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Biomedical subjects

Tatsuya Tsurumi

Publications and source records attributed to Tatsuya Tsurumi.

At least 19 recordsLinked to original sources
PubMed2006

Establishment of a novel foreign gene delivery system combining an HSV amplicon with an attenuated replication-competent virus, HSV-1 HF10.

Herpes simplex virus type 1 (HSV-1)-based amplicon vectors have been used widely in genetic engineering with many advantages for gene delivery, being easily constructed. An attenuated and replication-competent HSV-1 HF10 clone demonstrating an oncolytic effect on cancer cells in vitro and in vivo has been applied recently for clinical virotherapy of breast cancers and the present studies were conducted to test its efficacy in combination with an HSV-1 amplicon. For this purpose, a new system was developed to produce high titers of the HSV-1 amplicon vector and the results showed that its package efficiency and the titer ratio to HF10 were improved by passage through two cell lines. A high ratio of amplicon/helper virus HF10 (A/H) (>1) was required to express the foreign gene efficiently. Furthermore, in order to express the foreign gene conditionally, an HSV-1 ICP8 promoter was introduced in place of the human cytomegalovirus MIE promoter, this driving expression of the transgene when replication of HF10 progressed. The methodology for simple preparation of mixtures of viruses containing the amplicon with the oncolytic virus is documented. This system should find application for studies of cancer therapy.

Animals↗
PubMed2006

Postreplicative mismatch repair factors are recruited to Epstein-Barr virus replication compartments.

The mismatch repair (MMR) system, highly conserved throughout evolution, corrects nucleotide mispairing that arise during cellular DNA replication. We report here that proliferating cell nuclear antigen (PCNA), the clamp loader complex (RF-C), and a series of MMR proteins like MSH-2, MSH-6, MLH1, and hPSM2 can be assembled to Epstein-Barr virus replication compartments, the sites of viral DNA synthesis. Levels of the DNA-bound form of PCNA increased with progression of viral productive replication. Bromodeoxyuridine-labeled chromatin immunodepletion analyses confirmed that PCNA is loaded onto newly synthesized viral DNA as well as BALF2 and BMRF1 viral proteins during lytic replication. Furthermore, the anti-PCNA, -MSH2, -MSH3, or -MSH6 antibodies could immunoprecipitate BMRF1 replication protein probably via the viral DNA genome. PCNA loading might trigger transfer of a series of host MMR proteins to the sites of viral DNA synthesis. The MMR factors might function for the repair of mismatches that arise during viral replication or act to inhibit recombination between moderately divergent (homologous) sequences.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Immortalization of Epstein-Barr virus-negative human B lymphocytes with minimal chromosomal instability.

The genes required for immortalization of human B cells infected by Epstein-Barr virus are multiple, and the precise mechanism of this process remains to be elucidated. In the present study HPV16 E6 and E7 were retrovirally transduced into human primary B cells stimulated by CD40-CD40L interaction, thereby establishing an Epstein-Barr virus negative immortalized human B cell line, which continued to proliferate for more than 2 years (100 population doublings). The established cell line had a high telomerase activity from the beginning of the culture period, and no shortening of the telomere length was observed. A chromosomal analysis revealed that a large portion of the HPV16E6E7 transduced cells had retained a normal karyotype. Similar to human epithelial cells, human B lymphocytes seem to require two steps for immortalization, namely, the inactivation of the p16/Rb pathway and the activation of telomerase, the latter that can be induced by the CD40-CD40L interaction. Furthermore, using this system, it is possible to analyze the role of individual genes in human B lymphocyte immortalization without the influence of a pre-existing Epstein-Barr virus genome.

B-Lymphocytes↗
PubMed2006

Phosphorylation of MCM4 at sites inactivating DNA helicase activity of the MCM4-MCM6-MCM7 complex during Epstein-Barr virus productive replication.

