Protection by a recombinant Mycobacterium bovis Bacillus Calmette-Guerin vaccine expressing Shiga toxin 2 B subunit against Shiga toxin-producing Escherichia coli in mice.

We have developed a novel vaccine against Shiga toxin (Stx)-producing Escherichia coli (STEC) infection using a recombinant Mycobacterium bovis BCG (rBCG) system. Two intraperitoneal vaccinations with rBCG expressing the Stx2 B subunit (Stx2B) resulted in an increase of protective serum IgG and mucosal IgA responses to Stx2B in BALB/c mice. When orally challenged with 10(3) CFU of STEC strain B2F1 (O91: H21), the immunized mice survived statistically significantly longer than the nonvaccinated mice. We suggest that intraperitoneal immunization with rBCG expressing Stx2B would be a potential vaccine strategy for STEC.

Conformational restriction approach to ß-secretase (BACE1) inhibitors: effect of a cyclopropane ring to induce an alternative binding mode.

Improvement of a drug's binding activity using the conformational restriction approach with sp³ hybridized carbon is becoming a key strategy in drug discovery. We applied this approach to BACE1 inhibitors and designed four stereoisomeric cyclopropane compounds in which the ethylene linker of a known amidine-type inhibitor 2 was replaced with chiral cyclopropane rings. The synthesis and biologic evaluation of these compounds revealed that the cis-(1S,2R) isomer 6 exhibited the most potent BACE1 inhibitory activity among them. X-ray structure analysis of the complex of 6 and BACE1 revealed that its unique binding mode is due to the apparent CH-π interaction between the rigid cyclopropane ring and the Tyr71 side chain. A derivatization study using 6 as a lead molecule led to the development of highly potent inhibitors in which the structure-activity relationship as well as the binding mode of the compounds clearly differ from those of known amidine-type inhibitors.

Mode of action of Van-M-02, a novel glycopeptide inhibitor of peptidoglycan synthesis, in vancomycin-resistant bacteria.

Van-M-02, a novel glycopeptide, was revealed to exert potent activities against Gram-positive bacteria, including vancomycin-resistant enterococci (VRE) and vancomycin-resistant Staphylococcus aureus (VRSA). A crude assay system was then used to study the mode of action of Van-M-02 as a peptidoglycan synthesis model of both vancomycin-susceptible and -resistant strains. The results suggested that Van-M-02 inhibits the synthesis of lipid intermediates irrespective of their termini. This inhibitory activity may contribute to the anti-VRE and anti-VRSA activities observed.

Successful steroid pulse therapy for brain lesion caused by Shiga toxin 2 in rabbits.

Betamethasone sodium phosphate (BSP) is usually used as a steroid therapy for human brain edema. High doses of BSP (36mg/kg) twice a day for two days statistically reduced the mortality rate and improved the survival period of Stx2 (1.4mug/kg; 1.6LD(50))-toxemic rabbits. We made evaluations on three kinds of magnetic resonance images (MRI) including T1-weighted, T2-weighted, and enhanced MRI using gadopentetate dimeglumine (Gd-DTPA) to detect brain lesion induced by an intravenous injection of Stx2 in rabbits. Enhanced T1-weighted MRI was the most sensitive tool to find leakage of Gd-DTPA suggesting impairment of the blood brain barrier caused by Stx2. Enhanced MRI revealed that BSP treatment inhibited the leakage of Gd-DTPA, as directly evidenced by the protective effect of BSP against brain edema induced by intravenous injection of Stx2. Interleukin 1beta was not induced after Stx2 treatment in brain primary mixed cell culture.

Discovery of novel non-peptide thrombopoietin mimetic compounds that induce megakaryocytopoiesis.

