MOLECULAR MECHANISMS OF COMPLEX MIXTURE TOXICITY

Summary

Principal Investigator: Alvaro Puga
Abstract: DESCRIPTION (provided by applicant): Environmental exposures to toxic or carcinogenic compounds rarely result from the action of single toxicants. More often, the toxic agent is a complex mixture of chemical entities in numbers ranging from a few, such as in many occupational exposures, to several thousand, as in cigarette smoke. Frequently, these mixtures include a combination of carcinogenic metals and polycyclic aromatic hydrocarbons (PAH). Of these, hexavalent chromium, a carcinogenic metal often found as an environmental co-contaminant with PAHs, and benzo[a]pyrene (BaP), a prototypical PAH, are among the top 20 hazardous substances in the ATSDR/EPA priority list. The long-range goal of the research funded by this grant has been to develop an understanding of the mechanisms responsible for the adverse health effects of exposure to binary mixtures of BaP and chromium(VI). We have shown that high-dose acute chromium treatment interferes with the assembly of productive transcriptional complexes by cross-linking HDAC1.DNMT1 complexes to promoter chromatin and inhibiting phosphorylation, acetylation and methylation epigenetic marks established by BaP-induced gene transactivation in histones H3 and H4. These changes inhibit recruitment of RNA polymerase II to the Cyp1a1 promoter, block BaP-inducible gene expression and stimulate the formation of BPDE-DNA adducts. Similarly, sustained exposure to low doses of chromium leads to gradual changes in histone marks and signal transduction pathways that cumulatively affect gene expression and silencing. Specifically, environmentally relevant doses of chromium(VI) have opposite effects on the BaP-mediated induction of CYP1A1, CYP1B1 and CYP1A2 cytochrome P450 genes, repress tumor suppressor gene expression and induce expression of pro-apoptotic genes, leading us to the hypothesis that environmentally relevant binary mixtures of chromium(VI) and BaP have a synergistic effect on BaP toxicity and carcinogenicity. Based on our findings, the objectives for the next 5 years of this grant are, (1) to elucidate the epigenetic mechanisms by which low-dose, long-term exposure to chromium affects BaP-inducible gene expression;(2) to evaluate how chronic exposure to environmentally relevant chromium doses in drinking water affects BaP toxicity and carcinogenicity. Epigenetic modification of gene expression is a key element of the developmental and carcinogenic outcomes of exposure to chromium, alone or in combination with PAHs. Hypermethylation of the promoter of the tumor suppressor p16ink4a gene has been found in chromium-exposed workers who developed lung cancer, although p16ink4a promoter methylation accounts for only one third of cancer in this population, suggesting that there may be additional chromium targets and alternative mechanisms underlying cancer development. The knowledge derived from this research will have a major impact on the medical translation of these epidemiological findings and, by identifying molecular targets useful to reduce disease incidence, will significantly contribute to the development of therapeutic and preventative measures. PUBLIC HEALTH RELEVANCE: Environmental exposure to hexavalent chromium in drinking water and cigarette smoking and occupational exposure in the workplace are often compounded with concomitant exposures to aromatic hydrocarbon procarcinogens, resulting in health problems including lung, stomach and intestinal tract tumors. The objective of this grant proposal is to evaluate how mixtures of hexavalent chromium and aromatic hydrocarbons cooperate to cause greater toxicity and carcinogenicity than the sum of the toxicities and carcinogenicities of the two compounds. The knowledge derived from this research will identify molecular targets to reduce disease incidence and will significantly contribute to the development of therapeutic and preventative measures with major impact on the treatment of the diseases caused by these agents.
Funding Period: 2001-01-16 - 2015-12-31
more information: NIH RePORT

