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Hamar J, Cnaani A, Kültz D. Transcriptional upregulation of the myo-inositol biosynthesis pathway is enhanced by NFAT5 in hyperosmotically stressed tilapia cells. Am J Physiol Cell Physiol 2024; 327:C545-C556. [PMID: 38946247 DOI: 10.1152/ajpcell.00187.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2024] [Revised: 06/13/2024] [Accepted: 06/16/2024] [Indexed: 07/02/2024]
Abstract
Euryhaline fish experience variable osmotic environments requiring physiological adjustments to tolerate elevated salinity. Mozambique tilapia (Oreochromis mossambicus) possess one of the highest salinity tolerance limits of any fish. In tilapia and other euryhaline fish species, the myo-inositol biosynthesis (MIB) pathway enzymes, myo-inositol phosphate synthase (MIPS) and inositol monophosphatase 1 (IMPA1.1), are among the most upregulated mRNAs and proteins indicating the high importance of this pathway for hyperosmotic (HO) stress tolerance. These abundance changes must be precluded by HO perception and signaling mechanism activation to regulate the expression of MIPS and IMPA1.1 genes. In previous work using a O. mossambicus cell line (OmB), a reoccurring osmosensitive enhancer element (OSRE1) in both MIPS and IMPA1.1 was shown to transcriptionally upregulate these enzymes in response to HO stress. The OSRE1 core consensus (5'-GGAAA-3') matches the core binding sequence of the predominant mammalian HO response transcription factor, nuclear factor of activated T-cells (NFAT5). HO-challenged OmB cells showed an increase in NFAT5 mRNA suggesting NFAT5 may contribute to MIB pathway regulation in euryhaline fish. Ectopic expression of wild-type NFAT5 induced an IMPA1.1 promoter-driven reporter by 5.1-fold (P < 0.01). Moreover, expression of dominant negative NFAT5 in HO media resulted in a 47% suppression of the reporter signal (P < 0.005). Furthermore, reductions of IMPA1.1 (37-49%) and MIPS (6-37%) mRNA abundance were observed in HO-challenged NFAT5 knockout cells relative to control cells. Collectively, these multiple lines of experimental evidence establish NFAT5 as a tilapia transcription factor contributing to HO-induced activation of the MIB pathway.NEW & NOTEWORTHY In our study, we use a multi-pronged synthetic biology approach to demonstrate that the fish homolog of the predominant mammalian osmotic stress transcription factor nuclear factor of activated T-cells (NFAT5) also contributes to the activation of hyperosmolality inducible genes in cells of extremely euryhaline fish. However, in addition to NFAT5 the presence of other strong osmotically inducible signaling mechanisms is required for full activation of osmoregulated tilapia genes.
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Affiliation(s)
- Jens Hamar
- Department of Animal Sciences and Genome Center, University of California Davis, Davis, California, United States
| | - Avner Cnaani
- Department of Poultry and Aquaculture, Institute of Animal Sciences, Agricultural Research Organization, Rishon LeZion, Israel
| | - Dietmar Kültz
- Department of Animal Sciences and Genome Center, University of California Davis, Davis, California, United States
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Liu C, Lin J, Yang H, Li N, Tang L, Neumann D, Ding X, Zhu L. NFAT5 Restricts Bovine Herpesvirus 1 Productive Infection in MDBK Cell Cultures. Microbiol Spectr 2023; 11:e0011723. [PMID: 37227295 PMCID: PMC10434061 DOI: 10.1128/spectrum.00117-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2023] [Accepted: 05/04/2023] [Indexed: 05/26/2023] Open
Abstract
Bovine herpesvirus 1 (BoHV-1), an important bovine viral pathogen, causes severe disease in the upper respiratory tract and reproductive system. Tonicity-responsive enhancer-binding protein (TonEBP), also known as nuclear factor of activated T cells 5 (NFAT5), is a pleiotropic stress protein involved in a range of cellular processes. In this study, we showed that the knockdown of NFAT5 by siRNA increased BoHV-1 productive infection and overexpression of NFAT5 via plasmid transfection decreased virus production in bovine kidney (MDBK) cells. Virus productive infection at later stages significantly increased transcription of NFAT5 but not appreciably alter measurable NFAT5 protein levels. Virus infection relocalized NFAT5 protein and decreased the cytosol accumulation. Importantly, we found a subset of