Identification and Characterization of Transferrin Receptor 1 and Other Novel HCV Entry Factors

Hepatitis C virus (HCV) is a liver tropic virus spread via blood. Because the majority of infections fail to clear, approximately 80% of patients develop a chronic infection. As a result, approximately 170 million people worldwide are chronically infected with high risk of a wide variety of liver pathologies making HCV the leading cause of liver transplantation in the U.S. With no preventative vaccine available and relatively ineffective treatment options, investigation of the HCV entry process is of particular importance as this represents a promising therapeutic target. Currently four cellular factors have been identified as being involved in HCV entry; however, failure of these factors to confer permissiveness to HCV infection to non-permissive cells suggests more entry factors remain to be identified. This study identifies and characterizes the role of transferrin receptor 1 (TfR1) and Niemann Pick C 1 Like 1 (NPC1L1) in the HCV entry process. Monitoring mRNA and protein levels of the iron uptake receptor TfR1, we found that HCV infection caused a decrease in both TfR1 mRNA and protein. In functional studies, TfR1 siRNA knockdown inhibited HCV infection. Looking more specifically at HCV entry, pre-incubation of cells with TfR1-specific antibodies resulted in a decrease in HCV infection as well as specific inhibition of entry of HCV pseudoparticles (HCVpp), but did not affect HCV replicon replication. Further mechanistic studies indicated that the HCV virion may directly interact with TfR1 at a later step in entry after CD81 and SRB1 interactions. In an analogous study, we discovered that NPC1L1 knockdown and antibody blocking inhibited HCV infection initiation, but not HCV replication or secretion. Importantly, there is already a FDA approved drug, ezetimibe, which inhibits NPC1L1 cholesterol uptake. Using an in vivo xenorepopulation mouse model of HCV infection, we demonstrated that blocking NPC1L1 with ezetimibe can inhibit subsequent HCV infection. Likewise, when ezetimibe is co-administered with IFN to treat chronic HCV infection in cells or mice we observed enhanced HCV inhibition. Thus, our findings identify TfR1 and NPC1L1 as novel HCV entry factors and highlight the utility of HCV entry as a potential therapeutic target.