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Arenas-Huertero F, Zaragoza-Ojeda M, Sánchez-Alarcón J, Milić M, Šegvić Klarić M, Montiel-González JM, Valencia-Quintana R. Involvement of Ahr Pathway in Toxicity of Aflatoxins and Other Mycotoxins. Front Microbiol 2019; 10:2347. [PMID: 31681212 PMCID: PMC6798329 DOI: 10.3389/fmicb.2019.02347] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Accepted: 09/26/2019] [Indexed: 12/18/2022] Open
Abstract
The purpose of this review is to present information about the role of activation of aflatoxins and other mycotoxins, of the aryl hydrocarbon receptor (AhR) pathway. Aflatoxins and other mycotoxins are a diverse group of secondary metabolites that can be contaminants in a broad range of agricultural products and feeds. Some species of Aspergillus, Alternaria, Penicilium, and Fusarium are major producers of mycotoxins, some of which are toxic and carcinogenic. Several aflatoxins are planar molecules that can activate the AhR. AhR participates in the detoxification of several xenobiotic substances and activates phase I and phase II detoxification pathways. But it is important to recognize that AhR activation also affects differentiation, cell adhesion, proliferation, and immune response among others. Any examination of the effects of aflatoxins and other toxins that act as activators to AhR must consider the potential of the disruption of several cellular functions in order to extend the perception thus far about the toxic and carcinogenic effects of these toxins. There have been no Reviews of existing data between the relation of AhR and aflatoxins and this one attempts to give information precisely about this dichotomy.
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Affiliation(s)
- Francisco Arenas-Huertero
- Experimental Pathology Research Laboratory, Children’s Hospital of Mexico Federico Gómez, Mexico, Mexico
| | - Montserrat Zaragoza-Ojeda
- Experimental Pathology Research Laboratory, Children’s Hospital of Mexico Federico Gómez, Mexico, Mexico
| | - Juana Sánchez-Alarcón
- Rafael Villalobos-Pietrini Laboratory of Genomic Toxicology and Environmental Chemistry, Faculty of Agrobiology, Autonomous University of Tlaxcala, Tlaxcala, Mexico
| | - Mirta Milić
- Mutagenesis Unit, Institute for Medical Research and Occupational Health, Zagreb, Croatia
| | - Maja Šegvić Klarić
- Department of Microbiology, Faculty of Pharmacy and Biochemistry, University of Zagreb, Zagreb, Croatia
| | - José M. Montiel-González
- Rafael Villalobos-Pietrini Laboratory of Genomic Toxicology and Environmental Chemistry, Faculty of Agrobiology, Autonomous University of Tlaxcala, Tlaxcala, Mexico
| | - Rafael Valencia-Quintana
- Rafael Villalobos-Pietrini Laboratory of Genomic Toxicology and Environmental Chemistry, Faculty of Agrobiology, Autonomous University of Tlaxcala, Tlaxcala, Mexico
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2
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Abstract
Circadian oscillators are networks of biochemical feedback loops that generate 24-hour rhythms in organisms from bacteria to animals. These periodic rhythms result from a complex interplay among clock components that are specific to the organism, but share molecular mechanisms across kingdoms. A full understanding of these processes requires detailed knowledge, not only of the biochemical properties of clock proteins and their interactions, but also of the three-dimensional structure of clockwork components. Posttranslational modifications and protein–protein interactions have become a recent focus, in particular the complex interactions mediated by the phosphorylation of clock proteins and the formation of multimeric protein complexes that regulate clock genes at transcriptional and translational levels. This review covers the structural aspects of circadian oscillators, and serves as a primer for this exciting realm of structural biology.
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Affiliation(s)
- Reena Saini
- Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.,Max-Planck-Institut für Pflanzenzüchtungsforschung, Cologne, Germany
| | - Mariusz Jaskolski
- Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland.,Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland
| | - Seth J Davis
- Max-Planck-Institut für Pflanzenzüchtungsforschung, Cologne, Germany. .,Department of Biology, University of York, York, UK.
