Akihiko Taguchi

Yamaguchi University, Yamaguti, Yamaguchi, Japan

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Publications (14)39.67 Total impact

  • Annals of Hematology 06/2013; · 2.87 Impact Factor
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    ABSTRACT: Aryl hydrocarbon receptor nuclear translocator (ARNT) / hypoxia-inducible factor-1ß (HIF1- ß) has emerged as a potential determinant of pancreatic ß-cell dysfunction and type 2 diabetes in humans. An 82% reduction in Arnt expression was observed in islets from type 2 diabetic donors as compared to non-diabetic donors. However, few regulators of Arnt expression have been identified. Meanwhile, disruption of the clock components CLOCK and BMAL1 is known to result in hypoinsulinemia and diabetes, but the molecular details remain unclear. In this study, we identified a novel molecular connection between Arnt and two clock-controlled output genes, albumin D-element binding protein (Dbp) and E4 binding protein 4 (E4bp4). By conducting gene expression studies using the islets of Wfs1(-/-) A(y)/a mice that develop severe diabetes due to ß-cell apoptosis, we demonstrated clock-related gene expressions to be altered in the diabetic mice. Dbp mRNA decreased by 50%, E4bp4 mRNA increased by 50%, and Arnt mRNA decreased by 30% at Zeitgever Time (ZT) 12. Mouse pancreatic islets exhibited oscillations of clock gene expressions. E4BP4, a D-box negative regulator, oscillated anti-phase to DBP, a D-box positive regulator. We also found low-amplitude circadian expression of Arnt mRNA, which peaked at ZT4. Over-expression of DBP raised both mRNA and protein levels of ARNT in HEK293 and MIN6 cell lines. Arnt promoter-driven luciferase reporter assay in MIN6 cells revealed that DBP increased Arnt promoter activity by 2.5-fold and that E4BP4 competitively inhibited its activation. In addition, on ChIP assay, DBP and E4BP4 directly bound to D-box elements within the Arnt promoter in MIN6 cells. These results suggest that in mouse pancreatic islets mRNA expression of Arnt fluctuates significantly in a circadian manner and that the down-regulation of Dbp and up-regulation E4bp4 contribute to direct suppression of Arnt expression in diabetes.
    Biochemical and Biophysical Research Communications 04/2013; · 2.41 Impact Factor
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    ABSTRACT: Insulin secretion is precisely regulated by blood glucose with unique biphasic pattern. The regulatory mechanism of the second-phase insulin release is unclear. In this study, we report that DOC2b (double C2 domain protein isoform b), a SNARE related protein, was associated with insulin vesicles and translocated to plasma membrane within several minutes upon high-glucose stimulation followed by an interaction with syntaxin4, but not syntaxin1. This binding specificity and the time course of DOC2b translocation were suitable for the regulation of second-phase insulin release. Increased DOC2b expression enhanced glucose-stimulated insulin secretion. In contrast, silencing DOC2b inhibited delayed release of insulin, without affecting rapid (∼7 min) phase secretion. Interestingly, DOC2b had no effects on KCl-triggered insulin release. These data suggest that DOC2b may be a regulator for delayed (second-phase) insulin secretion in MIN6 cells.
    Biochemical and Biophysical Research Communications 01/2009; · 2.41 Impact Factor
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    ABSTRACT: Insulin stimulates glucose uptake in skeletal muscle and adipose tissues primarily by stimulating the translocation of vesicles containing a facilitative glucose transporter, GLUT4, from intracellular compartments to the plasma membrane. The formation of stable soluble N-ethyl-maleimide-sensitive fusion protein [NSF] attachment protein receptor (SNARE) complexes between vesicle-associated membrane protein-2 (VAMP-2) and syntaxin-4 initiates GLUT4 vesicle docking and fusion processes. Additional factors such as munc18c and tomosyn were reported to be negative regulators of the SNARE complex assembly involved in GLUT4 vesicle fusion. However, despite numerous investigations, the positive regulators have not been adequately clarified. We determined the intracellular localization of DOC2b by confocal immunoflorescent microscopy in 3T3-L1 adipocytes. Interaction between DOC2b and syntaxin-4 was assessed by the yeast two-hybrid screening system, immunoprecipitation, and in vitro glutathione S-transferase (GST) pull-down experiments. Cell surface externalization of GLUT4 and glucose uptake were measured in the cells expressing DOC2b constructs or silencing DOC2b. Herein, we show that DOC2b, a SNARE-related protein containing double C2 domains but lacking a transmembrane region, is translocated to the plasma membrane upon insulin stimulation and directly associates with syntaxin-4 in an intracellular Ca(2+)-dependent manner. Furthermore, this process is essential for triggering GLUT4 vesicle fusion. Expression of DOC2b in cultured adipocytes enhanced, while expression of the Ca(2+)-interacting domain mutant DCO2b or knockdown of DOC2b inhibited, insulin-stimulated glucose uptake. These findings indicate that DOC2b is a positive SNARE regulator for GLUT4 vesicle fusion and mediates insulin-stimulated glucose transport in adipocytes.
