Biomedical subjects

L Wang

Publications and source records attributed to L Wang.

At least 955 records · Page 53Linked to original sources

PubMed1999

Preparation of Uniform Needle-Like Aragonite Particles by Homogeneous Precipitation.

Uniform needle-like aragonite particles were obtained by aging solutions of calcium salts in the presence of urea at 90 degrees C. The effects of various experimental conditions, such as the concentration of reactants, temperature, aging time, agitation, mixing procedure, and the addition of divalent cations, surfactants, and polymers, on the precipitation of aragonite were investigated. It was found that the formation of different polymorphs of calcium carbonate was affected mostly by agitation and concentration of reactants, as well as by the mixing procedure. Thus, under otherwise the same experimental conditions, needles of aragonite were formed without stirring or at low-power ultrasound; rhombohedral calcite appeared when aging experiments were carried out under the influence of magnetic stirring, while irregular particles of mixed vaterite and calcite crystal structure were generated at higher CaCl(2) concentrations. Mixing the preheated reactant solutions resulted in unique "flower-type" vaterite particles. Finally, the presence of sulfonate or sulfate ions promoted precipitation of vaterite and calcite. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

Lack of sequence diversity in the gene encoding merozoite surface protein 5 of Plasmodium falciparum.

The gene encoding merozoite surface protein 5 (MSP5) of Plasmodium falciparum is situated between the genes encoding MSP2 and MSP4 on chromosome 2. Both MSP4 and MSP5 encode proteins that contain hydrophobic signal and glycosylphosphatidylinositol (GPI) attachment signals and a single epidermal growth factor (EGF)-like domain at their carboxyl termini. The similar gene organization, location and similar structural features of the two genes suggest that they have arisen from a gene duplication event. In this study we provide further evidence for the merozoite surface location of MSP5 by demonstrating that MSP5 is present in isolated merozoites, partitions in the detergent-enriched phase following Triton X-114 fractionation and shows a staining pattern consistent with merozoite surface location by indirect immunofluorescence confocal microscopy. Analysis of antigenic diversity of MSP5 shows a lack of sequence variation between various isolates of P. falciparum from different geographical locations, a feature unusual for surface proteins of merozoites and one that may simplify vaccine formulation.

Amino Acid Sequence↗

PubMed1999

Assignment of chromosomal locus and evidence for alternatively spliced mRNAs of a human sperm membrane protein (hSMP-1).

The gene (HSD-1) coding a human sperm membrane protein (hSMP-1) was isolated from a human testis cDNA expression library using antibodies found in the serum of an infertile woman. HSD-1 was localized to a single locus on chromosome 9 and assigned to band 9p12-p13 by fluorescent in situ hybridization (FISH) mapping and DAPI (4,6-diamidino-2-phenylindole) banding, using rat/human somatic cell hybrids and metaphase chromosomes of human lymphocytes. In rescreening a testis lambdagt10 cDNA expression library, the full-length cDNA (HSD-1) and several truncated cDNAs with heterologous regions were isolated from positive clones. The heterology consisted of deletion, insertion and alteration of the 5'-end. These heterologous truncated fragments may be produced by alternative splicing of mRNAs. Two recombinant prokaryotic expression vectors were constructed with one of the heterologous fragment (clone #26) with and without the alternative 5'-end. Escherichia coli transfected with the construct containing the alternative 5'-end failed to produce the recombinant product, whereas those transfected with the vector lacking the 5'-end produced hSMP-1. DNASIS analysis of the structure of #26 mRNA suggests that the 5'-end has a stable secondary configuration that may maintain the mRNA in an inactivated state, whereby hindering its translation and preventing the expression of the gene.

Amino Acid Sequence↗

PubMed1999

Generation of anti-hirudin antibodies in heparin-induced thrombocytopenic patients treated with r-hirudin.

