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Biomedical subjects

Y Xia

Publications and source records attributed to Y Xia.

At least 127 records · Page 7Linked to original sources
PubMed1999

Glutamate modulates neurotransmission in the submucosal plexus of guinea-pig small intestine.

Effects of glutamate on synaptic transmission in the submucosal plexus of guinea-pig small intestine were studied with intracellular electrophysiological recording methods. Glutamate suppressed stimulus-evoked slow excitatory postsynaptic potentials (EPSPs) and increased the amplitude of slow inhibitory postsynaptic potentials (IPSPs) in submucosal neurons. The actions of glutamate were mimicked by the group I metabotropic glutamate receptor (mGluRs) agonist DHPG, but not by the group II agonist S-4C3HPG, the group III agonist L-AP4, or selective agonists for ionotropic glutamate receptors (iGluRs). Glutamate actions were suppressed by the selective group I mGluRs antagonist S-4CPG, but not by group II and III mGluRs antagonist CPPG or iGluRs antagonists. Glutamate suppressed substance P- and 5-HT-evoked slow EPSP-like responses and potentiated norepinephrine-induced slow IPSP-like responses. The results suggest that group I mGluRs mediate glutamate-induced suppression of slow EPSPs and potentiation of slow IPSPs in S-type uniaxonal submucosal neurons.

Animals↗
PubMed1999

Beta-glucan, a "specific" biologic response modifier that uses antibodies to target tumors for cytotoxic recognition by leukocyte complement receptor type 3 (CD11b/CD18).

beta-Glucans were identified 36 years ago as a biologic response modifier that stimulated tumor rejection. In vitro studies have shown that beta-glucans bind to a lectin domain within complement receptor type 3 (CR3; known also as Mac-1, CD11b/CD18, or alphaMbeta2-integrin, that functions as an adhesion molecule and a receptor for factor I-cleaved C3b, i.e., iC3b) resulting in the priming of this iC3b receptor for cytotoxicity of iC3b-opsonized target cells. This investigation explored mechanisms of tumor therapy with soluble beta-glucan in mice. Normal mouse sera were shown to contain low levels of Abs reactive with syngeneic or allogeneic tumor lines that activated complement, depositing C3 onto tumors. Implanted tumors became coated with IgM, IgG, and C3, and the absent C3 deposition on tumors in SCID mice was reconstituted with IgM or IgG isolated from normal sera. Therapy of mice with glucan- or mannan-rich soluble polysaccharides exhibiting high affinity for CR3 caused a 57-90% reduction in tumor weight. In young mice with lower levels of tumor-reactive Abs, the effectiveness of beta-glucan was enhanced by administration of a tumor-specific mAb, and in SCID mice, an absent response to beta-glucan was reconstituted with normal IgM or IgG. The requirement for C3 on tumors and CR3 on leukocytes was highlighted by therapy failures in C3- or CR3-deficient mice. Thus, the tumoricidal function of CR3-binding polysaccharides such as beta-glucan in vivo is defined by natural and elicited Abs that direct iC3b deposition onto neoplastic cells, making them targets for circulating leukocytes bearing polysaccharide-primed CR3. Therapy fails when tumors lack iC3b, but can be restored by tumor-specific Abs that deposit iC3b onto the tumors.

Animals↗
PubMed1999

Mutational analysis of the PapB transcriptional regulator in Escherichia coli. Regions important for DNA binding and oligomerization.

PapB is a transcriptional regulator in the control of pap operon expression in Escherichia coli. There are PapB homologous proteins encoded by many fimbrial gene systems that are involved in the regulation of fimbriae-adhesin production, and previous studies suggested that PapB binds DNA through minor groove contact. Both deletion and alanine-scanning mutagenesis were used to identify functionally important regions of the PapB protein. Mutations altering Arg61 or Cys65 caused deficiency in DNA binding, indicating that these residues are critical for PapB binding to DNA. Alanine substitutions at positions 35-36, 53-56, and 74-76 resulted in mutants that were impaired in oligomerization. All these amino acid residues are conserved among the PapB homologous proteins, suggesting their importance in the whole family of regulatory proteins. The transcriptional efficiency of all the mutants was clearly reduced as compared with that of wild-type PapB. Taken together, we have localized regions in the PapB protein that are involved in DNA binding and oligomerization, and our results show that both functions are required for its activity as a transcriptional regulator.