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3
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Inamoto I, Chen G, Shin JA. The DNA target determines the dimerization partner selected by bHLHZ-like hybrid proteins AhRJun and ArntFos. MOLECULAR BIOSYSTEMS 2017; 13:476-488. [DOI: 10.1039/c6mb00795c] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The molecular basis of protein–partner selection and DNA binding of the basic helix–loop–helix (bHLH) and basic region-leucine zipper (bZIP) superfamilies of dimeric transcription factors is fundamental toward understanding gene regulation.
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Affiliation(s)
- Ichiro Inamoto
- Department of Chemistry
- University of Toronto
- Mississauga
- Canada L5L 1C6
| | - Gang Chen
- Department of Chemistry
- University of Toronto
- Mississauga
- Canada L5L 1C6
| | - Jumi A. Shin
- Department of Chemistry
- University of Toronto
- Mississauga
- Canada L5L 1C6
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Nucifora LG, Wu YC, Lee BJ, Sha L, Margolis RL, Ross CA, Sawa A, Nucifora FC. A Mutation in NPAS3 That Segregates with Schizophrenia in a Small Family Leads to Protein Aggregation. MOLECULAR NEUROPSYCHIATRY 2016; 2:133-144. [PMID: 27867938 DOI: 10.1159/000447358] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2016] [Accepted: 05/31/2016] [Indexed: 12/21/2022]
Abstract
Schizophrenia and other major mental illnesses result from a complex interplay of genetic and environmental factors. We previously identified a mutation in NPAS3 that results in a valine to isoleucine (V304I) amino acid substitution segregating with schizophrenia in a small family. The amino acid change occurs in a potentially critical region for protein function. Furthermore, the same amino acid substitution in proteins related to familial Alzheimer's disease and transthyretin amyloidosis has been associated with protein aggregation. In this study, we demonstrate that NPAS3 is prone to aggregation, and that the V304I mutation in NPAS3 increases this propensity in both bacterial and mammalian expression systems. We also show that NPAS3-V304I reduces soluble endogenous NPAS3, and increases insoluble endogenous NPAS3 and leads to alteration of transcriptional activity. These results suggest that protein aggregation, potentially leading to cell dysfunction via a loss of protein function through sequestration, may contribute to the pathogenesis of schizophrenia and other forms of mental illness. Further exploration of the mechanisms leading to abnormal protein quality control could lead to new therapeutic targets.
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Affiliation(s)
- Leslie G Nucifora
- Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Md., USA
| | - YeeWen Candace Wu
- Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Md., USA
| | - Brian J Lee
- Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Md., USA
| | - Li Sha
- Department of Biotechnology, Dalian Medical University, Dalian, China
| | - Russell L Margolis
- Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Md., USA
| | - Christopher A Ross
- Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Md., USA
| | - Akira Sawa
- Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Md., USA
| | - Frederick C Nucifora
- Department of Psychiatry, Johns Hopkins University School of Medicine, Baltimore, Md., USA
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5
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The Role of the Neuroprotective Factor Npas4 in Cerebral Ischemia. Int J Mol Sci 2015; 16:29011-28. [PMID: 26690124 PMCID: PMC4691091 DOI: 10.3390/ijms161226144] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 10/28/2015] [Accepted: 11/16/2015] [Indexed: 01/05/2023] Open
Abstract
Stroke is one of the leading causes of death and adult disability in the world. Although many molecules have been documented to have a neuroprotective effect, the majority of these molecules failed to improve the neurological outcomes for patients with brain ischemia. It has been proposed that neuroprotection alone may, in fact, not be adequate for improving the prognosis of ischemic stroke. Neuroprotectants that can regulate other processes which occur in the brain during ischemia could potentially be targets for the development of effective therapeutic interventions in stroke. Neuronal Per-Arnt-Sim domain protein 4 (Npas4) is an activity-dependent transcription factor whose expression is induced in various brain insults, including cerebral ischemia. It has been shown that Npas4 plays an important role in protecting neurons against many types of neurodegenerative insult. Recently, it was demonstrated that Npas4 indeed has a neuroprotective role in ischemic stroke and that Npas4 might be involved in modulating the cell death pathway and inflammatory response. In this review, we summarize the current knowledge of the roles that Npas4 may play in neuroinflammation and ischemia. Understanding how ischemic lesion size in stroke may be reduced through modulation of Npas4-dependent apoptotic and inflammatory pathways could lead to the development of new stroke therapies.
