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Biomedical subjects

A Yamazaki

Publications and source records attributed to A Yamazaki.

At least 91 records · Page 5Linked to original sources
PubMed1994

Enhancement of noradrenaline release from rat frontal cortex by thyrotropin releasing hormone and its analog, (3R,6R)-6-methyl-5-oxo-3-thiomorpholinylcarbonyl-L-histidyl-L-prolinami de, as studied by intracerebral microdialysis.

The effects of thyrotropin-releasing hormone (TRH) and NS-3 [CG-3703: (3R,6R)-6-methyl-5-oxo-3-thiomorpholinylcarbonyl-L-histidyl-L- prolinamide], a metabolically stable analog of TRH, on the extracellular concentration of noradrenaline (NA) in the frontal cortex of urethane anesthetized rats were examined by using intracerebral microdialysis coupled with high-performance liquid chromatography with electrochemical detection. NS-3 (0.1 and 0.3 mg/kg i.v.) produced a significant increase in NA release. This effect reached to its peak 20 to 40 min (174% of basal level) after NS-3 (0.3 mg/kg) injection and exhibited a duration of 80 min. TRH (10 mg/kg i.v.) also significantly increased NA concentrations to the same extent as that produced by 0.3 mg/kg of NS-3, although the effect of TRH was transient. Blockade of NA reuptake by perfusion with desipramine (10(-7) M) caused a gradual increase in extracellular NA concentration. NS-3 at 0.3 mg/kg (i.v.) produced a significant elevation of NA concentrations after desipramine perfusion. When NS-3 (10(-6) and 10(-5) M) was perfused to the frontal cortex through the dialysis probe for 1 hr, no significant change in cortical NA concentration was observed. In contrast, perfusion of NS-3 (10(-5) M) through the dialysis probe implanted into the locus ceruleus induced a significant increase in the cortical NA release. These results suggest that NS-3 is far more active than TRH in facilitating cortical NA release and that the locus ceruleus is one of sites of action of this drug.

Animals↗
PubMed1993

Regulation of G protein function by an effector in GTP-dependent signal transduction. An inhibitory subunit of cGMP phosphodiesterase inhibits GTP hydrolysis by transducin in vertebrate rod photoreceptors.

The regulation of cGMP phosphodiesterase in vertebrate rod photoreceptors is a typical G protein-dependent signal transduction mechanism. The interaction of P gamma, an inhibitory subunit of cGMP phosphodiesterase, with transducin alpha subunit (T alpha) is essential for the activation of cGMP phosphodiesterase. It has been shown that, in a homogenized preparation of frog (Rana catesbeiana) rods, P gamma interacts with GTP.T alpha and remains tightly bound to GDP.T alpha after GTP hydrolysis on T alpha. Association of this complex with beta gamma subunits of transducin (T beta gamma) triggers the release of P gamma from the complex and the subsequent inactivation of cGMP phosphodiesterase. In a system reconstituted with purified components, both GTP- and GDP-bound forms of T alpha were found to interact with P gamma. Under these conditions, P gamma inhibited GTP hydrolysis by transducin in a noncompetitive manner with a Ki of 92 nM. Binding of an hydrolysis-resistant GTP analog to T alpha was also inhibited by P gamma. These inhibitions of transducin function were resulted from the inhibition of both hydrolysis of GTP bound to T alpha and interaction of GDP.T alpha with membrane-bound T beta gamma. However, after GDP.T alpha reassociated with membrane-bound T beta gamma, the inhibitory effect of P gamma on the binding of an hydrolysis-resistant GTP analog to T alpha was greatly diminished, suggesting that the GTP/GDP exchange on T alpha was not inhibited by P gamma. These data indicate that the T alpha function is altered during complexing with P gamma. G protein functions may be modified by interacting with an effector in the G protein-dependent signal transduction.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1993

Cloning and sequencing of the gene for alpha antigen from Mycobacterium avium and mapping of B-cell epitopes.

