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Biomedical subjects

X Zheng

Publications and source records attributed to X Zheng.

At least 145 records · Page 8Linked to original sources
PubMed2000

[Study on the interaction between nuclease P1 and CuCl2 (II) by visible absorption spectra].

In this paper, we studied the directly interaction between nuclease Pl and CuCl2 in aqueous solution by visible absorption spectra. As a result, the zinc ion in the active site of nuclease Pl can be replaced by additional Cu(II). At the the same time, Cu(II) entered into the active site of enzyme forming the correspondent derivatives of "Cu(II)-Pl". The variety of pH value influenced the types of derivatives and the enzyme activity.

Catalysis↗
PubMed1999

Heats of adsorption of some organic compounds on beta-cyclodextrin determined by gas-solid chromatography.

Isosteric adsorptive enthalpies have been derived from the temperature dependence of retention volumes determined by eluted pulse gas-solid chromatography. The heat data were obtained for systems using more than 20 organic liquids as adsorbates, and beta-cyclodextrin as adsorbent. The experimental results have been discussed in the light of intermolecular force between molecules of adsorbate and adsorbent.

Adsorption↗
PubMed1999

Protein kinase C potentiation of N-methyl-D-aspartate receptor activity is not mediated by phosphorylation of N-methyl-D-aspartate receptor subunits.

N-methyl-D-aspartate receptors (NMDARs) are Ca(2+)-permeable glutamate-gated ion channels whose physiological properties in neurons are modulated by protein kinase C (PKC). The present study was undertaken to determine the role in PKC-induced potentiation of the NR1 and NR2A C-terminal tails, which serve as targets of PKC phosphorylation [Tingley, W. G., Ehlers, M. D., Kameyama, K., Doherty, C., Ptak, J. B., Riley, C. T. & Huganir, R. L. (1997) J. Biol. Chem. 272, 5157-5166]. Serine residue 890 in the C1 cassette is a primary target of PKC phosphorylation and a critical residue in receptor clustering at the membrane. We report herein that the presence of the C1 cassette reduces PKC potentiation and that mutation of Ser-890 significantly restores PKC potentiation. Splicing out or deletion of other C-terminal cassettes singly or in combination had little or no effect on PKC potentiation. Moreover, experiments involving truncation mutants reveal the unexpected finding that NMDARs assembled from subunits lacking all known sites of PKC phosphorylation can show PKC potentiation. These results indicate that PKC-induced potentiation of NMDAR activity does not occur by direct phosphorylation of the receptor protein but rather of associated targeting, anchoring, or signaling protein(s). PKC potentiation of NMDAR function is likely to be an important mode of NMDAR regulation in vivo and may play a role in NMDA-dependent long-term potentiation.

Alternative Splicing↗
PubMed1999

Identification of a novel 0.7-kb polyadenylated transcript in the LAT promoter region of HSV-1 that is strain specific and may contribute to virulence.

Herpes Simplex virus expresses latency-associated transcripts (LATs) the function of which remains obscure despite increasing knowledge of their structure and expression. Upstream of the LAT coding region is a region of the genome that is poorly characterized although it lies in an area that is responsible for modulation of reactivation efficiency in two different animal models. Transcript mapping with strains 17, McKrae, KOS, and F has revealed strain differences in this region of the viral genome. Strain 17 and McKrae expressed a novel polyadenylated 0.7-kb transcript that is absent from KOS and F. This transcript is expressed in the LAT direction and has the kinetics of a true late gene during the lytic cycle of infection. A deletion mutant, 17DeltaBsa, which does not express the 0.7-kb RNA, is less virulent than the parental strain 17. A rescuant with F sequence (17DeltaBsa/RF) shows virulence similar to F, whereas a rescuant with strain 17 sequence (17DeltaBsa/R17) is similar to strain 17. Virulence is altered by deletion or substitution in the region encoding the 0.7-kb transcript (BsaI-BsaI); however, reactivation in the mouse explant cocultivation assay or the adrenergically induced rabbit reactivation model remained unchanged. The importance of this region for virulence is discussed.

