Probing the Role of Cyclophilin A in Hepatitis C Virus Replication and Host Tropism

Abstract

Hepatitis C virus (HCV) is a globally significant pathogen whose study in vivo has been limited by the virus’ poorly understood host tropism and the lack of a suitable small animal model. Immunodeficient mice genetically engineered to express critical human HCV entry factors are permissive to infection, but viral replication remains low. One potential barrier could be the absence or incompatibility of murine orthologs of vital host factors necessary for viral replication. In this study, we sought to explore the contribution of interspecies deviations in cyclophilin A (CypA) – an essential HCV replication host factor – to the virus’ restricted host tropism and poor replication in murine cells by quantifying the ability of CypA orthologs from a variety of non-human primates and mouse to restore HCV replication in CypA knockdown Huh7.5 cells. Here we have shown that while CypA orthologs from all great apes, bonobo, and rhesus macaque support HCV replication, those of pig-tailed macaque, squirrel monkey, tree shrew, and mouse cannot. By comparing the sequences of mouse and human CypA, which differ in 6 amino acids, we mapped the critical residues that are responsible for the apparent species-specific effects on HCV replication to residues 12, 14, 52, or 76. However, ectopic expression of hCypA in engineered murine hepatoma cells that are minimally permissive to HCV infection fails to augment viral replication, potentially suggesting that the murine orthologs of other essential co-factors are not capable of supporting hCypA’s function. To identify such interactors, we performed an AP-MS yielding a myriad of candidates that could possibly account for the diminished replicative capacity of mCypA and serve as molecular targets for the genetic augmentation of viral replication in mice.