1
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Xue JY, Ikegawa S, Guo L. SLC4A2, another gene involved in acid-base balancing machinery of osteoclasts, causes osteopetrosis. Bone 2023; 167:116603. [PMID: 36343920 DOI: 10.1016/j.bone.2022.116603] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 09/30/2022] [Accepted: 11/01/2022] [Indexed: 11/06/2022]
Abstract
SLC4A2 belongs to the Na+-independent solute carrier family 4 (SLC4) of anion exchangers, which regulate electroneutral exchange of Cl- for HCO3- and mediate intra- and extra-cellular pH, chloride concentration and cell volume. Slc4a2 also participates in gastric acid secretion, spermatogenesis and osteoclastogenesis. During osteoclast differentiation, Slc4a2 is exclusively expressed at the contra-lacunar membrane and is up-regulated with osteoclast maturation. Bi-allelic Slc4a2 loss-of-function mutations have been known to cause osteopetrosis in mice and cattle, but not in human. Recently, we have identified bi-allelic pathogenic variants in SLC4A2 in a patient affected by osteopetrosis with severe renal insufficiency, suggesting SLC4A2 deficiency causes a new type of autosomal recessive osteopetrosis (osteopetrosis, Ikegawa type). In this article, we review the advances in exploring the multiple functions of SLC4A2 with emphasis on its roles in osteoclast. Our review would contribute to understanding of the phenotypic spectrum and the pathomechanism of SLC4A2-associated osteopetrosis.
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Affiliation(s)
- Jing-Yi Xue
- Shaanxi Institute for Pediatric Diseases, Xi'an Children's Hospital, Affiliated Children's Hospital of Xi'an Jiaotong University, Xi'an 710082, China
| | - Shiro Ikegawa
- Laboratory for Bone and Joint Diseases, RIKEN Center for Integrative Medical Sciences, Tokyo 108-8639, Japan
| | - Long Guo
- Shaanxi Institute for Pediatric Diseases, Xi'an Children's Hospital, Affiliated Children's Hospital of Xi'an Jiaotong University, Xi'an 710082, China; Department of Laboratory Animal Science, School of Basic Medical Sciences, Xi'an Jiaotong University, Xi'an 710061, China.
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2
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Quade BN, Marshall A, Parker MD. Corneal dystrophy mutations R125H and R804H disable SLC4A11 by altering the extracellular pH dependence of the intracellular pK that governs H +(OH -) transport. Am J Physiol Cell Physiol 2022; 323:C990-C1002. [PMID: 35993514 PMCID: PMC9484998 DOI: 10.1152/ajpcell.00221.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 08/11/2022] [Accepted: 08/11/2022] [Indexed: 11/22/2022]
Abstract
Mutations in the H+(OH-) conductor SLC4A11 result in corneal endothelial dystrophy. In previous studies using mouse Slc4a11, we showed that the pK value that governs the intracellular pH dependence of SLC4A11 (pKi) is influenced by extracellular pH (pHe). We also showed that some mutations result in acidic or alkaline shifts in pKi, indicating that the pH dependence of SLC4A11 is important for physiological function. An R125H mutant, located in the cytosolic amino terminus of SLC4A11, apparently causes a complete loss of function, yet the anion transport inhibitor 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) can partially rescue SLC4A11/R125H activity. In the present study we set out to determine whether the effect of R125H is explained by an extreme shift in pKi. In Xenopus oocytes, we measured SLC4A11-mediated H+(OH-) conductance while monitoring pHi. We find that 1) the human corneal variant SLC4A11-B has a more acidic pKi than mouse Slc4a11, likely due to the presence of an NH2-terminal appendage; 2) pKi for human SLC4A11 is acid-shifted by raising pHe to 10.00; and 3) R125H and R804H mutants mediate substantial H+(OH-) conductances at pHe = 10.00, with pKi shifted into the wild-type range. These data suggest that the defect in each is a shift in pKi at physiological pHe, brought about by a disconnection in the mechanisms by which pHe influences pKi. Using de novo modeling, we show that R125 is located at the cytosolic dimer interface and suggest that this interface is critical for relaying the influence of pHe on the external face of the transmembrane domain to the intracellular, pKi-determining regions.
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Affiliation(s)
- Bianca N Quade
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York
| | - Aniko Marshall
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York
| | - Mark D Parker
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York
- Department of Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York
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3
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Liu X, Liu HF, Li HL, An XH, Song LQ, You CX, Zhao LL, Tian Y, Wang XF. MdMYB10 affects nitrogen uptake and reallocation by regulating the nitrate transporter MdNRT2.4-1 in the red flesh apple. Hortic Res 2022; 9:uhac016. [PMID: 35184189 PMCID: PMC9016894 DOI: 10.1093/hr/uhac016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Revised: 12/24/2021] [Accepted: 01/04/2022] [Indexed: 06/14/2023]
Abstract
Nitrate is the major nitrogen sources for higher plants. In addition to serving not only as a nutrient, it is also a signaling molecule that regulates plant growth and development. Although membrane-bound nitrate transporter/peptide transporters (NRT/PTR) have been extensively studied and shown to regulate nitrate uptake and movement, little is known about how these factors are regulated by the external nitrogen environment. Red flesh apple, the coloration of which is determined by the transcription factor MdMYB10, had higher nitrate uptake efficiency than non-red flesh apple. Nitrate assimilation and utilization were increased in red flesh apple cultivar, and comparative transcriptome analysis showed that the expression of genes encoding the NRT2s was increased in red flesh apple. In vitro and in vivo experiments showed that MdMYB10 directly bound to the MdNRT2.4-1 promoter to transcriptionally activate its expression, resulting in enhanced nitrate uptake. MdMYB10 also controlled nitrate reallocation from old leaves to new leaves through MdNRT2.4-1. Overall, our findings provide novel insights into the mechanism by which MdMYB10 controls nitrate uptake and reallocation in apple, which facilitates adaptation to low nitrogen environment.
