The murine Sim-2 gene product inhibits transcription by active repression and functional interference.

The Drosophila single-minded (Dsim) gene encodes a master regulatory protein involved in cell fate determination during midline development. This protein is a member of a rapidly expanding family of gene products possessing basic helix-loop-helix (bHLH) and hydrophobic PAS (designated a conserved region among PER, ARNT [aryl hydrocarbon receptor nuclear translocator] and SIM) protein association domains. Members of this family function as central transcriptional regulators in cellular differentiation and in the response to environmental stimuli such as xenobiotics and hypoxia. We have previously identified a murine member of this family, called mSim-2, showing sequence homology to the bHLH and PAS domains of Dsim. Immunoprecipitation experiments with recombinant proteins indicate that mSIM-2 associates with the arnt gene product. In the present work, by using fine-structure mapping we found that the HLH and PAS motifs of both proteins are required for optimal association. Forced expression of GAL4/mSIM-2 fusion constructs in mammalian cells demonstrated the presence of two separable repression domains within the carboxy terminus of mSIM-2. We found that mSIM-2 is capable of repressing ARNT-mediated transcriptional activation in a mammalian two-hybrid system. This effect (i) is dependent on the ability of mSIM-2 and ARNT to heterodimerize, (ii) is dependent on the presence of the mSIM-2 carboxy-terminal repression domain, and (iii) is not specific to the ARNT activation domain. These results suggest that mSIM-2 repression activity can dominantly override the activation potential of adjacent transcription factors. We also demonstrated that mSIM-2 can functionally interfere with hypoxia-inducible factor 1alpha (HIF-1alpha)/ARNT transcription complexes, providing a second mechanism by which mSIM-2 may inhibit transcription.

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Histone demethylase KDM6A directly senses oxygen to control chromatin and cell fate

Science ◽

10.1126/science.aaw1026 ◽

2019 ◽

Vol 363 (6432) ◽

pp. 1217-1222 ◽

Cited By ~ 100

Author(s):

Abhishek A. Chakraborty ◽

Tuomas Laukka ◽

Matti Myllykoski ◽

Alison E. Ringel ◽

Matthew A. Booker ◽

...

Keyword(s):

Cell Fate ◽

Histone Methylation ◽

Mammalian Cells ◽

Control Cell ◽

Hypoxia Inducible Factor ◽

Histone Demethylase ◽

Histone Demethylases ◽

Independent Manner ◽

H3k27 Methylation ◽

Oxygen Sensitive

Oxygen sensing is central to metazoan biology and has implications for human disease. Mammalian cells express multiple oxygen-dependent enzymes called 2-oxoglutarate (OG)-dependent dioxygenases (2-OGDDs), but they vary in their oxygen affinities and hence their ability to sense oxygen. The 2-OGDD histone demethylases control histone methylation. Hypoxia increases histone methylation, but whether this reflects direct effects on histone demethylases or indirect effects caused by the hypoxic induction of the HIF (hypoxia-inducible factor) transcription factor or the 2-OG antagonist 2-hydroxyglutarate (2-HG) is unclear. Here, we report that hypoxia promotes histone methylation in a HIF- and 2-HG–independent manner. We found that the H3K27 histone demethylase KDM6A/UTX, but not its paralog KDM6B, is oxygen sensitive. KDM6A loss, like hypoxia, prevented H3K27 demethylation and blocked cellular differentiation. Restoring H3K27 methylation homeostasis in hypoxic cells reversed these effects. Thus, oxygen directly affects chromatin regulators to control cell fate.

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Role of aryl hydrocarbon receptor in modulation of the expression of the hypoxia marker carbonic anhydrase IX

Biochemical Journal ◽

10.1042/bj20080952 ◽

2009 ◽

Vol 419 (2) ◽

pp. 419-425 ◽

Cited By ~ 11

Author(s):

Martina Takacova ◽

Tereza Holotnakova ◽

Jan Vondracek ◽

Miroslav Machala ◽

Katerina Pencikova ◽

...

