Mechanisms of Inorganic Carcinogenesis

无机致癌机制

• 批准号: 7592531
• 负责人: MICHAEL WAALKES
• 金额: $ 162.05万
• 依托单位: DIVISION OF BASIC SCIENCES - NCI
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/7592531
• 关键词: Acute; Adrenal Glands; Adult; Androgen Receptor; Androgens; Animals; Apoptotic; Arsenic; Binding; Binding Proteins; Biological Models; Bladder; Brain; Cadmium; Cancer Model; Cancer Patient; Carcinogens; Carrier Proteins; Cell Line; Cell model; Cells; Clinical; Cooperative Human Tissue Network; DNA Methylation; Databases; Development; Diethylstilbestrol; Disease; Disruption; Dissection; Dose; Ductal Epithelial Cell; Environment; Environmental Estrogen; Epithelial Cells; Estrogen Receptors; Estrogens; Event; Exposure to; Future; Gene Expression; Genes; Genetic; Genitourinary system; Goals; Health Hazards; Human; Human Cell Line; In Vitro; Inclusion Bodies; Individual; Intervention; Kidney; Kidney Neoplasms; Knock-out; Knockout Mice; Knowledge; Lead; Lead Poisoning; Lesion; Life; Link; Liver; Lung; Malignant - descriptor; Malignant Neoplasms; Malignant neoplasm of kidney; Malignant neoplasm of pancreas; Malignant neoplasm of prostate; Metallothionein; Metals; Modeling; Molecular; Molecular Chaperones; Molecular Target; Mus; Nature; Nerve Degeneration; Neurodegenerative Disorders; Null Lymphocytes; Occupational; Organ; Ovary; Pancreas; Parkinson Disease; Pattern; Perinatal Exposure; Physiological; Physiology; Population; Precipitation; Predisposing Factor; Predisposition; Prevention; Process; Production; Prostate; Prostatic; Proteins; Public Health; Renal carcinoma; Resistance; Risk; Rodent Model; Role; Signal Transduction; Site; Skin; Skin Cancer; Staging; Stem cells; Surface; Testing; Time; Tissue Sample; Tissues; Transfection; Tumor Tissue; United States; Uterine Cancer; Uterus; Vagina; Work; Zinc; carcinogenesis; carcinogenicity; cell transformation; cellular targeting; design; exposed human population; fetal; hazard; human study; human tissue; imprint; in utero; in vivo Model; keratinocyte; kidney cell; lead exposure; outcome forecast; ovarian neoplasm; pollutant; postnatal; prenatal; prevent; promoter; research study; response; synuclein; toxic metal; tumor; tumor initiation; xenoestrogen

Many inorganics are known or suspected human carcinogens, such as arsenic, cadmium, and lead. These agents pose significant hazards to the population of the United States after environmental, occupational or intentional exposures. Defining carcinogenic mechanisms greatly aids in designing prevention or intervention strategies and in assigning appropriate levels of risk to these exposures. The primary goal of the ICS is to define the molecular mechanisms of carcinogenic action of arsenic, cadmium, and lead under the project titled Molecular Mechanisms of Inorganic Carcinogenesis. Since they can impact carcinogenicity and potentially provide a means for prevention or intervention, mechanisms of transport and acquired tolerance are studied as well. Emphasis is also placed on factors that may dictate heightened susceptibility to inorganics, such as early-life exposures and poor expression of critical adaptive genes. These inorganics attack various targets in humans. Arsenic causes skin, urinary bladder, lung, kidney, liver, and prostatic malignancies and possibly uterine cancers. Cadmium has been primarily associated with human lung, prostatic and kidney cancers and possibly pancreatic cancers. Lead exposure has been linked to kidney and brain malignancies. Thus, various in vitro and in vivo model systems have been developed to study important molecular targets and targets tissues, with an emphasis on human relevance. These inorganic carcinogens likely have multiple mechanisms that are site and cell specific, and our focus has been on epigentic factors. Significant advances and future directions include: ● A reproducible rodent model where inorganic arsenic acts a complete carcinogen has been developed in which brief in utero arsenic exposure in mice leads to tumors or proliferative lesions of the urogenital