Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cytopathic effects of broth-culture filtrates from eight clinical isolates and one reference strain of Helicobacter pylori on three cultured mammalian cell lines were investigated. All the strains, including NCTC 11637, produced cytotoxic factors that caused intracellular vacuolation on these cell lines. AGS and SflEp cells were more sensitive than HEp-2 cells. To examine the role of urease in the cytotoxic effect, a urease-negative mutant was produced. Filtrates from both wild-type and mutant strains produced similar vacuolation on SflEp cells in the absence of urea, suggesting that H. pylori produces a cytotoxic substance other than urease. In contrast, ammonia alone, or jack bean urease with urea, also induced rounding and detachment of SflEp cells, whereas ammonium salts induced the production of small vacuoles. The combination of the broth filtrate of the wild-type strain and urea induced vacuolation followed by rounding and detachment of SflEp cells. Evidence is presented that the latter changes are due to ammonia produced during incubation. Nevertheless, the amounts produced were less than that needed to induce cytopathic effects by itself. These results suggest that the cytotoxic substance induces intracellular vacuolation, and that the vacuolated cells are more susceptible to killing by ammonia. Thus both the cytotoxic substance and urease may contribute to the lethal cytotoxicity of H. pylori in vitro.
 ...
PMID:Cytopathic effects of Helicobacter pylori on cultured mammalian cells. 162 96

Helicobacter pylori is a bacterial pathogen of humans that infects the gastric mucosa. This infection has been associated with gastritis, peptic ulcers, and gastric carcinomas. Diverse in vitro studies have described efficient adherence of H. pylori to different types of epithelial cells. Because of its varied effects on host cells, we have analysed signal transduction events in H. pylori-infected epithelial cells. Our results show that H. pylori induces an increase in inositol phosphates in all cultured epithelial cells used, including HeLa, Henle 407, Hep-2, and the human gastric adenocarcinoma cell line AGS. Bacterial growth medium supernatants induce a similar response in the host cell. The increase in inositol phosphates is not related to redistribution of cytoskeletal proteins such as actin or alpha-actinin nor tyrosine-phosphorylation of host cell proteins. The inositol phosphate increase is also observed in cells infected with low or non-adherent H. pylori mutants or mutants defective in the vacuolating toxin or urease holoenzyme. These results indicate that inositol phosphate release in H. pylori-infected cells is not dependent on bacterial adherence, and that a soluble bacterial factor, but not the vacuolating toxin or urease holoenzyme, mediates such an effect.
 ...
PMID:Helicobacter pylori induces an increase in inositol phosphates in cultured epithelial cells. 760 12

Gastric infection with Helicobacter pylori activates a mucosal inflammatory response by mononuclear cells and neutrophils that includes expression of cytokines interleukin-1 beta (IL-1 beta), IL-6, tumor necrosis factor alpha, and IL-8. In this study, we analyzed the IL-8 response of human gastric cancer cell lines (Kato III, AGS, and MKN28) to H. pylori infection in vitro. IL-8 mRNA expression was detected by reverse transcription-PCR amplification of RNA extracted from epithelial cells after incubation with different H. pylori wild-type and mutant strains, and IL-8 secretion was measured by an enzyme-linked immunosorbent assay. Exposure to viable H. pylori induced IL-8 mRNA and protein synthesis in all three gastric cell lines but not in nongastric epithelial cell lines. Heat-killed H. pylori and a crude cytotoxin preparation did not induce significant IL-8 secretion. IL-8 mRNA peaked between 2 and 4 h postinfection, and IL-8 protein production was maximal 24 h postinfection. Exposure of gastric carcinoma cells to other gastrointestinal bacteria, such as Pseudomonas aeruginosa, Campylobacter jejuni, and Escherichia coli, but not Campylobacter fetus, induced IL-8 synthesis. Wild-type strains that expressed the vacuolating cytotoxin (Tox+) and a cytotoxin-associated gene (cagA) product (CagA+) induced significantly more IL-8 than did CagA- Tox- strains. However, there was no decrease in IL-8 induction by isogenic mutants of CagA-, Tox-, or Cag- Tox- strains or by a mutant lacking the urease subunits. These results indicate that exposure to H. pylori and other gram-negative organisms that do not colonize the gastric mucosa induces IL-8 production by gastric carcinoma cells in vitro. Although the CagA+ Tox+ phenotype of H. pylori is associated with enhanced IL-8 production by gastric cell lines, other bacterial constituents are clearly essential.
 ...
PMID:Interleukin-8 response of gastric epithelial cell lines to Helicobacter pylori stimulation in vitro. 772 72