BACKGROUND: Hirudin is a small protein with strong thrombin inhibition that may be antigenic. The generation and disappearance of anti-hirudin antibodies were investigated in patients with heparin-induced thrombocytopenia who were treated with recombinant hirudin (r-hirudin) for >/=5 days. METHODS AND RESULTS: The IgA, IgE, IgG, and IgM isotypes of anti-hirudin antibodies were determined by ELISA before and after the start of r-hirudin therapy. A total of 56% of patients (13 of 23) developed >/=1 antibody isotype during therapy. No IgE antibodies were generated. IgA, IgG, and IgM antibodies were detected in 30% (7 of 23), 52% (12 of 23), and 17% (4 of 23) of patients, respectively. Four patients generated only IgG, 2 patients developed either IgM or IgG and IgM, 5 patients IgG and IgA, and 2 patients IgG, IgM, and IgA antibodies. IgM antibodies disappeared within 8 days of the cessation of r-hirudin. IgA and IgG antibodies disappeared within 1 year in all but 1 patient. Binding of purified IgG to r-hirudin in IgG antibody-positive patients (n=7) was demonstrated by competitive ELISA for r-hirudin. Of the 7 IgG antibody samples, 1 each neutralized or enhanced the anticoagulant activity of r-hirudin. CONCLUSIONS: R-hirudin may be antigenic in patients with heparin-induced thrombocytopenia. More comprehensive investigations will be required to determine the biological relevance of this and to establish the antibody-generation pattern in other diseases.

Adult↗

PubMed1999

Crucial role of the interleukin 1 receptor family member T1/ST2 in T helper cell type 2-mediated lung mucosal immune responses.

T1/ST2 is an orphan receptor of unknown function that is expressed on the surface of murine T helper cell type 2 (Th2), but not Th1 effector cells. In vitro blockade of T1/ST2 signaling with an immunoglobulin (Ig) fusion protein suppresses both differentiation to and activation of Th2, but not Th1 effector populations. In a nascent Th2-dominated response, anti-T1/ST2 monoclonal antibody (mAb) inhibited eosinophil infiltration, interleukin 5 secretion, and IgE production. To determine if these effects were mediated by a direct effect on Th2 cells, we next used a murine adoptive transfer model of Th1- and Th2-mediated lung mucosal immune responses. Administration of either T1/ST2 mAb or T1/ST2-Ig abrogated Th2 cytokine production in vivo and the induction of an eosinophilic inflammatory response, but failed to modify Th1-mediated inflammation. Taken together, our data demonstrate an important role of T1/ST2 in Th2-mediated inflammatory responses and suggest that T1/ST2 may prove to be a novel target for the selective suppression of Th2 immune responses.

Allergens↗

PubMed1999

Increased susceptibility to carcinogen-induced mammary tumors in MMTV-Cdc25B transgenic mice.

Cdc25 phosphatases activate cyclin-dependent kinases (Cdks) by dephosphorylating critical phospho-tyrosine and phospho-threonine residues on these proteins. Several types of studies indicate that Cdc25s can enhance cell proliferation and oncogenesis. Furthermore, overexpression of Cdc25A and/or B have been detected in several types of primary human cancers, including breast cancers. To further assess the oncogenic capacity of Cdc25B in vivo, we have generated transgenic mice that overexpress Cdc25B in the mammary epithelium, driven by the MMTV - LTR promoter. Although these mice are grossly normal for up to 18 months, the ectopic expression of Cdc25B in their mammary glands increases the susceptibility of these mice to induction of mammary tumors by the carcinogen 9,10-dimethyl-1, 2-benzanthracene (DMBA).

9,10-Dimethyl-1,2-benzanthracene↗

PubMed1999

Arsenic in the Meager Creek hot springs environment, British Columbia, Canada.

