Reconstitution of a protective antiviral RNAi response in somatic human cells

描述（由申请人提供）：先前的工作已经证明，几种哺乳动物胚胎细胞系能够从转染的长dsRNA产生功能性siRNA，并且最近的报道已经证明胚胎干细胞也可以产生保护性抗病毒RNAi应答。相反，终末分化的哺乳动物体细胞不能从转染的长dsRNA或从病毒感染期间产生的dsRNA产生功能上显著水平的siRNA。我们假设这些胚胎细胞表达从dsRNA有效产生siRNA所需的因子，并且我们迄今为止集中于单个哺乳动物Dicer蛋白，部分原因是先前的生物化学工作已经证明存在抑制人Dicer在体外加工长dsRNA而不是pre-miRNA的能力的N-末端结构域。值得注意的是，我们的初步数据确实确定了N-末端截短形式的Dicer，其在胚胎畸胎瘤细胞中表达，但在人体细胞中不表达。该Dicer亚型的表征和功能分析是该资助申请的关键初始目标。 一旦确定了这种新型Dicer同种型的身份，我们将在实验室产生的称为NoDice的独特人类细胞系中表达这种蛋白质，以及人工N-末端人类Dicer缺失突变体和果蝇Dcr 1/locs-PB和Dcr 2/locs-PD蛋白伴侣，该细胞系缺乏任何功能性内源Dicer酶。然后，我们将确定我们是否可以在这些细胞中挽救microRNA加工并重建siRNA生产，在后一种情况下，在用RNA病毒攻击后。因此，这项研究的主要目标是确定为什么胚胎哺乳动物细胞能够在病毒感染时产生保护性RNAi反应，而体细胞缺乏这种能力，并在哺乳动物细胞中重建RNAi。然后，我们将分析RNAi是否可以保护细胞免受病毒的攻击，以便以后将这项研究扩展到病毒发病机制的体内模型中。总的来说，该项目不仅有可能揭示为什么RNAi在哺乳动物体细胞中无功能，而且还允许最初在培养的细胞中但随后也可能在体内有效重建这种潜在的高度保护性抗病毒先天免疫应答。

DESCRIPTION (provided by applicant): Previous work has demonstrated that several mammalian embryonic cell lines are able to generate functional siRNAs from transfected long dsRNAs and a recent report has demonstrated that embryonic stem cells can also mount a protective antiviral RNAi response. In contrast, terminally differentiated mammalian somatic cells are unable to generate a functionally significant level of siRNAs from either transfected long dsRNAs or from dsRNAs generated during viral infection. We hypothesize that these embryonic cells express a factor required for efficient siRNA production from dsRNAs and we have so far focused on the single mammalian Dicer protein, in part because previous biochemical work has documented the presence of an N- terminal domain that inhibits the ability of human Dicer to process long dsRNAs, but not pre-miRNAs, in vitro. Remarkably, our preliminary data have indeed identified an N-terminally truncated form of Dicer that is expressed in embryonic teratocarcinoma cells but not in human somatic cells. The characterization and functional analysis of this Dicer isoform are key initial goals of this grant application. Once th identity of this novel Dicer isoform is defined, we will express this protein, as well as artificia N-terminal human Dicer deletion mutants and the Drosophila Dcr1/locs-PB and Dcr2/locs-PD protein partners, in a unique human cell line generated in the laboratory, called NoDice, that lacks any functional endogenous Dicer enzyme. We will then determine if we can rescue microRNA processing and reconstitute siRNA production in these cells, in the latter case after challenge with RNA viruses. The main goal of this research is therefore to determine why embryonic mammalian cells are able to mount a protective RNAi response upon viral infection, while somatic cells lack this ability, and to reconstitute RNAi in mammalian cells. We will then analyze whether RNAi can protect cells against viral challenge with a view to later extending this research into in vivo models of viral pathogenesis. Overall, this project has the potential to not only reveal why RNAi is non- functional in mammalian somatic cells but also to allow the effective reconstitution of this potentially highly protective antiviral innate immune response, initially in cultured cells but potentially later also in vivo.