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Bersten DC, Bruning JB, Peet DJ, Whitelaw ML. Human variants in the neuronal basic helix-loop-helix/Per-Arnt-Sim (bHLH/PAS) transcription factor complex NPAS4/ARNT2 disrupt function. PLoS One 2014; 9:e85768. [PMID: 24465693 PMCID: PMC3894988 DOI: 10.1371/journal.pone.0085768] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Accepted: 12/06/2013] [Indexed: 11/25/2022] Open
Abstract
Neuronal Per-Arnt-Sim homology (PAS) Factor 4 (NPAS4) is a neuronal activity-dependent transcription factor which heterodimerises with ARNT2 to regulate genes involved in inhibitory synapse formation. NPAS4 functions to maintain excitatory/inhibitory balance in neurons, while mouse models have shown it to play roles in memory formation, social interaction and neurodegeneration. NPAS4 has therefore been implicated in a number of neuropsychiatric or neurodegenerative diseases which are underpinned by defects in excitatory/inhibitory balance. Here we have explored a broad set of non-synonymous human variants in NPAS4 and ARNT2 for disruption of NPAS4 function. We found two variants in NPAS4 (F147S and E257K) and two variants in ARNT2 (R46W and R107H) which significantly reduced transcriptional activity of the heterodimer on a luciferase reporter gene. Furthermore, we found that NPAS4.F147S was unable to activate expression of the NPAS4 target gene BDNF due to reduced dimerisation with ARNT2. Homology modelling predicts F147 in NPAS4 to lie at the dimer interface, where it appears to directly contribute to protein/protein interaction. We also found that reduced transcriptional activation by ARNT2 R46W was due to disruption of nuclear localisation. These results provide insight into the mechanisms of NPAS4/ARNT dimerisation and transcriptional activation and have potential implications for cognitive phenotypic variation and diseases such as autism, schizophrenia and dementia.
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Affiliation(s)
- David C Bersten
- School of Molecular and Biomedical Science (Biochemistry), and Australian Research Council Special Research Centre for the Molecular Genetics of Development, The University of Adelaide, Adelaide, South Australia, Australia
| | - John B Bruning
- School of Molecular and Biomedical Science (Biochemistry), and Australian Research Council Special Research Centre for the Molecular Genetics of Development, The University of Adelaide, Adelaide, South Australia, Australia
| | - Daniel J Peet
- School of Molecular and Biomedical Science (Biochemistry), and Australian Research Council Special Research Centre for the Molecular Genetics of Development, The University of Adelaide, Adelaide, South Australia, Australia
| | - Murray L Whitelaw
- School of Molecular and Biomedical Science (Biochemistry), and Australian Research Council Special Research Centre for the Molecular Genetics of Development, The University of Adelaide, Adelaide, South Australia, Australia
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8
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Abstract
The generation of blood vessels is a highly synchronized process requiring the coordinated efforts of several vascular and nonvascular cell populations as well as a stringent orchestration by the tissue being vascularized. Stereotyped angiogenesis is vital for both developmental growth and to restore tissue metabolic supply after ischemic events. Central neurons such as those found in the brain, spinal cord, and retina are vast consumers of oxygen and nutrients and therefore require high rates of perfusion by functional vascular networks to ensure proper sensory transmission. During a metabolic mismatch, such as that occurring during a cerebrovascular infarct or in ischemic retinopathies, there is increasing evidence that central neurons have an inherent ability to influence the vascular response to injury. With a focus on the retina and retinal ischemic disorders, this review explores the ever-growing evidence suggesting that central neurons have the propensity to impact tissue vascularization and reparative angiogenesis. Moreover, it addresses the paradoxical ability of severely ischemic neurons to hinder vascular regrowth and thus segregate the most severely injured zones of nervous tissue. The topics covered here are pertinent for future therapeutic strategies because promoting and steering vascular growth may be beneficial for ischemic disorders.
