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Biomedical subjects

K Fujisawa

Publications and source records attributed to K Fujisawa.

At least 19 recordsLinked to original sources
PubMed1999

Citron, a Rho-target, interacts with PSD-95/SAP-90 at glutamatergic synapses in the thalamus.

Proteins of the membrane-associated guanylate kinase family play an important role in the anchoring and clustering of neurotransmitter receptors in the postsynaptic density (PSD) at many central synapses. However, relatively little is known about how these multifunctional scaffold proteins might provide a privileged site for activity- and cell type-dependent specification of the postsynaptic signaling machinery. Rho signaling pathway has classically been implicated in mechanisms of axonal outgrowth, dendrogenesis, and cell migration during neural development, but its contribution remains unclear at the synapses in the mature CNS. Here, we present evidence that Citron, a Rho-effector in the brain, is enriched in the PSD fraction and interacts with PSD-95/synapse-associated protein (SAP)-90 both in vivo and in vitro. Citron colocalization with PSD-95 occurred, not exclusively but certainly, at glutamatergic synapses in a limited set of neurons, such as the thalamic excitatory neurons; Citron expression, however, could not be detected in the principal neurons of the hippocampus and the cerebellum in the adult mouse brain. In a heterologous system, Citron was shown to form a heteromeric complex not only with PSD-95 but also with NMDA receptors. Thus, Citron-PSD-95/SAP-90 interaction may provide a region- and cell type-specific link between the Rho signaling cascade and the synaptic NMDA receptor complex.

Animals↗
PubMed1999

Involvement of leukotriene B4 in arthritis models.

We investigated the role of leukotriene B4 (LTB4) in murine arthritis models using a leukotriene A4 (LTA4) hydrolase inhibitor, SA6541. SA6541 inhibited the severity of collagen-induced arthritis and muramyl dipeptide (MDP)-induced hyperproliferation of synovial cells in vivo. SA6541 also inhibited LTA4-induced hyperproliferation of synovial stromal cells in vitro. These results suggest that LTB4 may play an important role in arthritis models.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1999

[Three children with systemic cat scratch disease].

Three girls with systemic cat scratch disease, aged 10, 13 and 9 years, were reported. They presented a prolonged fever and back pain in the early stage of the disease, and had no regional lymphadenopathy. Two of them had hepatosplenic granulomas, one with multiple 5 mm hypoechoic lesions in the liver and spleen, and the other with a single 2.5 cm hypodense lesion in the left hepatic lobe. The latter patient underwent a partial left hepatic lobectomy. All patients had elevated titers of antibodies to Bartonella henselae. Polymerase chain reaction detected B. henselae DNA in tissue specimens of the patient who underwent a hepatic lobectomy. Cat scratch disease should be recognized as a cause of fever of unknown origin because the prevalence of B henselae infection might be higher in Japan.

Adolescent↗
PubMed1999

Conserved T cell receptor complementarity-determining region 3 of ocular T cells in mice with experimental autoimmune uveoretinitis.

PURPOSE: To characterize T cells infiltrating into the ocular tissues of mice with experimental autoimmune uveoretinitis (EAU) immunized with interphotoreceptor retinoid-binding protein (IRBP). METHODS: The T cell receptor (TCR) repertoire on T cells obtained from ocular lesions of EAU mice was analyzed by reverse transcriptase-polymerase chain reaction. The clonotype of the T cells was examined by the single-strand conformation polymorphism (SSCP) method, followed by sequence analysis of the TCR beta-chain complementarity-determining region 3 (CDR3). RESULTS: The repertoire of the TCR BV gene in T cells from inflamed lesions was heterogeneous. SSCP analysis showed accumulation of multiple T cells specifically in ocular tissues of EAU mice, suggesting that these cells were expanded by an antigen-driven stimulation. Junctional sequence analysis demonstrated the presence of highly conserved amino acid sequence motifs (AGTGG, AGD) in CDR3 of BV2-positive T cells. CONCLUSIONS: Our findings suggest that T cells infiltrating into ocular lesions of EAU mice recognize restricted T cell epitopes of IRBP, resulting in autoimmune uveoretinitis.

Amino Acid Sequence↗
PubMed1998

Overview and initial results of the very long baseline interferometry space observatory programme

High angular resolution images of extragalactic radio sources are being made with the Highly Advanced Laboratory for Communications and Astronomy (HALCA) satellite and ground-based radio telescopes as part of the Very Long Baseline Interferometry (VLBI) Space Observatory Programme (VSOP). VSOP observations at 1.6 and 5 gigahertz of the milli-arc-second-scale structure of radio quasars enable the quasar core size and the corresponding brightness temperature to be determined, and they enable the motions of jet components that are close to the core to be studied. Here, VSOP images of the gamma-ray source 1156+295, the quasar 1548+056, the ultraluminous quasar 0014+813, and the superluminal quasar 0212+735 are presented and discussed.

Journal Article↗
PubMed1998

Role of citron kinase as a target of the small GTPase Rho in cytokinesis.

During mitosis, a ring containing actin and myosin appears beneath the equatorial surface of animal cells. This ring then contracts, forms a cleavage furrow and divides the cell, a step known as cytokinesis. The two daughter cells often remain connected by an intercellular bridge which contains a refringent structure known as the midbody. How the appearance of this ring is regulated is unclear, although the small GTPase Rho, which controls the formation of actin structures, is known to be essential. Protein kinases are also thought to participate in cytokinesis. We now show that a splice variant of a Rho target protein, named citron, contains a protein kinase domain that is related to the Rho-associated kinases ROCK14 and ROK, which regulate myosin-based contractility. Citron kinase localizes to the cleavage furrow and midbody of HeLa cells; Rho is also localized in the midbody. We find that overexpression of citron mutants results in the production of multinucleate cells and that a kinase-active mutant causes abnormal contraction during cytokinesis. We propose that citron kinase regulates cytokinesis at a step after Rho in the contractile process.

