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Biomedical subjects

X Zhang

Publications and source records attributed to X Zhang.

At least 253 records · Page 14Linked to original sources
PubMed2001

Leukocyte integrin Mac-1 recruits toll/interleukin-1 receptor superfamily signaling intermediates to modulate NF-kappaB activity.

The leukocyte integrin Mac-1 (alphaMbeta2, CD11b/CD18) regulates important cell functions in inflammation, including adhesion, phagocytosis, and oxidative burst. Deficiency of Mac-1 reduces vessel wall inflammation and neointimal thickening after murine carotid artery injury. Although Mac-1 has been implicated in modulating AP-1 and NF-kappaB activity, the signal transduction pathways involved are undefined. cDNA array analysis of Mac-1-clustered compared with -nonclustered monocytic THP-1 cells showed increased expression of the signal transducer TRAF6 (TNF receptor-associated factor 6), leading us to consider the possibility that Mac-1 used a Toll/IL-1 receptor family-like signaling pathway. Mac-1-dependent activation of NF-kappaB was potentiated by wild-type, and attenuated by dominant negative, TRAF6- and TGF-beta-activated kinase (TAK1) constructs. IRAK1 (IL-1 receptor associated kinase), a kinase immediately upstream of TRAF6, coimmunoprecipitated with Mac-1. Taken together, these observations indicate that Mac-1 recruits a Toll/IL-1 receptor family-like cascade to modulate NF-kappaB activity. This represents a new pathway for integrin-dependent modulation of gene expression.

Adaptor Proteins, Signal Transducing↗
PubMed2001

The structure and function of a gene encoding a basic peptide from prawn white spot syndrome virus.

Prawn white spot syndrome virus (WSSV) is the major pathogen responsible for the high mortality of cultured prawns. A gene (termed as p6.8) encoding a basic peptide was found by screening the cDNA and DNA libraries of WSSV. The peptide was highly homologous with proteins rich in arginine and lysine. A fusion protein containing the p6.8 and green fluorescent protein (GFP) genes was cloned into pBV220 and expressed in E. coli. Gel mobility shift assay indicated that the peptide encoded by p6.8 had the capability of binding DNA and might be involved in DNA packaging.

Amino Acid Sequence↗
PubMed2001

Regulation of breast cancer cell motility by insulin receptor substrate-2 (IRS-2) in metastatic variants of human breast cancer cell lines.

Insulin-like growth factors (IGFs) regulate breast cancer cell proliferation, protect cells from apoptosis, and enhance metastasis. In this study, we examined the IGF signaling pathway in two breast cancer cell lines selected for metastatic behavior. LCC6 was selected for growth as an ascites tumor in athymic mice from parental MDA-MB-435 cells (435P). The MDA-231BO cell line was derived from osseous metastases that formed after intracardiac injection of the MDA-MB-231 cell line in athymic mice. Compared to the parental cell lines, IGF-I treatment enhanced IRS-2 phosphorylation over IRS-1 in the metastatic variants. IGF-I stimulated cell migration in the variant cells, but not in the parental cells. To determine the role for IRS-2 in IGF-mediated motility, we transfected MDA-231BO cells with an anti-sense IRS-2 construct. Transfected cells had decreased levels of IRS-2 with diminished IGF-mediated motility and anchorage independent growth when compared to control cells. However, adherence to fibronectin was enhanced in the transfected cells compared to MDA-231BO cells. Our data show that breast cancer cells selected for metastatic behavior in vivo have increased IRS-2 activation and signaling. In these cells, IGF-I enhances cell adhesion and motility suggesting that IRS-2 may mediate these aspects of the malignant phenotype.

Animals↗
PubMed2001

Dextran-methylprednisolone succinate as a prodrug of methylprednisolone: dose-dependent pharmacokinetics in rats.