NFAT5 resides in mitochondria, and virus infection led to the depletion of mitochondrial NFAT5. In addition to full-length NFAT5, another two isoforms with distinct molecular weights were exclusively detected in the nucleus, where the accumulation was differentially affected following virus infection. In addition, virus infection differentially altered mRNA levels of PGK1, SMIT, and BGT-1, the canonical downstream targets regulated by NFAT5. Taken together, NFAT5 is a potential host factor that restricts BoHV-1 productive infection, and virus infection hijacks NFAT5 signaling transduction by relocalization of NFAT5 molecules in cytoplasm, nucleus, and mitochondria, as well as altered expression of its downstream targets. IMPORTANCE Accumulating studies have revealed that NFAT5 regulates disease development due to infection of numerous viruses, underlying the importance of the host factor in virus pathogenesis. Here, we report that NFAT5 has capacity to restrict BoHV-1 productive infection in vitro. And virus productive infection at later stages may alter NFAT5 signaling pathway as observed by relocalization of NFAT5 protein, reduced accumulation of NFAT5 in cytosol, and differential expression of NFAT5 downstream targets. Importantly, for the first time, we found that a subset of NFAT5 resides in mitochondria, implying that NFAT5 may regulate mitochondrial functions, which will extend our knowledge on NFAT5 biological activities. Moreover, we found two NFAT5 isoforms with distinct molecular weights were exclusively detected in the nucleus, where the accumulation was differentially affected following virus infection, representing a novel regulation mechanism on NFAT5 function in response to BoHV-1infection.
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Affiliation(s)
- Chang Liu
- College of Life Sciences, Hebei University, Baoding, China
| | - Jiayu Lin
- College of Life Sciences, Hebei University, Baoding, China
| | - Hao Yang
- College of Life Sciences, Hebei University, Baoding, China
| | - Ningxi Li
- College of Life Sciences, Hebei University, Baoding, China
| | - Linke Tang
- College of Life Sciences, Hebei University, Baoding, China
| | - Donna Neumann
- Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Xiuyan Ding
- College of Life Sciences, Hebei University, Baoding, China
| | - Liqian Zhu
- College of Life Sciences, Hebei University, Baoding, China
- Key Laboratory of Microbial Diversity Research and Application of Hebei Province, College of Life Science, Hebei University, Baoding, China
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3
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The evolving role of TonEBP as an immunometabolic stress protein. Nat Rev Nephrol 2020; 16:352-364. [PMID: 32157251 DOI: 10.1038/s41581-020-0261-1] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/14/2020] [Indexed: 02/06/2023]
Abstract
Tonicity-responsive enhancer-binding protein (TonEBP), which is also known as nuclear factor of activated T cells 5 (NFAT5), was discovered 20 years ago as a transcriptional regulator of the cellular response to hypertonic (hyperosmotic salinity) stress in the renal medulla. Numerous studies since then have revealed that TonEBP is a pleiotropic stress protein that is involved in a range of immunometabolic diseases. Some of the single-nucleotide polymorphisms (SNPs) in TONEBP introns are cis-expression quantitative trait loci that affect TONEBP transcription. These SNPs are associated with increased risk of type 2 diabetes mellitus, diabetic nephropathy, inflammation, high blood pressure and abnormal plasma osmolality, indicating that variation in TONEBP expression might contribute to these phenotypes. In addition, functional studies have shown that TonEBP is involved in the pathogenesis of rheumatoid arthritis, atherosclerosis, diabetic nephropathy, acute kidney injury, hyperlipidaemia and insulin resistance, autoimmune diseases (including type 1 diabetes mellitus and multiple sclerosis), salt-sensitive hypertension and hepatocellular carcinoma. These pathological activities of TonEBP are in contrast to the protective actions of TonEBP in response to hypertonicity, bacterial infection and DNA damage induced by genotoxins. An emerging theme is that TonEBP is a stress protein that mediates the cellular response to a range of pathological insults, including excess caloric intake, inflammation and oxidative stress.