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Affiliation(s)
- Xin Liu
- State Key Laboratory of Crop Biology, Shandong Collaborative Innovation Center of Fruit & Vegetable Quality and Efficient Production, Shandong Green Fertilizer Technology Innovation Center, College of Horticulture Science and Engineering, Shandong Agricultural University, Taian 271018, Shandong, China
- Beijing Academy of Forestry and Pomology Sciences, Beijing, China
| | - Hao-Feng Liu
- State Key Laboratory of Crop Biology, Shandong Collaborative Innovation Center of Fruit & Vegetable Quality and Efficient Production, Shandong Green Fertilizer Technology Innovation Center, College of Horticulture Science and Engineering, Shandong Agricultural University, Taian 271018, Shandong, China
| | - Hong-Liang Li
- State Key Laboratory of Crop Biology, Shandong Collaborative Innovation Center of Fruit & Vegetable Quality and Efficient Production, Shandong Green Fertilizer Technology Innovation Center, College of Horticulture Science and Engineering, Shandong Agricultural University, Taian 271018, Shandong, China
| | - Xiu-Hong An
- National Engineering Research Center for Agriculture in Northern Mountainous Areas, Agricultural Technology Innovation Center in Mountainous Areas of Hebei Province, Hebei Agricultural University, Baoding, Hebei, China
| | - Lai-Qing Song
- Yantai Academy of Agricultural Sciences, Yantai, Shandong, China
| | - Chun-Xiang You
- State Key Laboratory of Crop Biology, Shandong Collaborative Innovation Center of Fruit & Vegetable Quality and Efficient Production, Shandong Green Fertilizer Technology Innovation Center, College of Horticulture Science and Engineering, Shandong Agricultural University, Taian 271018, Shandong, China
| | - Ling-Ling Zhao
- Yantai Academy of Agricultural Sciences, Yantai, Shandong, China
| | - Yi Tian
- National Engineering Research Center for Agriculture in Northern Mountainous Areas, Agricultural Technology Innovation Center in Mountainous Areas of Hebei Province, Hebei Agricultural University, Baoding, Hebei, China
| | - Xiao-Fei Wang
- State Key Laboratory of Crop Biology, Shandong Collaborative Innovation Center of Fruit & Vegetable Quality and Efficient Production, Shandong Green Fertilizer Technology Innovation Center, College of Horticulture Science and Engineering, Shandong Agricultural University, Taian 271018, Shandong, China
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4
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Xue JY, Grigelioniene G, Wang Z, Nishimura G, Iida A, Matsumoto N, Tham E, Miyake N, Ikegawa S, Guo L. SLC4A2 Deficiency Causes a New Type of Osteopetrosis. J Bone Miner Res 2022; 37:226-235. [PMID: 34668226 DOI: 10.1002/jbmr.4462] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Revised: 10/04/2021] [Accepted: 10/07/2021] [Indexed: 02/05/2023]
Abstract
Osteopetrosis is a group of rare inherited skeletal disorders characterized by a marked increase in bone density due to deficient bone resorption. Pathogenic variants in several genes involved in osteoclast differentiation and/or function have been reported to cause osteopetrosis. Solute carrier family 4 member 2 (SLC4A2, encoding anion exchanger 2) plays an important role in osteoclast differentiation and function by exchange of Cl- with HCO3- . Biallelic Slc4a2 loss-of-function mutations in mice and cattle lead to osteopetrosis with osteoclast deficiency; however, pathogenic SLC4A2 variants in humans have not been reported. In this study, we describe a patient with autosomal recessive osteopetrosis due to biallelic pathogenic variants in SLC4A2. We identified novel compound heterozygous variants in SLC4A2 (NM_003040.4: c.556G>A [p.A186T] and c.1658T>C [p.V553A]) by exome sequencing. The measurement of intracellular Cl- showed that the variants decrease the anion exchange activity of SLC4A2. The impact of the variants on osteoclast differentiation was assessed by a gene knockout-rescue system using a mouse macrophage cell line, RAW 264.7. The Slc4a2-knockout cells show impaired osteoclastogenesis, which was rescued by the wild-type SLC4A2, but not by the mutant SLC4A2s. Immunofluorescence and pit assay revealed that the mutant SLC4A2s leads to abnormal podosome belt formation with impaired bone absorption. This is the first report on an individual affected by SLC4A2-associated osteopetrosis (osteopetrosis, Ikegawa type). With functional studies, we prove that the variants lead to SLC4A2 dysfunction, which altogether supports the importance of SLC4A2 in human osteoclast differentiation. © 2021 American Society for Bone and Mineral Research (ASBMR).
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Affiliation(s)
- Jing-Yi Xue
- Laboratory for Bone and Joint Diseases, RIKEN Center for Integrative Medical Sciences, Tokyo, Japan.,Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan
| | - Giedre Grigelioniene
- Department of Molecular Medicine and Surgery, Karolinska Institutet, and Clinical Genetics, Karolinska University Laboratory, Karolinska University Hospital, Stockholm, Sweden
| | - Zheng Wang
- Laboratory for Bone and Joint Diseases, RIKEN Center for Integrative Medical Sciences, Tokyo, Japan.,Department of Medical Genetics, Institute of Basic Medical Sciences, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing, China
| | - Gen Nishimura
- Laboratory for Bone and Joint Diseases, RIKEN Center for Integrative Medical Sciences, Tokyo, Japan
| | - Aritoshi Iida
- Laboratory for Bone and Joint Diseases, RIKEN Center for Integrative Medical Sciences, Tokyo, Japan.,Department of Clinical Genome Analysis, Medical Genome Center, National Center of Neurology and Psychiatry, Kodaira, Japan
| | - Naomichi Matsumoto
- Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan
| | - Emma Tham
- Department of Molecular Medicine and Surgery, Karolinska Institutet, and Clinical Genetics, Karolinska University Laboratory, Karolinska University Hospital, Stockholm, Sweden
| | - Noriko Miyake
- Department of Human Genetics, Yokohama City University Graduate School of Medicine, Yokohama, Japan
| | - Shiro Ikegawa
- Laboratory for Bone and Joint Diseases, RIKEN Center for Integrative Medical Sciences, Tokyo, Japan
| | - Long Guo
- Laboratory for Bone and Joint Diseases, RIKEN Center for Integrative Medical Sciences, Tokyo, Japan
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5
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Abstract
The major transmembrane protein of the red blood cell, known as band 3, AE1, and SLC4A1, has two main functions: 1) catalysis of Cl-/HCO3- exchange, one of the steps in CO2 excretion; 2) anchoring the membrane skeleton. This review summarizes the 150 year history of research on red cell anion transport and band 3 as an experimental system for studying membrane protein structure and ion transport mechanisms. Important early findings were that red cell Cl- transport is a tightly coupled 1:1 exchange and band 3 is labeled by stilbenesulfonate derivatives that inhibit anion transport. Biochemical studies showed that the protein is dimeric or tetrameric (paired dimers) and that there is one stilbenedisulfonate binding site per subunit of the dimer. Transport kinetics and inhibitor characteristics supported the idea that the transporter acts by an alternating access mechanism with intrinsic asymmetry. The sequence of band 3 cDNA provided a framework for detailed study of protein topology and amino acid residues important for transport. The identification of genetic variants produced insights into the roles of band 3 in red cell abnormalities and distal renal tubular acidosis. The publication of the membrane domain crystal structure made it possible to propose concrete molecular models of transport. Future research directions include improving our understanding of the transport mechanism at the molecular level and of the integrative relationships among band 3, hemoglobin, carbonic anhydrase, and gradients (both transmembrane and subcellular) of HCO3-, Cl-, O2, CO2, pH, and NO metabolites during pulmonary and systemic capillary gas exchange.
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Affiliation(s)
- Michael L Jennings
- Department of Physiology and Cell Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States
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6
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Quade BN, Marshall A, Parker MD. pH dependence of the Slc4a11-mediated H + conductance is influenced by intracellular lysine residues and modified by disease-linked mutations. Am J Physiol Cell Physiol 2020; 319:C359-C370. [PMID: 32520610 DOI: 10.1152/ajpcell.00128.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
SLC4A11 is the only member of the SLC4 family that transports protons rather than bicarbonate. SLC4A11 is expressed in corneal endothelial cells, and its mutation causes corneal endothelial dystrophy, although the mechanism of pathogenesis is unknown. We previously demonstrated that the magnitude of the H+ conductance (Gm) mediated by SLC4A11 is increased by rises in intracellular as well as extracellular pH (pHi and pHe). To better understand this feature and whether it is altered in disease, we studied the pH dependence of wild-type and mutant mouse Slc4a11 expressed in Xenopus oocytes. Using voltage-clamp circuitry in conjunction with a H+-selective microelectrode and a microinjector loaded with NaHCO3, we caused incremental rises in oocyte pHi and measured the effect on Gm. We find that the rise of Gm has a steeper pHi dependence at pHe =8.50 than at pHe =7.50. Data gathered at pHe =8.50 can be fit to the Hill equation enabling the calculation of a pK value that reports pHi dependence. We find that mutation of lysine residues that are close to the first transmembrane span (TM1) causes an alkaline shift in pK. Furthermore, two corneal-dystrophy-causing mutations close to the extracellular end of TM1, E399K and T401K (E368K and T370K in mouse), cause an acidic shift in pK, while a third mutation in the fourth intracellular loop, R804H (R774H in mouse), causes an alkaline shift in pK. This is the first description of determinants of SLC4A11 pH dependence and the first indication that a shift in pH dependence could modify disease expressivity in some cases of corneal dystrophy.
