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A Lee

Publications and source records attributed to A Lee.

At least 469 records · Page 26Linked to original sources
PubMed1995

New microbiological features.

Recent developments in the microbiology of Helicobacter pylori have aimed to improve our understanding of the organism in order to define better methods of diagnosis and cure, and to explore possible methods of prevention. Investigations of the basic biochemistry of the bacterium have revealed many interesting physiological anomalies including characteristics of a eukaryotic parasite rather than a bacterium. The latest in a growing list of adhesins to be identified shows specificity for the Lewis b antigen, possibly providing an explanation for the postulated link between blood group and peptic ulceration. However, there are many contradictory features in the H. pylori adhesin story in urgent need of resolution. The search for the ulcerogenic strain has revealed only one possible candidate to date, the cagA phenotype, which appears to be inflammatory. Recently, the cloning frenzy has resulted in the sequencing of a multitude of putative virulence factors, the challenge now is to prove their importance in relevant animal models.

Adhesins, Bacterial↗
PubMed1995

MALToma-like lesions in the murine gastric mucosa after long-term infection with Helicobacter felis. A mouse model of Helicobacter pylori-induced gastric lymphoma.

The long-term consequences of helicobacter infection were observed in an established murine model of human helicobacter infection. Stomachs of specific pathogen-free BALB/c mice infected with Helicobacter felis were examined for inflammation with particular reference to lymphoid cell proliferation and lymphoepithelial lesions. There was little evidence of an inflammatory response in animals sacrificed up to 19 months after infection. In contrast, from 22 months, 38% of infected animals had lymphoid follicles, whereas no lymphoid follicles were found in noninfected control animals. Lymphoepithelial lesions were observed in 25% of infected mice compared with none in controls. Immunostaining confirmed the B-cell nature of the lymphoid infiltrate. The morphology of these lesions closely resemble those seen in human gastric MALToma. This animal model would provide an opportunity to study the pathogenesis of lymphoproliferative disease.

Animals↗
PubMed1995

Local acid production and Helicobacter pylori: a unifying hypothesis of gastroduodenal disease.

We aimed to produce a unifying hypothesis to explain the different locations of peptic ulcer and gastritis observed in different populations. The pre-Helicobacter pylori literature on patterns of gastroduodenal disease was reviewed and compared with recent human and animal findings on H. pylori infection. Early observations revealed that duodenal and non-pre-pyloric ulcers tend to be mutually exclusive. In duodenal ulcer patients, gastritis is usually restricted to the antrum, while gastric ulcer patients experience more severe pangastritis. The manipulation of acid output by surgery or acid suppressive therapy alters the distribution of gastritis. Recent experimental evidence in humans and animals has shown that these changes parallel changes in the distribution and cellular responses to H. pylori infection. We propose that the most important factor in the ecology of the H. pylori-infected stomach is local acid production. Local acid production determines the location and severity of inflammation and the clinical outcome of this bacterial infection. Priority research areas should be the investigation of the in vivo behaviour of H. pylori in the acid and the non-acid producing areas of the stomach and the measurement of acid output in populations known to have different patterns of gastroduodenal disease.

Animals↗
PubMed1995

Kappa opioid receptor-mediated suppression of voltage-activated potassium current in a catecholaminergic neuronal cell line.

