Mechanism and Function of ISG15 Conjugation

描述（由申请人提供）：1型干扰素（IFN）反应是抵抗病毒感染的第一道防线。在IFN刺激的细胞中诱导数百种蛋白质，并且这些蛋白质介导广谱抗病毒作用。ISG15是第一个被鉴定的IFN诱导的蛋白质之一，也是第一个被发现的泛素样蛋白（Ubl），然而多年来，其生物化学功能及其抗病毒活性的基础在很大程度上仍未被表征。 ISG15具有抗多种人类病毒的抗病毒活性，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是核糖体相关的，ISGylates蛋白以共翻译的方式，几乎没有靶蛋白特异性。我们进一步假设，在干扰素应答的背景下，新翻译的病毒蛋白，而不是细胞蛋白是该系统的主要目标，ISGylation是一种尝试，以取代病毒蛋白的功能。本提案的目的是检验这两种假设。 干扰素反应是一个多方面的防御盾牌，保护细胞免受各种各样的感染因子，但只有少数IFN诱导的蛋白质已在分子细节的特点。此外，干扰素在治疗上用于治疗病毒感染（例如，B和C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，但不知道哪些IFN诱导的蛋白介导有用的治疗效果以及哪些介导这些治疗的臭名昭著的副作用。对ISG15缀合的机制和功能的进一步理解将为在这些临床环境中上调或下调ISG化活性提供机会。 公共卫生相关性：ISG15缀合现在被认为是针对广泛的人类病毒感染的先天免疫应答的重要方面，并且干扰素疗法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治疗，必须表征干扰素应答系统的许多方面，包括ISG15途径。

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.