Sayers Charlotte L, Elliott Gillian
Section of Virology, Faculty of Medicine, Imperial College London, United Kingdom.
Section of Virology, Faculty of Medicine, Imperial College London, United Kingdom
J Virol. 2016 Oct 28;90(22):10379-10389. doi: 10.1128/JVI.01582-16. Print 2016 Nov 15.
Herpes simplex virus 1 (HSV-1) infects humans through stratified epithelia that are composed primarily of keratinocytes. The route of HSV-1 entry into keratinocytes has been the subject of limited investigation, but it is proposed to involve pH-dependent endocytosis, requiring the gD-binding receptor nectin-1. Here, we have utilized the nTERT human keratinocyte cell line as a new model for dissecting the mechanism of HSV-1 entry into the host. Although immortalized, these cells nonetheless retain normal growth and differentiation properties of primary cells. Using short interfering RNA (siRNA) depletion studies, we confirm that, despite nTERT cells expressing high levels of the alternative gD receptor HVEM, HSV-1 requires nectin-1, not HVEM, to enter these cells. Strikingly, virus entry into nTERT cells occurred with unusual rapidity, such that maximum penetration was achieved within 5 min. Moreover, HSV-1 was able to enter keratinocytes but not other cell types at temperatures as low as 7°C, conditions where endocytosis was shown to be completely inhibited. Transmission electron microscopy of early entry events at both 37°C and 7°C identified numerous examples of naked virus capsids located immediately beneath the plasma membrane, with no evidence of virions in cytoplasmic vesicles. Taken together, these results imply that HSV-1 uses the nectin-1 receptor to enter human keratinocyte cells via a previously uncharacterized rapid plasma membrane fusion pathway that functions at low temperature. These studies have important implications for current understanding of the relationship between HSV-1 and its relevant in vivo target cell.
The gold standard of antiviral treatment for any human virus infection is the prevention of virus entry into the host cell. In the case of HSV-1, primary infection in the human begins in the epidermis of the skin or the oral mucosa, where the virus infects keratinocytes, and it is therefore important to understand the molecular events involved in HSV-1 entry into this cell type. Nonetheless, few studies have looked specifically at entry into these relevant human cells. Our results reveal a new route for virus entry that is specific to keratinocytes, involves rapid entry, and functions at low temperatures. This may reflect the environmental conditions encountered by HSV-1 when entering its host through the skin and emphasizes the importance of studying virus-host interactions in physiologically relevant cells.
单纯疱疹病毒1型（HSV-1）通过主要由角质形成细胞组成的复层上皮感染人类。HSV-1进入角质形成细胞的途径研究有限，但据推测涉及pH依赖的内吞作用，需要gD结合受体nectin-1。在此，我们利用nTERT人角质形成细胞系作为剖析HSV-1进入宿主机制的新模型。尽管这些细胞已永生化，但仍保留原代细胞的正常生长和分化特性。通过小干扰RNA（siRNA）缺失研究，我们证实，尽管nTERT细胞表达高水平的替代gD受体HVEM，但HSV-1进入这些细胞需要nectin-1而非HVEM。令人惊讶的是，病毒进入nTERT细胞的速度异常快，以至于在5分钟内就能达到最大穿透率。此外，在低至7°C的温度下，HSV-1能够进入角质形成细胞，但不能进入其他细胞类型，而在这种条件下内吞作用被证明完全受到抑制。对37°C和7°C时早期进入事件的透射电子显微镜观察发现，大量裸露病毒衣壳紧邻质膜下方，没有证据表明病毒粒子存在于细胞质囊泡中。综上所述，这些结果表明HSV-1通过一种以前未被描述的快速质膜融合途径利用nectin-1受体进入人角质形成细胞，该途径在低温下起作用。这些研究对当前理解HSV-1与其体内相关靶细胞之间的关系具有重要意义。
对于任何人类病毒感染，抗病毒治疗的金标准是防止病毒进入宿主细胞。就HSV-1而言，人类的初次感染始于皮肤表皮或口腔黏膜，病毒在那里感染角质形成细胞，因此了解HSV-1进入这种细胞类型所涉及的分子事件很重要。然而，很少有研究专门关注进入这些相关人类细胞的情况。我们的结果揭示了一种特定于角质形成细胞的病毒进入新途径，涉及快速进入且在低温下起作用。这可能反映了HSV-1通过皮肤进入宿主时遇到的环境条件，并强调了在生理相关细胞中研究病毒-宿主相互作用的重要性。
