Biomedical subjects

J Zheng

Publications and source records attributed to J Zheng.

At least 55 records · Page 3Linked to original sources

PubMed2001

A novel dicyclodextrinyl ditelluride compound with antioxidant activity.

Reactive oxygen species (ROS) primarily arise from products of normal metabolic activities and are thought to be the etiology of many diseases. A novel dicyclodextrinyl ditelluride (2-TeCD) compound was designed to be a functional mimic of the glutathione peroxidase that normally removes ROS. 2-TeCD exhibited highly catalytic efficiency and good water solubility. Antioxidant activity was studied by using ferrous sulfate/ascorbate-induced mitochondria damage model system. 2-TeCD protected the mitochondria against oxidative damage in a dose-dependent manner and exhibited also great antioxidant ability in comparison with 2-phenyl-1,2-benziososelenazol-3(2H)-one. The mimic may result in better clinical therapies for the treatment of ROS-mediated diseases.

Animals↗

PubMed2001

Folic acid supplements during pregnancy and risk of miscarriage.

BACKGROUND: Although taking supplements that contain 400 microg of folic acid before and during early pregnancy reduces a woman's risk for having a baby with a neural-tube defect (NTD), the effects of such supplements on other pregnancy outcomes remain unclear. We examined whether the use of such supplements affects the occurrence of miscarriage. METHODS: Participants were women in China who had taken part in a recent folic acid campaign to prevent NTDs and who had registered in this campaign before they became pregnant for the first time. We examined the risk for miscarriage among women who had confirmed pregnancies and who had or had not taken pills containing only 400 microg of folic acid before and during early pregnancy. RESULTS: The overall rate of miscarriage was 9.1% (2155/23806). The rates of miscarriage among women who had and had not taken folic acid pills before and during the first trimester were 9.0% and 9.3%, respectively (risk ratio 0.97 [95% CI 0.84-1.12]). The distributions of gestational age at pregnancy diagnosis and at miscarriage were similar for both groups of women. INTERPRETATION: In this population-based study of a cohort of women whose use of folic acid supplements while pregnant had been previously documented and who had been pregnant for the first time, we found no evidence that daily consumption of 400 microg of folic acid before and during early pregnancy influenced their risk for miscarriage.

Abortion, Spontaneous↗

PubMed2001

Ultraviolet radiation alters the phosphorylation of RNA polymerase II large subunit and accelerates its proteasome-dependent degradation.

It has been shown that ultraviolet (UV) radiation induces the ubiquitination of the large subunit of RNA polymerase II (RNAP II-LS) as well as its proteasomal degradation. Studies in mammalian cells have indicated that highly phosphorylated forms of RNAP II-LS are preferentially ubiquitinated, but studies in Saccharomyces cerevisiae have provided evidence that unphosphorylated RNAP II-LS is an equally suitable substrate. In the present study, an antibody (ARNA-3) that recognizes all forms of RNAP II-LS, regardless of the phosphorylation status of its C-terminal domain (CTD), was utilized to evaluate the degradation of total cellular RNAP II-LS in human fibroblasts under basal conditions or after UV-C (10J/m(2)) irradiation. It was found that UV radiation rapidly shifted the phosphorylation profile of RNAP II-LS from a mixture of dephosphorylated and phosphorylated forms to entirely more phosphorylated forms. This shift in phosphorylation status was not blocked by pharmacologic inhibition of either the ERK or p38 pathways, both of which have been implicated in the cellular UV response. In addition to shifting the phosphorylation profile, UV radiation led to net degradation of total RNAP II-LS. UV-induced degradation of RNAP II-LS was also greatly reduced in the presence of the transcriptional and CTD kinase inhibitor DRB. Using a panel of protease inhibitors, it was shown that the bulk of UV-induced degradation is proteasome-dependent. However, the UV-induced loss of hypophosphorylated RNAP II-LS was proteasome-independent. Lastly, UV radiation induced a similar shift to all hyperphosphorylated RNAP II-LS in Cockayne syndrome (CS) cells of complementation groups A or B (CSA or CSB) when compared to appropriate controls. The UV-induced degradation rates of RNAP II-LS were not significantly altered when comparing CSA or CSB to repair competent control cells. The implications for the cellular UV response are discussed.

