Date Published: July 19, 2018
Publisher: Public Library of Science
Author(s): Janina Bruening, Lisa Lasswitz, Pia Banse, Sina Kahl, Carine Marinach, Florian W. Vondran, Lars Kaderali, Olivier Silvie, Thomas Pietschmann, Felix Meissner, Gisa Gerold, Aleem Siddiqui.
Hepatitis C virus (HCV) and the malaria parasite Plasmodium use the membrane protein CD81 to invade human liver cells. Here we mapped 33 host protein interactions of CD81 in primary human liver and hepatoma cells using high-resolution quantitative proteomics. In the CD81 protein network, we identified five proteins which are HCV entry factors or facilitators including epidermal growth factor receptor (EGFR). Notably, we discovered calpain-5 (CAPN5) and the ubiquitin ligase Casitas B-lineage lymphoma proto-oncogene B (CBLB) to form a complex with CD81 and support HCV entry. CAPN5 and CBLB were required for a post-binding and pre-replication step in the HCV life cycle. Knockout of CAPN5 and CBLB reduced susceptibility to all tested HCV genotypes, but not to other enveloped viruses such as vesicular stomatitis virus and human coronavirus. Furthermore, Plasmodium sporozoites relied on a distinct set of CD81 interaction partners for liver cell entry. Our findings reveal a comprehensive CD81 network in human liver cells and show that HCV and Plasmodium highjack selective CD81 interactions, including CAPN5 and CBLB for HCV, to invade cells.
The liver is the site of initial replication of diverse parenterally transmitted pathogens. Hepatitis C virus (HCV) and the malaria parasite Plasmodium both enter the liver through the sinusoids and infect hepatocytes using the two host proteins CD81 and scavenger receptor class B member 1 (SCARB1) [1–5]. In particular, CD81 is essential for infection with both pathogens as mice are only susceptible to HCV when expressing human CD81 and blocking CD81 on human hepatocytes impairs P. falciparum infection [4,6]. While HCV binds to the ectodomain of CD81 and co-internalizes with CD81 into clathrin-coated vesicles [5,7], P. falciparum and the murine parasite P. yoelii do not seem to directly interact with CD81, but still require CD81 for productive uptake into hepatocytes [4,8].
Our study identifies CAPN5 and CBLB as components of the CD81 receptor complex and as HCV entry facilitators. We demonstrate that HCV binding to CD81 on the liver cell surface is not an isolated event, but steady state CD81 protein interactions are required for virion uptake. Specifically, we mapped protein interactions of CD81 in resting human hepatocytes and demonstrate that a subset of preexisting CD81 interactions is necessary for HCV infection.