Levels of arsenic in water from Meager Creek hot springs, British Columbia, Canada, were found to be naturally elevated. Biota including microbial mats, green algae, sedge, cedar, fleabane, monkey flower, moss, mushrooms and lichens, that were expected to be impacted by the water, were analyzed for total levels of arsenic and for arsenic species. The major arsenic species extracted from all samples were arsenate and arsenite, which are toxic forms of arsenic. Additionally, small amounts of arsenosugars X and XI were detected in microbial mats and green algae, implying that cyanobacteria/bacteria, and possibly green algae are capable of synthesizing arsenosugars from arsenate. Low to trace amounts of arsenosugars X and XI were detected in lichens and the fungus Tarzetta cupularis. A large fraction (on average, greater than 50%) of arsenic was not extracted by using methanol/water (1:1) and the chemical and toxicological significance of this arsenic remains unknown.

Arsenic↗

PubMed1999

Health-related quality of life effects of modafinil for treatment of narcolepsy.

OBJECTIVE: To evaluate the burden of illness of narcolepsy and assess the health-related quality-of-life (HQL) effects of oral modafinil, a wake-promoting therapy for excessive daytime sleepiness associated with narcolepsy. METHODS: Subjects with narcolepsy enrolled in a nine-week, placebo-controlled, double-blind study and were randomized to placebo, modafinil 200 mg, or modafinil 400 mg. After the study, consenting subjects received modafinil in a 40-week open-label extension. A self-administered HQL questionnaire consisting of the 36-Item Short Form Health Survey (SF-36) and supplemental narcolepsy-specific scales was given to subjects at baseline, study endpoint, and several open-label timepoints. RESULTS: 481 subjects completed a baseline and double-blind endpoint HQL assessment. Compared to population norms, baseline HQL scores reflected substantial burden in vitality, social functioning, and performing usual activities. At study endpoint, subjects in the 400 mg modafinil group had significantly higher scores than placebo for 10 of the 17 HQL scales. The 400 mg modafinil group had more energy, fewer difficulties performing usual activities, fewer interferences with social activities, improved psychological well-being and higher productivity, attention and self-esteem compared to placebo subjects (p<.05). The positive treatment effects were sustained over the open-label extension. CONCLUSION: Modafinil significantly improves health-related quality of life in narcolepsy.

Adult↗

PubMed1999

Pyrrolidine-3-carboxylic acids as endothelin antagonists. 4. Side chain conformational restriction leads to ET(B) selectivity.

When the dialkylacetamide side chain of the ET(A)-selective antagonist ABT-627 is replaced with a 2,6-dialkylacetanilide, the resultant analogues show a complete reversal of receptor selectivity, preferring ET(B) over ET(A). By optimizing the aniline substitution pattern, as well as the alkoxy group on the 2-aryl substituent, it is possible to prepare antagonists with subnanomolar affinity for ET(B) and with selectivities in excess of 4000-fold. A number of these compounds also show promising pharmacokinetic profiles; a useful balance of properties is found in A-192621 (38). Pharmacology studies with A-192621 serve to reveal the role of the ET(B) receptor in modulating blood pressure; the observed hypertensive response to persistent ET(B) blockade is consistent with previous postulates and indicates that ET(B)-selective antagonists may not be suitable as agents for long-term systemic therapy.

Acetanilides↗

PubMed1999

Second-generation peptidomimetic inhibitors of protein farnesyltransferase demonstrating improved cellular potency and significant in vivo efficacy.

The synthesis and evaluation of analogues of previously reported farnesyltransferase inhibitors, pyridyl benzyl ether 3 and pyridylbenzylamine 4, are described. Substitution of 3 at the 5-position of the core aryl ring resulted in inhibitors of equal or less potency against the enzyme and decreased efficacy in a cellular assay against Ras processing by the enzyme. Substitution of 4 at the benzyl nitrogen yielded 26, which showed improved efficacy and potency and yet presented a poor pharmacokinetic profile. Further modification afforded 30, which demonstrated a dramatically improved pharmacokinetic profile. Compounds 26 and 29 demonstrated significant in vivo efficacy in nude mice inoculated with MiaPaCa-2, a human pancreatic tumor-derived cell line.