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Chen G, De Jong AT, Shin JA. Forced homodimerization of the c-Fos leucine zipper in designed bHLHZ-like hybrid proteins MaxbHLH-Fos and ArntbHLH-Fos. MOLECULAR BIOSYSTEMS 2012; 8:1286-96. [DOI: 10.1039/c2mb05354c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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Greb-Markiewicz B, Orłowski M, Dobrucki J, Ożyhar A. Sequences that direct subcellular traffic of the Drosophila methoprene-tolerant protein (MET) are located predominantly in the PAS domains. Mol Cell Endocrinol 2011; 345:16-26. [PMID: 21745535 DOI: 10.1016/j.mce.2011.06.035] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/24/2011] [Revised: 06/02/2011] [Accepted: 06/28/2011] [Indexed: 11/25/2022]
Abstract
Methoprene-tolerant protein (MET) is a key mediator of antimetamorphic signaling in insects. MET belongs to the family of bHLH-PAS transcription factors which regulate gene expression and determine essential physiological and developmental processes. The ability of many bHLH-PAS proteins to carry out their functions is related to the patterns of intracellular trafficking, which are determined by specific sequences and indicate that a nuclear localization signal (NLS) or a nuclear export signal (NES) is present and active. Therefore, the identification of NLS and NES signals is fundamental in order to understand the intracellular signaling role of MET. Nevertheless, data on the intracellular trafficking of MET are inconsistent, and until now there hasn't been any data on potential NLS and NES sequences. To analyze the trafficking of MET we designed a number of expression vectors encoding full-length MET, as well as various derivatives, that were fused to yellow fluorescent protein (YFP). Confocal microscopy analysis of the subcellular distribution of YFP-MET indicated that while this protein was localized mainly in the nucleus, it was also observed in the cytoplasm. This suggested the presence of both an NLS and NES in MET. Our work has shown that each of the two PAS domains of MET (PAS-A and PAS-B, respectively) contain one NLS and one NES sequence. Additional NES activity was present in the C-terminal fragment. The NLS activity located in PAS-B was dependent on the presence of juvenile hormone (JH), the potential ligand for MET. In contrast to this, JH didn't seem to be required for the NLS in PAS-A to be active. However, on the basis of current knowledge about the function of PAS-A in other bHLH-PAS proteins, we suggest there might be other proteins that control the activity of the NLS and possibly the NES located in the PAS-A of MET. Thus, the intracellular trafficking of MET seems to be regulated by a rather complicated network of different factors.
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Affiliation(s)
- Beata Greb-Markiewicz
- Department of Biochemistry, Faculty of Chemistry, Wrocław University of Technology, Poland.
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11
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Sapieha P, Joyal JS, Rivera JC, Kermorvant-Duchemin E, Sennlaub F, Hardy P, Lachapelle P, Chemtob S. Retinopathy of prematurity: understanding ischemic retinal vasculopathies at an extreme of life. J Clin Invest 2010; 120:3022-32. [PMID: 20811158 DOI: 10.1172/jci42142] [Citation(s) in RCA: 174] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Retinopathy of prematurity (ROP) is a major complication of preterm birth. It encompasses a spectrum of pathologies that affect vision, from mild disease that resolves spontaneously to severe disease that causes retinal detachment and subsequent blindness. The pathologies are characterized by an arrest in normal retinal vascular development associated with microvascular degeneration. The resulting ischemia and retinal hypoxia lead to excessive abnormal compensatory blood vessel growth. However, this neovascularization can lead to fibrous scar formation and culminate in retinal detachment. Present therapeutic modalities to limit the adverse consequences of aberrant neovascularization are invasive and/or tissue-destructive. In this Review, we discuss current concepts on retinal microvascular degeneration, neovascularization, and available treatments, as well as present future perspectives toward more profound elucidation of the pathogenesis of ROP.
