NORA Manufacturing Sector Strategic Goals
927ZGFU - Protection Against Occupational Disease by Xenobiotic-Activated Receptors
Principal Investigator (PI)
Primary Goal Addressed
Secondary Goal Addressed
Attributed to Manufacturing
The proposed studies are to obtain new insights into the mechanism of receptor-mediated toxic responses to occupational chemicals, and new approaches for designing better strategies for prevention of occupational diseases worldwide. Receptor-mediated gene regulation constitutes a major mechanism by which many occupational/environmental chemicals cause toxic effects or diseases, and by which antioxidants mediate chemoprotection against occupational disease. The role and mechanism of action of AhR, Nrf2, and MTF-1 in toxicity of HAHs/PAHs, chemoprotection by phenolic antioxidants, or responses to toxic heavy metals, are being examined in depth in experimental models, respectively. The studies, in particular target, on occupational cancer and cardiovascular and reproductive diseases and on risk assessment and chemoprotection. To date, the results indicate that AhR, NRF2 and MTF-1 play essential roles in determining toxic responses to work place-related oxidative chemicals, heavy metals and carcinogenic PAHs; that the receptor ligands can be utilized in protection against occupational chemical toxicity; and that effective biomarkers can be identified from the pathways of the receptors in response to the occupational chemicals.
Research projects are aimed at elucidating the role and mechanism of action of AhR, Nrf2, and MTF-1 in occupational disease and chemical toxicity, by using in vitro cell culture procedures, transgenic mouse models and, when possible, sampling of biological materials from humans with occupational exposure. The project's overall hypothesis can be summarized as receptor-mediated gene regulation may play a major role in pathological and protective responses to a large number of occupational/ environmental chemicals; understanding this process at the cellular and molecular level is essential for accurate risk assessment.
1. Study of the molecular mechanism of receptor signal transduction: The study is to elucidate the mechanism by which AhR, Nrf2, or MTF-1 transduces the signals of HAHs/PAHs, chemoprotective agents, or heavy metals.
A. Receptor activation. Unactivated AhR, Nrf2, and MTF-1 exist in cytoplasm with other proteins; the complexes play essential roles in determining the receptivity of receptors. Major effort will be made to identify the cytoplasmic protein complex of the receptors by biochemical and molecular approaches including tandom affinity purification and protein sequencing.
B. Receptor regulation. We will focus on (1) analyzing the mechanism of regulation of the receptors through ubiquitin-proteasome mediated receptor degradation, in particular, on cloning and analyzing the role of ADPF or related proteins in the degradation of AhR, Nrf2, and MTF-1 and (2) analyzing the role of phosphorylation/dephosphorylation in the regulation of Nrf2 and MTF1.
C. Regulation of gene expression. It is assumed that the mechanism of action of the receptors involves regulation of specific target gene expression. We will identify new target genes of AhR, Nrf2, and MTF-1 in response to specific chemical signals relevant to occupational diseases.
We found that Nrf2 mediates protective responses to toxic metals such as arsenic, chromium, cadmium, mercury, lead, and possibly particulates such as silica particles. Experiments are being conducted to further characterize the protective effects and the mechanism of the protection.
MTF-1 controls the basal and inducible expression of metallothioneins 1 and 2, which are high affinity metal-binding proteins. The mechanism by which metals and antioxidants induces MT-1 through MTF-1 will be examined for chemical-receptor, protein-DNA, and protein-protein interactions.
2. Examining mechanism of action of the receptors using knockout mouse models: The AhR knockout mice will be utilized to analyze the role and mechanism of action of AhR in dioxin-induced TCDD toxicity. The Nrf2 knockout mouse model will be used to examine the role of the receptors in the protection against the toxicity of occupational chemicals, such as the ovarian follicle loss induced by the occupational chemical 4-vinylcyclohexene (VCH) and its diepoxide (VCD), toxic metals, such as arsenic and chromium, and toxic particulates, such as silica and welding fumes. Mice will be treated with VCH/VCD and other occupational toxic chemicals. Toxicities will be examined and analyzed by comparing the knockout with wild type animals. Standard statistical analysis will be performed for data analysis and interpretation. The MTF-1-/- cells derived from MTF-1 knockout mice (embryonic lethal) will be utilized to assess the role of MTF-1 in the protection against heavy metal toxicity by phenolic antioxidants and other chemoprotective agents.
Applying chemoprotective agents in the prevention of occupational disease and chemical toxicity. The study is to examine the efficacy, potency, and safety of Nrf2 activators in the protection against occupational metal-induced toxicity and cancer and mouse models.
Use molecular and genetic approaches to assess the role and analyze the mechanism of action of the receptors in determining susceptibility to occupational disease and chemical toxicity.
Identify and characterize target genes of the receptors and regulatory proteins that modulate receptor activity, which are relevant to the etiology and development of occupational disease or can be used as biomarkers of occupational exposure and risk assessment.
Identify and develop receptor-based, new chemoprotective agents, such as Nrf2 activators, in the prevention and therapy of occupational disease. A research proposal was submitted to encompass part of these efforts.