Animals↗
PubMed1999

Knockdown of AMPA receptor GluR2 expression causes delayed neurodegeneration and increases damage by sublethal ischemia in hippocampal CA1 and CA3 neurons.

Considerable evidence suggests that Ca(2+)-permeable AMPA receptors are critical mediators of the delayed, selective neuronal death associated with transient global ischemia and sustained seizures. Global ischemia suppresses mRNA and protein expression of the glutamate receptor subunit GluR2 and increases AMPA receptor-mediated Ca(2+) influx into vulnerable neurons of the hippocampal CA1 before the onset of neurodegeneration. Status epilepticus suppresses GluR2 mRNA and protein in CA3 before neurodegeneration in this region. To examine whether acute downregulation of the GluR2 subunit, even in the absence of a neurological insult, can cause neuronal cell death, we performed GluR2 "knockdown" experiments. Intracerebral injection of antisense oligodeoxynucleotides targeted to GluR2 mRNA induced delayed death of pyramidal neurons in CA1 and CA3. Antisense-induced neurodegeneration was preceded by a reduction in GluR2 mRNA, as indicated by in situ hybridization, and in GluR2 protein, as indicated by Western blot analysis. GluR2 antisense suppressed GluR2 mRNA in the dentate gyrus but did not cause cell death. The AMPA receptor antagonist 6-cyano-7-nitroquinoxiline-2,3-dione (CNQX) and the Ca(2+)-permeable AMPA receptor channel blocker 1-naphthyl acetyl spermine protected against antisense-induced cell death. This result indicates that antisense-induced cell death is mediated by Ca(2+)-permeable AMPA receptors. GluR2 antisense and brief sublethal global ischemia acted synergistically to cause degeneration of pyramidal neurons, consistent with action by a common mechanism. These findings demonstrate that downregulation of GluR2 is sufficient to induce delayed death of specific neuronal populations.

Animals↗
PubMed1999

Cloning of mouse mitochondrial thymidine kinase 2 cDNA.

Phosphorylation of anti-viral nucleoside analogs by mitochondrial thymidine kinase 2 (TK2) has been implicated as a mechanism for the mitochondrial toxicity caused by several of these compounds. We have cloned the cDNA of mouse TK2 and shown that the enzyme is targeted to the mitochondria when expressed in fusion with the green fluorescent protein. This is the first report on the cloning of a mitochondrial TK2 and will contribute to elucidate the role of TK2 in the pharmacological activation of nucleoside analogs.

Amino Acid Sequence↗
PubMed1999

Crystal structure of enteropeptidase light chain complexed with an analog of the trypsinogen activation peptide.

Enteropeptidase is a membrane-bound serine protease that initiates the activation of pancreatic hydrolases by cleaving and activating trypsinogen. The enzyme is remarkably specific and cleaves after lysine residues of peptidyl substrates that resemble trypsinogen activation peptides such as Val-(Asp)4-Lys. To characterize the determinants of substrate specificity, we solved the crystal structure of the bovine enteropeptidase catalytic domain to 2.3 A resolution in complex with the inhibitor Val-(Asp)4-Lys-chloromethane. The catalytic mechanism and contacts with lysine at substrate position P1 are conserved with other trypsin-like serine proteases. However, the aspartyl residues at positions P2-P4 of the inhibitor interact with the enzyme surface mainly through salt bridges with the Nzeta atom of Lys99. Mutation of Lys99 to Ala, or acetylation with acetic anhydride, specifically prevented the cleavage of trypsinogen or Gly-(Asp)4-Lys-beta-naphthylamide and reduced the rate of inhibition by Val-(Asp)4-Lys-chloromethane 22 to 90-fold. For these reactions, Lys99 was calculated to account for 1.8 to 2.5 kcal mol(-1) of the free energy of transition state binding. Thus, a unique basic exosite on the enteropeptidase surface has evolved to facilitate the cleavage of its physiological substrate, trypsinogen.

