1
|
Cochary EF, Kikinis Z, Paulson KE. Positional and temporal regulation of lipogenic gene expression in mouse liver. Gene Expr 2018; 3:265-78. [PMID: 8019127 PMCID: PMC6081618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We have examined the dynamics of positional gene expression in mouse liver using the carbohydrate induction of lipogenic genes as a model. Using a protocol of fasting and refeeding a high-carbohydrate, no-fat diet to obtain maximal induction, we investigated the temporal expression and localization of malic enzyme (ME) and fatty acid synthase (FAS). In situ hybridization showed that both ME and FAS were expressed at low basal levels in all hepatocytes in livers of mice fed a control diet. Furthermore, dietary induction of ME and FAS mRNA occurred in periportal cells within 6 hours. After 12 hours, the portal cells were maximal; and after 24-36 hours, all cells showed high levels of message. This was coincident with expression of ME and FAS mRNAs, which appeared to be maximal between 24 and 36 hours. Both steady-state mRNA levels and pericentral localization then declined, until only periportal hepatocytes showed strong expression of ME and FAS. Nuclear transcription rates measured by run-on assay demonstrated that maximal transcription rates preceded maximum mRNA levels by peaking at 12 hours. Furthermore, run-on assays showed that the periportal induction by carbohydrates is primarily a transcriptional response for FAS, and both transcriptional and posttranscriptional for ME. These results indicate that lipogenic gene expression is a temporal response induced by carbohydrate feeding and is regulated by both positional and transcriptional mechanisms.
Collapse
Affiliation(s)
- E F Cochary
- Genetics Laboratory, USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111
| | | | | |
Collapse
|
2
|
Raghunath A, Sundarraj K, Nagarajan R, Arfuso F, Bian J, Kumar AP, Sethi G, Perumal E. Antioxidant response elements: Discovery, classes, regulation and potential applications. Redox Biol 2018; 17:297-314. [PMID: 29775961 PMCID: PMC6007815 DOI: 10.1016/j.redox.2018.05.002] [Citation(s) in RCA: 293] [Impact Index Per Article: 48.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Revised: 04/25/2018] [Accepted: 05/05/2018] [Indexed: 12/20/2022] Open
Abstract
Exposure to antioxidants and xenobiotics triggers the expression of a myriad of genes encoding antioxidant proteins, detoxifying enzymes, and xenobiotic transporters to offer protection against oxidative stress. This articulated universal mechanism is regulated through the cis-acting elements in an array of Nrf2 target genes called antioxidant response elements (AREs), which play a critical role in redox homeostasis. Though the Keap1/Nrf2/ARE system involves many players, AREs hold the key in transcriptional regulation of cytoprotective genes. ARE-mediated reporter constructs have been widely used, including xenobiotics profiling and Nrf2 activator screening. The complexity of AREs is brought by the presence of other regulatory elements within the AREs. The diversity in the ARE sequences not only bring regulatory selectivity of diverse transcription factors, but also confer functional complexity in the Keap1/Nrf2/ARE pathway. The different transcription factors either homodimerize or heterodimerize to bind the AREs. Depending on the nature of partners, they may activate or suppress the transcription. Attention is required for deeper mechanistic understanding of ARE-mediated gene regulation. The computational methods of identification and analysis of AREs are still in their infancy. Investigations are required to know whether epigenetics mechanism plays a role in the regulation of genes mediated through AREs. The polymorphisms in the AREs leading to oxidative stress related diseases are warranted. A thorough understanding of AREs will pave the way for the development of therapeutic agents against cancer, neurodegenerative, cardiovascular, metabolic and other diseases with oxidative stress.
Collapse
Affiliation(s)
- Azhwar Raghunath
- Molecular Toxicology Laboratory, Department of Biotechnology, Bharathiar University, Coimbatore 641046, Tamilnadu, India
| | - Kiruthika Sundarraj
- Molecular Toxicology Laboratory, Department of Biotechnology, Bharathiar University, Coimbatore 641046, Tamilnadu, India
| | - Raju Nagarajan
- Department of Biotechnology, Indian Institute of Technology Madras, Chennai 600036, Tamilnadu, India
| | - Frank Arfuso
- Stem Cell and Cancer Biology Laboratory, School of Biomedical Sciences, Curtin Health Innovation Research Institute, Curtin University, Perth, WA 6009, Australia
| | - Jinsong Bian
- Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, 117600 Singapore, Singapore
| | - Alan P Kumar
- Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, 117600 Singapore, Singapore; Cancer Science Institute of Singapore, National University of Singapore, Singapore 117599, Singapore; Medical Science Cluster, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Curtin Medical School, Faculty of Health Sciences, Curtin University, Perth, WA, Australia.
| | - Gautam Sethi
- Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, 117600 Singapore, Singapore.
| | - Ekambaram Perumal
- Molecular Toxicology Laboratory, Department of Biotechnology, Bharathiar University, Coimbatore 641046, Tamilnadu, India.
| |
Collapse
|
3
|
Moustafa GG, Hussein MM. New insight on using aged garlic extract against toxic impacts of titanium dioxide bulk salt triggers inflammatory and fibrotic cascades in male rats. Biomed Pharmacother 2016; 84:687-697. [DOI: 10.1016/j.biopha.2016.09.092] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Revised: 09/22/2016] [Accepted: 09/22/2016] [Indexed: 01/14/2023] Open
|
4
|
Regulations and Advisories. Toxicol Ind Health 2016. [DOI: 10.1177/074823370001600312] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
5
|
Abstract
Data about classification, nomenclature, structure, substrate specificity and role of many glutathione transferase's isoenzymes in cell functions have been summarised. The enzyme has been discovered more than 50 years ago. This family of proteins is updated continuously. It has very different composition and will have demand for system analysis for many years.
Collapse
|
6
|
Forman HJ, Davies KJA, Ursini F. How do nutritional antioxidants really work: nucleophilic tone and para-hormesis versus free radical scavenging in vivo. Free Radic Biol Med 2014; 66:24-35. [PMID: 23747930 PMCID: PMC3852196 DOI: 10.1016/j.freeradbiomed.2013.05.045] [Citation(s) in RCA: 487] [Impact Index Per Article: 48.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 05/29/2013] [Accepted: 05/30/2013] [Indexed: 02/07/2023]
Abstract
We present arguments for an evolution in our understanding of how antioxidants in fruits and vegetables exert their health-protective effects. There is much epidemiological evidence for disease prevention by dietary antioxidants and chemical evidence that such compounds react in one-electron reactions with free radicals in vitro. Nonetheless, kinetic constraints indicate that in vivo scavenging of radicals is ineffective in antioxidant defense. Instead, enzymatic removal of nonradical electrophiles, such as hydroperoxides, in two-electron redox reactions is the major antioxidant mechanism. Furthermore, we propose that a major mechanism of action for nutritional antioxidants is the paradoxical oxidative activation of the Nrf2 (NF-E2-related factor 2) signaling pathway, which maintains protective oxidoreductases and their nucleophilic substrates. This maintenance of "nucleophilic tone," by a mechanism that can be called "para-hormesis," provides a means for regulating physiological nontoxic concentrations of the nonradical oxidant electrophiles that boost antioxidant enzymes, and damage removal and repair systems (for proteins, lipids, and DNA), at the optimal levels consistent with good health.
Collapse
Affiliation(s)
- Henry J Forman
- University of California, Merced, 5200 North Lake Road, Merced, CA 95343, USA; Andrus Gerontology Center of the Davis School of Gerontology, University of Southern, California, 3715 McClintock Avenue, Los Angeles, CA 90089-0191, USA
| | - Kelvin J A Davies
- Andrus Gerontology Center of the Davis School of Gerontology, University of Southern, California, 3715 McClintock Avenue, Los Angeles, CA 90089-0191, USA; Division of Molecular & Computational Biology, Department of Biological Sciences, Dornsife College of Letters, Arts, and Sciences, University of Southern California, 3715 McClintock Avenue, Los Angeles, CA 90089-0191, USA
| | - Fulvio Ursini
- Department of Molecular Medicine, University of Padova, Viale G. Colombo 3, I-35121, Padova, Italy.
| |
Collapse
|
7
|
Effects of dietary tert-butylhydroquinone on domoic acid metabolism and transcription of detoxification-related liver genes in red sea bream Pagrus major. CHINESE SCIENCE BULLETIN-CHINESE 2013. [DOI: 10.1007/s11434-012-5643-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
8
|
Lu H, Gonzalez FJ, Klaassen C. Alterations in hepatic mRNA expression of phase II enzymes and xenobiotic transporters after targeted disruption of hepatocyte nuclear factor 4 alpha. Toxicol Sci 2010; 118:380-90. [PMID: 20935164 DOI: 10.1093/toxsci/kfq280] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Hepatocyte nuclear factor 4 alpha (HNF4a) is a liver-enriched master regulator of liver function. HNF4a is important in regulating hepatic expression of certain cytochrome P450s. The purpose of this study was to use mice lacking HNF4a expression in liver (HNF4a-HNull) to elucidate the role of HNF4a in regulating hepatic expression of phase II enzymes and transporters in mice. Compared with male wild-type mice, HNF4a-HNull male mouse livers had (1) markedly lower messenger RNAs (mRNAs) encoding the uptake transporters sodium taurocholate cotransporting polypeptide, organic anion transporting polypeptide (Oatp) 1a1, Oatp2b1, organic anion transporter 2, sodium phosphate cotransporter type 1, sulfate anion transporter 1, sodium-dependent vitamin C transporter 1, the phase II enzymes Uridine 5'-diphospho (UDP)-glucuronosyltransferase (Ugt) 2a3, Ugt2b1, Ugt3a1, Ugt3a2, sulfotransferase (Sult) 1a1, Sult1b1, Sult5a1, the efflux transporters multidrug resistance-associated protein (Mrp) 6, and multidrug and toxin extrusion 1; (2) moderately lower mRNAs encoding Oatp1b2, organic cation transporter (Oct) 1, Ugt1a5, Ugt1a9, glutathione S-transferase (Gst) m4, Gstm6, and breast cancer resistance protein; but (3) higher mRNAs encoding Oatp1a4, Octn2, Ugt1a1, Sult1e1, Sult2a2, Gsta4, Gstm1-m3, multidrug resistance protein (Mdr) 1a, Mrp3, and Mrp4. Hepatic signaling of nuclear factor E2-related factor 2 and pregnane X receptor appear to be activated in HNF4a-HNull mice. In conclusion, HNF4a deficiency markedly alters hepatic mRNA expression of a large number of phase II enzymes and transporters, probably because of the loss of HNF4a, which is a transactivator and a determinant of gender-specific expression and/or adaptive activation of signaling pathways important in hepatic regulation of these phase II enzymes and transporters.