Induction of Epstein-Barr virus (EBV) lytic replication blocks chromosomal DNA replication notwithstanding an S-phase-like cellular environment with high cyclin-dependent kinase (CDK) activity. We report here that the phosphorylated form of MCM4, a subunit of the MCM complex essential for chromosomal DNA replication, increases with progression of lytic replication, Thr-19 and Thr-110 being CDK2/CDK1 targets whose phosphorylation inactivates MCM4-MCM6-MCM7 (MCM4-6-7) complex-associated DNA helicase. Expression of EBV-encoded protein kinase (EBV-PK) in HeLa cells caused phosphorylation of these sites on MCM4, leading to cell growth arrest. In vitro, the sites of MCM4 of the MCM4-6-7 hexamer were confirmed to be phosphorylated with EBV-PK, with the same loss of helicase activity as with CDK2/cyclin A. Introducing mutations in the N-terminal six Ser and Thr residues of MCM4 reduced the inhibition by CDK2/cyclin A, while EBV-PK inhibited the helicase activities of both wild-type and mutant MCM4-6-7 hexamers, probably since EBV-PK can phosphorylate MCM6 and another site(s) of MCM4 in addition to the N-terminal residues. Therefore, phosphorylation of the MCM complex by redundant actions of CDK and EBV-PK during lytic replication might provide one mechanism to block chromosomal DNA replication in the infected cells through inactivation of DNA unwinding by the MCM4-6-7 complex.

Amino Acid Substitution↗
PubMed2005

Activation of ataxia telangiectasia-mutated DNA damage checkpoint signal transduction elicited by herpes simplex virus infection.

Eukaryotic cells are equipped with machinery to monitor and repair damaged DNA. Herpes simplex virus (HSV) DNA replication occurs at discrete sites in nuclei, the replication compartment, where viral replication proteins cluster and synthesize a large amount of viral DNA. In the present study, HSV infection was found to elicit a cellular DNA damage response, with activation of the ataxia-telangiectasia-mutated (ATM) signal transduction pathway, as observed by autophosphorylation of ATM and phosphorylation of multiple downstream targets including Nbs1, Chk2, and p53, while infection with a UV-inactivated virus or with a replication-defective virus did not. Activated ATM and the DNA damage sensor MRN complex composed of Mre11, Rad50, and Nbs1 were recruited and retained at sites of viral DNA replication, probably recognizing newly synthesized viral DNAs as abnormal DNA structures. These events were not observed in ATM-deficient cells, indicating ATM dependence. In Nbs1-deficient cells, HSV infection induced an ATM DNA damage response that was delayed, suggesting a functional MRN complex requirement for efficient ATM activation. However, ATM silencing had no effect on viral replication in 293T cells. Our data open up an interesting question of how the virus is able to complete its replication, although host cells activate ATM checkpoint signaling in response to the HSV infection.

Acid Anhydride Hydrolases↗
PubMed2005

Two Sp1/Sp3 binding sites in the major immediate-early proximal enhancer of human cytomegalovirus have a significant role in viral replication.

We previously demonstrated that the major immediate early (MIE) proximal enhancer containing one GC box and the TATA box containing promoter are minimal elements required for transcription and viral replication in human fibroblast cells (H. Isomura, T. Tsurumi, M. F. Stinski, J. Virol. 78:12788-12799, 2004). After infection, the level of Sp1 increased while Sp3 remained constant. Here we report that either Sp1 or Sp3 transcription factors bind to the GC boxes located at approximately positions -55 and -75 relative to the transcription start site (+1). Both the Sp1 and Sp3 binding sites have a positive and synergistic effect on the human cytomegalovirus (HCMV) major immediate-early (MIE) promoter. There was little to no change in MIE transcription or viral replication for recombinant viruses with one or the other Sp1 or Sp3 binding site mutated. In contrast, mutation of both the Sp1 and Sp3 binding sites caused inefficient MIE transcription and viral replication. These data indicate that the Sp1 and Sp3 binding sites have a significant role in HCMV replication in human fibroblast cells.

Binding Sites↗
PubMed2005

Architecture of replication compartments formed during Epstein-Barr virus lytic replication.

