Minimal Myc functional threshold for tumorigenesis

肿瘤发生的最小 Myc 功能阈值

基本信息

批准号：
10926353
负责人：
Susan Mackem
金额：
$ 14.77万
依托单位：
DIVISION OF BASIC SCIENCES - NCI
依托单位国家：
美国
项目类别：
财政年份：
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/10926353
关键词：
Acute Alleles Allografting Amplifiers Cells Compensation DNA Sequence Alteration Dependence Development Endothelium Future Gene Dosage Genetic Models Genetic Predisposition to Disease Genetic Recombination Genetic Transcription Genome Genomics Genotype Germ-Line Mutation Growth Hemangiosarcoma Immunohistochemistry Induction of Apoptosis Knockout Mice Li-Fraumeni Syndrome LoxP-flanked allele MYC Family Protein MYC gene Malignant Neoplasms Modeling Monitor Mus Neoplasms Oncogenic Outcome Pathologic Pathway interactions Patients Pharmaceutical Preparations Physiological RNA Recovery Reporter Role Siblings Spectral Karyotyping TP53 gene Tamoxifen Testing Therapeutic Thymic Lymphoma Tissues Tumor Promoters c-myc Genes cancer cell cell type conditional knockout design dosage effective therapy genetic testing mouse genetics mutant postnatal programs therapeutic target tumor tumor growth tumor progression tumorigenesis tumorigenic

项目摘要

We have designed a genetic test of the hypothesis that a minimum level of Myc function is required to "amplify" the transcriptional programs necessary for promoting and sustaining tumor formation. We employed the mouse p53 null mutant (p53 KO) as a robust tumor model to test for Myc-dependency by introducing modest changes in the endogenous c-Myc level (c-Myc+/-). Tumor-free survival times were compared in genetically similar p53 KO sibling mice that were either c-Myc+/+ (Myc WT; p53 KO), or c-Myc+/- (Myc-Het; p53 KO). Median tumor-free survival times doubled in the Myc-Het; p53 KO relative to Myc-WT (significant at P 0.0001). This difference was independent of the tumor type, with hemangiosarcoma and thymic lymphoma being the most common (83%) tumor types in both groups. Analyses of c-Myc genomic alterations and expression levels in p53 KO tumors, using Spectral Karyotyping (SKY), FISH, and quantitative RNA ISH and immunohistochemistry, revealed that compensation for the initially reduced endogenous c-Myc dosage had occurred in tumors arising in Myc-Het;p53 KO mice. Notably, in hemangiosarcomas, genome amplification achieved by several rounds of genome tetraploidization was consistently higher in the Myc-Het;p53 KO than in the Myc-WT;p53 KO tumors. Although thymic lymphomas of either genotype showed no genomic amplification, expression of Myc RNA and Myc protein were nevertheless comparably elevated in both the Myc-WT and Myc-Het tumors, suggesting that compensation for reduced Myc gene dosage had occurred at the transcriptional level. These results indicate that reduced endogenous c-Myc dosage substantially delays tumor development in mice that are genetically predisposed to neoplasia and that, in order for Myc-Het;p53 KO mice to develop tumors, a compensatory increase in expression of Myc, which can occur by multiple mechanisms, is required. We have also used allografts using of thymic lymphomas from p53 KO mice carrying conditional c-Myc-floxed and tamoxifen-dependent Cre alleles and a dual-fluorescent reporter to monitor recombination efficacy, in order to test whether reducing c-Myc will adversely impact established tumors (i.e. growth, progression) and found that after recovery from recombination induced apoptosis, tumor growth rate is substantially slowed when endogenous Myc dosage is acutely reduced. Our results strongly suggest that a modest reduction in Myc can curtail cancer growth and has important implications, particularly for extending tumor-free survival in patients with Li-Fraumeni syndrome (germline mutations in p53), as well as sporadic cancers. This study provides a framework and model for future analyses of c-Myc role in tumorigenesis and tumor progression and can be readily extended to other tumor types using analogous strategies, and other tumor promoters, such as oncogenic Ras. We are also exploring whether p53 tumors can arise at all in the context of severely reduced or absent c-Myc expression levels using a conditional knock-out approach to model hemangiosarcomas by removing both p53 and c-Myc selectively from endothelial tissues (Cdh5CreER) in post-natal young mice.

我们设计了一种基因检验，即需要最低水平的MYC功能来“放大”促进和维持肿瘤形成所需的转录程序。我们通过引入内源性C-MYC水平（C-MYC +/-）的适度变化来测试MYC依赖性的鲁棒肿瘤模型，以稳健的肿瘤模型（C-MYC +/-）来测试MYC依赖性。在遗传相似的p53 KO兄弟姐妹小鼠中比较了无肿瘤的生存时间，该小鼠是C-Myc+/+（Myc WT; p53 KO）或C-Myc +/-（myc-Het; p53 ko）。 MYC-HET中的无肿瘤中位生存时间翻了一番。 p53 KO相对于MYC-WT（p 0.0001显着）。这种差异与肿瘤类型无关，血管肉瘤和胸腺淋巴瘤是两组中最常见的（83％）肿瘤类型。使用光谱核分型（SKY），FISH和定量RNA ISH和免疫组织化学的C-MYC基因组改变和表达水平的分析表明，在Myc-Het; P53 Ko小鼠中，在Myc-Het; P53 Ko小鼠中都会在Myc-Het; P53 KO小鼠中发生肿瘤中最初减少的内源性C-Myc剂量的补偿。值得注意的是，在血管肉瘤中，MYC-HET中的几轮基因组四倍体化实现的基因组扩增始终高于Myc-WT； p53 KO肿瘤。尽管这两种基因型的胸腺淋巴瘤均未显示基因组扩增，但MYC-WT和MYC-HET肿瘤的MYC RNA和MYC蛋白的表达均相当升高，这表明在转录水平上发生了减少MYC基因剂量的补偿。这些结果表明，降低的内源性C-MYC剂量大大延迟了遗传上倾向于肿瘤的小鼠的肿瘤发育，并且为了Myc-Het； p53 KO小鼠发展肿瘤，是MYC表达的补偿性增加，MYC的表达增加可能是通过多种机制发生的。我们还使用了同种异体移植物使用来自p53 KO小鼠的胸腺淋巴瘤，这些胸膜淋巴瘤携带有条件的C-Myc氟纤维 - 氟和他莫昔芬依赖性CRE等位基因以及双荧光报告基因监测重置效率，以测试降低C-Myc的进展（即促进）的进展（即恢复），并恢复了良好的进展。当内源性myc剂量急性降低时，凋亡，肿瘤生长速率大大减慢。我们的结果强烈表明，MYC的适度降低可以减少癌症的生长并具有重要的影响，特别是对于扩大Li-Fraumeni综合征患者（p53中的生殖线突变）以及零星癌症患者的肿瘤生存期。这项研究提供了一个框架和模型，用于将来对C-MYC在肿瘤发生和肿瘤进展中的作用进行分析，并可以使用类似策略和其他肿瘤启动子（例如致癌RAS）轻松地扩展到其他肿瘤类型。我们还在探索p53肿瘤是否可以在严重降低或没有C-MYC表达水平的情况下使用有条件的敲除方法来通过从内皮组织（CDH5CREER）中删除p53和c-myc来对血管肉瘤进行建模，以模拟血管肉瘤。