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• Kaposi's Sarcoma-Associated Herpesvirus ORF21 Enhances the Phosphorylation of MEK and the Infectivity of Progeny Virus.

  Tatsuo Yamaguchi, Tadashi Watanabe, Yuki Iwaisako, Masahiro Fujimuro

  International journal of molecular sciences   24 ( 2 )   2023.01 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus-8, is the causative agent of Kaposi's sarcoma, Castleman's disease, and primary effusion lymphoma. Although the functions of the viral thymidine kinases (vTK) of herpes simplex virus-1/2 are well understood, that of KSHV ORF21 (an ortholog of vTK) is largely unknown. Here, we investigated the role of ORF21 in lytic replication and infection by generating two ORF21-mutated KSHV BAC clones: ORF21-kinase activity deficient KSHV (21KD) and stop codon-induced ORF21-deleted KSHV (21del). The results showed that both ORF21 mutations did not affect viral genome replication, lytic gene transcription, or the production of viral genome-encapsidated particles. The ORF21 molecule-dependent function, other than the kinase function of ORF21, was involved in the infectivity of the progeny virus. ORF21 was expressed 36 h after the induction of lytic replication, and endogenously expressed ORF21 was localized in the whole cytoplasm. Moreover, ORF21 upregulated the MEK phosphorylation and anchorage-independent cell growth. The inhibition of MEK signaling by U0126 in recipient target cells suppressed the number of progeny virus-infected cells. These suggest that ORF21 transmitted as a tegument protein in the progeny virus enhances the new infection through MEK up-regulation in the recipient cell. Our findings indicate that ORF21 plays key roles in the infection of KSHV through the manipulation of the cellular function.

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• The Contribution of Kaposi's Sarcoma-Associated Herpesvirus ORF7 and Its Zinc-Finger Motif to Viral Genome Cleavage and Capsid Formation.

  Yuki Iwaisako, Tadashi Watanabe, Manami Futo, Rimiko Okabe, Yuichi Sekine, Youichi Suzuki, Takashi Nakano, Masahiro Fujimuro

  Journal of virology     e0068422   2022.09 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  During Kaposi's sarcoma-associated herpesvirus (KSHV) lytic infection, lytic-related proteins are synthesized, viral genomes are replicated as a tandemly repeated form, and subsequently, capsids are assembled. The herpesvirus terminase complex is proposed to package an appropriate genome unit into an immature capsid, by cleavage of terminal repeats (TRs) flanking tandemly linked viral genomes. Although the mechanism of capsid formation in alpha- and betaherpesviruses are well-studied, in KSHV, it remains largely unknown. It has been proposed that KSHV ORF7 is a terminase subunit, and ORF7 harbors a zinc-finger motif, which is conserved among other herpesviral terminases. However, the biological significance of ORF7 is unknown. We previously reported that KSHV ORF17 is essential for the cleavage of inner scaffold proteins in capsid maturation, and ORF17 knockout (KO) induced capsid formation arrest between the procapsid and B-capsid stages. However, it remains unknown if ORF7-mediated viral DNA cleavage occurs before or after ORF17-mediated scaffold collapse. We analyzed the role of ORF7 during capsid formation using ORF7-KO-, ORF7&17-double-KO (DKO)-, and ORF7-zinc-finger motif mutant-KSHVs. We found that ORF7 acted after ORF17 in the capsid formation process, and ORF7-KO-KSHV produced incomplete capsids harboring nonspherical internal structures, which resembled soccer balls. This soccer ball-like capsid was formed after ORF17-mediated B-capsid formation. Moreover, ORF7-KO- and zinc-finger motif KO-KSHV failed to appropriately cleave the TR on replicated genome and had a defect in virion production. Interestingly, ORF17 function was also necessary for TR cleavage. Thus, our data revealed ORF7 contributes to terminase-mediated viral genome cleavage and capsid formation. IMPORTANCE In herpesviral capsid formation, the viral terminase complex cleaves the TR sites on newly synthesized tandemly repeating genomes and inserts an appropriate genomic unit into an immature capsid. Herpes simplex virus 1 (HSV-1) UL28 is a subunit of the terminase complex that cleaves the replicated viral genome. However, the physiological importance of the UL28 homolog, KSHV ORF7, remains poorly understood. Here, using several ORF7-deficient KSHVs, we found that ORF7 acted after ORF17-mediated scaffold collapse in the capsid maturation process. Moreover, ORF7 and its zinc-finger motif were essential for both cleavage of TR sites on the KSHV genome and virus production. ORF7-deficient KSHVs produced incomplete capsids that resembled a soccer ball. To our knowledge, this is the first report showing ORF7-KO-induced soccer ball-like capsids production and ORF7 function in the KSHV capsid assembly process. Our findings provide insights into the role of ORF7 in KSHV capsid formation.

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• Biomolecular Fluorescence Complementation Profiling and Artificial Intelligence Structure Prediction of the Kaposi's Sarcoma-Associated Herpesvirus ORF18 and ORF30 Interaction.

