Toshihiko Izumi

St. Marianna University School of Medicine, Kawasaki Si, Kanagawa, Japan

Are you Toshihiko Izumi?

Claim your profile

Publications (8)34.77 Total impact

  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Chronic hepatic damage leads to liver fibrosis, which is characterized by the accumulation of collagen-rich extracellular matrix. However, the mechanism by which E3 ubiquitin ligase is involved in collagen synthesis in liver fibrosis is incompletely understood. This study aimed to explore the involvement of the E3 ubiquitin ligase synoviolin (Syno) in liver fibrosis. The expression and localization of synoviolin in the liver were analyzed in CCl(4)-induced hepatic injury models and human cirrhosis tissues. The degree of liver fibrosis and the number of activated hepatic stellate cells (HSCs) was compared between wild type (wt) and Syno(+/-) mice in the chronic hepatic injury model. We compared the ratio of apoptosis in activated HSCs between wt and Syno(+/-) mice. We also analyzed the effect of synoviolin on collagen synthesis in the cell line from HSCs (LX-2) using siRNA-synoviolin and a mutant synoviolin in which E3 ligase activity was abolished. Furthermore, we compared collagen synthesis between wt and Syno(-/-) mice embryonic fibroblasts (MEF) using quantitative RT-PCR, western blotting, and collagen assay; then, we immunohistochemically analyzed the localization of collagen in Syno(-/-) MEF cells. In the hepatic injury model as well as in cirrhosis, synoviolin was upregulated in the activated HSCs, while Syno(+/-) mice developed significantly less liver fibrosis than in wt mice. The number of activated HSCs was decreased in Syno(+/-) mice, and some of these cells showed apoptosis. Furthermore, collagen expression in LX-2 cells was upregulated by synoviolin overexpression, while synoviolin knockdown led to reduced collagen expression. Moreover, in Syno(-/-) MEF cells, the amounts of intracellular and secreted mature collagen were significantly decreased, and procollagen was abnormally accumulated in the endoplasmic reticulum. Our findings demonstrate the importance of the E3 ubiquitin ligase synoviolin in liver fibrosis.
    PLoS ONE 10/2010; 5(10):e13590. DOI:10.1371/journal.pone.0013590 · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Invariant natural killer T (iNKT) cells are unique T cells that regulate the immune response to microbes, cancers, and autoimmunity. We assessed the characteristics of iNKT cells from persons infected with human T-lymphotropic virus type 1 (HTLV-1). Whereas most infected persons remain asymptomatic carriers (ACs) throughout their lives, a small proportion, usually with high equilibrium proviral loads,develop 2 diseases: HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and adult T-cell leukemia (ATL). We demonstrated that the frequency of iNKT, NK, and dendritic cells in the peripheral blood of HAM/TSP and ATL patients is decreased. We also observed an inverse correlation between the iNKT cell frequency and the HTLV-1 proviral load in the peripheral blood of infected persons. Notably, in vitro stimulation of peripheral blood cells with alpha-galactosylceramide led to an increase in the iNKT cell number and a subsequent decrease in the HTLV-1-infected T-cell number in samples from ACs but not HAM/TSP or ATL patients. Our results suggest that iNKT cells contribute to the immune defense against HTLV-1, and iNKT-cell depletion plays an important role in the pathogenesis of HAM/TSP and ATL. Therefore, iNKT cell-based immunotherapy may be an effective strategy for preventing these HTLV-1-associated disorders.
    Blood 09/2009; 114(15):3208-15. DOI:10.1182/blood-2009-02-203042 · 9.78 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Human T-lymphotropic virus type 1 (HTLV-1) is a human retrovirus associated with both HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), which is a chronic neuroinflammatory disease, and adult T-cell leukemia (ATL). The pathogenesis of HAM/TSP is known to be as follows: HTLV-1-infected T cells trigger a hyperimmune response leading to neuroinflammation. However, the HTLV-1-infected T cell subset that plays a major role in the accelerated immune response has not yet been identified. Here, we demonstrate that CD4(+)CD25(+)CCR4(+) T cells are the predominant viral reservoir, and their levels are increased in HAM/TSP patients. While CCR4 is known to be selectively expressed on T helper type 2 (Th2), Th17, and regulatory T (Treg) cells in healthy individuals, we demonstrate that IFN-gamma production is extraordinarily increased and IL-4, IL-10, IL-17, and Foxp3 expression is decreased in the CD4(+)CD25(+)CCR4(+) T cells of HAM/TSP patients as compared to those in healthy individuals, and the alteration in function is specific to this cell subtype. Notably, the frequency of IFN-gamma-producing CD4(+)CD25(+)CCR4(+)Foxp3(-) T cells is dramatically increased in HAM/TSP patients, and this was found to be correlated with disease activity and severity. We have defined a unique T cell subset--IFN-gamma(+)CCR4(+)CD4(+)CD25(+) T cells--that is abnormally increased and functionally altered in this retrovirus-associated inflammatory disorder of the central nervous system.
