Host RNA Processing Factors: Friend or Foe of Oncogenic Retroelements

描述（由申请人提供）：逆转录病毒是人类和动物中普遍存在的致癌物质。对于逆转录病毒小鼠乳腺肿瘤病毒（MMTV），当病毒遗传物质整合到宿主染色体并激活细胞原癌基因的表达时，癌症就会发生。虽然在20世纪30年代就被发现了，但像MMTV这样的逆转录病毒复制其基因组的机制以及细胞抵御逆转录病毒感染的策略还没有得到很好的理解。除了外源性逆转录病毒的威胁外，内源性逆转录因子，如LINE-1逆转录转座子，在细胞中积极复制，并通过失调控制细胞生长的细胞基因的表达、引起DNA双链断裂和诱导基因组不稳定，促进癌症的发生。我们的初步数据表明，MMTV可能与细胞质中与LINE-1逆转录转座子相同的宿主因子组相互作用，这提出了一种有趣的可能性，即一种共同的细胞途径已经进化到防御多种类型的逆转录因子。在MMTV的情况下，病毒衣壳在细胞质中与宿主mRNA加工因子Yb1、Mov10和Ago2相关的离散位点形成。我们设想MMTV RNA可能被运输到这些位点以避免翻译机制，而不是被包装成组装病毒衣壳。然而，对于LINE-1，这些相同的宿主因子似乎在宿主降解LINE-1 RNA和限制逆转录转位的防御努力中发挥核心作用。总之，这些观察结果导致了一个假设，即mRNA加工的细胞质位点代表了MMTV和LINE-1编码因子之间的战场，它们试图促进自身的复制，而宿主因子试图限制复制。我们将通过两个具体目标来检验这一假设。首先，聚焦于致癌逆转录病毒MMTV，我们将研究细胞mRNA加工因子表达水平改变对病毒衣壳组装、病毒生产和病毒感染性的影响。我们的目标是确定mRNA加工因子是促进病毒复制的步骤还是干扰MMTV的组装和传染性。无论结果如何，这些实验都将提供信息，并导致对MMTV生物学的更深入了解。其次，我们将通过检测MMTV衣壳和LINE-1编码核糖核蛋白复合物在同一细胞中的定位来确定是否有一个共同的细胞途径作用于MMTV和LINE-1逆转录因子。最后，控制其亚蜂窝传输的MMTV和LINE-1元件的特征将使用域交换功能增益方法进行识别。这些实验结果将为有助于癌症发展的后转录因子-宿主相互作用提供新的见解。在未来，我们可能会发现，如果这些宿主相互作用被其他逆转录元件共享，这些结果将广泛适用。最终，该研究可能为预防或治疗由逆转录病毒和反转录转座子引起的癌症提供新的靶点。

DESCRIPTION (provided by applicant): Retroviruses are ubiquitous agents that cause cancer in humans and animals. For the retrovirus mouse mammary tumor virus (MMTV), cancer arises when the viral genetic material becomes integrated into the host chromosome and activates the expression of cellular proto-oncogenes. Although discovered in the 1930s, the mechanisms used by retroviruses like MMTV to replicate their genomes and the strategies used by cells to defend against retrovirus infection are not well understood. In addition to the threat of exogenous retroviruses, endogenous retro-transcribing elements, like the LINE-1 retrotransposon, actively replicate in cells and contribute to cancer by dysregulating the expression of cellular genes that control cell growth, by causing DNA double-stranded breaks, and by inducing genomic instability. Our preliminary data suggest that MMTV may interact with the same group of host factors in the cytoplasm as reported for the LINE-1 retrotransposon, raising the intriguing possibility that a common cellular pathway has evolved to defend against multiple types of retro-transcribing elements. In the case of MMTV, viral capsids are formed at discrete sites in the cytoplasm that associate with host mRNA processing factors Yb1, Mov10, and Ago2. We envision that the MMTV RNA might be trafficking to these sites to avoid translation machinery, instead being packaged into assembling virus capsids. However, for LINE-1, these same host factors appear to play a central role in host defensive efforts to degrade LINE-1 RNA and limit retrotransposition. Together, these observations led to the hypothesis that cytoplasmic sites of mRNA processing represent the battleground between MMTV and LINE-1- encoded factors trying to promote their own replication and host factors trying to restrict replication. We will test this hypothesis through two specific aims. First, focusing on the oncogenic retrovirus MMTV, we will examine the effect of altered expression levels of cellular mRNA processing factors on viral capsid assembly, virus production, and virus infectivity. Our goal is to determine whether mRNA processing factors promote steps in virus replication or interfere with MMTV assembly and infectivity. Regardless of the outcome, these experiments will be informative and lead to a deeper understanding of MMTV biology. Second, we will determine whether a common cellular pathway acts on MMTV and LINE-1 retroelements by examining the localization of MMTV capsids and LINE-1 encoded ribonucleoprotein complexes in the same cells. Finally, features of MMTV and LINE-1 elements that control their subcellular trafficking will be identified using a domain-swapping gain-of-function approach. These experimental results will provide novel insights into retroelement-host interactions that contribute to the development of cancer. In the future, we may find that these results are broadly applicable if these host interactions are shared by other retro-transcribing elements. Ultimately, this research may provide new targets for the prevention or treatment of cancers caused by retroviruses and retrotransposons.