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Identification of a nuclear transport carrier common to flavivirus core proteins – Suggests potential as a therapeutic target against a wide range of flaviviruses –
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Assistant Professor Yumi Ito and Chief Professor Toru Okamoto of the Department of Microbiology, Juntendo University Graduate School of Medicine, have conducted extensive research in collaboration with Yoichi Miyamoto, Chief Researcher of the Biofunction Molecular Regulation Project, National Institute of Biomedical Innovation, Health and Nutrition. We investigated the significance of the nuclear localization and nuclear translocation mechanism of the core protein (*2) conserved in flaviviruses (*1). -7: IPO7) and 2. revealed that IPO7-mediated nuclear translocation of the core protein is important for the release of infectious virus from the cell. The research results were published online in the international scientific journal PLOS Pathogens on August 15, 2024 at 2:00 pm (ET).
■ Key points of this research result
We identified IPO7 as a factor responsible for the nuclear
translocation of core proteins common to Flaviviridae viruses. In cells lacking IPO7, inhibition of nuclear translocation of core protein and suppression of production of infectious virus particles was confirmed not only for Japanese encephalitis virus but also for dengue virus and Zika virus.
We revealed that IPO7-mediated nuclear translocation of core protein contributes to the release of infectious virus from the cell. ■ Background
Known flaviviruses transmitted by arthropods such as mosquitoes include Japanese encephalitis virus (JEV), dengue virus (DENV), Zika virus (ZIKV), and West Nile virus (WNV), all of which are known to be transmitted by arthropods such as mosquitoes. A virus that causes disease. In particular, DENV infects 400 million people every year and is endemic in many regions, including Southeast Asia and South America. Furthermore, in recent years, imported cases of infection that develop after returning from endemic areas have also been reported in Japan, which has become a problem. However, as there are currently no effective therapeutic drugs, symptomatic treatment is used when flavivirus-induced disease develops. Therefore, it is desired to develop therapeutic drugs that exhibit antiviral effects against a wide range of viruses, including JEV, DENV, and ZIKV. Previous studies have long known that the core protein that forms the virus particles of JEV, DENV, ZIKV, and WNV (Figure A) is localized not only in the cytoplasm but also in the nucleus (Figure B, J Virol (2005)). The nuclear localization of the core protein, which is common among flaviviruses, is thought to be a target for therapeutic drugs that are effective against a wide range of flaviviruses. In fact, we previously identified multiple compounds that inhibit the nuclear localization of flavivirus core proteins and discovered that these compounds inhibited the proliferation of not only JEV but also DENV and ZIKV (Virology (2020) ). However, the physiological significance of flavivirus core protein localization in the nucleus and the molecular mechanism of nuclear translocation remained unclear. Based on the above background, we conducted an investigation to identify host factors that contribute to nuclear translocation of flavivirus core proteins and to clarify the significance of nuclear localization in flavivirus proliferation.
■ Contents
In order to search for host factors that transport the core protein to the nucleus (factors present in infected cells), we detected host factors that bind to the JEV core protein using mass spectrometry, and found that IPO7, which belongs to the importin β family (*3). We successfully identified (Figure C). Furthermore, when we generated cells lacking IPO7 and examined the localization of the core protein during viral infection, we found that nuclear translocation was inhibited and most of it was localized in the cytoplasm. This phenomenon was confirmed not only in JEV but also in other
flaviviruses such as DENV, ZIKV, and WNV, indicating that IPO7 is a nuclear transporter for core proteins common to flaviviruses (Fig. D, E). Next, we examined the effect of inhibition of core protein nuclear translocation due to IPO7 deficiency on virus proliferation, and found that IPO7 deficiency significantly inhibited virus proliferation. Finally, to examine the significance of the nuclear localization of the core protein, single-infectious virus-like particles (SRIP) (*4) containing the core proteins of JEV, DENV, and ZIKV were tested in wild-type cells and IPO7-deficient cells. We created and evaluated the infectivity of the resulting SRIP. As a result, the infectivity of SRIP produced in IPO7-deficient cells was significantly reduced. These findings revealed that IPO7-mediated nuclear localization of the core protein is important for the release of infectious virus particles from the cell.