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4
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Wang X, Kültz D. Osmolality/salinity-responsive enhancers (OSREs) control induction of osmoprotective genes in euryhaline fish. Proc Natl Acad Sci U S A 2017; 114:E2729-E2738. [PMID: 28289196 PMCID: PMC5380061 DOI: 10.1073/pnas.1614712114] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Fish respond to salinity stress by transcriptional induction of many genes, but the mechanism of their osmotic regulation is unknown. We developed a reporter assay using cells derived from the brain of the tilapia Oreochromis mossambicus (OmB cells) to identify osmolality/salinity-responsive enhancers (OSREs) in the genes of Omossambicus Genomic DNA comprising the regulatory regions of two strongly salinity-induced genes, inositol monophosphatase 1 (IMPA1.1) and myo-inositol phosphate synthase (MIPS), was isolated and analyzed with dual luciferase enhancer trap reporter assays. We identified five sequences (two in IMPA1.1 and three in MIPS) that share a common consensus element (DDKGGAAWWDWWYDNRB), which we named "OSRE1." Additional OSREs that were less effective in conferring salinity-induced trans-activation and do not match the OSRE1 consensus also were identified in both MIPS and IMPA1.1 Although OSRE1 shares homology with the mammalian osmotic-response element/tonicity-responsive enhancer (ORE/TonE) enhancer, the latter is insufficient to confer osmotic induction in fish. Like other enhancers, OSRE1 trans-activates genes independent of orientation. We conclude that OSRE1 is a cis-regulatory element (CRE) that enhances the hyperosmotic induction of osmoregulated genes in fish. Our study also shows that tailored reporter assays developed for OmB cells facilitate the identification of CREs in fish genomes. Knowledge of the OSRE1 motif allows affinity-purification of the corresponding transcription factor and computational approaches for enhancer screening of fish genomes. Moreover, our study enables targeted inactivation of OSRE1 enhancers, a method superior to gene knockout for functional characterization because it confines impairment of gene function to a specific context (salinity stress) and eliminates pitfalls of constitutive gene knockouts (embryonic lethality, developmental compensation).
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Affiliation(s)
- Xiaodan Wang
- Biochemical Evolution Laboratory, Department of Animal Science, University of California, Davis, CA, 95616
- Laboratory of Aquaculture Nutrition and Environmental Health, School of Life Sciences, East China Normal University, Shanghai, 200241, China
| | - Dietmar Kültz
- Biochemical Evolution Laboratory, Department of Animal Science, University of California, Davis, CA, 95616;
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5
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Skorkina MY, Sladkova EA, Shamray EA, Cherkashina OV, Evstigneev MP, Buchelnikov AS, Prylutskyy YI, Ritter U. C60 fullerene affects elastic properties and osmoregulation reactions of human lymphocytes. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2015; 44:493-8. [PMID: 26071689 DOI: 10.1007/s00249-015-1050-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2015] [Revised: 05/16/2015] [Accepted: 05/25/2015] [Indexed: 11/25/2022]
Abstract
The influence of aqueous solution of pristine C60 fullerene (C60FAS) on functional activity of lymphocytes from a healthy person was studied for the first time. By means of atomic force microscopy, it was found that C60FAS in a concentration of 0.1 mg/ml increases the stiffness of the lymphocyte membrane by 41% (p < 0.05) and lowers the functional activity of the plasmalemma surface, thereby constraining the use of its membrane material in physiological reactions using a hypotonic model in vitro. However, a cell retains the ability to regulate its volume and demonstrates relative resistance to hypo-osmotic stress. The resistance of lymphocytes in hypo-osmotic medium is facilitated by activation of the nucleus by C60 fullerene particles, which regulates the implementation of two consistent phases of an increase and decrease of cell volume, thereby retaining cell viability. All these indicate the impact of C60 fullerene on the cellular nucleus.
