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T Tamura

Publications and source records attributed to T Tamura.

At least 595 records · Page 33Linked to original sources
PubMed1994

Isolation and characterization of alpha-type HC3 and beta-type HC5 subunit genes of human proteasomes.

Eukaryotic proteasomes from an evolutionarily conserved multi-gene family and are thought to have originated from a common ancestral gene and diverged into alpha-type and beta-type subgroups. To understand the molecular basis of the proteasome genes, we isolated and characterized two human proteasome genes econding the alpha-type HC3 and beta-type HC5 subunit. The functional genes for HC3 and HC5 are similar in being approximately 15 kb in length, but differ in having exon numbers of 9 and 6, respectively. Analyses of about 2.5 to 3.0 kb of the 5'-flanking regions of these two genes revealed the absence of TATA and CAAT promoter elements. However, two or three GC boxes were found. By analysis of the transcriptional regulatory activities in the 5'-flanking regions of the two genes, these GC boxes were found to function coordinately as promoters of the two genes. Interestingly, the HC3 gene possesses an additional silencer element in the 5'-upstream region near the first exon. This element is also able to repress the promoter activities of other genes, such as the HC5 and the type 1 glucose transporter genes, irrespective of whether it has a sense or antisense orientation, indicating that it acts as a general transcriptional silencer. The HC5 gene does not have this silence element, and its promoter activity is five to ten times that of HC3. These results show that the human proteasomal HC3 and HC5 genes differ not only in their genomic structures, such as their numbers of exons and their exon-intron organizations, but also in the mechanisms regulating their transcription, suggesting that they diverged at an early stage of evolution.

Animals↗
PubMed1994

Isolation of rat TATA factor as an active 75kDa protein complex.

A general transcription factor TFIID was purified from rat liver by a sequential column chromatography including organomercurial Sepharose and Sephacryl S-200 chromatographies, which were developed with an acidic buffer (pH5.5). Analyses by SDS-polyacrylamide gel electrophoresis, assay of eluants after renaturation, and immunoblotting showed that isolated TATA factor is an active 75kDa protein complex which contains 36kDa TATA-binding protein.

Animals↗
PubMed1994

Sequence analyses and inter-species comparisons of three novel human proteasomal subunits, HsN3, HsC7-I and HsC10-II, confine potential proteolytic active-site residues.

Proteasomes play a major role in non-lysosomal pathways of protein turnover mediated by distinct multiple proteolytic activities. Identification of their active-site residues is important for elucidating their catalytic mechanisms. Here we report the nucleotide sequences of three human proteasomal subunits, HsN3, HsC7-I and HsC10-II, coding for proteins with 264, 201 and 205 amino acid residues with calculated molecular weights of 29,192, 22,836 and 22,931, respectively. Sequence comparison showed that all three proteins belong to the beta-type superfamily and that they are the human counterparts of subunits reported to participate in the peptidyl-glutamyl-peptide hydrolyzing, chymotrypsin-like and trypsin-like activity of this complex. Alignments of the putative catalytically active subunits of various species revealed several family-specifically conserved serinyl residues within highly conserved amino acid stretches. Based on localization and hydrophobicity, the roles of these amino acid residues as active site and substrate binding site candidates are discussed.

Amino Acid Sequence↗
PubMed1994

cDNA cloning and interferon gamma down-regulation of proteasomal subunits X and Y.

Proteasomes are the proteolytic complex responsible for major histocompatibility complex (MHC) class I-restricted antigen presentation. Interferon gamma treatment increases expression MHC-encoded LMP2 and LMP7 subunits of the proteasome and decreases expression of two proteasome subunits, named X and Y, which alters the proteolytic specificity of proteasomes. Molecular cloning of complementary DNAs encoding X and Y showed that their proteins are proteasomal subunits with high amino acid similarity to LMP7 and LMP2, respectively. Thus, interferon gamma may induce subunit replacements of X and Y by LMP7 and LMP2, respectively, producing proteasomes perhaps more appropriate for the immunological processing of endogenous antigens.

Amino Acid Sequence↗
PubMed1994

Effect of high-fat diet on gene expression of GLUT4 and insulin receptor in soleus muscle.

