Virological and immunological mechanisms of hepatitis C virus persistence

• Antragsteller: Professor Dr. Ralf Friedrich Wilhelm Bartenschlager
• Fachliche Zuordnung: Virologie
• Förderung: Förderung von 2009 bis 2015
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 99161398

Hepatitis C virus (HCV) infections are characterized by a high rate of persistence. Although this phenomenon argues for viral strategies of immune evasion, the molecular mechanisms underlying inefficient virus control are still rather poorly defined. During the first funding period we established a cell culture system mimicking viral persistence and obtained evidence that HCV might exploit the stochastic of the interferon (IFN) response. Moreover, we demonstrated that domain 2 of nonstructural protein 5A suppresses induction of IFNα that is triggered by RIG-I and MDA5 in a serial- and LGP2-dependent manner. By using a siRNA based screen we identified effector proteins responsible for IFNα- and IFNγ-mediated suppression of HCV replication. Finally, by using live cell imaging we found that HCV triggers induction of stress granules in an IFNα-dependent manner. Their assembly and disassembly is highly dynamic which is important for cell survival and thus, persistence. In the next funding period we aim to continue our characterization of viral and cellular conditions essential for persistence. We will follow two complementary projects. The first one aims at understanding the dynamics of the IFN response and its impact on virus spread. Building on the results described above we will continue our studies by using live cell imaging to analyze the stochastic of the IFN response and its relation to virus spread. A caveat is that cell lines that are HCV permissive do not produce IFN and therefore, IFN response can only be studied upon exogenous addition of the cytokine. Thus, an important aim of this subproject is to establish HCV-permissive cell lines that are capable of endogenous IFN production, thus mimicking more closely the in vivo situation. Data generated in either system are used to set up and validate a mathematical model describing the stochastic of the IFN-response and predicting the outcome of HCV infection, i.e. persistence or virus elimination. Importantly, results will be validated with liver biopsies of HCV-infected patients and single cell analyses. Finally, we aim to measure T cell response in live cells and to study whether this response is also stochastic. The second project deals with the role of MDA5 in HCV-mediated activation of the IFN response and its suppression by NS5A. Here we will study two aspects: first, what is the recognition mechanism of HCV by MDA5 and how is it enhanced by LGP2? Second, what is the mechanism by which NS5A suppresses IFN production? The results of these studies will contribute to a better understanding of the strategies used by HCV to overcome innate immune responses.

• DFG-Verfahren: Forschungsgruppen
• Teilprojekt zu: FOR 1202: Mechanisms of persistence of hepatotropic viruses