    PLoS ONE 02/2009; 4(8):e6517. DOI:10.1371/journal.pone.0006517 · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Synoviolin is an E3 ubiquitin ligase, and its overexpression is implicated in the pathogenesis of rheumatoid arthritis (RA). We reported previously that Ets binding site 1 (EBS-1) within the synoviolin promoter is crucial for the expression of synoviolin, and GA binding protein (GABP) binds to this site. This study was undertaken to elucidate the precise mechanisms of transcriptional regulation via EBS-1. We performed purification and identification of complex components that bind to EBS-1 and inspected their contributions to the transcriptional regulation of synoviolin in rheumatoid synovial cells. We biochemically purified proteins that had EBS-1 binding activity and identified the proteins using liquid chromatography tandem mass spectrometry analysis. The identified proteins were verified to recruit and form the complex on EBS-1 using electrophoretic mobility shift assay and coimmunoprecipitation assay. Furthermore, their transcription activities were tested by reporter assays and RNA interference experiments. We identified interleukin enhancer binding factor 3 (ILF-3) as a novel factor in the complex. ILF-3 was demonstrated to activate the synoviolin promoter via association with GABPalpha in rheumatoid synovial cells. In addition, further activation was observed with ILF-2 and GABPbeta, previously reported interactants of ILF-3 and GABPalpha, respectively. Moreover, ILF-3-knockdown experiments showed reduced expression of the synoviolin gene. Our findings indicate that ILF-3, which has been known to regulate IL-2 expression in T cells, up-regulates synoviolin expression with GABPalpha in rheumatoid synovial cells. ILF-3 might be a target for RA treatment through its effect on IL-2 in T cells and synoviolin in rheumatoid synovial cells.
    Arthritis & Rheumatology 01/2009; 60(1):63-72. DOI:10.1002/art.24178 · 7.87 Impact Factor
  • PLoS ONE 01/2009; 4(8). DOI:10.1371/journal.pone.0006517.t001 · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The incidence of rheumatic fever (RF) has markedly increased in the last 10 years in Kyrgyzstan. Therefore, investigating the prevalence of group A β-hemolytic streptococcus (GABHS), which is the cause of RF, in the Kyrgyzstan population is crucial. We studied 189 subjects: 59 children [29 with RF and/or rheumatic heart disease (RHD)] and 130 adults (15 with RHD). The average age of the subjects was 41.0±10.0 years (range 8 months to 72 years). A general clinical examination and medical history including eating habits was carried out. The prevalence of GABHS was tested using the highly sensitive rapid antigen detection test (RADT) to detect the outcrop of streptococcus antigen in smears taken from the mucosal surface of the tonsils or the back of the throat. GABHS antigen was positive in 70 of a total 189 subjects [37.0%; 22/59 children (37.2%), 48/130 adults (36.9%)]. In patients with RF/RHD (n=44), GABHS was positive in 14 subjects [31.8%; 8/29 children (27.6%), 6/15 adults (40.0%)]. Thirty-two subjects with RF/RHD had frequent episodes of tonsillopharyngitis. In subjects without RF/RHD (n=145), GABHS was positive in 56 subjects [38.6%; 14/30 children (46.6%), 42/115 adults (36.5%)]. Thirty of these subjects had frequent episodes of tonsillopharyngitis. Of the 130 adults, the most-consumed dairy products included yoghurt (n=115; 88.4%), milk kasha (n=75; 57.7%) and milk (n=40; 30.7%). Of the 115 subjects in the yoghurt-consuming group, 44 (38.2%) had positive results for GABHS. In the non-yoghurt-consuming group, 4/15 subjects (26.6%) had positive results for GABHS. Using RADT for GABHS, a high prevalence of GABHS antigen was detected not only in patients with RF/RHD, but also in the healthy population (without RF/RHD). The low GABHS prevalence in children with RF/RHD (27.6%) was probably due to corresponding antibiotic therapy. In conclusion, the high prevalence of GABHS is one of the main reasons for the rapid increase in RF/RHD in Kyrgyzstan, and RADT would be an effective tool for its detection.
    Molecular Medicine Reports 11/2008; 1(6):869-74. DOI:10.3892/mmr_00000043 · 1.48 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Synoviolin is an E3 ubiquitin ligase localized in the endoplasmic reticulum (ER) and serving as ER-associated degradation system. Analysis of transgenic mice suggested that synoviolin gene dosage is implicated in the pathogenesis of arthropathy. Complete deficiency of synoviolin is fatal embryonically. Thus, alternation of Synoviolin could cause breakdown of ER homeostasis and consequently lead to disturbance of cellular homeostasis. Hence, the expression level of Synoviolin appears to be important for its biological role in cellular homeostasis under physiological and pathological conditions. To examine the control of protein level, we performed promoter analysis to determine transcriptional regulation. Here we characterize the role of synoviolin transcription in cellular homeostasis. The Ets binding site (EBS), termed EBS-1, from position -76 to -69 of the proximal promoter, is responsible for synoviolin expression in vivo and in vitro. Interestingly, transfer of EBS-1 decoy into NIH 3T3 cells conferred not only the repression of synoviolin gene expression but also a decrease in cell number. Fluorescence-activated cell sorter analysis using annexin V staining confirmed the induction of apoptosis by EBS-1 decoy and demonstrated recovery of apoptosis by overexpression of Synoviolin. Our results suggest that transcriptional regulation of synoviolin via EBS-1 plays an important role in cellular homeostasis. Our study provides novel insight into the transcriptional regulation for cellular homeostasis.
    Molecular and Cellular Biology 09/2005; 25(16):7344-56. DOI:10.1128/MCB.25.16.7344-7356.2005 · 5.04 Impact Factor