PubMed Health⌕ Search

Biomedical subjects

Masato Ikeda

Publications and source records attributed to Masato Ikeda.

At least 19 recordsLinked to original sources
PubMed2006

Cholesterol is critical for Epstein-Barr virus latent membrane protein 2A trafficking and protein stability.

Latent membrane protein 2A (LMP2A) of Epstein-Barr virus (EBV) plays a key role in regulating viral latency and EBV pathogenesis by functionally mimicking signals induced by the B cell receptor (BCR) altering normal B cell development. LMP2A specifically associates with Nedd4 family ubiquitin-protein ligases which downmodulate LMP2A activity by ubiquitinating LMP2A and LMP2A-associated protein tyrosine kinases (PTKs). Since specific ubiquitin tags provide an endocytic sorting signal for plasma membrane proteins which traffic to membrane vesicles, we examined LMP2A localization and trafficking. We found that LMP2A is secreted through exosomes, small endocytic membrane vesicles, as previously demonstrated for LMP1. Interestingly, the treatment of cells with methyl-beta-cyclodextrin (MCD), which depletes cholesterol from plasma membrane, dramatically increased LMP2A abundance and LMP2A exosome secretion. Cholesterol depletion also blocked LMP2A endocytosis resulting in the accumulation of LMP2A on plasma membrane. LMP2A phosphorylation and ubiquitination were blocked by cholesterol depletion. LMP2A in the exosomal fraction was ubiquitinated but not phosphorylated. These results indicate that cholesterol-dependent LMP2A trafficking determines the fate of LMP2A degradation.

Cell Line↗
PubMed2006

Disruption of malate:quinone oxidoreductase increases L-lysine production by Corynebacterium glutamicum.

Genomic analysis of a classically derived L-lysine-producing mutant, Corynebacterium glutamicum B-6, identified a nonsense mutation in the mqo gene, which encodes malate:quinone oxidoreductase (MQO). The effect of mqo disruption on L-lysine production was investigated in a defined L-lysine producer, C. glutamicum AHP-3, showing approximately 18% increased production. To explore the underlying mechanisms of the increase, the mqo-disrupted strain was analyzed from the viewpoints of redox balance, activities of membrane-bound dehydrogenases, and transcriptome. The intracellular [NADH]/[NAD] ratio in the strain remained unchanged. Also, there were no significant differences in the activities of the membrane-bound dehydrogenases examined. However, transcriptome analysis showed that some TCA cycle genes, such as acn, sucC, and sucD, were down-regulated in the strain. These results suggest that the loss of MQO activity down-regulates the flux of the TCA cycle to maintain the redox balance and results in redirection of oxaloacetate into L-lysine biosynthesis.

Corynebacterium glutamicum↗
PubMed2006

Down-regulation of survivin by ultraviolet C radiation is dependent on p53 and results in G(2)-M arrest in A549 cells.

Deregulation of survivin expression is implicated in tumorigenesis. To examine the regulation of survivin expression in response to DNA damage, we exposed A549 human lung cancer cells to ultraviolet C (UVC) radiation, which induces DNA single-strand breakage. UVC irradiation induced G(2)-M arrest that was accompanied by accumulation of p53 and subsequent down-regulation of survivin. Depletion of p53 by RNA interference prevented the UVC-induced down-regulation of survivin. Furthermore, depletion of survivin resulted in G(2)-M arrest, suggesting that down-regulation of survivin by p53 contributes to the p53-dependent G(2)-M checkpoint triggered by DNA damage.

Cell Cycle↗
PubMed2006

A leuC mutation leading to increased L-lysine production and rel-independent global expression changes in Corynebacterium glutamicum.

We previously found by transcriptome analysis that global induction of amino acid biosynthetic genes occurs in a classically derived industrial L-lysine producer, Corynebacterium glutamicum B-6. Based on this stringent-like transcriptional profile in strain B-6, we analyzed the relevant mutations from among those identified in the genome of the strain, with special attention to the genes that are involved in amino acid biosynthesis and metabolism. Among these mutations, a Gly-456-->Asp mutation in the 3-isopropylmalate dehydratase large subunit gene (leuC) was defined as a useful mutation. Introduction of the leuC mutation into a defined L-lysine producer, AHD-2 (hom59 and lysC311), by allelic replacement led to the phenotype of a partial requirement for L-leucine and approximately 14% increased L-lysine production. Transcriptome analysis revealed that many amino acid biosynthetic genes, including lysC-asd operon, were significantly upregulated in the leuC mutant in a rel-independent manner.

Corynebacterium glutamicum↗
PubMed2006

Construction of double-stranded metallosupramolecular polymers with a controlled helicity by combination of salt bridges and metal coordination.