Amino Acid Sequence↗
PubMed1999

Generation of recombinant fragments of CD11b expressing the functional beta-glucan-binding lectin site of CR3 (CD11b/CD18).

CR3 (Mac-1; alphaMbeta2 integrin) functions as both a receptor for the opsonic iC3b fragment of C3 triggering phagocytosis or cytotoxicity and an adhesion molecule mediating leukocyte diapedesis. Recent reports have suggested that a CR3 lectin site may be required for both cytotoxic responses and adhesion. Cytotoxic responses require dual recognition of iC3b via the I domain of CD11b and specific microbial surface polysaccharides (e.g., beta-glucan) via a separate lectin site. Likewise, adhesion requires a lectin-dependent membrane complex between CR3 and CD87. To characterize the lectin site further, a recombinant baculovirus (rBv) system was developed that allowed high level expression of rCD11b on membranes and in the cytoplasm of Sf21 insect cells. Six rBv were generated that contained truncated cDNA encoding various CD11b domains. Immunoblotting of rBv-infected Sf21 cells showed that some native epitopes were expressed by five of six rCD11b fragments. Lectin activity of rCD11b proteins was evaluated by both flow cytometry with beta-glucan-FITC and radioactive binding assays with [125I]beta-glucan. Sf21 cells expressing rCD11b that included the C-terminal region, with or without the I-domain, exhibited lectin activity that was inhibited by unlabeled beta-glucan or anti-CR3 mAbs. The smallest rCD11b fragment exhibiting lectin activity included the C-terminus and part of the divalent cation binding region. The beta-glucan binding affinities of the three C-terminal region-containing rCD11bs expressed on Sf21 cell membranes were not significantly different from each other and were similar to that of neutrophil CR3. These data suggest that the lectin site may be located entirely within CD11b, although lectin site-dependent signaling through CD18 probably occurs with the heterodimer.

Animals↗
PubMed1999

Signaling by proinflammatory cytokines: oligomerization of TRAF2 and TRAF6 is sufficient for JNK and IKK activation and target gene induction via an amino-terminal effector domain.

Interleukin-1 (IL-1) and tumor necrosis factor (TNF-alpha) stimulate transcription factors AP-1 and NF-kappaB through activation of the MAP kinases JNK and p38 and the IkappaB kinase (IKK), respectively. The TNF-alpha and IL-1 signals are transduced through TRAF2 and TRAF6, respectively. Overexpressed TRAF2 or TRAF6 activate JNK, p38, or IKK in the absence of extracellular stimulation. By replacing the carboxy-terminal TRAF domain of TRAF2 and TRAF6 with repeats of the immunophilin FKBP12, we demonstrate that their effector domains are composed of their amino-terminal Zn and RING fingers. Oligomerization of the TRAF2 effector domain results in specific binding to MEKK1, a protein kinase capable of JNK, p38, and IKK activation, and induction of TNF-alpha and IL-1 responsive genes. TNF-alpha also enhances the binding of native TRAF2 to MEKK1 and stimulates the kinase activity of the latter. Thus, TNF-alpha and IL-1 signaling is based on oligomerization of TRAF2 and TRAF6 leading to activation of effector kinases.

Calcium-Calmodulin-Dependent Protein Kinases↗
PubMed1999

Combinatorial interactions regulate cardiac expression of the murine adenylosuccinate synthetase 1 gene.

