Biomedical subjects

Kazuhisa Sekimizu

Publications and source records attributed to Kazuhisa Sekimizu.

At least 19 recordsLinked to original sources

PubMed2026

The Small Noncoding RNA, RsaC, Is Essential for Staphylococcus aureus Virulence.

BACKGROUND: Bacterial small noncoding RNAs (sRNAs) play critical roles in virulence, stress adaptation, and host-pathogen interactions. Transcriptomic analyses during infection can help reveal pathogen-derived sRNAs required for pathogenesis, providing valuable insights for the development of novel therapeutic strategies. However, the low abundance of pathogen biomass within the host tissues poses a significant challenge for such analyses. METHODS: We employed 2-step cell disruption to enrich Staphylococcus aureus cells from infected mouse organs and conducted RNA sequencing (RNA-seq) analysis to examine staphylococcal sRNAs expressed during infection. qRT-PCR was used to confirm the gene expression. A knockout mutant of highly expressed sRNA, RsaC, was generated, and RNA-seq under in vivo as well as in vitro aerobic and anaerobic conditions were compared between the wild-type and ΔrsaC strains. Virulence of S. aureus was assessed using both mouse and silkworm survival assays. RESULTS: We identified RsaC as one of the most highly expressed sRNAs in mouse organs with consistent increment over time postinfection. Through gene disruption and complementation, we demonstrated that RsaC is an independent virulence determinant required for full pathogenicity of S. aureus in a murine infection model. In addition, RsaC influenced gene expression in response to oxygen availability and host-associated stress. Further analysis revealed that mutation of 2 genes downregulated in ΔrsaC in vivo, NWMN_RS03420 (sodium: proton antiporter) and NWMN_RS12015 (hypothetical protein), reduced S. aureus virulence in a silkworm model. CONCLUSIONS: These findings identify RsaC as a novel independent virulence determinant that supports S. aureus adaptation within the host.

Animals↗

PubMed2006

Colony spreading in Staphylococcus aureus.

Wild-type Staphylococcus aureus rapidly expands on the surface of soft agar plates. The rates of expansion and the shapes of the resultant giant colonies were distinct for different strains of laboratory stocks and clinical isolates. The colony spreading abilities did not correlate with the biofilm-forming abilities in these strains. Insertional disruption of the dltABCD operon, which functions at the step of D-alanine addition to teichoic acids, and of the tagO gene, which is responsible for the synthesis of wall teichoic acids, decreased the colony spreading ability. The results indicate that wall teichoic acids and D-alanylation of teichoic acids are required for colony spreading.

Agar↗

PubMed2006

Antioxidant N-acetyl-L-cysteine inhibits erythropoietin-induced differentiation of erythroid progenitors derived from mouse fetal liver.

To determine the role of reactive oxygen species in erythroid differentiation, we investigated the effects of an antioxidant, N-acetyl-L-cysteine (NAC), on the differentiation of erythroid progenitors derived from mouse fetal liver. In response to erythropoietin (Epo), erythroid progenitors undergo differentiation in vitro and express erythroid-specific genes such as betamajor-globin, Alas2, MafK, p45, Eklf, and Gata1. Expression of these genes was decreased in the presence of NAC, whereas the expression of c-myb, which is downregulated during erythroid differentiation, remained constant. Moreover, NAC treatment inhibited an increase in the number of cells expressing high levels of erythroid-specific antigen TER119. Treatment with another antioxidant, pyrrolidine dithiocarbamate, also caused the attenuation of TER119 expression. These results suggest that reactive oxygen species are involved in Epo-mediated erythroid differentiation.

Acetylcysteine↗

PubMed2006

Use of silkworm larvae to study pathogenic bacterial toxins.