    Diabetes 12/2008; 58(2):377-84. · 7.90 Impact Factor
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    ABSTRACT: Insulin stimulates glucose uptake in fat and muscle primarily by stimulating the translocation of vesicles containing facilitative glucose transporters, GLUT4, from intracellular compartments to the plasma membrane. Although cell surface externalization of GLUT4 is critical for glucose transport, the mechanism regulating cell surface GLUT4 remains unknown. Using a yeast two-hybrid screening system, we have screened GLUT4-binding proteins, and identified a novel glycosyl phosphatidyl inositol (GPI)-linked proteoglycan, Glypican3 (GPC3). We confirmed their interaction using immunoprecipitation and a GST pull-down assay. We also revealed that GPC3 and GLUT4 to co-localized at the plasma membrane, using immunofluorescent microscopy. Furthermore, we observed that glucose uptake in GPC3-overexpressing adipocytes was increased by 30% as compared to control cells. These findings suggest that GPC3 may play roles in glucose transport through GLUT4.
    Biochemical and Biophysical Research Communications 06/2008; 369(4):1204-8. · 2.41 Impact Factor
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    Diabetologia 10/2006; 49(9):2217-8. · 6.49 Impact Factor
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    ABSTRACT: Tumor necrosis factor-alpha (TNF-alpha) signaling through the IkappaB kinase (IKK) complex attenuates insulin action via the phosphorylation of insulin receptor substrate 1 (IRS-1) at Ser307. However, the precise molecular mechanism by which the IKK complex phosphorylates IRS-1 is unknown. In this study, we report nuclear factor kappaB essential modulator (NEMO)/IKK-gamma subunit accumulation in membrane ruffles followed by an interaction with IRS-1. This intracellular trafficking of NEMO requires insulin, an intact actin cytoskeletal network, and the motor protein Myo1c. Increased Myo1c expression enhanced the NEMO-IRS-1 interaction, which is essential for TNF-alpha- induced phosphorylation of Ser307-IRS-1. In contrast, dominant inhibitory Myo1c cargo domain expression diminished this interaction and inhibited IRS-1 phosphorylation. NEMO expression also enhanced TNF-alpha-induced Ser307-IRS-1 phosphorylation and inhibited glucose uptake. In contrast, a deletion mutant of NEMO lacking the IKK-beta-binding domain or silencing NEMO blocked the TNF-alpha signal. Thus, motor protein Myo1c and its receptor protein NEMO act cooperatively to form the IKK-IRS-1 complex and function in TNF-alpha-induced insulin resistance.
    The Journal of Cell Biology 07/2006; 173(5):665-71. · 10.82 Impact Factor
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    ABSTRACT: A 24-year-old woman with acute promyelocytic leukemia was treated with all-trans retinoic acid (ATRA) as a remission induction therapy. After pneumonia in the neutropenic period was successfully treated with antibiotic treatment, there was recurrence of high fever alone, followed by the appearance of erythema nodosum with pain in her upper limbs on day 25 of ATRA therapy. Skin biopsy neither revealed infiltration of leukemic cells nor suggested Sweet's syndrome. We considered the eruptions to be associated with ATRA, and prednisolone (30 mg/day for 5 days) was administered. Although the administration of ATRA was continued until complete remission of the leukemia, the erythema nodosum rapidly disappeared following short-term steroid therapy and no recurrence was observed. ATRA-induced erythema nodosum is rare, however it should be recognized as a possible adverse effect in ATRA therapy.
    [Rinshō ketsueki] The Japanese journal of clinical hematology 04/2005; 46(3):202-5.
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    ABSTRACT: A 67-year-old male was admitted because of lymphocytosis and huge splenomegaly. Abnormal lymphocytes had cytoplasmic hairy projections and were negative for tartrate-resistant acid phosphatase staining. The bone marrow aspirate contained many lymphocytes with the same morphology. Flow cytometric analysis revealed an increase in IgM and kappa positive B cells. They were positive for CD11c, CD19, CD20 and FMC7, and negative for CD5, CD10 and CD25. The patient was diagnosed as having hairy cell leukemia, Japanese variant. Initially interferon-alpha was administered for a month, decreasing the numbers of leukemic cells but with little effect on splenomegaly. Subsequent administration of cladribine (0.09 mg/kg, 7 days) showed a remarkable effect, and the patient has been in complete remission for 8 months.
    [Rinshō ketsueki] The Japanese journal of clinical hematology 06/2004; 45(5):405-7.