We describe the construction of the first double-stranded metallosupramolecular helical polymers. We designed and synthesized a supramolecular duplex comprised of complementary m-terphenyl-based strands bearing a chiral amidine or achiral carboxylic acid together with two pyridine groups at the four ends. Supramolecular polymerization of the duplex with cis-PtPh2(DMSO)2 in 1,1,2,2-tetrachloroethane produced the double-stranded metallosupramolecular polymer with a controlled helicity of which the two complementary metallostrands are intertwined through the amidinium-carboxylate salt bridges. The structures and hydrodynamic dimensions of the metallosupramolecular polymers were characterized by 1H NMR, diffusion-ordered NMR, dynamic light scattering, absorption, and CD measurements. The polymeric structure was also visualized by atomic force microscopy.

Chemistry, Organic↗
PubMed2006

A genome-based approach to create a minimally mutated Corynebacterium glutamicum strain for efficient L-lysine production.

Based on the progress in genomics, we have developed a novel approach that employs genomic information to generate an efficient amino acid producer. A comparative genomic analysis of an industrial L-lysine producer with its natural ancestor identified a variety of mutations in genes associated with L-lysine biosynthesis. Among these mutations, we identified two mutations in the relevant terminal pathways as key mutations for L-lysine production, and three mutations in central metabolism that resulted in increased titers. These five mutations when assembled in the wild-type genome led to a significant increase in both the rate of production and final L-lysine titer. Further investigations incorporated with transcriptome analysis suggested that other as yet unidentified mutations are necessary to support the L-lysine titers observed by the original production strain. Here we describe the essence of our approach for strain reconstruction, and also discuss mechanisms of L-lysine hyperproduction unraveled by combining genomics with classical strain improvement.

Corynebacterium glutamicum↗
PubMed2006

Small interfering RNA targeting survivin sensitizes lung cancer cell with mutant p53 to adriamycin.

Survivin is a member of the inhibitor of apoptosis protein (IAP) family that is specifically overexpressed in cancer tissues. p53 is one of the tumor suppressor genes; its induction in response to DNA damage causes apoptosis and correlates with drug sensitivity. To investigate the possible regulation of survivin by p53, we examined the level of survivin expression in lung cancer cell lines in response to adriamycin. Levels of survivin mRNA and protein in cell lines with wild-type p53 decreased dramatically after p53 induction, but no such reduction of survivin was observed in cell lines with mutated or null p53. Inhibition of wild-type p53 in A549 cells by small interfering (si) RNA significantly upregulated the expression of survivin. Survivin inhibition by siRNA in PC9 cells with mutated p53 significantly depressed cell proliferation. To investigate the sensitivity of cancer cells to adriamycin after inhibition of survivin, we depressed survivin expression using siRNA, and then added adriamycin at an IC50 dose. After a further 48 hr incubation with adriamycin, proliferation was significantly depressed in the cells treated with siRNA targeting survivin, in comparison with siRNA targeting scramble. Furthermore, both TUNEL and pro-caspase3 expression assay showed a significant increase in apoptosis after combined treatment with adriamycin and siRNA targeting survivin. Our results demonstrate that survivin is downregulated by p53, and that siRNA targeting of survivin increases cell sensitivity to adriamycin and promotes apoptosis. siRNA targeting of survivin could be potentially useful for increasing sensitivity to anticancer drugs, especially in drug-resistant cells with mutated p53.

Antibiotics, Antineoplastic↗
PubMed2006

Synthesis and cross-linking activities of oligodeoxynucleotides containing a 4-oxoalkenal group.

The 4-oxoalkenal group, which has been characterized as part of a novel lipid-peroxidation-derived genotoxin, reacts with dG, dC, and dA, yielding etheno adducts. To develop a new interstrand cross-linking system based on the covalent bond formed between the 4-oxoalkenal group and DNA bases, we prepared 4-oxoalkenal-derivatized oligodeoxynucleotides. The protected 4-oxoalkenal derivative with a primary amino group was synthesized and incorporated to the 5' end of the oligodeoxynucleotide. In the presence of the complementary strand, cross-linking products were observed by HPLC and MALDI-MS analysis.

Chromatography, High Pressure Liquid↗
PubMed2006

Comparisons of potentials for L-lysine production among different Corynebacterium glutamicum strains.

Corynebacterium glutamicum is an industrially important organism that is most widely used for the production of various amino acids. A defined L-lysine-producing mutant was generated by introduction of the lysC mutation (T311I) into each of six representative C. glutamicum strains. The resulting six isogenic mutants were compared for L-lysine production under traditional 30 degrees C conditions and industrially more advantageous 40 degrees C conditions. It was found that there were significant differences in yield and productivity, especially at 40 degrees C. These results indicate the diversity among C. glutamicum strains in fermentative characters, as well as the importance of selecting a strain with industrially best performance.