Injection of stationary phase culture-supernatants of Staphylococcus aureus and Pseudomonas aeruginosa into the hemolymph of silkworm larvae caused their death, whereas a culture-supernatant of a non-pathogenic strain of Escherichia coli did not. A culture-supernatant of a mutant of agr, a global virulence regulator of S. aureus that is required for exotoxin production, was much less toxic to silkworm larvae. A culture-supernatant of a disruption mutant of the S. aureus beta-toxin gene did not kill larvae, whereas one of a deletion mutant of alpha-toxin, gamma-toxin, or aureolysin killed larvae, indicating that the beta-toxin gene is required for staphylococcal supernatant-mediated killing of silkworm larvae. The 50% lethal doses (LD50) of staphylococcal alpha-toxin and beta-toxin, Pseudomonas exotoxin A and diphtheria toxin were 12 microg/g, 9 microg/g, 0.14 microg/g and 1.1 microg/g, respectively. As the purified toxins killed the larvae, silkworm larvae could be used as a model to study the actions of pathogenic bacterial toxins in animal bodies.

Animals↗

PubMed2006

Cleavage and survival of Xenopus embryos exposed to 8 T static magnetic fields in a rotating clinostat.

In this study, we examined cleavage and survival of fertilized Xenopus embryos exposed to 8 T static magnetic fields (SMFs). We investigated fertilized Xenopus embryos exposed to magnetic field either in static chamber or in a rotating culture system. Our results showed that the exposure to the strong magnetic field of 8 T changed the third cleavage furrow from the usual horizontal one to a perpendicular one; however, when the direction of gravity was randomized by exposing embryos to magnetic field in a rotating culture system, the third cleavage furrow were formed horizontally, a finding which suggests that the observed distortion of the third cleavage furrow in magnetism-exposed embryos was accomplished by altering gravity effects which were elicited by diamagnetic force due to high gradient magnetic field. Our results also showed that the exposure to the strong magnetic field did not damage survival. These results demonstrate that SMF and altering gravity cause distortion of the third cleavage furrow and show that effects of exposing cleavage embryos to magnetic field were transient and did not affect the post-cleavage development. We also showed that strong magnetic field is not hazardous to the cleavage and blastula-gastrula transition of developing embryonic cells.

Animals↗

PubMed2006

Novel DNA binding protein SarZ contributes to virulence in Staphylococcus aureus.

We previously reported that the cvfA gene is a virulence regulatory gene in Staphylococcus aureus. Here, we identified a novel gene named sarZ that acts as a multicopy suppressor of decreased haemolysin production in the cvfA deletion mutant. The amount of sarZ transcripts was decreased in the cvfA mutant. The sarZ-deletion mutant produced less haemolysin and attenuated virulence in a silkworm-infection model and a mouse-infection model. The amino acid sequence of the sarZ gene product had 19% identity with the transcription factor MarR in Escherichia coli, and the internal region contained a winged helix-turn-helix motif (wHTH), a known DNA binding domain. Purified recombinant SarZ protein had binding affinity for the promoter region of the hla gene that encodes alpha-haemolysin. SarZ mutant proteins with an amino acid substitution in the N-terminal region or in the wHTH motif had significantly decreased DNA binding. The mutated sarZ genes encoding SarZ mutant proteins with a low affinity for DNA did not complement the decreased haemolysin production or the attenuated killing ability against silkworms in the sarZ mutant. These results suggest that the DNA binding activity of the SarZ protein is required for virulence in S. aureus.

Amino Acid Sequence↗

PubMed2006

Isolation of a temperature-sensitive dnaA mutant of Staphylococcus aureus.

Of 750 temperature-sensitive mutants of Gram-positive Staphylococcus aureus, one was complemented by the dnaA gene. This mutant had a single base transition in the dnaA gene causing the amino-acid substitution mutation, Ala40Thr. Phage transduction experiments showed that this temperature-sensitive phenotype was linked with a drug-resistant marker inserted near the dnaA gene, suggesting the dnaA mutation is responsible for the phenotype. Flow cytometric analysis revealed that the dnaA mutant was unable to initiate DNA replication at a restrictive temperature and exhibited asynchrony in the replication initiation at a permissive temperature. This is the first report of a temperature-sensitive dnaA mutant in S. aureus, and the results show that DnaA is required for the initiation of chromosomal replication and for the regulation of synchrony in the bacterial cells.

Bacterial Proteins↗

PubMed2006

Transcription elongation factor S-II is required for definitive hematopoiesis.