Gene expression of GLUT4 and insulin receptor in soleus muscle of high-fat and high-carbohydrate diet fed rats was studied by measuring mRNA. High-fat diet feeding increased plasma glucose but decreased plasma insulin level. Glucose uptake in soleus muscle measured by 2-deoxy-D-glucose technique was lower in high-fat than high-carbohydrate diet fed rats. GLUT4 mRNA level in soleus muscle was significantly decreased but insulin receptor mRNA was similar in high-fat compared with high-carbohydrate diet fed rats. Insulin receptor exists in two forms generated by alternative splicing of a primary gene transcript. There was no difference in the relative expression of insulin receptor isoform mRNAs between high-fat and high-carbohydrate diet fed rats. These results suggest that high-fat diet impairs glucose metabolism in muscle by reducing transcription of GLUT4 without affecting gene expression of insulin receptor.

Alternative Splicing↗
PubMed1994

ATP- and antizyme-dependent endoproteolysis of ornithine decarboxylase to oligopeptides by the 26 S proteasome.

Previously we reported that ornithine decarboxylase (ODC) is degraded ATP-dependently by the 26 S proteasome in the presence of antizyme (AZ), an ODC inhibitor (Murakami, Y., Matsufuji, S., Kameji, T., Hayashi, S., Igarashi, K., Tamura, T., Tanaka, K., and Ichihara, A. (1992) Nature 360, 597-599). Here we examined the cleavage of ODC by the 26 S proteasome. When ODC purified from ODC-overproducing cells was incubated with the 26 S proteasome and with AZ fused with maltose-binding protein (MBP) in the presence of ATP, ODC was degraded specifically without appreciable breakdown of MBP-AZ. The major degradation products of ODC, which were separated by high performance liquid chromatography on a reverse-phase column, were identified by N-terminal amino acid sequencing. The 26 S proteasome generated a variety of short peptides of 5-11 amino acid residues derived from regions throughout the ODC sequence. No detectable amounts of free amino acid residues were produced, indicating endoproteolytic degradation of ODC by the 26 S proteasome. Their major sites for cleavage of ODC by the 26 S proteasome were on the carboxyl sides of neutral/hydrophobic amino acid residues, but a few were on those of acidic or basic amino acid residues. These results demonstrate that the 26 S proteasome causes exhaustive endoproteolysis of the naturally occurring short-lived protein ODC in a multicatalytic and ATP-dependent manner.

Adenosine Triphosphate↗
PubMed1994

In vivo targeting function of N-linked oligosaccharides with terminating galactose and N-acetylgalactosamine residues.

N-Linked biantennary, triantennary, and core fucosylated biantennary oligosaccharides were isolated from animal glycoproteins and derivatized at their reducing end with Boc-tyrosine. The terminal Gal residues were enzymatically removed and replaced with GalNAc. Tyrosinamide-oligosaccharides were radioiodinated and administered intravenously to mice. Pharmacokinetic and biodistribution studies revealed structure-dependent differences in the steady-state volume of distribution, total body clearance rate, and targeting efficiency. Tyrosinamide-oligosaccharides were found to resist metabolism relative to a natural triantennary glycopeptide which was rapidly degraded in vivo. Triantennary oligosaccharides containing terminal Gal or Gal-NAc targeted the liver efficiently whereas biantennary oligosaccharides containing terminal Gal residues and differing only in their core fucosylation avoided recognition by the asialoglycoprotein receptor and were cleared unmetabolized by renal filtration. In contrast, biantennary oligosaccharides containing terminal Gal-NAc residues targeted the liver with much greater efficiency than Gal-terminated triantennary oligosaccharide. Core fucosylation reduced the metabolism rate of tyrosinamide-biantennary in the liver. The results establish the utility of tyrosinamide-oligosaccharides as probes to analyze the ligand specificity of mammalian lectins in vivo and demonstrate that a GalNAc-terminated biantennary is a potent ligand for the asialoglycoprotein receptor.

Acetylgalactosamine↗
PubMed1994

Synaptobrevin/vesicle-associated membrane protein (VAMP) of Aplysia californica: structure and proteolysis by tetanus toxin and botulinal neurotoxins type D and F.