Corynebacterium glutamicum↗
PubMed2006

Transcriptome analysis reveals global expression changes in an industrial L-lysine producer of Corynebacterium glutamicum.

Toward the elucidation of advanced mechanisms of L-lysine production by Corynebacterium glutamicum, a highly developed industrial strain B-6 was analyzed from the viewpoint of gene expression. Northern blot analysis showed that the lysC gene encoding aspartokinase, the key enzyme of L-lysine biosynthesis, was up-regulated by several folds in strain B-6, while no repression mechanism exists in L-lysine biosynthesis of this bacterium. To analyze the underlying mechanisms of the up-regulation, we compared the transcriptome between strain B-6 and its parental wild-type, finding that not only lysC but also many other amino acid-biosynthetic genes were up-regulated in the producer. These results suggest that a certain global regulatory mechanism is involved in the industrial levels of L-lysine production.

Carbon↗
PubMed2005

Towards bacterial strains overproducing L-tryptophan and other aromatics by metabolic engineering.

The aromatic amino acids, L-tryptophan, L-phenylalanine, and L-tyrosine, can be manufactured by bacterial fermentation. Until recently, production efficiency of classical aromatic amino-acid-producing mutants had not yet reached a high level enough to make the fermentation method the most economic. With the introduction of recombinant DNA technology, it has become possible to apply more rational approaches to strain improvement. Many recent activities in this metabolic engineering have led to several effective approaches, which include modification of terminal pathways leading to removal of bottleneck or metabolic conversion, engineering of central carbon metabolism leading to increased supply of precursors, and transport engineering leading to reduced intracellular pool of the aromatic amino acids. In this review, advances in metabolic engineering for the production of the aromatic amino acids and useful aromatic intermediates are described with particular emphasis on two representative producer organisms, Corynebacterium glutamicum and Escherichia coli.

Amino Acids, Aromatic↗
PubMed2005

A novel gnd mutation leading to increased L-lysine production in Corynebacterium glutamicum.

Toward more efficient L-lysine production, we have been challenging genome-based strain breeding by the approach of assembling only relevant mutations in a single wild-type background. Following the creation of a new L-lysine producer Corynebacterium glutamicum AHP-3 that carried three useful mutations (lysC311, hom59, and pyc458) on the relevant downstream pathways, we shifted our target to the pentose phosphate pathway. Comparative genomic analysis for the pathway between a classically derived L-lysine producer and its parental wild-type identified several mutations. Among these mutations, a Ser-361-->Phe mutation in the 6-phosphogluconate dehydrogenase gene (gnd) was defined as a useful mutation for L-lysine production. Introduction of the gnd mutation into strain AHP-3 by allelic replacement led to approximately 15% increased L-lysine production. Enzymatic analysis revealed that the mutant enzyme was less sensitive than the wild-type enzyme to allosteric inhibition by intracellular metabolites, such as fructose 1,6-bisphosphate, D-glyceraldehyde 3-phosphate, phosphoribosyl pyrophosphate, ATP, and NADPH, which were known to inhibit this enzyme. Isotope-based metabolic flux analysis demonstrated that the gnd mutation resulted in 8% increased carbon flux through the pentose phosphate pathway during L-lysine production. These results indicate that the gnd mutation is responsible for diminished allosteric regulation and contributes to redirection of more carbon to the pentose phosphate pathway that was identified as the primary source for NADPH essential for L-lysine biosynthesis, thereby leading to improved product formation.

Corynebacterium↗
PubMed2005

Hierarchical self-assembly of a bow-shaped molecule bearing self-complementary hydrogen bonding sites into extended supramolecular assemblies.

The bow-shaped molecule 1 bearing a self-complementary DAAD-ADDA (D=donor A=acceptor) hydrogen-bonding array generates, in hydrocarbon solvents, highly ordered supramolecular sheet aggregates that subsequently give rise to gels by formation of an entangled network. The process of hierarchical self-assembly of compound 1 was investigated by the concentration and temperature dependence of UV-visible and (1)H NMR spectra, fluorescence spectra, and electron microscopy data. The temperature dependence of the UV-visible spectra indicates a highly cooperative process for the self-assembly of compound 1 in decaline. The electron micrograph of the decaline solution of compound 1 (1.0 mM) revealed supramolecular sheet aggregates forming an entangled network. The selected area electronic diffraction patterns of the supramolecular sheet aggregates were typical for single crystals, indicative of a highly ordered assembly. The results exemplify the generation, by hierarchical self-assembly, of highly organized supramolecular materials presenting novel collective properties at each level of organization.

Journal Article↗
PubMed2005

Risk factors for encapsulating peritoneal sclerosis in patients who have experienced peritoneal dialysis treatment.