Collapse
Affiliation(s)
- Hong Lu
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, Kansas 66160, USA.
| | | | | |
Collapse
|
9
|
Bélanger AS, Tojcic J, Harvey M, Guillemette C. Regulation of UGT1A1 and HNF1 transcription factor gene expression by DNA methylation in colon cancer cells. BMC Mol Biol 2010; 11:9. [PMID: 20096102 PMCID: PMC2835698 DOI: 10.1186/1471-2199-11-9] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2009] [Accepted: 01/22/2010] [Indexed: 12/13/2022] Open
Abstract
Background UDP-glucuronosyltransferase 1A1 (UGT1A1) is a pivotal enzyme involved in metabolism of SN-38, the active metabolite of irinotecan commonly used to treat metastatic colorectal cancer. We previously demonstrated aberrant methylation of specific CpG dinucleotides in UGT1A1-negative cells, and revealed that methylation state of the UGT1A1 5'-flanking sequence is negatively correlated with gene transcription. Interestingly, one of these CpG dinucleotides (CpG -4) is found close to a HNF1 response element (HRE), known to be involved in activation of UGT1A1 gene expression, and within an upstream stimulating factor (USF) binding site. Results Gel retardation assays revealed that methylation of CpG-4 directly affect the interaction of USF1/2 with its cognate sequence without altering the binding for HNF1-alpha. Luciferase assays sustained a role for USF1/2 and HNF1-alpha in UGT1A1 regulation in colon cancer cells. Based on the differential expression profiles of HNF1A gene in colon cell lines, we also assessed whether methylation affects its expression. In agreement with the presence of CpG islands in the HNF1A promoter, treatments of UGT1A1-negative HCT116 colon cancer cells with a DNA methyltransferase inhibitor restore HNF1A gene expression, as observed for UGT1A1. Conclusions This study reveals that basal UGT1A1 expression in colon cells is positively regulated by HNF1-alpha and USF, and negatively regulated by DNA methylation. Besides, DNA methylation of HNF1A could also play an important role in regulating additional cellular drug metabolism and transporter pathways. This process may contribute to determine local inactivation of drugs such as the anticancer agent SN-38 by glucuronidation and define tumoral response.
Collapse
Affiliation(s)
- Anne-Sophie Bélanger
- Pharmacogenomics Laboratory, Centre Hospitalier Universitaire de Québec, 2705 Laurier, Quebec, G1V 4G2, Canada
| | | | | | | |
Collapse
|
10
|
Zhang Q, Pi J, Woods CG, Andersen ME. A systems biology perspective on Nrf2-mediated antioxidant response. Toxicol Appl Pharmacol 2009; 244:84-97. [PMID: 19716833 DOI: 10.1016/j.taap.2009.08.018] [Citation(s) in RCA: 157] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2009] [Revised: 08/07/2009] [Accepted: 08/18/2009] [Indexed: 12/13/2022]
Abstract
Cells in vivo are constantly exposed to reactive oxygen species (ROS) generated endogenously and exogenously. To defend against the deleterious consequences of ROS, cells contain multiple antioxidant enzymes expressed in various cellular compartments to scavenge these toxic species. Under oxidative stresses, these antioxidant enzymes are upregulated to restore redox homeostasis. Such an adaptive response results from the activation of a redox-sensitive gene regulatory network mediated by nuclear factor E2-related factor 2. To more completely understand how the redox control system is designed by nature to meet homeostatic goals, we have examined the network from a systems perspective using engineering approaches. As with man-made control devices, the redox control system can be decomposed into distinct functional modules, including transducer, controller, actuator, and plant. Cells achieve specific performance objectives by utilizing nested feedback loops, feedforward control, and ultrasensitive signaling motifs, etc. Given that endogenously generated ROS are also used as signaling molecules, our analysis suggests a novel mode of action to explain oxidative stress-induced pathological conditions and diseases. Specifically, by adaptively upregulating antioxidant enzymes, oxidative stress may inadvertently attenuate ROS signals that mediate physiological processes, resulting in aberrations of cellular functions and adverse consequences. Lastly, by simultaneously considering the two competing cellular tasks-adaptive antioxidant defense and ROS signaling-we re-examine the premise that dietary antioxidant supplements is generally beneficial to human health. Our analysis highlights some possible adverse effects of these widely consumed antioxidants.
Collapse
Affiliation(s)
- Qiang Zhang
- Division of Computational Biology, The Hamner Institutes for Health Sciences, 6 Davis Drive, Research Triangle Park, NC 27709, USA.
| | | | | | | |
Collapse
|
11
|
Phase I to II cross-induction of xenobiotic metabolizing enzymes: a feedforward control mechanism for potential hormetic responses. Toxicol Appl Pharmacol 2009; 237:345-56. [PMID: 19371757 DOI: 10.1016/j.taap.2009.04.005] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2008] [Revised: 04/01/2009] [Accepted: 04/05/2009] [Indexed: 11/22/2022]
Abstract
Hormetic responses to xenobiotic exposure likely occur as a result of overcompensation by the homeostatic control systems operating in biological organisms. However, the mechanisms underlying overcompensation that leads to hormesis are still unclear. A well-known homeostatic circuit in the cell is the gene induction network comprising phase I, II and III metabolizing enzymes, which are responsible for xenobiotic detoxification, and in many cases, bioactivation. By formulating a differential equation-based computational model, we investigated in this study whether hormesis can arise from the operation of this gene/enzyme network. The model consists of two feedback and one feedforward controls. With the phase I negative feedback control, xenobiotic X activates nuclear receptors to induce cytochrome P450 enzyme, which bioactivates X into a reactive metabolite X'. With the phase II negative feedback control, X' activates transcription factor Nrf2 to induce phase II enzymes such as glutathione S-transferase and glutamate cysteine ligase, etc., which participate in a set of reactions that lead to the metabolism of X' into a less toxic conjugate X''. The feedforward control involves phase I to II cross-induction, in which the parent chemical X can also induce phase II enzymes directly through the nuclear receptor and indirectly through transcriptionally upregulating Nrf2. As a result of the active feedforward control, a steady-state hormetic relationship readily arises between the concentrations of the reactive metabolite X' and the extracellular parent chemical X to which the cell is exposed. The shape of dose-response evolves over time from initially monotonically increasing to J-shaped at the final steady state-a temporal sequence consistent with adaptation-mediated hormesis. The magnitude of the hormetic response is enhanced by increases in the feedforward gain, but attenuated by increases in the bioactivation or phase II feedback loop gains. Our study suggests a possibly common mechanism for the hormetic responses observed with many mutagens/carcinogens whose activities require bioactivation by phase I enzymes. Feedforward control, often operating in combination with negative feedback regulation in a homeostatic system, may be a general control theme responsible for steady-state hormesis.
Collapse
|
12
|
Qadri I, Hu LJ, Iwahashi M, Al-Zuabi S, Quattrochi LC, Simon FR. Interaction of hepatocyte nuclear factors in transcriptional regulation of tissue specific hormonal expression of human multidrug resistance-associated protein 2 (abcc2). Toxicol Appl Pharmacol 2009; 234:281-92. [DOI: 10.1016/j.taap.2008.10.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2008] [Revised: 10/09/2008] [Accepted: 10/17/2008] [Indexed: 01/13/2023]
|
13
|
Hattori N, Suzuki T, Jinno S, Okeya H, Ishikawa A, Kondo C, Hayashi T, Ito M, Kanamori T, Kawai T, Noguchi T. Methyl Methacrylate Activates the Gsta1 Promoter. J Dent Res 2008; 87:1117-21. [DOI: 10.1177/154405910808701214] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Residual monomers in resin-based biomaterials cause cytotoxicity. We previously showed that methyl methacrylate (MMA) induced mRNA expression of the glutathione S-transferase alpha 1 gene ( Gsta1) located downstream of the cis-acting anti-oxidant responsive element (ARE). Herein, we tested the hypothesis that MMA activated the Gsta1 promoter through the ARE. HepG2 cells were transfected with a luciferase reporter vector containing the ARE and the Gsta1 promoter (−990 to +46 bp) and cultured for 12 hrs with MMA (initial concentration, 10 mM). Analysis of the expressed luciferase activity indicated that MMA activated the promoter 2.6-fold. MMA (from 1 to 30 mM) dose-dependently increased the promoter activity, which reached a plateau between 6 and 12 hrs. In HepG2 cells transfected with a reporter vector containing 2 AREs and a TATA-like promoter, 10 mM MMA increased the reporter expression 2.8-fold. These results suggest that MMA increases Gsta1 transcription through ARE-mediated promoter activation.
Collapse
Affiliation(s)
- N. Hattori
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - T. Suzuki
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - S. Jinno
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - H. Okeya
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - A. Ishikawa
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - C. Kondo
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - T. Hayashi
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - M. Ito
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - T. Kanamori
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - T. Kawai
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| | - T. Noguchi
- Department of Periodontology,
- Department of Biochemistry,
- The Second Department of Prosthodontics, and
- Department of Dental Material Science, School of Dentistry, Aichi Gakuin University, 1–100 Kusumoto-cho, Chikusa-ku, Nagoya 464–8650, Japan
| |
Collapse
|
14
|
Hayes JD, Pulford DJ. The Glut athione S-Transferase Supergene Family: Regulation of GST and the Contribution of the lsoenzymes to Cancer Chemoprotection and Drug Resistance Part II. Crit Rev Biochem Mol Biol 2008. [DOI: 10.3109/10409239509083492] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
|
15
|
Sato S, Shirakawa H, Tomita S, Ohsaki Y, Haketa K, Tooi O, Santo N, Tohkin M, Furukawa Y, Gonzalez FJ, Komai M. Low-dose dioxins alter gene expression related to cholesterol biosynthesis, lipogenesis, and glucose metabolism through the aryl hydrocarbon receptor-mediated pathway in mouse liver. Toxicol Appl Pharmacol 2008; 229:10-9. [DOI: 10.1016/j.taap.2007.12.029] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2007] [Revised: 12/25/2007] [Accepted: 12/28/2007] [Indexed: 02/07/2023]
|
16
|
Tan X, Yuan Y, Zeng G, Apte U, Thompson MD, Cieply B, Stolz DB, Michalopoulos GK, Kaestner KH, Monga SP. Beta-catenin deletion in hepatoblasts disrupts hepatic morphogenesis and survival during mouse development. Hepatology 2008; 47:1667-79. [PMID: 18393386 PMCID: PMC4449338 DOI: 10.1002/hep.22225] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
UNLABELLED Beta-catenin, the central component of the canonical Wnt pathway, plays important roles in the processes of liver regeneration, growth, and cancer. Previously, we identified temporal expression of beta-catenin during liver development. Here, we characterize the hepatic phenotype, resulting from the successful deletion of beta-catenin in the developing hepatoblasts utilizing Foxa3-cyclization recombination and floxed-beta-catenin (exons 2 through 6) transgenic mice. Beta-catenin loss in developing livers resulted in significantly underdeveloped livers after embryonic day 12 (E12) with lethality occurring at around E17 stages. Histology revealed an overall deficient hepatocyte compartment due to (1) increased cell death due to oxidative stress and apoptosis, and (2) diminished expansion secondary to decreased cyclin-D1 and impaired proliferation. Also, the remnant hepatocytes demonstrated an immature phenotype as indicated by high nuclear to cytoplasmic ratio, poor cell polarity, absent glycogen, and decreased expression of key liver-enriched transcription factors: CCAAT-enhancer binding protein-alpha and hepatocyte nuclear factor-4alpha. A paucity of primitive bile ducts was also observed. While the stem cell assays demonstrated no intrinsic defect in hematopoiesis, distorted hepatic architecture and deficient hepatocyte compartments resulted in defective endothelial cell organization leading to overall fetal pallor. CONCLUSION Beta-catenin regulates multiple, critical events during the process of hepatic morphogenesis, including hepatoblast maturation, expansion, and survival, making it indispensable to survival.
