Mechanism and Function of ISG15 Conjugation

描述（由申请人提供）：1 型干扰素 (IFN) 反应是抵御病毒感染的第一道防线。干扰素刺激的细胞中会诱导数百种蛋白质，这些蛋白质介导广泛的抗病毒作用。 ISG15 是第一个被鉴定的 IFN 诱导蛋白，也是第一个被发现的泛素样蛋白 (Ubl)，但多年来其生化功能和抗病毒活性的基础在很大程度上仍未得到表征。 ISG15 对多种人类病毒具有抗病毒活性，包括流感病毒、逆转录病毒、辛德比斯病毒、埃博拉病毒，并且 ISG15 与其他蛋白质缀合的能力可能对其在所有情况下的抗病毒活性至关重要。 ISG15 与 IFN 刺激的细胞中的数百种细胞蛋白缀合，并且单个 IFN 诱导的连接酶 Herc5 介导与几乎所有这些靶蛋白的缀合。基于大量的初步数据，我们假设 Herc5 与核糖体相关，并以共翻译方式 ISG 化蛋白质，几乎没有靶蛋白特异性。我们进一步假设，在干扰素反应的背景下，新翻译的病毒蛋白而不是细胞蛋白是该系统的主要目标，并且ISGylation是试图使病毒蛋白的功能失活。该提案的目的将检验这两个假设。 干扰素反应是一个多方面的防御屏障，可以保护细胞免受多种感染因子的侵害，但只有少数干扰素诱导的蛋白质得到了分子细节的表征。此外，干扰素还用于治疗病毒感染（例如乙型和丙型肝炎以及乳头瘤病毒）以及某些类型的癌症和多发性硬化症，但尚不清楚哪些干扰素诱导的蛋白质介导有用的治疗效果以及哪些介导这些疗法的臭名昭著的副作用。进一步了解 ISG15 缀合的机制和功能将为在这些临床环境中上调或下调 ISGylation 活性提供机会。 公共卫生相关性：ISG15 结合现在被认为是针对多种人类病毒感染的先天免疫反应的一个重要方面，并且干扰素疗法已被批准用于许多疾病状态。为了改善和调节抗病毒和干扰素疗法，必须表征干扰素反应系统的许多方面，包括 ISG15 通路。

DESCRIPTION (provided by applicant): The type 1-interferon (IFN) response is the first line of defense against viral infections. Hundreds of proteins are induced in IFN-stimulated cells, and these proteins mediate a wide spectrum of anti-viral effects. ISG15 was one of the first IFN-induced proteins to be identified and the first ubiquitin-like protein (Ubl) to be discovered, however its biochemical function and the basis of its antiviral activities have remained largely uncharacterized for many years. ISG15 has anti-viral activity against a wide range of human viruses, including influenza, retroviruses, sindbis, ebola, and the ability of ISG15 to be conjugated to other proteins is likely to be essential for its anti-viral activity in all cases. ISG15 is conjugated to hundreds of cellular proteins in IFN-stimulated cells, and a single IFN-induced ligase, Herc5, mediates conjugation to nearly all of these target proteins. Based on extensive preliminary data, we hypothesize that Herc5 is ribosome-associated and ISGylates proteins in a co-translational manner, with little target protein specificity. We further hypothesize that in the context of an interferon response, newly translated viral proteins, rather than cellular proteins are the primary targets of this system, and that ISGylation is an attempt to inactivate the function of viral proteins. The aims of this proposal will test both of these hypotheses. The interferon response is a mutli-faceted defensive shield that protects cells against a wide range of infectious agents, yet only a small number of IFN-induced proteins have been characterized in molecular detail. In addition, interferon is used therapeutically in treating viral infections (e.g., hepatitis B and C and papillomaviruses), as well as certain types of cancers and multiple sclerosis, yet it is not known which IFN-induced proteins mediate useful therapeutic effects and which mediate the notorious side effects of these therapies. A further understanding of the mechanism and function of ISG15 conjugation will present opportunities for either up- or down-modulating ISGylation activity in these clinical settings. PUBLIC HEALTH RELEVANCE: ISG15 conjugation is now recognized to be an important aspect of the innate immune response against a wide range of human viral infections, and interferon therapies are approved for many disease states. It is essential to characterize the many facets of the interferon response system, including the ISG15 pathway, in order to improve and modulate anti-viral and interferon therapies.