We have identified a series of novel non-peptide compounds that activate the thrombopoietin-dependent cell line Ba/F3-huMPL. The compounds stimulated proliferation of Ba/F3-huMPL in the absence of other growth factors, but did not promote proliferation of the thrombopoietin-independent parent cell line Ba/F3. The thrombopoietin-mimetic compounds elicited signal-transduction responses comparable with recombinant human thrombopoietin, such as tyrosine phosphorylation of the thrombopoietin receptor, JAK (Janus kinase) 2, Tyk2 (tyrosine kinase 2), STAT (signal transducer and activator of transcription) 3, STAT5, MAPKs (mitogen-activated protein kinases), PLCgamma (phospholipase Cgamma), Grb2 (growth-factor-receptor-bound protein 2), Shc (Src homology and collagen homology), Vav, Cbl and SHP-2 (Src homology 2 domain-containing protein tyrosine phosphatase 2) and increased the number of CD41(+) cells (megakaryocyte lineage) in cultures of human CD34(+) bone-marrow cells (haematopoietic stem cells). These findings suggest that this series of compounds are novel agonists of the human thrombopoietin receptor and are possible lead compounds for the generation of anti-thrombocytopaenia drugs.

Shiga toxin 2 causes apoptosis in human brain microvascular endothelial cells via C/EBP homologous protein.

Shiga toxin 1 (Stx1) and Stx2 produced by Escherichia coli O157 are known to be cytotoxic to Vero and HeLa cells by inhibiting protein synthesis and by inducing apoptosis. In the present study, we have demonstrated that 10 ng/ml Stx2 induced DNA fragmentation in human brain microvascular endothelial cells (HBMEC), with cleavage activation of caspase-3, -6, -8, and -9. A microarray approach used to search for apoptotic potential signals in response to Stx2 revealed that Stx2 treatment induced a marked upregulation of C/EBP homologous protein (CHOP)/growth arrest and DNA damage-inducible protein 153 (GADD153). Increased CHOP expression was dependent on enzymatically active Stx1. Knockdown of CHOP mRNA reduced the activation of caspase-3 and prevented apoptotic cell death. These results suggest that Stx2-induced apoptosis is mediated by CHOP in HBMEC and involves activation of both the intrinsic and extrinsic pathways of apoptosis.

Staphylococcus aureus MurC participates in L-alanine recognition via histidine 343, a conserved motif in the shallow hydrophobic pocket.

UDP-N-acetylmuramic acid:L-alanine ligase that is encoded by the murC gene, is indispensable for bacterial peptidoglycan biosynthesis and an important target for the development of antibacterial agents. Structure of MurC ligase with substrates has been described, however, little validation via studying the effects of mutations on the structure of MurC has been performed. In this study, we carried out a functional in vitro and in vivo characterization of Staphylococcus aureus MurCH343Y protein that has a temperature-sensitive mutation of a conserved residue in the predicted shallow hydrophobic pocket that holds a short L-alanine side chain. Purified H343Y and wild-type MurC had K(m) values for L-alanine of 3.2 and 0.44 mM, respectively, whereas there was no significant difference in their K(m) values for ATP and UDP-N-acetylmuramic acid, suggesting the specific alteration of L-alanine recognition in MurCH343Y protein. In a synthetic medium that excluded L-alanine, S. aureus murCH343Y mutant cells showed an allele-specific slow growth phenotype that was suppressed by addition of L-alanine. These results suggest that His343 of S. aureus MurC is essential for high-affinity binding to L-alanine both in vitro and in vivo and provide experimental evidence supporting the structural information of MurC ligase.

Rapid apoptosis induced by Shiga toxin in HeLa cells.

