Lyssaviruses, including rabies virus (RABV), are the etiological agents of rabies, an incurable disease with a case fatality rate of 100% that causes >60,000 human deaths/year. In common with other human-pathogenic viruses, RABV infection depends on evasion of host interferon (IFN)-mediated immunity, which is mediated through the interaction of the RABV IFN-antagonist P-protein with IFN-activated signal transducers and activators of transcription (STATs) 1 and 2, which has been shown to be critical to disease progression in vivo. Intriguingly, recent data indicate that RABV P-protein also targets STAT3, a major mediator of signaling by IFNs and by members of the IL-6 cytokine family. Similar reports for IFN-antagonists of several paramyxoviruses indicate that STAT3 targeting might play critical roles in infection by many viruses. However the molecular details underlying STAT3 targeting, and outcomes in terms of cytokine signaling and disease, remain largely unresolved.

Using quantitative cell imaging, protein interaction analysis and immune signaling assays, we have analysed STAT3 targeting by P-proteins from a panel of diverse lyssaviruses, finding that P-protein inhibits STAT3 responses to cytokines of BOTH the IFN and IL-6 families, and that STAT3-targeting is highly conserved across the genus, indicative of important roles. Nevertheless, we also identified subtle but significant differences in STAT3 targeting between different lyssaviruses, and identified specific mutations of P-protein able to prevent STAT3 interaction. Importantly, these mutations also reduce pathogenicity in mice. Using these tools, we are currently determining the precise molecular basis of P-protein’s interaction with STAT3, and the roles of P-protein-STAT3 complexes in modulating antiviral immune signaling. This work should significantly enhance our understanding of the interaction of RABV with multiple cytokine signaling pathways, to reveal the extent of viral interference in immune signaling and its importance to disease, identifying new strategies to combat currently incurable rabies disease.