Despite the induction of an immunological reaction, Helicobacter pylori-associated gastritis is a chronic disease, suggesting that this microbe can evade the host immune defense. Previous studies by our group showed that H. pylori suppresses the in vitro proliferative response of human mononuclear cells to mitogens and antigens. Here we demonstrate that the antiproliferative activity of H. pylori also affects the proliferation of various mammalian cell lines (U937, Jurkat, AGS, Kato-3, HEP-2, and P388D1). This effect is detectable in the first 16 h of incubation and maximal between 24 and 48 h. In addition, the presence of H. pylori significantly diminished the protein synthesis of cells in the first 6 h of incubation, comparable to the results with cycloheximide and diphtheria toxin. The urease enzyme, the cagA gene product, and the vacuolizing cytotoxin of H. pylori were excluded as causative agents of the antiproliferative effect by using isogenic knockout mutant strains. The inhibitory effect was not due to a lytic activity of this bacterium. The results reported here indicate that the responsible factor is a protein with an apparent native molecular mass of 100 +/- 10 kDa. Our work implicates the presence of a protein factor in H. pylori (termed PIP [for proliferation-inhibiting protein]) with antiproliferative activity for mammalian cells, including immunocompetent and epithelial cells. Thus, it is reasonable to presume that this property may contribute to the pathogenesis of H. pylori-induced diseases. It may be involved on the one hand in immune response evasion and on the other hand in the suppression of epithelial repair mechanisms.
 ...
PMID:Partial characterization of a cell proliferation-inhibiting protein produced by Helicobacter pylori. 875 89

Helicobacter pylori resists gastric acidity by modulating the proton-gated urea channel UreI, allowing for pH(out)-dependent regulation of urea access to intrabacterial urease. We employed pH- and Ca(2+)-sensitive fluorescent dyes and confocal microscopy to determine the location, rate, and magnitude of pH changes in an H. pylori-AGS cell coculture model, comparing wild-type bacteria with nonpolar ureI-deletion strains (ureI-ve). Addition of urea at pH 5.5 to the coculture resulted first in elevation of bacterial periplasmic pH, followed by an increase of medium pH and then pH in AGS cells. No change in periplasmic pH occurred in ureI-deletion mutants, which also induced a slower increase in the pH of the medium. Pretreatment of the mutant bacteria with the detergent C(12)E(8) before adding urea resulted in rapid elevation of bacterial cytoplasmic pH and medium pH. UreI-dependent NH(3) generation by intrabacterial urease buffers the bacterial periplasm, enabling acid resistance at the low urea concentrations found in gastric juice. Perfusion of AGS cells with urea-containing medium from coculture at pH 5.5 did not elevate pH(in) or [Ca(2+)](in), unless the conditioned medium was first neutralized to elevate the NH(3)/NH(4)(+) ratio. Therefore, cellular effects of intrabacterial ammonia generation under acidic conditions are indirect and not through a type IV secretory complex. The pH(in) and [Ca(2+)](in) elevation that causes the NH(3)/NH(4)(+) ratio to increase after neutralization of infected gastric juice may contribute to the gastritis seen with H. pylori infection.
 ...
PMID:Local pH elevation mediated by the intrabacterial urease of Helicobacter pylori cocultured with gastric cells. 1093 Apr 37

