[Hepatic tropism of hepatitis C virus infection].

Hepatitis C virus (HCV) infects over 170 million people worldwide and is a major cause of life-threatening liver diseases such as liver cirrhosis and hepatocellular carcinoma. In current research, we aimed to clarify the mechanism of hepatic tropism of HCV infection. Although non-hepatic cells could not permit replication of HCV RNA, exogenous expression of liver specific miRNA, miR-122 facilitated efficient replication of viral RNA through direct interaction with 5'UTR of viral genome, indicating that miR-122 is one of the key determinants for hepatic tropism of HCV infection. In spite of efficient replication of viral RNA, formation of infectious particles was not observed in non-hepatic cells exogenously expressing miR-122. We found that expression of apolipoprotein E (ApoE) facilitated the formation of infectious HCV particles in non-hepatic cells, indicating that not only miR-122 but also ApoE participate in tissue tropism of HCV infection. To understand the exact roles of miR-122 and apolipoproteins in hepatic tropism of HCV, we established miR-122 and ApoB/ApoE knockout (KO) Huh7 cells, respectively. Although slight increase of intracellular HCV RNA and infectious titers in the culture supernatants was observed, propagation of HCV was impaired in miR-122 KO Huh7 cells. After serial passages of HCV in miR-122 KO cells, we obtained an adaptive mutant that possessed G28A substitutions in the 5'UTR of the HCV genome and exhibited efficient translation and replication in both miR-122 KO Huh7 and non-hepatic cells without exogenous expression of miR-122. These results suggest that HCV mutants replicating in non-hepatic cells in an miR-122-independent manner participate in the induction of extrahepatic manifestations in chronic hepatitis C patients. Deficiency of both ApoB and ApoE strongly inhibited the formation of infectious HCV particles. Interestingly, expression not only of ApoE but also of ApoA or ApoC could rescue the production of infectious HCV particles in ApoB/ApoE KO cells, suggesting that exchangeable apolipoproteins redundantly participate in the formation of infectious HCV particles.