The dose-dependency in the pharmacokinetics of a macromolecular prodrug of methylprednisolone (MP), dextran-methylprednisolone succinate (DMP), was investigated in rats. Single doses (MP equivalent) of 2.5, 5.0, 10, 20, and 30 mg/kg of DMP were administered intravenously to rats (n=5/group), and serial blood samples (0-96 h) and spleen and liver tissues (96 h) were collected. The concentrations of DMP in plasma and spleen were analyzed using a size-exclusion chromatographic method. The concentrations of DMP in the liver samples were determined by an indirect method after sequential hydrolysis by dextranase and esterase enzymes, followed by HPLC analysis of MP. The kinetics of DMP were analyzed by non-compartmental methods. The systemic clearance of DMP decreased approximately 5-fold (from 42.1+/-11.0 to 7.72+/-1.84 ml/h per kg) when the dose was increased from 2.5 to 30 mg/kg. The nonlinearity in the clearance of DMP could be adequately described by a Michaelis-Menten type elimination with a maximum velocity of elimination of 1.72 mg/h per kg and a constant of 24.9 microg/ml. Additionally, the percent of the dose of DMP found at 96 h in the liver and spleen, where the prodrug is sequestered and gradually eliminated, significantly decreased with an increase in the dose. It is concluded that the clearance of DMP in rats is modestly dose-dependent in the dosage range of 2.5-30 mg/kg.

Animals↗
PubMed2001

Differential effects of transforming growth factor on cell cycle regulatory molecules in human myeloid leukemia cells.

In this report we have studied the mechanism by which Transforming Growth Factor beta (TGF beta) inhibits growth of human myeloid leukemia cell lines. TGF beta 1 arrested cells in G1 phase and significantly downregulated the expression of cyclin D2, cyclin D3, cdk4, cyclin A, and cdk2. The downregulation of the molecules resulted in approximately 50-90% decrease of the molecule-dependent kinase activity, varying with each molecule. Although treatment of cells with TGF beta 1 up-regulated accumulation of p27(kip1) in both nucleus and cytoplasm, the association of the p27(kip1) with cdk2, cyclin A, cyclin D2, cyclin D3, and cdk4 was markedly down-regulated, suggesting that p27(kip1) is not responsible for the downregulation of the kinase activity. In contrast, TGF beta 1 upregulated cyclin E-associated p27(kip1) with no effect on the expression of cyclin E. p27(kip1)-immunodepletion upregulated cyclin E-dependent kinase activity by more than 10-fold in TGF beta 1-treated cells but not in proliferating cells; whereas immunodepletion of p27(kip1) from cdk2-immunoprecipitates markedly downregulated cdk2 kinase activity in the lysates extracted from both proliferating and TGF beta-treated cells. Consistent with this observation, TGF beta 1 and p27(kip1) antisense cDNA had a synergistic or additive inhibitory effect on cdk2 but not cyclin E-dependent kinase activity. Our data suggest that (1) TGF beta 1-mediated growth inhibition is accomplished through multiple pathways and (2) p27(kip1) has opposing effects on cdk2 and cyclin E activity in response to TGF beta 1.

CDC2-CDC28 Kinases↗
PubMed2001

Saccharomyces cerevisiae multidrug resistance gene expression inversely correlates with the status of the F(0) component of the mitochondrial ATPase.

Loss of the mitochondrial genome (rho(0) cell) or elimination of the mitochondrial inner membrane protein Oxa1p causes a dramatic increase in expression of the ATP binding cassette transporter-encoding gene PDR5 in the yeast Saccharomyces cerevisiae. This increase in gene expression occurs via activation of the function of the Cys(6)-Zn(II)(2) cluster transcription factor Pdr3p, which in turn autoregulates expression of its structural gene. Surprisingly, the acquisition of PDR5-dependent multidrug resistance occurs at a very high frequency, consistent with the appearance of rho(-) cells in a fermentatively growing culture (approximately 2%). The degree of activation of Pdr3p target genes was found to vary considerably and to be influenced by the presence of the homologous protein, Pdr1p. Mutagenesis and overexpression studies provided evidence that the control of Pdr3p expression was the major control point of this transcription factor by mitochondrial retrograde signaling. Because both rho(0) and oxa1 mutant cells have multiple defects including loss of normal respiratory chain function and oxidative phosphorylation, a series of mutant strains with more selective defects in mitochondrial function was employed to identify the molecular signal that triggers PDR5 transcriptional activation. Only mutations that influenced the functional status of the F(0) subunit of the mitochondrial ATPase were found to lead to activation of PDR5 expression.