system, liver, lung and adrenal in the offspring as adults. The urogenital system lesions include transplacental arsenic-induced or initiated tumors of the ovaries, uterus, vagina, and bladder and proliferative lesions of the kidney. These results are in accord with human studies that indicate the liver, urinary bladder, lung, kidney and uterus are target tissues of arsenic carcinogenesis. Molecular mechanism studies indicate disruption of estrogen signaling by in utero exposure to arsenic contributes to the liver, lung and urogenital system malignancies, in part through aberrant activation of estrogen receptor-α. Indeed, we find that tumors and proliferative lesions of the urogenital system, including the uterus, ovary, vagina and urinary bladder, are greatly enhanced by postnatal exposure to synthetic estrogens like diethylstilbestrol. We also find evidence of aberrant estrogen signaling in arsenic exposed human liver. Further molecular characterization of arsenic-induced in utero tumor initiation is underway, including aberrant gene imprinting, using this model of arsenic carcinogenesis. We hypothesize that arsenic in utero may attack a critical pool of progenitor cells in target organs and induces aberrant genetic reprogramingas part of its carcinogenic mechanism. These studies have important public health implications, including the identification of fetal period as a time of very high sensitivity to arsenic and the possibility that co-exposure to pharmacological or environmental estrogens could enhance development of arsenic-initiated cancer. Further study will include prenatal arsenic exposure combined with exposures to urinary bladder and renal tumor promoters in mice to enhance the carcinogenic response to arsenic in these key human target organs. ● Various in vitro cell transformation model systems have also been developed to study inorganic carcinogenesis. In doing these studies we select cells with relevance to the human targets of arsenic, cadmium or lead carcinogenesis, and use low-level exposures for long periods, which approximates typical human exposures and avoids supra-physiological responses associated with acute high doses that could have limited relevance to the carcinogenic process. A human prostate epithelial cell line has been malignantly transformed with cadmium and arsenic, both potential human prostatic carcinogens. Additional work indicates the arsenic and cadmium transformants both acquire androgen independence, an event associated with a very poor clinical prognosis in prostatic cancer patients, largely through androgen receptor by-pass related mechanisms. Molecular dissection of the events associated with arsenic- or cadmium-induced malignant transformation in this and other human cell lines will continue with a focus of aberrant expression of genes critical to the carcinogenic process. In addition, a human prostate progenitor cell has been developed and will be studied as a potential target cell population of these carcinogenic inorganics. Furthermore, we have successfully transformed a human pancreatic ductal cell with cadmium, which fortifies a possible role of cadmium in this deadly disease. Similarly, arsenic has induced malignant transformation of human skin keratinocytes. The study of this arsenic-induced skin cancer model indicates that it occurs through a very different mechanism from internal cancers, one which involves apoptotic by-pass and aberrant survival of damaged skin cells. Transformation experiments of human renal cells with cadmium and lead are underway. Finally, we are developing a data base that provides unique patterns of gene expression and altered DNA methylation that may allow us to molecularly define sub-sets of prostate, pancreatic, skin, or renal cancers in humans as being attributable to arsenic, cadmium and/or lead exposures with tumor tissue obtained through the cooperative human tissue network. ● Lead exposure causes inclusion body formation, and although these aggresomes contain precipitated protein and the majority of the lead