The complete nucleotide sequence of alpha antigen secreted from Mycobacterium avium (A-alpha) was determined. The gene encodes 330 amino acids, including 40 amino acids for the signal peptide, followed by 290 amino acids for the mature protein with a molecular mass of 30,811 Da. This is the first sequence of A-alpha. Comparisons between A-alpha and alpha antigens of Mycobacterium leprae, Mycobacterium bovis BCG, and Mycobacterium kansasii showed highly homologous regions which suggested a conserved functional domain and two less-homologous regions. Serological analysis of recombinant A-alpha, expressed by a series of deletion constructs, indicated the possibility that A-alpha carries at least six B-cell epitopes. The three antigenic determinants were common to Mycobacterium tuberculosis, M. kansasii, and M. avium. The results also suggested the possibility that there are three species-specific epitopes.

Amino Acid Sequence↗
PubMed1992

Heterogeneity of the retinal G-protein transducin from frog rod photoreceptors. Biochemical identification and characterization of new subunits.

Transducin, a retinal G-protein, has been shown to exist as heterotrimers of alpha (39,000), beta (36,000), and gamma (approximately 7,000) subunits. Blue Sepharose CL-6B column chromatography of a transducin preparation extracted with a metal-free, low salt buffer containing GTP showed three distinct alpha and two distinct beta gamma activities in frog (Rana catesbeiana) rod outer segment. The binding of a hydrolysis-resistant GTP analog in these alpha fractions was proportional to the amount of the M(r) 39,000 protein. The first alpha was eluted in a complex with an inhibitory subunit of cGMP phosphodiesterase, but alpha subunits in the second and the third fractions were not complexed with any proteins. Two-dimensional gel electrophoresis and characterization with regard to the interaction with the inhibitory subunit of cGMP phosphodiesterase suggested that the first and the second alpha s were the same protein; however, the third alpha showed different characters as follows. We designated alpha in the first two fractions as alpha 1, and alpha in the third fraction as alpha 2. Nonlinear regression analysis for the binding of a hydrolysis-resistant GTP analog to both alpha subunits revealed a single class of GTP binding sites with an apparent stoichiometry of 1 mol of GTP/mol of alpha. Compared with alpha 1, alpha 2 required larger amounts of rhodopsin and beta gamma for the binding of a hydrolysis-resistant GTP analog. alpha 2 also showed less binding with the inhibitory subunit of cGMP phosphodiesterase. Both alpha 1 and alpha 2 complexed with beta gamma or beta delta (described below) were substrates for pertussis toxin-dependent ADP-ribosylation. The protein profiles of two beta gamma fractions revealed that the main fraction was composed of a beta gamma complex; however, the second active fraction was composed of beta complexed with delta (M(r) 12,000). Compared with beta gamma, beta delta stimulated GTP binding to alpha 1 at approximately 10-fold higher concentration. Two-dimensional gel electrophoresis revealed five beta and two gamma isoforms in beta gamma. Only one beta isoform was present in beta delta. The diversity of transducin subunits may reflect different signaling pathways in visual signal transduction.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1992

Functional alterations of G-proteins in diabetic rat retina: a possible explanation for the early visual abnormalities in diabetes mellitus.

We examined changes in guanosine triphosphate-dependent signal transduction mechanisms in the retina from the early stages of the streptozotocin-diabetic rat, a model for Type 1 (insulin-dependent) diabetes mellitus. Guanosine triphosphate binding, guanosine triphosphatase activity, and binding of (azido) guanosine triphosphate decreased significantly in the retina as early as 2 weeks after the induction of diabetes. The ability of guanosine triphosphate to inhibit forskolin-stimulatable adenyl cyclase was also abolished. These data suggest functional deterioration of G-proteins, especially Gi, in diabetic retina. Further studies using retinal rod outer segments revealed deterioration in light-sensitive, guanosine triphosphate-dependent functions of transducin in diabetic rats. Pertussis toxin-catalysed ADP ribosylation of the alpha subunit of transducin, a heterotrimeric G-protein of rod outer segments, was also reduced in diabetes. No functional effects were seen in purified subunits of transducin subjected to non-enzymatic glycation in vitro. On the other hand, incubation of non-diabetic rod outer segments with (12-0-tetradeconyl) phorbol-13-acetate, a protein kinase C agonist, in the presence of magnesium and adenosine triphosphate resulted in the reduction of guanosine triphosphate-binding and hydrolysis, thus indicating that protein kinase C may be involved in the regulation of these activities. The significance of these observations in the early visual abnormalities associated with diabetes is discussed.