Cell Line↗

PubMed2001

Plasma levels of soluble CD14 and tumor necrosis factor-alpha type II receptor correlate with cognitive dysfunction during human immunodeficiency virus type 1 infection.

The relationship between monocyte immune responses and cognitive impairment during progressive human immunodeficiency virus type 1 (HIV-1) infection was investigated in 28 subjects receiving highly active antiretroviral therapy. The mean+/-SEM CD4(+) T lymphocyte count and virus load for all patients were 237+/-41 cells/mm(3) and 77,091+/-195,372 HIV-1 RNA copies/mL, respectively. Levels of soluble tumor necrosis factor-alpha type II receptor (sTNF-RII) and soluble CD14 (sCD14) were measured in plasma by ELISA and were correlated with results from neuropsychological, magnetic resonance imaging, and magnetic resonance spectroscopy tests. Plasma sCD14 and sTNF-RII levels were elevated in subjects with cognitive impairment and in those with brain atrophy. Furthermore, both factors were correlated with spectroscopic choline:creatine ratios. These findings support the idea that peripheral immune responses are linked to cognitive dysfunction during advanced HIV-1 disease.

Adult↗

PubMed2001

Cellular characterization of leukotoxin diol-induced mitochondrial dysfunction.

Leukotoxin, a cytochrome P450-derived epoxide of linoleic acid, has been implicated as a causative factor in acute respiratory distress syndrome. Conversion of this fatty acid epoxide to leukotoxin diol by epoxide hydrolase has been hypothesized as the critical activation step in leukotoxin-induced cellular toxicity. In both human and insect cells, we observed that leukotoxin diol causes acute cellular toxicity and that cyclosporin A, an inhibitor of the mitochondrial permeability transition, ameliorates leukotoxin diol-associated toxicity. To evaluate mitochondria as a target of leukotoxin diol, multiple aspects of mitochondrial integrity were evaluated in both cell- and organelle-based assays. Leukotoxin diol specifically activated the mitochondrial permeability transition, resulting in release of cytochrome c and subsequent cell death. Pretreatment with cyclosporin A inhibited these effects and, furthermore, limited in vivo toxicity. While the mechanisms underlying leukotoxin-mediated toxicity remain to be fully elucidated, the observation that leukotoxin diol disrupts mitochondrial function specifically through activation of the mitochondrial permeability transition suggests at least one mechanism through which leukotoxin diol may exert its activity in physiological contexts.

Animals↗

PubMed2001

Determinants of drug delivery and transport to solid tumors.

This presentation addresses the barriers and determinants and the importance of drug-induced apoptosis in drug transport and delivery to organs and solid tumors. In particular, we examined the roles of interstitial space, drug removal by capillaries, tissue structure and tissue composition on drug distribution. Drug transport in bladder tissues is described by the distributed model which combined monodimensional Fickian diffusion and first order removal of drug by the perfusing blood. Microscopic evaluation of the spatial drug distribution in bladder, prostate and tongue indicates heterogeneous drug distribution with large and erratic concentration gradient. In general, drug distribution favors interstitial space and vasculature, with little penetration in muscles. Drug penetration into 3-dimensional solid tumors is typically 5- to 10-fold slower than in monolayer cultures. The transport of highly protein-bound drugs such as paclitaxel and doxorubicin in a solid tumor is retarded by a high tumor cell density and enhanced by drug-induced apoptosis. Accordingly, the delivery of a highly protein-bound drug to cells in a solid tumor is affected by its apoptotic effects and is therefore determined by the drug concentration and the treatment duration, i.e. treatment schedule. Under in vitro and in vivo conditions, the delivery of highly protein-bound drugs to tumor can be enhanced by using a pretreatment that induces apoptosis and reduction in cell density, and by using treatment schedules designed to take advantage of these drug-induced changes in tumor tissue composition. In conclusion, in addition to the usual processes involved in drug transport such as distribution through vascular space, transport across microvessel walls, and diffusion through interstitial space in tumor tissue, other factors including tissue structure and composition and alteration by drug-induced apoptosis are important determinants of drug distribution in organs and solid tumors.