  Yoshiko Maeda, Tadashi Watanabe, Taisuke Izumi, Kazushi Kuriyama, Shinji Ohno, Masahiro Fujimuro

  International journal of molecular sciences   23 ( 17 )   2022.08 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of Kaposi's sarcoma, primary effusion lymphoma (PEL), and multicentric Castleman's disease. During KSHV lytic infection, lytic-related genes, categorized as immediate-early, early, and late genes, are expressed in a temporal manner. The transcription of late genes requires the virus-specific pre-initiation complex (vPIC), which consists of viral transcription factors. However, the protein-protein interactions of the vPIC factors have not been completely elucidated. KSHV ORF18 is one of the vPIC factors, and its interaction with other viral proteins has not been sufficiently revealed. In order to clarify these issues, we analyzed the interaction between ORF18 and another vPIC factor, ORF30, in living cells using the bimolecular fluorescence complementation (BiFC) assay. We identified four amino-acid residues (Leu29, Glu36, His41, and Trp170) of ORF18 that were responsible for its interaction with ORF30. Pull-down assays also showed that these four residues were required for the ORF18-ORF30 interaction. The artificial intelligence (AI) system AlphaFold2 predicted that the identified four residues are localized on the surface of ORF18 and are in proximity to each other. Thus, our AI-predicted model supports the importance of the four residues for binding ORF18 to ORF30. These results indicated that wet experiments in combination with AI may enhance the structural characterization of vPIC protein-protein interactions.

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• A comprehensive list of the Bunyavirales replication promoters reveals a unique promoter structure in Nairoviridae differing from other virus families.

  Yutaro Neriya, Shohei Kojima, Arata Sakiyama, Mai Kishimoto, Takao Iketani, Tadashi Watanabe, Yuichi Abe, Hiroshi Shimoda, Keisuke Nakagawa, Takaaki Koma, Yusuke Matsumoto

  Scientific reports   12 ( 1 ) 13560 - 13560   2022.08 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Members of the order Bunyavirales infect a wide variety of host species, including plants, animals and humans, and pose a threat to public health. Major families in this order have tri-segmented negative-sense RNA genomes, the 5' and 3' ends of which form complementary strands that serve as a replication promoter. Elucidation of the mechanisms by which viral polymerases recognize the promoter to initiate RNA synthesis is important for understanding viral replication and pathogenesis, and developing antivirals. A list of replication promoter configuration patterns may provide details on the differences in the replication mechanisms among bunyaviruses. By using public sequence data of all known bunyavirus species, we constructed a comprehensive list of the replication promoters comprising 40 nucleotides in both the 5' and 3' ends of the genome that form a specific complementary strand. Among tri-segmented bunyaviruses, members of the family Nairoviridae, including the highly pathogenic Crimean-Congo hemorrhagic fever virus, have evolved a GC-rich promoter structure differing from that of other families. The unique promoter structure might be related to the large genome size of the family Nairoviridae among bunyaviruses, and the large genome architecture might confer pathogenic advantages. The promoter list provided in this report is useful for predicting the virus family-specific replication mechanisms of bunyaviruses.

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• A pyridinium‑type fullerene derivative suppresses primary effusion lymphoma cell viability via the downregulation of the Wnt signaling pathway through the destabilization of β‑catenin.

  Ayano Kadota, Misato Moriguchi, Tadashi Watanabe, Yuichi Sekine, Shigeo Nakamura, Takumi Yasuno, Tomoyuki Ohe, Tadahiko Mashino, Masahiro Fujimuro

  Oncology reports   47 ( 3 )   2022.03 [ Peer Review Accepted ]

  Type of publication: Research paper (scientific journal)

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  Primary effusion lymphoma (PEL) is defined as a rare subtype of non‑Hodgkin's B cell lymphoma, which is caused by Kaposi's sarcoma‑associated herpesvirus (KSHV) in immunosuppressed patients. PEL is an aggressive type of lymphoma and is frequently resistant to conventional chemotherapeutics. Therefore, the discovery of novel drug candidates for the treatment of PEL is of utmost importance. In order to discover potential novel anti‑tumor compounds against PEL, the authors previously developed a pyrrolidinium‑type fullerene derivative, 1,1,1',1'‑tetramethyl [60]fullerenodipyrrolidinium diiodide (derivative #1), which induced the apoptosis of PEL cells via caspase‑9 activation. In the present study, the growth inhibitory effects of pyrrolidinium‑type (derivatives #1 and #2), pyridinium‑type (derivatives #3 and #5 to #9) and anilinium‑type fullerene derivatives (derivative #4) against PEL cells were evaluated. This analysis revealed a pyridinium‑type derivative (derivative #5; 3‑​5'‑(etho xycarbonyl)‑1',5'‑dihydro‑2'H‑[5,6]fullereno‑C60‑Ih‑[1,9‑c]pyrrol‑2'‑yl]‑1‑methylpyridinium iodide), which exhibited antitumor activity against PEL cells via the downregulation of Wnt/β‑catenin signaling. Derivative #5 suppressed the viability of KSHV‑infected PEL cells compared with KSHV‑uninfected B‑lymphoma cells. Furthermore, derivative #5 induced the destabilization of β‑catenin and suppressed β‑catenin‑TCF4 transcriptional activity in PEL cells. It is known that the constitutive activation of Wnt/β‑catenin signaling is essential for the growth of KSHV‑infected cells. The Wnt/β‑catenin activation in KSHV‑infected cells is mediated by KSHV latency‑associated nuclear antigen (LANA). The data demonstrated that derivative #5 increased β‑catenin phosphorylation, which resulted in β‑catenin polyubiquitination and subsequent degradation. Thus, derivative #5 overcame LANA‑mediated β‑catenin stabilization. Furthermore, the administration of derivative #5 suppressed the development of PEL cells in the ascites of SCID mice with tumor xenografts derived from PEL cells. On the whole, these findings provide evidence that the pyridinium‑type fullerene derivative #5 exhibits antitumor activity against PEL cells in vitro and in vivo. Thus, derivative #5 may be utilized as a novel therapeutic agent for the treatment of PEL.

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• Replication Machinery of Kaposi's Sarcoma-associated Herpesvirus and Drug Discovery Research

  Watanabe Tadashi, Fujimuro Masahiro

  YAKUGAKU ZASSHI ( The Pharmaceutical Society of Japan )  139 ( 1 ) 69 - 73   2019  [Refereed]

   

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