Exposure to carcinogens and toxic chemicals potentially result in cancers and chronic diseases that accounts for a major portion of occupational illnesses worldwide. Xenobiotic-activated receptors (XARs) are a group of chemical-activated transcription factors that sense specific changes in the chemical environment in the body and integrate a wide range of defensive responses against the chemical insults, thereby playing critical roles in the defence against the toxic chemicals. When the defence response by XARs is defective or not appropriate to the chemicals in specificity and intensity, cancer and disease occur. On the other hand, XARs can be activated by chemoprotective ligands to boost the defensive response and therefore, serve as preventive/therapeutic targets for occupational disease. In addition, receptor-mediated responses to chemicals are highly specific and sensitive, and thus can be utilized to provide sensitive and quantitative risk assessment of occupational/environmental carcinogens and toxic chemicals.
The research of interest seeks to understand the mechanism of action of three xenobiotic receptors in occupational disease and chemical toxicity: (1) the aryl hydrocarbon receptor (AhR), which mediates adaptive and adverse responses to halogenated aromatic hydrocarbons (HAHs); (2) the NFE2-related factor 2 (Nrf2), which mediates the induction of phase 2 drug metabolizing enzymes and the antioxidative stress, anti-cancer functions by chemoprotective agents; and (3) the metal-activated transcription factor 1 (MTF-1), which mediates the induction of protective proteins against heavy metals. A combination of genetic, molecular and biochemical, and toxicological approaches are used in the studies. Knockout mice of AhR or Nrf2 provide sensitive animal models for examining the function and mechanism of action of the receptors in toxic response to occupational chemicals. Systematic molecular approaches will delineate the molecular events of XAR-mediated defense responses to various types of toxicants. Antioxidants and other chemoprotective agents that potently activate the XARs will be examined for protection against occupational disease and chemical toxicity in animal and other laboratory systems.
Toxic metals, particles, and fibers are major classes of occupational carcinogens and toxicants. Humans are exposed to carcinogenic polycyclic aromatic hydrocarbons and HAHs from a wide range of occupational and environmental sources. Cumulative evidence indicates a close relation between these chemicals and xenobiotic-activated receptors in the carcinogenesis and toxicity of the chemicals, which are major health threats in mining, manufacturing, construction, and agriculture industries.
Research results from this project will address the following strategic goals:
Sector Program Goals:
Manufacturing sector (100%), Strategic Goal 5 (09PPMNFSG5), Reduce the number of respiratory conditions and diseases due to exposures in the manufacturing sector.
Manufacturing sector (100%), Strategic Goal 6 (09PPMNFSG6), Reduce the prevalence of cancer due to exposures in the manufacturing sector.
Cross-Sector Health Outcome Program Goals:
Cancer, Reproductive, and Cardiovascular Diseases (100%), Strategic Goal 1 (09PPCRCSG1), Reduce the incidence of work-related cancer.
Intermediate Goal 1.2 (09PPCRCIG1.2), Promote carcinogen-free workplaces in the U.S.
Activity/Output Goal 1.2.3 (09PPCRCAOG1.2.3), Enhance the relevance and utility of interventions and recommendations by transferring research findings, technologies, and information into practice by publishing in technical trade journals, developing methods for inclusion into NMAM or similar collections, and developing workplace or trade documents.
Cancer, Reproductive, and Cardiovascular Diseases (100%), Strategic Goal 2 (09PPCRCSG2), Reduce mortality from work-related cancer through early-interventions.
Cancer, Reproductive, and Cardiovascular Diseases (100%), Strategic Goal 3 (09PPCRCSG3), Reduce the incidence of work-related adverse reproductive outcome.
Intermediate Goal 3.2 (09PPCRCIG3.2), Foster the dissemination of information and technologies to protect the reproductive health of workers.
Activity/Output Goal 3.2.1 (09PPCRCAOG3.2.1), Transfer research findings, technologies, and information into practice.
1.2.aa, Publish in technical and trade journals and develop workplace or trade documents to enhance the relevance and utility of interventions and recommendations.
Intermediate Goal 3.3 (09PPCRCIG3.3), Enhance global workplace reproductive health awareness through international collaborations.
Activity/Output Goal 3.3.1 (09PPCRCAOG3.3.1), Provide world leadership in addressing reproductive hazards in the workplace through development of new methods, formation of research collaborations and communication of research findings.
Cancer, Reproductive, and Cardiovascular Diseases (100%), Strategic Goal 4 (09PPCRCSG4), Reduce the incidence of work-related cardiovascular disease.
Intermediate Goal 4.2 (09PPCRCIG4.2), Promote cardiovascular health in the workplace.
Activity/Output Goal 4.2.1 (09PPCRCAOG4.2.1), Enhance the relevance and utility of interventions and recommendations by transferring research findings, technologies, and information into practice by publishing in technical and trade journals and developing workplace or trade documents.
Intermediate Goal 4.3 (09PPCRCIG4.3), Enhance global workplace cardiovascular health through international collaborations
Activity/Output Goal 4.3.1 (09PPCRCAOG4.3.1), Provide world leadership in addressing risk factors for cardiovascular disease in the workplace through research collaborations and communication of research findings.
Other Cross-Sector Program Goals:
Exposure Assessment (30%), Strategic Goal 2 (09PPEXASG2), Develop or improve specific methods and tools to assess worker exposures to critical occupational agents and stressors.
Intermediate Goal 2.8 (09PPEXAIG2.8), Develop and incorporate data from toxicity studies (including the mechanism of action of chemical, physical, and biological agents, including mixed exposures) or epidemiologic studies into the evaluation and improvement of exposure assessment strategies for priority occupational hazards.
Global Collaborations (25%), Strategic Goal 1 (09PPGLCSG1), Enhance global occupational safety and health through international collaborations.