Opioid sensitivity of a catecholaminergic cell line (CATH.a) of brainstem origin was examined using whole-cell voltage-clamp techniques. Morphine produced a preferential and concentration-dependent decrease of the amplitude of voltage-activated potassium current, IK (ED50 = approximately 4 microM, maximum inhibition 52%, n = 33). The mu-selective opiate agonist [D-Ala2, MePhe, Gly-ol5] enkephalin (2-20 microM; n = 6) and the delta-selective agonist [D-Pen2, D-Pen5] enkephalin (2-20 microM; n = 7) produced no effect. However, the kappa-selective agonist trans-(+/-)-3,4-dichloro-N-methyl-N-(2-[1-pyrrolidinyl]cyclohexyl)ben zene-acetamide reduced IK in a concentration-dependent manner (EC50 = 2.3 microM, maximum inhibition 44%, n = 40). The kappa receptor antagonist nor-binaltorphimine (10 nM) blocked the effect of either morphine (10 microM, n = 6) or U50,488 (10 microM, n = 7). Kappa agonist-mediated IK reduction was prevented by intracellular dialysis with an inactive form of guanosine diphosphate, guanosine 5'-O-(2-thio)diphosphate (100-200 microM; n = 10) but was unchanged by incubation with pertussis toxin (500 ng/ml, 24-48 h, n = 10). These results suggest that opioid suppression of IK is mediated by kappa-opioid receptors coupled to a pertussis toxin-insensitive G-protein.

Catecholamines↗
PubMed1995

Diagnostic efficacy of plasma urokinase-type plasminogen activator and plasminogen activator inhibitor-2 in differentiation of hepatocellular carcinoma from cirrhosis.

We determined the plasma antigen levels of urokinase-type plasminogen activator(u-PA) and plasminogen activator inhibitor 2(PAI-2) in 41 patients with hepatocellular carcinoma and 28 patients with different stages of liver cirrhosis. No significant differences of u-PA and PAI-2 levels were calculated between the two groups of tumor patients (HCC) and liver cirrhosis without tumor (non-HCC). Within both study groups, no significant differences were found in u-PA and PAI-2 levels of the different Child categories. Discriminative functions of both u-PA and PAI-2 (total error count estimates of 43.1% and 43.6%, respectively), were low compared to that (29.0%) of alpha-fetoprotein (AFP). The combinations of AFP and u-PA lowered the total error rate (21.9%) more than that of each marker alone. However, whether plasma u-PA and PAI-2 may be considered as a risk factor further investigation was needed and our findings raise the question as to whether these markers could be considered as useful screening markers for earlier detection of HCC in liver cirrhosis because discriminant functions of u-PA and PAI-2 were not significant. Sensitivities and specificities of u-PA and PAI-2 were also not high enough, resulting in the ranges of total diagnostic efficiency from 43% to 50%, and, from 49% to 63%, respectively, at different cut-off values. No direct relationship was detected between AFP and u-PA, between AFP and PAI-2, and between u-PA and PAI-2.

Adult↗
PubMed1994

Site-directed mutagenesis of the yeast PRP20/SRM1 gene reveals distinct activity domains in the protein product.

Prp20/Srm1, a homolog of the mammalian protein RCC1 in Saccharomyces cerevisiae, binds to double-stranded DNA (dsDNA) through a multicomponent complex in vitro. This dsDNA-binding capability of the Prp20 complex has been shown to be cell-cycle dependent; affinity for dsDNA is lost during DNA replication. By analyzing a number of temperature sensitive (ts) prp20 alleles produced in vivo and in vitro, as well as site-directed mutations in highly conserved positions in the imperfect repeats that make up the protein, we have determined a relationship between the residues at these positions, cell viability, and the dsDNA-binding abilities of the Prp20 complex. These data reveal that the essential residues for Prp20 function are located mainly in the second and the third repeats at the amino-terminus and the last two repeats, the seventh and eighth, at the carboxyl-terminus of Prp20. Carboxyl-terminal mutations in Prp20 differ from amino-terminal mutations in showing loss of dsDNA binding: their conditional lethal phenotype and the loss of dsDNA binding affinity are both suppressible by overproduction of Gsp1, a GTP-binding constituent of the Prp20 complex, homologous to the mammalian protein TC4/Ran. Although wild-type Prp20 does not bind to dsDNA on its own, two mutations in conserved residues were found that caused the isolated protein to bind dsDNA. These data imply that, in situ, the other components of the Prp20 complex regulate the conformation of Prp20 and thus its affinity for dsDNA. Gsp1 not only influences the dsDNA-binding ability of Prp20 but it also regulates other essential function(s) of the Prp20 complex. Overproduction of Gsp1 also suppresses the lethality of two conditional mutations in the penultimate carboxyl-terminal repeat of Prp20, even though these mutations do not eliminate the dsDNA binding activity of the Prp20 complex. Other site-directed mutants reveal that internal and carboxyl-terminal regions of Prp20 that lack homology to RCC1 are dispensable for dsDNA binding and growth.

