Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada.
Department of Biomedical and Molecular Sciences, Queen's University, Kingston, Ontario, Canada
J Virol. 2020 Jun 16;94(13). doi: 10.1128/JVI.00738-20.
Viral proteins pUL16 and pUL21 are required for efficient nuclear egress of herpes simplex virus 2 capsids. To better understand the role of these proteins in nuclear egress, we established whether nuclear egress complex (NEC) distribution and/or function was altered in the absence of either pUL16 or pUL21. NEC distribution in cells infected with pUL16-deficient viruses was indistinguishable from that observed in cells infected with wild-type viruses. In contrast, NEC distribution was aberrant in cells infected with pUL21-deficient virus and, instead, showed some similarity to the aberrant NEC distribution pattern observed in cells infected with pUs3-deficient virus. These results indicated that pUL16 plays a role in nuclear egress that is distinct from that of pUL21 and pUs3. Higher-resolution examination of nuclear envelope ultrastructure in cells infected with pUL21-deficient viruses by transmission electron microscopy showed different types of nuclear envelope perturbations, including some that were not observed in cells infected with pUs3 deficient virus. The formation of the nuclear envelope perturbations observed in pUL21-deficient virus infections was dependent on a functional NEC, revealing a novel role for pUL21 in regulating NEC activity. The results of comparisons of nuclear envelope ultrastructure in cells infected with viruses lacking pUs3, pUL16, or both pUs3 and pUL16 were consistent with a role for pUL16 in advance of primary capsid envelopment and shed new light on how pUs3 functions in nuclear egress. The membrane deformation activity of the herpesvirus nuclear egress complex (NEC) allows capsids to transit through both nuclear membranes into the cytoplasm. NEC activity must be precisely controlled during viral infection, and yet our knowledge of how NEC activity is controlled is incomplete. To determine how pUL16 and pUL21, two viral proteins required for nuclear egress of herpes simplex virus 2, function in nuclear egress, we examined how the lack of each protein impacted NEC distribution. These analyses revealed a function of pUL16 in nuclear egress distinct from that of pUL21, uncovered a novel role for pUL21 in regulating NEC activity, and shed new light on how a viral kinase, pUs3, regulates nuclear egress. Nuclear egress of capsids is required for all herpesviruses. A complete understanding of all aspects of nuclear egress, including how viral NEC activity is controlled, may yield strategies to disrupt this process and aid the development of herpes-specific antiviral therapies.
病毒蛋白 pUL16 和 pUL21 是单纯疱疹病毒 2 衣壳有效核输出所必需的。为了更好地理解这些蛋白在核输出中的作用，我们研究了在缺乏 pUL16 或 pUL21 的情况下，核输出复合物（NEC）的分布和/或功能是否发生改变。感染 pUL16 缺陷型病毒的细胞中 NEC 的分布与感染野生型病毒的细胞中观察到的分布没有区别。相比之下，感染 pUL21 缺陷型病毒的细胞中 NEC 的分布异常，并且与感染 pUs3 缺陷型病毒的细胞中观察到的异常 NEC 分布模式有些相似。这些结果表明，pUL16 在核输出中的作用与 pUL21 和 pUs3 不同。透射电子显微镜对感染 pUL21 缺陷型病毒的细胞中核膜超微结构的更高分辨率检查显示出不同类型的核膜扰动，其中一些在感染 pUs3 缺陷型病毒的细胞中没有观察到。在 pUL21 缺陷型病毒感染中观察到的核膜扰动的形成依赖于功能性的 NEC，揭示了 pUL21 在调节 NEC 活性方面的新作用。比较感染缺失 pUs3、pUL16 或 pUs3 和 pUL16 的病毒的核膜超微结构的结果与 pUL16 在原发性衣壳包被之前的作用一致，并为 pUs3 在核输出中的作用提供了新的认识。疱疹病毒核输出复合物（NEC）的膜变形活性允许衣壳穿过两个核膜进入细胞质。在病毒感染过程中，必须精确控制 NEC 活性，但我们对 NEC 活性如何受到控制的了解并不完整。为了确定单纯疱疹病毒 2 核输出所必需的两种病毒蛋白 pUL16 和 pUL21 如何发挥作用，我们研究了每种蛋白缺失如何影响 NEC 的分布。这些分析揭示了 pUL16 在核输出中的作用与 pUL21 不同，揭示了 pUL21 在调节 NEC 活性方面的新作用，并为 pUs3 如何调节核输出提供了新的认识。衣壳的核输出是所有疱疹病毒所必需的。全面了解核输出的各个方面，包括如何控制病毒 NEC 活性，可能会产生破坏这一过程的策略，并有助于开发针对疱疹病毒的特异性抗病毒疗法。
