A dive into the complexity of type I interferon antiviral functions

StephenW

http://www.journal-of-hepatology.eu/article/S0168-8278%2811%2900570-8/fulltext#back-b0020
Journal of Hepatology
Volume 56, Issue 3 , Pages 726-728, March 2012


A dive into the complexity of type I interferon antiviral functions

• Maxime Touzot
  ,
• Vassili Soumelis
  ,
• Tarik Asselah
  

Received 19 July 2011; accepted 20 July 2011.  published online 28 July 2011.

Article Outline

• Introduction
• Unresolved questions
• Novelty of this article
• Perspectives, unanswered questions
• Conclusions
• Conflict of interest
• References
• Copyright
  

COMMENTARY ON:
A diverse range of gene products are effectors of the type I interferon antiviral response. Schoggins JW, Wilson SJ, Panis M, Murphy MY, Jones CT, Bieniasz P, Rice CM. Nature. 2011 Apr 28;472(7344):481–485. Copyright (2011). Abstract reprinted by permission from Macmillan Publishers Ltd.http://www.ncbi.nlm.nih.gov/pubmed/21478870
Abstract: The type I interferon response protects cells against invading viral pathogens. The cellular factors that mediate this defense are the products of interferon-stimulated genes (ISGs). Although hundreds of ISGs have been identified since their discovery more than 25years ago, only a few have been characterized with respect to antiviral activity. For most ISG products, little is known about their antiviral potential, their target specificity, and their mechanisms of action. Using an overexpression screening approach, here we show that different viruses are targeted by unique sets of ISGs. We find that each viral species is susceptible to multiple antiviral genes, which together encompass a range of inhibitory activities. To conduct the screen, more than 380 human ISGs were tested for their ability to inhibit the replication of several important human and animal viruses, including hepatitis C virus, yellow fever virus, West Nile virus, chikungunya virus, Venezuelan equine encephalitis virus, and human immunodeficiency virus type-1. Broadly acting effectors included IRF1, C6orf150 (also known as MB21D1), HPSE, RIG-I (also known as DDX58), MDA5 (also known as IFIH1), and IFITM3, whereas more targeted antiviral specificity was observed with DDX60, IFI44L, IFI6, IFITM2, MAP3K14, MOV10, NAMPT (also known as PBEF1), OASL, RTP4, TREX1, and UNC84B (also known as SUN2). Combined expression of pairs of ISGs showed additive antiviral effects similar to those of moderate type I interferon doses. Mechanistic studies uncovered a common theme of translational inhibition for numerous effectors. Several ISGs, including ADAR, FAM46C, LY6E, and MCOLN2, enhanced the replication of certain viruses, highlighting another layer of complexity in the highly pleiotropic type I interferon system.

Back to Article Outline

Introduction Type I interferons are a family of major innate immune cytokines produced by host cells in response to viral infection [1]. Since their discovery 50years ago, fundamental and biomedical research has greatly improved our understanding of their molecular mechanisms of action, and led to the development of the first “cytokine-based” therapy in the 70s, now licensed worldwide for viral disease, malignant and even immune disorders [1], [2].
Interferon remains the therapeutic backbone of chronic hepatitis C. The standard of care, in HCV genotype 1 infected patients, is the addition of direct-acting antivirals (DAAs) with a protease inhibitor (telaprevir or boceprevir) to pegylated interferon plus ribavirin [3].
The type I interferon family is composed of 5 members in humans: the well described IFNα and IFNβ, along with IFNκ, IFNε, IFNω that are less characterized, and more tissue targeted [4], [5].
There are 13 IFNα and one IFNβ isoforms, all acting through a unique ubiquitous heterodimeric receptor IFNAR1/IFNAR2. Downstream signaling pathways have been extensively described: phosphorylation of tyrosine kinases JAK1 and TYK2 results in the recruitment of STAT1 and STAT2 which migrate into the nucleus and associate with IFN regulatory factor 9 (IRF9) to form the IFN-stimulated gene factor 3 (ISGF3). This complex then activates the transcription of all the IFN Stimulated Genes (ISGs), which mediate diverse cellular effects in the infected cell. The study of highly induced ISGs (MX1, OAS, dsRNA-activated protein kinase PKR) led to fundamental discoveries concerning the translational control and regulation of RNA stability [6].