The mammalian heart begins contracting at the linear tube stage during embryogenesis and continuously pumps, nonstop, throughout the entire lifetime of the animal. Therefore, the cardiac energy metabolizing pathways must be properly established and efficiently functioning. While the biochemistry of these pathways is well defined, limited information regarding the regulation of cardiac metabolic genes is available. Previously, we reported that 1.9 kilobase pairs of murine adenylosuccinate synthetase 1 gene (Adss1) 5'-flanking DNA directs high levels of reporter expression to the adult transgenic heart. In this report, we define the 1.9-kilobase pair fragment as a cardiac-specific enhancer that controls correct spatiotemporal expression of a reporter similar to the endogenous Adss1 gene. A 700-base pair fragment within this region activates a heterologous promoter specifically in adult transgenic hearts. Proteins present in a cardiac nuclear extract interact with potential transcription factor binding sites of this region and these cis-acting sites play important regulatory roles in the cardiac expression of this reporter. Finally, we report that several different cardiac transcription factors trans-activate the 1.9HSCAT construct through these sites and that combinations result in enhanced reporter expression. Adss1 appears to be one of the first target genes identified for the bHLH factors Hand1 and Hand2.

Adenylosuccinate Synthase↗
PubMed1999

Bioassay for growth hormone releasing hormone (GHRH) using a recombinant receptor and cAMP-responsive reporter system.

Growth hormone releasing hormone (GHRH) receptors are members of the G-protein receptor family that use cAMP as a second messenger. A human fetal kidney 293-derived cell line stably expressing the porcine GHRH receptor (pGHRHr/293 cells) and a cAMP-responsive reporter system were used to develop a bioassay for human GHRH. The reporter system (ph alpha180SEAP) was constructed by subcloning the tandem cAMP response elements from the human glycoprotein hormone alpha subunit gene promoter (h alpha180) upstream from the secreted alkaline phosphatase cDNA of reporter plasmid pSEAP-Basic. To generate a stable cell line expressing both the GHRH receptor and SEAP reporter system, a DNA fragment from pPUR that confers puromycin resistance was subcloned downstream from the reporter construct of ph alpha180SEAP. Tranfection of ph alpha180SEAPpur into pGHRHr/293 cells yielded pGHRHr/SEAP/293 cell lines that responded to recombinant GHRH with dose-dependent increases in SEAP activity. The GHRH receptor-SEAP reporter bioassay was compared to a conventional bioassay using cultured rat anterior pituitary cells. Synthetic and recombinant GHRH induced a 3.1-fold increase in growth hormone release by rat pituitary cells with ED50's of 3.6 and 2.2 x 10(-10) M, respectively. Recombinant GHRH was 1.7 +/- 0.7 times more potent than synthetic GHRH in the pituitary cell bioassay. In an analogous experiment, pGHRHr/SEAP/293 cells responded to synthetic and recombinant GHRH with a 9.1-fold increase in SEAP activity. The ED50's were 7.8 and 4.3 x 10(-11) M, respectively, with recombinant GHRH being 1.8 +/- 0.1 times more potent than the synthetic preparation. Thus, the GHRH receptor-SEAP reporter bioassay is a sensitive, accurate, precise and efficient method for measuring GHRH biological activity.

Animals↗
PubMed1999

Oxidative stress induces amyloid-like aggregate formation of NACP/alpha-synuclein in vitro.

The precursor of non-amyloid beta protein component of Alzheimer's disease amyloid (NACP/alpha-synuclein), found in Lewy bodies of Parkinson's disease (PD), is a presynaptic protein genetically linked to some familial types PD. Mechanisms of abnormal NACP/alpha-synuclein aggregation in neurodegenerative diseases are unclear. Since oxidative stress might play a role in PD pathogenesis, we investigated the role of iron and peroxide in NACP/alpha-synuclein aggregation. Immunoblot analysis showed that human NACP/alpha-synuclein (but not beta-synuclein) aggregated in the presence of ferric ion and was inhibited by the iron chelator deferoxamine. Ferrous ion was not effective by itself, but it potentially aggregated NACP/alpha-synuclein in the presence of hydrogen peroxide. NACP/ alpha-synuclein aggregates displayed strong thioflavine-S and congo-red reactivity, reminiscent of amyloid. This study suggests that NACP/alpha-synuclein aggregation might be closely related to oxidative reactions which may play a critical role in neurodegeneration in disorders with Lewy bodies.

