c-Myc-regulated microRNAs in normal and pathologic cellular physiology

描述(申请人提供)：c-myc原癌基因表达异常是人类恶性肿瘤中最常见的异常之一。通过一个庞大的靶基因网络的控制，这种转录因子驱动增殖，在某些情况下，诱导细胞死亡。尽管在c-Myc调控基因的鉴定方面取得了很大进展，但该癌基因促进肿瘤发生的机制尚不完全清楚。MicroRNAs是一类18-24个核苷酸的RNA分子，是真核基因表达的主要调控因子。我们最近发现了一组被c-Myc直接上调的microRNAs，称为mir-17簇。独立地，这些microRNAs被证明在促进肿瘤形成方面与c-Myc协同作用。我们现在还发现了一组被c-Myc直接抑制的microRNAs。其中许多已知在癌症中被缺失或突变，这表明它们具有肿瘤抑制活性。我们现在提出的研究旨在检验这一假设，即这些c-Myc调控的microRNAs是c-Myc靶基因网络的关键组成部分，调控细胞增殖、凋亡和肿瘤转化。在这个项目的目标1中，我们将研究mir-17簇在多种细胞类型中表达或抑制的表型后果。这些实验对于对这些microRNA影响致癌表型的机制进行详细的分子分析是必要的。我们将在这个目标的后半部分开始研究这些机制，在那里我们检验了mir-17簇通过调节p21WAF1影响细胞周期控制的假设。在目标2中，我们将继续剖析mir-17簇影响细胞表型的机制。在这里，我们将测试这样的假设，即mir-17簇参与了一个生理负反馈电路，该电路在未转化的细胞中维持c-Myc和其他Myc家族成员的严格控制表达。最后，在目标3中，我们将研究microRNA抑制在c-Myc介导的肿瘤发生中的作用。将确定c-Myc直接抑制的microRNAs的特征，并确定这些microRNAs在体外和体内淋巴瘤模型中强制表达的后果。我们设想，这些实验将揭示在癌症中异常发挥作用的新的调节电路，并可能最终服从于治疗干预。

DESCRIPTION (provided by applicant): Dysregulated expression of the c-MYC proto-oncogene is one of the most frequent abnormalities in human malignancies. Through the control of an expansive target gene network, this transcription factor drives proliferation and, in some settings, induces cell death. Despite great advances in the identification of c-Myc-regulated genes, the mechanisms through which this oncogene promotes tumorigenesis are not yet fully understood. MicroRNAs are ~18-24 nucleotide RNA molecules that have emerged as major regulators of eukaryotic gene expression. We recently identified a group of microRNAs, known as the mir-17 cluster, that are directly upregulated by c-Myc. Independently, these microRNAs were shown to cooperate with c-Myc in promoting tumorigenesis. We have now also identified a cohort of microRNAs that are directly repressed by c-Myc. Many of these are known to be deleted or mutated in cancer, suggesting that they possess tumor suppressor activity. We now propose studies designed to test the hypothesis that these c-Myc-regulated microRNAs are critical components of the c-Myc target gene network that regulate cellular proliferation, apoptosis, and neoplastic transformation. In Aim 1 of this project, we will investigate the phenotypic consequences of expression or inhibition of the mir-17 cluster in multiple cell types. These experiments are necessary to set the stage for detailed molecular analyses of the mechanisms through which these microRNAs influence oncogenic phenotypes. We will begin to investigate these mechanisms in the latter part of this aim, where the hypothesis that the mir-17 cluster influences cell-cycle control through regulation of p21WAF1 is tested. In Aim 2, we will continue to dissect the mechanisms through which the mir-17 cluster influences cellular phenotypes. Here, we will test the hypothesis that the mir-17 cluster participates in a physiologic negative-feedback circuit that maintains tightly-controlled expression of c-Myc and other Myc family members in non-transformed cells. Finally, in Aim 3, we will investigate the role of microRNA repression in c-Myc-mediated tumorigenesis. MicroRNAs that are directly repressed by c-Myc will be characterized and the consequences of enforced expression of these microRNAs in in vitro and in vivo models of lymphoma will determined. We envision that these experiments will reveal novel regulatory circuitry that functions abnormally in cancer and may ultimately be amenable to therapeutic intervention.