Transcription elongation factor S-II/TFIIS promotes readthrough of transcriptional blocks by stimulating nascent RNA cleavage activity of RNA polymerase II in vitro. The biologic significance of S-II function in higher eukaryotes, however, remains unclear. To determine its role in mammalian development, we generated S-II-deficient mice through targeted gene disruption. Homozygous null mutants died at midgestation with marked pallor, suggesting severe anemia. S-II(-/-) embryos had a decreased number of definitive erythrocytes in the peripheral blood and disturbed erythroblast differentiation in fetal liver. There was a dramatic increase in apoptotic cells in S-II(-/-) fetal liver, which was consistent with a reduction in Bcl-x(L) gene expression. The presence of phenotypically defined hematopoietic stem cells and in vitro colony-forming hematopoietic progenitors in S-II(-/-) fetal liver indicates that S-II is dispensable for the generation and differentiation of hematopoietic stem cells. S-II-deficient fetal liver cells, however, exhibited a loss of long-term repopulating potential when transplanted into lethally irradiated adult mice, indicating that S-II deficiency causes an intrinsic defect in the self-renewal of hematopoietic stem cells. Thus, S-II has critical and nonredundant roles in definitive hematopoiesis.

Animals↗

PubMed2005

Occurrence of pre-MBT synthesis of caspase-8 mRNA and activation of caspase-8 prior to execution of SAMDC (S-adenosylmethionine decarboxylase)-induced, but not p53-induced, apoptosis in Xenopus late blastulae.

Overexpression of S-adenosylmethionine decarboxylase (SAMDC) in Xenopus fertilized eggs activates caspase-9 and executes maternal program of apoptosis shortly after midblastula transition (MBT). We find that overexpression of caspase-8 and p53, like that of SAMDC, induces apoptosis in Xenopus late blastulae. The apoptosis induced by p53 was abolished by injection of mRNA for xdm-2, a negative regulator of p53, and by injection of a peptide inhibitor or a dominant-negative type mutant of caspase-9, but not caspase-8. The apoptosis induced by SAMDC was not abolished by injection of xdm-2 mRNA, but was abolished by injection of a peptide inhibitor or a dominant-negative type mutant mRNA of both caspase-9 and caspase-8. Unlike caspase-9 mRNA, caspase-8 mRNA did not occur as a maternal mRNA rather induced to be expressed during cleavage stage (pre-MBT stage) by overexpression of SAMDC but not p53. Furthermore, while activities to process procaspase-8 and procaspase-9 appeared in SAMDC-overexpressed apoptotic embryos, the activity to process procaspase-8 did not appear in p53-overexpressed apoptotic embryos. We conclude there are at least two pathways in the execution of the maternal program of apoptosis in Xenopus embryos; one being through do novo expression of caspase-8 gene during cleavage stage, and the other without involvement of caspase-8.

Adenosylmethionine Decarboxylase↗

PubMed2005

Identification and characterization of amino acid residues essential for the active site of UDP-N-acetylenolpyruvylglucosamine reductase (MurB) from Staphylococcus aureus.

The enzymes essential for bacterial peptidoglycan biosynthesis are attractive targets for antimicrobial drug development. One of these is MurB, which contains FAD as a cofactor and catalyzes the NADPH-dependent reduction of UDP-N-acetylenolpyruvylglucosamine (UDP-GlcNAcEP) to UDP-N-acetylmuramic acid. This study examined the roles of the conserved amino acid residues of Staphylococcus aureus MurB, which are located near the active site in x-ray crystal structures. Seven of 11 site-directed mutated murB genes lost the ability to complement a temperature-sensitive S. aureus murB mutant. Biochemical characterization of the seven mutated MurB proteins revealed that they cannot carry out the reduction of UDP-GlcNAcEP, although they can all catalyze the intramolecular reduction of FAD via NADPH. Spectrometric analyses of the oxidized form of the mutated proteins in the presence and absence of NADP+ or UDP-GlcNAcEP revealed that these essential amino acid residues play four distinct roles in substrate interactions: Arg213 is essential for maintenance of the electronic state of FAD; Arg176 is required for interaction with UDP-GlcNAcEP; His259 is required for interaction with both UDP-GlcNAcEP and NADP+; and Asn71, Tyr175, Ser226, and Glu296 are not apparently required for interaction with either ligand. The results presented here identify for the first time the amino acid residues of MurB that are required for the interaction with UDP-Glc-NAcEP and NADP+.