Alzheimer Disease↗
PubMed1999

Effects of Th2 cytokines on chemokine expression in the lung: IL-13 potently induces eotaxin expression by airway epithelial cells.

Airway inflammation associated with asthma is characterized by massive infiltration of eosinophils, mediated in part by specific chemoattractant factors produced in the lung. Allergen-specific Th2 cells appear to play a central role in asthma; for example, adoptively transferred Th2 cells induced lung eosinophilia associated with induction of specific chemokines. Interestingly, Th2 supernatant alone administered intranasally to naive mice induced eotaxin, RANTES, monocyte-chemotactic protein-1, and KC expression along with lung eosinophilia. We tested the major cytokines individually and found that IL-4 and IL-5 induced higher levels of macrophage-inflammatory protein-1alpha and KC; IL-4 also increased the production of monocyte-chemotactic protein-1; IL-13 and IL-4 induced eotaxin. IL-13 was by far the most potent inducer of eotaxin; indeed, a neutralizing anti-IL-13 Ab removed most of the eotaxin-inducing activity from Th2 supernatants, although it did not entirely block the recruitment of eosinophils. While TNF-alpha did not stimulate eotaxin production by itself, it markedly augmented eotaxin induction by IL-13. IL-13 was able to induce eotaxin in the lung of JAK3-deficient mice, suggesting that JAK3 is not required for IL-13 signaling in airway epithelial cells; however, eosinophilia was not induced in this situation, suggesting that JAK3 transduces other IL-13-mediated mechanisms critical for eosinophil recruitment. Our study suggests that IL-13 is an important mediator in the pathogenesis of asthma and therefore a potential target for asthma therapy.

Animals↗
PubMed1999

The beta-glucan-binding lectin site of mouse CR3 (CD11b/CD18) and its function in generating a primed state of the receptor that mediates cytotoxic activation in response to iC3b-opsonized target cells.

Mouse leukocyte CR3 (Mac-1, alphaMbeta2 integrin) was shown to function as a receptor for beta-glucans in the same way as human CR3. Soluble zymosan polysaccharide (SZP) or pure beta-glucans labeled with FITC or 125I bound in a saturable and reversible manner to neutrophils, macrophages, and NK cells. This lectin activity was blocked by anti-CD11b mAb M1/70 or 5C6 and did not occur with leukocytes from CR3-/- (CD11b-deficient) mice. SZP preparations containing primarily mannose or glucose bound to CR3, and the binding of 125I-labeled beta-glucan to CR3 was competitively inhibited by beta-glucans from barley or seaweed, but not by yeast alpha-mannan. Also, as with human CR3, the lectin site of mouse CR3 was inhibited by alpha- or beta-methylglucoside (but not D-glucose), alpha- or beta-methylmannoside, and N-acetyl-D-glucosamine. Phagocytosis of zymosan and serum-opsonized zymosan was partially inhibited by anti-CR3 and was reduced to <40% of normal with leukocytes from CR3-/- mice. As with neutrophils from patients with CD18 deficiency, neutrophils from CR3-/- mice exhibited no phagocytosis of particulate beta-glucan. SZP or beta-glucans primed CR3 of neutrophils, macrophages, and NK cells for cytotoxicity of iC3b-opsonized tumor cells that otherwise did not trigger killing. beta-Glucan priming for cytotoxicity was inhibited by anti-CR3 and did not occur with leukocytes from CR3-/- mice. The primed state of macrophage and NK cell CR3 remained detectable for 18 to 24 h after pulsing with beta-glucans. The similarity of mouse and human CR3 in response to beta-glucans highlights the utility of mouse tumor models for development of therapeutic beta-glucans.

