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Belghasem M, Roth D, Richards S, Napolene MA, Walker J, Yin W, Arinze N, Lyle C, Spencer C, Francis JM, Thompson C, Andry C, Whelan SA, Lee N, Ravid K, Chitalia VC. Metabolites in a mouse cancer model enhance venous thrombogenicity through the aryl hydrocarbon receptor-tissue factor axis. Blood 2019; 134:2399-2413. [PMID: 31877217 PMCID: PMC6933294 DOI: 10.1182/blood.2019001675] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2019] [Accepted: 10/17/2019] [Indexed: 12/13/2022] Open
Abstract
Patients with malignancy are at 4- to 7-fold higher risk of venous thromboembolism (VTE), a potentially fatal, yet preventable complication. Although general mechanisms of thrombosis are enhanced in these patients, malignancy-specific triggers and their therapeutic implication remain poorly understood. Here we examined a colon cancer-specific VTE model and probed a set of metabolites with prothrombotic propensity in the inferior vena cava (IVC) ligation model. Athymic mice injected with human colon adenocarcinoma cells exhibited significantly higher IVC clot weights, a biological readout of venous thrombogenicity, compared with the control mice. Targeted metabolomics analysis of plasma of mice revealed an increase in the blood levels of kynurenine and indoxyl sulfate (tryptophan metabolites) in xenograft-bearing mice, which correlated positively with the increase in the IVC clot size. These metabolites are ligands of aryl hydrocarbon receptor (AHR) signaling. Accordingly, plasma from the xenograft-bearing mice activated the AHR pathway and augmented tissue factor (TF) and plasminogen activator inhibitor 1 (PAI-1) levels in venous endothelial cells in an AHR-dependent manner. Consistent with these findings, the endothelium from the IVC of xenograft-bearing animals revealed nuclear AHR and upregulated TF and PAI-1 expression, telltale signs of an activated AHR-TF/PAI-1 axis. Importantly, pharmacological inhibition of AHR activity suppressed TF and PAI-1 expression in endothelial cells of the IVC and reduced clot weights in both kynurenine-injected and xenograft-bearing mice. Together, these data show dysregulated tryptophan metabolites in a mouse cancer model, and they reveal a novel link between these metabolites and the control of the AHR-TF/PAI-1 axis and VTE in cancer.
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Affiliation(s)
| | - Daniel Roth
- Department of Pathology and Laboratory Medicine and
| | - Sean Richards
- Department of Medicine, Boston University School of Medicine, Boston, MA
| | | | - Joshua Walker
- Department of Medicine, Boston University School of Medicine, Boston, MA
| | - Wenqing Yin
- Department of Medicine, Boston University School of Medicine, Boston, MA
| | - Nkiruka Arinze
- Department of Surgery, Boston University Medical Center, Boston, MA
| | - Chimera Lyle
- Department of Medicine, Boston University School of Medicine, Boston, MA
| | | | - Jean M Francis
- Department of Medicine, Boston University School of Medicine, Boston, MA
| | - Cristal Thompson
- Department of Medicine, Boston University School of Medicine, Boston, MA
- Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA
| | | | | | - Norman Lee
- Chemical Instrumentation Center, Boston University, Boston, MA
| | - Katya Ravid
- Department of Medicine, Boston University School of Medicine, Boston, MA
- Whitaker Cardiovascular Institute, Boston University School of Medicine, Boston, MA
| | - Vipul C Chitalia
- Department of Medicine, Boston University School of Medicine, Boston, MA
- Veterans Affairs Boston Healthcare System, Boston, MA; and
- Global Co-Creation Labs, Institute of Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA
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2
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Polouliakh N, Nock R. An Advanced Omic Approach to Identify Co-Regulated Clusters and Transcription Regulation Network with AGCT and SHOE Methods. Methods Mol Biol 2017; 1598:373-389. [PMID: 28508373 DOI: 10.1007/978-1-4939-6952-4_19] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
To obtain the global picture of genetic machinery for massive high-throughput gene expression data, novel data-driven unsupervised learning approaches are becoming essentially important. For this purpose, basic analytic workflow has been established and should include two steps: first, unsupervised clustering to identify genes with similar behavior upon exposure to a signal, and second, identification of transcription factors regulating those genes. In this chapter, we will describe an advanced tool that can be used for analyzing and characterizing large-scale time-series gene expression composed of a two-step approach. For the first step, we developed an original method "A Geometric Clustering Tool" (AGCT) that unveils the complex architecture of large-scale time-series gene expression data in a real-time manner using cutting edge techniques of low dimension manifold learning, data clustering, and visualization. For the second step, we established an original method "Sequence Homology in Eukaryotes" (SHOE) executing comparative genomic analysis on humans, mice, and rats.