Keyword(s):

Carbonic Anhydrase ◽

Aryl Hydrocarbon Receptor ◽

Transcriptional Activation ◽

Hypoxia Inducible Factor ◽

Carbonic Anhydrase Ix ◽

Independent Manner ◽

Hypoxic Induction ◽

Aryl Hydrocarbon ◽

Ca Ix ◽

Tcdd Treatment

Tumour-associated expression of CA IX (carbonic anhydrase IX) is to a major extent regulated by HIF-1 (hypoxia-inducible factor-1) which is important for transcriptional activation and consists of the oxygen-regulated subunit HIF-1α and the partner factor ARNT [AhR (aryl hydrocarbon receptor) nuclear translocator]. We have previously observed that HIF-1α competes with the AhR for interaction with ARNT under conditions when both conditionally regulated factors are activated. We have therefore investigated whether TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)-induced activation of the AhR pathway might interfere with CA IX expression. The results from the present study suggest that TCDD treatment reduces hypoxic induction of both CA IX mRNA and protein expression. Moreover, the transcriptional activity of the CA9 promoter was significantly reduced by expression of CAAhR (constitutively active AhR), which activates transcription in a ligand-independent manner. Finally, we found that ARNT is critical for both hypoxic induction and the TCDD-mediated inhibition of CA9 expression.

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Hypoxia-inducible factor 1 levels vary exponentially over a physiologically relevant range of O2 tension

AJP Cell Physiology ◽

10.1152/ajpcell.1996.271.4.c1172 ◽

1996 ◽

Vol 271 (4) ◽

pp. C1172-C1180 ◽

Cited By ~ 786

Author(s):

B. H. Jiang ◽

G. L. Semenza ◽

C. Bauer ◽

H. H. Marti

Keyword(s):

Dna Binding ◽

Transcriptional Activation ◽

Mammalian Cells ◽

Functional Characterization ◽

Hypoxia Inducible Factor ◽

Binding Activity ◽

Maximal Response ◽

Hypoxia Inducible Factor 1 ◽

Dna Binding Activity

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric basic helix-loop-helix protein implicated in the transcriptional activation of genes encoding erythropoietin, glycolytic enzymes, and vascular endothelial growth factor in hypoxic mammalian cells. In this study, we have quantitated HIF-1 DNA-binding activity and protein levels of the HIF-1 alpha and HIF-1 beta subunits in human HeLa cells exposed to O2 concentrations ranging from 0 to 20% in the absence or presence of 1 mM KCN to inhibit oxidative phosphorylation and cellular O2 consumption. HIF-1 DNA-binding activity, HIF-1 alpha protein and HIF-1 beta protein each increased exponentially as cells were subjected to decreasing O2 concentrations, with a half maximal response between 1.5 and 2% O2 and a maximal response at 0.5% O2, both in the presence and absence of KCN. The HIF-1 response was greatest over O2 concentrations associated with ischemic/hypoxic events in vivo. These results provide evidence for the involvement of HIF-1 in O2 homeostasis and represent a functional characterization of the putative O2 sensor that initiates hypoxia signal transduction leading to HIF-1 expression.

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MondoA, a Novel Basic Helix-Loop-Helix–Leucine Zipper Transcriptional Activator That Constitutes a Positive Branch of a Max-Like Network

Molecular and Cellular Biology ◽

10.1128/mcb.20.23.8845-8854.2000 ◽

2000 ◽

Vol 20 (23) ◽

pp. 8845-8854 ◽

Cited By ~ 77

Author(s):

Andrew N. Billin ◽

Alanna L. Eilers ◽

Kathryn L. Coulter ◽

Jennifer S. Logan ◽

Donald E. Ayer

Keyword(s):

Transcriptional Activation ◽

Nuclear Export ◽

Mammalian Cells ◽

Leucine Zipper ◽

Functional Characterization ◽

Nuclear Accumulation ◽

Cytoplasmic Localization ◽

Basic Helix Loop Helix ◽

Helix Loop Helix

ABSTRACT Max is a common dimerization partner for a family of transcription factors (Myc, Mad [or Mxi]), and Mnt [or Rox] proteins) that regulate cell growth, proliferation, and apoptosis. We recently characterized a novel Max-like protein, Mlx, which interacts with Mad1 and Mad4. Here we describe the cloning and functional characterization of a new family of basic helix-loop-helix–leucine zipper heterodimeric partners for Mlx termed the Mondo family. MondoA forms homodimers weakly and does not interact with Max or members of the Myc or Mad families. MondoA and Mlx associate in vivo, and surprisingly, they are localized primarily to the cytoplasm of cultured mammalian cells. Treatment of cells with the nuclear export inhibitor leptomycin B results in the nuclear accumulation of MondoA and Mlx, demonstrating that they shuttle between the cytoplasmic and nuclear compartments rather than having exclusively cytoplasmic localization. MondoA preferentially forms heterodimers with Mlx, and this heterocomplex can bind to, and activate transcription from, CACGTG E-boxes when targeted to the nucleus via a heterologous nuclear localization signal. The amino termini of the Mondo proteins are highly conserved among family members and contain separable and autonomous cytoplasmic localization and transcription activation domains. Therefore, Mlx can mediate transcriptional repression in conjunction with the Mad family and can mediate transcriptional activation via the Mondo family. We propose that Mlx, like Max, functions as the center of a transcription factor network.