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Affiliation(s)
- Przemyslaw Sapieha
- Department of Ophthalmology, Children’s Hospital Boston, Harvard Medical School, Boston, Massachusetts, USA
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12
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Aguado-Llera D, Goormaghtigh E, de Geest N, Quan XJ, Prieto A, Hassan BA, Gómez J, Neira JL. The basic helix-loop-helix region of human neurogenin 1 is a monomeric natively unfolded protein which forms a "fuzzy" complex upon DNA binding. Biochemistry 2010; 49:1577-89. [PMID: 20102160 DOI: 10.1021/bi901616z] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Neuronal specification is regulated by the activity of transcription factors containing the basic helix-loop-helix motif (bHLH); these regulating proteins include, among others, the neurogenin (Ngn) family, related to the atonal family of genes. Neurogenin 1 (NGN1) is a 237-residue protein that contains a bHLH domain and is involved in neuronal differentiation. In this work, we synthesized the bHLH region of NGN1 (bHLHN) comprising residues 90-150 of the full-length NGN1. The domain is a monomeric natively unfolded protein with a pH-dependent premolten globule conformation, as shown by several spectroscopic techniques (namely, NMR, fluorescence, FTIR, and circular dichroism). The unfolded character of the domain also explains, first, the impossibility of its overexpression in several Escherichia coli strains and, second, its insolubility in aqueous buffers. To the best of our knowledge, this is the first extensive study of the conformational preferences of a bHLH domain under different solution conditions. Upon binding to two DNA E-boxes, the protein forms "fuzzy" complexes (that is, the complexes were not fully folded). The affinities of bHLHN for both DNA boxes were smaller than those of other bHLH domains, which might explain why the protein-DNA complexes were not fully folded.
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Affiliation(s)
- David Aguado-Llera
- Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, 03202 Elche (Alicante), Spain
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Furness SGB, Whelan F. The pleiotropy of dioxin toxicity--xenobiotic misappropriation of the aryl hydrocarbon receptor's alternative physiological roles. Pharmacol Ther 2009; 124:336-53. [PMID: 19781569 DOI: 10.1016/j.pharmthera.2009.09.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2009] [Accepted: 09/01/2009] [Indexed: 10/20/2022]
Abstract
The aryl hydrocarbon receptor is a signal regulated transcription factor that has best been characterised as regulating the xenobiotic response to a variety of planar aromatic hydrocarbons. There is compelling evidence that it mediates most, if not all, of the toxic effects of dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin). Dioxin exposure results in a wide variety of toxic outcomes including severe wasting syndrome, chloracne, thymic involution, severe immune suppression, reduced fertility, hepatotoxicity, teratogenicity, tumour promotion and death. The pleiotropy of toxic outcomes implies the disruption of a wide range of normal physiological functions. The aryl hydrocarbon receptor has developmentally restricted expression as well as developmental defects in gene-targeted mice. It has a wide range of target genes that do not fit into the classical xenobiotic metabolising gene battery and has recently been shown to interact with NF-kappa B and the estrogen receptor. There is also evidence for its activation in the absence of exogenous ligand, all of which point to various roles outside xenobiotic metabolism. Ligands so far identified display differential activation potential with respect to receptor activity. This article addresses activities of the aryl hydrocarbon receptor that are outside the xenobiotic response. Known physiological roles are discussed as well as how their disruption contributes to the pleiotropic toxicity of TCDD.
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Affiliation(s)
- Sebastian G B Furness
- Drug Discovery Biology Laboratory, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia.
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14
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Xu J, Chen G, De Jong AT, Shahravan SH, Shin JA. Max-E47, a designed minimalist protein that targets the E-box DNA site in vivo and in vitro. J Am Chem Soc 2009; 131:7839-48. [PMID: 19449889 PMCID: PMC2734406 DOI: 10.1021/ja901306q] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Max-E47 is a designed hybrid protein comprising the Max DNA-binding basic region and E47 HLH dimerization subdomain. In the yeast one-hybrid system (Y1H), Max-E47 shows strong transcriptional activation from the E-box site, 5'-CACGTG, targeted by the Myc/Max/Mad network of transcription factors; two mutants, Max-E47Y and Max-E47YF, activate more weakly from the E-box in the Y1H. Quantitative fluorescence anisotropy titrations to gain free energies of protein:DNA binding gave low nanomolar K(d) values for the native MaxbHLHZ, Max-E47, and the Y and YF mutants binding to the E-box site (14, 15, 9, and 6 nM, respectively), with no detectable binding to a nonspecific control duplex. Because these minimalist, E-box-binding hybrids have no activation domain and no interactions with the c-MycbHLHZ, as shown by the yeast two-hybrid assay, they can potentially serve as dominant-negative inhibitors that suppress activation of E-box-responsive genes targeted by transcription factors including the c-Myc/Max complex. As proof-of-principle, we used our modified Y1H, which allows direct competition between two proteins vying for a DNA target, to show that Max-E47 effectively outcompetes the native MaxbHLHZ for the E-box; weaker competition is observed from the two mutants, consistent with Y1H results. These hybrids provide a minimalist scaffold for further exploration of the relationship between protein structure and DNA-binding function and may have applications as protein therapeutics or biochemical probes capable of targeting the E-box site.
