Interfering with interferon: developing a reporter system to study the interaction between hepatitus C viral proteins and the interferon signalling pathway

Abstract

The aim of the project was to investigate the mechanism by which HCV evades therapeutic IFN treatment. This involved the development of novel testing systems and their application to patient samples. Initial experiments focused on flavivirus replicons and novel observations on effects of one of these replicons (dengue virus) on interferon signalling were made. The dengue replicon system was demonstrated to inhibit IFNa signalling by reducing the expression of STAT2, an essential component of the type I IFN signalling pathway. This phenomenom was then further examined in dengue virus infected human cells and again it was observed that the expression of STAT2 was reduced. The mechanism of STAT2 degradation was further explored and STAT2 expression was found to be restored using a proteasomal inhibitor. A second flavivirus replicon system involving BVDV was also developed as a reporter system, again with novel observations. The BVDV replicon system was shown to be sensitive to the antiviral effects of I FNa and was not shown to inhibit the IFNa signalling pathway. The BVDV replicon was tested as a reporter system using a well-known viral inhibitor of I FNa. The viral inhibitor, inhibited the antiviral action of IFNa on the BVDV reporter. Having developed and validated this system, the effects of a small number of patient derived samples were assessed and it was demonstrated that NS5a derived from a patient who failed to respond to IFNa treatment inhibited the effects of IFNa on the BVDV reporter. To increase the senstitivity of the assay the reporter cassette was then changed to a destabilised GFP for use in a FACS based assay.