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Affiliation(s)
- Natalia Polouliakh
- Sony Computer Science Laboratories, Inc., 3-14-13 Hogashigotanda, Shinagawa-ku, Tokyo, 141-0022, Japan
- Department of Ophthalmology and Visual Sciences, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, Japan
| | - Richard Nock
- Data61 & the Australian National University, Locked Bag 9013, Alexandria, NSW, 1435, Australia
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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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4
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Wu D, Rastinejad F. Structural characterization of mammalian bHLH-PAS transcription factors. Curr Opin Struct Biol 2016; 43:1-9. [PMID: 27721191 DOI: 10.1016/j.sbi.2016.09.011] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Revised: 09/06/2016] [Accepted: 09/21/2016] [Indexed: 11/28/2022]
Abstract
The mammalian basic helix-loop-helix-PER-ARNT-SIM (bHLH-PAS) transcription factors share common architectural features that include a bHLH DNA-binding domain and tandemly positioned PAS domains. The sixteen members of this family include the hypoxia-inducible factors (HIF-1α and HIF-2α), ARNT (also known as HIF-1β), CLOCK and BMAL1. Most bHLH-PAS proteins have been genetically linked to variety of diseases in humans, including cancers, metabolic syndromes and psychiatric conditions. To function as transcription factors, the bHLH-PAS proteins must form heterodimeric complexes. Recent crystallographic studies of HIF-α-ARNT and CLOCK-BMAL1 complexes have unveiled the organization of their multi-domain bHLH-PAS-A-PAS-B segments, revealing how these architectures can give rise to unique patterns of heterodimerization. As our structural understanding becomes better integrated with ligand-discovery and target gene identification, a more comprehensive picture of their architectural and functional properties will emerge.
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Affiliation(s)
- Dalei Wu
- Integrative Metabolism Program, Sanford Burnham Prebys Medical Discovery Institute, Orlando, FL 32827, USA; State Key Laboratory of Microbial Technology, School of Life Sciences, Shandong University, Qingdao, 266237, China
| | - Fraydoon Rastinejad
- Integrative Metabolism Program, Sanford Burnham Prebys Medical Discovery Institute, Orlando, FL 32827, USA.
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5
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Swartley OM, Foley JF, Livingston DP, Cullen JM, Elmore SA. Histology Atlas of the Developing Mouse Hepatobiliary Hemolymphatic Vascular System with Emphasis on Embryonic Days 11.5-18.5 and Early Postnatal Development. Toxicol Pathol 2016; 44:705-25. [PMID: 26961180 DOI: 10.1177/0192623316630836] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
A critical event in embryo development is the proper formation of the vascular system, of which the hepatobiliary system plays a pivotal role. This has led researchers to use transgenic mice to identify the critical steps involved in developmental disorders associated with the hepatobiliary vascular system. Vascular development is dependent upon normal vasculogenesis, angiogenesis, and the transformation of vessels into their adult counterparts. Any alteration in vascular development has the potential to cause deformities or embryonic death. Numerous publications describe specific stages of vascular development relating to various organs, but a single resource detailing the stage-by-stage development of the vasculature pertaining to the hepatobiliary system has not been available. This comprehensive histology atlas provides hematoxylin & eosin and immunohistochemical-stained sections of the developing mouse blood and lymphatic vasculature with emphasis on the hepatobiliary system between embryonic days (E) 11.5-18.5 and the early postnatal period. Additionally, this atlas includes a 3-dimensional video representation of the E18.5 mouse venous vasculature. One of the most noteworthy findings of this atlas is the identification of the portal sinus within the mouse, which has been erroneously misinterpreted as the ductus venosus in previous publications. Although the primary purpose of this atlas is to identify normal hepatobiliary vascular development, potential embryonic abnormalities are also described.
