# Influenza virus host shutoff mechanism

> **NIH NIH R01** · UNIVERSITY OF ROCHESTER · 2021 · $385,000

## Abstract

Virus infection induces a wide range of host defense mechanisms, such as the innate immune
response and inflammation. Some viruses express accessory proteins to induce general shutoff of host
protein synthesis, which is considered to be one of the major viral strategies to counteract host antiviral
activity and immune response. Influenza A virus is one of these viruses and expresses two proteins
NS1 and PA-X to induce host shutoff. PA-X is a novel protein found to be expressed from PA mRNA by
ribosomal frameshifting. PA-X is composed of an endonuclease domain of PA with a unique C-terminal
region. Recent studies including ours indicate that mRNA degradation is the major strategy for host
shutoff. The PA-X is more active in shutoff activity than NS-1, and it contains multiple regions involved
in specific mRNA degradation. Characterization of a mutant 2009 pandemic H1N1 virus expressing
reduced amount of PA-X indicates that PA-X plays a significant role in antagonizing host innate and
acquired immune responses. The mechanism of how PA-X induces shutoff is not known. However, a
recent study showed that PA-X selectively degrades host RNA polymerase II transcripts, and that pre-
mRNAs under 3’-processing are susceptible for PA-X degradation. We also found that PA-X localizes
and degrades mRNAs in both the nucleus and cytoplasm, suggesting that PA-X has multiple strategies
to capture and degrade pre-mRNAs and mature mRNAs in cells. This project will reveal the mechanism
of how PA-X targets and degrades host pre-mRNA in the nucleus (Aim 1), and mature mRNAs in the
cytoplasm (Aim 2). Using viruses having various shutoff activities, we will determine the functional
interaction between PA-X and NS1 to unveil how IAV adjusts the level of shutoff to create optimum
condition for viral replication. Because the shutoff activity directly affects host immune responses, we
will test a hypothesis that efficacy of live attenuated vaccine can be improved by suppressing shutoff
activity. Overall, the proposed study will provide a foundation for understanding 1) the mechanism by
which influenza viruses modulate host gene expression, 2) the mechanism by which viral gene
expression is optimized, and 3) the impact of PA-X on viral pathogenicity and host immune response.
Upon completion of these studies, we will learn the unique multiple strategy of PA-X in inducing host
shutoff in infected cells, and its impact on viral pathogenicity and immune evasion.

## Key facts

- **NIH application ID:** 10237177
- **Project number:** 5R01AI129988-05
- **Recipient organization:** UNIVERSITY OF ROCHESTER
- **Principal Investigator:** TORU TAKIMOTO
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $385,000
- **Award type:** 5
- **Project period:** 2017-09-25 → 2023-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10237177

## Citation

> US National Institutes of Health, RePORTER application 10237177, Influenza virus host shutoff mechanism (5R01AI129988-05). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10237177. Licensed CC0.

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