Collapse
Affiliation(s)
- Xinping Tan
- Department of Pathology, University of Pennsylvania, School of Medicine, Philadelphia, PA
| | - Youzhong Yuan
- Department of Surgery, University of Pennsylvania, School of Medicine, Philadelphia, PA
| | - Gang Zeng
- Department of Pathology, University of Pennsylvania, School of Medicine, Philadelphia, PA
| | - Udayan Apte
- Department of Pathology, University of Pennsylvania, School of Medicine, Philadelphia, PA
| | | | - Benjamin Cieply
- Department of Pathology, University of Pennsylvania, School of Medicine, Philadelphia, PA
| | - Donna B. Stolz
- Department of Pathology, University of Pennsylvania, School of Medicine, Philadelphia, PA,Department of Cell Biology, University of Pennsylvania, School of Medicine, Philadelphia, PA
| | | | - Klaus H. Kaestner
- Department of Genetics, University of Pennsylvania, School of Medicine, Philadelphia, PA
| | - Satdarshan P.S. Monga
- Department of Pathology, University of Pennsylvania, School of Medicine, Philadelphia, PA,Department of Medicine, University of Pennsylvania, School of Medicine, Philadelphia, PA
| |
Collapse
|
17
|
Falkner KC, Prough RA. Regulation of the rat glutathione S-transferase A2 gene by glucocorticoids: crosstalk through C/EBPs. Drug Metab Rev 2007; 39:401-18. [PMID: 17786629 PMCID: PMC2423428 DOI: 10.1080/03602530701511216] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Regulation of the rat glutathione S-transferase A2 (GSTA2) gene by glucocorticoids is biphasic in its concentration dependence to glucocorticoids, with concentrations of 10-100 nM repressing gene activity (GR-dependent), and concentrations above 1 microM increasing transactivation (PXR-dependent) in adult rat hepatocytes or transient transfection assays. Over-expression of either C/EBP alpha or beta negatively regulates basal and inducible expression of a 1.65 Kb GSTA2 luciferase reporter, and synergizes the response to glucocorticoids (GC). C/EBP responsive elements have been identified in the GSTA2 5'-flanking sequence, associated with the palindrominic Glucocorticoid Responsive Element (GRE), the Ah receptor response elements, and the antioxidant response element. In reporters lacking the palindromic GRE, negative regulation by GC is observed only when C/EBP alpha is co-expressed. Co-transfection of C/EBP alpha/beta induced gene expression of the GSTA2 XRE reporter, but negatively regulated the GSTA2 ARE-reporter. In contrast, the ARE from the rat NAD(P)H quinone oxidoreductase gene was induced by co-transfection of C/EBPs, but was still negatively regulated by GC. PXR-induction of the GSTA2 reporter was partially ablated by co-transfection of C/EBP alpha and enhanced by co-transfection of C/EBPbeta. We conclude that C/EBP alpha and beta are involved in GC-dependent repression of GSTA2 gene expression and ARE sequences that bind C/EBPs appears to be critical for these responses.
Collapse
Affiliation(s)
- K Cameron Falkner
- Department of Biochemistry and Molecular Biology, University of Louisville School of Medicine, Louisville, Kentucky 40292, USA
| | | |
Collapse
|
18
|
Köhle C, Bock KW. Coordinate regulation of Phase I and II xenobiotic metabolisms by the Ah receptor and Nrf2. Biochem Pharmacol 2007; 73:1853-62. [PMID: 17266942 DOI: 10.1016/j.bcp.2007.01.009] [Citation(s) in RCA: 261] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2006] [Revised: 12/21/2006] [Accepted: 01/03/2007] [Indexed: 11/21/2022]
Abstract
The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor with important roles in metabolic adaptation, normal physiology and dioxin toxicology. Metabolic adaptation is based on coordinate regulation of a set of xenobiotic-metabolizing enzymes (XMEs), termed AhR battery. Coordination is achieved by AhR/Arnt-binding to XREs (xenobiotic response elements), identified in the 5' upstream region of AhR target genes. The AhR battery encodes Phase I and II enzymes. Interestingly, these Phase II genes are linked to the Nrf2 gene battery that encodes enzymes that are essential in protection against oxidative/electrophile stress. Nrf2 binds to AREs (antioxidant response elements) in the regulatory region of a large and distinct set of target genes. Functionally characterized response elements such as XREs and AREs in the regulatory region of target genes may provide a genetic basis to understand AhR- and Nrf2-induced genes. Linkage between AhR and Nrf2 batteries is probably achieved by multiple mechanisms, including Nrf2 as a target gene of the AhR, indirect activation of Nrf2 via CYP1A1-generated reactive oxygen species, and direct cross-interaction of AhR/XRE and Nrf2/ARE signaling. Linkage appears to be species- and cell-dependent. However, mechanisms linking XRE- and ARE-controlled Phase II genes need further investigation. Tightened coupling between Phases I and II by AhR- and Nrf2-induced XMEs may greatly attenuate health risks posed by CYP1A1-generated toxic intermediates and reactive oxygen species. Better recognition of coordinate Phase I and II metabolisms may improve risk assessment of reactive toxic intermediates in the extrapolation to low level endo- and xenobiotic exposure.
Collapse
Affiliation(s)
- Christoph Köhle
- Department of Toxicology, Institute of Pharmacology and Toxicology, University of Tübingen, Germany
| | | |
Collapse
|
19
|
Maher JM, Slitt AL, Callaghan TN, Cheng X, Cheung C, Gonzalez FJ, Klaassen CD. Alterations in transporter expression in liver, kidney, and duodenum after targeted disruption of the transcription factor HNF1alpha. Biochem Pharmacol 2006; 72:512-22. [PMID: 16806085 DOI: 10.1016/j.bcp.2006.03.016] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2006] [Revised: 03/18/2006] [Accepted: 03/20/2006] [Indexed: 10/24/2022]
Abstract
The transcription factor hepatocyte nuclear factor 1alpha (HNF1alpha) is involved in regulation of glucose metabolism and transport, and in the expression of several drug and bile acid metabolizing enzymes. Targeted disruption of the HNF1alpha gene results in decreased Cyp1a2, and Cyp2e1 expression, and increased Cyp4a1 and Cyp7a1 expression, suggesting these enzymes are HNF1alpha target genes. Since hepatic metabolism can be coordinately linked with drug and metabolite transport, this study aims to demonstrate whether HNF1alpha regulates expression of a variety of organic anion and cation transporters through utilization of an HNF1alpha-null mouse model. Expression of 32 transporters, including members of the Oat, Oatp, Oct, Mrp, Mdr, bile acid and sterolin families, was quantified in three different tissues: liver, kidney, and duodenum. The expression of 17 of 32 transporters was altered in liver, 21 of 32 in kidney, and 6 of 32 in duodenum of HNF1alpha-null mice. This includes many novel observations, including marked downregulation of Oats in kidney, as well as upregulation of many Mrp and Mdr family members in all three tissues. These data indicate that disruption of HNF1alpha causes a marked attenuation of several Oat and Oatp uptake transporters in liver and kidney, and increased expression of efflux transporters such as Mdrs and Mrps, thus suggesting that HNF1alpha is a central mediator in regulating hepatic, renal, and intestinal transporters.
Collapse
Affiliation(s)
- J M Maher
- Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | | | | | | | | | | | | |
Collapse
|
20
|
Fletcher N, Wahlström D, Lundberg R, Nilsson CB, Nilsson KC, Stockling K, Hellmold H, Håkansson H. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) alters the mRNA expression of critical genes associated with cholesterol metabolism, bile acid biosynthesis, and bile transport in rat liver: a microarray study. Toxicol Appl Pharmacol 2005; 207:1-24. [PMID: 16054898 DOI: 10.1016/j.taap.2004.12.003] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2004] [Revised: 12/02/2004] [Accepted: 12/03/2004] [Indexed: 12/30/2022]
Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a potent hepatotoxin that exerts its toxicity through binding to the aryl hydrocarbon receptor (AhR) and the subsequent induction or repression of gene transcription. In order to further identify novel genes and pathways that may be associated with TCDD-induced hepatotoxicity, we investigated gene changes in rat liver following exposure to single oral doses of TCDD. Male Sprague-Dawley rats were administered single doses of 0.4 microg/kg bw or 40 microg/kg bw TCDD and killed at 6 h, 24 h, or 7 days, for global analyses of gene expression. In general, low-dose TCDD exposure resulted in greater than 2-fold induction of genes coding for a battery of phase I and phase II metabolizing enzymes including CYP1A1, CYP1A2, NADPH quinone oxidoreductase, UGT1A6/7, and metallothionein 1. However, 0.4 microg/kg bw TCDD also altered the expression of Gadd45a and Cyclin D1, suggesting that even low-dose TCDD exposure can alter the expression of genes indicative of cellular stress or DNA damage and associated with cell cycle control. At the high-dose, widespread changes were observed for genes encoding cellular signaling proteins, cellular adhesion, cytoskeletal and membrane transport proteins as well as transcripts coding for lipid, carbohydrate and nitrogen metabolism. In addition, decreased expression of cytochrome P450 7A1, short heterodimer partner (SHP; gene designation nr0b2), farnesyl X receptor (FXR), Ntcp, and Slc21a5 (oatp2) were observed and confirmed by RT-PCR analyses in independent rat liver samples. Altered expression of these genes implies major deregulation of cholesterol metabolism and bile acid synthesis and transport. We suggest that these early and novel changes have the potential to contribute significantly to TCDD induced hepatotoxicity and hypercholesterolemia.