Adenosine Diphosphate Ribose↗
PubMed1992

Reversal of multidrug resistance by an immunosuppressive agent FK-506.

FK-506, a novel immunosuppressive agent, was examined for its reversing effect on multidrug-resistant tumor cells. FK-506 at 3 microM completely reversed the resistance against vincristine (VCR) in vitro in VCR-resistant mouse leukemia P388 cells (P388/VCR). FK-506 also enhanced the cytotoxicity of VCR in Adriamycin(ADM)-resistant human ovarian cancer A2780 cells (AD10) and ADM-resistant human myelogenous leukemia K562 cells (K562/ADM) in vitro. FK-506 was also effective in modulating sensitivity to ADM in AD10 cells in vitro. FK-506 enhanced the chemotherapeutic effect of VCR in P388/VCR-bearing mice. When 20 mg/kg FK-506 was combined with 200 micrograms/kg VCR, a T/C value of 151% was obtained. Under the protocol used in this study, FK-506 was more potent than cyclosporin A (CsA) and verapamil. FK-506 inhibited [3H]azidopine binding to P-glycoprotein efficiently. The binding of VCR to K562/ADM plasma membrane was inhibited by FK-506 as effectively as by CsA. Moreover, the accumulation of VCR in AD10 cells was increased by FK-506 as efficiently as that of CsA and verapamil. These results indicate that FK-506 directly interacts with P-glycoprotein like CsA and verapamil, inhibits the active efflux of vincristine from resistant cells, increases the vincristine accumulation in resistant cells, and thus overcomes multidrug resistance in vitro and in vivo.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Possible site of action of 2-methylserotonin in inducing relaxation of acetylcholine-induced contraction in the molluscan (Mytilus edulis) smooth muscle.

1. The present study investigated the presence of 5-HT3 receptor using 2-methylserotonin (2-Me-5-HT) in the smooth muscle of Mytilus ABRM. 2. 2-Me-5-HT relaxed the acetylcholine-induced contraction in a dose-dependent manner ranging from 10(-6) to 3 x 10(-4) M (pD2 = 5.55 +/- 0.32). 3. 2-Me-5-HT-induced relaxation was antagonized by 3 x 10(-5) M ketanserin in a competitive manner (pA2 = 5.14 +/- 0.1), but not by cypropheptadine, mianserin, MDL 72222 or ICS 205-930 at a concentration of 3 x 10(-5) M. 4. 2-Me-5-HT (3 x 10(-4) M) did not alter the content of cyclic AMP and cyclic GMP in the ABRM. 5. These findings suggested that the 2-Me-5-HT-induced relaxation was mediated through 5-HT2-like receptors and was not linked to cyclic AMP or GMP systems, and, further, that 5-HT3 receptor subtype was not present in the ABRM.

Acetylcholine↗
PubMed1992

Highly conserved epitope domain in major core protein p24 is structurally similar among human, simian and feline immunodeficiency viruses.

Linear B cell epitopes were mapped on the major core protein p24 of human immunodeficiency virus type 1 (HIV-1), simian immunodeficiency virus (SIVAGM) and feline immunodeficiency virus (FIV) using a fusion protein-based method and murine monoclonal antibodies reactive against the p24 antigens expressed on the surface of HIV-1- and FIV-infected cells. The results suggest that the sites identified here are encoded at similar positions in the three virus genomes and consist of highly conserved epitopes, which could exhibit immunodominance.

Amino Acid Sequence↗
PubMed1992

Impaired long-term T cell immunity to Epstein-Barr virus in patients with nasopharyngeal carcinoma.

The long-term T cell immunity to Epstein-Barr virus (EBV) is considered to play an important role in suppressing proliferation of EBV-infected B cells and outgrowth of EBV-associated tumors. It can be manifested and quantified by the EBV-induced focus regression assay. In the present study, we examined the strength of T cell immunity to EBV in patients with nasopharyngeal carcinoma (NPC) and other cancers originating from the head and neck region. In contrast to patients with other types of cancers, including EBV-negative NPC, patients with EBV-positive NPC were found to have a profound impairment in the long-term T cell immunity to EBV.