Alleles↗
PubMed1994

Molecular cloning of the small (gamma) subunit of human TFIIA reveals functions critical for activated transcription.

TFIIA is thought to play an important role in transcriptional regulation in higher eukaryotes, but its precise function is unclear. A human cDNA encoding a protein with 45% identity to the small subunit of yeast TFIIA has been isolated. TFIIA activity could be reconstituted by the mixing of recombinant large (alpha beta) and small (gamma) subunits. TFIIA-depleted HeLa nuclear extracts were used to demonstrate that TFIIA is essential for basal and activated transcription by several distinct classes of activators. Recombinant TFIIA functioned in transcriptional activation whether expressed as a dimer (alpha beta+gamma) or as a trimer (alpha+beta+gamma), which closely resembles the native form. Yeast TFIIA also functioned in transcriptional activation, and the human gamma subunit was functionally interchangeable with TOA2, its yeast homolog. Recombinant TFIIA mediated the stimulation of TFIID binding to the TATA region and downstream promoter sequences by the Zta transcriptional activator. Significantly, we found that TFIIA bound directly to Zta in an activation domain-dependent manner. One consequence of the TFIIA-mediated interaction between Zta and TFIID was the formation of a promoter-bound complex resistant to TATA oligonucleotide competition. These results demonstrate that TFIIA is an evolutionarily conserved general factor critical for activator-regulated transcription.

Amino Acid Sequence↗
PubMed1994

Purification and characterization of three inhibitors of voltage-dependent K+ channels from Leiurus quinquestriatus var. hebraeus venom.

Three new toxins from the venom of the scorpion Leiurus quinquestriatus var. hebraeus have been identified on the basis of their ability to block the Shaker K+ channel. These toxins have been purified using HPLC techniques and characterized as 38 amino acid peptides by mass spectroscopy, amino acid analysis, and sequence determination. Their chemical identity was confirmed by producing fully functional synthetic toxins using recombinant methods. These peptides are potent inhibitors of the Shaker K+ channel (Kd < 1 nM) as well as the mammalian homologues of Shaker. They are related to other previously described K+ channel toxins, but form a new subclass within the larger family of K+ channel inhibitors derived from scorpion venom. We have named these toxins agitoxin 1, 2, and 3, respectively.

Amino Acid Sequence↗
PubMed1994

Isolation and characterization of the Xenopus terminal deoxynucleotidyl transferase.

A cDNA clone containing the sequence of the Xenopus homologue of terminal deoxynucleotidyl transferase (TdT) was isolated and analyzed. The derived amino acid sequence shares > 50% identity with the human, mouse, and bovine TdT sequences. By hybridization and PCR analyses Xenopus TdT mRNA was found in the thymus and not in the spleen, kidney, intestine, or liver. During ontogeny TdT appears in significant amounts in the thymus of tadpoles at metamorphic climax but little in the earlier midlarval stages. The emergence of TdT only late in development correlates with the paucity of N region addition in larval Ig heavy chain sequences. Past experiments on the ontogeny of the Xenopus immune system revealed a less efficacious tadpole immune response in skin graft rejection and Ab heterogeneity; the absence of TdT in the tadpole stages fits well with the notion of lower larval TCR and Ab diversity.

Amino Acid Sequence↗
PubMed1994

Polymer-encapsulated cells genetically modified to secrete human nerve growth factor promote the survival of axotomized septal cholinergic neurons.