Alkyl and Aryl Transferases↗

PubMed1999

Oligomeric complexes involved in translocation of proteins across the membrane of the endoplasmic reticulum.

Proteins involved in protein translocation across the membrane of the endoplasmic reticulum assemble into different oligomeric complexes depending on their state of function. To analyse such membrane protein complexes we fractionated proteins of mammalian rough microsomes and analysed them using blue native PAGE and immunoblotting. Among the proteins characterised are the Sec61p complex, the oligosaccharyl transferase (OST) complex, the translocon-associated protein (TRAP) complex, the TRAM and RAMP4 proteins, the signal recognition particle (SRP) and the SRP receptor (SR). Interestingly, the RAMP4 protein, SR and OST complex display more than one oligomeric form.

Animals↗

PubMed1999

ATP-sensitive K+ channel openers prevent Ca2+ overload in rat cardiac mitochondria.

1. Mitochondrial dysfunction, secondary to excessive accumulation of Ca2+, has been implicated in cardiac injury. We here examined the action of potassium channel openers on mitochondrial Ca2+ homeostasis, as these cardioprotective ion channel modulators have recently been shown to target a mitochondrial ATP-sensitive K+ channel. 2. In isolated cardiac mitochondria, diazoxide and pinacidil decreased the rate and magnitude of Ca2+ uptake into the mitochondrial matrix with an IC50 of 65 and 128 microM, respectively. At all stages of Ca2+ uptake, the potassium channel openers depolarized the mitochondrial membrane thereby reducing Ca2+ influx through the potential-dependent mitochondrial uniporter. 3. Diazoxide and pinacidil, in a concentration-dependent manner, also activated release of Ca2+ from mitochondria. This was prevented by cyclosporin A, an inhibitor of Ca2+ release through the mitochondrial permeability transition pore. 4. Replacement of extramitochondrial K+ with mannitol abolished the effects of diazoxide and pinacidil on mitochondrial Ca2+, while the K+ ionophore valinomycin mimicked the effects of the potassium channel openers. 5. ATP and ADP, which block K+ flux through mitochondrial ATP-sensitive K+ channels, inhibited the effects of potassium channel openers, without preventing the action of valinomycin. 6. In intact cardiomyocytes, diazoxide also induced mitochondrial depolarization and decreased mitochondrial Ca2+ content. These effects were inhibited by the mitochondrial ATP-sensitive K+ channel blocker 5-hydroxydecanoic acid. 7. Thus, potassium channel openers prevent mitochondrial Ca2+ overload by reducing the driving force for Ca2+ uptake and by activating cyclosporin-sensitive Ca2+ release. In this regard, modulators of an ATP-sensitive mitochondrial K+ conductance may contribute to the maintenance of mitochondrial Ca2+ homeostasis.

Adenosine Diphosphate↗

PubMed1999

The "random-coil" state of proteins: comparison of database statistics and molecular simulations.

This study presents a comparison of two models of the random-coil state, one based on statistical distributions from the structural database and the other based on molecular dynamics simulations. The database model relies on the assumption that the random- or statistical-coil state of a particular residue can be described by its conformational distribution in a sufficiently diverse subset of protein structures. The molecular dynamics model is based on distributions from molecular simulations carried out on "dipeptide" models (single residues with N-terminal acetyl and C-terminal N'-methyl amide blocking groups). A comparison of the two models for the residues Ala, Asn, Asp, Gly, and Val indicates that the database distributions are greatly influenced by long-range interactions and dominated by specific recognizable elements of protein structure. In contrast, the limited structural scope of the dipeptide models presents the extreme case of a peptide under the influence of only short-range interactions. The models were evaluated by a comparison of scalar coupling constants calculated from the conformational distributions and compared with experimentally values determined for unstructured peptides. Although the models gave different distributions, there was similar agreement with experiment. This comparison emphasizes the differences and limitations in each model and highlights the difficulty in presenting an accurate picture of the random-coil state. Proteins 1999;36:407- 418.

