Biomedical subjects

N Murata

Publications and source records attributed to N Murata.

At least 73 records · Page 4Linked to original sources

PubMed2000

Ionic and osmotic effects of NaCl-induced inactivation of photosystems I and II in Synechococcus sp.

We report here that osmotic effects and ionic effects are both involved in the NaCl-induced inactivation of the photosynthetic machinery in the cyanobacterium Synechococcus sp. PCC 7942. Incubation of the cyanobacterial cells in 0.5 M NaCl induced a rapid and reversible decline and subsequent slow and irreversible loss of the oxygen-evolving activity of photosystem (PS) II and the electron transport activity of PSI. An Na(+)-channel blocker protected both PSII and PSI against the slow, but not the rapid, inactivation. The rapid decline resembled the effect of 1.0 M sorbitol. The presence of both an Na(+)-channel blocker and a water-channel blocker protected PSI and PSII against the short- and long-term effects of NaCl. Salt stress also decreased cytoplasmic volume and this effect was enhanced by the Na(+)-channel blocker. Our observations suggested that NaCl had both osmotic and ionic effects. The osmotic effect decreased the amount of water in the cytosol, rapidly increasing the intracellular concentration of salts. The ionic effect was caused by an influx of Na(+) ions through potassium/Na(+) channels that also increased concentrations of salts in the cytosol and irreversibly inactivated PSI and PSII.

Aquaporins↗

PubMed2000

Acclimation of the photosynthetic machinery to high temperature in Chlamydomonas reinhardtii requires synthesis de novo of proteins encoded by the nuclear and chloroplast genomes.

The mechanism responsible for the enhancement of the thermal stability of the oxygen-evolving machinery of photosystem II during acclimation of Chlamydomonas reinhardtii to high temperatures such as 35 degrees C remains unknown. When cells that had been grown at 20 degrees C were transferred to 35 degrees C, the thermal stability of the oxygen-evolving machinery increased and within 8 h it was equivalent to that in cells grown initially at 35 degrees C. Such enhancement of thermal stability was prevented by cycloheximide and by lincomycin, suggesting that the synthesis de novo of proteins encoded by both the nuclear and the chloroplast genome was required for this process. No increase in thermal stability was observed when cells that had been grown at 35 degrees C were exposed to heat shock at 41 degrees C, optimum conditions for the induction of the synthesis of homologs of three heat shock proteins (Hsps), namely, Hsp60, Hsp70, and Hsp22. Moreover, no synthesis of these homologs of Hsps was induced at 35 degrees C. Thus it appears likely that Hsps are not involved in the enhancement of the thermal stability of the oxygen-evolving machinery.

Acclimatization↗

PubMed2000

Genetic engineering of glycinebetaine synthesis in plants: current status and implications for enhancement of stress tolerance.

Metabolic acclimation via the accumulation of compatible solutes is regarded as a basic strategy for the protection and survival of plants in extreme environments. Certain plants accumulate significant amounts of glycinebetaine (betaine), a compatible quaternary amine, in response to high salinity, cold and drought. It is likely that betaine is involved in the protection of macrocomponents of plant cells, such as protein complexes and membranes, under stress conditions. Genetic engineering of the biosynthesis of betaine from choline has been the focus of considerable attention as a potential strategy for increasing stress tolerance in stress-sensitive plants that are incapable of synthesizing this compatible/protective solute. Three distinct pathways for the synthesis of betaine have been identified in spinach, Escherichia coli and Arthrobacter globiformis, and various genes and cDNAs for the proteins involved are available. Moreover, each of the pathways has been exploited to a greater or lesser extent in efforts to convert betaine-deficient plants to betaine accumulators. In this review, the potential of several recent examples of transgenic approaches to the enhancement of stress tolerance in plants is summarized and discussed.

Adaptation, Physiological↗

PubMed2000

[Combination chemotherapy with irinotecan hydrochloride plus carboplatin for patients with advanced or recurrent colorectal cancer--a pilot study].