Animals↗
PubMed1999

Ab initio protein structure prediction using a combined hierarchical approach.

As part of the third Critical Assessment of Structure Prediction meeting (CASP3), we predict the three-dimensional structures for 13 proteins using a hierarchical approach. First, all possible compact conformations of a protein sequence are enumerated using a highly simplified tetrahedral lattice model. We select a large subset of these conformations using a lattice-based scoring function and build detailed all-atom models incorporating predicted secondary structure. A combined all-atom knowledge-based scoring function is then used to select three smaller subsets from these all-atom models. Finally, a consensus-based distance geometry procedure is used to generate the best conformations from each of the all-atom subsets. With this method, we are able to predict the global topology/shape for all or a large part of the sequence for six out of the thirteen proteins. For two other proteins, the topology/shape for shorter fragments are predicted. This represents a marked improvement in ab initio prediction since CASP was first instigated in 1994.

Algorithms↗
PubMed1999

Study on relationship between anticardiolipin antibody and cerebrovascular diseases.

Serum anticardiolipin antibody (ACA) was measured in 91 patients with cerebral infarction (CI), 42 patients with cerebral hemorrhage (CH) and 30 healthy controls. The results showed that the ACA in CI and CH patients was significantly higher than in controls and IgG-ACA was the most important isotype. Stroke in ACA positive group tended to be recurrent and of multi-focuses. Positive rate of IgG-ACA reached its peak within the first week after stroke onset. The results suggested that ACA was an independent risk factor in CI and CH and might be valuable in stroke prediction.

Aged↗
PubMed1999

Therapeutic intervention with complement and beta-glucan in cancer.

Complement (C) has two major effector systems available for host defense. The membrane attack complex (MAC) generated from components C5-C9 can form membrane-penetrating lesions that lead to cell death by causing a rapid loss of cytoplasmic components. The MAC is only effective against pathogens with outer phospholipid membranes, and cannot kill gram-positive bacteria or yeast whose membranes are protected by cell walls. The most important effector mechanism of C is the opsonization of microbial pathogens with the serum protein C3 that leads to their high avidity attachment to the C3-receptors of phagocytic cells. Pathogens that activate complement are first coated with the C3b fragment of C3, which is rapidly proteolyzed into the iC3b fragment by serum factor I. These iC3b fragments serve to promote the high avidity attachment of the 'iC3b-opsonized' pathogens to the iC3b-receptors (CR3, CD11b/CD18) of phagocytic cells and natural killer (NK) cells, stimulating phagocytosis and/or cytotoxic degranulation. Host cells, including neoplastic tumor cells, have been endowed with natural mechanisms for self-protection against both the MAC and the cytotoxic activation of CR3. This review discusses a novel type of immunotherapy for cancer that uses soluble yeast beta-glucan to override the normal resistance of iC3b-opsonized tumor cells to the cytotoxic activation of phagocyte and NK cell CR3, allowing this important effector mechanism of the C system to function against tumor cells in the same way that it normally functions against bacteria and yeast. Moreover, the cytotoxic activation of beta-glucan-primed NK cell CR3 by iC3b-opsonized tumors is shown to be accompanied by a tumor-localized secretion of the cytokines TNFalpha, IFNalpha, IFNgamma, and IL-6.

Animals↗
PubMed1999

Effect of prolonged O2 deprivation on Na+ channels: differential regulation in adult versus fetal rat brain.

