Porcine reproductive and respiratory syndrome (PRRS) is a serious viral disease affecting the global swine industry. Its causative agent, PRRS virus (PRRSV), is an enveloped virus, and therefore membrane fusion between its envelope and host cell target membrane is critical for viral infection. Though much research has focused on PRRSV infection, the detailed mechanisms involved in its membrane fusion remain to be elucidated. In the present study, we performed confocal microscopy in combination with a constitutively active (CA) or dominant negative (DN) mutant, specific inhibitors, and small interfering RNAs (siRNAs), as well as multiple other approaches, to explore PRRSV membrane fusion. We first observed that PRRSV membrane fusion occurred in Rab11-recycling endosomes during early infection using labeled virions and subcellular markers. We further demonstrated that low pH and cathepsin E in Rab11-recycling endosomes are critical for PRRSV membrane fusion. Moreover, PRRSV glycoprotein 5 (GP5) is identified as being cleaved by cathepsin E during this process. Taken together, our findings provide in-depth information regarding PRRSV pathogenesis, which support a novel basis for the development of antiviral drugs and vaccines.IMPORTANCE PRRS, caused by PRRSV, is an economically critical factor in pig farming worldwide. As PRRSV is a lipid membrane-wrapped virus, merging of the PRRSV envelope with the host cell membrane is indispensable for viral infection. However, there is a lack of knowledge on its membrane fusion. Here, we first explored when and where PRRSV membrane fusion occurs. Furthermore, we determined which host cell factors were involved in the process. Importantly, PRRSV GP5 is shown to be cleaved by cathepsin E during membrane fusion. Our work not only provides information on PRRSV membrane fusion for the first time but also deepens our understanding of the molecular mechanisms of PRRSV infection, which provides a foundation for future applications in the prevention and control of PRRS.

中文翻译：

---

组织蛋白E在猪的生殖和呼吸系统综合症病毒膜融合过程中切割糖蛋白5。

猪繁殖与呼吸综合症（PRRS）是一种严重的病毒性疾病，影响着全球养猪业。它的病原体PRRS病毒（PRRSV）是一种包膜病毒，因此其包膜和宿主细胞靶膜之间的膜融合对于病毒感染至关重要。尽管许多研究集中在PRRSV感染上，但其膜融合所涉及的详细机制仍有待阐明。在本研究中，我们与组成型活性（CA）或显性阴性（DN）突变体，特异性抑制剂和小干扰RNA（siRNA）以及多种其他方法结合使用共聚焦显微镜，以探索PRRSV膜融合。我们首先观察到PRRSV膜融合发生在Rab11回收内体中，在早期感染期间使用标记的病毒粒子和亚细胞标记物。我们进一步证明了Rab11回收内体中的低pH和组织蛋白酶E对于PRRSV膜融合至关重要。此外，在此过程中，PRRSV糖蛋白5（GP5）被组织蛋白酶E切割。综上所述，我们的发现为PRRSV的发病机理提供了深入的信息，为抗病毒药物和疫苗的开发提供了新的基础。重要提示PRRSV引起的PRRS是全世界养猪业的经济关键因素。由于PRRSV是包裹脂质膜的病毒，因此PRRSV包膜与宿主细胞膜的融合对于病毒感染是必不可少的。然而，缺乏关于其膜融合的知识。在这里，我们首先探讨了PRRSV膜融合的时间和地点。此外，我们确定了该过程涉及哪些宿主细胞因子。重要的，PRRSV GP5显示在膜融合过程中被组织蛋白酶E裂解。我们的工作不仅首次提供有关PRRSV膜融合的信息，而且加深了我们对PRRSV感染的分子机制的了解，这为将来在PRRS的预防和控制中提供了基础。