Amino Acid Sequence↗
PubMed1999

[Distribution of lead in fetal rat tissue at different days of pregnancy].

In order to reveal the mechanism of the transplacental transfer of lead from mothers to fetus, tissues lead content of fetal rat at different days of pregnancy were determined and compared. Lead was administered to four groups of 4 week-old female Wistar rats for 50 days. The doses of lead were 0, 10, 50 and 200 mg/L in drinking water respectively. Rats were mated with non-lead-treated male rats. The pregnant rats in each group were then divided into four sub-groups by random. The pregnant rats in four sub-group of each group were sacrificed in turn at 10, 14, 17 and 20 days of gestation (dg). Blood lead of pregnant rats, lead burden of whole fetus, lead concentration of fetal brain, fetal liver and placenta were determined. Results indicated that lead concentration in fetal brain kept unchanged during the period of gestation, but lead content in whole fetus and fetal brain were increased with the days of gestation. But the lead concentration in fetus at 10 dg was higher than that at 14 dg. It seemed that higher lead absorption by the fetus was related to the newly emerged lead bonding-site in fetus, especially during the calcification of bones.

Animals↗
PubMed1999

Vitronectin inhibits the thrombotic response to arterial injury in mice.

Vitronectin (VN) binds to plasminogen activator inhibitor-1 (PAI-1) and integrins and may play an important role in the vascular response to injury by regulating fibrinolysis and cell migration. However, the role of VN in the earliest response to vascular injury, thrombosis, is not well characterized. The purpose of this study was to test the hypothesis that variation in vitronectin expression alters the thrombotic response to arterial injury in mice. Ferric chloride (FeCl3) injury was used to induce platelet-rich thrombi in mouse carotid arteries. Wild-type (VN +/+, n = 14) and VN-deficient (VN -/-, n = 15) mice, matched for age and gender, were studied. Time to occlusion after FeCl3 injury was determined by application of a Doppler flowprobe to the carotid artery. Occlusion times of VN -/- mice were significantly shorter than those of VN +/+ mice (6.0 +/- 1.2 minutes v 17.8 +/- 2.3 minutes, respectively, P < .001). Histologic analysis of injured arterial segments showed that thrombi from VN +/+ and VN -/- mice consisted of dense platelet aggregates. In vitro studies of murine VN +/+ and VN -/- platelets showed no significant differences in ADP-induced aggregation, but a trend towards increased thrombin-induced aggregation in VN -/- platelets. Purified, denatured VN inhibited thrombin-induced platelet aggregation, whereas native VN did not. Thrombin times of plasma from VN -/- mice (20.5 +/- 2.1 seconds, n = 4) were significantly shorter than those of VN +/+ mice (34.2 +/- 6.7 seconds, n = 4, P < .01), and the addition of purified VN to VN -/- plasma prolonged the thrombin time into the normal range, suggesting that VN inhibits thrombin-fibrinogen interactions. PAI-1-deficient mice (n = 6) did not demonstrate significantly enhanced arterial thrombosis compared with wild-type mice (n = 6), excluding a potential indirect antithrombin function of VN mediated by interactions with PAI-1 as an explanation for the accelerated thrombosis observed in VN -/- mice. These results suggest that vitronectin plays a previously unappreciated antithrombotic role at sites of arterial injury and that this activity may be mediated, at least in part, by inhibiting platelet-platelet interactions and/or thrombin procoagulant activity.

Adenosine Diphosphate↗
PubMed1999

Apical sorting of bovine enteropeptidase does not involve detergent-resistant association with sphingolipid-cholesterol rafts.