Effective treatments for neurodegenerative disorders are limited by our inability to alter the progression of the diseases. A number of proteins have specific neuroprotective activities in vitro; however, the delivery of these factors into the central nervous system over the long term at therapeutic levels has been difficult to achieve. BHK cells engineered to express and release human nerve growth factor were encapsulated in an immunoisolation polymeric device and transplanted into both fimbria-fornix-lesioned rat brains and naive controls. In the lesioned rat brain, chronic delivery of human nerve growth factor by the encapsulated BHK cells provided nearly complete protection of axotomized medial septal cholinergic neurons. Human nerve growth factor continued to be released by encapsulated cells upon removal from the aspirative site after 3 weeks or from normal rat striatum after 3 and 6 months in vivo. Long-term encapsulated cell survival was confirmed by histologic analysis. This encapsulated xenogeneic system may provide therapeutically effective amounts of a number of neurotrophic factors, alone or in combination, to virtually any site within the body.

Analysis of Variance↗
PubMed1994

Legionnaires' disease outbreak in south western Sydney, 1992. Clinical aspects.

OBJECTIVES: To document the clinical, laboratory and radiological features of patients with Legionella pneumophila serogroup 1 pneumonia during an outbreak, and probe for any relationship between clinical or laboratory features and outcome. DESIGN AND SETTING: Prospective identification of patients with Legionnaires' disease in an outbreak from 15-26 April 1992 in the South Western Sydney Area Health Service, centred on the Fairfield area. PATIENTS: Twenty-six patients (22 men, four women) were confirmed to have the disease, based on the presence of clinical features of pneumonia, with L. pneumophila serogroup 1 isolated on culture, or evidence of seroconversion. RESULTS: Seventeen patients (65.4%) were culture-positive for L. pneumophila serogroup 1 and nine were diagnosed on serological criteria. A direct fluorescent antibody (DFA) test of sputum performed well as a rapid diagnostic method. Twenty-three patients (89%) presented with hyponatraemia, 14 (54%) with renal impairment and nine of 19 (47%) with elevated serum creatinine phosphokinase levels. Overall mortality was 23% (71% for patients requiring mechanical ventilation). Eleven of 119 patients (10.2%) who did not have Legionnaires' disease showed serological evidence of previous exposure. CONCLUSIONS: The duration of symptoms and severity of biochemical abnormalities at presentation were not related to outcome. The sputum DFA test is useful for rapid diagnosis during outbreaks.

Adult↗
PubMed1994

Lack of protection against gastric Helicobacter infection following immunisation with jack bean urease: the rejection of a novel hypothesis.

The common mucosal immune system was stimulated by oral immunisation with jack bean urease and the adjuvant cholera toxin. A high level of local antibody and serum antibody was induced in mice following hyperimmunisation with this combination. No cross-reacting antibody was found against either Helicobacter pylori or Helicobacter felis. No protection was observed against oral challenge of immunised mice with living H. felis thus disproving the interesting hypothesis of Pallen and Clayton that plant urease might induce a protective immunity against helicobacter infection.

Animals↗
PubMed1994

Involvement of pp60c-src with two major signaling pathways in human breast cancer.

The phosphotyrosine residues of receptor tyrosine kinases serve as unique binding sites for proteins involved in intracellular signaling, which contain SRC homology 2 (SH2) domains. Since overexpression or activation of the pp60c-src kinase has been reported in a number of human tumors, including primary human breast carcinomas, we examined the interactions of the SH2 and SH3 domains of human SRC with target proteins in human carcinoma cell lines. Glutathione S-transferase fusion proteins containing either the SH2, SH3, or the entire SH3/SH2 region of human SRC were used to affinity purify tyrosine-phosphorylated proteins from human breast carcinoma cell lines. We show here that in human breast carcinoma cell lines, the SRC SH2 domain binds to activated epidermal growth factor receptor (EGFR) and p185HER2/neu. SRC SH2 binding to EGFR was also observed in a nontumorigenic cell line after hormone stimulation. Endogenous pp60c-src was found to tightly associate with tyrosine-phosphorylated EGFR. Association of the SRC SH2 with the EGFR was blocked by tyrosyl phosphopeptides containing the sequences surrounding tyrosine-530, the regulatory site in the SRC C terminus, or sequences surrounding the major sites of autophosphorylation in the EGFR. These results raise the possibility that association of pp60c-src with these receptor tyrosine kinases is an integral part of the signaling events mediated by these receptors and may contribute to malignant transformation.