Computer Simulation↗

PubMed1999

Cloning and characterization of mouse deoxyguanosine kinase. Evidence for a cytoplasmic isoform.

Deoxyguanosine kinase (dGK) is a nuclear gene product that catalyzes the phosphorylation of purine deoxyribonucleosides and their analogues. The human enzyme is located predominantly in the mitochondria, as shown by biochemical fractionation studies and in situ localization of the overexpressed recombinant protein. Here we describe the cloning of mouse dGK cDNA and the identification of a novel amino-terminally truncated isoform that corresponds to about 14% of the total dGK mRNA population in mouse spleen. In situ fluorescence assays suggest that the new isoform cannot translocate into the mitochondria and thus may represent a cytoplasmic enzyme. Expression of mouse dGK mRNA was highly tissue-specific and differed from the tissue distribution observed in humans. Recombinant mouse dGK showed similar specific activity and substrate specificity as compared with the human enzyme. The broad specificity, restricted tissue distribution, and location of mouse dGK in multiple cellular compartments raise new considerations with respect to the role of the individual deoxynucleoside kinases in nucleotide metabolism.

Amino Acid Sequence↗

PubMed1999

Serotonin receptor subtypes that depolarize guinea pig inferior mesenteric ganglion neurons.

Our previous studies indicated that serotonin (5-HT) depolarized a majority of guinea pig inferior mesenteric ganglion (IMG) neurons and may be another transmitter for the noncholinergic late slow excitatory postsynaptic potential (ls-EPSP) in the IMG. However, the subtypes of 5-HT receptor mediating these responses have not yet been identified. Using intracellular recording, we examined the effect of 5-HT receptor antagonists with specificity to various 5-HT receptor subtypes on the 5-HT-mediated depolarization and ls-EPSP in IMG neurons in vitro. Cyproheptadine, a 5-HT(1/2) receptor antagonist, reversibly inhibited the slow, but not the fast, depolarization and ls-EPSP in the 5-HT-sensitive neurons. Both mianserin and spiperone, 5-HT(2) and 5-HT(1A) receptor antagonists, did not significantly alter either the fast or slow depolarizing responses or the ls-EPSP. The 5-HT(3) receptor antagonist MDL 72222 (Bemesetron) completely inhibited the fast depolarization with little diminution of the slow depolarization and ls-EPSP. Superfusion of putative 5-HT(1P) receptor antagonist, BRL 24924 (Renzapride), reversibly attenuated both the depolarization and ls-EPSP. However, 5-HT-insensitive neurons with ls-EPSP were found to be insensitive to both cyproheptadine and BRL 24924. In most 5-HT-sensitive neurons, the 5-HT(3) receptor agonist, 2-methyl-5-HT, and the selective 5-HT(1P) agonist, MCPP or 5-OHIP, evoked a fast and a slow depolarization in 55.6 and 71.4% of the neurons, respectively, without a significant effect on the membrane potential in 85.7 and 100% of the 5-HT-insensitive neurons. In 5-HT-sensitive neurons, MDL 72222 reversibly abolished the fast depolarization induced by 2-methyl-5-HT; BRL 24924 significantly inhibited the slow depolarization induced by MCPP or 5-OHIP, but not by SP. Prolonged superfusion of 5-HT-sensitive neurons with MCPP abolished the evoked ls-EPSP without inhibition of action potential. These results suggest that the fast and slow depolarizations in these neurons are mediated by 5-HT(3) and 5-HT(1P) receptor subtypes, respectively. The latter may also mediate the ls-EPSP in 5-HT-sensitive neurons.

Animals↗

PubMed1999

NMR study of the binding of all-trans-retinoic acid to type II human cellular retinoic acid binding protein.