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Affiliation(s)
- Bianca N Quade
- Department of Physiology and Biophysics, The State University of New York: The University at Buffalo, Buffalo, New York
| | - Aniko Marshall
- Department of Physiology and Biophysics, The State University of New York: The University at Buffalo, Buffalo, New York
| | - Mark D Parker
- Department of Physiology and Biophysics, The State University of New York: The University at Buffalo, Buffalo, New York.,Department of Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York.,State University of New York Eye Institute, University at Buffalo: The State University of New York, Buffalo, New York
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7
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Abstract
The SLC4 family Cl-/[Formula: see text] cotransporters (NBCe1, NBCe2, NBCn1, and NBCn2) contribute to a variety of vital physiological processes including pH regulation and epithelial fluid secretion. Accordingly, their dysfunction can have devastating effects. Disorders such as epilepsy, hemolytic anemia, glaucoma, hearing loss, osteopetrosis, and renal tubular acidosis are all genetically linked to SLC4-family gene loci. This review summarizes how studies of Slc4-modified mice have enhanced our understanding of the etiology of SLC4-linked pathologies and the interpretation of genetic linkage studies. The review also surveys the novel disease signs exhibited by Slc4-modified mice which could either be considered to presage their description in humans, or to highlight interspecific differences. Finally, novel Slc4-modified mouse models are proposed, the study of which may further our understanding of the basis and treatment of SLC4-linked disorders of [Formula: see text]-transporter dysfunction.
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Affiliation(s)
- Mark D Parker
- Department of Physiology and Biophysics, The State University of New York: The University at Buffalo , Buffalo, New York.,Department of Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York , Buffalo, New York.,State University of New York Eye Institutes, University at Buffalo: The State University of New York , Buffalo, New York
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8
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Fan X, Tang Z, Tan Y, Zhang Y, Luo B, Yang M, Lian X, Shen Q, Miller AJ, Xu G. Overexpression of a pH-sensitive nitrate transporter in rice increases crop yields. Proc Natl Acad Sci U S A 2016; 113:7118-23. [PMID: 27274069 DOI: 10.1073/pnas.1525184113] [Citation(s) in RCA: 185] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Cellular pH homeostasis is fundamental for life, and all cells adapt to maintain this balance. In plants, the chemical form of nitrogen supply, nitrate and ammonium, is one of the cellular pH dominators. We report that the rice nitrate transporter OsNRT2.3 is transcribed into two spliced isoforms with a natural variation in expression ratio. One splice form, OsNRT2.3b is located on the plasma membrane, is expressed mainly in the phloem, and has a regulatory motif on the cytosolic side that acts to switch nitrate transport activity on or off by a pH-sensing mechanism. High OsNRT2.3b expression in rice enhances the pH-buffering capacity of the plant, increasing N, Fe, and P uptake. In field trials, increased expression of OsNRT2.3b improved grain yield and nitrogen use efficiency (NUE) by 40%. These results indicate that pH sensing by the rice nitrate transporter OsNRT2.3b is important for plant adaption to varied N supply forms and can provide a target for improving NUE.
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9
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Abstract
The solute carrier SLC4 family consists of 10 members, nine of which are [Formula: see text] transporters, including three Na(+)-independent Cl(-)/[Formula: see text] exchangers AE1, AE2, and AE3, five Na(+)-coupled [Formula: see text] transporters NBCe1, NBCe2, NBCn1, NBCn2, and NDCBE, as well as "AE4" whose Na(+)-dependence remains controversial. The SLC4 [Formula: see text] transporters play critical roles in pH regulation and transepithelial movement of electrolytes with a broad range of demonstrated physiological relevances. Dysfunctions of these transporters are associated with a series of human diseases. During the past decades, tremendous amount of effort has been undertaken to investigate the topological organization of the SLC4 transporters in the plasma membrane. Based upon the proposed topology models, mutational and functional studies have identified important structural elements likely involved in the ion translocation by the SLC4 transporters. In the present article, we review the advances during the past decades in understanding the structure and function of the SLC4 transporters.
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Affiliation(s)
- Ying Liu
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
| | - Jichun Yang
- Department of Physiology and Pathophysiology, School of Basic Medical Sciences, Peking University Health Science CenterBeijing, China
| | - Li-Ming Chen
- Key Laboratory of Molecular Biophysics of Ministry of Education, Department of Biophysics and Molecular Physiology, School of Life Science and Technology, Huazhong University of Science and TechnologyWuhan, China
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10
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Concepcion AR, Salas JT, Sarvide S, Sáez E, Ferrer A, López M, Portu A, Banales JM, Hervás-Stubbs S, Oude Elferink RPJ, Prieto J, Medina JF. Anion exchanger 2 is critical for CD8(+) T cells to maintain pHi homeostasis and modulate immune responses. Eur J Immunol 2014; 44:1341-51. [PMID: 24515893 DOI: 10.1002/eji.201344218] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2013] [Revised: 12/24/2013] [Accepted: 02/04/2014] [Indexed: 01/11/2023]
Abstract
Mitogenic stimulation of lymphocytes involves alkalinization of intracellular pH (pHi ). Subsequent pHi regulation may involve HCO3 (-) extrusion through Cl(-) /HCO3 (-) exchangers and/or Na(+) -HCO3 (-) co-transporters with acid-loading capability. Abnormalities in these mechanisms could result in immune dysfunctions, as suggested by the CD8(+) T-cell expansion encountered in mice lacking Ae2 (a widely expressed acid loader with electroneutral and Na(+) -independent Cl(-) /HCO3 (-) anion-exchange activity). Here we report that CD8(+) T cells but not CD4(+) T cells or other lymphocyte populations, are crucially dependent on Ae2 for pHi regulation. While total lymphocytes (including isolated CD4(+) T cells) exhibit Ae1 expression and Na(+) -HCO3 (-) co-transport with acidifying potential, CD8(+) T cells lack these acid-loading mechanisms. In Ae2-KO mice, CD4(+) but not CD8(+) T cells upregulate these potential Ae2 surrogates. As a consequence, Ae2-KO CD8(+) T cells exhibit alkalinized pHi , and dramatically increase their pHi upon CD3 stimulation. Moreover, stimulated Ae2-deficient CD8(+) T cells show enhanced intracellular production of IL-2 and membrane expression of its receptor IL-2Rα, together with increased cell proliferation and activation. These findings demonstrate that CD8(+) T cells are critically dependent on Ae2 for pHi homeostasis and tuning of cell proliferation and activation. Ae2 thus constitutes a novel target to modulate CD8(+) T-cell responses.