Alternative Splicing↗
PubMed1998

Different regions of Rho determine Rho-selective binding of different classes of Rho target molecules.

Based on their Rho binding motifs several Rho target molecules can be classified into three groups; class I includes the protein kinase PKN, rhophilin, and rhotekin, class II includes the protein kinases, Rho-associated coiled-coil containing protein kinases, ROCK-I and ROCK-II, and class III includes citron. Taking advantage of the selectivity in recognition by these targets between Rho and Rac, we examined the regions in Rho required for selective binding of each class of Rho target molecules. Yeast two-hybrid assays were performed using Rho/Rac chimeras and either rhophilin, ROCK-I, or citron. This study showed the existence of at least two distinct regions in Rho (amino acids 23-40 and 75-92) that are critical for the selective binding of these targets. The former was required for binding to citron, whereas the latter was necessary for binding to rhophilin. On the other hand, either region showed affinity to ROCK-I. This was further confirmed by ligand overlay assay using both recombinant ROCK-I and ROCK-II proteins. Consistently, Rho/Rac chimeras containing either region can induce stress fibers in transfected HeLa cells, and this induction is suppressed by treatment with Y-27632, a specific inhibitor of ROCK kinases. These results suggest that the selective binding of different classes of Rho targets to Rho is determined by interaction between distinct Rho-binding motifs of the targets and different regions of Rho.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Evidence for autoantigens of Env/Tax proteins in human T cell leukemia virus type I Env-pX transgenic mice.

OBJECTIVE: To examine T cell clonotypes infiltrating into arthritic joints and to investigate whether human T cell leukemia virus type I (HTLV-I) env-pX gene products act as autoantigens in HTLV-I env-pX transgenic mice. METHODS: Complementary DNA (cDNA) encoding the V-D-J (third complementarity-determining region [CDR3]) region of T cell receptor beta chain was amplified by Vbeta family polymerase chain reaction. T cell clonotypes were detected by a single-strand conformational polymorphism method, and sequence analysis of the CDR3 region was performed. RESULTS: Distinct oligoclonal T cell expansion was observed in arthritic joints, and a conserved amino acid motif in the CDR3 region was found in T cells infiltrating joints. Moreover, several intraarticular T cells recognized HTLV-I Env and Tax proteins. CONCLUSION: Our results suggest that HTLV-I Env and Tax proteins act as autoantigens that are recognized by autoreactive T cells in inflamed arthritic lesions in the HTLV-I env-pX transgenic mouse. Thus, some T cells infiltrating the joint recognize Env or Tax protein. These cells may trigger chronic arthritis in HTLV-I env-pX transgenic mice.

Amino Acid Sequence↗
PubMed1998

Extracellular human T cell leukemia virus type I tax protein stimulates the proliferation of human synovial cells.

OBJECTIVE: The present study was designed to investigate whether the proliferation of normal synovial cells from patients with meniscus injury is stimulated by human T cell leukemia virus type I (HTLV-I) Tax protein. METHODS: The effect of Tax protein on the proliferation of synovial cells was evaluated using a 3H-thymidine incorporation assay. Production of cytokines was determined by enzyme-linked immunosorbent assay. Nuclear factor kappaB (NF-kappaB) DNA binding activity and the transcription of several NF-kappaB-mediated genes was detected by electrophoretic mobility shift assay and reverse transcriptase-polymerase chain reaction. RESULTS: The proliferation of synovial cells, as well as their expression of tumor necrosis factor alpha, granulocyte-macrophage colony-stimulating factor, and interleukin-6, was significantly enhanced by extracellular Tax at concentrations of 2.5 pM to 25 nM. In contrast, extracellular bacterial extract did not change the cytokine expression or the proliferation of these cells. Proliferation of synovial cells induced by Tax protein may be due to activated expression of several cytokines and protooncogenes that contain NF-kappaB regulatory sequences. CONCLUSION: Our results suggest that extracellular Tax can regulate the expression of endogenous cellular genes in synovial cells and may contribute to the NF-kappaB-mediated synovial hyperplasia.

Cell Division↗
PubMed1998

High-turnover osteopenia in preterm infants: determination of urinary pyridinium cross-links of collagen.

Osteopenia is a frequent condition in preterm infants, but its pathogenesis is uncertain. In the present study, we measured longitudinal changes in the excretion of pyridinium cross-links of collagen (specific markers of bone resorption) and evaluated the relationship between collagen cross-links and other indexes of bone and renal function in preterm infants. In these infants, urinary collagen cross-links were markedly increased on day 7 and day 30 of life and at estimated full-term gestation. The values were several times higher than those of older children and almost comparable to those of healthy full-term infants. Cross-link excretion did not correlate with beta2-microglobulin (B2M) or N-acetyl-beta-D-glucosaminidase (NAG) activity (markers of renal function), indicating that cross-link excretion is not influenced directly by infantile renal function. High serum osteocalcin and low bone mineral density (BMD) in the lumbar spine were also observed at estimated full-term gestation. There was no significant correlation between collagen cross-link excretion and either serum osteocalcin or spine BMD. We conclude that a state of high bone turnover underlies the development of osteopenia in preterm infants.

Aging↗