A pilot study was performed to evaluate the feasibility and efficacy of irinotecan hydrochloride (CPT-11) plus carboplatin (CBDCA) for treatment of advanced or recurrent colorectal cancer. Fifteen patients with colorectal cancer (nonresectable, 1; noncurative resection, 5; recurrent disease, 9) were treated with CPT-11 (40-50 mg/m2) plus CBDCA (70-100 mg/m2) once a week for 2-3 weeks followed by a one-week rest. This treatment was repeated until disease progression or severe toxic effects were found. The total dose of CPT-11 ranged from 135 to 1,214 (median, 467) mg/m2 and that of CBDCA ranged from 267 to 2,022 (median, 933) mg/m2. Adverse effects included nausea (grade 2) in 2 (13.3%) diarrhea (grade 2) in 2 (13.3%), leukopenia (grade 3) in 2 (13.3%), thrombocytopenia (grade 1) in one (6.7%), and hair falling (grade 3) in one (6.7%). The response rate of 14 evaluable patients was 14.3% (CR, 1; PR,1; NC,7; PD,5). The median survival time of all patients was 405 days from the start of chemotherapy. The survival time of patients with CR, PR, and NC (n = 9) tended to be longer than that of those with PD (n = 5) (p = 0.06). The median time to disease progression was 105 days. These results suggest that this combination chemotherapy is feasible and effective in the treatment of advanced or recurrent colorectal cancer.

Adult↗

PubMed2000

[Clinical significance of determinations of dihydropyrimidine dehydrogenase levels in primary and hepatic lesions of colorectal cancer patients].

Dihydropyrimidine dehydrogenase (DPD) levels were determined by enzyme-linked immunosorbent assay in primary tumors and adjacent normal mucosa from 114 colorectal cancer patients, including 9 with synchronous liver metastases. The level of intratumoral DPD was 55.0 +/- 38.7 unit/mg protein (n = 114) and that of mucosal DPD was 55.0 +/- 38.7 unit/mg protein (n = 114). The ratio of intratumoral DPD to mucosal DPD was 1.8 +/- 0.8 in patients developing metachronous liver metastases (n = 7), 1.0 +/- 0.5 in patients without recurrence (n = 61), and 1.0 +/- 1.1 in patients with synchronous liver metastases (n = 31) (p = 0.01, metachronous liver metastasis group versus recurrence-free and synchronous liver metastasis groups). The levels of DPD were higher in primary lesions than in synchronous liver metastasis (n = 9, p < 0.05). These results indicate that: (1) degradation of 5-fluorouracil (5-FU) is enhanced in hepatic lesions more than in primary lesions, which is consistent with previous findings showing the therapeutic advantage of hepatic arterial infusion over intravenous infusion in relation to the treatment of 5-FU for liver metastases of colorectal cancer patients; and (2) predicting the effectiveness of hepatic arterial infusion of 5-FU for patients with metachronous liver metastases is difficult based on DPD determination of primary lesions alone.

Colorectal Neoplasms↗

PubMed2000

Perception and transduction of low-temperature signals to induce desaturation of fatty acids.

When cells of the cyanobacterium Synechocystis sp. PCC 6803 are exposed to a low temperature, genes for fatty acid desaturases are expressed with resultant increases in the degree of unsaturation of fatty acids in membrane lipids. However, the sensor and transducers of low-temperature signals had not yet been identified. In order to identify these components we applied to the cyanobacterium Synechocystis sp. PCC 6803 the systematic disruption of all 43 putative genes for histidine kinases and random mutagenesis of the whole genome in conjunction with screening by the transcriptional activity of the promoter of the desB gene for the omega3 desaturase. This allowed us to identify two histidine kinases and a response regulator as components of the perception and transduction of low-temperature signals for the expression of genes for fatty acid desaturases.

Cold Temperature↗

PubMed2000

Plant glycerol-3-phosphate-1-acyltransferase (GPAT): structure selectivity studies.

Squash glycerol-3-phosphate-1-acyltransferase has been crystallized and the structure of the enzyme determined, at 1.9-A resolution, using multiple isomorphous replacement of the wild type and a series of individual cysteine mutants. Competitive in vitro substrate selectivity assays have been established that differentiate between selective and non-selective forms of the enzyme. Particular care was taken to use near-physiological concentrations of both substrates. Clear substrate selectivity can be demonstrated with the natural substrate acyl-acyl carrier protein but not with the substrate analogue acyl-CoA. The use of site-directed mutagenesis, coupled to three-dimensional structural determinations, should provide a rational basis for elucidating structural components important in determining the substrate selectivity of this enzyme.

Arabidopsis↗

PubMed1999

Anti-angiogenic activity of a novel synthetic agent, 9alpha-fluoromedroxyprogesterone acetate.