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Affiliation(s)
- Axel R Concepcion
- Center for Applied Medical Research (CIMA), Clinic and School of Medicine University of Navarra, Pamplona, Spain; CIBERehd, the "Carlos III" Institute of Health, Madrid, Spain
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11
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Shnitsar V, Li J, Li X, Calmettes C, Basu A, Casey JR, Moraes TF, Reithmeier RAF. A substrate access tunnel in the cytosolic domain is not an essential feature of the solute carrier 4 (SLC4) family of bicarbonate transporters. J Biol Chem 2013; 288:33848-33860. [PMID: 24121512 DOI: 10.1074/jbc.m113.511865] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Anion exchanger 1 (AE1; Band 3; SLC4A1) is the founding member of the solute carrier 4 (SLC4) family of bicarbonate transporters that includes chloride/bicarbonate AEs and Na(+)-bicarbonate co-transporters (NBCs). These membrane proteins consist of an amino-terminal cytosolic domain involved in protein interactions and a carboxyl-terminal membrane domain that carries out the transport function. Mutation of a conserved arginine residue (R298S) in the cytosolic domain of NBCe1 (SLC4A4) is linked to proximal renal tubular acidosis and results in impaired transport function, suggesting that the cytosolic domain plays a role in substrate permeation. Introduction of single and double mutations at the equivalent arginine (Arg(283)) and at an interacting glutamate (Glu(85)) in the cytosolic domain of human AE1 (cdAE1) had no effect on the cell surface expression or the transport activity of AE1 expressed in HEK-293 cells. In addition, the membrane domain of AE1 (mdAE1) efficiently mediated anion transport. A 2.1-Å resolution crystal structure of cdΔ54AE1 (residues 55-356 of cdAE1) lacking the amino-terminal and carboxyl-terminal disordered regions, produced at physiological pH, revealed an extensive hydrogen-bonded network involving Arg(283) and Glu(85). Mutations at these residues affected the pH-dependent conformational changes and stability of cdΔ54AE1. As these structural alterations did not impair functional expression of AE1, the cytosolic and membrane domains operate independently. A substrate access tunnel within the cytosolic domain is not present in AE1 and therefore is not an essential feature of the SLC4 family of bicarbonate transporters.
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Affiliation(s)
- Volodymyr Shnitsar
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Jing Li
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Xuyao Li
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Charles Calmettes
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
| | - Arghya Basu
- Department of Biochemistry and Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Joseph R Casey
- Department of Biochemistry and Membrane Protein Disease Research Group, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Trevor F Moraes
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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12
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Abstract
The mammalian Slc4 (Solute carrier 4) family of transporters is a functionally diverse group of 10 multi-spanning membrane proteins that includes three Cl-HCO3 exchangers (AE1-3), five Na(+)-coupled HCO3(-) transporters (NCBTs), and two other unusual members (AE4, BTR1). In this review, we mainly focus on the five mammalian NCBTs-NBCe1, NBCe2, NBCn1, NDCBE, and NBCn2. Each plays a specialized role in maintaining intracellular pH and, by contributing to the movement of HCO3(-) across epithelia, in maintaining whole-body pH and otherwise contributing to epithelial transport. Disruptions involving NCBT genes are linked to blindness, deafness, proximal renal tubular acidosis, mental retardation, and epilepsy. We also review AE1-3, AE4, and BTR1, addressing their relevance to the study of NCBTs. This review draws together recent advances in our understanding of the phylogenetic origins and physiological relevance of NCBTs and their progenitors. Underlying these advances is progress in such diverse disciplines as physiology, molecular biology, genetics, immunocytochemistry, proteomics, and structural biology. This review highlights the key similarities and differences between individual NCBTs and the genes that encode them and also clarifies the sometimes confusing NCBT nomenclature.
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Affiliation(s)
- Mark D Parker
- Dept. of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4970, USA.
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13
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Reimold FR, Stewart AK, Stolpe K, Heneghan JF, Shmukler BE, Alper SL. Substitution of transmembrane domain Cys residues alters pH(o)-sensitive anion transport by AE2/SLC4A2 anion exchanger. Pflugers Arch 2012; 465:839-51. [PMID: 23271450 DOI: 10.1007/s00424-012-1196-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Revised: 11/19/2012] [Accepted: 11/30/2012] [Indexed: 10/27/2022]
Abstract
AE2/SLC4A2 is the most widely expressed of the Na(+)-independent SLC4 Cl(-)/HCO3 (-) exchangers and is essential for postnatal survival, but its structure remains unknown. We have generated and expressed a mouse AE2 construct devoid of transmembrane domain cysteine (Cys) residues, mAE2Cys-less, to enhance the utility of Cys-substitution mutagenesis for structural and structure-function studies of mAE2. mAE2Cys-less expressed in Xenopus oocytes exhibited partial reduction of stilbene disulfonate-sensitive anion exchange activity. This activity was independent of the mAE2 N-terminal cytosolic domain and was accompanied by near-normal surface expression, without change in K 1/2 for extracellular Cl(-). mAE2Cys-less exhibited wildtype activation of anion exchange by hypertonicity and by NH4Cl, and wildtype inhibition of anion exchange by acidic intracellular pH (pHi) in the absence of NH4 (+). However, inhibition of anion exchange by extracellular pH (pHo) exhibited an alkaline shifted pHo(50) value of at least 0.6-0.7 pH units. Although SO4 (2-) transport by mAE2Cys-less resembled wildtype mAE2 in its stimulation by acidic pHo, the absence of transmembrane domain Cys residues abrogated activation of oxalate transport by acidic pHo. The contrasting enhancement of SO4 (2-) transport by alkaline pHo in the mAE1 anion translocation pathway mutant E699Q (Am J Physiol Cell Physiol 295: C302) was phenocopied by the corresponding mutant E1007Q in both AE2 and AE2Cys-less. However, the absence of transmembrane domain Cys residues exacerbated the reduced basal anion transport function exhibited by this and other missense substitutions at AE2 residue E1007. AE2Cys-less will be a valuable experimental tool for structure-function studies of the SLC4 gene family, but its utility for studies of AE2 regulation by extracellular pH must be evaluated in the context of its alkaline-shifted pHo sensitivity, resembling that of AE2 gastric parietal cell variant AE2c1.
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Affiliation(s)
- Fabian R Reimold
- Renal Division and Molecular and Vascular Medicine Division, Beth Israel Deaconess Medical Center, 99 Brookline Avenue, RN-380F, Boston, MA 02215, USA
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14
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Abstract
During amelogenesis, extracellular matrix proteins interact with growing hydroxyapatite crystals to create one of the most architecturally complex biological tissues. The process of enamel formation is a unique biomineralizing system characterized first by an increase in crystallite length during the secretory phase of amelogenesis, followed by a vast increase in crystallite width and thickness in the later maturation phase when organic complexes are enzymatically removed. Crystal growth is modulated by changes in the pH of the enamel microenvironment that is critical for proper enamel biomineralization. Whereas the genetic bases for most abnormal enamel phenotypes (amelogenesis imperfecta) are generally associated with mutations to enamel matrix specific genes, mutations to genes involved in pH regulation may result in severely affected enamel structure, highlighting the importance of pH regulation for normal enamel development. This review summarizes the intra- and extracellular mechanisms employed by the enamel-forming cells, ameloblasts, to maintain pH homeostasis and, also, discusses the enamel phenotypes associated with disruptions to genes involved in pH regulation.