Collapse
Affiliation(s)
- Nick Fletcher
- Institute of Environmental Medicine, Karolinska Institutet, Nobels vag 13, Stockholm, Sweden
| | | | | | | | | | | | | | | |
Collapse
|
21
|
Thackaberry EA, Jiang Z, Johnson CD, Ramos KS, Walker MK. Toxicogenomic profile of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the murine fetal heart: modulation of cell cycle and extracellular matrix genes. Toxicol Sci 2005; 88:231-41. [PMID: 16120747 DOI: 10.1093/toxsci/kfi301] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and similar environmental contaminants have been demonstrated to be potent cardiovascular teratogens in developing piscine and avian species. In the present study, we investigated the effects of TCDD on gene expression during murine cardiovascular development. C57Bl6N pregnant mice were dosed with 1.5, 3.0, or 6.0 microg TCDD/kg on gestational day (GD) 14.5, and microarray analysis was used to characterize the global changes in fetal cardiac gene expression on GD 17.5. TCDD significantly altered expression of a number of genes involved in xenobiotic metabolism, cardiac homeostasis, extracellular matrix production/remodeling, and cell cycle regulation. Interestingly, while the AhR-responsive genes Cyp1A1, Cyp1B1, Ugt1a6, and Ahrr, were all induced by TCDD in the fetal murine heart, other AhR-responsive genes, Cyp1a2, Nqo1, and Gsta1, were not. Quantitative real-time polymerase chain reactions confirmed the changes in expression of several G1/S-type cyclins and extracellular matrix-related genes. These results demonstrate the global changes in cardiac gene expression that result from TCDD exposure of the fetal murine heart and implicate genes involved in cell cycle and extracellular matrix regulation in TCDD-induced cardiac teratogenicity and functional deficits.
Collapse
Affiliation(s)
- E A Thackaberry
- College of Pharmacy, University of New Mexico Health Sciences Center, Albuquerque, New Mexico 87131, USA
| | | | | | | | | |
Collapse
|
22
|
Marchand A, Barouki R, Garlatti M. Regulation of NAD(P)H:Quinone Oxidoreductase 1 Gene Expression by CYP1A1 Activity. Mol Pharmacol 2004; 65:1029-37. [PMID: 15044633 DOI: 10.1124/mol.65.4.1029] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The dioxin 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) induces phase I and II xenobiotic metabolizing enzymes (XME) which act sequentially to eliminate different classes of xenobiotics. The transcriptional effects of TCDD are generally mediated by the arylhydrocarbon receptor (AhR). We hypothesized that TCDD could also act indirectly, by increasing the activity of cytochrome P450 1A1 (CYP1A1), a phase I gene, which could then mediate the induction of other XME genes, such as the NAD(P)H:quinone oxidoreductase 1 (NQO1). To test this hypothesis, NQO1 gene expression was monitored after either overexpression of CYP1A1 or siRNA-mediated knock-down of CYP1A1 activity in the hepatoma cell line HepG2. Overexpression of CYP1A1 in the absence of TCDD was carried out using either adenoviral infection or the "Tet-off" system. Recombinant adenoviruses were produced encoding no protein, CYP1A1 (Ad1A1), or a mutated inactive CYP1A1 (Ad1A1mut). In the HepG2 Tet-off cell line, CYP1A1 expression was induced by the removal of doxycycline (dox) from the cell medium. Ad1A1 infection or dox removal induced CYP1A1 activity and H(2)O(2) production similarly to TCDD treatment. Moreover, in both systems, the amount of NQO1 mRNA increased to the same level as after TCDD treatment (approximately 2-fold). The UDP-glucuronosyl transferase 1A6 (UGT1A6) gene is also similarly regulated. NQO1 gene expression was not induced when mutant, inactive CYP1A1 was overexpressed or when the antioxidant N-acetyl cysteine (NAC) was added to Ad1A1. Finally, either NAC or siRNA directed against CYP1A1 mRNA decreased the induction of NQO1 gene expression by TCDD. We conclude that, after exposure to TCDD, the NQO1 gene expression can be controlled by CYP1A1 activity through an oxidative stress mediated pathway.
Collapse
Affiliation(s)
- A Marchand
- Institut National de la Santé et de la Recherche Médicale, Unité-490, 45 rue des Saints-Pères, 75006 Paris, France.
| | | | | |
Collapse
|
23
|
Holtzclaw WD, Dinkova-Kostova AT, Talalay P. Protection against electrophile and oxidative stress by induction of phase 2 genes: the quest for the elusive sensor that responds to inducers. ACTA ACUST UNITED AC 2004; 44:335-67. [PMID: 15581500 DOI: 10.1016/j.advenzreg.2003.11.013] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- W David Holtzclaw
- The Lewis B. and Dorothy Cullman Cancer Chemoprotection Center, Department of Pharmacology and Molecular Sciences, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA
| | | | | |
Collapse
|
24
|
Lamb JG, Franklin MR. Cell-based studies reveal differences in glutathione S-transferase induction between oltipraz and tert-butylhydroquinone. J Biochem Mol Toxicol 2002; 16:154-61. [PMID: 12242683 DOI: 10.1002/jbt.10033] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Selective induction of Phase II over Phase I drug-metabolizing enzymes has been proposed as a mechanism for reduction of chemical carcinogenesis. Enzymes likely to play a role in this amelioration include the glutathione S-transferases (GSTs) and among compounds that selectively induce key GSTs are tert-butylhydroquinone (tBHQ) and oltipraz [4-methyl-5-(2-pyrazinyl)-3H-1,2-dithiole-3-thione]. In vivo, and in hepatoma cells (H4IIE), these two agents induce rat GSTA2 mRNA to a similar extent. However, with a luciferase reporter construct containing 1651 bp of the proximal 5' flanking region of the rGSTA2 gene in the same cell line and under similar conditions, luciferase activity was induced to a much greater extent by tBHQ than by oltipraz. A similar large intercompound differential was seen with reporter constructs containing either the rGSTA2 ARE enhancer and HNF1 site (-872 to -582) or XRE enhancer and HNF1 site (-1110 to -812). In H4IIE cells, the rGSTA2 mRNA response to each agent was completely inhibited by 1 microM actinomycin-D cotreatment. With 1 microM cycloheximide cotreatment however, some induction by tBHQ remained, while induction by oltipraz was completely abolished. The induction response to tBHQ but not oltipraz was augmented by pretreatment with PD98059, a MEK1/2 specific inhibitor. Notwithstanding induction characteristics in common, oltipraz, and tBHQ have sufficient dissimilarities to indicate that rGSTA2 upregulation by the two agents is not identical.
Collapse
Affiliation(s)
- John G Lamb
- Department of Pharmacology and Toxicology, University of Utah, Salt Lake City, Utah 84112, USA
| | | |
Collapse
|
25
|
Li J, Johnson JA. Time-dependent changes in ARE-driven gene expression by use of a noise-filtering process for microarray data. Physiol Genomics 2002; 9:137-44. [PMID: 12045294 DOI: 10.1152/physiolgenomics.00003.2002] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The current study was designed to identify the time-dependent gene expression profiles of antioxidant responsive element (ARE)-driven genes induced by tert-butylhydroquinone (tBHQ). A set of simple noise-filtering methods was introduced to evaluate and minimize the variance of microarray datasets. Gene expression induced by tBHQ (10 microM) in IMR-32 human neuroblastoma cells was analyzed by means of large-scale oligonucleotide microarray. Rank analysis was used to determine the acceptable number of independent samples necessary to eliminate false positives from the dataset. A dramatic reduction in the number of genes passing the rank analysis was achieved by using a 3 x 3 matrix comparison. Reproducibility was evaluated based on the coefficient of variation for average difference change. Completion of these analyses revealed that 101 of the 9,670 genes examined showed dynamic changes with treatment ranging from 4 h to 48 h. Since certain ARE-driven genes have been already identified, gene clustering would presumably group them together based on similar regulation. Self-organizing map grouped the genes induced by tBHQ into 12 (4x3) distinct clusters. Those previously identified ARE-driven genes were shown to group into different clusters. Since all potential ARE-driven genes did not cluster together, we speculate that multiple transcription factors and/or multiple signal transduction pathways contribute to transcriptional activation of the ARE. In conclusion, many novel potential ARE-driven genes were identified in this study. They function in detoxification and antioxidant defense, neuronal proliferation and differentiation, and signal transduction. The noise-filtering process applied to these microarray data, therefore, has proven to be very useful in identification of the time-dependent changes in ARE-drive gene expression.
Collapse
Affiliation(s)
- Jiang Li
- School of Pharmacy, University of Wisconsin, Madison, Wisconsin 53705, USA
| | | |
Collapse
|
26
|
Nie M, Blankenship AL, Giesy JP. Interactions between aryl hydrocarbon receptor (AhR) and hypoxia signaling pathways. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2001; 10:17-27. [PMID: 11382553 DOI: 10.1016/s1382-6689(01)00065-5] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Most if not all of the toxic responses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are mediated through the AhR, which requires ARNT to regulate gene expression. ARNT is also required by HIF-1alpha to enhance the expression of various genes in response to hypoxia. Since both the AhR and hypoxia transcriptional pathways require ARNT, some of the effects of TCDD and similar types of ligands could be explained by interaction between the AhR and hypoxia pathways involving ARNT. The studies on which we report here were conducted to test the hypothesis that there is cross talk between AhR- and HIF-1-mediated transcription pathways. TCDD significantly reduced the hypoxia-mediated reporter gene activity in B-1 cells. Reciprocally, the hypoxia response inducers desferrioxamine or CoCl(2) inhibited AhR-mediated CYP1A1 enzyme activity in B-1 and Hepa 1 cells, and the AhR-mediated luciferase reporter gene activity in H1L1.1c2 cells. The inhibition of AhR-mediated transcription by hypoxia inducers, however, was not observed in H4IIE-luc cells. The interaction between the AhR- and HIF-1-mediated transcription can be attributed to changes in DNA binding activities. TCDD-induced protein binding to dioxin responsive element (DRE) was diminished by desferrioxamine, and TCDD reduced the binding activity to HIF-1 binding site in desferrioxamine-treated Hepa 1 cells. This mutual repression may provide an underlying mechanism for many TCDD-induced toxic responses. The results reported here indicate that there is cross talk between ARNT-requiring pathways. Since ARNT is possibly required by a number of pathways, this type of interaction may explain some of the pleiotropic effects caused by TCDD.