Amino Acid Sequence↗
PubMed1994

Isolation and characterization of gap junctions in the osteoblastic MC3T3-E1 cell line.

Gap junctions are channels connecting cells that function in cell-to-cell communication. Gap junctions are abundant in osteoblastic cells. Membranes enriched for gap junction plaques were obtained by differential centrifugation, followed by treatment of the membranes with potassium iodide and sarkosyl before sucrose density gradient centrifugation. Electron microscopy showed that the preparation was enriched for electron-dense membranes consistent with gap junctions. Coomassie Blue staining of SDS-PAGE preparations revealed a prominent band at approximately 41 kD. Western analysis with a site-directed antibody, CT-360 (D. Laird, California Institute of Technology, Pasadena, CA), to the C-terminal portion of the rat heart connexin 43 molecule was positive in the MC3T3-E1 cell line, a phenotypic osteoblastic cell line derived from normal neonatal mouse calvariae. Western analysis using a monoclonal antibody, R5.21C, to rat liver connexin 32 was negative. Additionally, a prominent band at 59 kD was detected by CT-360 in both gap junction-enriched preparations and cell lysates. Treatment of diluted samples of gap junction-enriched preparations with sulfhydryl reducing agents in combination with detergents resulted in the enhancement and diminution of the 41 and 59 kD bands, respectively. Immunoprecipitation following [35S]methionine/[35S]cysteine labeling revealed a significant band detected at 122 kD in addition to the 41 kD band. To demonstrate functional gap junctions, transfer of lucifer yellow dye to surrounding cells was monitored after microinjection of a target cell. Between passages 10 and 25 in culture, functional cell coupling was found in approximately 70% of injected cells. Coupling was detected within 1-2 minutes after injection. Simultaneous microinjection of the CT-360 antibody with lucifer yellow resulted in the decoupling of cells. In conclusion, (1) MC3T3-E1 cells possess a 41 kD protein that is recognized by connexin 43 antibody to rat heart gap junction; (2) multimers of the MC3T3-E1 gap junctions occur in the preparation; and (3) functional coupling demonstrated by dye transfer may be regulated by region(s) in the C terminus of the connexin molecule.

3T3 Cells↗
PubMed1994

Prostaglandin-stimulated second messenger signaling in bone-derived endothelial cells is dependent on confluency in culture.