Synaptobrevin/vesicle-associated membrane protein (VAMP) and syntaxin are potential vesicle donor and target membrane receptors of a docking complex that requires N-ethylmaleimide-sensitive factor (NSF) and soluble NSF-attachment proteins as soluble factors for vesicle fusion with target membranes. Members of this docking complex are the target of clostridial neurotoxins that act as zinc-dependent proteases. Molecular cloning of the Aplysia californica synaptobrevin cDNA revealed a 180-residue polypeptide (M(r), 19,745) with a central transmembrane region and an atypically large C-terminal intravesicular domain. This polypeptide integrates into membranes at both the co- and posttranslational level, as shown by modification of an artificially introduced N-glycosylation site. The soluble and membrane-anchored forms of synaptobrevin are cleaved by the light chains of the botulinal toxins type D and F and by tetanus toxin involving the peptide bonds Lys49-Ile50, Gln48-Lys49, and Gln66-Phe67, respectively. The active center of teh tetanus toxin light chain was identified by site-specific mutagenesis. His233, His237, Glu234, and Glu270/271 are essential to this proteolytic activity. Modification of histidine residues resulted in loss of zinc binding, whereas a replacement of Glu234 only slightly reduced the zinc content.

Amino Acid Sequence↗
PubMed1994

Phase I clinical trial of irinotecan (CPT-11), 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxy-camptothecin, and cisplatin in combination with fixed dose of vindesine in advanced non-small cell lung cancer.

Irinotecan hydrochloride (CPT-11), a semisynthetic derivative of camptothecin, has been demonstrated to be active against solid tumors such as non-small cell lung cancer and colorectal cancer. Two combination phase I trials were undertaken to determine the maximum tolerated dose of CPT-11 in combination with cisplatin and vindesine in patients with advanced non-small cell lung cancer. All 46 patients (age 32-73 years) entered into these trials had a good performance status (Eastern Cooperative Oncology Group score, 0-1) and had received no prior chemotherapy or radiotherapy. In the first trial, 14 stage IV and 2 stage IIIb patients were studied; in the second trial 30 patients with stage IV disease were accrued. In the first trial, CPT-11 was given as a 90-min i.v. infusion on days 1 and 8 in combination with a fixed dose of cisplatin (100 mg/m2, i.v., on day 1) and vindesine (3 mg/m2, i.v., on days 1 and 8), every 4 weeks. The starting dose of CPT-11 was 25 mg/m2, and the dose was increased in increments of 25 mg/m2. In the second trial, the doses of either CPT-11 (days 1 and 8) or cisplatin (day 1) were escalated with a fixed dose of vindesine (same dose as the first study) given in a 4-week cycle. The starting doses of CPT-11 and cisplatin were 20 and 60 mg/m2, respectively, and the dose of either CPT-11 or cisplatin was increased in increments of 20 mg/m2. At least 3 patients were entered at each dose level in both trials. Use of granulocyte colony-stimulating factor or granulocyte-macrophage colony-stimulating factor was not permitted in this trial. In the first trial, grade 4 granulocytopenia and grade > or = 3 diarrhea were dose limiting at 50 mg/m2 CPT-11, which represented the maximum tolerated dose. At the subsequent dose of CPT-11, 7 new patients were requited at the 50% reduced dose level of 37.5 mg/m2 on days 1 and 8. Nine patients were evaluated for response, and 4 of them achieved a partial response. In spite of a low dose of CPT-11 (25-37.5 mg/m2), the maximum concentration in plasma of CPT-11 (> 0.4 micrograms/ml) reached > 10-fold the in vitro concentration of CPT-11 required for 50% inhibition of growth. In the second trial, the dose-limiting toxicities were grade 4 granulocytopenia lasting for > or = 7 days and grade > or = 3 diarrhea.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1994

Replacement of proteasome subunits X and Y by LMP7 and LMP2 induced by interferon-gamma for acquirement of the functional diversity responsible for antigen processing.

Proteasomes catalyze the non-lysosomal, ATP-dependent selective breakdown of ubiquitinated proteins and are thought to be responsible for MHC class I-restricted antigen presentation. Recently, we reported that gamma interferon (IFN-gamma) induced not only marked synthesis of the MHC-encoded proteasome subunits LMP2 and LMP7, but also almost complete loss of two unidentified proteasome subunits tentatively designated as X and Y in various human cells. Here, we show that subunit X is a new proteasomal subunit highly homologous to LMP7, and that subunit Y is identical to the LMP2-related proteasomal subunit delta. Thus, IFN-gamma appears to induce subunit replacements of X and Y by LMP7 and LMP2, respectively, producing 'immuno-proteasomes' with the functional diversity responsible for processing of endogenous antigens.