Collapse
Affiliation(s)
- M Nie
- National Food Safety and Toxicology Center, Department of Zoology and Institute for Environmental Toxicology, Michigan State University, 48824-1311, East Lansing, MI, USA
| | | | | |
Collapse
|
27
|
Abstract
The prostaglandin endoperoxide H synthases-1 and 2 (PGHS-1 and PGHS-2; also cyclooxygenases-1 and 2, COX-1 and COX-2) catalyze the committed step in prostaglandin synthesis. PGHS-1 and 2 are of particular interest because they are the major targets of nonsteroidal anti-inflammatory drugs (NSAIDs) including aspirin, ibuprofen, and the new COX-2 inhibitors. Inhibition of the PGHSs with NSAIDs acutely reduces inflammation, pain, and fever, and long-term use of these drugs reduces fatal thrombotic events, as well as the development of colon cancer and Alzheimer's disease. In this review, we examine how the structures of these enzymes relate mechanistically to cyclooxygenase and peroxidase catalysis, and how differences in the structure of PGHS-2 confer on this isozyme differential sensitivity to COX-2 inhibitors. We further examine the evidence for independent signaling by PGHS-1 and PGHS-2, and the complex mechanisms for regulation of PGHS-2 gene expression.
Collapse
Affiliation(s)
- W L Smith
- Department of Biochemistry, Michigan State University, East Lansing, MI 48824, USA.
| | | | | |
Collapse
|
28
|
Miller KP, Ramos KS. Impact of cellular metabolism on the biological effects of benzo[a]pyrene and related hydrocarbons. Drug Metab Rev 2001; 33:1-35. [PMID: 11270659 DOI: 10.1081/dmr-100000138] [Citation(s) in RCA: 230] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Polycyclic aromatic hydrocarbons are ubiquitous contaminants in the environment. Benzo[a]pyrene (BaP), a prototypical member of this class of chemicals, has been extensively studied for its toxic effects in laboratory animals and human populations. BaP toxicity is often mediated by oxidative metabolism to reactive intermediates that interact with macromolecules leading to alterations in target cell structure and function. More recent evidence suggests that disruption of cellular signaling pathways involved in the regulation of growth and differentiation contribute significantly to the toxicity of BaP and its metabolites. This review summarizes recent advances in our understanding of biological mechanisms of BaP toxicity at the molecular level, and the role of metabolic intermediates in carcinogenesis, atherogenesis, and teratogenesis.
Collapse
Affiliation(s)
- K P Miller
- Department of Veterinary Physiology and Pharmacology & Center for Environmental and Rural Health, Texas A&M University, College Station, USA
| | | |
Collapse
|
29
|
Chen YH, Ramos KS. A CCAAT/Enhancer-binding Protein Site within Antioxidant/Electrophile Response Element Along with CREB-binding Protein Participate in the Negative Regulation of RatGST-Ya Gene in Vascular Smooth Muscle Cells. J Biol Chem 2000. [DOI: 10.1016/s0021-9258(19)61520-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
|
30
|
Thurmond TS, Staples JE, Silverstone AE, Gasiewicz TA. The aryl hydrocarbon receptor has a role in the in vivo maturation of murine bone marrow B lymphocytes and their response to 2,3,7,8-tetrachlorodibenzo-p-dioxin. Toxicol Appl Pharmacol 2000; 165:227-36. [PMID: 10860871 DOI: 10.1006/taap.2000.8942] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The ligand-activated aryl hydrocarbon receptor (AHR) is a cytosolic DNA binding protein. Although no biologic role for AHR has been elucidated, it mediates the immunotoxicity of xenobiotics such as 2, 3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), and its targeted inactivation produces abnormal immune system development. While investigators have demonstrated AHR's involvement in TCDD-induced B lymphocyte functional alterations, little is known about the receptor's possible role in early B cell maturation and whether exogenous ligands change this process. The purpose of this study was to determine, (1) whether bone marrow B lymphocyte maturation is affected by AHR presence, (2) if so, its relative importance in hematopoietic and/or nonhematopoietic elements and, (3) whether TCDD alters this process. Radiation chimeras were produced that were AHR positive (Ahr+/+) or negative (Ahr-/-) in either their nonhematopoietic or hematopoietic elements, or both. Marrow cells were analyzed for alterations in B lymphocyte maturation stage cell numbers in both vehicle- and TCDD-treated animals. Our results showed that (1) Ahr-/- animals had significantly higher numbers of pro/pre-B cells than Ahr+/+ animals, (2) TCDD treatment of Ahr+/+ animals produced a decrease in pro/pre-B cell numbers, whereas no effect was observed on Ahr-/- animals, and (3) AHR is required in both hematopoietic and stromal elements for maintenance of B cell subset maturation profiles.
Collapse
Affiliation(s)
- T S Thurmond
- Department of Environmental Medicine, University of Rochester, Rochester, New York 14642, USA
| | | | | | | |
Collapse
|
31
|
Selim N, Branum GD, Liu X, Whalen R, Boyer TD. Differential lobular induction in rat liver of glutathione S-transferase A1/A2 by phenobarbital. Am J Physiol Gastrointest Liver Physiol 2000; 278:G542-50. [PMID: 10762607 DOI: 10.1152/ajpgi.2000.278.4.g542] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Phenobarbital and other xenobiotics induce drug-metabolizing enzymes, including glutathione S-transferase A1/A2 (rGSTA1/A2). We examined the mechanism of induction of rGSTA1/A2 in rat livers after phenobarbital treatment. The induction of rGSTA1/A2 was not uniform across the hepatic lobule; steady-state transcript levels were threefold higher in perivenous hepatocytes relative to periportal hepatocytes when examined by in situ hybridization 12 h after a single dose of phenobarbital. Administration of a second dose of phenobarbital 12 or 24 h after the first dose did not equalize the induction of rGSTA1/A2 across the lobule. The transcriptional activity of the rGSTA1/A2 gene was increased 3.5- to 5.5-fold in whole liver by phenobarbital, but activities were the same in enriched periportal and perivenous subpopulations of hepatocytes from phenobarbital-treated animals. The half-life of rGSTA1/A2 mRNA in control animals was 3.6 h, whereas it was 10.2 h in phenobarbital-treated animals. We conclude that phenobarbital induces rGSTA1/A2 expression by increasing transcriptional activity across the lobule but induction of rGSTA1/A2 is greater in perivenous hepatocytes due to localized stabilization of mRNA transcripts.
Collapse
Affiliation(s)
- N Selim
- Department of Surgery, Emory University School of Medicine, Atlanta, Georgia 30322, USA
| | | | | | | | | |
Collapse
|
32
|
Tsukaguchi H, Weremowicz S, Morton CC, Hediger MA. Functional and molecular characterization of the human neutral solute channel aquaporin-9. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:F685-96. [PMID: 10564231 DOI: 10.1152/ajprenal.1999.277.5.f685] [Citation(s) in RCA: 91] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In metabolically active cells, the coordinated transport of water and solutes is important for maintaining osmotic homeostasis. We recently identified a broad selective-neutral solute channel, AQP9, from rat liver that allows the passage of a wide variety of water and neutral solutes (H. Tsukaguchi, C. Shayakul, U. V. Berger, B. Mackenzie, S. Devidas, W. B. Guggino, A. N. van Hoek, and M. A. Hediger. J. Biol. Chem. 273: 24737-24743, 1998). A human homolog (hAQP9) with 76% amino acid sequence identity to rat AQP9 (rAQP9) was described, but its permeability was found to be restricted to water and urea (K. Ishibashi, M. Kuwahara, Y. Gu, Y. Tanaka, F. Marumo, and S. Sasaki. Biochem. Biophys. Res. Commun. 244: 268-274, 1998). Here we report a reevaluation of the functional characteristics of hAQP9, its tissue distribution, the structure of its gene, and its chromosomal localization. When expressed in Xenopus oocytes, hAQP9 allowed passage of a wide variety of noncharged solutes, including carbamides, polyols, purines, and pyrimidines in a phloretin- and mercurial-sensitive manner. These functional characteristics are similar to those of rAQP9. Based on Northern blot analysis, both rat and human AQP9 are abundantly expressed in liver, whereas, in contrast to rAQP9, hAQP9 is also expressed in peripheral leukocytes and in tissues that accumulate leukocytes, such as lung, spleen, and bone marrow. The human AQP9 gene is composed of 6 exons and 5 introns distributed over approximately approximately 25 kb. The gene organization is strikingly similar to that reported for human AQP3 and AQP7, suggesting their evolution from a common ancestral gene. The promoter region contains putative tonicity and glucocorticoid-responsive elements, suggesting that AQP9 may be regulated by osmolality and catabolism. Fluorescence in situ hybridization assigned its locus to chromosome 15 q22.1-22.2. Our data show that hAQP9 serves as a promiscuous solute channel expressed in both liver and peripheral leukocytes, where it is ideally suited to transport of metabolites and/or nutrients into and out of these cells
Collapse
Affiliation(s)
- H Tsukaguchi
- Membrane Biology Program, Department of Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA
| | | | | | | |
Collapse
|
33
|
Chen Y, Ramos KS. Negative regulation of rat GST-Ya gene via Antioxidant/Electrophile response element is directed by a C/EBP-like site. Biochem Biophys Res Commun 1999; 265:18-23. [PMID: 10548484 DOI: 10.1006/bbrc.1999.1609] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The present studies were conducted to evaluate functional interactions between aryl hydrocarbon and antioxidant/electrophile response elements (AhRE and ARE/EpRE, respectively) in transcriptional regulation of the rat (r)GST-Ya gene. Transient transfection of an AhRECAT reporter construct into vascular smooth muscle cells (vSMCs) or HepG2 cells showed that benzo(a)pyrene (BaP) (0.3-30 microM) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (0. 1-10 nM), but not hydrogen peroxide (H(2)O(2)) (100-400 microM), increased gene transcription. ARE/EpRE did not mediate gene inducibility by any of the chemicals in vSMCs but increased transcription in HepG2 cells treated with BaP or H(2)O(2), but not TCDD. Gene inducibility in response to all chemicals was repressed in both cell types transfected with a 1.6CAT full-length promoter construct containing the AhRE and ARE/EpRE in genomic context. Site-directed mutagenesis of 1.6CAT showed that a CCAAT/enhancer-binding protein (C/EBP)-like site within the ARE/EpRE directed negative regulation of the rGST-Ya gene in vSMCs and HepG2 cells. These results show that ARE/EpRE in rGST-Ya does not function as a positive cis-acting regulatory element in all cell types, and that in the context of the full-length rGST-Ya promoter a C/EBP-like site directs negative regulation of the gene by BaP and related chemicals.