Top Publications

  1. pmc Long term low-dose arsenic exposure induces loss of DNA methylation
    John F Reichard
    Center for Environmental Genetics and Department of Environmental Health, University of Cincinnati Medical Center, Cincinnati, OH 45267 0056, USA
    Biochem Biophys Res Commun 352:188-92. 2007
  2. pmc Effects of arsenic exposure on DNA methylation and epigenetic gene regulation
    John F Reichard
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, 3223 Eden Avenue, Cincinnati, OH 45267 0056, USA
    Epigenomics 2:87-104. 2010
  3. pmc Perspectives on the potential involvement of the AH receptor-dioxin axis in cardiovascular disease
    Alvaro Puga
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, Cincinnati, Ohio 45220, USA
    Toxicol Sci 120:256-61. 2011
  4. pmc Aryl hydrocarbon receptor ligands of widely different toxic equivalency factors induce similar histone marks in target gene chromatin
    Jerald L Ovesen
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati Medical Center, Cincinnati, Ohio 45267 0056, USA
    Toxicol Sci 121:123-31. 2011
  5. pmc Arsenic toxicology: translating between experimental models and human pathology
    J Christopher States
    Department of Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA
    Environ Health Perspect 119:1356-63. 2011
  6. pmc Long-term exposure to hexavalent chromium inhibits expression of tumor suppressor genes in cultured cells and in mice
    Yunxia Fan
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, College of Medicine, 3223 Eden Ave, Cincinnati, OH 45267, USA
    J Trace Elem Med Biol 26:188-91. 2012
  7. pmc Lead induces similar gene expression changes in brains of gestationally exposed adult mice and in neurons differentiated from mouse embryonic stem cells
    Francisco Javier Sánchez-Martín
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, College of Medicine, Cincinnati, Ohio, United States of America
    PLoS ONE 8:e80558. 2013
  8. pmc Pluripotency factors and Polycomb Group proteins repress aryl hydrocarbon receptor expression in murine embryonic stem cells
    Chia I Ko
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, 3223 Eden Avenue, Cincinnati, OH 45267, USA
    Stem Cell Res 12:296-308. 2014
  9. pmc Long-term exposure to low-concentrations of Cr(VI) induce DNA damage and disrupt the transcriptional response to benzo[a]pyrene
    Jerald L Ovesen
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, 3223 Eden Avenue, Cincinnati, OH 45267, United States
    Toxicology 316:14-24. 2014
  10. pmc The Ah Receptor Recruits IKKα to Its Target Binding Motifs to Phosphorylate Serine-10 in Histone H3 Required for Transcriptional Activation
    Hisaka Kurita
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, College of Medicine, 3223 Eden Avenue, Cincinnati, OH 45267
    Toxicol Sci 139:121-32. 2014