Epstein-Barr virus (EBV) productive DNA replication occurs at discrete sites, called replication compartments, in nuclei. In this study we performed comprehensive analyses of the architecture of the replication compartments. The BZLF1 oriLyt binding proteins showed a fine, diffuse pattern of distribution throughout the nuclei at immediate-early stages of induction and then became associated with the replicating EBV genome in the replication compartments during lytic infection. The BMRF1 polymerase (Pol) processivity factor showed a homogenous, not dot-like, distribution in the replication compartments, which completely coincided with the newly synthesized viral DNA. Inhibition of viral DNA replication with phosphonoacetic acid, a viral DNA Pol inhibitor, eliminated the DNA-bound form of the BMRF1 protein, although the protein was sufficiently expressed in the cells. These observations together with the findings that almost all abundantly expressed BMRF1 proteins existed in the DNA-bound form suggest that the BMRF1 proteins not only act at viral replication forks as Pol processive factors but also widely distribute on newly replicated EBV genomic DNA. In contrast, the BALF5 Pol catalytic protein, the BALF2 single-stranded-DNA binding protein, and the BBLF2/3 protein, a component of the helicase-primase complex, were colocalized as distinct dots distributed within replication compartments, representing viral replication factories. Whereas cellular replication factories are constructed based on nonchromatin nuclear structures and nuclear matrix, viral replication factories were easily solubilized by DNase I treatment. Thus, compared with cellular DNA replication, EBV lytic DNA replication factories would be simpler so that construction of the replication domain would be more relaxed.

Antigens, Viral↗
PubMed2004

Epstein-Barr virus lytic replication elicits ATM checkpoint signal transduction while providing an S-phase-like cellular environment.

When exposed to genotoxic stress, eukaryotic cells demonstrate a DNA damage response with delay or arrest of cell-cycle progression, providing time for DNA repair. Induction of the Epstein-Barr virus (EBV) lytic program elicited a cellular DNA damage response, with activation of the ataxia telangiectasia-mutated (ATM) signal transduction pathway. Activation of the ATM-Rad3-related (ATR) replication checkpoint pathway, in contrast, was minimal. The DNA damage sensor Mre11-Rad50-Nbs1 (MRN) complex and phosphorylated ATM were recruited and retained in viral replication compartments, recognizing newly synthesized viral DNAs as abnormal DNA structures. Phosphorylated p53 also became concentrated in replication compartments and physically interacted with viral BZLF1 protein. Despite the activation of ATM checkpoint signaling, p53-downstream signaling was blocked, with rather high S-phase CDK activity associated with progression of lytic infection. Therefore, although host cells activate ATM checkpoint signaling with response to the lytic viral DNA synthesis, the virus can skillfully evade this host checkpoint security system and actively promote an S-phase-like environment advantageous for viral lytic replication.

Ataxia Telangiectasia Mutated Proteins↗
PubMed2004

In vivo dynamics of EBNA1-oriP interaction during latent and lytic replication of Epstein-Barr virus.

The Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is required for maintenance of the viral genome DNA during the latent phase of EBV replication but continues to be synthesized after the induction of viral productive replication. An EBV genome-wide chromatin immunoprecipitation assay revealed that EBNA1 constantly binds to oriP of the EBV genome during not only latent but also lytic infection. Although the total levels of EBNA1 proved constant throughout the latter, the levels of the oriP-bound form were increased as lytic infection proceeded. EBV productive DNA replication occurs at discrete sites in nuclei, called replication compartments, where viral replication proteins are clustered. Confocal laser microscopic analyses revealed that whereas EBNA1 was distributed broadly in nuclei as fine punctate dots during the latent phase of infection, the protein became redistributed to the viral replication compartments and localized as distinct spots within and/or nearby the compartments after the induction of lytic replication. Taking these findings into consideration, oriP regions of the EBV genome might be organized by EBNA1 into replication domains that may set up scaffolding for lytic replication and transcription.

Binding Sites↗
PubMed2004

Quantitative analysis of Epstein-Barr virus (EBV)-specific CD8+ T cells in patients with chronic active EBV infection.