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Affiliation(s)
- Jing Xu
- Department of Chemistry, University of Toronto, Mississauga, Ontario L5L 1C6, Canada
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15
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Partch CL, Card PB, Amezcua CA, Gardner KH. Molecular basis of coiled coil coactivator recruitment by the aryl hydrocarbon receptor nuclear translocator (ARNT). J Biol Chem 2009; 284:15184-92. [PMID: 19324882 DOI: 10.1074/jbc.m808479200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The aryl hydrocarbon receptor nuclear translocator (ARNT) serves as the obligate heterodimeric partner for bHLH-PAS proteins involved in sensing and coordinating transcriptional responses to xenobiotics, hypoxia, and developmental pathways. Although its C-terminal transactivation domain is dispensable for transcriptional activation in vivo, ARNT has recently been shown to use its N-terminal bHLH and/or PAS domains to interact with several transcriptional coactivators that are required for transcriptional initiation after xenobiotic or hypoxic cues. Here we show that ARNT uses a single PAS domain to interact with two coiled coil coactivators, TRIP230 and CoCoA. Both coactivators interact with the same interface on the ARNT PAS-B domain, located on the opposite side of the domain used to associate with the analogous PAS domain on its heterodimeric bHLH-PAS partner HIF-2alpha. Using NMR and biochemical studies, we identified the ARNT-interacting motif of one coactivator, TRIP230 as an LXXLL-like nuclear receptor box. Mutation of this motif and proximal sequences disrupts the interaction with ARNT PAS-B. Identification of this ARNT-coactivator interface illustrates how ARNT PAS-B is used to form critical interactions with both bHLH-PAS partners and coactivators that are required for transcriptional responses.
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Affiliation(s)
- Carrie L Partch
- Department of Biochemistry, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA
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ARNT PAS-B has a fragile native state structure with an alternative beta-sheet register nearby in sequence space. Proc Natl Acad Sci U S A 2009; 106:2617-22. [PMID: 19196990 DOI: 10.1073/pnas.0808270106] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The aryl hydrocarbon receptor nuclear translocator (ARNT) is a basic helix-loop-helix Period/ARNT/Single-minded (bHLH-PAS) protein that controls various biological pathways as part of dimeric transcriptional regulator complexes with other bHLH-PAS proteins. The two PAS domains within ARNT, PAS-A and PAS-B, are essential for the formation of these complexes because they mediate protein-protein interactions via residues located on their beta-sheet surfaces. While investigating the importance of residues in ARNT PAS-B involved in these interactions, we uncovered a point mutation (Y456T) on the solvent-exposed beta-sheet surface that allowed this domain to interconvert with a second, stable conformation. Although both conformations are present in equivalent quantities in the Y456T mutant, this can be shifted almost completely to either end point by additional mutations. A high-resolution solution structure of a mutant ARNT PAS-B domain stabilized in the new conformation revealed a 3-residue slip in register and accompanying inversion of the central Ibeta-strand. We have demonstrated that the new conformation has >100-fold lower in vitro affinity for its heterodimerization partner, hypoxia-inducible factor 2alpha PAS-B. We speculate that the pliability in beta-strand register is related to the flexibility required of ARNT to bind to several partners and, more broadly, to the abilities of some PAS domains to regulate their activities in response to small-molecule cofactors.