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Affiliation(s)
- Olivia M Swartley
- College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - Julie F Foley
- Cellular and Molecular Pathology Branch, National Toxicology Program, NIEHS, NIH, Research Triangle Park, North Carolina, USA
| | - David P Livingston
- USDA, Washington, DC, USA North Carolina State University, Raleigh, North Carolina, USA
| | - John M Cullen
- College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina, USA
| | - Susan A Elmore
- Cellular and Molecular Pathology Branch, National Toxicology Program, NIEHS, NIH, Research Triangle Park, North Carolina, USA
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Solaimani P, Wang F, Hankinson O. SIN3A, generally regarded as a transcriptional repressor, is required for induction of gene transcription by the aryl hydrocarbon receptor. J Biol Chem 2014; 289:33655-62. [PMID: 25305016 DOI: 10.1074/jbc.m114.611236] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
CYP1A1 bioactivates several procarcinogens and detoxifies several xenobiotic compounds. Transcription of CYP1A1 is highly induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via the aryl hydrocarbon receptor. We recently described an RNAi high throughput screening performed in the Hepa-1 mouse hepatoma cell line, which revealed that SIN3A is necessary for the induction of CYP1A1-dependent ethoxyresorufin-o-deethylase (EROD) enzymatic activity by TCDD. In the current studies, we sought to provide insight into the role of SIN3A in this process, particularly because studies on SIN3A have usually focused on its repressive activity on transcription. We report that ectopic expression of human SIN3A in Hepa-1 cells enhanced EROD induction by TCDD and efficiently rescued TCDD induction of EROD activity in cells treated with an siRNA to mouse SIN3A, thus validating a role for SIN3A in CYP1A1 induction. We demonstrate that SIN3A is required for TCDD induction of the CYP1A1 protein in Hepa-1 cells but not for expression of the aryl hydrocarbon receptor protein. In addition, siRNAs for SIN3A decreased TCDD-mediated induction of CYP1A1 mRNA and EROD activity in human hepatoma cell line Hep3B. We establish that TCDD treatment of Hepa-1 cells rapidly increases the degree of SIN3A binding to both the proximal promoter and enhancer of the Cyp1a1 gene and demonstrate that increased binding to the promoter also occurs in human Hep3B, HepG2, and MCF-7 cells. These studies establish that SIN3A physically interacts with the CYP1A1 gene and extends the transcriptional role of SIN3A to a gene that is very rapidly and dramatically induced.
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Affiliation(s)
- Parrisa Solaimani
- From the Department of Pathology and Laboratory Medicine, Molecular Toxicology Interdepartmental Program, and the Jonsson Comprehensive Cancer Center and
| | - Feng Wang
- the Department of Chemistry and Biochemistry, UCLA, Los Angeles, California 90095
| | - Oliver Hankinson
- From the Department of Pathology and Laboratory Medicine, Molecular Toxicology Interdepartmental Program, and the Jonsson Comprehensive Cancer Center and
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7
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Solaimani P, Damoiseaux R, Hankinson O. Genome-wide RNAi high-throughput screen identifies proteins necessary for the AHR-dependent induction of CYP1A1 by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicol Sci 2013; 136:107-19. [PMID: 23997114 DOI: 10.1093/toxsci/kft191] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The aryl hydrocarbon receptor (AHR) has a plethora of physiological roles, and upon dysregulation, carcinogenesis can occur. One target gene of AHR encodes the xenobiotic and drug-metabolizing enzyme CYP1A1, which is inducible by the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) via the AHR. An siRNA library targeted against over 5600 gene candidates in the druggable genome was used to transfect mouse Hepa-1 cells, which were then treated with TCDD, and subsequently assayed for CYP1A1-dependent ethoxyresorufin-o-deethylase (EROD) activity. Following redundant siRNA activity (RSA) statistical analysis, we identified 93 hits that reduced EROD activity with a p value ≤ .005 and substantiated 39 of these as positive hits in a secondary screening using endoribonuclease-prepared siRNAs (esiRNAs). Twelve of the corresponding gene products were subsequently confirmed to be necessary for the induction of CYP1A1 messenger RNA by TCDD. None of the candidates were deficient in aryl hydrocarbon nuclear translocator expression. However 6 gene products including UBE2i, RAB40C, CRYGD, DCTN4, RBM5, and RAD50 are required for the expression of AHR as well as for induction of CYP1A1. We also found 2 gene products, ARMC8 and TCF20, to be required for the induction of CYP1A1, but our data are ambiguous as to whether they are required for the expression of AHR. In contrast, SIN3A, PDC, TMEM5, and CD9 are not required for AHR expression but are required for the induction of CYP1A1, implicating a direct role in Cyp1a1 transcription. Our methods, although applied to Cyp1a1, could be modified for identifying proteins that regulate other inducible genes.
