The Role of Cyclophilin a in Hepatitis C Virus Life Cycle
Yang, Feng (author)
Tang, Hengli (professor directing dissertation)
Stefanovic, Branko (university representative)
Bass, Hank W. (committee member)
Roux, Kenneth H. (committee member)
Zhu, Fanxiu (committee member)
Department of Biological Science (degree granting department)
Florida State University (degree granting institution)
Hepatitis C virus (HCV) infection leads to acute and chronic liver disease for thousands of people every year. With the absence of an effective treatment method, new classes of anti-HCV therapies are needed. Cyclosporine (CsA) and its derivatives potently suppress HCV replication. Recently, CsA resistant HCV replicons have been identified in vitro. We examined the dependence of the wild-type and CsA resistant HCV replicons on various cyclophilins for replication. A strong correlation between CsA resistance and reduced dependency on cyclophilin A (CyPA) for replication was identified. Silencing CyPB or CyPC expression had no significant effect on replication, whereas various forms of small interfering RNA (siRNA) directed at CyPA inhibited HCV replication of wild-type but not CsA-resistant replicons. The efficiency of a particular siRNA in suppressing CyPA expression was correlated with its potency in inhibiting HCV replication, and expression of a siRNA-resistant CyPA cDNA rescued replication. In addition, an anti-CyPA antibody blocked replication of the wild-type but not the resistant replicon in an in vitro replication assay. Depletion of CyPA alone in the CsA-resistant replicon cells eliminated CsA resistance, indicating that CyPA is the chief mediator of the observed CsA resistance. The dependency on CyPA for replication was observed for both genotype (GT) 1a and 1b replicons as well as a GT 2a infectious virus. An interaction between CyPA and HCV RNA as well as the viral polymerase that is sensitive to CsA treatment in wild-type but not in resistant replicons was detected. These findings reveal the molecular mechanism of CsA resistance and identify CyPA as a critical cellular cofactor for HCV replication and infection. In addition, we selected mutant viruses that were able to infect CyPA-knock down cells. Five independent selections revealed related mutations in a single dipeptide motif (D316 and Y317) located in a proline-rich region of NS5A domain II, which has been implicated in CyPA binding by nuclear magnetic resonance. Engineering the mutations into wild-type HCV fully recapitulated the CyPA-independent and CsA-resistant phenotype. Four putative proline substrates of CyPA were mapped to the vicinity of the DY motif. This study describes a new genetic approach to identifying viral targets of cellular cofactors and identifies a major regulator of HCV's susceptibility to CsA and its derivatives that are currently in clinical trials. This approach could be applied broadly to other cofactors in other viruses as large numbers of cellular cofactors important for viral infection have been discovered since the advent of genome-wide small interfering RNA screening.
Hepatitis C viurs, Cyclophilin, Cyclosporin A, NS5A, NS5B
June 25, 2010.
A Dissertation submitted to the Department of Biological Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
Hengli Tang, Professor Directing Dissertation; Branko Stefanovic, University Representative; Hank W. Bass, Committee Member; Kenneth H. Roux, Committee Member; Fanxiu Zhu, Committee Member.
Florida State University
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