Adolescent↗
PubMed1992

Induction of interleukin-1 beta mRNA in rat brain after transient forebrain ischemia.

The expression of interleukin-1 beta (IL-1 beta) mRNA in the cerebral cortex, hippocampus, striatum, and thalamus of rats was studied after transient forebrain ischemia. IL-1 beta mRNA was not detected in all these regions of sham-operated control rats. IL-1 beta mRNA was induced after transient forebrain ischemia and reached a detectable level in all regions examined 15 min after the start of recirculation. The induction of IL-1 beta mRNA had a few peaks, that is, peaks were observed at 30 and 240 min in the four regions examined, and another peak was observed at 90 min in the striatum. One day after the start of recirculation, IL-1 beta mRNA levels were markedly decreased, but even 7 days after that, IL-1 beta mRNA was found at very low levels in all regions examined. The amounts of c-fos and beta-actin mRNAs on the same blots were also examined. The induction of c-fos mRNA was transient and had only one peak in all regions examined, whereas the levels of beta-actin mRNA in these regions were fairly constant throughout the recirculation period. Thus, we provide the first evidence for a characteristic expression of IL-1 beta mRNA in several brain regions after transient forebrain ischemia.

Actins↗
PubMed1992

Cloning and expression of the gene for the Avi-3 antigen of Mycobacterium avium and mapping of its epitopes.

The Avi-3 antigen, which is found only in Mycobacterium avium culture sonic extracts, is species specific and results in strong skin test activity in guinea pigs sensitized with heat-killed M. avium. Its gene was cloned by using a previously developed single-probe method and was sequenced. The gene encoded a 194-amino-acid polypeptide with a molecular weight of 21,500. A recombinant Avi-3 antigen expressed in Escherichia coli reacted with monoclonal and polyclonal antibodies raised against the native Avi-3 antigen. To identify epitopes on this protein for immunodiagnostic purposes, various parts of the Avi-3 antigen were expressed as beta-galactosidase fusion proteins, using pUR and pURS expression vectors. The clones screened by both antibody reactivity and T-cell proliferative activity defined fragments with coexisting B- and T-cell epitopes. A B-cell epitope (Asn-176 to Ala-186) and two T-cell epitopes (Glu-75 to Ile-86 and Arg-155 to Leu-164) were thus defined. The synthetic polymerized peptides of the T-cell epitopes were proven to elicit a delayed cutaneous hypersensitivity reaction in guinea pigs. This mapping method would be useful in the development of a subunit vaccine consisting of an immunodominant B-cell epitope linked to a T-cell epitope in the vicinity.

Amino Acid Sequence↗
PubMed1991

Insulin-like growth factor I rapidly induces tyrosine phosphorylation of a Mr 150,000 and a Mr 160,000 protein in highly metastatic mouse colon carcinoma 26 NL-17 cells.

Insulin-like growth factor I (IGF-I) stimulates the proliferation of highly metastatic NL-17 cells to a greater extent than poorly metastatic NL-44 cells, both of which are derived from mouse colon carcinoma 26. The NL-17 cells have been compared with NL-44 cells for the signal transduction pathway of IGF-I. IGF-I receptors of both cell types were identified by affinity labeling, and there was no significant difference between the two cell types in the amount or the autophosphorylation activity of the IGF-I receptors. However, when IGF-I-dependent tyrosine phosphorylation of cellular components was examined, remarkable tyrosine phosphorylation of proteins with molecular weights of 150,000 (pp150) and 160,000 (pp160) was found in NL-17 cells. In contrast, this phosphorylation stayed at significantly lower levels in NL-44 cells than in NL-17 cells. The phosphorylation of pp150 and pp160 was induced within 10 s after the addition of IGF-I and reached its maximal level by 30 s. After the removal of IGF-I, the phosphorylation of pp150 and pp160 was reduced to the basal level within 30 min. This phosphorylation was not induced by platelet-derived or epidermal growth factor. The pp150 and pp160 were not absorbed by wheat germ agglutinin-agarose. They were found in the soluble fraction of cytoplasm but not in the membrane or the cytoskeleton. The pp150 and pp160 might be endogenous substrates of IGF-I receptor kinase. These results suggest that tyrosine phosphorylation of pp150 and pp160 mediates the higher proliferative response of NL-17 cells to IGF-I.