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Andronic J, Shirakashi R, Pickel SU, Westerling KM, Klein T, Holm T, Sauer M, Sukhorukov VL. Hypotonic activation of the myo-inositol transporter SLC5A3 in HEK293 cells probed by cell volumetry, confocal and super-resolution microscopy. PLoS One 2015; 10:e0119990. [PMID: 25756525 PMCID: PMC4355067 DOI: 10.1371/journal.pone.0119990] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Accepted: 01/21/2015] [Indexed: 11/19/2022] Open
Abstract
Swelling-activated pathways for myo-inositol, one of the most abundant organic osmolytes in mammalian cells, have not yet been identified. The present study explores the SLC5A3 protein as a possible transporter of myo-inositol in hyponically swollen HEK293 cells. To address this issue, we examined the relationship between the hypotonicity-induced changes in plasma membrane permeability to myo-inositol Pino [m/s] and expression/localization of SLC5A3. Pino values were determined by cell volumetry over a wide tonicity range (100–275 mOsm) in myo-inositol-substituted solutions. While being negligible under mild hypotonicity (200–275 mOsm), Pino grew rapidly at osmolalities below 200 mOsm to reach a maximum of ∼3 nm/s at 100–125 mOsm, as indicated by fast cell swelling due to myo-inositol influx. The increase in Pino resulted most likely from the hypotonicity-mediated incorporation of cytosolic SLC5A3 into the plasma membrane, as revealed by confocal fluorescence microscopy of cells expressing EGFP-tagged SLC5A3 and super-resolution imaging of immunostained SLC5A3 by direct stochastic optical reconstruction microscopy (dSTORM). dSTORM in hypotonic cells revealed a surface density of membrane-associated SLC5A3 proteins of 200–2000 localizations/μm2. Assuming SLC5A3 to be the major path for myo-inositol, a turnover rate of 80–800 myo-inositol molecules per second for a single transporter protein was estimated from combined volumetric and dSTORM data. Hypotonic stress also caused a significant upregulation of SLC5A3 gene expression as detected by semiquantitative RT-PCR and Western blot analysis. In summary, our data provide first evidence for swelling-mediated activation of SLC5A3 thus suggesting a functional role of this transporter in hypotonic volume regulation of mammalian cells.
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Affiliation(s)
- Joseph Andronic
- Department of Biotechnology and Biophysics, University of Würzburg, Biozentrum, Am Hubland, Würzburg, Germany
| | - Ryo Shirakashi
- Institute of Industrial Science, The University of Tokyo, Tokyo, Japan
| | - Simone U. Pickel
- Department of Biotechnology and Biophysics, University of Würzburg, Biozentrum, Am Hubland, Würzburg, Germany
| | - Katherine M. Westerling
- Department of Biotechnology and Biophysics, University of Würzburg, Biozentrum, Am Hubland, Würzburg, Germany
| | - Teresa Klein
- Department of Biotechnology and Biophysics, University of Würzburg, Biozentrum, Am Hubland, Würzburg, Germany
| | - Thorge Holm
- Department of Biotechnology and Biophysics, University of Würzburg, Biozentrum, Am Hubland, Würzburg, Germany
| | - Markus Sauer
- Department of Biotechnology and Biophysics, University of Würzburg, Biozentrum, Am Hubland, Würzburg, Germany
| | - Vladimir L. Sukhorukov
- Department of Biotechnology and Biophysics, University of Würzburg, Biozentrum, Am Hubland, Würzburg, Germany
- * E-mail:
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Kim JA, Kwon MJ, Lee-Kwon W, Choi SY, Sanada S, Kwon HM. Modulation of TonEBP activity by SUMO modification in response to hypertonicity. Front Physiol 2014; 5:200. [PMID: 24994984 PMCID: PMC4063170 DOI: 10.3389/fphys.2014.00200] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Accepted: 05/09/2014] [Indexed: 01/06/2023] Open
Abstract