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The role of iron and 2-oxoglutarate oxygenases in signalling

Biochemical Society Transactions ◽

10.1042/bst0310510 ◽

2003 ◽

Vol 31 (3) ◽

pp. 510-515 ◽

Cited By ~ 40

Author(s):

K.S. Hewitson ◽

L.A. McNeill ◽

J.M. Elkins ◽

C.J. Schofield

Keyword(s):

Transcriptional Activation ◽

Hypoxia Inducible Factor ◽

Transcriptional Response ◽

Transactivation Domain ◽

Von Hippel Lindau ◽

Helix Loop Helix ◽

Hypoxic Conditions ◽

Tumour Suppressor Protein ◽

Dependent Modification

Sensing of ambient dioxygen levels and appropriate feedback mechanisms are essential processes for all multicellular organisms. In animals, moderate hypoxia causes an increase in the transcription levels of specific genes, including those encoding vascular endothelial growth factor and erythropoietin. The hypoxic response is mediated by hypoxia-inducible factor (HIF), an αβ heterodimeric transcription factor in which both the HIF subunits are members of the basic helix–loop–helix PAS (PER-ARNT-SIM) domain family. Under hypoxic conditions, levels of HIFα rise, allowing dimerization with HIFβ and initiating transcriptional activation. Two types of dioxygen-dependent modification to HIFα have been identified, both of which inhibit the transcriptional response. Firstly, HIFα undergoes trans-4-hydroxylation at two conserved proline residues that enable its recognition by the von Hippel-Lindau tumour-suppressor protein. Subsequent ubiquitinylation, mediated by an ubiquitin ligase complex, targets HIFα for degradation. Secondly, hydroxylation of an asparagine residue in the C-terminal transactivation domain of HIFα directly prevents its interaction with the co-activator p300. Hydroxylation of HIFα is catalysed by enzymes of the iron(II)- and 2-oxoglutarate-dependent dioxygenase family. In humans, three prolyl hydroxylase isoenzymes (PHD1–3) and an asparagine hydroxylase [factor inhibiting HIF (FIH)] have been identified. The role of 2-oxoglutarate oxygenases in the hypoxic and other signalling pathways is discussed.

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Corepressor/Coactivator Paradox: Potential Constitutive Coactivation by Corepressor Splice Variants

Nuclear Receptor Signaling ◽

10.1621/nrs.04022 ◽

2006 ◽

Vol 4 (1) ◽

pp. nrs.04022 ◽

Cited By ~ 3

Author(s):

Xianwang Meng ◽

Vishnuka D. Arulsundaram ◽

Ahmed F. Yousef ◽

Paul Webb ◽

John D. Baxter ◽

...

Keyword(s):

Thyroid Hormone ◽

Transcriptional Activation ◽

Mammalian Cells ◽

Thyroid Hormone Receptor ◽

Splice Variants ◽

Human Adenovirus ◽

Peptide Sequence ◽

Human Thyroid ◽

Yeast Saccharomyces Cerevisiae ◽

Transcription Complexes

The functional consequences of the interaction of transcriptional coregulators with the human thyroid hormone receptor (TR) in mammalian cells are complex. We have used the yeast, Saccharomyces cerevisiae, which lack endogenous nuclear receptors (NRs) and NR coregulators, as a model to decipher mechanisms regulating transcriptional activation by TR. In effect, this system allows the reconstitution of TR mediated transcription complexes by the expression of specific combinations of mammalian proteins in yeast. In this yeast system, human adenovirus 5 early region 1A (E1A), a natural N-CoR splice variant (N-CoRI) or an artificial N-CoR truncation (N-CoRC) coactivate unliganded TRs and these effects are inhibited by thyroid hormone (TH). E1A contains a short peptide sequence that resembles known corepressor-NR interaction motifs (CoRNR box motif, CBM), and this motif is required for TR binding and coactivation. N-CoRI and N-CoRC contain three CBMs, but only the C-terminal CBM1 is critical for coactivation. These observations in a yeast model system suggest that E1A and N-CoRI are naturally occurring TR coactivators that bind in the typical corepressor mode. These findings also raise the possibility that alternative splicing events which form corepressor proteins containing only C-terminal CBM motifs could represent a novel mechanism in mammalian cells for regulating constitutive transcriptional activation by TRs.

