Final Report Summary - VIRAL HOST FACTORS (Identification of Host Determinants for VirusEntry using a Haploid Genetic Approach)
The studies carried out for this project have yielded important new insights into the entry tactics used by different viruses that cause human disease. A new genetics approach using human cells that contain genes in only a single copy (haploid human cells) was applied to identify mutations in human genes that attenuate the entry of viruses. This pointed out new receptors that viruses use to enter human cells as well as genes that were required to prepare these receptors for engagement with pathogens. Identification of such 'receptor modifiers' pointed out additional genes that cause the severe heritable syndrome called Walker-Warburg syndrome. Upon binding to human cells most viruses are taken up into vesicles through a process referred to as endocytosis. It was thought that exit from endo-lysosomal vesicles was relatively uncomplicated and did not involve the requirement of specific human host factors. Our host factor surveys have expanded that view. First, we demonstrated that Ebola virus binds to a specific receptor protein in the endo-lysosomal compartment, NPC1, in order to reach the cytoplasm of human cells. Subsequently, we found that Lassa virus also requires a specific intracellular receptor (LAMP1) to exit endo-lysosomal vesicles. Most likely also Lujo virus uses a specific lysosomal receptor to reach the cytoplasm. Last, we found that Picornaviruses gained access to human cells in a special way: when the virus opens the endosomal membrane, this leads to the recruitment of different host factors. Whereas one host factor stimulates clearance of the 'infected' organelle the other host factor stimulates release of the viral RNA into the cytoplasm leading to the infection of human cells. Thus, these studies have provided important new insights into the interactions of viral pathogens with human cells.