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Chow HK, Xu J, Shahravan SH, De Jong AT, Chen G, Shin JA. Hybrids of the bHLH and bZIP protein motifs display different DNA-binding activities in vivo vs. in vitro. PLoS One 2008; 3:e3514. [PMID: 18949049 PMCID: PMC2568859 DOI: 10.1371/journal.pone.0003514] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2008] [Accepted: 10/02/2008] [Indexed: 12/18/2022] Open
Abstract
Minimalist hybrids comprising the DNA-binding domain of bHLH/PAS (basic-helix-loop-helix/Per-Arnt-Sim) protein Arnt fused to the leucine zipper (LZ) dimerization domain from bZIP (basic region-leucine zipper) protein C/EBP were designed to bind the E-box DNA site, CACGTG, targeted by bHLHZ (basic-helix-loop-helix-zipper) proteins Myc and Max, as well as the Arnt homodimer. The bHLHZ-like structure of ArntbHLH-C/EBP comprises the Arnt bHLH domain fused to the C/EBP LZ: i.e. swap of the 330 aa PAS domain for the 29 aa LZ. In the yeast one-hybrid assay (Y1H), transcriptional activation from the E-box was strong by ArntbHLH-C/EBP, and undetectable for the truncated ArntbHLH (PAS removed), as detected via readout from the HIS3 and lacZ reporters. In contrast, fluorescence anisotropy titrations showed affinities for the E-box with ArntbHLH-C/EBP and ArntbHLH comparable to other transcription factors (K(d) 148.9 nM and 40.2 nM, respectively), but only under select conditions that maintained folded protein. Although in vivo yeast results and in vitro spectroscopic studies for ArntbHLH-C/EBP targeting the E-box correlate well, the same does not hold for ArntbHLH. As circular dichroism confirms that ArntbHLH-C/EBP is a much more strongly alpha-helical structure than ArntbHLH, we conclude that the nonfunctional ArntbHLH in the Y1H must be due to misfolding, leading to the false negative that this protein is incapable of targeting the E-box. Many experiments, including protein design and selections from large libraries, depend on protein domains remaining well-behaved in the nonnative experimental environment, especially small motifs like the bHLH (60-70 aa). Interestingly, a short helical LZ can serve as a folding- and/or solubility-enhancing tag, an important device given the focus of current research on exploration of vast networks of biomolecular interactions.
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Affiliation(s)
- Hiu-Kwan Chow
- Department of Chemistry, University of Toronto, Mississauga, Ontario, Canada
| | - Jing Xu
- Department of Chemistry, University of Toronto, Mississauga, Ontario, Canada
| | - S. Hesam Shahravan
- Department of Chemistry, University of Toronto, Mississauga, Ontario, Canada
| | - Antonia T. De Jong
- Department of Chemistry, University of Toronto, Mississauga, Ontario, Canada
| | - Gang Chen
- Department of Chemistry, University of Toronto, Mississauga, Ontario, Canada
| | - Jumi A. Shin
- Department of Chemistry, University of Toronto, Mississauga, Ontario, Canada
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada
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18
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Berg T. Inhibition of transcription factors with small organic molecules. Curr Opin Chem Biol 2008; 12:464-71. [DOI: 10.1016/j.cbpa.2008.07.023] [Citation(s) in RCA: 98] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2008] [Revised: 07/14/2008] [Accepted: 07/17/2008] [Indexed: 11/26/2022]
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Burcham PC. Toxicology down under: past achievements, present realities, and future prospects. Chem Res Toxicol 2008; 21:967-70. [PMID: 18442270 DOI: 10.1021/tx8001252] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Abstract
The hypoxia-inducible factors (HIFs) are critical for cellular adaptation to limiting oxygen and regulate a wide array of genes when cued by cellular oxygen-sensing mechanisms. HIF is able to direct transcription from either of two transactivation domains, each of which is regulated by distinct mechanisms. The oxygen-dependent asparaginyl hydroxylase factor-inhibiting HIF-1alpha (FIH-1) is a key regulator of the HIF C-terminal transactivation domain, and provides a direct link between oxygen sensation and HIF-mediated transcription. Additionally, there are phosphorylation and nitrosylation events reported to modulate HIF transcriptional activity, as well as numerous transcriptional coactivators and other interacting proteins that together provide cell and tissue specificity of HIF target gene regulation.