Collapse
Affiliation(s)
- Y Chen
- College of Veterinary Medicine, Texas A & M University, College Station, Texas, 77843-4466, USA
| | | |
Collapse
|
34
|
Hayes JD, McLellan LI. Glutathione and glutathione-dependent enzymes represent a co-ordinately regulated defence against oxidative stress. Free Radic Res 1999; 31:273-300. [PMID: 10517533 DOI: 10.1080/10715769900300851] [Citation(s) in RCA: 1022] [Impact Index Per Article: 40.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Increases in the intracellular levels of reactive oxygen species (ROS), frequently referred to as oxidative stress, represents a potentially toxic insult which if not counteracted will lead to membrane dysfunction, DNA damage and inactivation of proteins. Chronic oxidative stress has numerous pathological consequences including cancer, arthritis and neurodegenerative disease. Glutathione-associated metabolism is a major mechanism for cellular protection against agents which generate oxidative stress. It is becoming increasingly apparent that the glutathione tripeptide is central to a complex multifaceted detoxification system, where there is substantial inter-dependence between separate component members. Glutathione participates in detoxification at several different levels, and may scavenge free radicals, reduce peroxides or be conjugated with electrophilic compounds. Thus, glutathione provides the cell with multiple defences not only against ROS but also against their toxic products. This article discusses how glutathione biosynthesis, glutathione peroxidases, glutathione S-transferases and glutathione S-conjugate efflux pumps function in an integrated fashion to allow cellular adaption to oxidative stress. Co-ordination of this response is achieved, at least in part, through the antioxidant responsive element (ARE) which is found in the promoters of many of the genes that are inducible by oxidative and chemical stress. Transcriptional activation through this enhancer appears to be mediated by basic leucine zipper transcription factors such as Nrf and small Maf proteins. The nature of the intracellular sensor(s) for ROS and thiol-active chemicals which induce genes through the ARE is described. Gene activation through the ARE appears to account for the enhanced antioxidant and detoxification capacity of normal cells effected by many cancer chemopreventive agents. In certain instances it may also account for acquired resistance of tumours to cancer chemotherapeutic drugs. It is therefore clear that determining the mechanisms involved in regulation of ARE-driven gene expression has enormous medical implications.
Collapse
Affiliation(s)
- J D Hayes
- Biomedical Research Centre, Ninewells Hospital and Medical School, University of Dundee, Scotland, UK
| | | |
Collapse
|
35
|
Thurmond TS, Silverstone AE, Baggs RB, Quimby FW, Staples JE, Gasiewicz TA. A chimeric aryl hydrocarbon receptor knockout mouse model indicates that aryl hydrocarbon receptor activation in hematopoietic cells contributes to the hepatic lesions induced by 2,3,7, 8-tetrachlorodibenzo-p-dioxin. Toxicol Appl Pharmacol 1999; 158:33-40. [PMID: 10387930 DOI: 10.1006/taap.1999.8681] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Pathologic changes associated with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) exposure have been reported in the livers of a wide range of species. While these changes have been extensively described, the mechanisms of toxic interaction(s) that produce these lesions remain unclear. Using an aryl hydrocarbon receptor (Ahr) knockout male mouse chimeric model, we investigated whether the presence of this receptor in hematopoietic and/or parenchymal cells affects TCDD-induced hepatotoxicity. Bone marrow chimeras were produced by hematopoietic reconstitution of irradiated mice. Specifically, chimeras were generated with aryl hydrocarbon receptor (AHR) positive hematopoietic and parenchymal cells (Ahr+/+ animal bone marrow cells into irradiated Ahr+/+ animals), AHR positive hematopoietic and negative parenchymal cells (Ahr+/+ into Ahr-/-), AHR negative hematopoietic and positive parenchymal cells (Ahr-/- into Ahr+/+), and AHR negative hematopoietic and parenchymal cells (Ahr-/- into Ahr-/-). Male wild-type (Ahr+/+) and knockout (Ahr-/-) animals were used as nonchimeric controls. Following TCDD treatment (30 microg/kg body wt), liver sections from mice in each control and chimeric group were histologically evaluated for necrotic and inflammatory changes. TCDD treatment produced moderate inflammation in Ahr+/+ controls and Ahr+/+ into Ahr+/+ chimeras. This response was mild in TCDD-treated Ahr-/-, Ahr-/- into Ahr-/-, Ahr+/+ into Ahr-/-, and Ahr-/- into Ahr+/+ animals and was not different from the corresponding vehicle-treated groups. Moderate necrosis was observed in all TCDD-treated controls or chimeras with AHR-positive parenchyma. No or mild necrosis was observed in TCDD- and vehicle-treated animals containing AHR-negative parenchyma. These data indicate that the presence of AHR in hepatic parenchyma alone is sufficient for TCDD induction of hepatic necrosis, and its presence in hematopoietic cells is necessary for the inflammatory response to TCDD-induced hepatic lesions.
Collapse
Affiliation(s)
- T S Thurmond
- Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
| | | | | | | | | | | |
Collapse
|
36
|
Tjalkens RB, Luckey SW, Kroll DJ, Petersen DR. Alpha, beta-unsaturated aldehydes mediate inducible expression of glutathione S-transferase in hepatoma cells through activation of the antioxidant response element (ARE). ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1999; 463:123-31. [PMID: 10352677 DOI: 10.1007/978-1-4615-4735-8_15] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- R B Tjalkens
- Department of Pharmaceutical Sciences, University of Colorado Health Sciences Center, Denver, USA
| | | | | | | |
Collapse
|
37
|
Choi JH, Lou W, Vancura A. A novel membrane-bound glutathione S-transferase functions in the stationary phase of the yeast Saccharomyces cerevisiae. J Biol Chem 1998; 273:29915-22. [PMID: 9792709 DOI: 10.1074/jbc.273.45.29915] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The glutathione S-transferases (GSTs) represent a significant group of detoxification enzymes that play an important role in drug resistance in all eukaryotic species. In this paper we report an identification and characterization of the two Saccharomyces cerevisiae genes, GTT1 and GTT2 (glutathione transferase 1 and 2), coding for functional GST enzymes. Despite only limited similarity with GSTs from other organisms (approximately 50%), recombinant Gtt1p and Gtt2p exhibit GST activity with 1-chloro-2, 4-dinitrobenzene as a substrate. Both Gtt1p and Gtt2p are able to form homodimers, as determined by two hybrid assay. Subcellular fractionation demonstrated that Gtt1p associates with the endoplasmic reticulum. Expression of GTT1 is induced after diauxic shift and remains high throughout the stationary phase. Strains deleted for GTT1 and/or GTT2 are viable but exhibit increased sensitivity to heat shock in stationary phase and limited ability to grow at 39 degreesC.
Collapse
Affiliation(s)
- J H Choi
- Department of Biological Sciences, St. John's University, Jamaica, New York 11439, USA
| | | | | |
Collapse
|
38
|
Tjalkens RB, Luckey SW, Kroll DJ, Petersen DR. Alpha,beta-unsaturated aldehydes increase glutathione S-transferase mRNA and protein: correlation with activation of the antioxidant response element. Arch Biochem Biophys 1998; 359:42-50. [PMID: 9799558 DOI: 10.1006/abbi.1998.0895] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A series of alpha,beta-unsaturated aldehydes was evaluated to determine if these compounds could mediate inducible expression of glutathione S-transferase (GST) through the 5'-flanking antioxidant response element (ARE). The ARE from rGST A1 was subcloned into a luciferase reporter construct and used to transiently transfect rat Clone 9 hepatoma cells. Transfected cells were treated with 4-hydroxy-trans-2-nonenal (4-HNE), trans-2-hexenal (t-2-HE), 2-propenal (acrolein, 2-PE), and ethacrynic acid (EA), a control compound also containing an alpha,beta-unsaturated carbonyl moiety. Each compound was evaluated for cytotoxicity to construct dosing regimens in transfection studies. IC50 values for growth inhibition were measured using 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide. IC50 values in Clone 9 cells were: 4-HNE, 6.3 +/- 0.7 microM; t-2-HE, 16.0 +/- 0.7 microM; 2-PE, 2.2 +/- 0.4 microM; and EA, 38.0 +/- 1.6 microM. A dose-dependent increase in luciferase activity was observed in transfected cells with all four compounds tested, indicating that alpha, beta-unsaturated aldehydes function as direct activators of the ARE. To determine whether or not the observed promoter activation led to increased transcriptional and translational induction of GST, cells were treated with the various compounds and assayed for increases in GST mRNA, protein, and enzyme activity. Studies in Clone 9 cells revealed increased steady-state message for GST A1 and A4, increased GST A4-4 protein by Western blotting, and increased GST activity toward 1-chloro-2,4-dinitrobenzene in response to treatment with all four compounds evaluated. Collectively, these studies demonstrate that EA and certain alpha,beta-unsaturated aldehydes produced as a result of cellular membrane lipid peroxidation are activators of the ARE and efficient inducers of GST A1-1 and A4-4.
Collapse
Affiliation(s)
- R B Tjalkens
- Department of Pharmaceutical Sciences, University of Colorado Health Sciences Center, Denver, Colorado, 80262, USA
| | | | | | | |
Collapse
|
39
|
Lavin AL, Hahn DJ, Gasiewicz TA. Expression of functional aromatic hydrocarbon receptor and aromatic hydrocarbon nuclear translocator proteins in murine bone marrow stromal cells. Arch Biochem Biophys 1998; 352:9-18. [PMID: 9521805 DOI: 10.1006/abbi.1998.0587] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) acting through the aromatic hydrocarbon receptor (AhR) and its dimerization partner, the AhR nuclear translocator protein (arnt), elicits numerous toxicological effects including immunosuppression and thymic atrophy. Previous work has shown that TCDD alters bone marrow prothymocyte populations. These effects could be mediated at the lymphocyte level directly and/or through effects on bone marrow stromal cells, a population important in the support of lymphopoiesis. The purpose of this study was to characterize AhR and arnt expression in three murine bone marrow stromal cell lines (S17, M2-10B4, and BMS2) and in primary stromal cell cultures. Immunoblot analysis detected AhR protein in M2-10B4 and BMS2 cells. AhR protein was also detected in the primary cultures. Arnt protein could be detected in all cell cultures. Electrophoretic mobility shift assays detected TCDD-dependent dioxin-responsive element (DRE) binding in all three cell lines. DNA binding was sequence-specific and dependent on AhR, as demonstrated by the addition of unlabeled DRE DNA or of anti-AhR antibody. Results obtained with the primary cultures paralleled those seen with the stromal cell lines. The ED50 for induction of TCDD-dependent DRE binding in M2-10B4 cells was 0.21 nM. TCDD treatment did not induce stromal P4501A1 mRNA expression but did increase P4501B1 mRNA levels in all three cell lines and in the primary cultures. These results indicate that murine bone marrow stromal cells express AhR and arnt proteins. Furthermore, these proteins are functional in terms of their DRE-binding ability and potential to regulate mRNA levels in a gene-specific fashion.