Apoptosis was induced rapidly in HeLa cells after exposure to bacterial Shiga toxin (Stx1 and Stx2; 10 ng/ml). Approximately 60% of HeLa cells became apoptotic within 4 h as detected by DNA fragmentation, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assay, and electron microscopy. Stx1-induced apoptosis required enzymatic activity of the Stx1A subunit, and apoptosis was not induced by the Stx2B subunit alone or by the anti-globotriaosylceramide antibody. This activity was also inhibited by brefeldin A, indicating the need for toxin processing through the Golgi apparatus. The intracellular pathway leading to apoptosis was further defined. Exposure of HeLa cells to Stx1 activated caspases 3, 6, 8, and 9, as measured both by an enzymatic assay with synthetic substrates and by detection of proteolytically activated forms of these caspases by Western immunoblotting. Preincubation of HeLa cells with substrate inhibitors of caspases 3, 6, and 8 protected the cells against Stx1-dependent apoptosis. These results led to a more detailed examination of the mitochondrial pathway of apoptosis. Apoptosis induced by Stx1 was accompanied by damage to mitochondrial membranes, measured as a reduced mitochondrial membrane potential, and increased release of cytochrome c from mitochondria at 3 to 4 h. Bid, an endogenous protein known to permeabilize mitochondrial membranes, was activated in a Stx1-dependent manner. Caspase-8 is known to activate Bid, and a specific inhibitor of caspase-8 prevented the mitochondrial damage. Although these data suggested that caspase-8-mediated cleavage of Bid with release of cytochrome c from mitochondria and activation of caspase-9 were responsible for the apoptosis, preincubation of HeLa cells with a specific inhibitor of caspase-9 did not protect against apoptosis. These results were explained by the discovery of a simultaneous Stx1-dependent increase in endogenous XIAP, a direct inhibitor of caspase-9. We conclude that the primary pathway of Stx1-induced apoptosis and DNA fragmentation in HeLa cells is unique and includes caspases 8, 6, and 3 but is independent of events in the mitochondrial pathway.

Cysteine protease activity and histamine release from the human mast cell line HMC-1 stimulated by recombinant streptococcal pyrogenic exotoxin B/streptococcal cysteine protease.

We constructed the expression vector pSK-SCP containing the streptococcal exotoxin B gene (spe b) which expressed protease activity. We showed that the recombinant streptococcal pyogenic exotoxin B/streptococcal cysteine protease (rSPE B/SCP) was secreted into the culture supernatant of the transformant and retained its SCP activity, which was equivalent to or greater than that of the naturally occurring molecule. The secreted rSPE B/SCP induced histamine release and degranulation of the human mast cell line HMC-1. This study may contribute to the understanding of the pathogenic role of SPE B/SCP in streptococcal infection and streptococcal toxic shock syndrome.

Shiga toxin 1 and 2 induce apoptosis in the amniotic cell line WISH.

OBJECTIVE: The aim of this study was to evaluate the toxicity of Shiga toxin (Stx) 1 and 2 on amniotic cells in vitro. METHODS: WISH cells, which were derived from human amniotic cells, and Vero cells were cultured with or without Stxs. After 24 hours of culture, cell viability was measured by Cell Counting Kit-8, and extracted DNA was electrophoresed on a 1% agarose gel. The morphologic changes were observed by Papanicolaou staining, and the apoptotic index (percentage of apoptotic nuclei per total nuclei) was calculated. Quantification of apoptotic cells was also measured by an enzyme-linked immunosorbent assay. RESULTS: The viability of WISH cells decreased in proportion to the concentrations of Stxs. Cellular ladder formation was observed by DNA electrophoresis of Stx-treated WISH cells, and the typical morphologic changes were observed by Papanicolaou staining. The proportion of apoptotic cells increased in response to Stxs. CONCLUSIONS: Stxs injured WISH cells directly and induced apoptosis in vitro. WISH cells were as sensitive as Vero cells to Stxs and cell death occurred by apoptosis.

Mitogenic factor secreted by Streptococcus pyogenes is a heat-stable nuclease requiring His122 for activity.

The gene encoding a mitogenic factor, termed MF, was cloned from Streptococcus pyogenes and the recombinant MF was overexpressed in Escherichia coli. Both the natural and recombinant MF had heat-resistant nuclease activity. The nuclease activity of MF was characterized using the recombinant protein. MF showed endonuclease activity, digesting ssDNA, dsDNA and tRNA. The optimal pH for the DNase activity of MF was 9.5. The DNase activity was enhanced approximately tenfold by the simultaneous presence of two divalent cations, Mg2+ and Ca2+, compared to either alone and was inhibited by EDTA or NaCl. The heat stability of MF was biphasic; the DNase activity was heat-stable from 0 to 50 degrees C over 80 degrees C but very unstable at around 60 degrees C. DNA digested by MF possessed 5'-phosphorylated and 3'-hydroxylated termini, identical to those obtained by digestion of DNA by pancreatic deoxyribonuclease I. A mutant clone revealed that His122 was a residue essential to the nuclease activity.