Project Summary/Abstract
The respiratory viruses, including coronaviruses, the paramyxo/pneumoviruses, and the 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
function virus and cell-specifically, are insufficiently understood. Furthermore, IFN, as antiviral therapy, has
numerous side effects. 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 the virus-
induced autophagy pathway, which is 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 unknown. To investigate this, we generated preliminary results to show that: (a) TDRD7
interacts directly with AMPK to inhibit its activation, (b) the ubiquitination of TDRD7 regulates its functions, and
(c) the newly-engineered conditional Tdrd7 KO mice and the derived primary cells show elevated viral
replication and pathogenesis. These compelling new 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. Based on the preliminary results, our future studies 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 with broader
therapeutic implications in viral and non-viral diseases.