Enteropeptidase is a heterodimeric type II membrane protein of the brush border of duodenal enterocytes. In this location, enteropeptidase cleaves and activates trypsinogen, thereby initiating the activation of other intestinal digestive enzymes. Recombinant bovine enteropeptidase was sorted directly to the apical surface of polarized Madin-Darby canine kidney cells. Replacement of the cytoplasmic and signal anchor domains with a cleavable signal peptide (mutant proenteropeptidase lacking the amino-terminal signal anchor domain (dSA-BEK)) caused apical secretion. The additional amino-terminal deletion of a mucin-like domain (HL-BEK) resulted in secretion both apically and basolaterally. Further deletion of the noncatalytic heavy chain (L-BEK) resulted in apical secretion. Thus enteropeptidase appears to have at least three distinct sorting signals as follows: the light chain (L-BEK) directs apical sorting, addition of most of the heavy chain (HL-BEK) inhibits apical sorting, and addition of the mucin-like domain (dSA-BEK) restores apical sorting. Inhibition of N-linked glycosylation with tunicamycin or disruption of microtubules with colchicine caused L-BEK to be secreted equally into apical and basolateral compartments, whereas brefeldin A caused basolateral secretion of L-BEK. Full-length BEK was not found in detergent-resistant raft domains of Madin-Darby canine kidney cells or baby hamster kidney cells. These results suggest apical sorting of enteropeptidase depends on N-linked glycosylation of the serine protease domain and an amino-terminal segment that includes an O-glycosylated mucin-like domain and three potential N-glycosylation sites. In contrast to many apically targeted proteins, enteropeptidase does not form detergent-resistant associations with sphingolipid-cholesterol rafts.

Animals↗
PubMed1999

Spermine and arcaine block and permeate N-methyl-D-aspartate receptor channels.

Polyamines such as spermine are thought to be endogenous regulators of NMDA (N-methyl-D-aspartate)-type glutamate receptors. Polyamine block of NMDA receptors was studied in excised outside-out patches from rat hippocampal neurons and Xenopus oocytes expressing recombinant receptors. Extracellular spermine and arcaine reduced NMDA single-channel conductance in a voltage-dependent manner, with partial relief of block evident at large inside negative membrane potentials. Reducing extracellular Na+ concentration increased the apparent affinities for spermine and arcaine, indicating strong interaction between spermine and permeant ions. Internal spermine also blocked NMDA channels in a voltage-dependent manner, with relief of block evident at large inside positive potentials. The Woodhull model of channel block by an impermeant ion adequately described the actions of external spermine from -60 to +60 mV, but failed for more negative potentials. Eyring rate theory for a permeable blocker with two barriers and one binding site adequately described the voltage-dependent block and relief from block by both external and internal spermine over the range of -120 to +60 mV. These findings indicate that polyamines block and permeate neuronal NMDA receptor channels from the extracellular and intracellular sides, although sensitivity to internal spermine is probably too low to be physiologically relevant.

Animals↗
PubMed1999

Leukemia inhibitory factor is synthesized and released by human eosinophils and modulates activation state and chemotaxis.

BACKGROUND: The cytokine leukemia inhibitory factor (LIF) is known to be produced by both inflamed peripheral autonomic nerves and several cell types involved in the regulation of the immune response. We have recently demonstrated that several structural cell types in human airways produce LIF in response to inflammatory stimuli and that LIF augments contractile responses to tachykinins in airway explants. Because the eosinophil is a major effector cell in asthma and often found adjacent to the nerves, we hypothesized that eosinophils produce LIF and that LIF primes and upregulates eosinophil recruitment and function, allowing bidirectional neuroimmune interactions and augmentation of eosinophil-mediated injury. OBJECTIVE: The purpose of this study was to demonstrate that human eosinophils synthesize and release LIF, to determine the effects of LIF on eosinophil functions (ie, chemotaxis, granule protein release, expression of the activation marker CD69, and apoptosis), and to compare serum LIF levels between atopic and nonatopic individuals. METHODS: Reverse-transcription PCR, ELISA, immunocytochemistry, chemotaxis assay, and flow cytometry were used. RESULTS: Peripheral blood eosinophils express LIF and messenger RNA for LIF and LIF receptor. Serum LIF levels were higher in atopic patients with mild asthma than in nonatopic normal donors. Eosinophils from nonatopic donors were stimulated by calcium ionophore to release small amounts of LIF (from almost none to 5.3 +/- 1.8 pg/10(6) cells). Eosinophils from atopic donors showed a 10-fold increase (from 45.1 +/- 38.7 pg/106 cells to 414.5 +/- 189.9 pg/10(6) cells). Preincubation of eosinophils with LIF increased eosinophil peroxidase release 4-fold. LIF was not chemotactic for eosinophils but augmented chemotaxis mediated by substance P by 82% and by platelet-activating factor by 31%. LIF did not effect eosinophil apoptosis but increased CD69 expression. CONCLUSION: LIF has proinflammatory roles in eosinophil-dependent airway disorders.