To clarify the pathogenesis of chronic active Epstein-Barr virus (EBV) infection, EBV-specific CD8+ T cells were enumerated, by use of human leukocyte antigen (HLA)-A*2402-restricted tetramers, in 8 patients with chronic active EBV infection, 10 patients with infectious mononucleosis, and 16 EBV-seropositive healthy control subjects. In most of the patients with chronic active EBV infection, EBV-specific CD8+ T cells were not detected. Of note, latent membrane protein 2-specific CD8+ T cells were not detectable in any patients with chronic active EBV infection. In contrast, EBV-specific CD8+ T cells were detected in patients with infectious mononucleosis and in healthy control subjects. Low frequencies of EBV-specific CD8+ T cells may be one of the immunological features of chronic active EBV infection.

Adolescent↗
PubMed2004

Cdt1 phosphorylation by cyclin A-dependent kinases negatively regulates its function without affecting geminin binding.

The current concept regarding cell cycle regulation of DNA replication is that Cdt1, together with origin recognition complex and CDC6 proteins, constitutes the machinery that loads the minichromosome maintenance complex, a candidate replicative helicase, onto chromatin during the G(1) phase. The actions of origin recognition complex and CDC6 are suppressed through phosphorylation by cyclin-dependent kinases (Cdks) after S phase to prohibit rereplication. It has been suggested in metazoan cells that the function of Cdt1 is blocked through binding to an inhibitor protein, geminin. However, the functional relationship between the Cdt1-geminin system and Cdks remains to be clarified. In this report, we demonstrate that human Cdt1 is phosphorylated by cyclin A-dependent kinases dependent on its cyclin-binding motif. Cdk phosphorylation resulted in the binding of Cdt1 to the F-box protein Skp2 and subsequent degradation. In contrast, in vitro DNA binding activity of Cdt1 was inhibited by the phosphorylation. However, geminin binding to Cdt1 was not affected by the phosphorylation. Finally we provide evidence that inactivation of Cdk1 results in Cdt1 dephosphorylation and rebinding to chromatin in murine FT210 cells synchronized around the G(2)/M phase. Taken together, these findings suggest that Cdt1 function is also negatively regulated by the Cdk phosphorylation independent of geminin binding.

Amino Acid Motifs↗
PubMed2004

Analysis of HLA-A24-restricted CMVpp65 peptide-specific CTL with HLA-A*2402-CMVpp65 tetramer.

Developing precise and efficient methods of monitoring immune responses against cytomegalovirus (CMV) infection in immunocompromised transplantation patients is important. With the aim of optimizing the monitoring strategy, an HLA-A24-CMVpp65 tetramer-based analysis of CMVpp65 peptide-specific CTL lines was performed. Previously, the HLA-A24-restricted CTL epitope of CMVpp65 matrix protein was identified (QYDPVAALF aa 341-349). In the present study, CMVpp65 (aa 341-349) peptide-specific CTL lines were obtained from PBLs of 12 HLA-A24+ healthy donors by two stimulations with peptide-pulsed dendritic cells (DC). Among 12 CTL lines, 9 showed HLA-A*2402-CMVpp65 tetramer staining, which was found to be strongly co-related to the amount of IFN-gamma produced by CMVpp65 peptide-restimulated CTL lines (r=0.943, P<0.001). These results suggested that HLA-A*2402-CMVpp65 tetramer staining was an efficient way to monitor immune responses against CMV infection in HLA-A24+ immunocompromised hosts.

Apoptosis↗
PubMed2004

Inhibition of S-phase cyclin-dependent kinase activity blocks expression of Epstein-Barr virus immediate-early and early genes, preventing viral lytic replication.

