Role of cytokine induction in APOBEC3-mediated virus restriction

描述（由申请人提供）：APOBEC3 （A3）蛋白是赋予病毒感染内在免疫力的宿主细胞蛋白。人类有7种A3蛋白，包括人类A3 （hA3G）和hA3F. hA3G限制培养细胞受vif缺陷的人类免疫缺陷病毒1 （HIV-1）、灵长类动物泡沫病毒（PFV）、乙型肝炎病毒（HBV）、小鼠白血病病毒（MuLV）和小鼠乳腺肿瘤病毒（MMTV）的感染。与人类不同，小鼠基因组编码一个A3基因（mA3），该基因限制HIV-1、MuLV和MMTV的感染。最近，我们首次提供了体内证据，证明A3是一种抗病毒限制因子。通过比较mA3缺乏小鼠和mA3充足小鼠的MMTV感染，我们发现mA3在体内限制了该病毒的感染。最近，我们发现mA3限制了树突状细胞（dc）中的MMTV感染，树突状细胞是许多逆转录病毒感染的初始目标。本研究将利用MMTV-mA3模型系统，探讨mmtv诱导的促炎细胞因子诱导与mA3之间的关系。最近有研究表明，许多细胞因子可诱导培养细胞中hA3G和hA3F的表达。MMTV在感染途径中通过两个步骤诱导细胞因子的产生：首先，当病毒包膜蛋白与先天免疫受体toll样受体4 （TLR4）相互作用时，其次，当病毒感染的抗原呈递细胞（如dc）向T细胞呈递病毒超抗原（Sag）时。因此，MMTV感染也可能触发mA3的细胞表达。通过体外培养mA3-/-和mA3+/+小鼠的dc，我们将研究细胞因子处理是否诱导mA3表达以及这种诱导对MMTV感染的影响。我们还将进行动物研究，并在体内检测细胞因子诱导、mA3表达和病毒限制。为了确定mA3在感染途径的哪一步被诱导，我们将使用缺乏mA3、MyD88、TRIP和TLR4基因的小鼠和无法对病毒Sag蛋白产生反应的小鼠。由于其抗病毒特性，在感染早期阶段较高的mA3表达可能有助于让宿主免疫系统有时间限制病毒感染。

DESCRIPTION (provided by applicant): APOBEC3 (A3) proteins are host cellular proteins that confer intrinsic immunity to viral infections. Human have seven A3 proteins, including human A3 (hA3G) and hA3F. hA3G restricts infection of cells in culture by Vif-deficient human immunodeficiency virus 1 (HIV-1), primate foamy virus (PFV), hepatitis B virus (HBV), murine leukemia virus (MuLV), and mouse mammary tumor virus (MMTV). In contrast to humans, the mouse genome encodes a single A3 gene (mA3) which restrict infection by HIV-1, MuLV, and MMTV. Recently, we provided the first in vivo evidence that A3 is an antiviral restriction factor. By comparing MMTV infection in mice deficient in mA3 and their mA3-sufficient counterparts, we showed that mA3 restricted infection by this virus in vivo. More recently, we showed that mA3 restricts MMTV infection in dendritic cells (DCs), the initial targets of infection by many retroviruses. The studies proposed here will take advantage of the MMTV-mA3 model system to explore the relationship between mA3 and MMTV-induced pro-inflammatory cytokine induction. Recently, it has been shown that a number of cytokines induce expression of hA3G and hA3F in cultured cells. It is well-established that MMTV induces cytokine production at two steps in the infection pathway: first, when the virus envelope protein interacts with the innate immune receptor Toll-like receptor 4 (TLR4) and second, when virus-infected antigen presenting cells such as DCs present the viral superantigen (Sag) to T cells. Thus, it is likely that MMTV infection also triggers cellular expression of mA3. Using ex vivo cultures of DCs from mA3-/- and mA3+/+ mice, we will investigate if cytokine treatment induces mA3 expression and the effect of such induction on MMTV infection. We will also carry out animal studies and examine cytokine induction, mA3 expression and virus restriction in vivo. To determine at which step in the infection pathway mA3 is induced, we will use mice lacking mA3, MyD88, TRIP and TLR4 genes and mice unable to respond to the viral Sag protein. Because of its antiviral properties, higher mA3 expression during the early stages of infection may serve to allow the host's immune system time to limit virus infection. RELEVANCE: The proposed studies will use MMTV-mA3 model system to explore the regulatory mechanism(s) of mA3 and its interaction with the broader immune system. Indeed, it has been suggested that increasing hA3G expression through the use of agents that induce cytokine production could be used as an anti-HIV-1 therapy. Thus our studies will increase understanding of the cross-talk between A3 and the immune system and will set the stage for the use of this protein as a means of developing new anti-retroviral therapies