Wiens Mayim E, Smith Jason G
Department of Microbiology, University of Washington, Seattle, Washington, USA.
Department of Microbiology, University of Washington, Seattle, Washington, USA
J Virol. 2015 Mar;89(5):2866-74. doi: 10.1128/JVI.02901-14. Epub 2014 Dec 24.
Human papillomavirus (HPV) is a significant oncogenic virus, but the innate immune response to HPV is poorly understood. Human α-defensin 5 (HD5) is an innate immune effector peptide secreted by epithelial cells in the genitourinary tract. HD5 is broadly antimicrobial, exhibiting potent antiviral activity against HPV at physiologic concentrations; however, the specific mechanism of HD5-mediated inhibition against HPV is unknown. During infection, the HPV capsid undergoes several critical cell-mediated viral protein processing steps, including unfolding and cleavage of the minor capsid protein L2 by host cyclophilin B and furin. Using HPV16 pseudovirus, we show that HD5 interacts directly with the virus and inhibits the furin-mediated cleavage of L2 at the cell surface during infection at a step downstream of the cyclophilin B-mediated unfolding of L2. Importantly, HD5 does not affect the enzymatic activity of furin directly. Thus, our data support a model in which HD5 prevents furin from accessing L2 by occluding the furin cleavage site via direct binding to the viral capsid.
Our study elucidates a new antiviral action for α-defensins against nonenveloped viruses in which HD5 directly interferes with a critical host-mediated viral processing step, furin cleavage of L2, at the cell surface. Blocking this key event has deleterious effects on the intracellular steps of virus infection. Thus, in addition to informing the antiviral mechanisms of α-defensins, our studies highlight the critical role of furin cleavage in HPV entry. Innate immune control, mediated in part by α-defensins expressed in the genital mucosa, may influence susceptibility to HPV infections that lead to cervical cancer. Moreover, understanding the mechanism of these natural antivirals may inform the design of therapeutics to limit HPV infection.
人乳头瘤病毒（HPV）是一种重要的致癌病毒，但对HPV的先天免疫反应了解甚少。人α-防御素5（HD5）是泌尿生殖道上皮细胞分泌的一种先天免疫效应肽。HD5具有广泛的抗菌作用，在生理浓度下对HPV表现出强大的抗病毒活性；然而，HD5介导的针对HPV的抑制作用的具体机制尚不清楚。在感染过程中，HPV衣壳会经历几个关键的细胞介导的病毒蛋白加工步骤，包括宿主亲环素B和弗林蛋白酶对次要衣壳蛋白L2的展开和切割。使用HPV16假病毒，我们发现HD5在感染过程中在亲环素B介导的L2展开的下游步骤直接与病毒相互作用，并抑制弗林蛋白酶在细胞表面对L2的切割。重要的是，HD5不直接影响弗林蛋白酶的酶活性。因此，我们的数据支持一种模型，即HD5通过直接结合病毒衣壳封闭弗林蛋白酶切割位点，阻止弗林蛋白酶接近L2。
我们的研究阐明了α-防御素对非包膜病毒的一种新的抗病毒作用，其中HD5在细胞表面直接干扰关键的宿主介导的病毒加工步骤，即弗林蛋白酶对L2的切割。阻断这一关键事件对病毒感染的细胞内步骤有有害影响。因此，除了揭示α-防御素的抗病毒机制外，我们的研究还强调了弗林蛋白酶切割在HPV进入中的关键作用。由生殖黏膜中表达的α-防御素介导的先天免疫控制可能会影响导致宫颈癌的HPV感染的易感性。此外，了解这些天然抗病毒药物的机制可能会为限制HPV感染的治疗方法设计提供信息。