Detail Information

Publications25

  1. pmc Long term low-dose arsenic exposure induces loss of DNA methylation
    John F Reichard
    Center for Environmental Genetics and Department of Environmental Health, University of Cincinnati Medical Center, Cincinnati, OH 45267 0056, USA
    Biochem Biophys Res Commun 352:188-92. 2007
    ..Possibly as a consequence of these two complementary mechanisms, long-term exposure to arsenic results in DNA hypomethylation...
  2. pmc Effects of arsenic exposure on DNA methylation and epigenetic gene regulation
    John F Reichard
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, 3223 Eden Avenue, Cincinnati, OH 45267 0056, USA
    Epigenomics 2:87-104. 2010
    ..Here, we discuss the evidence supporting changes in DNA methylation as a cause of arsenic carcinogenesis and highlight the strengths and limitations of these studies, as well as areas where consistencies and inconsistencies exist...
  3. pmc Perspectives on the potential involvement of the AH receptor-dioxin axis in cardiovascular disease
    Alvaro Puga
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, Cincinnati, Ohio 45220, USA
    Toxicol Sci 120:256-61. 2011
    ..Research to define the mechanisms responsible for the lifelong cardiovascular malformations resulting from TCDD exposure during embryonic development will be highly significant to the prevention of environmental cardiovascular injury...
  4. pmc Aryl hydrocarbon receptor ligands of widely different toxic equivalency factors induce similar histone marks in target gene chromatin
    Jerald L Ovesen
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati Medical Center, Cincinnati, Ohio 45267 0056, USA
    Toxicol Sci 121:123-31. 2011
    ....
  5. pmc Arsenic toxicology: translating between experimental models and human pathology
    J Christopher States
    Department of Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky, USA
    Environ Health Perspect 119:1356-63. 2011
    ..We propose phenotypic anchoring as a means to unify experimental observations and disease outcomes...
  6. pmc Long-term exposure to hexavalent chromium inhibits expression of tumor suppressor genes in cultured cells and in mice
    Yunxia Fan
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, College of Medicine, 3223 Eden Ave, Cincinnati, OH 45267, USA
    J Trace Elem Med Biol 26:188-91. 2012
    ....
  7. pmc Lead induces similar gene expression changes in brains of gestationally exposed adult mice and in neurons differentiated from mouse embryonic stem cells
    Francisco Javier Sánchez-Martín
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, College of Medicine, Cincinnati, Ohio, United States of America
    PLoS ONE 8:e80558. 2013
    ..We conclude that our ESC-derived model of toxicant exposure during neural differentiation promises to be a useful model to analyze mechanisms of neurotoxicity induced by Pb and other environmental agents. ..
  8. pmc Pluripotency factors and Polycomb Group proteins repress aryl hydrocarbon receptor expression in murine embryonic stem cells
    Chia I Ko
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, 3223 Eden Avenue, Cincinnati, OH 45267, USA
    Stem Cell Res 12:296-308. 2014
    ..Our results suggest that reversible Ahr repression in ES cells holds the gene poised for expression and allows for a quick switch to activation during embryonic development. ..
  9. pmc Long-term exposure to low-concentrations of Cr(VI) induce DNA damage and disrupt the transcriptional response to benzo[a]pyrene
    Jerald L Ovesen
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, 3223 Eden Avenue, Cincinnati, OH 45267, United States
    Toxicology 316:14-24. 2014
    ..We conclude that the combined effect of these two toxicants appears to be neither synergistic nor additive, generating a toxic/adaptive condition that cannot be predicted from the effect of each toxicant alone...
  10. pmc The Ah Receptor Recruits IKKα to Its Target Binding Motifs to Phosphorylate Serine-10 in Histone H3 Required for Transcriptional Activation
    Hisaka Kurita
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, College of Medicine, 3223 Eden Avenue, Cincinnati, OH 45267
    Toxicol Sci 139:121-32. 2014
    ..Given the role of H3S10ph in regulation of chromosome condensation, AHR-IKKα cross-talk may be a mediator of chromatin remodeling by environmental agents. ..
  11. pmc Dioxin exposure disrupts the differentiation of mouse embryonic stem cells into cardiomyocytes
    Ying Wang
    Department of Environmental Health, University of Cincinnati Medical Center, Cincinnati, Ohio 45267 0056, USA
    Toxicol Sci 115:225-37. 2010
    ....
  12. pmc The aryl hydrocarbon receptor functions as a tumor suppressor of liver carcinogenesis
    Yunxia Fan
    Department of Environmental Health, University of Cincinnati Medical Center, College of Medicine, Cincinnati, Ohio 45267 0056, USA
    Cancer Res 70:212-20. 2010
    ..These data support the concept that in its basal state in the absence of a xenobiotic ligand, the Ahr gene functions as a tumor suppressor gene, and that its silencing may be associated with cancer progression...