Animals↗

PubMed2001

Prestin topology: localization of protein epitopes in relation to the plasma membrane.

Computer modeling of the outer hair cell (OHC) motor protein prestin produces ambiguous results regarding transmembrane regions and localization of its termini. To determine the location of prestin's N- and C-termini, we created prestin constructs with synthetic epitopes located immediately upstream or downstream of prestin. The spatial distribution of these epitopes was studied in prestin-transfected cells using immunofluorescence. In permeabilized cells, antibodies label the plasma membrane of 30% of the cells, reflecting transfec- tion efficiency. Under non-permeabilizing conditions, the few labeled cells also displayed a lack of plasma membrane integrity. These data suggest that prestin's N-and C-termini are cytoplasmic. Furthermore, prestin staining in OHCs was observed only under permeabilizing conditions. These results implicate prestin's N- and C-termini as portions that may interact with other cytoplasmic proteins. A model of prestin membrane topology is also considered based on the results.

Animals↗

PubMed2001

Glutamate is a mediator of neurotoxicity in secretions of activated HIV-1-infected macrophages.

We sought to identify neurotoxin(s) secreted by HIV-1-infected mononuclear phagocytes that could contribute to the pathophysiology of HIV-1-associated dementia (HAD). Neurotoxic factors were characterized in batches of conditioned media (CM) from human monocyte-derived macrophages (MDM) infected with HIV-1(ADA) and/or activated with lipopolysaccharide (LPS). All of the neurotoxicity was: present in the <3000-Da fraction; blocked by 5 microM MK801; and not trypsin sensitive or extractable into polar organic solvents. Glutamate measured in CM accounted for all neurotoxic effects observed from HIV/LPS CM in astrocyte-poor neuronal cultures and may contribute to the pathophysiology of HIV-1-associated dementia.

AIDS Dementia Complex↗

PubMed2001

Predicting the wettability of quartz surfaces exposed to dense nonaqueous phase liquids.

A model incorporating electrostatic and van der Waals forces was used to predict the wetting behavior of several systems containing a quartz surface, water, and a dense nonaqueous phase liquid (DNAPL). The disjoining pressure between the quartz/water and a water/DNAPL interface as a function of their separation was calculated from a full solution of the nonlinear Poisson-Boltzmann equation allowing for charge regulation. For the pH regime associated with a positive pressure barrier, the quartz surface was predicted to be water wetting. The model takes into account the charging behavior of an isolated DNAPL/water interface as inferred from electrophoretic mobility data. It provides excellent predictions for four coal tar and creosote samples tested, where the quartz was oil-wetting below pH 5 and water-wetting at higher pH values. In a fifth sample, the transition occurred above pH 7, which indicates that mechanisms other than electrostatic interaction control the wetting behavior in this sample.

Environmental Pollution↗

PubMed2001

Ovine caveolin-1: cDNA cloning, E. coli expression, and association with endothelial nitric oxide synthase.