TonEBP is a DNA binding transcriptional enhancer that enables cellular adaptation to hypertonic stress by promoting expression of specific genes. TonEBP expression is very high in the renal medulla because local hypertonicity stimulates its expression. Given the high level of expression, it is not well understood how TonEBP activity is modulated. Here we report that TonEBP is post-translationally modified by SUMO, i.e., sumoylated, in the renal medulla but not in other isotonic organs. The sumoylation is reproduced in cultured cells when switched to hypertonicity. Analyses of site-directed TonEBP mutants reveal that K556 and K603 are independently sumoylated in response to hypertonicity. DNA binding is required for the sumoylation. Functional analyses of non-sumoylated mutants and SUMO-conjugated constructs show that sumoylation inhibits TonEBP in a dose-dependent manner but independent of the site of SUMO conjugation. Sumoylation inhibits transactivation without affecting nuclear translocation or DNA binding. These data suggest that sumoylation modulates the activity of TonEBP in the hypertonic renal medulla to prevent excessive action of TonEBP.
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Affiliation(s)
- Jeong-Ah Kim
- Department of Biological Sciences, Ulsan National Institute of Science and Technology Ulsan, South Korea ; Department of Medicine, University of Maryland Baltimore, MD, USA
| | - Mi Jin Kwon
- Department of Biological Sciences, Ulsan National Institute of Science and Technology Ulsan, South Korea
| | - Whaseon Lee-Kwon
- Department of Biological Sciences, Ulsan National Institute of Science and Technology Ulsan, South Korea
| | - Soo Youn Choi
- Department of Biological Sciences, Ulsan National Institute of Science and Technology Ulsan, South Korea
| | - Satoru Sanada
- Department of Biological Sciences, Ulsan National Institute of Science and Technology Ulsan, South Korea ; Department of Medicine, University of Maryland Baltimore, MD, USA
| | - Hyug Moo Kwon
- Department of Biological Sciences, Ulsan National Institute of Science and Technology Ulsan, South Korea ; Department of Medicine, University of Maryland Baltimore, MD, USA
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8
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Li M, Shoemaker BA, Thangudu RR, Ferraris JD, Burg MB, Panchenko AR. Mutations in DNA-binding loop of NFAT5 transcription factor produce unique outcomes on protein-DNA binding and dynamics. J Phys Chem B 2013; 117:13226-34. [PMID: 23734591 PMCID: PMC3807822 DOI: 10.1021/jp403310a] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The nuclear factor of activated T
cells 5 (NFAT5 or TonEBP) is
a Rel family transcriptional activator and is activated by hypertonic
conditions. Several studies point to a possible connection between
nuclear translocation and DNA binding; however, the mechanism of NFAT5
nuclear translocation and the effect of DNA binding on retaining NFAT5
in the nucleus are largely unknown. Recent experiments showed that
different mutations introduced in the DNA-binding loop and dimerization
interface were important for DNA binding and some of them decreased
the nuclear–cytoplasm ratio of NFAT5. To understand the mechanisms
of these mutations, we model their effect on protein dynamics and
DNA binding. We show that the NFAT5 complex without DNA is much more
flexible than the complex with DNA. Moreover, DNA binding considerably
stabilizes the overall dimeric complex and the NFAT5 dimer is only
marginally stable in the absence of DNA. Two sets of NFAT5 mutations
from the same DNA-binding loop are found to have different mechanisms
of specific and nonspecific binding to DNA. The R217A/E223A/R226A
(R293A/E299A/R302A using isoform c numbering) mutant is characterized
by significantly compromised binding to DNA and higher complex flexibility.
On the contrary, the T222D (T298D in isoform c) mutation, a potential
phosphomimetic mutation, makes the overall complex more rigid and
does not significantly affect the DNA binding. Therefore, the reduced
nuclear–cytoplasm ratio of NFAT5 can be attributed to reduced
binding to DNA for the triple mutant, while the T222D mutant suggests
an additional mechanism at work.
