Cathepsin L Processing of the Henipavirus F Proteins

Hendra and Nipah are zoonotic viruses with high mortality rates in humans, and both have been placed on MAID priority pathogens list. The fusion (F) proteins of Hendra and Nipah virus promote both virus-cell and cell-cell membrane fusion, thus mediating critical steps in viral infection. Recent work from our laboratory and others has shown that the cellular endosomal protease cathepsin L is critical for the proteolytic processing of both the Hendra and Nipah virus F proteins, delineating a novel mechanism for primary processing of viral glycoproteins. We have also demonstrated that cathepsin L-mediated proteolytic processing is necessary for promotion of cell-cell membrane fusion, making inhibition of cathepsin L a potentially viable strategy for antiviral therapy. Finally, endocytosis has been shown to play a role in the processing of both the Hendra F protein and the Nipah F protein, suggesting complex trafficking of the Henipavirus F proteins occurs prior to viral assembly. The reasons for this complex mechanism and its consequences for multiple facets of the viral Life cycle are currently unknown, but the requirement for cathepsin L processing suggests that this host enzyme may be an effective target for antiviral therapy. In this developmental grant, we will address the role of this unique activation mechanism in viral propagation and pathogenesis, and explore the utilization of cathepsin inhibitors as antiviral therapeutics for the -lenipaviruses. In Aim 1, we will define the impact of F protein trafficking and cathepsin cleavage on processes critical for viral propagation by examining whether viral particles containing uncleaved, non- Fusogenic F protein can promote entry via endocytosis followed by cathepsin L cleavage, and assessing Nhether F protein trafficking and/or cleavage modulates subsequent critical F-attachment (C) protein associations or virus-like particle (VLP) formation. In Aim 2, we will examine the utilization of cathepsin nhibitors as Henipavirus antivirals by identification of new inhibitors in a compound library screen, and ~xamination of the effects of identified inhibitors on F protein function, both in established cell-cell fusion assays and in endothelial and neuronal cells known to play critical roles in viral pathogenesis.