Amino Acid Sequence↗
PubMed1994

Multimerization of the mouse TATA-binding protein (TBP) driven by its C-terminal conserved domain.

The conformational states of the mouse TATA-binding protein (TBP) in solution were studied. A histidine tag and a factor Xa recognition site-carrying mouse TBP was expressed in E. coli, highly purified, and its fundamental functions as a TBP were demonstrated. We analyzed the molecular states of mouse TBP by gel filtration and glycerol gradient sedimentation, and found that TBP forms heterogeneous multimers in solution. Direct binding of TBP molecules to each other was proven by the far-Western procedure. Analyses using TBPs truncated at the N- and C-termini demonstrated that the functionally important C-terminal domain was responsible for homomultimer formation, and the N-terminal domain enhances multimerization. Furthermore, it was found that the TATA sequence dissociates homomultimers, and only monomeric TBP binds to the TATA-box. We suggest that TBP shares structural motifs in the C-terminal conserved domain for intermolecular interaction and TATA-binding.

Animals↗
PubMed1994

A comparison of GC content and the proportion of Alu/KpnI-repetitive sequences in a single dark- and light-band region from a human chromosome.

To obtain direct evidence for a molecular basis of differentiation between regular Giemsa dark (G)- and light (R)-band regions of human chromosomes, two regions of chromosome 11, q14-q22 (G-band) and q23-q25 (R-band), were microdissected. The DNA fragments were amplified by the linker-primer polymerase chain reaction and cloned into pUC19. Microclones from each library were then compared by colony hybridization with repetitive DNA sequences, by Southern blot hybridization of each microclone to total human genomic DNA and mouse-human hybrid cell DNA containing only human chromosome 11, and by sequencing of unique and Alu-repetitive clones. Among the G-band-derived microclones analyzed, 43.0% were single-copy (unique) sequences and 23.2% contained highly repetitive sequence elements; in the R-band-derived library, 54.2% were unique clones and 20.3% had highly repetitive elements. The G-band library was significantly richer in clones positive for KpnI sequences (4.1% in the G-band library vs 2.8% in the R-band library). No significant difference was found in the proportion of Alu repetitive clones present in the two libraries, but Class IV Alu sequence derivatives were more frequently observed in the R-library than in the G-library. Sequence analysis revealed no significant difference in GC content or in the ratio of CpG sequence to GpC dinucleotide between 30 microclones derived from G-bands and 29 microclones derived from R-bands.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Composition↗
PubMed1994

Mechanisms of T cell contact-dependent B cell activation.

It has been reported that activated Th cells express CD40 ligand, and the interaction of the CD40 ligand and CD40 on B cells results in B cell cycle entry. In this report, mechanisms of B cell activation induced by CD40-CD40 ligand interaction were studied by using an activated Th cell membrane as a source of CD40 ligand. The rise in cAMP concentration and tyrosine phosphorylation of a 69-kDa protein were induced in B cells stimulated with the activated Th cell membrane, and both of them were suppressed by the inclusion of soluble CD40 in cultures. The membrane stimulation did not elicit either inositol phosphates metabolism nor elevation of intracellular Ca2+ concentration. Protein kinase C depletion did not affect the proliferation, rise in cAMP level, or the 69-kDa protein tyrosine phosphorylation. Addition of anti-CD45 to the culture resulted in suppression of the B cell proliferation as well as the 69-kDa protein tyrosine phosphorylation. Furthermore, a protein kinase A inhibitor, H-89, suppressed the B cell proliferation induced by the membrane. These results indicate that both protein tyrosine kinase and protein kinase A were involved in the signal transduction pathway for the B cell proliferation evoked by the CD40-CD40 ligand interaction in Th cell contact-dependent B cell proliferation.

Animals↗
PubMed1994

Reducing-end modification of N-linked oligosaccharides with tyrosine.