  13. pmc Genomewide analysis of aryl hydrocarbon receptor binding targets reveals an extensive array of gene clusters that control morphogenetic and developmental programs
    Maureen A Sartor
    Laboratory for Statistical Genomics and Systems Biology, Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, Cincinnati, Ohio 45220, USA
    Environ Health Perspect 117:1139-46. 2009
    ..The naive receptor is believed to reside in an inactive cytosolic complex that translocates to the nucleus and induces transcription of xenobiotic detoxification genes after activation by ligand...
  14. pmc Ligand-independent regulation of transforming growth factor beta1 expression and cell cycle progression by the aryl hydrocarbon receptor
    Xiaoqing Chang
    Department of Environmental Health, University of Cincinnati Medical Center, and Shriners Hospital for Children, Cincinnati, OH 45267 0056, USA
    Mol Cell Biol 27:6127-39. 2007
    ....
  15. pmc Chromium cross-links histone deacetylase 1-DNA methyltransferase 1 complexes to chromatin, inhibiting histone-remodeling marks critical for transcriptional activation
    Michael Schnekenburger
    Department of Environmental Health, University of Cincinnati Medical Center, P O Box 670056, Cincinnati, OH 45267 0056, USA
    Mol Cell Biol 27:7089-101. 2007
    ..Epigenetic modification of gene expression patterns may be a key element of the developmental and carcinogenic outcomes of exposure to chromium and to other environmental agents...
  16. pmc HDAC1 bound to the Cyp1a1 promoter blocks histone acetylation associated with Ah receptor-mediated trans-activation
    Michael Schnekenburger
    Center for Environmental Genetics and Department of Environmental Health, University of Cincinnati Medical Center, P O Box 670056, Cincinnati, Ohio 45267 0056, USA
    Biochim Biophys Acta 1769:569-78. 2007
    ....
  17. pmc Heme oxygenase-1 induction by NRF2 requires inactivation of the transcriptional repressor BACH1
    John F Reichard
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, Cincinnati, OH 45267 0056, USA
    Nucleic Acids Res 35:7074-86. 2007
    ..Thus, BACH1 confers an additional level of regulation to ARE-dependent genes that reveals a new dimension to the oxidative stress response...
  18. pmc Repression of Ah receptor and induction of transforming growth factor-beta genes in DEN-induced mouse liver tumors
    Li Peng
    Center for Environmental Genetics, Department of Environmental Health, University of Cincinnati Medical Center, P O Box 670056, Cincinnati, OH 45267 00567, USA
    Toxicology 246:242-7. 2008
    ..Ahr was significantly repressed in tumors from both sets of mice, supporting the concept that Ahr silencing may be associated with cancer progression...
  19. pmc Recruitment of CREB1 and histone deacetylase 2 (HDAC2) to the mouse Ltbp-1 promoter regulates its constitutive expression in a dioxin receptor-dependent manner
    Aurea Gomez-Duran
    Departamento de Bioquimica y Biologia Molecular, Facultad de Ciencias, Universidad de Extremadura, Avenida de Elvas s n, 06071 Badajoz, Spain
    J Mol Biol 380:1-16. 2008
    ..Thus, epigenetics can contribute to constitutive Ltbp-1 repression by a mechanism requiring AhR activity...
  20. pmc The aryl hydrocarbon receptor binds to E2F1 and inhibits E2F1-induced apoptosis
    Jennifer L Marlowe
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, Cincinnati, OH 45267 0056, USA
    Mol Biol Cell 19:3263-71. 2008
    ..These results point to a proproliferative, antiapoptotic function of the Ah receptor that likely plays a role in tumor progression...
  21. pmc BACH1 is a specific repressor of HMOX1 that is inactivated by arsenite
    John F Reichard
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati, Cincinnati, Ohio 45267, USA
    J Biol Chem 283:22363-70. 2008
    ..The loss of BACH1 function in human keratinocytes results almost exclusively in HMOX1 induction, suggesting that BACH1 may function as a rheostat regulating levels of intracellular free heme...
  22. pmc The aryl hydrocarbon receptor cross-talks with multiple signal transduction pathways
    Alvaro Puga
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, Cincinnati, OH 45220, USA
    Biochem Pharmacol 77:713-22. 2009
    ..Ultimately, the effect of a particular AHR ligand may depend as much on the adaptive interactions that it established with pathways and proteins expressed in a specific cell or tissue as on the toxic responses that it raises...
  23. pmc Distinct contributions of JNK and p38 to chromium cytotoxicity and inhibition of murine embryonic stem cell differentiation
    Liang Chen
    Department of Environmental Health, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267, USA
    Environ Health Perspect 117:1124-30. 2009
    ..Cr(VI) exposure leads to activation of mitogen-activated protein kinases (MAPKs), including c-Jun N-terminal kinase (JNK)1/2, p38, and extracellular-signal regulated kinase (ERK)1/2...
  24. pmc Formaldehyde-Assisted Isolation of Regulatory Elements (FAIRE) analysis uncovers broad changes in chromatin structure resulting from hexavalent chromium exposure
    Jerald L Ovesen
    Department of Environmental Health and Center for Environmental Genetics, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
    PLoS ONE 9:e97849. 2014
    ....