Technologies for Proteome-Wide Discovery of Extracellular Host-Pathogen Interactions

Martinez-Martin, Nadia

In a later study, Carette et al. generated a KBM7-derived cell line named HAP1, haploid for all chromosomes [47] . Similarly to previous studies, the authors used the retroviral gene-trap approach to mutagenize HAP1 cells followed by deep sequencing to map more than 800.000 insertions. In this study, using a replication competent vesicular stomatitis virus (VSV) carrying the Ebola virus glycoprotein, a previously unknown entry receptor for Ebola virus was identified. Notably, these haploid cell screens identified six members of the HOPS complex, proteins known to play functions in endosomal/lysosomal trafficking, as well as the Niemann-Pick C1 (NPC1) transporter as the most prominent hit of the assay. It is worth noting that NPC1 is not a surface molecule but rather an endosomal receptor. These findings led the authors to propose a novel mechanism of entry by which Ebola virus is internalized into the endocytic pathway, followed by endosome maturation and cleavage of the surface glycoprotein of the virus. Endosome fusion, mediated by the HOPS complex, would allow interaction with NCP1 containing endosomes, triggering fusion and release of the viral genome into the cytosol. Multiple cell surface receptors can lead to internalization of the Ebola virus into the endocytic pathway [131] ; such redundancy in receptor usage likely explains why these receptors were not identified in the haploid cell screen [47] . Notably, independent studies have confirmed that NCP1 acts an intracellular receptor for Ebola, including a chemical screen approach, a study showing NCP1 dependence for infection of otherwise nonsusceptible cells, and more recently the elucidation of the crystal structure of this receptor bound to the Ebola virus glycoprotein [132] [133] [134] .