Caveolin-1 (Cav-1), the principal coat protein of caveolae, plays an obligatory role in regulating the activity of endothelial nitric oxide (NO) synthase (eNOS). We propose that Cav-1 may be critical to eNOS-NO mediated uterine vasodilatation during pregnancy and estrogen replacement therapy. To test this hypothesis in the sheep model, we isolated the full-length cDNA of ovine Cav-1 (oCav-1) from a Lambda ZAP cDNA library of ovine placental artery endothelial cells. Thirty-two positive oCav-1 clones were recognized by a partial oCav-1 cDNA from this library, of which eight were sequenced. Restriction digestion of these clones revealed that the cDNAs of oCav-1 ranged from approximately 2.1 to 2.7 kb. Northern analysis of Cav-1 mRNAs in ovine uterine artery endothelial cells (UAEC) showed two transcripts of approximately 2.1 and 2.7 kb, respectively. Immunoreactive Cav-1 protein, but not caveolin-2 or caveolin-3, was detected in UAEC. Sequence analysis revealed that in addition to a 537-bp open reading frame encoding a 178 amino acid oCav-1 protein, full-length oCav-1 cDNAs apparently possess a approximately 1.6-2.1 kb 3'-untranslated region. Database searches with oCav-1 cDNA revealed that the coding region of mammalian Cav-1 genes is highly conserved. We prepared a recombinant full-length oCav-1 protein in which six consecutive histidine residues were tagged at the end of its COOH-terminus and developed a [His]6-tagged oCav-1 'pull-down assay' for studying the association of eNOS with Cav-1. Incubation of exogenous [His]6-tagged oCav-1 with resting UAEC extracts led to the formation of a [His]6-tagged oCav-1-eNOS complex. In the presence of a synthetic caveolin-scaffolding domain (CSD, aa 82-101) peptide, but not a mutated CSD peptide, [His]6-tagged oCav-1 associated eNOS was dose (0-10 microM)-dependently inhibited. eNOS association with Cav-1 in UAEC was further confirmed by the facts that eNOS co-immunoprecipitated with Cav-1 and vice versa, and that eNOS co-existed with Cav-1 during the isolation of caveolae membranes. Because dissociation of eNOS from Cav-1 is required for the activation of eNOS, eNOS association with Cav-1 in UAEC suggests an important role of Cav-1 in regulating UAEC production of NO and possibly NO-mediated uterine vasodilatation.

Animals↗

PubMed2001

Measurement of the relative branching fraction of upsilon(4S) to charged and neutral B-meson pairs.

We analyze 9.7x10(6) B_B pairs recorded with the CLEO detector to determine the production ratio of charged to neutral B-meson pairs produced at the Upsilon(4S) resonance. We measure the rates for B0-->J/psiK((*)0) and B+-->J/psiK((*)+) decays and use the world-average B-meson lifetime ratio to extract the relative widths f(+-) / f(00) = gamma(Upsilon(4S)-->B+B-) / gamma(Upsilon(4S)-->B0 B-0)) = 1.04+/-0.07(stat)+/-0.04(syst). With the assumption that f(+-)+f(00) = 1, we obtain f(00) = 0.49+/-0.02(stat)+/-0.01(syst) and f(+-) = 0.51+/-0.02(stat)+/-0.01(syst). This production ratio and its uncertainty apply to all exclusive B-meson branching fractions measured at the Upsilon(4S) resonance.

Journal Article↗

PubMed2001

Effects of membrane potential and tension on prestin, the outer hair cell lateral membrane motor protein.

1. Under whole-cell voltage clamp, the effects of initial voltage conditions and membrane tension on gating charge and voltage-dependent capacitance were studied in human embryonic kidney cells (TSA201 cell line) transiently transfected with the gene encoding the gerbil protein prestin. Conformational changes in this membrane-bound protein probably provide the molecular basis of the outer hair cell (OHC) voltage-driven mechanical activity, which spans the audio spectrum. 2. Boltzmann characteristics of the charge movement in transfected cells were similar to those reported for OHCs (Q(max) = 0.99 +/- 0.16 pC, z = 0.88 +/- 0.02; n = 5, means +/- S.E.M.). Unlike that of the adult OHC, the voltage at peak capacitance (V(pkcm)) was very negative (-74.7 +/- 3.8 mV). Linear capacitance in transfected cells was 43.7 +/- 13.8 pF and membrane resistance was 458 +/- 123 Mohms. 3. Voltage steps from the holding potential preceding the measurement of capacitance-voltage functions caused a time- and voltage-dependent shift in V(pkcm). For a prepulse to -150 mV, from a holding potential of 0 mV, V(pkcm) shifted 6.4 mV, and was fitted by a single exponential time constant of 45 ms. A higher resolution analysis of this time course was made by measuring the change in capacitance during a fixed voltage step and indicated a double exponential shift (tau(0) = 51.6 ms, tau(1) = 8.5 s) similar to that of the native gerbil OHC. 4. Membrane tension, delivered by increasing pipette pressure, caused a positive shift in V(pkcm). A maximal shift of 7.5 mV was obtained with 2 kPa of pressure. The effect was reversible. 5. Our results show that the sensitivity of prestin to initial voltage and membrane tension, though present, is less than that observed in adult OHCs. It remains possible that some other interacting molecular species within the lateral plasma membrane of the native OHC amplifies the effect of tension and prior voltage on prestin's activity.