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Affiliation(s)
- Minghui Li
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health , Bethesda, MD, United States
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Cheung CY, Ko BC. NFAT5 in cellular adaptation to hypertonic stress - regulations and functional significance. J Mol Signal 2013; 8:5. [PMID: 23618372 PMCID: PMC3655004 DOI: 10.1186/1750-2187-8-5] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Accepted: 04/11/2013] [Indexed: 12/22/2022] Open
Abstract
The Nuclear Factor of Activated T Cells-5 (NFAT5), also known as OREBP or TonEBP, is a member of the nuclear factors of the activated T cells family of transcription factors. It is also the only known tonicity-regulated transcription factor in mammals. NFAT5 was initially known for its role in the hypertonic kidney inner medulla for orchestrating a genetic program to restore the cellular homeostasis. Emerging evidence, however, suggests that NFAT5 might play a more diverse functional role, including a pivotal role in blood pressure regulation and the development of autoimmune diseases. Despite the growing significance of NFAT5 in physiology and diseases, our understanding of how its activity is regulated remains very limited. Furthermore, how changes in tonicities are converted into functional outputs via NFAT5 remains elusive. Therefore, this review aims to summarize our current knowledge on the functional roles of NFAT5 in osmotic stress adaptation and the signaling pathways that regulate its activity.
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Affiliation(s)
- Chris Yk Cheung
- Department of Anatomical and Cellular Pathology, and The State Key Laboratory in Oncology in South China, The Chinese University of Hong Kong, The Prince of Wales Hospital, Rm 38019, Clinical Sciences Building, Shatin, Hong Kong, China.
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Izumi Y, Li J, Villers C, Hashimoto K, Burg MB, Ferraris JD. Mutations that reduce its specific DNA binding inhibit high NaCl-induced nuclear localization of the osmoprotective transcription factor NFAT5. Am J Physiol Cell Physiol 2012; 303:C1061-9. [PMID: 22992674 PMCID: PMC3492838 DOI: 10.1152/ajpcell.00265.2012] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Accepted: 09/10/2012] [Indexed: 11/22/2022]
Abstract
The transcription factor nuclear factor of activated T cell 5 (NFAT5) is activated by the stress of hypertonicity (e.g., high NaCl). Increased expression of NFAT5 target genes causes accumulation of protective organic osmolytes and heat shock proteins. Under normotonic conditions (∼300 mosmol/kgH(2)O), NFAT5 is distributed between the nucleus and cytoplasm, hypertonicity causes it to translocate into the nucleus, and hypotonicity causes it to translocate into the cytoplasm. The mechanism of translocation is complex and not completely understood. NFAT5-T298 is a known contact site of NFAT5 with its specific DNA element [osmotic response element (ORE)]. In the present study, we find that mutation of NFAT5-T298 to alanine or aspartic acid not only reduces binding of NFAT5 to OREs (EMSA) but also proportionately reduces high NaCl-induced nuclear translocation of NFAT5. Combined mutation of other NFAT5 DNA contact sites (R293A/E299A/R302A) also greatly reduces both specific DNA binding and nuclear localization of NFAT5. NFAT5-T298 is a potential phosphorylation site, but, using protein mass spectrometry, we do not find phosphorylation at NFAT5-T298. Further, decreased high NaCl-induced nuclear localization of NFAT5 mutated at T298 does not involve previously known regulatory mechanisms, including hypotonicity-induced export of NFAT5, regulated by phosphorylation of NFAT5-S155, XPO1 (CRM1/exportin1)-mediated export of NFAT5 from the nucleus, or hypertonicity-induced elevation of NUP88, which enhances nuclear localization of NFAT5. We conclude that specific DNA binding of NFAT5 contributes to its nuclear localization, by mechanisms, as yet undetermined, but independent of ones previously described to regulate NFAT5 distribution.