Back to Article Outline

Unresolved questions The function of many ISGs, however, remains unknown, limiting our ability to manipulate IFN in a rational manner and predict its therapeutic and side effects. In particular, it is not known whether all ISGs share the same antiviral potential and/or mechanism of action.
In the issue of April 2011 of Nature, Schoggins and colleagues succeeded in answering these questions [7]. They proposed a new model to analyze the antiviral function of ISG in a systematic and large-scale manner. They developed a cell-based assay using a lentiviral vector co-expressing an ISG and a red fluorescent protein, TagRFP, in order to overexpress the ISG in different cell types. They subsequently challenged these cells with different green fluorescent proteins (GFP)-expressing viruses (including HCV) to assess the inhibitory capacity of all the ISG on viral replication by flow cytometry.
Interestingly, they identified 3 main categories of ISGs for each virus: a small group with strong inhibitory effect that probably has a feedback into the IFN-mediated signaling pathway; a major group with moderate inhibitory functions, and a small group that surprisingly enhances viral replication. Moreover, the use of combinations of two inhibitory ISGs increased the inhibition to 90% for HCV, HIV, and yellow fever virus replication.
Nucleic acid binding, hydrolase, and helicase activities were the main molecular functions of the ISG. The authors then investigated the potential mechanism of action of selected inhibitory ISGs. Translational inhibition appears to be a common mechanism of ISG-mediated antiviral effect which correlates with percent of inhibition. In the case of HCV, IRF1, IRF2, IRF7 MDA5, RIG-I, MAP3K14, and OASL were the most efficient ISG and inhibited primary translation by 25–70% after 4h of infection. None of them was able to significantly impair viral entry into the cell.
These results support the concept that the downstream effectors of Type I interferon exploit multiple strategies to block viral replication at an early stage, in an additive manner. Some of the ISGs, however, have the paradoxical effect of enhancing viral replication at least in this experimental model.

Back to Article Outline

Novelty of this article This is the first study on IFN downstream effectors to screen such large numbers of ISGs (380) in a systematic manner. Moreover, the reported findings point out new differences between ISGs in terms of viral replication and mechanism of action, which change our current view of ISG function (Fig. 1).

• 
• Fig. 1.

  New view of ISG’s function in viral replication. Interferon stimulated genes (ISG) can be divided in 3 groups: strong inhibitors, modest inhibitors or enhancers. ISGs use multiple strategies to inhibit viral replication: either by targeting specific phase of viral replication (e.g. primary translational inhibition) or/and by potentiating IFN response by a positive feedback loop. IFNAR, Interferon receptor; ISRE, Interferon response stimulating elements, IRF9, Interferon response factor 9.

  
  

Some ISGs have broad effects on different viruses (IRF1, C6orf150, RIG-1, MDA5) whereas others are more target-specific (IFI44l, IFI6, OASL, IFIT3M). Even if they don’t share the same mechanism of action, they can have additive effects to maximize viral inhibition. Capacity of viral inhibition varies among ISGs, and the authors showed for the first time that few of them could indeed enhance viral replication. It would be interesting now to test the ISGs on other viruses in order to have a complete view of ISGs functions.

Back to Article Outline

Perspectives, unanswered questions An important question remains whether the in vitro over-expression of the ISGs reflects in vivo expression. It is crucial to validate the targeted set of ISGs on in vivo or ex vivo samples. To date, several studies on liver gene expression in chronic hepatitis C have already identified a type I interferon signature (MX1, OAS1, IFI27, viperin) [8], [9], [10], [11]. None of these molecules appear to have a strong “inhibitory potential” for HCV replication according to the Shoggins study. Interestingly, in chronic hepatitis C, prior to the initiation of treatment, gene expression profiles differ between non-responders and responders. The most notable changes in gene expression are mainly observed in the IFN stimulated genes [12]. A two-gene signature (IFI27 and CXCL9) was able to predict treatment response. Interestingly, the baseline liver levels of expression of IFN stimulated genes were higher in non-responders than in sustained virological responders. The failure to respond to exogenous PEG-IFN in non-responders could indicate a blunted response to IFN. This suggests that IFN stimulated genes are already maximally induced in non-responders.
Furthermore, it seems also that some ISGs can enhance HCV replication but these were not described in details. Another paradoxical finding is that HCV through NS3-4A expression may inhibit the RIG-1 and MDA pathway that was found to be the most efficient inhibitor of HCV replication [13]. Follow up studies are necessary to extend and validate the Schoggins’ findings in complementary model systems, as well as on patient material.

Back to Article Outline

Conclusions In their study, Schoggins and colleagues bring new insight into the effector mechanisms of type I IFN responses. The understanding of antiviral mechanisms of IFN is crucial for the discovery of new treatment biomarkers for efficacy and toxicity. Moreover, there is a need for improvement of IFN therapy with regard to the clinical side effect and viral resistance. Focus on specific sets of ISGs could lead to the development of a more targeted therapy, by specifically inhibiting viral replication, while diminishing the side effects observed with type I IFNs. Future investigation and therapeutic clinical trials will be crucial to validate the potential of using ISGs in vivo.

Back to Article Outline

Conflict of interest The authors declared that they do not have anything to disclose regarding funding of conflict of interest with respect to this manuscript.