Antigens, CD↗
PubMed1999

Mutation of structural determinants lining the N-methyl-D-aspartate receptor channel differentially affects phencyclidine block and spermine potentiation and block.

Spermine and other endogenous polyamines potentiate, block and permeate the N-methyl-D-aspartate receptor channel. To identify structural determinants of the N-methyl-D-aspartate channel that mediate spermine's actions, we generated mutant receptors with asparagine (N) to glutamine (Q) or arginine (R) substitutions in the selectivity filter of the channel. We demonstrate that mutation of the three critical asparagines in this domain differentially affects block by phencyclidine and both potentiation and block by spermine. N-to-Q and N-to-R mutations in the N site of the NR1 subunit (N598 in NR1(011), N619 in NR1(100)) and N-to-Q mutations in the N and N + 1 sites (N595 and N596 in NR2A, respectively) of the NR2 subunit (Q/NN, R/NN, N/QN, N/NQ, Q/QN and Q/NQ receptors) reduced affinity for phencyclidine. The Q/NN receptor showed markedly reduced potentiation by spermine, with little or no change in spermine block. The R/NN receptor showed markedly reduced spermine potentiation and affinity for spermine at its block site. The N/QN, N/NQ and Q/QN mutant receptors showed somewhat enhanced spermine block, while the Q/ NQ double mutant exhibited significantly more enhanced spermine block. Thus, the asparagine residues critical to Ca2+ permeability and Mg2+ block of N-methyl-D-aspartate channels are also critical to block by spermine and phencyclidine. To examine the interaction of spermine and phencyclidine within the channel, we performed competition studies. Spermine appeared to compete with phencyclidine for binding to the receptor; however, blocks by phencyclidine and by spermine were not additive. The findings suggest that spermine can bind to a site in the external vestibule of the channel to impede phencyclidine binding, but allow Na+ influx.

Algorithms↗
PubMed1999

Apoptosis in meatal skin, cholesteatoma and squamous cell carcinoma of the ear.

Apoptosis in normal meatal skin, cholesteatoma and squamous cell carcinoma (SCC) of the ear was investigated by using morphological analysis and in-situ specific labelling of fragmented DNA. In meatal skin, apoptotic cells were localized mainly in the granular layers, but were not so restricted in cholesteatoma, while in SCC they were even more dispersed. The apoptotic index (AI) was low (1.59 +/- 0.10 SEM) in normal skin. It was increased in cholesteatoma (2.09 +/- 0.11), and was intermediate in SCC (1.72 +/- 0.14). By contrast, the mitotic index (MI) increased from 0.19 +/- 0.02 in normal skin, to 0.25 +/- 0.01 in cholesteatoma and to 0.25 +/- 0.02 in SCC. Our findings indicate that apoptosis is involved in the epithelial homeostasis of meatal skin, cholesteatoma and SCC of the ear. The hyperproliferation of epithelial cells in cholesteatoma is counteracted by an increased apoptosis rate, while in SCC the increased cell proliferation without a compensatory increase in apoptosis may be associated with the malignant transformation.

Adolescent↗