The induction of lytic replication of the Epstein-Barr virus (EBV) completely arrests cell cycle progression, in spite of elevation of S-phase cyclin-dependent kinase (CDK) activity, thereby causing accumulation of hyperphosphorylated forms of retinoblastoma (Rb) protein (A. Kudoh, M. Fujita, T. Kiyono, K. Kuzushima, Y. Sugaya, S. Izuta, Y. Nishiyama, and T. Tsurumi, J. Virol. 77:851-861, 2003). Thus, the EBV lytic program appears to promote specific cell cycle-associated activity involved in the progression from G1 to S phase. We have proposed that this provides a cellular environment that is advantageous for EBV productive infection. Purvalanol A and roscovitine, inhibitors of S-phase CDKs, blocked the viral lytic replication when cells were treated at the early stage of lytic infection, while well-characterized inhibitors of enzymes, such as mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and protein kinase C, known to be involved in BZLF1 gene expression did not. Inhibition of CDK activity resulted in the accumulation of the hypophosphorylated form of Rb protein and inhibition of expression of EBV immediate-early and early proteins. Cycloheximide block-and-release experiments clearly demonstrated that even in the presence of enough amounts of the BZLF1 protein, purvalanol A blocked expression of lytic viral proteins at transcription level. Furthermore, reporter gene experiments confirmed that BZLF1-induced activation of early EBV promoters was impaired in the presence of the CDK inhibitor. We conclude here that the EBV lytic program promotes specific cell cycle-associated activity involved in the progression from G1 to S phase because the S-phase-like cellular environment is essential for the expression of immediate-early and early genes supplying the viral replication proteins and hence for lytic viral replication.

Cell Line↗
PubMed2004

Role of the proximal enhancer of the major immediate-early promoter in human cytomegalovirus replication.

The human cytomegalovirus (CMV) enhancer has a distal component (positions -550 to -300) and a proximal component (-300 to -39) relative to the transcription start site (+1) of the major immediate-early (MIE) promoter. Without the distal enhancer, human CMV replicates slower and has a small-plaque phenotype. We determined the sequence requirements of the proximal enhancer by making 5'-end deletions to positions -223, -173, -116, -67, and -39. Even though recombinant virus with the proximal enhancer deleted to -39 has the minimal TATA box-containing MIE promoter element, it cannot replicate independently in human fibroblast cells. Recombinant virus with a deletion to -67 has an Sp-1 transcription factor binding site which may represent a minimal enhancer element for recombinant virus replication in human fibroblast cells. Although recombinant virus with a deletion to -223 replicates to titers at least 100-fold less than that of the wild-type virus, it replicates to titers 8-fold higher than that of recombinant virus with a deletion to -173 and 20-fold higher than that of virus with a deletion to -67. Recombinant virus with a deletion to -173 replicates more efficiently than that with a deletion to -116. There was a direct correlation between the level of infectious virus replication and time after infection, amount of MIE gene transcription, MIE and early viral protein synthesis, and viral DNA synthesis. The extent of the proximal enhancer determines the efficiency of viral replication.

Activating Transcription Factors↗
PubMed2004

Reconstitution of HLA-A*2402-restricted cytomegalovirus-specific T-cells following stem cell transplantation.

Cytomegalovirus (CMV)-specific immune reconstitution early after stem cell transplantation (SCT) was evaluated prospectively by detecting CD8+ T-cells, which recognize the peptide QYDPVAALF in the context of HLA-A*2402. Fifteen allogeneic SCT recipients were included in the study. All recipients and donors were seropositive for CMV and had the HLA-A*2402 allele. CMV-specific T-cells were detected as early as 1 month after transplantation, and their numbers increased to peak levels 2 to 5 months after transplantation. The numbers of CMV-specific T-cells in patients who developed grade II to IV acute graft-versus-host disease (GVHD) and received corticosteroids for acute GVHD were low in the early period after allogeneic SCT. There was a trend toward earlier reconstitution of CMV-specific CD8+ T-cells in allogeneic peripheral blood SCT (PBSCT) patients than in allogeneic bone marrow transplantation patients. The contribution of T-cells in the graft to the recovery of CMV-specific immune responses was also suggested by the finding that the reconstitution of CMV-specific CD8+ T-cells was delayed in CD34-selected autologous PBSCT compared with unpurged autologous PBSCT. The reconstitution of CMV-specific CD8+ T-cells was delayed in patients with CMV disease or recurrent CMV reactivation. These observations suggest that the detection of CMV-specific T-cells with an HLA-peptide tetramer is useful to assess immune reconstitution against CMV and to identify patients at risk for CMV disease or recurrent CMV reactivation after SCT.

Adrenal Cortex Hormones↗