within the cell, they are otherwise poorly characterized. Lead-induced inclusions appear to protect critical cellular targets by sequestering large amounts of this poorly excreted metal. Metallothionein (MT) is a metal-binding protein that normally binds zinc but also detoxicates toxic metals. We find that MT-knockout (MT-null) mice are hypersensitive to lead toxicity, including nephrocarcinogenicity, because they cannot make lead inclusion bodies. Similarly lead exposed MT-null cells do not form inclusions in vitro. MT appears on the outer surface of inclusions in lead-exposed MT-wild type (MT-WT) mice. Many diseases show similar aggresomes, like Parkinsons and Alzheimers, which are tentatively linked with lead exposure. Precipitated α-synuclein (SN), a chaperone protein, is found in these neurodegenerative inclusions. In fact, we find MT-null cells poorly express SN but transfection of MT into MT-null cells restores expression. Co-precipitation experiments indicate MT may directly bind to SN. Studies are underway to test the hypothesis that SN may assist formation of lead-induced aggresomes. These studies could have important implications for lead carcinogenesis, zinc physiology and neurodegenerative diseases potentially linked to lead. Furthermore, MT levels in humans vary widely for unknown reasons and poor MT production may be a key predisposing factor to lead toxicity and carcinogenesis. Studies are underway to further test this hypothesis. For instance, our work in MT competent mice shows transplacental lead exposure induces a modest level of kidney tumor formation in the offspring as adults, so we are now studying the nephrocarcinogenicity of transplacental lead in MT-null mice to see if this response is enhanced. Because there are clearly human populations particularly sensitive to lead, any factor that predisposes individuals to lead toxicity takes on great importance

许多无机物是已知或疑似人类致癌物，例如砷、镉和铅。这些物质在环境、职业或故意接触后对美国人口构成重大危害。定义致癌机制极大地有助于设计预防或干预策略以及为这些暴露分配适当的风险水平。 ICS 的主要目标是在名为“无机致癌作用的分子机制”的项目下确定砷、镉和铅致癌作用的分子机制。由于它们可以影响致癌性并可能提供预防或干预的手段，因此还研究了运输机制和获得性耐受性。重点还放在可能导致对无机物敏感性升高的因素上，例如生命早期的接触和关键适应性基因的表达不良。这些无机物攻击人类的各种目标。砷会导致皮肤癌、膀胱癌、肺癌、肾癌、肝癌、前列腺癌以及可能的子宫癌。镉主要与人类肺癌、前列腺癌和肾癌以及可能的胰腺癌有关。铅暴露与肾脏和脑部恶性肿瘤有关。因此，已经开发了各种体外和体内模型系统来研究重要的分子靶点和靶组织，重点是人类相关性。这些无机致癌物可能具有多种位点和细胞特异性机制，我们的重点是表观因素。重大进展和未来方向包括： ● 已开发出一种可重复的啮齿动物模型，其中无机砷完全致癌，小鼠在子宫内短暂接触砷会导致后代泌尿生殖系统、肝脏、肺和肾上腺出现肿瘤或增殖性病变。作为成年人。泌尿生殖系统病变包括经胎盘砷诱发或引发的卵巢、子宫、阴道和膀胱肿瘤以及肾脏的增殖性病变。这些结果与人体研究一致，表明肝脏、膀胱、肺、肾和子宫是砷致癌的靶组织。分子机制研究表明，子宫内接触砷会破坏雌激素信号传导，从而导致肝脏、肺和泌尿生殖系统恶性肿瘤，部分原因是雌激素受体α的异常激活。事实上，我们发现泌尿生殖系统（包括子宫、卵巢、阴道和膀胱）的肿瘤和增殖性病变因产后接触己烯雌酚等合成雌激素而大大增强。我们还在砷暴露的人类肝脏中发现了异常雌激素信号的证据。砷诱导的子宫内肿瘤发生的进一步分子表征正在进行中，包括使用砷致癌模型的异常基因印记。我们假设子宫内的砷可能会攻击靶器官中的关键祖细胞库，并诱导异常的基因重编程，作为其致癌机制的一部分。这些研究具有重要的公共卫生意义，包括确定胎儿期是对砷非常敏感的时期，以及同时接触药物或环境雌激素可能会促进砷引发的癌症的发展。进一步的研究将包括产前砷暴露与小鼠膀胱和肾肿瘤促进剂的暴露相结合，以增强这些关键人类靶器官对砷的致癌反应。 ● 还开发了各种体外细胞转化模型系统来研究无机致癌作用。在进行这些研究时，我们选择与砷、镉或铅致癌作用的人类目标相关的细胞，并长期使用低水平暴露，这接近典型的人类暴露，并避免与急性高剂量相关的超生理反应，这些反应可能会导致与致癌过程的相关性有限。人类前列腺上皮细胞系已被镉和砷恶性转化，这两种物质都是潜在的人类前列腺致癌物。其他工作表明砷和镉转化体都获得了雄激素独立性，这一事件与前列腺癌患者的临床预后非常差相关，主要是通过雄激素受体旁路相关机制。对该人类细胞系和其他人类细胞系中与砷或镉诱导的恶性转化相关的事件的分子剖析将继续关注对致癌过程至关重要的基因的异常表达。此外，人类前列腺祖细胞已被开发出来，并将作为这些致癌无机物的潜在靶细胞群进行研究。此外，我们成功地用镉转化了人类胰腺导管细胞，这强化了镉在这种致命疾病中可能发挥的作用。同样，砷也会诱导人类皮肤角质形成细胞的恶性转化。对这种砷诱发的皮肤癌模型的研究表明，它的发生机制与内部癌症非常不同，其中涉及细胞凋亡旁路和受损皮肤细胞的异常存活。镉和铅对人体肾细胞的转化实验正在进行中。最后，我们正在开发一个数据库，提供独特的基因表达模式和改变的 DNA 甲基化，这可能使我们能够从分子水平上定义人类前列腺癌、胰腺癌、皮肤癌或肾癌的亚组，这些癌症可归因于砷、镉和/或或通过合作人体组织网络获得的肿瘤组织的铅暴露。 ● 铅暴露会导致包涵体形成，尽管这些聚集体含有沉淀的蛋白质和细胞内的大部分铅，但它们的特征却很差。铅诱导的夹杂物似乎可以通过隔离大量这种排泄不良的金属来保护关键的细胞靶标。金属硫蛋白 (MT) 是一种金属结合蛋白，通常与锌结合，但也能解毒有毒金属。我们发现 MT 敲除（MT-null）小鼠对铅毒性（包括肾癌性）过敏，因为它们不能产生铅包涵体。同样，暴露于铅的 MT-null 细胞在体外也不会形成包涵体。 MT 出现在铅暴露 MT 野生型 (MT-WT) 小鼠内含物的外表面上。许多疾病都表现出类似的攻击性，如帕金森病和阿尔茨海默病，这些疾病暂时与铅暴露有关。在这些神经退行性内含物中发现了沉淀的 α-突触核蛋白 (SN)，一种伴侣蛋白。事实上，我们发现 MT 缺失细胞很少表达 SN，但将 MT 转染到 MT 缺失细胞中可以恢复表达。共沉淀实验表明MT可能直接与SN结合。目前正在进行研究来检验 SN 可能有助于铅诱导聚集体形成的假设。这些研究可能对铅致癌、锌生理学和可能与铅相关的神经退行性疾病产生重要影响。此外，由于未知原因，人类体内的 MT 水平差异很大，MT 产生不良可能是导致铅中毒和致癌的关键诱发因素。正在进行研究以进一步检验这一假设。例如，我们对 MT 小鼠的研究表明，经胎盘铅暴露会在成年后的后代中诱导适度水平的肾肿瘤形成，因此我们现在正在研究 MT 无效小鼠中经胎盘铅的肾致癌性，看看这种反应是否会增强。由于显然有一些人群对铅特别敏感，因此任何导致个体铅中毒的因素都非常重要