Collapse
Affiliation(s)
- A L Lavin
- Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
| | | | | |
Collapse
|
40
|
Metz RP, Ritter JK. Transcriptional activation of the UDP-glucuronosyltransferase 1A7 gene in rat liver by aryl hydrocarbon receptor ligands and oltipraz. J Biol Chem 1998; 273:5607-14. [PMID: 9488689 DOI: 10.1074/jbc.273.10.5607] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
UDP-glucuronosyltransferase UGT1A7 catalyzes the glucuronidation of benzo(a)pyrene metabolites and other bulky aromatic compounds. Both UGT1A7 mRNA and an associated enzyme activity (benzo(a)pyrene7, 8-dihydrodioltransferase activity) are markedly increased in livers of rats treated with beta-naphthoflavone or 4-methyl-5-pyrazinyl-3H-1,2-dithiole-3-thione (oltipraz). Nuclear runoff assays show that the effects of both inducers are primarily due to transcriptional activation. A 27-kilobase region that included the UGT1A7/UGT1A6 promoter regions was cloned. Primer extension and RNase protection studies indicated >/=30 transcription start sites in five clusters between bases -85 and -40 respective to the translation start codon. There was no recognizable TATA box, but the promoter region is TA-rich. Sequence analysis revealed potential binding sites for CCAAT enhancer-binding protein, activator protein 1, and hepatic nuclear factors 1, 3, and 4, but no xenobiotic response elements or antioxidant response elements, implicated in the regulation of other genes by beta-naphthoflavone or oltipraz, were found. A UGT1A7 gene reporter plasmid directed strong constitutive expression in transient transfection assays using primary rat hepatocytes. Treatment with 3-methylcholanthrene or oltipraz had no effect compared with similarly treated pGL3-Basic-transfected cells. These results suggest that the regulatory elements controlling xenobiotic inducibility of UGT1A7 transcription are located either 5' or 3' of bases -1600 to +54. One possibility is that the polycyclic aromatic-mediated regulation of UGT1A7 occurs via the xenobiotic response element flanking the UGT1A6 locus 7 kilobase pairs downstream.
Collapse
Affiliation(s)
- R P Metz
- Department of Pharmacology and Toxicology, Virginia Commonwealth University, Medical College of Virginia, Richmond, Virginia 23298, USA
| | | |
Collapse
|
41
|
Lindros KO, Oinonen T, Kettunen E, Sippel H, Muro-Lupori C, Koivusalo M. Aryl hydrocarbon receptor-associated genes in rat liver: regional coinduction of aldehyde dehydrogenase 3 and glutathione transferase Ya. Biochem Pharmacol 1998; 55:413-21. [PMID: 9514075 DOI: 10.1016/s0006-2952(97)00495-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The tumor-associated aldehyde dehydrogenase 3 (ALDH3) and the glutathione transferase (GST)Ya form are coded by members of the Ah (aryl hydrocarbon) battery group of genes activated in the liver by polycyclic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The physiological role of the Ah receptor (AHR), its gene-activating mechanism and its endogenous ligands are still poorly clarified. We had previously observed that 3-methylcholanthrene (3MC) and beta-naphthoflavone (betaNF) induced the AHR-associated CYP1A1/1A2 pair in different liver regions, an effect not explained by the acinar distribution of the AHR protein. Here, we investigated AHR-associated regional induction by comparing the expression patterns of ALDH3 and GSTYa. Analysis of samples from periportal and perivenous cell lysates from 3MC-treated animals revealed that ALDH3 mRNA, protein and benzaldehyde-NADP associated activity were all confined to the perivenous region. In contrast, such regio-specific induction was not seen after beta-NF induction. Immunohistochemically, a peculiar mono- or oligocellular induction pattern of ALDH3 was seen, consistently surrounding terminal hepatic veins after 3MC but mainly in the midzonal region after betaNF. A ligand-specific difference in regional induction of GSTYa1 mRNA was also observed: The constitutive perivenous dominance was preserved after 3MC while induction by betaNF was mainly periportal. A 3MC-betaNF difference was also seen by immunohistochemistry and at the GSTYa protein level, in contrast to that of the AHR-unassociated GSTYb protein. However, experiments with hepatocytes isolated from the periportal or perivenous region to replicate these inducer-specific induction responses in vitro were unsuccessful. These data demonstrate that the different acinar induction patterns by 3MC and betaNF previously observed for CYP1A1 and CYP1A2 are seen also for two other Ah battery genes, GSTYa1 and ALDH3, but in a modified, gene-specific form. We hypothesize that unknown protein(s) operating in vivo and modifying the Ah-mediated response at the common XRE element located upstream of these genes is affected zonespecifically by 3MC and betaNF.
Collapse
Affiliation(s)
- K O Lindros
- National Public Health Institute, Alcohol Research Center, Helsinki, Finland.
| | | | | | | | | | | |
Collapse
|
42
|
Hoivik D, Wilson C, Wang W, Willett K, Barhoumi R, Burghardt R, Safe S. Studies on the relationship between estrogen receptor content, glutathione S-transferase pi expression, and induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin and drug resistance in human breast cancer cells. Arch Biochem Biophys 1997; 348:174-82. [PMID: 9390189 DOI: 10.1006/abbi.1997.0380] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces both phase I and phase II drug-metabolizing enzymes in rodent liver and hepatoma cell lines and this induction is mediated by the aryl hydrocarbon (Ah) receptor. Induction of CYP1A1 by TCDD in human breast cancer cells has been reported and results of several studies suggest that the estrogen receptor (ER) may be required for Ah responsiveness. This study investigates the induction of GST pi by TCDD in human breast cancer cells and the role of the ER in mediating this response. TCDD did not induce chloramphenicol acetyl transferase (CAT) activity in ER positive (ER+) MCF-7 and ER- MDA-MB-468 and MDA-MB-231 human breast cancer cell lines transiently transfected with GST pi (human) or GSTP (rat) promoter-reporter constructs containing the -291/+36 and -2.9/+59 region, respectively, of the GST pi and GSTP gene promoters. Furthermore, TCDD did not induce GST pi or GSTP in MDA-MB-468 and MDA-MB-231 human breast cancer cells stably transfected with the ER. RT-PCR confirmed that GST pi mRNA levels were low in ER+ MCF-7 cells and high in ER- MDA-MB-468 and MDA-MB-231 cells; however, in MDA-MB-468 and MDA-MB-231 cells stably transfected with the ER GST pi mRNA levels remained elevated and were not inducible. MDA-MB-468 and MDA-MB-231 cells stably transfected with the ER exhibited increased GST activity and decreased GSH content compared to wild-type cells; however, in MDA-MB-468 cells stably transfected with ER, the susceptibility to doxorubicin, ellipticine, chlorambucil, malphalan, or cisplatin was similar to that observed in wild-type cells. Adriamycin accumulation was similar in wild-type and ER stably transfected cells and verapamil did not affect this response, suggesting that ER expression did not influence p-glycoprotein activity. Taken together these data suggest that not all GST isoforms are responsive to TCDD and stable transfection of ER- cells with ER is not sufficient to restore the ER+ phenotype in some breast cancer cell lines.
Collapse
Affiliation(s)
- D Hoivik
- Department of Physiology and Pharmacology, Texas A&M University, College Station 77843, USA
| | | | | | | | | | | | | |
Collapse
|
43
|
Wasserman WW, Fahl WE. Comprehensive analysis of proteins which interact with the antioxidant responsive element: correlation of ARE-BP-1 with the chemoprotective induction response. Arch Biochem Biophys 1997; 344:387-96. [PMID: 9264553 DOI: 10.1006/abbi.1997.0215] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Transcriptional activation of the mouse glutathione S-transferase Ya gene by chemoprotective molecules is mediated through the interaction of trans-acting factors with an antioxidant responsive element (ARE) in the promoter region of this gene. In a step toward identifying those factors which bind productively to the GST Ya ARE, all of the discernible, specific ARE-binding proteins (ARE-BP) in nuclear extracts from HepG2 cells were systematically characterized. By gel-mobility-shift analysis, seven specific ARE-BPs, termed ARE-BP-1 through 7 in order of increasing mobility, were observed that did not vary in concentration or migration between induced and uninduced cell extracts. The molecular weights of the individual ARE-BP subunits were determined by a two-dimensional electrophoresis protocol. Ferguson gel analysis of native protein size indicated that several of the ARE-BP-DNA complexes are composed of multiple protein subunits. Wild-type AREs and GST Ya ARE fragments and mutant sequences were evaluated for their ability to mediate induction in a reporter gene system in HepG2 cells. This same panel of sites was tested in an in vitro binding assay for the ability to compete for the ARE-BPs. A binding profile for each ARE-BP was compiled. Correlation between the ARE-BP binding profiles and induction results indicated that: (i) the ARE-BP-1 and ARE-BP-2 complexes formed only with AREs that supported induction, and (ii) the ARE-BP-4 complex formed with all inducible AREs, but it also bound to ARE mutants that failed to support induction. Based on the studies, an early composite regulatory element model for ARE-mediated expression is presented. ARE-BP-1 is proposed to be the mediator of the ARE's unique induction response to chemoprotective agents.
Collapse
Affiliation(s)
- W W Wasserman
- McArdle Laboratory for Cancer Research, University of Wisconsin, Madison 53706, USA
| | | |
Collapse
|
44
|
Schrenk D, Riebniger D, Till M, Vetter S, Fiedler HP. Tryptanthrins: a novel class of agonists of the aryl hydrocarbon receptor. Biochem Pharmacol 1997; 54:165-71. [PMID: 9296363 DOI: 10.1016/s0006-2952(97)00150-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin and related environmental pollutants exert most of their adverse effects such as immunosuppression, induction of endocrine dysfunction, tumor promotion, and teratogenicity via the aryl hydrocarbon or dioxin receptor. While most potent agonists of the aryl hydrocarbon receptor are of synthetic origin, an increasing number of natural compounds are now recognized as receptor agonists. Our findings demonstrated that some tryptanthrin derivatives biosynthesized in incubations of Candida lipolytica with tryptophan and anthranilic acid or its derivatives were agonists of the aryl hydrocarbon receptor. The biosynthetic products 8-methyltryptanthrin, 8-chlorotryptanthrin, and 8-bromotryptanthrin induced cytochrome P4501A1 mRNA and protein in rat hepatocytes in primary culture, characteristic features of aryl hydrocarbon receptor agonists. Log-probit analysis of the catalytic activity of cytochrome P4501A1, 7-ethoxyresorufin O-deethylase (EROD), revealed EC50 induction values of 1.7, 0.25, and 0.17 microM for 8-methyltryptanthrin, 8-chlorotryptanthrin, and 8-bromotryptanthrin, respectively. Interestingly, the nonsubstituted tryptanthrin molecule, biosynthesized from the common physiological precursors tryptophan and anthranilic acid, was also active as an inducer. The specificity of the inducing effect of tryptanthrins was demonstrated in gel retardation experiments in Hepa-1 mouse hepatoma cells, showing the characteristic interaction of the activated aryl hydrocarbon receptor with an oligonucleotide containing a xenobiotic-responsive element. It is suggested that the receptor may be part of a defense system protecting higher organisms from secondary metabolites formed by the microflora of the host or its environment.
