Molecular mechanisms of Myc-induced tumor neovascularization

描述(申请人提供)：本项目的目标是研究Myc癌蛋白促进肿瘤新生血管(新生肿瘤血管的生长)的分子机制。我们已经开发了一种实验系统，在该系统中，这种癌蛋白在小鼠结肠癌细胞中的过度表达会导致血管丰富的表型。我们确定，这在没有增加血管内皮生长因子(VEGF)产生的情况下发生。相反，Myc下调了强大的血管生成内源性抑制因子血栓反应蛋白-1和TSR超家族的其他几个成员。凝血酶敏感蛋白-1主要在信使核糖核酸周转水平下调，提示参与了介导信使核糖核酸降解的微RNA(MiRNAs)。事实上，Myc上调了其中一个miRNA簇(miR17-92)，其预测的目标包括血栓反应蛋白-1和其他TSR蛋白。用反义2‘-O-甲基寡核苷酸敲除miR17-92可部分恢复TSP1和CTGF的表达。相反，用miR17-92编码的逆转录病毒转导仅RAS细胞会降低TSP1和CTGF水平。这些关键发现也在HCT116人结肠癌细胞中重现。值得注意的是，miR17-92转导的小鼠细胞形成更大、更好灌流的肿瘤。因此，我们提出了以下总体假设：Myc对肿瘤新生血管的贡献是基于凝血酶反应蛋白-1和相关蛋白的下调，涉及miR17-92 microRNA簇的转录后机制。为了证实这一假设，我们建议实现以下特定目标：1.剖析miR17-92簇下调TSR蛋白的分子机制。2.探讨Myc依赖的TSR蛋白下调在Myc/RAS结肠癌细胞和人结肠癌移植瘤生长中的意义。3.探讨一过性Myc基因下调对肿瘤血管生成和整体生长的影响。在实现这些目标后，我们将能够开始大规模的临床前研究，进一步验证miR17-92和Myc作为体内非细胞自主治疗靶点。与公众健康相关：目前正在进行临床试验的有前景的抗癌药物之一是ABT-510。这种药物模仿了天然的肿瘤抑制因子凝血酶敏感蛋白的作用。我们的研究将有助于确定哪些类型的结直肠癌可能对ABT-510特别敏感，并允许有针对性的患者登记。此外，我们的研究确定某些microRNAs是抗血管生成治疗的潜在靶点。

DESCRIPTION (provided by applicant): The goal of this project is to investigate the molecular mechanisms by which the Myc oncoprotein enhances tumor neovascularization (the ingrowth of blood vessels into the nascent neoplasm). We have developed an experimental system wherein overexpression of this oncoprotein in murine colon carcinoma cells results in the hypervascular phenotype. We determined that this occurs without increased production of vascular endothelial growth factor (VEGF). Instead, Myc down-regulates the potent endogenous inhibitor of angiogenesis thrombospondin-1 and several other members of the TSR superfamily. Thrombospondin-1 is down-regulated primarily at the level of mRNA turnover, suggesting the involvement of microRNAs (miRNAs) which are known to mediate mRNA degradation. Indeed, Myc upregulates one of the miRNA clusters (miR17-92) whose predicted targets include thrombospondin-1 and other TSR proteins. miR17-92 knockdown with antisense 2'-O-methyl oligoribonucleotide partly restores Tsp1 and CTGF expression. Conversely, transduction of Ras-only cells with a miR17-92-encoding retrovirus reduces Tsp1 and CTGF levels. These key findings were also reproduced in HCT116 human colon carcinoma cells. Notably, miR17-92-transduced murine cells form larger, better-perfused tumors. Thus, we have formulated the following overall hypothesis: The contribution of Myc to tumor neovascularization is based on down-regulation of thrombospondin-1 and related proteins via a post-transcriptional mechanism involving the miR17-92 microRNA cluster. To corroborate this hypothesis, we propose to fulfill the following Specific Aims: 1. To dissect the molecular mechanisms underlying downregulation of TSR proteins by the miR17-92 cluster. 2. To establish the significance of Myc-dependent TSR protein down-regulation for neoplastic growth of Myc/Ras colonocytes and human colon cancer xenografts. 3. To elucidate the effects of transient Myc down-regulation on tumor vascularity and overall growth. After having fulfilled these Aims, we will be able to commence large-scale pre-clinical studies further validating miR17-92 and Myc as non-cell-autonomous therapeutic targets in vivo. RELEVANCE TO PUBLIC HEALTH: One of the promising anti-cancer drugs currently undergoing clinical trials is ABT-510. This drug mimics the effects of the natural tumor suppressor thrombospondin. Our research will help determine what types of colorectal cancer might be particularly sensitive to ABT-510 and allow for targeted patient enrollment. Additionally, our studies identify certain microRNAs as potential targets for anti-angiogenic therapies.