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Affiliation(s)
- Parrisa Solaimani
- * Molecular Toxicology Interdepartmental Program, Department of Pathology and Laboratory Medicine, and the Jonsson Comprehensive Cancer Center and
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Hao N, Bhakti VLD, Peet DJ, Whitelaw ML. Reciprocal regulation of the basic helix-loop-helix/Per-Arnt-Sim partner proteins, Arnt and Arnt2, during neuronal differentiation. Nucleic Acids Res 2013; 41:5626-38. [PMID: 23599003 PMCID: PMC3675461 DOI: 10.1093/nar/gkt206] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Basic helix-loop-helix/Per-Arnt-Sim (bHLH/PAS) transcription factors function broadly in development, homeostasis and stress response. Active bHLH/PAS heterodimers consist of a ubiquitous signal-regulated subunit (e.g., hypoxia-inducible factors, HIF-1α/2α/3α; the aryl hydrocarbon receptor, AhR) or tissue-restricted subunit (e.g., NPAS1/3/4, Single Minded 1/2), paired with a general partner protein, aryl hydrocarbon receptor nuclear translocator (Arnt or Arnt2). We have investigated regulation of the neuron-enriched Arnt paralogue, Arnt2. We find high Arnt/Arnt2 ratios in P19 embryonic carcinoma cells and ES cells are dramatically reversed to high Arnt2/Arnt on neuronal differentiation. mRNA half-lives of Arnt and Arnt2 remain similar in both parent and neuronal differentiated cells. The GC-rich Arnt2 promoter, while heavily methylated in Arnt only expressing hepatoma cells, is methylation free in P19 and ES cells, where it is bivalent with respect to active H3K4me3 and repressive H3K27me3 histone marks. Typical of a 'transcription poised' developmental gene, H3K27me3 repressive marks are removed from Arnt2 during neuronal differentiation. Our data are consistent with a switch to predominant Arnt2 expression in neurons to allow specific functions of neuronal bHLH/PAS factors and/or to avoid neuronal bHLH/PAS factors from interfering with AhR/Arnt signalling.
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Affiliation(s)
- Nan Hao
- School of Molecular and Biomedical Science (Biochemistry), The University of Adelaide, Adelaide, South Australia 5005, Australia
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9
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Choi SM, Oh H, Park H. Microarray analyses of hypoxia-regulated genes in an aryl hydrocarbon receptor nuclear translocator (Arnt)-dependent manner. FEBS J 2008; 275:5618-34. [PMID: 18959748 DOI: 10.1111/j.1742-4658.2008.06686.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
We investigated hypoxia-inducible factor (HIF)-dependent changes in the expression of 5592 genes in response to hypoxia (0.1% O(2), 16 h) by performing cDNA microarray analyses of mouse hepa1c1c7 and BpRc1 cells. BpRc1 cells are a hepa1c1c7 variant defective in HIF-beta/aryl hydrocarbon receptor nuclear translocator (Arnt), and are therefore unable to induce HIF target genes in response to hypoxia. By comparing hepa1c1c7 cells with BpRc1 cells, we were able to investigate hypoxia-regulated gene expression as well as the role played by HIF in regulating the hypoxic-dependent response of gene expression. This study identified 50 hypoxia-induced genes and 36 hypoxia-repressed genes. Quantitative PCR analysis of nine genes confirmed our ability to accurately analyze changes in hypoxia-induced gene expression by microarray analysis. By comparing quantitative PCR analyses of these nine genes in BpRc1 and hepa1c1c7 cells, we determined that eight of the nine hypoxia-induced genes are Arnt dependent. Additional quantitative PCR analyses of eight hypoxia-repressed genes confirmed, with a 50% probability, that microarray analysis was able to predict hypoxia-repressed gene expression. Only two of the four confirmed genes were found to be repressed in an Arnt-dependent manner. Collectively, six of these 13 genes (46.2% probability) showed a pattern of expression consistent with the microarray analysis with regard to Arnt dependence. Finally, we investigated the HIF-1alpha dependence of these 13 genes by quantitative PCR analysis in HIF-1alpha knockdown 3T3-L1 cells. These analyses identified novel hypoxia-regulated genes and confirmed the role of Arnt and HIF-1alpha in regulating their expression. These results identify additional HIF target genes and provide a more complete understanding of hypoxia signaling.
