905, USA
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13
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Matsuda JJ, Filali MS, Collins MM, Volk KA, Lamb FS. The ClC-3 Cl-/H+ antiporter becomes uncoupled at low extracellular pH. J Biol Chem 2009; 285:2569-79. [PMID: 19926787 DOI: 10.1074/jbc.m109.018002] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Adenovirus expressing ClC-3 (Ad-ClC-3) induces Cl(-)/H(+) antiport current (I(ClC-3)) in HEK293 cells. The outward rectification and time dependence of I(ClC-3) closely resemble an endogenous HEK293 cell acid-activated Cl(-) current (ICl(acid)) seen at extracellular pH <or= 5.5. ICl(acid) was present in smooth muscle cells from wild-type but not ClC-3 null mice. We therefore sought to determine whether these currents were related. ICl(acid) was larger in cells expressing Ad-ClC-3. Protons shifted the reversal potential (E(rev)) of I(ClC-3) between pH 8.2 and 6.2, but not pH 6.2 and 5.2, suggesting that Cl(-) and H(+) transport become uncoupled at low pH. At pH 4.0 E(rev) was completely Cl(-) dependent (55.8 +/- 2.3 mV/decade). Several findings linked ClC-3 with native ICl(acid); 1) RNA interference directed at ClC-3 message reduced native ICl(acid); 2) removal of the extracellular "fast gate" (E224A) produced large currents that were pH-insensitive; and 3) wild-type I(ClC-3) and ICl(acid) were both inhibited by (2-sulfonatoethyl)methanethiosulfonate (MTSES; 10-500 microm)-induced alkanethiolation at exposed cysteine residues. However, a ClC-3 mutant lacking four extracellular cysteine residues (C103_P130del) was completely resistant to MTSES. C103_P130del currents were still acid-activated, but could be distinguished from wild-type I(ClC-3) and from native ICl(acid) by a much slower response to low pH. Thus, ClC-3 currents are activated by protons and ClC-3 protein may account for native ICl(acid). Low pH uncouples Cl(-)/H(+) transport so that at pH 4.0 ClC-3 behaves as an anion-selective channel. These findings have important implications for the biology of Cl(-)/H(+) antiporters and perhaps for pH regulation in highly acidic intracellular compartments.
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Affiliation(s)
- James J Matsuda
- Department of Pediatrics, University of Iowa Children's Hospital, Iowa City, Iowa 52242, USA
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Shi CY, Wang R, Liu CX, Jiang H, Ma ZY, Li L, Zhang W. Simvastatin inhibits acidic extracellular pH-activated, outward rectifying chloride currents in RAW264.7 monocytic-macrophage and human peripheral monocytes. Int Immunopharmacol 2008; 9:247-52. [PMID: 19084616 DOI: 10.1016/j.intimp.2008.11.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2008] [Revised: 11/17/2008] [Accepted: 11/20/2008] [Indexed: 11/29/2022]
Abstract
Extracellular acidic pH activated chloride channels (I(Cl,acid)) have been characterized in HEK 293 cells and mammalian cardiac myocytes. This study was designed to evaluate the expression of I(Cl,acid) in RAW264.7 monocytic-macrophage and human peripheral monocytes and to investigate the effect of simvastatin on I(Cl,acid). In two kinds of cells, the activation and deactivation of the current rapidly and repeatedly followed the change of the extracellular solution to pH=4.3. Compared with the outward current (pA/pF) activated at pH 4.3, the currents inhibited by simvastatin at concentrations of 0.1 microM were all decreased a little, however the currents at concentrations of 1 microM and 10 microM simvastatin were decreased significantly. The IC(50) for simvastatin inhibiting I(Cl,acid) of RAW264.7 was 13.77 microM. In summary, we report for the first time that simvastatin inhibits the I(Cl,acid) of RAW264.7 monocytic-macrophage and human peripheral monocytes in a concentration-dependent manner.
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Affiliation(s)
- Cheng-Yao Shi
- Department of Pharmacy, QiLu Hospital, Shandong University, Jinan 250012, China
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