Amino Acid Sequence↗

PubMed2005

Direct interaction between metastasis-associated protein 1 and endophilin 3.

The yeast two-hybrid system was used to search for partners of mouse metastasis-associated protein 1 (Mta1). Screening of a cDNA library prepared from mouse embryo yielded positive clones coding for endophilin 3. The site of interaction was suggested to be the SH-3-binding domain of Mta1 and SH-3 domain of endophilin 3. This interaction was confirmed by GST pull-down assay in vitro and immunoprecipitation in vivo. The Mta1 and endophilin 3 transcripts were highly expressed in testis and brain. But, Mta1 localized mainly in nucleus and to a lesser extent in cytoplasm while endophilin 3 localized mainly in cytoplasm. If Mta1 functions in cytoplasm, it might be involved in the regulation of endocytosis mediated by endophilin 3.

Adaptor Proteins, Signal Transducing↗

PubMed2005

Effects of molecular mass and hydrophobicity on transport rates through non-specific pathways of the silkworm larva midgut.

We previously reported that therapeutic drug effects in the silkworm infection model are largely influenced by midgut permeability. In this report, we describe the effects of drug molecular mass and hydrophobicity on transport through the silkworm larva midgut membrane. Hydrophilic compounds with a molecular mass of greater than 400Da did not permeate the silkworm larva midgut, and the hydrophobicity of similar-sized compounds had positive effects on the transport rate. Furthermore, we compared transport rates through the midgut membrane between cefcapene sodium (CFPN-Na) and cefcapene pivoxil (CFPN-PI), which is a CFPN-Na prodrug. The in vitro transport rate of CFPN-PI was three times faster than that of CFPN-Na. Moreover, when CFPN-PI and CFPN-Na were injected into the living silkworm larva midgut, CFPN-PI appeared rapidly in the haemolymph, whereas CFPN-Na did not. The 50% effective dose (ED50) of CFPN-PI administered via the midgut was one-sixth that of CFPN-Na. These findings suggest that the general features of the non-specific transport route are similar between silkworm larvae and mammals.

Animals↗

PubMed2005

Erythrocyte surface glycosylphosphatidyl inositol anchored receptor for the malaria parasite.

Parasitophorous vacuole formation is a critical step for the successful invasion of host erythrocytes by the malaria parasite. Rhoptry proteins are believed to have essential roles in vacuole formation, although their biological roles are poorly understood. To understand the molecular interactions between parasite rhoptry proteins and the erythrocyte during invasion, we have characterized the binding specificity of the high molecular mass rhoptry protein (RhopH) complex to erythrocytes using the rodent malaria parasite, Plasmodium yoelii. RhopH complex binding to erythrocytes was species-specific, observed with mouse but not rabbit or human erythrocytes. Binding is abolished following treatment of erythrocytes with trypsin or chymotrypsin. Because host cell cholesterol-rich membrane domains are recruited into the nascent parasitophorous vacuole, we evaluated a possible role of RhopH complex binding to the cholesterol-rich membrane domain-associated glycosylphosphatidyl inositol (GPI)-anchored protein. Using chimeric mice harboring GPI-deficient erythrocytes, RhopH complex binding to GPI-deficient mouse erythrocytes was undetectable, indicating involvement of GPI-anchored protein in PyRhopH complex binding. Furthermore, a significant reduction of P. yoelii parasite infection of GPI-deficient erythrocytes was observed in vivo, probably due to inefficient invasion. We conclude that the major erythrocyte receptor for PyRhopH complex is a protein attached to the erythrocyte surface via GPI-anchor and that GPI-deficient erythrocytes are resistant to P. yoelii invasion.

Animals↗

PubMed2005

D-Glutamic acid-induced muscle contraction in the silkworm, Bombyx mori.

Agonists for muscle contraction in silkworms were screened by injecting test solutions into the hemolymph of decapitated silkworm larvae. Kainic acid, a glutamate receptor agonist, and D-glutamic acid induced muscle contractions, and D-aspartic acid was partially effective, whereas NMDA and AMPA, representative mammalian glutamate receptor agonists, did not induce contraction. L-Glutamic acid inhibited the kainic acid or D-glutamic acid-induced contraction. Amino acid analysis revealed that 3% of the total glutamic acid in the silkworm hemolymph is D-glutamic acid. These results suggest that d-glutamic acid acts physiologically as an agonist for muscle contraction in silkworms, and that L-glutamic acid functions as an inhibitor.