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Affiliation(s)
- K Lisy
- The School of Molecular and Biomedical Science, and the ARC Special research Centre for the Molecular Genetics of Development, University of Adelaide, Adelaide, SA 5005, Australia
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21
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Affiliation(s)
- Aba Losi
- *Department of Physics, University of Parma, Viale G. P. Usberti 7A, 43100 Parma, Italy; and
| | - Wolfgang Gärtner
- Max Planck Institute for Bioinorganic Chemistry, Stiftstrasse 34-36, D-45470 Mülheim, Germany
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22
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Jiang L, Crews ST. Transcriptional specificity of Drosophila dysfusion and the control of tracheal fusion cell gene expression. J Biol Chem 2007; 282:28659-28668. [PMID: 17652079 PMCID: PMC2742625 DOI: 10.1074/jbc.m703803200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Drosophila Dysfusion basic-helix-loop-helix-PAS (bHLH-PAS) protein controls the transcription of genes that mediate tracheal fusion. Dysfusion is highly related to the mammalian Nxf protein that has been implicated in nervous system gene regulation. Toward the goal of understanding how Dysfusion controls fusion cell gene expression, the biochemical properties of Dysfusion were investigated using protein interaction experiments, cell culture-based transcription assays, and in vivo transgenic analyses. Dysfusion dimerizes with the Tango bHLH-PAS protein, and together they act as a DNA binding transcriptional activator. Dysfusion/Tango binds multiple NCGTG binding sites, with the following preference: TCGTG > GCGTG > ACGTG > CCGTG. This binding site promiscuity differs from the restricted binding site preferences of other bHLH-PAS/Tango heterodimers. However, it is identical to the binding site preferences of mammalian Nxf/Arnt, indicating that the specificity is evolutionarily conserved. Germ line transformation experiments using a fragment of the CG13196 Dysfusion target gene allowed identification of a fusion cell enhancer. Experiments in which NCGTG sites were mutated individually and in combination revealed that TCGTG sites were required for fusion cell expression but that the single ACGTG and GCGTG sites present were not. Finally, a reporter transgene containing four tandemly arranged TCGTG elements has strong expression in tracheal fusion cells. Transgenic misexpression of dysfusion further revealed that Dysfusion has the ability to activate transcription in multiple cell types, although it does this most effectively in tracheal cells and can only function at mid-embryogenesis and later.
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Affiliation(s)
- Lan Jiang
- Departments of Biochemistry and Biophysics, Biology, and Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill, North Carolina 27599-3280
| | - Stephen T Crews
- Departments of Biochemistry and Biophysics, Biology, and Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill, North Carolina 27599-3280.
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Furness SGB, Lees MJ, Whitelaw ML. The dioxin (aryl hydrocarbon) receptor as a model for adaptive responses of bHLH/PAS transcription factors. FEBS Lett 2007; 581:3616-25. [PMID: 17459381 DOI: 10.1016/j.febslet.2007.04.011] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2007] [Revised: 04/03/2007] [Accepted: 04/04/2007] [Indexed: 11/19/2022]
Abstract
This review examines the common theme of adaptive responses of bHLH/PAS proteins, using the dioxin receptor as a prototype. The bHLH/PAS family of transcriptional regulators are a group of key developmental and environmental stress sensing proteins. They employ a variety of post-translational control mechanisms to regulate their transcriptional output. Amongst this family, the dioxin receptor is best known for its ability to elicit toxic responses to dioxin and dioxin like chemicals even though it mediates more benign adaptive responses to non-toxic xenobiotics. We discuss what is known about dioxin receptor physiology, both adaptive and inherent, along with its molecular regulation and put this into the context of the wider bHLH/PAS family. We also raise the issue of its toxic responses, in particular the idea that it is the dysregulation of its poorly characterised housekeeping functions that leads to these outcomes.
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Affiliation(s)
- Sebastian G B Furness
- Drug Discovery Laboratory, Department of Pharmacology, Building 13E, Monash University, Wellington Road, Clayton, Victoria 3800, Australia.
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