(6.合.彩)足球.篮球...各类投注开户下注

第一投注现金网:招代理年薪10万以上:yyu.cc

StephenW

StephenW

Type I型干扰素的抗病毒功能的复杂性

    马克西姆Touzot
    ，
    Vassili个人Soumelis
    ，
    的塔里克Asselahemail地址

7月19日收到2011年，2011年7月20日。 2011年7月28日网上公布。

   
文章大纲

    介绍
    悬而未决的问题
    新奇的这篇文章
    的角度来看，没有答案的问题
    结论
    利益冲突
    参考文献
    版权



述评：

各种不同的基因产物的I型干扰素的抗病毒反应的效应。 schoggins炜，威尔逊律政司司长，潘尼斯，墨菲我，琼斯CT，Bieniasz带够，水稻厘米。的性质。 2011年04月28日; 472（7344）:481-485。版权所有（2011）。摘要重印从麦克米伦出版Ltd.http :/ / www.ncbi.nlm.nih.gov/pubmed/21478870许可

摘要：I型干扰素反应保护细胞抵御入侵的病毒性病原体。调解这种防御的细胞因子，干扰素刺激基因（ISGs）的产品。虽然ISGs数百以来已超过他们的发现25年前确定，只有少数已具有抗病毒活性方面。对于大多数的ISG产品，他们的抗病毒药物的潜力，他们的目标专一，和它们的作用机制知之甚少。使用过度的筛选方法，在这里，我们表明，不同的病毒是针对独特的ISGs套。我们发现，每一个病毒的种类是易受多种抗病毒基因，它们共同抑制活动涵盖范围。为了进行屏幕进行了测试，超过380人ISGs他们的能力，抑制了几个重要的人类和动物的病毒，包括丙型肝炎病毒，黄热病病毒，西尼罗河病毒，基孔肯雅热病毒，委内瑞拉马脑炎病毒的复制，和人类免疫缺陷病毒1型。广泛行事效应包括IRF1，C6orf150（也作为MB21D1已知）的RIG-I（HPSE的，也被称为DDX58），MDA5（也称为IFIH1），IFITM3，而更有针对性的抗病毒的特异性与DDX60观察，IFI44L，IFI6 ，IFITM2，MAP3K14，MOV10，NAMPT（也PBEF1），OASL，RTP4，TREX1，UNC84B（也称为SUN2）。联合表达对ISGs表明中度I型干扰素剂量的添加剂类似的抗病毒效果。机理研究发现了一个共同的主题转化为众多效应抑制。几个ISGs，包括亚达，FAM46C，LY6E，MCOLN2，提高了某些病毒的复制，强调在高度多效性的I型干扰素系统的复杂性的另一个层。


介绍

I型干扰素是宿主细胞在病毒感染[1]的主要先天免疫细胞因子的家庭。由于他们的发现50years前，基本和生物医学研究已大大提高我们行动的分子机制的了解，并导致许可病毒性疾病，恶性肿瘤，甚至全球的发展，在70年代的第一个“细胞因子为主的”治疗免疫系统疾病[1] [2]。

干扰素仍然是治疗慢性丙型肝炎的护理标准的骨干，在丙型肝炎病毒基因型1感染的病人，是一种蛋白酶抑制剂（telaprevir治疗或boceprevir）聚乙二醇干扰素联合利巴韦林[3]除了直接作用抗病毒药物（DAAS） 。

I型干扰素家族成员5人组成的描述与IFNκIFNα和IFNβ，IFNε，IFNω，少的特点，多组织有针对性的[4] [5]。

有13IFNα和IFNβ亚型之一，通过一个独特的无处不在的异二聚体受体IFNAR1/IFNAR2行事。下游信号通路已被广泛描述：磷酸化酪氨酸激酶的JAK1和TYK2结果在招聘STAT1和STAT2迁移到细胞核与干扰素调节因子9（IRF9）联营公司，形成干扰素刺激基因因子3（ISGF3） 。这种复杂的，然后激活所有的干扰素刺激基因（ISGs），其中调解不同细胞的影响，在被感染的细胞的转录。关于平移的控制和调节RNA稳定性的基本发现导致研究的高度诱导ISGs（MX1，美洲国家组织，双链RNA激活的蛋白激酶PKR的）[6]。


悬而未决的问题

然而，许多ISGs的功能，仍是未知，限制了我们的能力去操纵干扰素在一个合理的方式，并预测其疗效和副作用。特别是，它不知道是否所有的ISGs共享相同的抗病毒药物的潜力和/或作用机制。

