Biomedical subjects

Hiroyuki Fujisaki

Publications and source records attributed to Hiroyuki Fujisaki.

6 recordsLinked to original sources

PubMed2005

Structural basis for mRNA Cap-Binding regulation of eukaryotic initiation factor 4E by 4E-binding protein, studied by spectroscopic, X-ray crystal structural, and molecular dynamics simulation methods.

Taking advantage of the Trp73 residue located close to the 4E-BP binding site of eIF4E, the interaction between the 4E-BP isoform and eIF4E was investigated by the Trp fluorescence titration method. Although no significant difference was observed among the association constants of three 4E-BP isoforms, the binding preference of 4E-BP2 over 4E-BP1 and -BP3 was shown, probably due to the effect of a 4E-BP2-specific LDRR (60-63) sequence for the binding with eIF4E. By contrast, surface plasmon resonance (SPR) analyses showed the binding preference of 4E-BP1, although the difference among the isoforms was also not significant. This inconsistency with fluorescence analysis likely resulted from the different observation points of the interaction, i.e., local and overall interactions observed by the fluorescence and SPR methods, respectively. To clarify the structural basis for these spectroscopic results, the crystal structure of the ternary complex of m7GpppA-eIF4E-4E-BP1 fragment (Thr36-Thr70) was analyzed by the X-ray diffraction method. Crystal structure analysis at 2.1 A resolution revealed that the 4E-BP1 fragment, assigned to the Pro47-Pro66 peptide moiety, adopted a reverse L-shaped conformation involving the beta sheet and alpha-helical structures and was located at the root of the handle of the temple-bell-shaped eIF4E through hydrophilic and hydrophobic interactions. Based on the observed binding mode, possible interactions with the three 4E-BP isoforms have been discussed. On the other hand, since the crystal structural comparison with the previously determined m7GpppA-eIF4E-4E binary complex showed that the docking of the 4E-BP1 fragment does not significantly affect the overall tertiary structure and cap-binding scaffold of eIF4E, the dynamic regulation of the cap-binding of eIF4E by 4E-BP1 was investigated by molecular dynamics (MD) simulations. Consequently, the simulation suggested that (i) the helical region of the 4E-BP1 peptide is important for the binding with eIF4E, (ii) the existence of a cap structure stabilizes the binding of eIF4E with 4E-BP, (iii) the binding of 4E-BP stabilizes the cap-binding pocket of eIF4E, and (iv) the phosphorylation of Ser67 alone does not induce the separation of 4E-BP from eIF4E, but increases the structural rigidity of 4E-BP. These results provide the structural basis for the mRNA cap-binding regulation of eIF4E by 4E-BP.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Tacrolimus-related encephalopathy following allogeneic stem cell transplantation in children.

Tacrolimus is a potent immunosuppressive drug widely used to prevent and treat graft-versus-host disease (GVHD) in stem cell transplantation (SCT). Among 49 patients receiving tacrolimus who underwent SCT from January 2000 to July 2003, 10 patients (20%) developed encephalopathy. The commonly observed symptoms were convulsions and drowsiness, and most patients complained of signal symptoms such as headache, nausea, and cortical blindness before onset. The most common abnormality on neuroimages was high-intensity lesions in white matter on magnetic resonance imaging T2-weighted or fluid-attenuated inversion recovery images. At onset, all patients were receiving treatment for acute GVHD (grade II/III) or extensive chronic GVHD and demonstrated an abrupt increase in blood pressure from baseline levels. The serum tacrolimus concentration was generally within acceptable levels at onset. Symptoms gradually improved in all patients when the blood pressure was lowered with antihypertensive medication, regardless of continued tacrolimus administration following a short-term suspension. The pathogenesis of tacrolimus-related encephalopathy is multifactorial, although refractory GVHD and a sudden increase in blood pressure seem to be major predisposing factors. Because the withdrawal of tacrolimus or switching to less potent anti-GVHD agents usually worsens the GVHD, the administration of tacrolimus should be managed by closely monitoring serum levels and controlling blood pressure.

Antihypertensive Agents↗

PubMed2004

LRRC8 involved in B cell development belongs to a novel family of leucine-rich repeat proteins.

In a previous study, we isolated a novel gene, LRRC8 (leucine-rich repeat-containing 8), in a girl with congenital agammaglobulinemia. We have now identified four unknown LRRC8-like genes, named TA-LRRP, AD158, LRRC5, and FLJ23420. Their predicted structures are very similar to each other, and highly conserved between humans and the mouse. All five genes encode proteins consisting of 16 extracellular leucine-rich repeats (LRRs), all of which have four transmembrane regions except for FLJ23420. These genes belong to a novel family, designated the LRRC8 family, within the superfamily of LRR proteins. TA-LRRP, AD158, and LRRC5 might be implicated in proliferation and activation of lymphocytes and monocytes.