9Alpha-fluoromedroxyprogesterone acetate (FMPA) is a novel synthetic analog of medroxyprogesterone acetate (MPA), widely used as therapeutic agent for breast and endometrium cancers. FMPA showed almost the same binding affinities to the progesterone and glucocorticoid receptors as MPA. In the rabbit corneal assay, FMPA, MPA and fumagillin significantly inhibited the angiogenic response induced by rat mammary tumor at doses of 0. 1, 1 and 50 microg/pellet, respectively, so FMPA showed greater anti-angiogenic activity than MPA and fumagillin. In the mouse dorsal air sac method, FMPA inhibited the mouse sarcoma 180 cell-induced angiogenesis by oral administration at a dose of 200 mg/kg. FMPA inhibited the activity of plasminogen activator (PA) in bovine endothelial cells. These results suggest that FMPA may be useful for diseases associated with angiogenesis by oral administration.

Angiogenesis Inhibitors↗

PubMed1999

Dominant and shared T cell receptor beta chain variable regions of T cells inducing synovial hyperplasia in rheumatoid arthritis.

Previously, we demonstrated the presence of at least two distinct subpopulations of patients with rheumatoid arthritis (RA) employing a cell-transfer experiment using severe combined immunodeficient (SCID) mice. One group of patients, whose T cells derived from the rheumatoid joints, induced synovial hyperplasia (SH) in the SCID mice (the positive group). The other group did not display the induction of SH (the negative group). TCR/Vbeta gene usage analysis indicated that some dominant T cell subpopulations were oligoclonally expanding only in the rheumatoid joints, and not in the periphery of the patients of the positive group. Moreover, these T cell subpopulations were not seen in the joints of patients in the negative group or in non-RA patients. In addition, the preferential uses of certain TCR/Vbetas (Vbeta8, Vbeta12, Vbeta13, and Vbeta14) genes were demonstrated in these T cells. In this study, to investigate whether these T cells are driven by a certain antigen(s), the third complementarity determining regions (CDR3s) of TCR/Vbeta, especially Vbeta8 and Vbeta14 PCR products, were cloned and sequenced. As a result, a dominant CDR3 sequence, CASS-PRERAT-YEQ, was found in Vbeta14+ T cells from the rheumatoid joint of a patient (Patient 1) of the positive group with a Vbeta14 skew. The identical CDR3 sequence also predominated in Vbeta14+ T cells from the rheumatoid joint of another patient (Patient 7) of the positive group with a Vbeta14 skew. In addition, in the patients (Patients 4, 7, 8) of the positive group with a Vbeta8 skew, other dominant CDR3 sequences, CASS-ENS-YEQ and CASS-LTEP-DTQ, were found as in the case of Vbeta14. However, no identical CDR3 sequences were detected dominantly in the joints of the patients in the negative group or in non-RA patients. A Vbeta14+ T cell clone (TCL), named G3, with the identical CDR3 sequence, CASS-PRERAT-YEQ, was isolated successfully from Patient 1, and cell transfer of G3 with autologous irradiated peripheral mononuclear cells induced SH in the SCID mice. Taken together, these results suggest that T cells inducing SH, thought to be pathogenic for RA, might be driven by a certain shared antigen(s).

Amino Acid Sequence↗

PubMed1999

Comparison of intrinsic activities of the putative sphingosine 1-phosphate receptor subtypes to regulate several signaling pathways in their cDNA-transfected Chinese hamster ovary cells.

We examined the actions of sphingosine 1-phosphate (S1P) on signaling pathways in Chinese hamster ovary cells transfected with putative S1P receptor subtypes, i.e. Edg-1, AGR16/H218 (Edg-5), and Edg-3. Among these receptor-transfected cells, there was no significant difference in the expressing numbers of the S1P receptors and their affinities to S1P, which were estimated by [(3)H]S1P binding to the cells. In vector-transfected cells, S1P slightly increased cytosolic Ca(2+) concentration ([Ca(2+)](i)) in association with inositol phosphate production, reflecting phospholipase C activation; the S1P-induced actions were markedly enhanced in the Edg-3-transfected cells and moderately so in the AGR16-transfected cells. In comparison with vector-transfected cells, the S1P-induced [Ca(2+)](i) increase was also slightly enhanced in the Edg-1-transfected cells. In all cases, the inositol phosphate and Ca(2+) responses to S1P were partially inhibited by pertussis toxin (PTX). S1P also significantly increased cAMP content in a PTX-insensitive manner in all the transfected cells; the rank order of their intrinsic activity of S1P receptor subtypes was AGR16 > Edg-3 > Edg-1. In the presence of forskolin, however, S1P significantly inhibited cAMP accumulation at a lower concentration (1-100 nM) of S1P in a manner sensitive to PTX in the Edg-1-transfected cells but not in either the Edg-3 or AGR16-transfected cells. As for cell migration activity evaluated by cell number across the filter of blind Boyden chamber, Edg-1 and Edg-3 were equally potent, but AGR16 was ineffective. Thus, S1P receptors may couple to both PTX-sensitive and -insensitive G-proteins, resulting in the selective regulation of the phospholipase C-Ca(2+) system, adenylyl cyclase-cAMP system, and cell migration activity, according to the receptor subtype.