[Image: https://prtimes.jp/i/21495/672/resize/d21495-672-7d95805c029a8053d97a-0.jpg&s3=21495-672-3aead9c747358ab2abf90b56dccb9de9-1203×1001.jpg] ■ Significance of research results
In this study, we were the first in the world to demonstrate that the flavivirus core protein translocates to the nucleus via the host factor IPO7 and contributes to the efficient release of infectious viruses from the cell. . Until now, the physiological significance of the nuclear localization of flavivirus core proteins was unknown, but the results obtained in this study are expected to further deepen our understanding of the flavivirus life cycle. In addition, it has been confirmed that IPO7 deficiency inhibits the nuclear localization of core proteins and suppresses virus production in a wide range of flaviviruses, indicating that it may serve as a target for therapeutic drugs that are effective against various flaviviruses. , the development of therapeutic drugs targeting IPO7 is expected. ■ Glossary
*1 Flavivirus
A virus transmitted by arthropods such as mosquitoes and ticks. These include Japanese encephalitis virus, dengue virus, and Zika virus. These viruses sometimes cause serious illnesses, and it is known that hemorrhagic fever caused by dengue virus and Zika virus infection during pregnancy can cause microcephaly in the fetus.
*2 Core protein
A protein that makes up the capsid of a virus. The virus genome is enclosed in a shell called a capsid that exists inside the virus particle, and is located inside the envelope.
*3 Importin β family
Many proteins can move between the nucleus and the cytoplasm through nuclear pores. The importin β family is a nuclear-cytoplasmic transport factor and is involved in the transport of many proteins into and out of the nucleus.
*4 Single-infectious virus-like particle (SRIP)
Unlike normal viruses, the virus-like particles produced can infect cells only once. Therefore, when infected with SRIP, the culture supernatant does not contain virus-like particles, and the infectivity of the virus-like particles can be evaluated.
■ Special notes
This research was supported by the Japan Agency for Medical Research and Development (AMED), a research project to promote the development of innovative medicines for emerging and re-emerging infectious diseases, “Research and development contributing to the development of therapeutic drugs for arthropod-borne flaviviruses using new imaging technology”, and Japan Society for the Promotion of Science. This research was supported by the Japan Society for Scientific Research, Grants-in-Aid for Scientific Research/Fundamental Research B, and Boehringer Ingelheim. We would like to express our deepest gratitude to everyone who cooperated with this research.
■ Paper information
This study was published online in the journal PLoS Pathogens on August 15, 2024.
Title: Importin-7-dependent nuclear translocation of the Flavivirus core protein is required for infectious virus production.
Title (Japanese translation): IPO7-dependent nuclear translocation by the core protein of Flaviviridae viruses is involved in the release of infectious viruses
Author: Yumi Itoh1¶, Yoichi Miyamoto2,3¶, Makoto Tokunaga4, Tatsuya Suzuki1, Akira Takada4, Akinori Ninomiya5, Tomomi Hisinuma1, Mami Matsuda6, Yoshihiro Yoneda7, Masahiro Oka2, Ryosuke Suzuki6, Yoshiharu Matsuura8*, Toru Okamoto1*
Author (Japanese): Yumi Ito1), Yoichi Miyamoto2,3), Akira Tokunaga4), Tatsuya Suzuki1), Akira Takada4), Akinori Ninomiya5), Tomomi Hishinuma1), Asami Matsuda6), Yoneda Etsukei7), Masahiro Oka2), Ryosuke Suzuki6), Yoshiharu Matsuura8), Toru Okamoto1)
Author affiliation: 1) Department of Microbiology, Juntendo
University, 2) National Institute of Biomedical Innovation, Health and Nutrition, Cell Nuclear Transport Dynamics Project, 3) National Institute of Biomedical Innovation, Health and Nutrition, Biofunction Molecular Control Project, 4) Osaka University Research Institute for Microbial Diseases, Advanced Collaborative Research Institute, 5) Osaka University Research Institute for Microbial Diseases, Central Laboratory, 6) National Institute of Infectious Diseases, Virus II Department, 7) Osaka University Research Group for Microbial Diseases, 8 ) Osaka University Infectious Disease Comprehensive Education and Research Center
DOI: 10.1371/journal.ppat.1012409