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Affiliation(s)
- Su Mi Choi
- Department of Life Science, University of Seoul, South Korea
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Leonard MO, Howell K, Madden SF, Costello CM, Higgins DG, Taylor CT, McLoughlin P. Hypoxia selectively activates the CREB family of transcription factors in the in vivo lung. Am J Respir Crit Care Med 2008; 178:977-83. [PMID: 18689465 DOI: 10.1164/rccm.200712-1890oc] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
RATIONALE Pulmonary hypertension is a common complication of chronic hypoxic lung diseases and is associated with increased morbidity and reduced survival. The pulmonary vascular changes in response to hypoxia, both structural and functional, are unique to this circulation. OBJECTIVES To identify transcription factor pathways uniquely activated in the lung in response to hypoxia. METHODS After exposure to environmental hypoxia (10% O(2)) for varying periods (3 h to 2 wk), lungs and systemic organs were isolated from groups of adult male mice. Bioinformatic examination of genes the expression of which changed in the hypoxic lung (assessed using microarray analysis) identified potential lung-selective transcription factors controlling these changes in gene expression. In separate further experiments, lung-selective activation of these candidate transcription factors was tested in hypoxic mice and by comparing hypoxic responses of primary human pulmonary and cardiac microvascular endothelial cells in vitro. MEASUREMENTS AND MAIN RESULTS Bioinformatic analysis identified cAMP response element binding (CREB) family members as candidate lung-selective hypoxia-responsive transcription factors. Further in vivo experiments demonstrated activation of CREB and activating transcription factor (ATF)1 and up-regulation of CREB family-responsive genes in the hypoxic lung, but not in other organs. Hypoxia-dependent CREB activation and CREB-responsive gene expression was observed in human primary lung, but not cardiac microvascular endothelial cells. CONCLUSIONS These findings suggest that activation of CREB and AFT1 plays a key role in the lung-specific responses to hypoxia, and that lung microvascular endothelial cells are important, proximal effector cells in the specific responses of the pulmonary circulation to hypoxia.
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Affiliation(s)
- Martin O Leonard
- University College Dublin, School of Medicine and Medical Science, and Conway Institute of Biomolecular and Biomedical Research, Dublin, Ireland
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Arpiainen S, Lämsä V, Pelkonen O, Yim SH, Gonzalez FJ, Hakkola J. Aryl hydrocarbon receptor nuclear translocator and upstream stimulatory factor regulate Cytochrome P450 2a5 transcription through a common E-box site. J Mol Biol 2007; 369:640-52. [PMID: 17466327 DOI: 10.1016/j.jmb.2007.03.075] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2007] [Revised: 03/28/2007] [Accepted: 03/28/2007] [Indexed: 12/15/2022]
Abstract
The aryl hydrocarbon receptor nuclear translocator (ARNT) belongs to the basic-helix-loop-helix (bHLH) transcription factors and regulates several genes as heterodimers with other bHLH proteins. ARNT is also able to homodimerize, but no mammalian target genes for the homodimer have been shown. We identified a palindromic E-box element in the 5' regulatory region of the murine cytochrome P450 (Cyp) 2a5 gene that was found to be important for Cyp2a5 transcription in primary hepatocytes, and was found by chromatin immunoprecipitation assays to interact with ARNT. Electrophoretic mobility-shift assay experiments with in vitro translated ARNT showed binding without heterodimerization partner, indicating binding as a homodimer. Transfection studies in wild-type and ARNT-deficient Hepa-1 cells revealed that ARNT expression is necessary for full activity of the Cyp2a5 promoter. In the liver-specific Arnt-null mouse line, the level of hepatic CYP2A5 mRNA was decreased significantly. Co-transfection studies with an ARNT expression vector lacking the transactivation domain (TAD) demonstrated that the ARNT TAD is needed for Cyp2a5 activation, which suggests that ARNT transactivates Cyp2a5 as a homodimer. In primary hepatocytes, the mRNA levels of both CYP2A5 and ARNT splice variant 1 were increased during cultivation. Upstream stimulatory factors 1 and 2a were also able to bind to the same E-box as ARNT, indicating that there may be competition for DNA binding between these factors. Indeed, the upstream stimulatory factors activated the Cyp2a5 promoter through the E-box only in the presence of hepatocyte nuclear factor-4alpha, while ARNT transactivation was independent of hepatocyte nuclear factor-4alpha. In conclusion, these results indicate that ARNT controls Cyp2a5 transcription and thus, for the first time, suggest active involvement of the ARNT homodimer in mammalian gene regulation.
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Affiliation(s)
- Satu Arpiainen
- Department of Pharmacology and Toxicology, University of Oulu, Oulu, Finland
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