The Glycoprotein 5 Is Cleaved by Cathepsin E during Porcine Reproductive and Respiratory Virus Membrane Fusion.

Hou, Jie; Li, Rui; Qiao, Songlin; Chen, Xin-Xin; Xing, Guangxu; Zhang, Gaiping

Porcine reproductive and respiratory syndrome (PRRS) is a serious viral disease affecting 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. Despite much research has been focusing on PRRSV infection, the detailed mechanisms involved in its membrane fusion remain to be elucidated. In the current study, we performed confocal microscopy in combination with constitutive active (CA) or dominant negative (DN) mutant, specific inhibitors and small interference RNAs (siRNAs), as well as other multiple approaches to explore PRRSV membrane fusion. We first observed that PRRSV membrane fusion occurred in Rab11-recycling endosomes during early infection with labeled virions and subcellular markers. We further demonstrated that low pH and cathepsin E in Rab11-recycling endosomes were critical for PRRSV membrane fusion. Moreover, PRRSV glycoprotein 5 (GP5) is identified to be cleaved by cathepsin E during this process. Taken together, our work actually provides in-depth information for PRRSV pathogenesis, which supports novel opportunities for the development of antiviral drugs and vaccines.IMPORTANCEPRRS, caused by PRRSV, is an economically critical factor in pig farming worldwide. As a lipid membrane-wrapped virus, merging of PRRSV envelope with host cell membrane is indispensible for viral infection. However, there is a lack of knowledge on its membrane fusion. Here, we first explored when and where PRRSV membrane fusion occurred. Furthermore, we determined which host cell factors were involved in the process. Importantly, PRRSV GP5 was 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 the molecular mechanisms of PRRSV infection, which lay a foundation for future applications in prevention and control of PRRS.