Helicobacter pylori is a major aetiological agent in gastroduodenal disorders and adherence of the bacteria to the gastric mucosa is one of the initial stages of infection. Although a number of specific adhesins has been identified, other H. pylori virulence factors may play a role in adherence to gastric epithelial cells directly or through interaction with other adhesins. This study assessed the effect of 16 H. pylori virulence factors on the adherence of the bacteria to gastric AGS cells and on gastric epithelial cell cycle distribution. Defined isogenic H. pylori SS1 mutants were used. After co-incubation of gastric AGS cells and bacteria, adherence of H. pylori to AGS cells was visualised by immunofluorescence microscopy and quantified by flow cytometry. Cell cycle phase distribution was analysed by flow cytometry with propidium iodide staining. Mutants were tested for their ability to adhere to AGS cells and compared with the wild-type SS1 strain. Mutations in genes in the cag pathogenicity island showed that cagP and cagE mutants adhered less than the wild-type strain to AGS cells, whereas a cagF mutant showed no reduction in adherence. Mutations in genes involved in flagellar biosynthesis showed that the adherence ability of fliQ, fliM and fliS mutants was reduced, but a flhB mutant possessed wild-type levels of adherence. Mutations in genes coding for the urease (ureB) and phospholipase (pldA) enzymes did not affect adherence, but mutation of the tlyA gene encoding an H. pylori haemolysin resulted in a reduced adherence. A fliQ mutant, with reduced adherence to AGS cells, was less able to induce AGS cell apoptosis than SS1. The ability to induce G0G1 cell cycle arrest was also abolished in the fliQ mutant. However, an increased cell number in S phase was observed when AGS cells were exposed to the fliQ mutant compared with SS1, suggesting that unattached bacteria may still be able to stimulate cell proliferation. In addition to known adhesins, other bacterial virulence factors such as CagE, CagP, FliQ, FliM, FliS and TlyA appear to play a role in H. pylori adherence to gastric epithelial cells. Mutations in these genes may affect H. pylori pathogenicity by reducing either the ability of the bacteria to attach to gastric epithelial cells or the intensity of bacteria-host cell interactions.
 ...
PMID:Helicobacter pylori adherence to gastric epithelial cells: a role for non-adhesin virulence genes. 1201 57

The present study evaluated the potential use of immunoglobulin prepared from the egg yolk of hens immunized with Helicobacter pylori (immunoglobulin Y [IgY]-Hp) in the treatment of H. pylori infections. The purity of our purified IgY-Hp was 91.3%, with a yield of 9.4 mg of IgY per ml of egg yolk. The titer for IgY-Hp was 16 times higher than that for IgY in egg yolk from nonimmunized hens, and IgY-Hp significantly inhibited the growth and urease activity of H. pylori in vitro. Bacterial adhesion on AGS cells was definitely reduced by preincubation of both H. pylori (10(8) CFU/ml) and 10 mg of IgY-Hp/ml. In Mongolian gerbil models, IgY-Hp decreased H. pylori-induced gastric mucosal injury as determined by the degree of lymphocyte and neutrophil infiltration. Therefore, in this experimental model, H. pylori-associated gastritis could be successfully treated by orally administered IgY-Hp. The immunological activity of IgY-Hp stayed active at 60 degrees C for 10 min, suggesting that pasteurization can be applied to sterilize the product. Fortification of food products with this immunoglobulin would significantly decrease the H. pylori infection. In conclusion, the IgY-Hp obtained from hens immunized by H. pylori could provide a novel alternative approach to treatment of H. pylori infection.
 ...
PMID:Use of egg yolk-derived immunoglobulin as an alternative to antibiotic treatment for control of Helicobacter pylori infection. 1220 60