Cellular RA binding proteins are thought to play important roles in the (RA), a hormonally active metabolite of vitamin A that has profound effects on cell growth, + differentiation and morphogenesis. Binding of RA to type II human cellular RA binding proteins (CRABPII) has been investigated by NMR spectroscopy. The sequential resonance assignments of +CRABPII in the presence of RA were established by heteronuclear three-dimensional NMR at pH 7.3. The resonance assignments of the bound RA were achieved by homonucl NMR. The secondary structures of holo-CRABPII determined by NMR were ess as revealed by the crystal structure of holo-CRABPII. Most of the nuclear Overhauser effects (NOEs) between CRABPII and the bound RA were consistent with those predicted crystal structure of holo-CRABPII. The results suggested that the conformations in solution and in the crystalline state are highly similar. Compared to the ligand binding pocket, especially the ligand entrance, was stabilize Ser12-Leu18, one of the structure elements that constitute the ligand binding pocket, became more mobile upon binding of RA. Intramolecular NOEs between protons of the bo the carboxylate end of the bound RA is well fixed but the β-ionone

Amino Acid Sequence↗

PubMed1999

Expression of the T cell antigen receptor zeta chain following activation is controlled at distinct checkpoints. Implications for cell surface receptor down-modulation and re-expression.

The multisubunit T cell antigen receptor (TCR) is involved in antigen recognition and signal transduction, leading to T cell activation and rapid down-modulation of the cell surface expressed TCRs. Although the levels of TCR cell surface expression are pivotal to the efficiency and duration of the immune response, the molecular mechanisms controlling TCR down-modulation and re-expression upon activation, remain obscure. Here, we provide a biochemical characterization of the regulatory mechanisms governing TCR expression following long-term T cell activation. We focused primarily on the TCR zeta chain, as this is considered the limiting factor in TCR complex formation and transport to the cell surface. We found that following TCR-mediated activation zeta mRNA is up-regulated by a transcription-dependent mechanism. Concomitantly, zeta protein levels are modified according to a biphasic pattern: rapid degradation coinciding with TCR cell surface down-regulation, followed by a rebound to normal levels 24 h subsequent to T cell activation. Even though there are adequate levels of all the TCR subunits within the cell following 24 h of activation, TCR cell surface expression remained very low, provided the activating antibody is continuously present. Correlative with the latter, we detected a previously undescribed monomeric form of the zeta chain. This form could be indicative of adverse endoplasmic reticulum conditions affecting correct protein folding, dimerization, and TCR assembly, all critical for optimal receptor surface re-expression. Cumulatively, our results indicate that the levels of TCR expression following activation, are tightly controlled at several checkpoints.

Animals↗

PubMed1999

Crystal structure and mechanism of histone acetylation of the yeast GCN5 transcriptional coactivator.

The yeast GCN5 (yGCN5) transcriptional coactivator functions as a histone acetyltransferase (HAT) to promote transcriptional activation. Here, we present the high resolution crystal structure of the HAT domain of yGCN5 and probe the functional importance of a conserved glutamate residue. The structure reveals a central protein core associated with AcCoA binding that appears to be structurally conserved among a superfamily of N-acetyltransferases, including yeast histone acetyltransferase 1 and Serratia marcescens aminoglycoside 3-N-acetyltransferase. A pronounced cleft lying above this core, and flanked by N- and C-terminal regions that show no sequence conservation within N-acetyltransferase enzymes, is implicated by cross-species conservation and mutagenesis studies to be a site for histone substrate binding and catalysis. Located at the bottom of this cleft is a conserved glutamate residue (E173) that is in position to play an important catalytic role in histone acetylation. Functional analysis of an E173Q mutant yGCN5 protein implicates glutamate 173 to function as a general base for catalysis. Together, a correlation of the yGCN5 structure with functionally debilitating yGCN5 mutations provides a paradigm for understanding the structure/function relationships of the growing number of transcriptional regulators that function as histone acetyltransferase enzymes.

Acetylation↗