ATP-Binding Cassette Transporters↗
PubMed2001

Activation of CD25(+)CD4(+) regulatory T cells by oral antigen administration.

CD25(+)CD4(+) T cells are naturally occurring regulatory T cells that are anergic and have suppressive properties. Although they can be isolated from the spleens of normal mice, there are limited studies on how they can be activated or expanded in vivo. We found that oral administration of OVA to OVA TCR transgenic mice resulted in a modification of the ratio of CD25(+)CD4(+) to CD25(-)CD4(+) cells with an increase of CD25(+)CD4(+) T cells accompanied by a decrease of CD25(-)CD4(+) T cells. The relative increase in CD25(+)CD4(+) T cells persisted for as long as 4 wk post feeding. We also found that CTLA-4 was dominantly expressed in CD25(+)CD4(+) T cells and there was an increase in the percentage of CD25(+)CD4(+) T cells expressing CTLA-4 in OVA-fed mice. In contrast to CD25(-)CD4(+) cells, CD25(+)CD4(+) cells from fed mice proliferated only minimally to OVA or anti-CD3 and secreted IL-10 and elevated levels of TGF-beta(1) following anti-CD3 stimulation. CD25(+)CD4(+) cells from fed mice suppressed the proliferation of CD25(-)CD4(+) T cells in vitro more potently than CD25(+)CD4(+) T cells isolated from unfed mice, and this suppression was partially reversible by IL-10 soluble receptor or TGF-beta soluble receptor and high concentration of anti-CTLA-4. With anti-CD3 stimulation, CD25(+)CD4(+) cells from unfed mice secreted IFN-gamma, whereas CD25(+)CD4(+) cells from fed mice did not. Adoptive transfer of CD25(+)CD4(+) T cells from fed mice suppressed in vivo delayed-type hypersensitivity responses in BALB/c mice. These results demonstrate an Ag-specific in vivo method to activate CD25(+)CD4(+) regulatory T cells and suggest that they may be involved in oral tolerance.

Abatacept↗
PubMed2001

Cdc42 interacts with the exocyst and regulates polarized secretion.

Polarized delivery and incorporation of proteins and lipids to specific domains of the plasma membrane is fundamental to a wide range of biological processes such as neuronal synaptogenesis and epithelial cell polarization. The exocyst complex is specifically localized to sites of active exocytosis and plays essential roles in secretory vesicle targeting and docking at the plasma membrane. Sec3p, a component of the exocyst, is thought to be a spatial landmark for polarized exocytosis. In a search for proteins that regulate the localization of the exocyst in the budding yeast Saccharomyces cerevisiae, we found that certain cdc42 mutants affect the polarized localization of the exocyst proteins. In addition, we found that these mutant cells have a randomized protein secretion pattern on the cell surface. Biochemical experiments indicated that Sec3p directly interacts with Cdc42 in its GTP-bound form. Genetic studies demonstrated synthetically lethal interactions between cdc42 and several exocyst mutants. These results have revealed a role for Cdc42 in exocytosis. We propose that Cdc42 coordinates the vesicle docking machinery and the actin cytoskeleton for polarized secretion.

Actins↗
PubMed2001

Self-assembled monolayers of new dendron-thiols: manipulation of the patterned surface and wetting properties.

