Novel Antiviral Mechanisms of the Interferon System

Contact PD/PI: Chattopadhyay, Saurabh Project Summary/Abstract The respiratory viruses, including coronaviruses, the paramyxo/pneumoviruses, and influenza virus, cause lethal human diseases, and the treatment options are limited or non-existent. The interferon (IFN) system is the first line of host defense against a wide range of viral infections. Viral infection is sensed by the cellular pattern recognition receptors, which via a series of signaling proteins, trigger the transcriptional induction of IFNs and IFN-stimulated genes (ISGs). The ISG-encoded proteins, either alone or in combination with other ISGs, inhibit one or more viral life cycle stages. The molecular mechanisms of these restriction factors, many of which act virus and cell-specifically, are insufficiently understood. Moreover, IFN, as an antiviral therapy, has numerous side effects. In order to identify viral restriction factors against paramyxoviruses, we used a high throughput genetic screen of a human ISG shRNA library. Our screen identified a novel viral restriction factor, TDRD7, which we demonstrated, for the first time, as an antiviral ISG. We reported that TDRD7 inhibits virus-induced autophagy pathway, required for the replication of paramyxoviruses (SeV, HPIV3), as well as the pneumoviruses (RSV). TDRD7 inhibits autophagy by suppressing the autophagy-initiating kinase, AMP- activated kinase (AMPK). In support of this antiviral mechanism, we recently demonstrated that TDRD7 inhibits the replication of herpesviruses, which surprisingly require AMPK but not its autophagy branch. Therefore, we discovered a new antiviral mechanism of the IFN system, mediated by TDRD7/AMPK. Currently, the molecular mechanism by which TDRD7 inhibits the pro-viral AMPK and the contribution of TDRD7 to prevent viral pathogenesis is not known. To investigate this, we generated preliminary results: a) TDRD7 interacts directly with AMPK to inhibit its activation, b) the ubiquitination of TDRD7 regulates its functions, and c) primary cells from the newly-engineered conditional Tdrd7-/- mice show elevated viral replication. These results led to our hypothesis that TDRD7, a newly-identified viral restriction factor, interacts directly with the pro-viral AMPK to inhibit its activation and respiratory viral replication and pathogenesis, and the TDRD7 functions are regulated by its ubiquitination. To test this, we will: SA1) determine the molecular mechanisms by which TDRD7 inhibits AMPK, and SA2) evaluate the contribution of TDRD7 to host antiviral responses. Our study is significant because we offer a novel concept that TDRD7-mediated inhibition of pro-viral AMPK is a new antiviral pathway of the IFN system, with implications beyond virus infection. Our study is innovative, both conceptually and technically, with a team of complementary expertise. Our future studies, based on convincing preliminary results, will further reveal how TDRD7 inhibits the lethal respiratory pathogen, the influenza A virus. The results obtained will uncover novel cellular mechanisms to restrict virus infection and an AMPK-inhibitory function of the IFN system that has broader therapeutic implications in viral and non-viral diseases. Project Summary/Abstract Page 6