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Affiliation(s)
- Yuichiro Izumi
- Systems Biology Center, National Heart, Lung, and Blood Institute, Bethesda, Maryland, USA
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11
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Hsin YH, Tang CH, Lai HT, Lee TH. The role of TonEBP in regulation of AAD expression and dopamine production in renal proximal tubule cells upon hypertonic challenge. Biochem Biophys Res Commun 2011; 414:598-603. [PMID: 21982764 DOI: 10.1016/j.bbrc.2011.09.128] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2011] [Accepted: 09/24/2011] [Indexed: 12/13/2022]
Abstract
Renal proximal tubule cells overexpress aromatic l-amino acid decarboxylase (AAD) to produce dopamine, which inhibits salt absorption in the hypertonic environment. We examined the effect of TonEBP on AAD expression in human proximal tubule epithelial cells, HK-2 cell line. Confocal microscopy showed that after 2h of exposure to the hypertonic medium, TonEBP accumulation in nuclei increased as compared to the isotonic control. The activated TonEBP enhanced the mRNA expression of the representative downstream genes (i.e., SMIT and TauT). Meanwhile, AAD protein abundance also increased with TonEBP activation. EMSA and luciferase reporter assay showed that TonEBP was involved in transcriptional regulation of AAD upon hypertonic stress. Inactivation of TonEBP by the p38 inhibitor SB203580, or TonEBP shRNA significantly reduced AAD expression, which was rescued by re-expressing Myc-tagged TonEBP. Up-regulation of AAD increased dopamine synthesis, and dopamine inhibited NKA activity in hypertonic condition. These results suggested that TonEBP played an important role in the epithelial cells of renal proximal tubule upon hypertonic stress by enhancing AAD expression, which could promote dopamine secretion to negative regulate NKA activity. The elucidation of a new mechanism described in this study combined with previous findings provides more insights into this issue.
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Affiliation(s)
- Yi-Hong Hsin
- Department of Life Sciences, National Chung-Hsing University, Taichung 402, Taiwan
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Pedersen SF, Kapus A, Hoffmann EK. Osmosensory mechanisms in cellular and systemic volume regulation. J Am Soc Nephrol 2011; 22:1587-97. [PMID: 21852585 DOI: 10.1681/asn.2010121284] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Perturbations of cellular and systemic osmolarity severely challenge the function of all organisms and are consequently regulated very tightly. Here we outline current evidence on how cells sense volume perturbations, with particular focus on mechanisms relevant to the kidneys and to extracellular osmolarity and whole body volume homeostasis. There are a variety of molecular signals that respond to perturbations in cell volume and osmosensors or volume sensors responding to these signals. The early signals of volume perturbation include integrins, the cytoskeleton, receptor tyrosine kinases, and transient receptor potential channels. We also present current evidence on the localization and function of central and peripheral systemic osmosensors and conclude with a brief look at the still limited evidence on pathophysiological conditions associated with deranged sensing of cell volume.
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Affiliation(s)
- Stine Falsig Pedersen
- Department of Biology, University of Copenhagen, Universitetsparken 13, DK-2100, Copenhagen, Denmark.