Neuronal Na+ channels are functionally inhibited in the adult in response to acute O2 deprivation. Since prolonged hypoxia may not only affect channel function, but also its expression, we hypothesized that long-term hypoxia alters Na+ channel density. This alteration may depend on age, because we have found major differences in neuronal responses to hypoxia between the immature and adult. In the present work, we used northern blots, slot blots, saxitoxin binding and autoradiography to ask whether: (i) prolonged hypoxia alters Na+ channel messenger RNA and protein levels in the brain; (ii) there is a difference between the adult and prenatal brains regarding Na+ channel expression with hypoxic exposure; and (iii) regional differences in Na+ channel expression occur in hypoxia-exposed brains. Our results show the following. (1) Na+ channel messenger RNA and saxitoxin binding density decreased after prolonged hypoxia in adult brain homogenates; this is in sharp contrast to the changes observed in fetal brains, which tended to increase Na+ channel messenger RNA and protein after hypoxia. (2) Changes in saxitoxin binding density are related to alterations in the number of saxitoxin binding sites and not to binding affinity, since there was no major change in Kd values between the hypoxia and naive groups. (3) The hypoxia-induced Na+ channel expression was heterogeneous, with major differences between rostral regions (e.g., the cortex) and caudal regions (e.g., the medulla and pons). We speculate that down-regulation of Na+ channels during long-term hypoxia in mature brains is an adaptive cellular response, aimed at minimizing the mismatch between energy supply and demand, since maintenance of Na+ gradients is a major energy-requiring process. However, the prenatal brain does not depend on this adaptive mechanism in response to hypoxic stress.

Aging↗
PubMed1999

Glutathione peroxidase activity modulates fatty acid profiles of plasma and breast milk in Chinese women.

Since little is known about the effect of selenium on the fatty acid profiles (FAP) of human breast milk, the purpose of this study was to measure the effect of habitual dietary selenium (Se) intake on this profile in plasma and breast milk. Subjects were lactating women from three locations in China where habitual selenium intakes are extremely low (Xichang), adequate (Beijing), or extremely high (Enshi). Plasma and milk samples were obtained within seven days of parturition (early samples) or within eighteen months postpartum (mature samples) and analyzed for selenium concentration, glutathione peroxidase (Gpx) activity and FAP. Plasma and milk selenium concentrations were significantly lower in the samples from women from Xichang and significantly higher in those from Enshi when compared to those from Beijing. Plasma Gpx activity, however, was higher in samples from Beijing than Xichang or Enshi. In contrast, the early breast milk samples had similar Gpx activity regardless of location. The mature samples, however, followed the same trend as plasma with the samples obtained from the women in Beijing having the highest activity. Of the unsaturated fatty acids examined, the concentration of linoleic acid, 18:2(n-6), in both plasma and milk was greater in the samples from Beijing when compared to those from Xichang or Enshi. Thus dietary selenium appears to influence the fatty acid composition in human breast milk, but influences Gpx activity only in mature milk samples.

Adult↗
PubMed1999

Effect of dietary selenium restriction on selected parameters of selenium status in men with high life-long intake.

The influence of selenium (Se) restriction on disposition in plasma and urine fractions of infused (74)Se (selenite) was studied when adult males (Enshi City, Hubei Province, PRC) whose habitual daily Se intake is approximately 480 microg per day were transferred to Lichuan County, where the daily intake is approximately 30 microg. The subjects received an infusion (106 microg Se) on the day before consuming foods low in Se and a second infusion (113 microg Se) 63 days later. Blood and 24-hour urine samples were collected each day for 7 days after the first infusion and on days 22, 43, and 62 following the first infusion. Urine and blood were also collected daily for the next 7 days after the second infusion. Plasma total Se concentration increased for 7 days after each of the two infusions and urine Se decreased exponentially following both the first and second infusions. The excretion of trimethylselenonium followed the same pattern as the total urinary Se. Surprisingly, there was not a significant difference in selenite retention between the two infusion periods, and the data indicated that, regardless of the chemical form of Se present in various organs, its catabolism leading to excretion in urine followed the same pathway as that of selenite. Labeled Se was incorporated predominantly in the plasma selenoprotein P fraction and the half-life of Se in this fraction was determined to be 1.9 to 2.9 days. Thus, a longer depletion period is required in these subjects to obtain more significant changes.

Journal Article↗