SAMs based on a novel dendron-thiol system, which maintain the alkanethiols' active site, but with the -SH group connected to independently variable groups by a dendron-linker, showed a controllable surface pattern and wetting properties. The precisely tailored structure of dendron-thiols with locally controlled hydrophobic and hydrophilic peripheries allows the formation of designed surface structures on a gold surface, e.g. nano-stripes, honeycomb and homogeneous structures.

Journal Article↗
PubMed2001

Disruption of replication protein A/single-stranded DNA complexes during apoptosis in HL-60 cells.

Replication protein A (RPA) is a single-stranded DNA-binding protein which plays a role in DNA replication, repair, and recombination. We used gel mobility shift, super gel mobility shift, and Western blot to determine the fate of RPA during Hoechst 33342-induced apoptosis in HL-60 cells. Multiple bands were detected by gel mobility shift after the incubation of single-stranded gamma-(32)P-labeled oligo(dT)(30) with the nuclear extracts of HL-60 cells. Super gel mobility shift results indicated that only the highest molecular weight protein/oligo(dT)(30) complexes bound with anti-human RPA-32 and/or anti-human RPA-70 antibodies forming RPA/oligo(dT)(30) complexes. After the treatment of HL-60 cells with 15 microg/ml Hoechst 33342 for 3 h, the bands of RPA/oligo(dT)(30) complexes were decreased and bands of the lowest molecular weight protein/oligo(dT)(30) complexes were significantly increased when compared to the control group. These low-molecular-weight bands did not bind with RPA-32 or RPA-70 antibodies. Western blotting results showed that both RPA-32 and RPA-70 were decreased significantly in a time-dependent manner after 1 h of incubation with Hoechst 33342. These results demonstrate that in HL-60 cells, Hoechst 33342-induced apoptosis is associated with a rapid loss of the binding capacity of RPA to oligo(dT)(30) as well as immunoactive RPA-70 and RPA-32.

Apoptosis↗
PubMed2001

Aberrant induction of Par-4 is involved in apoptosis of hippocampal neurons in presenilin-1 M146V mutant knock-in mice.

Mutations in presenilin-1 (PS-1) have been shown to increase neuronal vulnerability to apoptosis in Alzheimer's disease (AD). Par-4 is a novel cell-death-promoting protein associated with neuronal degeneration in AD. We previously reported that, in transfected PC12 cells, Par-4 seems to be involved in the neurodegenerative mechanisms of PS-1 mutations. However, direct evidence for a necessary role of Par-4 in the pathogenic mechanisms of PS-1 mutations in neurons is lacking. We recently generated and characterized presenilin-1 mutant M146V knock-in (PS-1 M146V KI) mice. We now report that expression of the mutant presenilin-1 in these mice induces early and exaggerated increase in Par-4 expression in hippocampal neurons following glucose deprivation (an insult relevant to the pathogenesis of AD). Importantly, inhibition of Par-4 expression by antisense par-4 oligonucleotide treatment counteracts neuronal apoptosis promoted by M146V mutation of PS-1. Mitochondrial dysfunction and caspase-3 activity induced by glucose deprivation was significantly exacerbated in hippocampal neurons expressing the mutant PS-1. Antisense par-4 treatment largely suppressed the adverse effect of the mutant PS-1 on mitochondrial dysfunction and caspase activation. These results provide evidence in hippocampal neurons that Par-4 is involved in the neurodegenerative cascades associated with PS-1 M146V mutation by acting relatively early in the apoptotic process before mitochondrial dysfunction and caspase-3 activation. Since levels of Par-4 are significantly increased in the hippocampus in human AD brain, the results of this study may provide a significant link between aberrant induction of Par-4 and the neurodegenerative cascades promoted by PS-1 mutations in AD.

Alzheimer Disease↗
PubMed2001

Electrical currents and liquid flow rates in micro-reactors.