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Affiliation(s)
- Rodrigo S. Lacruz
- School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, 2250 Alcazar Street, CSA Room 103, Los Angeles, CA 90033 USA
| | - Antonio Nanci
- Faculty of Dentistry, Université de Montréal, P.O. Box 6128, Station Centre-Ville, Montreal, QC H3C 3J7 Canada
| | - Ira Kurtz
- David Geffen School Medicine at the University of California at Los Angeles, Los Angeles, 10833 Le Conte Ave., Los Angeles, CA 90095 USA
| | - J. Timothy Wright
- Department of Pediatric Dentistry, School of Dentistry, University of North Carolina at Chapel Hill, CB No. 7450 Brauer Hall, Chapel Hill, NC 27599 USA
| | - Michael L. Paine
- School of Dentistry, Center for Craniofacial Molecular Biology, University of Southern California, 2250 Alcazar Street, CSA Room 103, Los Angeles, CA 90033 USA
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15
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Abstract
The parietal cell is responsible for secreting concentrated hydrochloric acid into the gastric lumen. To fulfill this task, it is equipped with a broad variety of functionally coupled apical and basolateral ion transport proteins. The concerted scientific effort over the last years by a variety of researchers has provided us with the molecular identity of many of these transport mechanisms, thereby contributing to the clarification of persistent controversies in the field. This article will briefly review the current model of parietal cell physiology and ion transport in particular and will update the existing models of apical and basolateral transport in the parietal cell.
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Affiliation(s)
- Sascha Kopic
- Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut
| | - Michael Murek
- Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut
| | - John P. Geibel
- Department of Surgery, Yale University, School of Medicine, New Haven, Connecticut
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16
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Piermarini PM, Grogan LF, Lau K, Wang L, Beyenbach KW. A SLC4-like anion exchanger from renal tubules of the mosquito (Aedes aegypti): evidence for a novel role of stellate cells in diuretic fluid secretion. Am J Physiol Regul Integr Comp Physiol 2009; 298:R642-60. [PMID: 20042685 DOI: 10.1152/ajpregu.00729.2009] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Transepithelial fluid secretion across the renal (Malpighian) tubule epithelium of the mosquito (Aedes aegypti) is energized by the vacuolar-type (V-type) H(+)-ATPase and not the Na(+)-K(+)-ATPase. Located at the apical membrane of principal cells, the V-type H(+)-ATPase translocates protons from the cytoplasm to the tubule lumen. Secreted protons are likely to derive from metabolic H(2)CO(3), which raises questions about the handling of HCO(3)(-) by principal cells. Accordingly, we tested the hypothesis that a Cl/HCO(3) anion exchanger (AE) related to the solute-linked carrier 4 (SLC4) superfamily mediates the extrusion of HCO(3)(-) across the basal membrane of principal cells. We began by cloning from Aedes Malpighian tubules a full-length cDNA encoding an SLC4-like AE, termed AeAE. When expressed heterologously in Xenopus oocytes, AeAE is both N- and O-glycosylated and mediates Na(+)-independent intracellular pH changes that are sensitive to extracellular Cl(-) concentration and to DIDS. In Aedes Malpighian tubules, AeAE is expressed as two distinct forms: one is O-glycosylated, and the other is N-glycosylated. Significantly, AeAE immunoreactivity localizes to the basal regions of stellate cells but not principal cells. Concentrations of DIDS that inhibit AeAE activity in Xenopus oocytes have no effects on the unstimulated rates of fluid secretion mediated by Malpighian tubules as measured by the Ramsay assay. However, in Malpighian tubules stimulated with kinin or calcitonin-like diuretic peptides, DIDS reduces the diuretic rates of fluid secretion to basal levels. In conclusion, Aedes Malpighian tubules express AeAE in the basal region of stellate cells, where this transporter may participate in producing diuretic rates of transepithelial fluid secretion.
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Affiliation(s)
- Peter M Piermarini
- Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA.
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17
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Bronckers ALJJ, Lyaruu DM, Jansen IDC, Medina JF, Kellokumpu S, Hoeben KA, Gawenis LR, Oude-Elferink RPJ, Everts V. Localization and function of the anion exchanger Ae2 in developing teeth and orofacial bone in rodents. J Exp Zool B Mol Dev Evol 2009; 312B:375-87. [PMID: 19206174 DOI: 10.1002/jez.b.21267] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
To explore the functions of the anion exchanger 2 (Ae2) in the development of bones and teeth we examined the distribution of Ae2 in cells involved in the formation of teeth and surrounding bone in young hamsters, mice and rats. In all three species strongest immunostaining for Ae2 was obtained in basolateral membranes of maturation ameloblasts and in osteoclasts resorbing bone. In hamsters a weaker staining was also seen in the Golgi apparatus of secretory ameloblasts, young osteoblasts and osteocytes, odontoblasts and fibroblasts of the forming periodontal ligament. In adult Ae2(a,b) (-/-) mice, in which Ae2-targeted disruption precluded the expression of Ae2a, Ae2b1 and Ae2b2 isoforms, the immunostaining for Ae2 in ameloblasts and osteoclasts was totally abolished. The enamel formation was abnormal but teeth erupted, osteoclasts in jaw bone were functional and structure of dentin and bone was normal. In another mouse model, Ae2(-/-) mice in which the expression of all five Ae2 isoforms was disrupted, teeth failed to erupt and the alveolar bone proved poorly formed with giant but apparently functional osteoclasts. Our data indicate that basolaterally located Ae2a, Ae2b1 or Ae2b2 (or a combination of these) is present in maturation ameloblasts critical for the cells' normal functioning. Although isoforms of Ae2 were also present in basolateral membranes of osteoclasts, they proved to be not critical to osteoclast resorption of orofacial bone. Poorly formed bone and the failure of teeth to erupt seen in the Ae2(-/-) mice with gene disruption affecting all isoforms may result from secondary (systemic) changes that are different from Ae2(a,b) (-/-) mice.
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Affiliation(s)
- Antonius L J J Bronckers
- Department of Oral Cell Biology, Academic Centre for Dentistry Amsterdam (ACTA), MOVE Research Institute, University of Amsterdam and VU University Amsterdam, Amsterdam, The Netherlands.
