CARCINOGEN INACTIVATION OF TUMOR SUPPRESSOR GENES IN P53 HAPLOINSUFFICIENT MICE.

P53 单倍体不足小鼠中肿瘤抑制基因的致癌灭活。

• 批准号: 6289910
• 负责人: JOHN EDGAR FRENCH
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF ENVIRONMENTAL HEALTH SCIENCES
• 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/6289910
• 关键词: bladder neoplasm; carbopolycyclic compound; carcinogen testing; carcinogens; chemical carcinogenesis; gene dosage; genetic models; immunocytochemistry; in situ hybridization; laboratory mouse; lymphoma; mutagen testing; mutagens; neoplasm /cancer genetics; sarcoma; single strand conformation polymorphism; southern blotting; tumor suppressor genes; tumor suppressor proteins

Human and rodent carcinogens (trans-species carcinogens) often demonstrate similar organotropic patterns of neoplasia. Understanding the role of p53 haploinsufficieny (i.e. synchronization of critical genetic events) in carcinogen specific induction of tissue specific neoplasia in genetically altered rodents is critical to determining the phenotypic similarities between humans and rodents. Rodent model systems have the advantage of being subject to experimental investigation. Only where relevant mechanisms between human and rodents can be investigated are we able to remove some of the uncertainty of extrapolation between mouse and human.After demonstrating different patterns of p53 LOH by Southern blotting, we are currently examining residual chromosome 11 heterozygosity in N5 generation C57BL/6 and 129/Sv alleles (C57BL/6 backcross strain) in order to better understand the mechanism of LOH. Three distinct patterns of LOH of LOH have been detected in the C57BL/6 p53 haploinsufficient mouse exposed to model carcinogens: 1) complete loss at each chromosome 11 SSLP loci, 2) LOH at each chromosome 11 but on a background of heterozygosity and, 3) LOH on a background of heterozygosity and linked to Trp53.LOH was common among the phenolphthalein-induced lymphomas and benzene-induced sarcoma. LOH was sporadic among the p-cresidine-induced bladder carcinomas. We contend that the mechanism underlying the difference between the lymphoma and sarcoma LOH profiles is related to the actions of the individual chemical or the pathophysiology of the specific tissue. We considered the possibility that normal cell contamination was the source of the background heterozygosity detected in the sarcomas. However, wildtype contamination appeared unlikely because the amount of background heterozygosity was consistent among the eight sarcomas examined. We speculate that the background heterozygosity is more likely related to the pathophysiology of the specific tissue. Efficient culling of damaged cells is consistent with a profile of complete LOH and the p53-dependent apoptotic potential of the thymus. It is not known if the mesothelium from which the sarcomas arose is less efficient in this regard. The background heterozygosity in the sarcomas was consistent with tumor heterogeneity. Therefore, loss of Trp53 was not prerequisite for the induction of benzene-induced sarcomagenesis. In contrast, Trp53 occurred in the lymphomas prior to clonal expansion as evidenced by the lack of background heterozygosity. Finding that a complete copy of chromosome 11 was lost suggested that, in lymphomas and sarcomas, Trp53 was lost through a mechanism involving dysfunctional segregation. A complete copy of chromosome 11 was also retained in these tumors. This may indicate the clastogenic actions of phenolphthalein and benzene was secondary. The LOH profiles of the p- cresidine-induced bladder tumors showed some tumors do retain a truncated copy of chromosome 11. Finding only sporadic loss of Trp53 suggested loss was not prerequisite for initiation of cresidine-induced bladder carcinogenesis. The possibility that loss of Trp53 was masked by normal cell contamination in some bladder tumors was eliminated from consideration since p53 (+/-) and p53 (+/+) templates were easily distinguishable (Figure 1, C). In the bladder tumors, Trp53 loss appeared on a background of heterozygosity, consistent with loss during late stages when genomic instability is generalized. However, loss of Trp53 was not insignificant in the bladder tumors. Selection for cells that lost Trp53 did occurred since LOH at SSLP markers was limited to loci closely linked to Trp53. - allele loss, loss of heterozygosity, p53, environmental carcinogens, neoplasia, mutagenesis, carcinogenesis, benzene, p-cresidine, phenolphthalein

人类和啮齿动物致癌物（跨物种致癌物）通常表现出类似的肿瘤嗜器官模式。了解p53单倍体不足（即关键遗传事件的同步）在致癌物特异性诱导转基因啮齿动物组织特异性瘤变中的作用，对于确定人类和啮齿动物之间的表型相似性至关重要。啮齿动物模型系统具有便于实验研究的优点。只有对人与啮齿动物之间的相关机制进行研究，我们才能消除鼠与人之间外推的一些不确定性。在通过Southern blotting证明了p53 LOH的不同模式后，我们目前正在检测N5代C57BL/6和129/Sv等位基因（C57BL/6回交菌株）的11号染色体剩余杂合性，以便更好地了解LOH的机制。在暴露于模型致癌物的C57BL/6 p53单倍体缺陷小鼠中检测到三种不同的LOH模式：1)每条染色体11号SSLP位点完全缺失，2)每条染色体11号位点存在杂合性背景的LOH， 3)杂合性背景的LOH与Trp53相关。LOH常见于苯致淋巴瘤和苯致肉瘤。LOH在p-cresidine诱导的膀胱癌中是散发性的。我们认为，淋巴瘤和肉瘤LOH谱之间差异的机制与个体化学物质或特定组织的病理生理作用有关。我们考虑了正常细胞污染可能是肉瘤中检测到的背景杂合性的来源。然而，野生型污染似乎不太可能，因为在检查的8个肉瘤中，背景杂合性的数量是一致的。我们推测背景杂合性更可能与特定组织的病理生理有关。对受损细胞的有效剔除符合完全LOH和胸腺p53依赖性凋亡电位的特征。目前尚不清楚产生肉瘤的间皮层在这方面是否效率较低。肉瘤的背景杂合性与肿瘤的异质性一致。因此，Trp53的缺失并不是苯诱导肉瘤发生的先决条件。相反，Trp53在克隆扩增之前发生在淋巴瘤中，缺乏背景杂合性证明了这一点。发现11号染色体的完整拷贝丢失表明，在淋巴瘤和肉瘤中，Trp53的丢失是通过一种涉及功能失调分离的机制。在这些肿瘤中也保留了11号染色体的完整拷贝。这可能表明酚酞和苯的致裂作用是次要的。对吖啶醇诱导膀胱肿瘤的LOH谱显示，一些肿瘤确实保留了11号染色体的截短拷贝。仅发现零星的Trp53缺失，提示缺失并不是克瑞辛诱导膀胱癌发生的先决条件。由于p53（+/-）和p53（+/+）模板很容易区分，因此排除了一些膀胱肿瘤中正常细胞污染掩盖Trp53缺失的可能性（图1，C）。在膀胱肿瘤中，Trp53缺失出现在杂合性背景下，与基因组不稳定普遍化的晚期缺失一致。然而，在膀胱肿瘤中，Trp53的缺失并非微不足道。由于SSLP标记上的LOH仅限于与Trp53密切相关的位点，因此确实发生了对失去Trp53的细胞的选择。-等位基因缺失，杂合性缺失，p53，环境致癌物，肿瘤，诱变，致癌，苯，对吖啶，酚酞