Helicobacter pylori, the main cause of chronic gastritis, plays a central role in the etiology of peptic ulcer disease and gastric cancer. In vitro studies have shown that H. pylori increases gastric epithelial cell turnover, thus increasing the risk for the development of neoplastic clones. The mechanisms by which H. pylori promotes perturbation of cell proliferation are not yet elucidated. To investigate whether products released by H. pylori in culture media interfere with cell cycle progression of human gastric epithelial cells, four cell lines (MKN 28, MKN 7, MKN 74, and AGS) were incubated in the presence of H. pylori broth culture filtrate. Cell cycle analysis showed that a H. pylori-released factor(s) significantly inhibited the G1- to S-phase progression of MKN 28 and MKN 7 cell lines, with a reversible, nonlethal mechanism, independent of the expression of VacA, CagA, and/or urease. The cell cycle inhibition occurred concomitantly with an increase in p27(KIP1) protein levels, a reduction in Rb protein phosphorylation on serine residues 807-811, and a significant decrease in cyclin E-associated cdk2 activity. In contrast, the cell cycle progression of MKN 74 and AGS cell lines was not affected by the H. pylori-released factor(s). In normal human fibroblasts, G1-phase cell accumulation was concomitant with the reduction in Rb protein phosphorylation; that, however, appeared to be dependent on p21(WAF1/CIP1) rather than on p27(KIP1) protein. A preliminary characterization showed that the molecular mass of the partially purified cell cycle inhibitory factor(s) was approximately 40 kDa. These results suggest that H. pylori releases a soluble factor(s) that may affect cell cycle progression of gastric epithelial cells through elevated levels of cdk inhibitor p27(KIP1). This factor(s) might act in vivo on noncolonized distant cells, the most proliferating cells of human gastric mucosa.
 ...
PMID:Helicobacter pylori releases a factor(s) inhibiting cell cycle progression of human gastric cell lines by affecting cyclin E/cdk2 kinase activity and Rb protein phosphorylation through enhanced p27(KIP1) protein expression. 1244 Nov 36

Helicobacter mustelae is a gastric pathogen of ferrets, where it causes disorders similar to those caused by Helicobacter pylori in humans. The H. mustelae ferret model therefore has potential for the in vivo study of Helicobacter pathogenesis in general. In this study a library of 500 individual H. mustelae mutants was generated using an in vitro random insertion mutagenesis technique. Mutants were subsequently tested for motility and adherence, and 43 of the 500 mutants tested were found to be nonmotile in a soft agar assay. Of these 43 mutants, seven were subsequently identified as deficient in their ability to adhere to AGS cells. Insertion had taken place in different positions in the H. mustelae genome, and included mutants in or near to genes involved in motility and urease activity (e.g. the chemotaxis gene cheV and the urease accessory gene ureH). The development of a mutant library for a natural animal model of Helicobacter infection provides the opportunity to study in vivo the role of candidate Helicobacter virulence genes.
 ...
PMID:Random mutagenesis to identify novel Helicobacter mustelae virulence factors. 1731 71

Helicobacter pylori infection is the most common cause of gastritis, gastric ulcer and adenocarcinoma. It has proven difficult to cure because of its capability to develop strains resistant to antibiotics. The effect of three strains of lactic acid bacteria (LAB) and bovine colostral preparations on the adhesion of H. pylori NCTC 11637 on gastric adenocarcinoma (AGS) cells and on the interleukin (IL)-8 production was studied. Before infection, H. pylori were pretreated with Lactobacillus plantarum MLBPL1, Lactobacillus rhamnosus GG, Lactococcus lactis, or with a colostral preparation with or without specific H. pylori antibodies. The relative number of H. pylori adhered on AGS cells was determined by urease test. IL-8 produced by the cells was studied by enzyme-linked immunosorbent assay. Colostral preparations with and without specific antibodies reduced the adhesion of H. pylori on AGS cells in a dose-dependent manner. Live LAB at a concentration of 10(10) CFU/ml reduced the adhesion by approximately 50% (P < 0.05). After the infection of AGS cells by H. pylori, the IL-8 level rose up to about 10-fold (5500 +/- 1600 pg/ml). Pretreatment of H. pylori with colostral preparations or high concentrations of LAB prevented this IL-8 rise. Similar effect was seen with live and heat-killed LAB, the live LAB being more effective. Heat-killed LAB at a concentration of 10(10) CFU/ml rose the IL-8 level of non-infected cells significantly. Suppression of IL-8 production by LAB or colostral products could have a suppressive effect on inflammation in Helicobacter infection.
 ...
PMID:Effect of specific colostral antibodies and selected lactobacilli on the adhesion of Helicobacter pylori on AGS cells and the Helicobacter-induced IL-8 production. 1862 49


1 2 3 Next >>