For micro-reactor devices in which liquids are pumped by electro-osmotic flow (EOF), in situ monitoring of the electrical currents in the channel networks provides a valuable diagnostic tool. We demonstrate here that the voltage-current characteristics of a micro-reactor channel network can be accurately modelled using measurements of the full 3-D geometry of the channel network, the liquid conductivity and the channel wall-liquid surface conductivity. It is shown that surface conductivity provides a significant contribution to the overall measured electrical currents in channel networks for which the ratio of surface area to volume is high. Following correction for surface conductivity, the electrical currents are proportional to the liquid volumetric flow rates measured in the different branches of the channel network. The constant of proportionality is related to the zeta potential of the channel wall-liquid surface. Measurements of the variation of electrical currents and volumetric flow rates as a function of the applied voltages allows the determination of the surface conductivity and zeta potential within the micro-reactor which enables the prediction of the voltages required to produce the desired flow rates in any channel section. In situ logging of the electrical currents, incorporated within the control system, allows continuous monitoring of the liquid flow rates during micro-reactor operation.

Journal Article↗
PubMed2001

P instability factor: an active maize transposon system associated with the amplification of Tourist-like MITEs and a new superfamily of transposases.

Miniature inverted-repeat transposable elements (MITEs) are widespread and abundant in both plant and animal genomes. Despite the discovery and characterization of many MITE families, their origin and transposition mechanism are still poorly understood, largely because MITEs are nonautonomous elements with no coding capacity. The starting point for this study was P instability factor (PIF), an active DNA transposable element family from maize that was first identified following multiple mutagenic insertions into exactly the same site in intron 2 of the maize anthocyanin regulatory gene R. In this study we report the isolation of a maize Tourist-like MITE family called miniature PIF (mPIF) that shares several features with PIF elements, including identical terminal inverted repeats, similar subterminal sequences, and an unusual but striking preference for an extended 9-bp target site. These shared features indicate that mPIF and PIF elements were amplified by the same or a closely related transposase. This transposase was identified through the isolation of several PIF elements and the identification of one element (called PIFa) that cosegregated with PIF activity. PIFa encodes a putative protein with homologs in Arabidopsis, rice, sorghum, nematodes, and a fungus. Our data suggest that PIFa and these PIF-like elements belong to a new eukaryotic DNA transposon superfamily that is distantly related to the bacterial IS5 group and are responsible for the origin and spread of Tourist-like MITEs.

Base Sequence↗
PubMed2001

Direct measurements of the enthalpy of solution of solid solute in supercritical fluids: study on the CO2-naphthalene system.

A setup for a calorimeter for simultaneously measuring the solubility and the solution enthalpy of solid solutes in supercritical fluids (SCFs) has been established. The enthalpy of solution of naphthalene in supercritical CO2 was measured at 308.15 K in the pressure range from 8.0-11.0 MPa. It was found that the enthalpy of solution (deltaH) was negative in the pressure range from 8.0 to 9.5 MPa, and the absolute value decreased with increasing pressure. In this pressure range, the dissolution of the solute was enthalpy driven. However, the deltaH became positive at pressures higher than 9.5 MPa, and the dissolution was entropy driven. Monte Carlo simulation was performed to analyze the local structural environment of the solvated naphthalene molecules in supercritical CO2 under the experimental conditions for the calorimetric measurements. By combining the enthalpy data and the simulation results, it can be deduced that the energy level of CO2 in the high compressible region is higher than that at higher pressures, which results in the large negative enthalpy of solution and the larger degree of solvent-solute clustering in the high compressible region.

Journal Article↗
PubMed2001

Oral cancer in vivo gene expression profiling assisted by laser capture microdissection and microarray analysis.

Large scale gene expression profiling was carried out on laser capture microdissected (LCM) tumor and normal oral epithelial cells and analysed on high-density oligonucleotide microarrays. About 600 genes were found to be oral cancer associated. These oral cancer associated genes include oncogenes, tumor suppressors, transcription factors, xenobiotic enzymes, metastatic proteins, differentiation markers, and genes that have not been implicated in oral cancer. The database created provides a verifiable global profile of gene expression during oral carcinogenesis, revealing the potential role of known genes as well as genes that have not been previously implicated in oral cancer.