Adenylate Cyclase Toxin↗

PubMed1999

Genetic engineering of the unsaturation of fatty acids in membrane lipids alters the tolerance of Synechocystis to salt stress.

The role of unsaturated fatty acids in membrane lipids in the tolerance of the photosynthetic machinery to salt stress was studied by comparing the desA-/desD- mutant of Synechocystis sp. PCC 6803, which contained monounsaturated fatty acids, with the wild-type strain, which contained a full complement of polyunsaturated fatty acids. In darkness, the loss of oxygen-evolving photosystem II activity in the presence of 0.5 M NaCl or 0.5 M LiCl was much more rapid in desA-/desD- cells than in wild-type cells. Oxygen-evolving activity that had been lost during incubation with 0.5 M NaCl in darkness returned when cells were transferred to conditions that allowed photosynthesis or respiration. Recovery was much greater in wild-type than in desA-/desD- cells, and it was prevented by lincomycin. Thus, the unsaturation of fatty acids is important in the tolerance of the photosynthetic machinery to salt stress. It appears also that the activity and synthesis of the Na+/H+ antiporter system might be suppressed under high-salt conditions and that this effect can be reversed, in part, by the unsaturation of fatty acids in membrane lipids.

Cyanobacteria↗

PubMed1999

Thioredoxin peroxidase in the Cyanobacterium Synechocystis sp. PCC 6803.

The amino acid sequence deduced from the open reading frame designated sll0755 in Synechocystis sp. PCC 6803 is similar to the amino acid sequences of thioredoxin peroxidases from other organisms. In the present study, we found that a recombinant SLL0755 protein that was expressed in Escherichia coli was able to reduce H2O2 and tertiary butyl hydroperoxide with thioredoxin from E. coli as the electron donor. Targeted disruption of open reading frame sll0755 in Synechocystis sp. PCC 6803 cells completely eliminated the H2O2-dependent and tertiary butyl hydroperoxide-dependent photosynthetic evolution of oxygen and the electron flow in photosystem II. These results indicate that the product of open reading frame sll0755 is a thioredoxin peroxidase whose activities are coupled to the photosynthetic electron transport system in Synechocystis sp. PCC 6803.

Amino Acid Sequence↗

PubMed1999

Balanced regulation of expression of the gene for cytochrome cM and that of genes for plastocyanin and cytochrome c6 in Synechocystis.

The cytM gene for cytochrome cM was previously found in Synechocystis sp. PCC 6803. Northern blotting analysis revealed that the cytM gene was scarcely expressed under normal growth conditions but its expression was enhanced when cells were exposed to low temperature or high-intensity light. By contrast, the expression of the genes for cytochrome c6 and plastocyanin was suppressed at low temperature or under high-intensity light. These observations suggest that plastocyanin and/or cytochrome c6, which are dominant under non-stressed conditions, are replaced by cytochrome cM under the stress conditions.

Bacterial Proteins↗

PubMed1999

Activation of phospholipase C-Ca2+ system by sphingosine 1-phosphate in CHO cells transfected with Edg-3, a putative lipid receptor.

Sphingosine 1-phosphate (S1P) induces phospholipase C (PLC) activation and Ca2+ mobilization in many types of cells. We examined the possible involvement of Edg-3, one of the putative S1P receptors, in the phospholipase C (PLC)-Ca2+ system. S1P increased the cytoplasmic free Ca2+ concentration without detectable inositol phosphate production in vector-transfected CHO cells. In the Edg-3-transfected cells, however, the S1P-induced Ca2+ response was clearly enhanced, which was associated with a significant production of inositol phosphate. These S1P-induced responses in the Edg-3-transfected cells were inhibited by U73122, a potent PLC inhibitor. We conclude that Edg-3 may be one of the S1P receptors participating in the activation of the PLC-Ca2+ system.