Animals↗

PubMed2001

Measurement of the lambda(+)(c) lifetime.

The Lambda+c lifetime is measured using 9.0 fb(-1) of e+e- annihilation data collected on or just below the Upsilon(4S) resonance with the CLEO II.V detector at CESR. Using an unbinned maximum likelihood fit, the Lambda+c lifetime is measured to be 179.6+/-6.9(stat)+/-4.4(syst) fs. The precision of this colliding beam measurement is comparable to other measurements, which are based on fixed-target experiments, with different systematic uncertainties.

Journal Article↗

PubMed2001

The F-box protein SKP2 binds to the phosphorylated threonine 380 in cyclin E and regulates ubiquitin-dependent degradation of cyclin E.

Cyclin E is required for S phase entry. The subsequent ubiquitin-dependent degradation of cyclin E contributes to an orderly progression of the S phase. It has been shown that phosphorylation of threonine 380 (Thr380) in cyclin E provides a signal for its ubiquitin-dependent proteolysis. We report that SKP2, an F-box protein and a substrate-targeting component of the SCF(SKP2) ubiquitin E3 ligase complex, mediates cyclin E degradation. In vitro, SKP2 specifically interacted with the cyclin E peptide containing the phosphorylated-Thr380 but not with a cognate nonphosphorylated peptide. In vivo, expression of SKP2 induced cyclin E polyubiquitination and degradation. Conversion of Thr380 into nonphosphorylatable amino acids caused significant resistance of cyclin E to SKP2. The presence of the CDK inhibitor p27(Kip1) also prevented the SKP2-dependent degradation of cyclin E. Our findings suggest that SKP2 regulates cyclin E stability, thus contributing to the control of S phase progression.

Amino Acid Sequence↗

PubMed2001

Reduction in glial immunity and neuropathology by a PAF antagonist and an MMP and TNFalpha inhibitor in SCID mice with HIV-1 encephalitis.

The effects of anti-inflammatory drugs on glial immunity and neuropathology were determined in a severe combined immune deficiency (SCID) mouse model of HIV-1 encephalitis. HIV-1-infected human monocyte-derived macrophages (MDM) are stereotactically inoculated into basal ganglia resulting in a multinucleated giant cell encephalitis. A platelet activating factor antagonist and a matrix metalloproteinase inhibitor, which also inhibits tumor necrosis factor alpha release, were administered to animals at the time of the MDM inoculation. The drugs administered in combination markedly reduced brain inflammation, astrogliosis and microglia activation. These findings demonstrate that reduction of brain inflammatory responses, independent of viral replication, can affect HIVE pathology in an animal model system of disease.

AIDS Dementia Complex↗

PubMed2001

[Mechanism of the activation of extracellular signal-regulated kinase (ERK) in prostate cancer cell lines with different metastatic potential].