在自然2011年4月的问题，Schoggins和他的同事成功地回答了这些问题[7]。他们提出了一个新的模型来分析抗病毒功能的ISG系统和大规模的方式。他们开发了一种基于细胞的检测，使用共表达慢病毒载体ISG和红色荧光蛋白，TagRFP，为了在不同类型的细胞过度的ISG。随后他们与不同的绿色荧光蛋白（GFP）的表达病毒（HCV）的挑战，这些细胞来评估所有的ISG通过流式细胞仪检测病毒复制的抑制能力。

有趣的是，他们发现3 ISGs每一个病毒的种类主要为：小群具有很强的抑制作用，很可能有一个干扰素介导的信号转导通路的反馈，一个温和的抑制功能的主要群体，小组令人惊讶的增强病毒复制。此外，两个抑制ISGs组合使用，增加了90％的抑制丙型肝炎病毒，艾滋病毒和黄热病病毒复制。

核酸结合，水解酶，解旋酶的活动，主要分子功能的ISG。然后提交调查选择抑制ISGs行动的潜在机制。翻译抑制，似乎是一个ISG-介导的抗病毒效应的共同机制，抑制％相关。在丙型肝炎病毒，IRF1，IRF2，IRF7 MDA5的RIG-I，MAP3K14，OASL的情况下，最有效的ISG和4h后的25-70％的感染主要翻译抑制。他们没有能够大大削弱进入细胞的病毒进入。

这些结果支持这一概念，I型干扰素的下游效应，利用多种策略，阻止病毒复制，在添加剂的方式，在早期阶段。然而，一些ISGs有矛盾的影响，加强病毒的复制，至少在这个实验模型。


新奇的这篇文章

这是干扰素下游效应的第一项研究中有系统地筛选等大型ISGs号码（380）。此外，该报告的调查结果指出，在病毒复制的作用机制，其中ISG功能改变我们当前视图（图1）新ISGs之间的差异。

    查看完整大小的图片。
      
图1。

    ISG的病毒复制功能的新观点。干扰素刺激基因（ISG）可分为3组：强抑制剂，适度抑制剂或增强剂。 ISGs使用多种策略，以抑制病毒复制：通过针对特定阶段（如初级翻译抑制病毒复制）或/和potentiating一个正反馈循环干扰素反应。 ; ISRE IFNAR，干扰素受体，干扰素反应的刺激元素，IRF9，干扰素响应因子9。

有些ISGs有广泛的影响在不同的病毒（IRF1，C6orf150的RIG-1，MDA5），而另一些特定目标（IFI44l，IFI6，OASL，IFIT3M）。即使他们不共享相同的行动机制，他们可以有累加效应，以最大限度地提高病毒抑制。病毒抑制能力各不相同ISGs，作者第一次表明，其中一些确实可以增强病毒复制。这将是有趣的，现在其他病毒测试ISGs ISGs功能有一个完整的视图。

的角度来看，没有答案的问题

一个重要的问题仍然是，无论是在体外，在体内表达过度表达的ISGs反映。关键是要验证在体内或体外样本ISGs针对性。到今天为止，慢性丙型肝炎对肝脏基因表达的几个研究已经发现了I型干扰素的签名（MX1，OAS1，IFI27，viperin）[8] [9] [10] [11]。这些分子都没有出现有强烈的“抑制潜在的”丙型肝炎病毒复制，根据Shoggins研究。有趣的是，在慢性丙型肝炎，治疗开始前，基因表达谱不同非应答和响应。在基因表达的最显着的变化主要是观察干扰素刺激基因[12]。两基因签名（IFI27和CXCL9）是能够预测治疗反应。有趣的是，在基线肝干扰素刺激基因的表达水平高于非应答在持续病毒学应答。未能响应外源性PEG-干扰素无应答干扰素可能表明迟钝反应。这表明，干扰素刺激基因已经最大限度地诱导无反应。

此外，似乎也有些ISGs可以提高丙型肝炎病毒复制，但这些都没有详细描述。另一个似是而非的结论是可能抑制丙型肝炎病毒，通过病毒NS3-4A表达的RIG-1和MDA的途径，被认为是最有效的丙型肝炎病毒复制抑制剂[13]。跟进研究是必要的延伸和互补模型系统验证了Schoggins的调查结果，以及对病人的材料。


结论

在他们的研究中，Schoggins和他的同事们分为I型干扰素反应的效应机制带来了新的见解。干扰素的抗病毒机制的理解是至关重要的新的治疗方法的疗效和毒性的生物标志物的发现。此外，有需要改善干扰素治疗方面的临床副作用和病毒抗性。专注于特定的ISGs套可能导致更有针对性的治疗，特别是抑制病毒复制，发展，同时减少侧面观察效果与I型干扰素。未来的调查和治疗的临床试验将是至关重要的，以验证使用ISGs在体内的潜力。


利益冲突

作者宣称，他们没有任何关于这个手稿披露利益冲突有关的资金。