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18
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Abstract
In the intact eye, the transition from light to dark alters pH, [Ca2+], and [K] in the subretinal space (SRS) separating the photoreceptor outer segments and the apical membrane of the retinal pigment epithelium (RPE). In addition to these changes, oxygen consumption in the retina increases with a concomitant release of CO2 and H2O into the SRS. The RPE maintains SRS pH and volume homeostasis by transporting these metabolic byproducts to the choroidal blood supply. In vitro, we mimicked the transition from light to dark by increasing apical bath CO2 from 5 to 13%; this maneuver decreased cell pH from 7.37 ± 0.05 to 7.14 ± 0.06 (n = 13). Our analysis of native and cultured fetal human RPE shows that the apical membrane is significantly more permeable (≈10-fold; n = 7) to CO2 than the basolateral membrane, perhaps due to its larger exposed surface area. The limited CO2 diffusion at the basolateral membrane promotes carbonic anhydrase–mediated HCO3 transport by a basolateral membrane Na/nHCO3 cotransporter. The activity of this transporter was increased by elevating apical bath CO2 and was reduced by dorzolamide. Increasing apical bath CO2 also increased intracellular Na from 15.7 ± 3.3 to 24.0 ± 5.3 mM (n = 6; P < 0.05) by increasing apical membrane Na uptake. The CO2-induced acidification also inhibited the basolateral membrane Cl/HCO3 exchanger and increased net steady-state fluid absorption from 2.8 ± 1.6 to 6.7 ± 2.3 µl × cm−2 × hr−1 (n = 5; P < 0.05). The present experiments show how the RPE can accommodate the increased retinal production of CO2 and H2O in the dark, thus preventing acidosis in the SRS. This homeostatic process would preserve the close anatomical relationship between photoreceptor outer segments and RPE in the dark and light, thus protecting the health of the photoreceptors.
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Affiliation(s)
- Jeffrey Adijanto
- Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, MD 20742, USA
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19
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Jansen IDC, Mardones P, Lecanda F, de Vries TJ, Recalde S, Hoeben KA, Schoenmaker T, Ravesloot JH, van Borren MMGJ, van Eijden TM, Bronckers ALJJ, Kellokumpu S, Medina JF, Everts V, Oude Elferink RPJ. Ae2(a,b)-deficient mice exhibit osteopetrosis of long bones but not of calvaria. FASEB J 2009; 23:3470-81. [PMID: 19564250 DOI: 10.1096/fj.08-122598] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Extracellular acidification by osteoclasts is essential to bone resorption. During proton pumping, intracellular pH (pH(i)) is thought to be kept at a near-neutral level by chloride/bicarbonate exchange. Here we show that the Na(+)-independent chloride/bicarbonate anion exchanger 2 (Ae2) is relevant for this process in the osteoclasts from the long bones of Ae2(a,b)(-/-) mice (deficient in the main isoforms Ae2a, Ae2b(1), and Ae2b(2)). Although the long bones of these mice had normal numbers of multinucleated osteoclasts, these cells lacked a ruffled border and displayed impaired bone resorption activity, resulting in an osteopetrotic phenotype of long bones. Moreover, in vitro osteoclastogenesis assays using long-bone marrow cells from Ae2(a,b)(-/-) mice suggested a role for Ae2 in osteoclast formation, as fusion of preosteoclasts for the generation of active multinucleated osteoclasts was found to be slightly delayed. In contrast to the abnormalities observed in the long bones, the skull of Ae2(a,b)(-/-) mice showed no alterations, indicating that calvaria osteoclasts may display normal resorptive activity. Microfluorimetric analysis of osteoclasts from normal mice showed that, in addition to Ae2 activity, calvaria osteoclasts--but not long-bone osteoclasts--possess a sodium-dependent bicarbonate transporting activity. Possibly, this might compensate for the absence of Ae2 in calvaria osteoclasts of Ae2(a,b)(-/-) mice.
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Affiliation(s)
- Ineke D C Jansen
- Department of Periodontology, Academic Centre for Dentistry Amsterdam (ACTA), VU University Amsterdam, van der Boechorststraat 7, Amsterdam, Netherlands 1081 BT.
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20
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Abstract
Plasmalemmal Cl(-)/HCO(3)(-) exchangers are encoded by the SLC4 and SLC26 gene superfamilies, and function to regulate intracellular pH, [Cl(-)] and cell volume. The Cl(-)/HCO(3)(-) exchangers of polarized epithelial cells also contribute to transepithelial secretion and reabsorption of acid-base equivalents and Cl(-). This review focuses on Na(+)-independent electroneutral Cl(-)/HCO(3)(-) exchangers of the SLC4 family. Human SLC4A1/AE1 mutations cause the familial erythroid disorders of spherocytic anemia, stomatocytic anemia and ovalocytosis. A largely discrete set of AE1 mutations causes familial distal renal tubular acidosis. The Slc4a2/Ae2(-/-) mouse dies before weaning with achlorhydria and osteopetrosis. A hypomorphic Ae2(-/-) mouse survives to exhibit male infertility with defective spermatogenesis and a syndrome resembling primary biliary cirrhosis. A human SLC4A3/AE3 polymorphism is associated with seizure disorder, and the Ae3(-/-) mouse has increased seizure susceptibility. The transport mechanism of mammalian SLC4/AE polypeptides is that of electroneutral Cl(-)/anion exchange, but trout erythroid Ae1 also mediates Cl(-) conductance. Erythroid Ae1 may mediate the DIDS-sensitive Cl(-) conductance of mammalian erythrocytes, and, with a single missense mutation, can mediate electrogenic SO(4)(2-)/Cl(-) exchange. AE1 trafficking in polarized cells is regulated by phosphorylation and by interaction with other proteins. AE2 exhibits isoform-specific patterns of acute inhibition by acidic intracellular pH and independently by acidic extracellular pH. In contrast, AE2 is activated by hypertonicity and, in a pH-independent manner, by ammonium and by hypertonicity. A growing body of structure-function and interaction data, together with emerging information about physiological function and structure, is advancing our understanding of SLC4 anion exchangers.
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Affiliation(s)
- Seth L Alper
- Renal Division and Molecular and Vascular Medicine Unit, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.
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21
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Stewart AK, Kurschat CE, Vaughan-Jones RD, Alper SL. Putative re-entrant loop 1 of AE2 transmembrane domain has a major role in acute regulation of anion exchange by pH. J Biol Chem 2008; 284:6126-39. [PMID: 19103596 DOI: 10.1074/jbc.m802051200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Normal pH sensitivity of the SLC4A2/AE2 anion exchanger requires transmembrane domain (TMD) amino acid (aa) residues not conserved in the homologous but relatively pH-insensitive SLC4A1/AE1 polypeptide. We tested the hypothesis that the nonconserved aa cluster 1075DKPK1078 within the first putative re-entrant loop (RL1) of AE2 TMD contributes to pH sensor function by studying anion exchange function of AE2 mutants in which these and other RL1 aa were systematically substituted with corresponding RL1 aa from AE1. Regulation of Cl-/Cl- and Cl-/HCO(-)3 exchange by intracellular pH (pHi) or extracellular pH (pHo) was measured as 4,4'-di-isothiocyanatostilbene-2,2' disulfonic acid-sensitive 36Cl- efflux from Xenopus oocytes. AE2 RL1 mutants 1075AAAQ1078 and 1075AAAQN1079 showed reduced pHi sensitivity and pHo sensitivity was acid-shifted by approximately 1 pH unit. Individual mutants D1075A and P1077A exhibited moderately altered pH sensitivity, whereas a range of substitutions at conserved AE2 Ile-1079 substantially altered sensitivity to pHo and/or pHi. Substitution of the complete AE1 RL1 with AE2 RL1 failed to confer AE2-like pH sensitivity onto AE1. Replacement, however, of AE1 RL1 763SGPGAAAQ770 with AE2 1071VAPGDKPK1078 restored pHi sensitivity to the chimera AE2(1-920)/AE1(613-929) without affecting its low sensitivity to pHo. The results show that acute regulation of AE2 by pH requires RL1 of the TMD. We propose that critical segments of RL1 constitute part of an AE2 pH sensor that, together with residues within the N-terminal half of the TMD, constrain the AE2 polypeptide in a conformation required for regulation of anion exchange by pHi.