Collapse
Affiliation(s)
- D Schrenk
- Institute of Toxicology, University of Tübingen, Germany.
| | | | | | | | | |
Collapse
|
45
|
Schmitz HJ, Weber R, Hagenmaier A, Hagenmaier H, Poellinger L, Schrenk D. 2,3,7,8-Tetrafluorodibenzo-p-dioxin: a potent agonist of the murine dioxin receptor. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 1997; 3:105-113. [PMID: 21781767 DOI: 10.1016/s1382-6689(96)00146-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/1996] [Revised: 12/05/1996] [Accepted: 12/11/1996] [Indexed: 05/31/2023]
Abstract
2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and related polychlorinated aromatic hydrocarbons exert a pattern of toxicity related to their binding to a common receptor, the Ah (aryl hydrocarbon) or dioxin receptor. No information is available, however, on the toxicological properties of 2,3,7,8-tetrafluorodibenzo-p-dioxin (TFDD). In our experiments, TFDD was found to act as a highly potent dioxin receptor agonist leading to a transient induction of cytochrome P450(CYP)1A1 mRNA and protein in receptor-proficient mouse Hepa-1 hepatoma cells treated with 10(-10) M TFDD. However, no significant induction of 7-ethoxyresorufin O-deethylase (EROD) activity was observable in TFDD-treated Hepa-1 cells or mouse hepatocytes in primary culture, suggesting an interference with the catalytic activity of CYP1A1. Parallel experiments with 10(-10) M TCDD showed a sustained induction of CYP1A1 mRNA and protein, and of EROD activity. When a reporter gene construct comprising a xenobiotic-responsive element (XRE) in 5'-position was transfected in Hepa-1c-1c-7 cells, 5×10(-8) M TFDD and 5×10(-9) M TCDD induced transcription to a comparable extent. Both inducers were inactive when a mutant XRE with a guanine replaced by thymine was transfected. In metabolism studies in mouse liver homogenate, TFDD was rapidly degraded in the presence of an NADPH-regenerating system, and metabolism was enhanced in liver homogenate from β-naphthoflavone-pretreated mice indicating that TFDD is metabolized in a CYP-catalyzed pathway. The open ring products dihydroxytetrafluororbiphenyl ether, and 1,2-difluoro-o-benzoquinone, probably derived from 1,2-difluorocatechol, were identified by GC-MS analysis of the incubation mixtures, whereas no phenolic metabolites/and or metabolites with an intact dioxin ring could be found. It is concluded that TFDD, in contrast to its chlorinated analogue, is metabolically unstable, and thus currently does not fulfill the criteria for the recommendation of a TCDD or toxicity equivalency factor (TEF).
Collapse
Affiliation(s)
- H J Schmitz
- Institut für Toxikologie, Universität Tübingen, D-72074 Tübingen, Germany
| | | | | | | | | | | |
Collapse
|
46
|
Bulla GA. Selective loss of the hepatic phenotype due to the absence of a transcriptional activation pathway. SOMATIC CELL AND MOLECULAR GENETICS 1997; 23:185-201. [PMID: 9330630 DOI: 10.1007/bf02721370] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Liver-enriched trans-acting factors hepatocyte nuclear factor-1 alpha (HNF1 alpha) and -4 (HNF4) are components of a transcriptional activation pathway that is thought to play a major role in hepatic gene activation. We previously described the isolation and characterization of distinct classes of hepatoma variants which lack the HNF4-->HNF1 alpha pathway (1). In order to determine the influence of the HNF4-->HNF1 alpha pathway on hepatic gene expression, genetic rescue experiments were done using hepatoma variant line H11 as a model system. Results suggest that this pathway is required for basal expression of a number of endogenous hepatocyte-specific genes. Complementation groups were established by fusion of H11 cells with other variant lines. Lastly, introduction of human chromosome 20 (containing the HNF4 locus) or randomly-marked human chromosomes into H11 cells failed to rescue the hepatic phenotype, suggesting that what appears to be a 'simple' defect may involve multiple genetic loci.
Collapse
Affiliation(s)
- G A Bulla
- Department of Pediatrics, St. Louis University Health Sciences Center, Missouri, USA
| |
Collapse
|
47
|
Abstract
The aryl hydrocarbon (or dioxin) receptor (AhR) is a ligand-activated basic helix-loop-helix (bHLH) protein that heterodimerizes with the bHLH protein ARNT (aryl hydrocarbon nuclear translocator) forming a complex that binds to xenobiotic regulatory elements in target gene enhancers. Genetic, biochemical, and molecular biology studies have revealed that the AhR mediates the toxic and biological effects of environmentally persistent dioxins and related compounds. Cloning of the receptor and its DNA-binding partner, ARNT, has facilitated detailed efforts to understand the mechanisms of AhR-mediated signal transduction. These studies have determined that this unique receptor consists of several functional domains and belongs to a subfamily of bHLH proteins that share a conserved motif termed the PAS domain. In addition, recent genetic studies have revealed that expression of the AhR is a requirement for proper embryonal development, which appears to be a common function shared by many other bHLH proteins. This review is a summary of recent molecular studies of AhR-mediated gene regulation.
Collapse
Affiliation(s)
- J C Rowlands
- Department of Bioscience, Karolinska Institute, NOVUM, Huddinge, Sweden
| | | |
Collapse
|
48
|
Gasiewicz TA, Kende AS, Rucci G, Whitney B, Willey JJ. Analysis of structural requirements for Ah receptor antagonist activity: ellipticines, flavones, and related compounds. Biochem Pharmacol 1996; 52:1787-803. [PMID: 8986142 DOI: 10.1016/s0006-2952(96)00600-4] [Citation(s) in RCA: 105] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
A number of studies have examined the structure-activity relationships for the agonist activity of Ah receptor (AhR) ligands. Fewer studies have considered the structural basis for potential antagonist properties. Certain ellipticine derivatives have been reported to bind to the AhR and inhibit the ability of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to transform the AhR to a form that recognizes a dioxin-responsive enhancer element (DRE) upstream of the cytochrome P4501A1 gene. In the present study, over 30 ellipticine derivatives and structurally related compounds were examined for their ability to bind to the AhR, activate it to a DRE-binding form, induce the luciferase gene under control of a DRE-containing enhancer, and block activation of the AhR by TCDD. The ability of several ellipticine derivatives to inhibit TCDD-elicited DRE binding and TCDD-induced luciferase activity was inversely related to their ability to alone stimulate these responses. The most potent antagonist activity was related to good AhR binding characteristics in terms of conforming to previously predicted 14 x 12 x 5 A van der Waals dimensions and the presence of an electron-rich ring nitrogen at or near a relatively unsubstituted X-axis terminal position. Based on these data, a number of flavone derivatives were synthesized and tested for their relative agonist/antagonist activity. These additional data were consistent with the hypothesis that an electron-rich center near or along a lateral position of the van der Waals binding cavity is a characteristic that enhances AhR antagonist activity.
Collapse
Affiliation(s)
- T A Gasiewicz
- Department of Environmental Medicine, University of Rochester, NY 14642, USA
| | | | | | | | | |
Collapse
|
49
|
Abstract
The aryl hydrocarbon (Ah) receptor has occupied the attention of toxicologists for over two decades. Interest arose from the early observation that this soluble protein played key roles in the adaptive metabolic response to polycyclic aromatic hydrocarbons and in the toxic mechanism of halogenated dioxins and dibenzofurans. More recent investigations have provided a fairly clear picture of the primary adaptive signaling pathway, from agonist binding to the transcriptional activation of genes involved in the metabolism of xenobiotics. Structure-activity studies have provided an understanding of the pharmacology of this receptor; recombinant DNA approaches have identified the enhancer sequences through which this factor regulates gene expression; and functional analysis of cloned cDNAs has allowed the characterization of the major signaling components in this pathway. Our objective is to review the Ah receptor's role in regulation of xenobiotic metabolism and use this model as a framework for understanding the less well-characterized mechanism of dioxin toxicity. In addition, it is hoped that this information can serve as a model for future efforts to understand an emerging superfamily of related signaling pathways that control biological responses to an array of environmental stimuli.
Collapse
Affiliation(s)
- J V Schmidt
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, Illinois 60611, USA
| | | |
Collapse
|
50
|
Kirby GM, Batist G, Alpert L, Lamoureux E, Cameron RG, Alaoui-Jamali MA. Overexpression of cytochrome P-450 isoforms involved in aflatoxin B1 bioactivation in human liver with cirrhosis and hepatitis. Toxicol Pathol 1996; 24:458-67. [PMID: 8864187 DOI: 10.1177/019262339602400408] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Studies were carried out to test the hypothesis that inflammatory liver disease increases the expression of specific cytochrome P-450 isoenzymes involved in aflatoxin B1 (AFB) activation. The immunohistochemical expression and localization of various human cytochrome P-450 isoforms, including CYP2A6, CYP1A2, CYP3A4, and CYP2B1, were examined in normal human liver and liver with hepatitis and cirrhosis. The constitutive expression of CYP3A4 in normal liver showed a characteristic pattern of distribution in centrilobular hepatocytes, whereas CYP1A2, CYP2A6, and CYP2B1 were expressed uniformly throughout the liver acinus. In sections of liver infected with hepatitis B virus (HBV) or hepatitis C virus (HCV), the expression of CYP2A6 was markedly increased in hepatocytes immediately adjacent to areas of fibrosis and inflammation. CYP3A4 and CYP2B1 were induced to a lesser degree, and expression of CYP1A2 was unaffected. In HBV-infected liver, double immunostaining revealed that overexpression of CYP2A6 occurred in hepatocytes expressing the HBV core antigen. In HCV-infected liver, CYP2A6, CYP3A4, and CYP2B1 were overexpressed in hepatocytes with hemosiderin pigmentation. These results suggest that alterations in phenotypic expression of specific P-450 isoenzymes in hepatocytes associated with hepatic inflammation and cirrhosis might increase susceptibility to AFB genotoxicity.
Collapse
Affiliation(s)
- G M Kirby
- Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, Canada
| | | | | | | | | | | |
Collapse
|