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Activation of aryl hydrocarbon receptor mediates suppression of hypoxia-inducible factor-dependent erythropoietin expression by indoxyl sulfate

AJP Cell Physiology ◽

10.1152/ajpcell.00172.2015 ◽

2016 ◽

Vol 310 (2) ◽

pp. C142-C150 ◽

Cited By ~ 18

Author(s):

Hirobumi Asai ◽

Junya Hirata ◽

Ayumi Hirano ◽

Kazuya Hirai ◽

Sayaka Seki ◽

...

Keyword(s):

Aryl Hydrocarbon Receptor ◽

Mrna Expression ◽

Transcriptional Activation ◽

Hypoxia Inducible Factor ◽

Indoxyl Sulfate ◽

Renal Anemia ◽

Nuclear Accumulation ◽

Blood Levels ◽

Uremic Toxin ◽

Aryl Hydrocarbon

Indoxyl sulfate (IS) is a representative uremic toxin that accumulates in the blood of patients with chronic kidney disease (CKD). In addition to the involvement in the progression of CKD, a recent report indicates that IS suppresses hypoxia-inducible factor (HIF)-dependent erythropoietin (EPO) production, suggesting that IS may also contribute to the progression of renal anemia. In this report, we provide evidence that aryl hydrocarbon receptor (AhR) mediates IS-induced suppression of HIF activation and subsequent EPO production. In HepG2 cells, IS at concentrations similar to the blood levels in CKD patients suppressed hypoxia- or cobalt chloride-induced EPO mRNA expression and transcriptional activation of HIF. IS also induced AhR activation, and AhR blockade resulted in abolishment of IS-induced suppression of HIF activation. The HIF transcription factor is a heterodimeric complex composed of HIF-α subunits (HIF-1α and HIF-2α) and AhR nuclear translocator (ARNT). IS suppressed nuclear accumulation of the HIF-α-ARNT complex accompanied by an increase of the AhR-ARNT complex in the nucleus, implying the involvement of interactions among AhR, HIF-α, and ARNT in the suppression mechanism. In rats, oral administration of indole, a metabolic precursor of IS, inhibited bleeding-induced elevation of renal EPO mRNA expression and plasma EPO concentration and strongly induced AhR activation in the liver and renal cortex tissues. Collectively, this study is the first to elucidate the detailed mechanism by which AhR plays an indispensable role in the suppression of HIF activation by IS. Hence, IS-induced activation of AhR may be a potential therapeutic target for treating renal anemia.

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Antioxidant Functions of the Aryl Hydrocarbon Receptor

Stem Cells International ◽

10.1155/2016/7943495 ◽

2016 ◽

Vol 2016 ◽

pp. 1-10 ◽

Cited By ~ 36

Author(s):

Cornelia Dietrich

Keyword(s):

Polycyclic Aromatic Hydrocarbons ◽

Aryl Hydrocarbon Receptor ◽

Aromatic Hydrocarbons ◽

Transcriptional Activation ◽

Antioxidant Response ◽

Protective Role ◽

Helix Loop Helix ◽

Aryl Hydrocarbon ◽

Polycyclic Aromatic

The aryl hydrocarbon receptor (AhR) is a transcription factor belonging to the basic helix-loop-helix/PER-ARNT-SIM family. It is activated by a variety of ligands, such as environmental contaminants like polycyclic aromatic hydrocarbons or dioxins, but also by naturally occurring compounds and endogenous ligands. Binding of the ligand leads to dimerization of the AhR with aryl hydrocarbon receptor nuclear translocator (ARNT) and transcriptional activation of several xenobiotic phase I and phase II metabolizing enzymes. It is generally accepted that the toxic responses of polycyclic aromatic hydrocarbons, dioxins, and structurally related compounds are mediated by activation of the AhR. A multitude of studies indicate that the AhR operates beyond xenobiotic metabolism and exerts pleiotropic functions. Increasing evidence points to a protective role of the AhR against carcinogenesis and oxidative stress. Herein, I will highlight data demonstrating a causal role of the AhR in the antioxidant response and present novel findings on potential AhR-mediated antioxidative mechanisms.