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Affiliation(s)
- Andrew K Stewart
- Department of Medicine, Harvard Medical School, and Molecular and Vascular Medicine Unit, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA
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22
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Arenas F, Hervias I, Uriz M, Joplin R, Prieto J, Medina JF. Combination of ursodeoxycholic acid and glucocorticoids upregulates the AE2 alternate promoter in human liver cells. J Clin Invest 2008; 118:695-709. [PMID: 18188457 DOI: 10.1172/jci33156] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2007] [Accepted: 11/14/2007] [Indexed: 01/01/2023] Open
Abstract
Primary biliary cirrhosis (PBC) is a cholestatic disease associated with autoimmune phenomena and alterations in both biliary bicarbonate excretion and expression of the bicarbonate carrier AE2. The bile acid ursodeoxycholic acid (UCDA) is currently used in treatment of cholestatic liver diseases and is the treatment of choice in PBC; however, a subset of PBC patients respond poorly to UDCA monotherapy. In these patients, a combination of UDCA and glucocorticoid therapy appears to be beneficial. To address the mechanism of this benefit, we analyzed the effects of UDCA and dexamethasone on AE2 gene expression in human liver cells from hepatocyte and cholangiocyte lineages. The combination of UDCA and dexamethasone, but not UDCA or dexamethasone alone, increased the expression of liver-enriched alternative mRNA isoforms AE2b1 and AE2b2 and enhanced AE2 activity. Similar effects were obtained after replacing UDCA with UDCA conjugates. In in vitro and in vivo reporter assays, we found that a UDCA/dexamethasone combination upregulated human AE2 alternate overlapping promoter sequences from which AE2b1 and AE2b2 are expressed. In chromatin immunoprecipitation assays, we demonstrated that combination UCDA/dexamethasone treatment induced p300-related interactions between HNF1 and glucocorticoid receptor on the AE2 alternate promoter. Our data provide a potential molecular explanation for the beneficial effects of the combination of UDCA and glucocorticoids in PBC patients with inadequate response to UDCA monotherapy.
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Affiliation(s)
- Fabián Arenas
- Division of Gene Therapy and Hepatology, Center for Applied Medical Research, Clínica Universitaria, University of Navarra School of Medicine, CIBERehd, Pamplona, Spain
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23
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Abstract
Anion exchanger 2 (AE2, SLC4A2) is a ubiquitously expressed membrane solute carrier that regulates intracellular pH (pH(i)) by exchanging cytosolic bicarbonate for extracellular chloride. We used fibroblasts from Ae2-deficient (Ae2(a,b)(-/-)) mice to study the effects of an alkaline shift in resting intracellular pH (pH(i)) on the activation of cAMP signaling and gene expression. Ae2(a,b)(-/-) fibroblasts show increased pH(i) (by 0.22 +/- 0.03 unit) compared with wild type cells at extracellular pH (pH(o)) 7.4 and 37 degrees C. This shift in resting pH(i) is associated with an up-regulation of bicarbonate-activated soluble adenylyl cyclase expression, increased cAMP production, Creb phosphorylation, inducible cAMP early repressor 1 mRNA expression, and impaired activation of c-Fos transcription by forskolin. These results highlight the importance of bicarbonate transport via Ae2 in maintaining pH(i) homeostasis in cultured mouse fibroblasts and unveil the role of cAMP in the cellular response to chronic alkalization, which putatively includes an inducible cAMP early repressor 1-mediated attenuation of phosphorylated Creb activity.
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Affiliation(s)
- Pablo Mardones
- Academic Medical Center Liver Center, Academic Medical Center, University of Amsterdam, 1105 BK, Amsterdam, The Netherlands
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24
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Kurschat CE, Shmukler BE, Jiang L, Hevi S, Kim EH, Stewart AK, Alper SL. Mouse strain-specific coding polymorphism in the Slc4a2/Ae2 gene encodes Ae2c2 variants differing in isoform-specific dominant negative activity. Exp Physiol 2008; 93:458-67. [PMID: 18192337 DOI: 10.1113/expphysiol.2007.040931] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The Slc4a2/Ae2 gene encodes multiple polypeptides arising from alternate promoter usage. The Ae2c promoter gives rise to only one Ae2c transcript from the human Ae2 gene, but to two, alternatively spliced, Ae2c1 and Ae2c2 transcripts from the mouse and rat genes. Unlike in the rat, the mouse Ae2c2 transcript encodes a novel Ae2c2 polypeptide. Here we report that the Ae2c2 residue 9 can be either proline or serine in a mouse strain-specific manner. Both Ae2c2 polypeptides express low function in Xenopus oocytes secondary to reduced or absent surface expression. Ae2c2S, but not Ae2c2P, exerts a dominant negative effect when coexpressed with Ae2a polypeptide, has a less prominent effect when coexpressed with Ae2b1 or Ae2c1 polypeptides, but has no effect on the function of coexpressed Ae2b2 polypeptide. Coexpression of Ae2c2P does not reduce activity of any Ae2 polypeptide variant. Ae2c2S and Ae2c2P also express low functional activity in HEK-293 cells. Knowledge of strain-specific coding polymorphisms with potential functional consequences such as that of Ae2c2 should aid in interpretation of strain-specific phenotypes investigated in the mouse phenome project.
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Affiliation(s)
- Christine E Kurschat
- Molecular and Vascular Medicine and Renal Units, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215, USA
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25
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Zolotarev AS, Unnikrishnan M, Shmukler BE, Clark JS, Vandorpe DH, Grigorieff N, Rubin EJ, Alper SL. Increased sulfate uptake by E. coli overexpressing the SLC26-related SulP protein Rv1739c from Mycobacterium tuberculosis. Comp Biochem Physiol A Mol Integr Physiol 2007; 149:255-66. [PMID: 18255326 DOI: 10.1016/j.cbpa.2007.12.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2007] [Revised: 12/13/2007] [Accepted: 12/14/2007] [Indexed: 12/21/2022]
Abstract
Growth and virulence of mycobacteria requires sulfur uptake. The Mycobacterium tuberculosis genome contains, in addition to the ABC sulfate permease cysTWA, three SLC26-related SulP genes of unknown function. We report that induction of Rv1739c expression in E. coli increased bacterial uptake of sulfate, but not Cl(-), formate, or oxalate. Uptake was time-dependent, maximal at pH 6.0, and exhibited a K(1/2) for sulfate of 4.0 muM. Na(+)-independent sulfate uptake was not reduced by bicarbonate, nitrate, or phosphate, but was inhibited by sulfite, selenate, thiosulfate, N-ethylmaleimide and carbonyl cyanide 3-chloro-phenylhydrazone. Sulfate uptake was also increased by overexpression of the Rv1739c transmembrane domain, but not of the cytoplasmic C-terminal STAS domain. Mutation to serine of the three cysteine residues of Rv1739c did not affect magnitude, pH-dependence, or pharmacology of sulfate uptake. Expression of Rv1739c in a M. bovis BCG strain lacking the ABC sulfate permease subunit CysA could not complement sulfate auxotrophy. Moreover, inducible expression of Rv1739c in an E. coli strain lacking CysA did not increase sulfate uptake by intact cells. Our data show that facilitation of bacterial sulfate uptake by Rv1739c requires CysA and its associated sulfate permease activity, and suggest that Rv1739c may be a CysTWA-dependent sulfate transporter.