The N-linked oligosaccharides from bovine fetuin were purified using newly developed preparative purification methodology. N-linked oligosaccharides were released from tryptic glycopeptides utilizing N-glycosidase F on the 5-g scale. Selective desialylation with neuraminidase from Clostridium perfringens resulted in the formation of a mono-sialyl-oligosaccharide and asialo-oligosaccharides. The reducing ends of the oligosaccharides were converted to the glycosylamine and reacted with the N-hydroxysuccinimide ester of Boctyrosine. The tyrosinated oligosaccharides were resolved into individual peaks on RP-HPLC and then characterized by proton NMR and FAB-MS. A single asialo-triantennary, an asialo-biantennary, and a mono-sialyl-triantennary oligosaccharide were recovered in good yield. Each product contained a single Boc-Tyr residue attached to the reducing-end GlcNAc residue through a beta-glycosylamide linkage. The procedure was utilized to isolate multi-micromole quantities of oligosaccharides from gram quantities of glycoprotein, thus providing a new route to purify large quantities of N-linked oligosaccharides which contain a terminal tyrosine residue. The tyrosinated oligosaccharides are valuable glycoconjugate ligands which contain a chromophore that absorbs at 280 nm and has sufficient hydrophobicity to facilitate RP-HPLC separations. Furthermore, this group can be deprotected by removal of Boc to reveal a primary amine suitable for further derivatization and can also be radioiodinated for tracking during biological experiments.

Amidohydrolases↗
PubMed1994

Glucocorticoid regulation of calcitonin receptor in mouse osteoclast-like multinucleated cells.

Abundant multinucleated cells (MNCs) are formed in cocultures of mouse osteoblastic cells and marrow cells in the presence of 1 alpha, 25-dihydroxyvitamin D3 [1 alpha, 25(OH)2D3], and these cells have the properties of osteoclasts (OCs). In this study using the mammalian OCs, we tried to clarify the role of glucocorticoids (GCs) in calcitonin receptors (CTR) and CT-responsive cAMP production in OCs. Dexamethasone (DEX) dose and time dependently enhanced the specific binding of [125I]salmon calcitonin (sCT). When the MNCs were preincubated with DEX for 24 h, the effect was evident at 10(-9) M and the maximum effect was obtained at 10(-7) M. The effect developed over 12-48 h at doses of 10(-9) and 10(-6) M DEX. The numbers of CTR-positive mononuclear cells and MNCs were not altered by the DEX treatment. Prednisolone and triamcinolone reproduced the DEX effect, but 17 beta-estradiol, progesterone, testosterone, aldosterone, and 1 alpha, 25(OH)2D3 did not. RU486, a GC receptor antagonist, attenuated the effect of DEX to enhance the specific binding of [125I]sCT. From a Scatchard plot analysis, DEX enhanced CTR number (212 +/- 64%) with a minimal change in the affinity to sCT. Autoradiographic studies using [125I]sCT showed that DEX enhanced the density of the grains on the tartrate-resistant acid phosphatase (TRAP)-positive MNCs and mononuclear cells, but not on other types of cells. DEX preincubation also enhanced sCT-stimulated but not prostaglandin E2- or forskolin-stimulated cAMP production.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Tyrosine derivatization and preparative purification of the sialyl and asialy-N-linked oligosaccharides from porcine fibrinogen.

The N-linked oligosaccharides from porcine fibrinogen were purified following their release from glycopeptides using N-glycosidase F. In separate experiments, both sialyl and asialyl oligosaccharides were prepared from 5 g of fibrinogen. The reducing oligosaccharides were reacted with ammonium bicarbonate to form/oligosaccharide-glycosylamines and then derivatized with tert-butoxycarbonyl-L-tyrosine N-hydroxysuccinimidyl ester. Tyrosinamide--oligosaccharides were purified first by gel filtration chromatography and then by reverse-phase HPLC and the products were characterized by proton NMR and fast atom bombardment-MS. Porcine fibrinogen was found to have predominantly a single asialyl biantennary oligosaccharide containing a fucose linked alpha 1-6 to GlcNAc 1. The oligosaccharide possesses two sialylation patterns with a major form (70%) having a single N-acetyl neuraminic acid (NeuAc) residue linked alpha 2-6 to galactose on only one antenna and a minor form (30%) possessing two NeuAc residues linked alpha 2-6 to both terminal galactose residues. In addition to developing an isolation procedure and establishing the structures of porcine fibrinogen oligosaccharides, this study improves on the tyrosine derivatization technique as a general approach to isolate structurally diverse N-linked oligosaccharides from glycoproteins.

Animals↗