BACKGROUND: The present study was conducted to clarify the clinical risk factors related to the development of encapsulating peritoneal sclerosis (EPS), which is one of the most serious complications in patients undergoing peritoneal dialysis (PD). METHODS: The records of 78 patients with a history of PD treatment, including 18 with EPS, were retrospectively analyzed (male/female, 51:27; age, 51.8 +/- 11.0 years; PD treatment, 94.1 +/- 42.7 months). The inclusion criteria were: duration of PD more than 24 months; 36-month follow up after discontinuation of PD; available data for dialysate-to-plasma creatinine ratio (D/P Cr), by fast peritoneal equilibration test within 3 months before PD discontinuation; and absence of EPS at PD discontinuation. Analytical parameters included age, sex, underlying renal disease, duration of PD, membrane transport state (higher transporter or lower transporter: D/P cr ratio more than or less than 0.75), number of episodes of peritonitis during PD treatment, performance of peritoneal lavage after PD discontinuation, and reasons for PD withdrawal (ultrafiltration failure, acute peritonitis, social matters). RESULTS: Significant differences were noted regarding the PD duration, D/P cr, higher membrane transport state, and number of peritonitis episodes during PD. On receiver operating characteristic curves, the cutoff points for EPS were: D/P cr ratio, 0.74; number of peritonitis episodes, 2; and PD duration (months), 115.2. Multivariate analysis, employing the factors age, PD duration, higher membrane transport state, and number of peritonitis episodes, which were selected by stepwise analysis, identified the latter two factors as significant for the development of EPS (odds ratio [OR], 4.0; P = 0.046 and OR, 12.0; P = 0.049, respectively). CONCLUSIONS: A higher transporter membrane state and the number of peritonitis episodes are factors contributing to the occurrence of EPS in patients who have experienced PD treatment.

Adult↗
PubMed2005

Restoration of peritoneal integrity after withdrawal of peritoneal dialysis: characteristic features of the patients at risk of encapsulating peritoneal sclerosis.

BACKGROUND: The epidemiological characteristics of encapsulating peritoneal sclerosis (EPS), such as its high incidence in patients with long-term peritoneal dialysis (PD) treatment, and the onset of EPS after patients are switched to hemodialysis (HD) may indicate an activated pathological process after PD withdrawal, especially in long-term PD patients. Accordingly, we aimed to observe changes in peritoneal function after the stoppage of PD, and to clarify the characteristic features of the patients at risk of EPS. METHODS: Thirty-three patients who were switched from continuous ambulatory peritoneal dialysis (CAPD) to HD were enrolled in this trial. Changes in the dialysate/plasma creatinine (D/P Cr) and CA125 levels in the effluent of the peritoneal equilibration test were observed for 6 months. Furthermore, each patient was followed-up for 36 months after PD withdrawal to monitor for the development of EPS. RESULTS: D/P Cr decreased significantly, while CA125 levels tended to increase. Nine patients developed EPS during the follow-up period and they specifically showed significant increases of D/P Cr levels and significantly lower levels of CA125 at PD withdrawal. The accumulation of high transporters in the EPS group at 0 and 6 months after PD withdrawal was significant. CONCLUSIONS: Peritoneal recovery may take place after withdrawal from PD treatment and such recover indicated by improvement of transport states and a rise of the CA125 level. The present study revealed that a high-transport state and lack of increase of CA125 in the effluent were associated with EPS development after PD withdrawal. This may suggest that the lack of peritoneal recovery after PD withdrawal is predictive for EPS development.

CA-125 Antigen↗
PubMed2005

Bilateral decompression of multilevel lumbar spinal stenosis through a unilateral approach.

Lumbar canal stenosis due to hypertrophy and calcification of the facet joints and/or ligamentum flavum is a common condition in the elderly. Although a large number of individuals are symptom-free, the degenerative process, usually encroaching on both central and lateral pathways, may lead to symptoms of itself or decompensate a preexisting narrow canal. Even at an advanced age, decompression surgery is effective for symptomatic stenosis. Less invasive procedures preserving maximal bony and ligamentous structures have recently been recommended to reduce associated morbidity. This paper introduces a unilateral surgical approach for bilateral decompression by ligamentectomy, partial facetectomy and foraminal unroofing. Using a specially designed, one-side retractor, after the ipsilateral nerve root decompression the contralateral dural sac and nerve roots were approached through an 8 x 15 mm window in the interspinous ligament. The contralateral ligamentum flavum, facet joints and foraminal roof were resected, preserving the supraspinous ligament complex and much of the contralateral musculature. This technique, preserving anatomy and biomechanical function of the lumbar spine, is useful for surgery on multilevel lumbar canal stenoses.

Decompression, Surgical↗