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Affiliation(s)
- Alexander S Zolotarev
- Molecular and Vascular Medicine and Renal Divisions, Beth Israel Deaconess Medical Center, USA
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26
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Shmukler BE, Clark JS, Hsu A, Vandorpe DH, Stewart AK, Kurschat CE, Choe SK, Zhou Y, Amigo J, Paw BH, Alper SL. Zebrafish ae2.2 encodes a second slc4a2 anion exchanger. Am J Physiol Regul Integr Comp Physiol 2007; 294:R1081-91. [PMID: 18046018 DOI: 10.1152/ajpregu.00690.2007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The genome of zebrafish (Danio rerio) encodes two unlinked genes equally closely related to the SLC4A2/AE2 anion exchanger genes of mammals. One of these is the recently reported zebrafish ae2 gene (Shmukler BE, Kurschat CE, Ackermann GE, Jiang L, Zhou Y, Barut B, Stuart-Tilley AK, Zhao J, Zon LI, Drummond IA, Vandorpe DH, Paw BH, Alper SL. Am J Physiol Renal Physiol Renal Physiol 289: F835-F849, 2005), now called ae2.1. We now report the structural and functional characterization of Ae2.2, the product of the second zebrafish Ae2 gene, ae2.2. The ae2.2 gene of zebrafish linkage group 24 encodes a polypeptide of 1,232 aa in length, sharing 70% amino acid identity with zebrafish Ae2.1 and 67% identity with mouse AE2a. Zebrafish Ae2.2 expressed in Xenopus oocytes encodes a 135-kDa polypeptide that mediates bidirectional, DIDS-sensitive Cl(-)/Cl(-) exchange and Cl(-)/HCO3(-) exchange. Ae2.2-mediated Cl(-)/Cl(-) exchange is cation independent, voltage insensitive, and electroneutral. Acute regulation of anion exchange mediated by Ae2.2 includes activation by NH4+ and independent inhibition by acidic intracellular pH and by acidic extracellular pH. In situ hybridization reveals low-level expression of Ae2.2 mRNA in zebrafish embryo, most notably in posterior tectum, eye, pharynx, epidermal cells, and axial vascular structures, without notable expression in the Ae2.1-expressing pronephric duct. Knockdown of Ae2.2 mRNA, of Ae2.1 mRNA, or of both with nontoxic or minimally toxic levels of N-morpholino oligomers produced no grossly detectable morphological phenotype, and preserved normal structure of the head and the pronephric duct at 24 h postfertilization.
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Affiliation(s)
- Boris E Shmukler
- Molecular and Vascular Medicine and Renal Units, Beth Israel Deaconess Medical Center E/RW763, 330 Brookline Ave., Boston, MA 02215, USA
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Stewart AK, Kurschat CE, Vaughan-Jones RD, Shmukler BE, Alper SL. Acute regulation of mouse AE2 anion exchanger requires isoform-specific amino acid residues from most of the transmembrane domain. J Physiol 2007; 584:59-73. [PMID: 17690150 PMCID: PMC2277056 DOI: 10.1113/jphysiol.2007.136119] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The widely expressed anion exchanger polypeptide AE2/SLC4A2 is acutely inhibited by acidic intracellular (pH(i)), by acidic extracellular pH (pH(o)), and by the calmodulin inhibitor, calmidazolium, whereas it is acutely activated by NH(4)(+). The homologous erythroid/kidney AE1/SLC4A1 polypeptide is insensitive to these regulators. Each of these AE2 regulatory responses requires the presence of AE2's C-terminal transmembrane domain (TMD). We have now measured (36)Cl(-) efflux from Xenopus oocytes expressing bi- or tripartite AE2-AE1 chimeras to define TMD subregions in which AE2-specific sequences contribute to acute regulation. The chimeric AE polypeptides were all functional at pH(o) 7.4, with the sole exception of AE2((1-920))/AE1((613-811))/AE2((1120-1237)). Reciprocal exchanges of the large third extracellular loops were without effect. AE2 regulation by pH(i), pH(o) and NH(4)(+) was retained after substitution of C-terminal AE2 amino acids 1120-1237 (including the putative second re-entrant loop, two TM spans and the cytoplasmic tail) with the corresponding AE1 sequence. In contrast, the presence of this AE2 C-terminal sequence was both necessary and sufficient for inhibition by calmidazolium. All other tested TMD substitutions abolished AE2 pH(i) sensitivity, abolished or severely attenuated sensitivity to pH(o) and removed sensitivity to NH(4)(+). Loss of AE2 pH(i) sensitivity was not rescued by co-expression of a complementary AE2 sequence within separate full-length chimeras or AE2 subdomains. Thus, normal regulation of AE2 by pH and other ligands requires AE2-specific sequence from most regions of the AE2 TMD, with the exceptions of the third extracellular loop and a short C-terminal sequence. We conclude that the individual TMD amino acid residues previously identified as influencing acute regulation of AE2 exert that influence within a regulatory structure requiring essential contributions from multiple regions of the AE2 TMD.
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Affiliation(s)
- A K Stewart
- Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
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Recalde S, Muruzábal F, Looije N, Kunne C, Burrell MA, Sáez E, Martínez-Ansó E, Salas JT, Mardones P, Prieto J, Medina JF, Elferink RPJO. Inefficient chronic activation of parietal cells in Ae2a,b(-/-) mice. Am J Pathol 2006; 169:165-76. [PMID: 16816370 PMCID: PMC1698767 DOI: 10.2353/ajpath.2006.051096] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In parietal cells, basolateral Ae2 Cl(-)/HCO(3)(-) exchanger (Slc4a2) appears to compensate for luminal H(+) pumping while providing Cl(-) for apical secretion. In mouse and rat, mRNA variants Ae2a, Ae2b1, Ae2b2, and Ae2c2 are all found in most tissues (although the latter at very low levels), whereas Ae2c1 is restricted to the stomach. We studied the acid secretory function of gastric mucosa in mice with targeted disruption of Ae2a, Ae2b1, and Ae2b2 (but not Ae2c) isoforms. In the oxyntic mucosa of Ae2(a,b)(-/-) mice, total Ae2 protein was nearly undetectable, indicating low gastric expression of the Ae2c isoforms. In Ae2(a,b)(-/-) mice basal acid secretion was normal, whereas carbachol/histamine-stimulated acid secretion was impaired by 70%. These animals showed increased serum gastrin levels and hyperplasia of G cells. Immunohistochemistry and electron microscopy revealed baseline activation of parietal cells with fusion of intracellular H(+)/K(+)-ATPase-containing vesicles with the apical membrane and degenerative changes (but not substantial apoptosis) in a subpopulation of these cells. Increased expression of proliferating cell nuclear antigen in the oxyntic glands suggested enhanced Ae2(a,b)(-/-) parietal cell turnover. These data reveal a critical role of Ae2a-Ae2b1-Ae2b2 isoforms in stimulated gastric acid secretion whereas residual Ae2c isoforms could account to a limited extent for basal acid secretion.
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Affiliation(s)
- Sergio Recalde
- Laboratory of Experimental Hepatology, Academic Medical Center Liver Center, Amsterdam, The Netherlands
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