Aged↗
PubMed2001

An isoform of branched-chain aminotransferase is a novel co-repressor for thyroid hormone nuclear receptors.

The functions of thyroid hormone receptors (TRs) are regulated by a host of co-regulatory proteins. Tissue-specific expression of these co-regulators leads to distinct expression patterns and regulation of thyroid hormone (T3) target genes in tissues. Previously we have found that human colon carcinoma RKO cells exhibit strong T3-independent transcriptional activity. We therefore searched for co-regulatory proteins in RKO cells using a yeast two-hybrid system with the intact TRbeta1 as bait. One of the three positive clones, designated as P3, was identified to be an isoform of human mitochondria branched-chain aminotransferase (BCATm). P3 was a spliced variant of BCATm with an internal 12-amino acid deletion near the carboxyl-terminal region and was abundantly expressed in RKO cells. The expressed protein localized both to the mitochondria and the nucleus of transfected CV1 cells. P3 physically interacted with TRbeta1 in a T3-independent manner that led to the inhibition in binding of TRbeta1 to thyroid hormone-responsive element. P3 not only enhanced the repressor activity of the unliganded TR but also repressed the ligand-dependent activation of TR. This repression was reversed by treatment of cells with trichostatin A, suggesting that in addition to the inhibition of DNA binding, the repression activity of P3 on TR may also be mediated by histone deacetylase activity. Thus, unlike the currently known co-repressors, P3 is a novel ligand-independent co-repressor for TR.

Animals↗
PubMed2001

[Establishment of model of aristolochic acid-induced chronic renal interstitial fibrosis in rats].

OBJECTIVE: To study chronic renal interstitial fibrosis induced by aristolochic acid (AA) in animal models. METHODS: Female Wistar rats were divided into two groups: AA group (n = 42) peritoneally injected with AA (5 mg.kg-1.d-1) for 16 weeks and control group (n = 5) peritoneally injected with normal saline (2 ml/d) for 16 weeks. The body weight of rats was taken. At week 8, 12, 16, and 24 six rats were killed in the AA group. The five rats in the control group were killed at week 24. Specimens of lood and urine were taken before the animals were killed. Specimens of renal tissue were taken after the animals were killed. Twenty-four hour urine protein, urine beta 2 microglobulin (beta 2-MG), and renal function were tested regularly. Pathological examination, including tubulo-interstitial area calculation, was made to the renal specimens. RESULTS: The body weight of rats in AA group became significantly lower than that of the control rats after 16 weeks' AA injection (P < 0.01). The blood urea nitrogen (BUN) and serum creatinine (Scr) in AA group increased significantly than those of the control group at the 16th, 20th, and 24th weeks (P < 0.05). Optical microscopy showed tubular-interstitial damage in AA group in 16 weeks. Renal tubular atrophy and multifocal renal interstitial fibrosis were shown in 24 weeks. The area of renal tubule increased and the area of the lumen remarkably decreased at week 16 compared with those in the control group. The area of renal tubule decreased remarkably and the area of renal interstitial greatly in the AA group at week 24. Electrical microscopy showed increase of primary and secondary lysosomes and diasappearence of part of brush border of tubular endothelial cells at week 16, and accumulation of secondary lysosome in cytoplasm at weeks 20 and 24 in the AA group. Histoimmunofluorescence showed that IgG, IgA, IgM, C3, and C1q were negative in the renal tissue of experimental animals. CONCLUSION: Animal models with chronic renal tubuloointerstitial nephropathy induced by aristolochic acid were successfully established. Aristolochic acid may have chronic toxicity to renal tissues, and cause chronic renal interstitial fibrosis in rats.

Animals↗