Animals↗

PubMed1999

A new simple technique for performing intraoperative endoscopic resection of small-bowel polyps in patients with Peutz-Jeghers syndrome.

We describe herein a simple method for performing intraoperative endoscopic resection of small-bowel polyps associated with Peutz-Jeghers syndrome, using a corrugated anesthetic tube. A 34-year-old man with Peutz-Jeghers syndrome underwent emergency surgery for an ileo-ileo-colic intussusception. A sterile corrugated anesthetic tube was inserted into the small-bowel, proximal to the affected lesion. The small bowel was then telescoped sequentially over the tube using a pleating technique. Consequently, a colonoscope inserted through the tube was easily able to reach the duodeno-jejunal junction, and ten small-bowel polyps were removed using a wire snare and electrocauterization. All resected specimens were washed out by the instillation of saline through a nasogastric tube, then collected on gauze placed near the outlet of the tube. Our technique has the following merits: it is feasible even in emergency surgery; it prevents contamination of the surgical field; and it facilitates the easy collection of polypectomized specimens.

Adult↗

PubMed1999

Laparoscopic gastropexy for acute gastric volvulus: a case report.

A 7-year-old girl presented with an acute gastric volvulus that was reduced with a nasogastric catheter. An anterior gastropexy was undertaken laparoscopically. The gastrocolic omentum was deficient along most of the greater curvature, which had allowed organoaxial volvulus. Two years later, gastric volvulus has not recurred. Laparoscopy is an acceptable approach for the evaluation and treatment of children with acute gastric volvulus.

Acute Disease↗

PubMed1999

Enhanced tolerance to light stress of transgenic Arabidopsis plants that express the codA gene for a bacterial choline oxidase.

Arabidopsis thaliana was transformed with the codA gene from Arthrobacter globiformis. This gene encodes choline oxidase, an enzyme that converts choline to glycinebetaine. The photosynthetic activity, monitored in terms of chlorophyll fluorescence, of transformed plants was more tolerant to light stress than that of wild-type plants. This enhanced tolerance to light stress was caused by acceleration of the recovery of the photosystem II (PS II) complex from the photo-inactivated state. The transformed plants synthesized glycinebetaine, but no changes were detected in the relative levels of membrane lipids or in the relative levels of fatty acids in the various membrane lipids. Transformation with the codA gene increased levels of H2O2, a by-product of the reaction catalyzed by choline oxidase, by only 50% to 100% under stress or non-stress conditions. The activity of ascorbate peroxidase and, to a lesser extent, that of catalase in transformed plants were significantly higher than in the wild-type plants. These observations suggest that H2O2 produced by choline oxidase in the transformed plants might have stimulated the expression of H2O2 scavenging enzymes, with resultant maintenance of the level of H2O2 within a certain limited range. It appears that glycinebetaine produced in vivo, but not changes in membrane lipids or in the level of H2O2, protected the PS II complex in transformed plants from damage due to light stress.

Adaptation, Physiological↗

PubMed1999

PsbU, a protein associated with photosystem II, is required for the acquisition of cellular thermotolerance in synechococcus species PCC 7002

PsbU is an extrinsic protein of the photosystem II complex of cyanobacteria and red algae. Our previous in vitro studies (Y. Nishiyama, D.A. Los, H. Hayashi, N. Murata [1997] Plant Physiol 115: 1473-1480) revealed that PsbU stabilizes the oxygen-evolving machinery of the photosystem II complex against heat-induced inactivation in the cyanobacterium Synechococcus sp. PCC 7002. To elucidate the role of PsbU in vivo, we inactivated the psbU gene in Synechococcus sp. PCC 7002 by targeted mutagenesis. Inactivation of the psbU gene resulted in marked changes in the acclimative responses of cells to high temperature: Mutated cells were unable to increase the thermal stability of their oxygen-evolving machinery when grown at moderately high temperatures. Moreover, the cellular thermotolerance of the mutated cells failed to increase upon acclimation of cells to high temperature. The heat-shock response, as assessed in terms of the levels of homologs of the heat-shock proteins Hsp60, Hsp70, and Hsp17, was unaffected by the mutation in psbU, suggesting that heat-shock proteins were not involved in the changes in the acclimative responses. Our observations indicate that PsbU is involved in the mechanism that underlies the enhancement of the thermal stability of the oxygen-evolving machinery and that the stabilization of the oxygen-evolving machinery is crucial for the acquisition of cellular thermotolerance.

Journal Article↗