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    ABSTRACT: A 54-year-old woman complained of fever and hepato-splenomegaly. The pathological findings of a liver biopsy specimen revealed the infiltration of lymphocytes in the sinusoids and that of the laparoscopically resected spleen revealed the infiltration of lymphocytes in the red pulp, which was positive for CD3, CD43, CD45RO and T-cell intracellular antigen-1 (TIA-1) and was negative for betaF1, while the white pulp was spared. Genetic analysis of the spleen cells revealed the rearrangement of T-cell receptor (TCR) Cbeta1, Jdelta1 and Jgamma. Epstein-Barr virus (EBV) genomic DNA was detected in the spleen cells. Atypical lymphocytes appeared in the peripheral blood and bone marrow, chromosomal analysis revealed del (13) (q12 q14), trisomy 8 and breakage of RB gene. Elevated level of serum vascular endothelial growth factor (VEGF) was observed. Hepatosplenic gammadelta T cell lymphoma (GDTL) was diagnosed. The patient was treated with chemotherapy by cyclophosphamide, hydroxydoxorubicin, vincristine and prednisolone (CHOP), however, it was ineffective, and the patient died of hemorrhage from the lymphoma involvement of the intestine 5 months after the onset of disease.
    Internal Medicine 03/2004; 43(2):120-5. · 0.97 Impact Factor
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    ABSTRACT: A 75-year-old women, who had been well until 2 weeks ago, consulted a phychiatrist because of stupor and appetite loss. A high serum calcium level (16.4mg/dl) was found and she was referred to our department. Calcium level rapidly increased to 25.2 mg/dl within a week regardless of a large amount of saline infusion with simultaneous administation of diuretics, calcitonin and prednisolone. Serum calsium level decreased gradually after six times of hemodialyses and infusion of bisphosphonate, pamidronate disodium. The level of intact PTH turned out to be extremely high (520pg/ml) and PTH-related protain was in the normal range. Parathyroid crisis due to primary hyparathyroidism was diagnosed. Procedures aim to localize the affected parathyroid glands including ultrasonography, computed tomography, magnetic resonance imaging and subtraction scintigraphy failed. Technetium 99m sestamibi scan after sedation with diazepan showed an abnormal image just below the right lobe of the thyroid. During the neck operation, an adenoma (3 x 1 cm) was detected and resected completely. No other affected glands were found. The levels of serum calcium due to persistent hypercalcemia remained six months later after the operation.
    01/2004;
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    ABSTRACT: Two cases of acute myeloblastic leukemia (AML) evolving from aplastic anemia are presented. The first case was diagnosed 18 years ago, and treatment with bolus methylprednisolone, prednisolone, and androgens resulted in partial hematological response. Severe pancytopenia recurred, and AML M0 by French-American-British classification developed. The second case was diagnosed 7 years ago. The patient had HLA DRB1*1501, and treatment with granulocyte colony-stimulating factor (G-CSF), cyclosporine, and methenolone resulted in complete hematological response. Thrombocytopenia recurred and did not respond to cyclosporine and methenolone or to later treatment with antithymocyte globulin, and AML M1 developed. Cytogenetic studies demonstrated 7q- in the first patient and +8 in the second patient. No mutations of N-ras or p53 were observed in either patient. These patients were treated with cytosine arabinoside, aclacinomycin, and G-CSF (CAG) chemotherapy, and the number of leukemic cells decreased substantially. However, pancytopenia after CAG chemotherapy persisted, and the first patient died of pneumonia and the second patient of cerebral hemorrhage.
    International Journal of Hematology 07/2003; 77(5):471-5. · 1.68 Impact Factor
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    ABSTRACT: A 54-year-old man with colon cancer underwent hemicolectomy. He received postoperative adjuvant chemotherapy with UFT (tegafur/uracil at a 1 : 4 molar ratio) and mitomycin C (MMC) for 3 years. Three years and 4 months after the start of chemotherapy, pancytopenia was noted. Bone marrow aspiration smear demonstrated an increased number of immature erythroblasts, including megaloblasts and myeloblasts. Chromosomal analysis demonstrated structural and numerical abnormalities of 5, 7, 15, and 17. Therapy-related erythroleukemia, acute myeloid leukemia (AML), M6, was diagnosed. The disease progressed after 5 months, and the patient was received chemotherapy with cytosine arabinoside, aclacinomycin, and granulocyte colony-stimulating factor (CAG), and showed a partial hematological response. Careful monitoring for the generation of therapy-related leukemia is needed when UFT and MMC are used for postoperative adjuvant chemotherapy for colorectal cancer.
    International Journal of Clinical Oncology 03/2003; 8(1):56-9. · 1.73 Impact Factor
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    ABSTRACT: We encountered two cases of autoimmune hemolytic anemia (AIHA) with undetectable glycosylated hemoglobin (HbA1C) level at diagnosis. Hemolytic anemia improved by administration of prednisolone (PSL) and HbA1C became measurable after response.