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Molecular characteristics and induction profiles of hypoxia-inducible factor-1αand other basic helix–loop–helix and Per–Arnt–Sim domain-containing proteins identified in a carcinogenic liver flukeClonorchis sinensis

Parasitology ◽

10.1017/s0031182018001245 ◽

2018 ◽

Vol 146 (2) ◽

pp. 176-186

Author(s):

Seon-Hee Kim ◽

Gyu-Seok Oh ◽

Woon-Mok Sohn ◽

Kihyun Lee ◽

Hyun-Jong Yang ◽

...

Keyword(s):

Nitric Oxide ◽

Clonorchis Sinensis ◽

Hypoxia Inducible Factor ◽

Hypoxic Condition ◽

Molecular Structures ◽

Molecular Characteristics ◽

Basic Helix Loop Helix ◽

Helix Loop Helix ◽

Aryl Hydrocarbon ◽

Oxygen Condition

AbstractClonorchis sinensis(C. sinensis), a trematode parasite that invades the hypoxic hepatobiliary tract of vertebrate hosts requires a considerable amount of oxygen for its sexual reproduction and energy metabolism. However, little is known regarding the molecular mechanism ofC. sinensisinvolved in the adaptation to the hypoxic environments. In this study, we investigated the molecular structures and induction patterns of hypoxia-inducible factor-1α(HIF-1α) and other basic helix–loop–helix and Per–Arnt–Sim (bHLH–PAS) domain-containing proteins such as HIF-1β, single-minded protein and aryl hydrocarbon receptor, which might prompt adaptive response to hypoxia, inC. sinensis. These proteins possessed various bHLH–PAS family-specific domains. Expression ofC. sinensis HIF-1α(CsHIF-1α) was highly induced in worms which were either exposed to a hypoxic condition or co-incubated with human cholangiocytes. In addition to oxygen, nitric oxide and nitrite affected theCsHIF-1αexpression depending on the surrounding oxygen concentration. Treatment using a prolyl hydroxylase-domain protein inhibitor under 20%-oxygen condition resulted in an increase in the CsHIF-1αlevel. Conversely, the otherbHLH–PASgenes were less responsive to these exogenous stimuli. We suggest that nitrite and nitric oxide, as well as oxygen, coordinately involve in the regulation of HIF-1αexpression to adapt to the hypoxic host environments inC. sinensis.

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The pro-apoptotic protein death-associated protein 3 (DAP3) interacts with the glucocorticoid receptor and affects the receptor function

Biochemical Journal ◽

10.1042/bj3490885 ◽

2000 ◽

Vol 349 (3) ◽

pp. 885-893 ◽

Cited By ~ 24

Author(s):

Sanna M. HULKKO ◽

Hideki WAKUI ◽

Johanna ZILLIACUS

Keyword(s):

Glucocorticoid Receptor ◽

Transcriptional Activation ◽

Heat Shock Protein 90 ◽

Dominant Negative ◽

Dependent Manner ◽

Interaction Domain ◽

Helix Loop Helix ◽

Aryl Hydrocarbon ◽

Apoptotic Protein

The yeast two-hybrid system was used to isolate cDNAs encoding proteins that interact with the glucocorticoid receptor (GR) ligand-binding domain in a ligand-dependent manner. One isolated cDNA encoded a fragment of death-associated protein 3 (DAP3), which has been implicated as a positive mediator of apoptosis. In vitro experiments showed that the full-length DAP3 also interacted with GR. The main interaction domain was mapped to the N-terminal region of DAP3 that had previously been shown to function in a dominant-negative fashion, protecting cells from apoptosis. Co-transfection experiments in COS-7 cells showed that DAP3 had a stimulatory effect on the ligand-induced transcriptional activation by GR and also increased the steroid-sensitivity. Furthermore, DAP3 formed a complex with several other nuclear receptors and some basic helix–loop–helix/Per–Arnt–Sim proteins, as well as with heat-shock protein 90 (hsp90) (Arnt is the aryl-hydrocarbon-receptor nuclear translocator, and Per and Sim are the Drosophila proteins Period and Single-minded). The results suggest that DAP3 could have an important role in GR action, possibly by modulating the cytoplasmic GR–hsp90 complex. Since glucocorticoids can induce apoptosis, the pro-apoptotic DAP3 protein may be involved in this function of GR.

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