OBJECTIVE: To investigate the mechanism of the activation of signal transduction of ERK induced by purinergic receptor agonist ATP in prostate cancer cells with different metastatic potential. METHODS: Cell counts and MTT method were used to detect the influence of ATP on the growth of 1E8 (metastatic) and 2B4 (non-metastatic) cells derived from human prostate cancer cell line PC3M. The activity of ERK1/2 was analyzed with phosphospecific antibodies directed against the dually phosphorylated, active forms of ERK1/2 (p44/p42) by Western Blot. RESULTS: ATP can significantly inhibit the growth of 1E8 and 2B4 cells in vitro (inhibition rate in the 6th and the 8th day were 54% and 59% for 1E8 and 67% and 39% for 2B4 respectively). ATP activated both ERK1 and ERK2 in 1E8 and 2B4 cells with a time and dose dependent pattern. The activation of ERK1/2 by ATP was blocked by the P2 purinoceptor antagonist, suramin with an inhibitory rate of 82% +/- 9% for 1E8 and an inhibitory rate of 81% +/- 6% for 2B4. The activation of ERK1/2 by ATP can be inhibited by the inhibitor of the upstream kinase MEK- PD098059 with an inhibitory rate of 94% +/- 4% for 1E8 and 91% +/- 4% for 2B4,which suggests a link between the G protein coupled P2 purinoceptor and activation of Ras MEK MAPK pathway. ATP-stimulated ERK activation was sensitive to treatment with G protein modulator pertussis toxin (PTX) with an inhibitory rate of 50% +/- 3% for 1E8 and 51% +/- 4% for 2B4. The activating potential of ATP to ERK1/2 in metastatic 1E8 cells is greater than that to nonmetastatic 2B4 cells, and the response of 1E8 cells to TPA was quite different from the response of 2B4 cells, thus implying a potential signaling mechanism in regulating metastasis phenotypes. CONCLUSION: The metastatic 1E8 and non-metastatic 2B4 cells show differential response to ATP-induced ERK activation. This may provide an instructive clue to cancer metastasis research.

Adenosine Triphosphate↗

PubMed2001

Aggrecan domains expected to traffic through the exocytic pathway are misdirected to the nucleus.

In this article, we report the misdirected targeting of expressed aggrecan domains. Aggrecan, the chondroitin sulfate (CS) proteoglycan of cartilage, normally progresses through the exocytic pathway. Proteins expressed from constructs containing the putative aggrecan signal sequence (i.e., the first 23 N-terminal amino acids), specified globular (G) domains G1 and/or G3, and a segment of the CS domain were detected in the endoplasmic reticulum (ER) and Golgi complex. Although proteins expressed from constructs containing the putative signal and G3, but lacking G1, were detected to a limited extent in the secretory pathway, they primarily accumulated in nuclei. Discrete nuclear inclusions were seen when G3 was expressed. Immunoelectron microscopic characterization of the inclusions suggested the association of nuclear G3 with other proteins. When signal-free G3 constructs and those with G3 immediately following the N-terminal signal were expressed, abundant dispersed accumulations filled the nucleoplasm. The data suggest first, that signal-free and signal-containing G3 proteins enter the nucleus from the cytosol, and second, that the entry of signal-containing G3 proteins into the ER lumen is inefficient. Hsp25, Hsp70, and ubiquitin were colocalized with nuclear G3, indicating the involvement of chaperones and the degradative machinery in the formation and/or attempted disposal of the abnormal nuclear inclusions. Overall, the results focus attention on (1) intracellular protein trafficking at the ER membrane and the nuclear envelope and (2) chaperone interactions and mechanisms leading to abnormal protein deposition in the nucleus.

Aggrecans↗

PubMed2001

Discrimination between native and non-native disulfides by protein-disulfide isomerase.

The folding assistant and chaperone protein-disulfide isomerase (PDI) catalyzes disulfide formation, reduction, and isomerization of misfolded proteins. PDI substrates are not restricted to misfolded proteins; PDI catalyzes the dithiothreitol (DTT)-dependent reduction of native ribonuclease A, microbial ribonuclease, and pancreatic trypsin inhibitor, suggesting that an ongoing surveillance by PDI can test even native disulfides for their ability to rearrange. The mechanism of reduction is consistent with an equilibrium unfolding of the substrate, attack by the nucleophilic cysteine of PDI followed by direct attack of DTT on a covalent intermediate between PDI and the substrate. For native proteins, the rate constants for PDI-catalyzed reduction correlate very well with the rate constants for uncatalyzed reduction by DTT. However, the rate is weakly correlated with disulfide stability, surface exposure, or local disorder in the crystal. Compared with native proteins, scrambled ribonuclease is a much better substrate for PDI than predicted from its reactivity with DTT; however, partially reduced bovine pancreatic trypsin inhibitor (des(14-38)) is not. An extensively unfolded polypeptide may be required by PDI to distinguish native from non-native disulfides.

Animals↗