Department of Microbiology, University of Alabama at Birminghamgrid.265892.2, Birmingham, Alabama, USA.
J Virol. 2022 Apr 27;96(8):e0202821. doi: 10.1128/jvi.02028-21. Epub 2022 Apr 7.
BK polyomavirus (PyV) infects the genitourinary tract of >90% of the adult population. Immunosuppression increases the risk of viral reactivation, making BKPyV a leading cause of graft failure in kidney transplant recipients. Polyomaviruses have a small double-stranded DNA (dsDNA) genome that requires host replication machinery to amplify the viral genome. Specifically, polyomaviruses promote S phase entry and delay S phase exit by activating the DNA damage response (DDR) pathway via an uncharacterized mechanism requiring viral replication. BKPyV infection elevates expression of MutSα, a mismatch repair (MMR) pathway protein complex that senses and repairs DNA mismatches and can activate the DDR. Thus, we investigated the role of the MMR pathway by silencing the MutSα component, Msh6, in BKPyV-infected primary cells. This resulted in severe DNA damage that correlated with weak DNA damage response activation and a failure to arrest the cell cycle to prevent mitotic entry during infection. Furthermore, silencing Msh6 expression resulted in significantly fewer infectious viral particles due to significantly lower levels of VP2, a minor capsid protein important for trafficking during subsequent infections. Since viral assembly occurs in the nucleus, our findings are consistent with a model in which entry into mitosis disrupts viral assembly due to nuclear envelope breakdown, which disperses VP2 throughout the cell, reducing its availability for encapsidation into viral particles. Thus, the MMR pathway may be required to activate the ATR (ATM-Rad3-related) pathway during infection to maintain a favorable environment for both viral replication and assembly. Since there are no therapeutics that target BKPyV reactivation in organ transplant patients, it is currently treated by decreasing immunosuppression to allow the natural immune system to fight the viral infection. Antivirals would significantly improve patient outcomes since reducing immunosuppression carries the risk of graft failure. PyVs activate the DDR, for which there are several promising inhibitors. However, a better understanding of how PyVs activate the DDR and what role the DDR plays during infection is needed. Here, we show that a component of the mismatch repair pathway is required for DDR activation during PyV infection. These findings show that the mismatch repair pathway is important for DDR activation during PyV infection and that inhibiting the DDR reduces viral titers by generating less infectious virions that lack the minor capsid protein VP2, which is important for viral trafficking.
BK 多瘤病毒（PyV）感染了超过 90%的成年人口的泌尿生殖道。免疫抑制会增加病毒重新激活的风险，使 BKPyV 成为肾移植受者移植物失败的主要原因。多瘤病毒具有一个小的双链 DNA（dsDNA）基因组，需要宿主复制机制来扩增病毒基因组。具体而言，多瘤病毒通过一种未被描述的机制激活 DNA 损伤反应（DDR）途径，从而促进 S 期进入并延迟 S 期退出，这种机制需要病毒复制。BKPyV 感染会增加 MutSα的表达，MutSα 是一种错配修复（MMR）途径蛋白复合物，可感知和修复 DNA 错配，并能激活 DDR。因此，我们通过在 BKPyV 感染的原代细胞中沉默 MutSα 成分 Msh6 来研究 MMR 途径的作用。这导致了严重的 DNA 损伤，与 DDR 激活较弱以及在感染期间无法阻止细胞周期进入有丝分裂有关。此外，由于次要衣壳蛋白 VP2 的水平显著降低，因此沉默 Msh6 的表达导致传染性病毒颗粒显著减少，VP2 对于随后感染期间的运输很重要。由于病毒组装发生在核内，我们的发现与一种模型一致，即进入有丝分裂会由于核膜破裂而破坏病毒组装，核膜破裂会将 VP2 分散到整个细胞中，从而降低其封装到病毒颗粒中的可用性。因此，MMR 途径可能需要在感染期间激活 ATR（ATM-Rad3 相关）途径，以维持有利于病毒复制和组装的有利环境。由于目前尚无针对器官移植患者 BKPyV 重新激活的治疗方法，因此目前通过减少免疫抑制来治疗，以使天然免疫系统对抗病毒感染。抗病毒药物将显著改善患者的预后，因为减少免疫抑制会增加移植物失败的风险。PyV 激活 DDR，针对 DDR 有几种有前途的抑制剂。然而，需要更好地了解 PyV 如何激活 DDR 以及 DDR 在感染过程中扮演什么角色。在这里，我们表明，错配修复途径的一个组成部分是 PyV 感染期间 DDR 激活所必需的。这些发现表明，在 PyV 感染期间，错配修复途径对于 DDR 激活很重要，并且抑制 DDR 会通过生成缺乏次要衣壳蛋白 VP2 的传染性较低的病毒颗粒来降低病毒滴度，VP2 对于病毒运输很重要。