Animals↗
PubMed1991

Polymorphism in purified guanylate cyclase from vertebrate rod photoreceptors.

Guanylate cyclase from rod photoreceptors of amphibian (toad, Bufo marinus, and frog, Rana catesbeiana) and bovine retinas was solubilized and purified by a single chromatography step on a GTP-agarose column. Silver staining of purified amphibian enzymes in SDS/polyacrylamide gels disclosed a doublet band (110 and 115 kDa), while the bovine enzyme appeared as a singlet band (110 kDa). The identification of these guanylate cyclases was confirmed using three chromatography systems with the purified enzymes. Specific binding to Con A-Sepharose suggested that rod guanylate cyclase is a glycoprotein. Two-dimensional gel electrophoresis of purified toad, frog, and bovine enzymes resolved two, three, and five variants, respectively, that differed in isoelectric point. Two variants of toad guanylate cyclase showed differences in various characterizations. These data suggest multiple mechanisms for regulation of guanylate cyclase activity in vertebrate rod photoreceptors.

Animals↗
PubMed1991

Phosphatidylinositol-stimulated phosphorylation of an inhibitory subunit of cGMP phosphodiesterase in vertebrate rod photoreceptors.

An inhibitory subunit (P gamma) of cGMP phosphodiesterase from vertebrate rod photoreceptors (frog, toad, and bovine) was phosphorylated by cytosolic protein kinase(s) derived from intact frog rod outer segments. The phosphorylation of frog P gamma was stimulated by phosphatidylinositol but not by cAMP or cGMP. One- and two-dimensional gel electrophoresis revealed that 70-80% of P gamma was phosphorylated with 1 mol of phosphate per frog P gamma under optimal conditions. A peptide that derived from an active domain of bovine P gamma was also phosphorylated. Phosphorylation of frog P gamma was inhibited by addition of the peptide to the reaction mixture. Phosphorylation of frog P gamma was also inhibited by addition of transducin subunits or active (P gamma-less) cGMP phosphodiesterase. Okadaic acid, on the other hand, enhanced P gamma phosphorylation, suggesting the presence of protein phosphatase(s) in the cytosolic fraction. These data suggest another mechanism for the regulation of cGMP phosphodiesterase in vertebrate rod photoreceptors.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1991

Magnetic resonance imaging and histologic study of hypertrophic cervical posterior longitudinal ligament. A case report.

Magnetic resonance imaging and histologic features of hypertrophic cervical posterior longitudinal ligament were determined in a cervical myelopathy patient. On T1-weighted images, the thickened ligament and the prolapsed nucleus pulposus showed isointensity shadows, making it impossible to differentiate these tissues. On T2-weighted images, the thickened ligament and prolapsed nucleus pulposus were visualized at high and low intensity, respectively. Sagittal T1-weighted images after gadolinium-diethylene triamine pentaacetic acid injection showed obvious enhancement of the thickened ligament.

Cervical Vertebrae↗
PubMed1991

Fusion protein based epitope mapping of the MPB57 protein from Mycobacterium bovis BCG and its epitope insertion into the native protein.

The gene coding for the 12-kDa protein (MPB57) of Mycobacterium bovis BCG has recently been cloned and sequenced (R. Yamaguchi, K. Matsuo, A. Yamazaki, S. Nagai, K. Terasaka, and T. Yamada. 1988. FEBS Lett. 240: 115-117). To map linear B-cell epitopes by beta-galactosidase fusion proteins, we have constructed convenient vectors (pUR278S, pUR288S, and pUR289S) with the SmaI site. Based on recognition by polyclonal antibodies, two epitope regions on the MPB57 protein were identified, both of which corresponded to the amino acid sequences Glu20 to Val45 (26 residues, epitope I region) and Ile78 to Leu86 (9 residues, epitope II). Complementary oligonucleotides encoding epitope II were synthesized, polymerized by a ligase reaction, inserted into the native MPB57 protein gene, and expressed in Escherichia coli, giving rise to epitope-inserted proteins. Their stability and potential uses are described.

Amino Acid Sequence↗