New bone formation is associated with an increase in blood flow by the invasion of capillaries. Endothelial cells that line the capillaries can produce paracrine factors that affect bone growth and development, and in turn, could be affected by products produced by bone cells, in particular the osteoblasts. Since osteoblasts produce prostaglandins E2 and F2 alpha (PGE2, PGF2 alpha), it was investigated if these PGs were agonists to bone-derived endothelial cells (BBE) by assessing changes in cAMP and free cytosolic calcium concentration ([Ca2+]i) second messenger generation. We found that confluent cultures of BBE cells, a clonal endothelial cell line derived from bovine sternal bone, responded to 1 microM PGE2 by an increase in cAMP. PGF2 alpha at the same concentration was less potent in stimulating an increase in cAMP production in confluent BBE cells. Subconfluent cells with a morphology similar to that of fibroblastic cells were not as sensitive to PGE2-stimulated cAMP generation. PGF2 alpha failed to elicit any cAMP production in subconfluent cultures. PGE2 and PGF2 alpha both stimulated an increase in [Ca2+]i concentration in a dose-dependent manner. The potency of PGE2 was similar to that of PGF2 alpha in stimulating an increase in [Ca2+]i. The Ca2+ response was mostly independent of extracellular Ca+, was unchanged even with prior indomethacin treatment, was unaffected by caffeine pretreatment, but was abolished subsequent to thapsigargin pretreatment. The PG-induced increase in [Ca2+]i was also dependent on the confluency of the cells. In a subconfluent state, the responses to PGE2, or PGF2 alpha were either negligible, or only small increases in [Ca2+]i were noted with high concentrations of these two PGs. Consistent, dose-dependent increases in [Ca2+]i were stimulated by these PGs only when the cells were confluent and had a cobblestoned appearance. Since it was previously demonstrated that BBE cells respond to parathyroid hormone (PTH) by the production of cAMP, we tested if bovine PTH(1-34) amide ]bPTH(1-34) also increased [Ca2+]i in these cells. No change in [Ca2+]i was found in response to bPTH (1-34), although bPTH (1-34) stimulated a nine to tenfold increase in cAMP. We conclude that BBE cells respond to PGE2 and PGF2 alpha but not to bPTH(1-34) by an increase in [Ca2+]i probably secondary to stimulation of phospholipase C and that the cAMP and [Ca2+]i second messenger responses in BBE cells are dependent on the state of confluency of the cells.

Animals↗
PubMed1994

Investigation of cytomegalovirus infection as a risk factor for coronary atherosclerosis in the explanted hearts of patients undergoing heart transplantation.

Infection with a human herpes virus, particularly cytomegalovirus (CMV), has been hypothesized to be a cofactor in the development of atherosclerosis in humans. We investigated the association of prior CMV infection with the presence of atherosclerosis in the coronary arteries of the native heart of 314 individuals undergoing heart transplantation. Age, male gender, race, tobacco use, and previous general and cardiac surgery were also studied as covariables. Factors associated with the presence of coronary atherosclerosis by univariate analysis were age greater than the median of 48 years (odds ratio [OR] = 5.9, 95% confidence intervals [CI] 3.0-11.6; P < 0.0001), tobacco use (OR = 3.8, 95% CI 2.1-7.0; P < 0.005), CMV seropositivity (OR = 3.1, 95% CI 1.8-5.5; P < 0.001), and male gender (OR = 3.0, 95% CI 1.6-5.4; P < 0.0005). When patients were divided into quartiles based on age, coronary atherosclerosis was shown to be associated with CMV seropositive status only in the youngest quartile of patients (OR = 3.6, 95% CI 1.4-8.9; P < 0.01) but not in the older three quartiles of patients (OR = 0.9, 95% CI = 0.3-2.4; P > 0.5). In multiple logistic regression analyses, CMV seropositivity was not a significant independent variable in the whole group of patients (P = 0.13) but remained a significant variable in the youngest quartile of patients (P = 0.01). However, 43% of these younger patients and 29% of all patients with coronary atherosclerosis were seronegative for CMV.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Nucleotide sequence of the SAC2 gene of Saccharomyces cerevisiae.

A temperature-sensitive mutation (act1-1) in the essential actin gene of Saccharomyces cerevisiae can be suppressed by mutations in the SAC2 gene. A cloned genomic DNA fragment that complements the cold-sensitive growth phenotype associated with such a suppressor mutation (sac2-1) was sequenced. The fragment contained an open reading frame that encodes a 641 amino acid predicted hydrophilic protein with a molecular weight of 74,445. No sequences with significant similarity to SAC2 were found in the GenBank and EMBL databases. A SAC2 disruption mutation was constructed which had phenotypes similar to the sac2-1 point mutation. A haploid SAC2 disruption strain failed to grow at low temperature and the disruption allele suppressed the temperature-sensitive act1-1 growth defect. The suppression phenotype was dependent on the strain background.

Amino Acid Sequence↗