Animals↗

PubMed2005

Involvement of EDTP, an egg-derived tyrosine phosphatase, in the early development of Drosophila melanogaster.

Previously, we purified a novel protein tyrosine phosphatase from eggs of the flesh fly, Sarcophaga peregrina. This protein tyrosine phosphatase, named egg-derived tyrosine phosphatase (EDTP), is expressed during oogenesis and early embryogenesis but is rapidly degraded in middle embryogenesis by lysosomal cathepsin L. Here, we demonstrate the requirement of EDTP in the development of the fruit fly, Drosophila melanogaster. Deletion of the Drosophila EDTP gene using transposase-catalyzed imprecise excision resulted in homozygous lethals during embryogenesis. Additionally, germline clones generated using the FLP-FRT-ovo(D) system showed severe defects in ovarian development during oogenesis. These results indicate that the Drosophila EDTP gene is crucial in oogenesis and embryogenesis.

Animals↗

PubMed2005

Participation of Rho-dependent transcription termination in oxidative stress sensitivity caused by an rpoB mutation.

The role of transcription termination process for gene expression regulation is poorly understood. Either a multicopy supply of the rof gene or bicyclomycin, both of which inhibit the transcription termination Rho factor, suppressed the increased sensitivity to oxidative stress of the rifampicin-resistant rpoB mutation in Escherichia coli. Multi-copy supply of the rnk gene also suppressed oxidative stress sensitivity, coincident with the recovery of the reduced concentration of nucleoside triphosphates in the mutant cells, which is one of the factors that affects transcription termination efficiency in vitro. Thus, an appropriate, nonexcessive termination frequency at Rho-dependent transcription terminators might contribute to oxidative stress survival. Clinical application of oxidative stress against drug resistant bacteria is also discussed.

DNA-Directed RNA Polymerases↗

PubMed2005

Silkworm pathogenic bacteria infection model for identification of novel virulence genes.

Silkworms are killed by injection of pathogenic bacteria, such as Staphylococcus aureus and Streptococcus pyogenes, into the haemolymph. Gene disruption mutants of S. aureus whose open reading frames were previously uncharacterized and that are conserved among bacteria were examined for their virulence in silkworms. Of these 100 genes, three genes named cvfA, cvfB, and cvfC were required for full virulence of S. aureus in silkworms. Haemolysin production was decreased in these mutants. The cvfA and cvfC mutants also had attenuated virulence in mice. S. pyogenes cvfA-disrupted mutants produced less exotoxin and had attenuated virulence in both silkworms and mice. These results indicate that the silkworm-infection model is useful for identifying bacterial virulence genes.

Animals↗

PubMed2004

Induction of fusion-competent myoblast-specific gene expression during myogenic differentiation of Drosophila Schneider cells by DNA double-strand breaks or replication inhibition.

Differentiation of Drosophila Schneider cells caused by DNA double-strand break (DSB)-inducing topoisomerase II (topo II) inhibitors were attenuated by ICRF-193, a non-DNA-damaging topo II inhibitor. ICRF-193 did not inhibit differentiation induced by neocarzinostatin (NCS), a drug that causes DNA DSBs independent of topo II. Schneider cells differentiated upon treatment with gamma-ray. These results suggest that DNA DSBs induce myogenic differentiation of Schneider cells. We also found DNA replication inhibitors, hydroxyurea (HU), aphidicolin, and ethylmethanesulfonate (EMS) induced myogenic differentiation of Schneider cells. HU-induced differentiation was inhibited upon pretreatment of cells with chemical inhibitors of PP 1/2A, p38 MAPK, JNK, and proteasome. RT-PCR analysis revealed that the expressions of fusion-competent myoblast-specific genes lmd, sns, and del were induced in Schneider cells upon treatment with NCS or HU, whereas expressions of three founder cell-specific genes, duf, ants, and rols, were undetectable. These results indicate that the expression of fusion competent-myoblast-specific genes is induced during myogenic differentiation of Drosophila Schneider cells by DNA DSBs or replication inhibition.

Animals↗