Hendra virus trafficking and assembly

Hendra virus and Nipah virus, members of the Henipavirus genus of the paramyxovirus family, are zoonotic viruses with high mortality rates in humans. Like other paramyxoviruses, Henipaviruses spread infections from cell to cell and from host to host in the form of particles which are formed by budding from infected cell membranes. Particle assembly is coordinated by the viral matrix (M) proteins, which link together the viral glycoproteins and the viral ribonucleoproteins. We have recently defined a novel trafficking pathway involving the fusion (F) glycoprotein of Hendra virus which has important implications for Henipavirus particle assembly. The F protein initially reaches the cell surface in its immature, uncleaved form. It is then endocytosed from the plasma membrane and cleaved by the endosomal protease cathepsin L. Finally, the mature, fusion-active F protein is recycled to the plasma membrane and incorporated into budding virus particles. Combining our expertise in viral glycoprotein trafficking and paramyxovirus assembly, the Dutch and Schmitt laboratories examined the effect of Hendra F protein endosomal trafficking on virus assembly. Excitingly, our preliminary results suggest that an F mutant defective in endocytosis fails to efficiently incorporate into virus-like particles (VLPs). This assembly defect is not related to a requirement for cathepsin processing, as our preliminary data demonstrates that inhibition of cathepsin processing leads to efficient incorporation of uncleaved wt F protein into VLPs. We therefore hypothesize that the unique trafficking of the Hendra F protein is critical for virus assembly, potentially by facilitating interactions with key viral and host cell proteins. To examine this hypothesis, we will pursue three Specific Aims. In Aim 1, we will examine the role of Hendra virus F protein trafficking in virus assembly, through use of a comprehensive set of trafficking-altered F protein mutants. Our second aim is to define protein interactions that drive incorporation of the Hendra virus G protein into budding particles. Finally, in Aim 3 we will seek to identify host factors that interact with Hendra virus F protein and determine their role in viral assembly. These studies will provide new insight into the role endocytic trafficking of the Hendra F protein plays in the viral life cycle, provide exciting new insights into the assembly mechanism for this important human pathogen, and potentially identify new antiviral targets through characterization of host proteins involved in the assembly process.