Amino Acid Sequence↗

PubMed2004

Hepatocyte growth factor plays roles in the induction and autocrine maintenance of bone marrow stromal cell IL-11, SDF-1 alpha, and stem cell factor.

OBJECTIVE: Bone marrow (BM) stroma provides the microenvironment required for long-term hematopoiesis, and this is supported by direct interaction between stromal cells and hematopoietic cells, mediated by adhesion molecules, and through cytokine releases from the BM stroma. In a previous study, we demonstrated that hepatocyte growth factor (HGF) is one of the cytokines constitutively produced from BM stromal cells, promoting hematopoiesis mainly in an indirect way. We also showed that stromal cells themselves express HGF receptor c-MET. It was therefore postulated that HGF exerts its effect on hematopoiesis and maintenance of the hematopoietic microenvironment in a paracrine and autocrine manner. METHODS: The effect of HGF on stromal cells was analyzed by neutralizing intrinsic HGF. RESULTS: Addition of neutralizing anti-HGF antibody inhibited the ability of BM stromal cells to support colony formation from CD34(+) cells and reduced production of significant cytokines from stromal cells, interleukin-11 (IL-11), stromal cell-derived factor-1 alpha (SDF-1 alpha), and to a lesser extent, stem cell factor (SCF). Furthermore, this neutralizing antibody reduced proliferation of stromal cells and inhibited adhesion of stromal cells to collagen type IV and fibronectin. Inhibition of adhesion to fibronectin was mediated by inhibition of alpha(5)beta(1)-integrin. CONCLUSION: These findings indicate that HGF constitutively produced from BM stromal cells is an autocrine regulator, which is able to maintain the hematopoietic microenvironment through stimulating proliferation and adhesion to the extracellular matrix and promoting hematopoiesis through inducing constitutive production of IL-11, SDF-1 alpha, and SCF by stromal cells themselves.

Autocrine Communication↗

PubMed2003

A congenital mutation of the novel gene LRRC8 causes agammaglobulinemia in humans.

A girl with congenital agammaglobulinemia and minor facial anomalies lacked B cells in peripheral blood: karyotypic analysis of white blood cells showed balanced translocation, t(9;20)(q33.2;q12). In the current study, we isolated a novel gene, leucine-rich repeat-containing 8 (LRRC8), at the translocation site on chromosome 9. It has four transmembrane helices with one isolated and eight sequentially located leucine-rich repeats (LRRs) and constitutes a new protein family. It is expressed on T cells as well as on B-lineage cells. Translocation truncates the LRRC8 gene, resulting in deletion of the eighth, ninth, and half of the seventh LRR domains located close to the C-terminal. The truncated form of the LRRC8 gene is transcribed with sequences from the noncoding region adjacent to the truncated seventh LRR. Protein products derived from the truncated gene are coexpressed on white blood cells with the intact LRRC8 protein from the untranslocated allele. Transplantation experiments with murine bone marrow cells that were forced to express the truncated LRRC8 show that expression of the truncated protein inhibited B cell development. These results indicate that LRRC8 is responsible for the B cell deficiency in this patient and is required for B cell development.

Adolescent↗

PubMed2002

Establishment of a monosomy 7 leukemia cell line, MONO-7, with a ras gene mutation.

A monosomy 7 leukemia cell line, designated MONO-7, was established from the peripheral blood of a patient with monosomy 7 acute myelocytic leukemia (French-American-British classification M0). The cells were cultured continuously for more than 24 months in RPMI-1640 medium supplemented with 10% heat-inactivated fetal calf serum. The cell line exhibits an unclassified appearance. Cytochemically, alpha-naphthol-acetate esterase and myeloperoxidase are negative. Immunophenotypically, the cell line expresses CD33, CD13, CD56, CD34, CD38, HLA-DR, and CD45, but lacks T and B cell-associated antigens. Karyotypic analysis of the cell line showed only 45,XY,-7. Analysis of the N-ras gene mutation demonstrated identical mutations in fresh leukemic cells and the MONO-7 cell line. Clonal rearrangements of the immunoglobulin heavy-chain gene, T-cell receptor beta-chain gene, or T-cell receptor gamma-chain gene were not found in DNA extracted from MONO-7 cells. The growth of MONO-7 cells in vitro was stimulated by recombinant human granulocyte-macrophage colony-stimulating factor or interleukin 3. To our knowledge, this is the first report of the establishment of a cell line with the karyotype 45,XY,-7 without any other abnormality and with a ras gene mutation.

Acute Disease↗