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Estrada-Gelonch A, Aramburu J, López-Rodríguez C. Exclusion of NFAT5 from mitotic chromatin resets its nucleo-cytoplasmic distribution in interphase. PLoS One 2009; 4:e7036. [PMID: 19750013 PMCID: PMC2737149 DOI: 10.1371/journal.pone.0007036] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2009] [Accepted: 08/06/2009] [Indexed: 12/02/2022] Open
Abstract
Background The transcription factor NFAT5 is a major inducer of osmoprotective genes and is required to maintain the proliferative capacity of cells exposed to hypertonic stress. In response to hypertonicity, NFAT5 translocates to the nucleus, binds to regulatory regions of osmoprotective genes and activates their transcription. Besides stimulus-specific regulatory mechanisms, the activity of transcription factors in cycling cells is also regulated by the passage through mitosis, when most transcriptional processes are downregulated. It was not known whether mitosis could be a point of control for NFAT5. Methodology/Principal Findings Using confocal microscopy we observed that NFAT5 was excluded from chromatin during mitosis in both isotonic and hypertonic conditions. Analysis of NFAT5 deletions showed that exclusion was mediated by the carboxy-terminal domain (CTD). NFAT5 mutants lacking this domain showed constitutive binding to mitotic chromatin independent of tonicity, which caused them to localize in the nucleus and remain bound to chromatin in the subsequent interphase without hypertonic stimulation. We analyzed the contribution of the CTD, DNA binding, and nuclear import and export signals to the subcellular localization of this factor. Our results indicated that cytoplasmic localization of NFAT5 in isotonic conditions required both the exclusion from mitotic DNA and active nuclear export in interphase. Finally, we identified several regions within the CTD of NFAT5, some of them overlapping with transactivation domains, which were separately capable of causing its exclusion from mitotic chromatin. Conclusions/Significance Our results reveal a multipart mechanism regulating the subcellular localization of NFAT5. The transactivating module of NFAT5 switches its function from an stimulus-specific activator of transcription in interphase to an stimulus-independent repressor of binding to DNA in mitosis. This mechanism, together with export signals acting in interphase, resets the cytoplasmic localization of NFAT5 and prevents its nuclear accumulation and association with DNA in the absence of hypertonic stress.
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Affiliation(s)
- Anaïs Estrada-Gelonch
- Immunology Unit, Department of Experimental and Health Sciences (DCEXS), Universitat Pompeu Fabra, Parc de Recerca Biomèdica de Barcelona, Barcelona, Spain
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Kwon MS, Na KY, Moeckel G, Lee SD, Kwon HM. Urea promotes TonEBP expression and cellular adaptation in extreme hypertonicity. Pflugers Arch 2009; 459:183-9. [PMID: 19585141 DOI: 10.1007/s00424-009-0696-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2009] [Revised: 06/23/2009] [Accepted: 06/25/2009] [Indexed: 12/24/2022]
Abstract
The transcriptional activator TonEBP is a central regulator of osmolality in the renal medulla and whole body water homeostasis. In order to understand the regulation of TonEBP in the renal medulla, we examined MDCK cells, a kidney-derived epithelial cell line, under conditions mimicking the renal medulla. Moderate changes in ambient tonicity, which was tolerated without prior adaptation, displayed lasting effects on TonEBP in bidirectional manner-stimulated by hypertonicity and inhibited by hypotonicity. TonEBP expression was further enhanced by extreme hypertonicity observed in the inner medullae of antidiuretic animals. Urea stimulated TonEBP expression and promoted cellular proliferation under the conditions of extreme hypertonicity. On the other hand, the TonEBP activity was negatively modulated under these conditions presumably to temper the highly abundant TonEBP. We conclude that urea is critical to the cellular adaptation to extreme hypertonicity and the high level of TonEBP expression in the inner medulla.
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Affiliation(s)
- Min Seong Kwon
- Department of Medicine, University of Maryland, 655 West Baltimore Street, Bressler 8029, Baltimore, MD 21201, USA
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Kwon MS, Lim SW, Kwon HM. Hypertonic Stress in the Kidney: A Necessary Evil. Physiology (Bethesda) 2009; 24:186-91. [DOI: 10.1152/physiol.00005.2009] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The interstitium of the renal medulla is hypertonic, imposing deleterious effects on local cells. At the same time, the hypertonicity provides osmotic gradient for water reabsorption and is a local signal for tissue-specific gene expression and differentiation of the renal medulla, which is a critical organ for water homeostasis.
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Affiliation(s)
- Min Seong Kwon
- Department of Medicine, University of Maryland, Baltimore, Maryland
| | - Sun Woo Lim
- Department of Medicine, University of Maryland, Baltimore, Maryland
| | - H. Moo Kwon
- Department of Medicine, University of Maryland, Baltimore, Maryland
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