Biomedical subjects

H Wang

Publications and source records attributed to H Wang.

At least 1,045 records · Page 58Linked to original sources

PubMed1999

Clastogenicity of chromium contaminated soil samples evaluated by Vicia root-micronucleus assay.

Chromium compounds have been known to be highly toxic in biological systems and to some individuals act as strong allergens. A chromium processing plant in Tianjin city has been abandoned for many years and the chromium residue has been dispersed into the nearby soil. This study was designed to detect the genotoxicity of contaminated soil samples collected at various distances of 100 to 1000 m from the source using the Vicia faba root micronucleus test. Water solutions extracted from the soil samples were used to treat the roots of the Vicia beans. Micronuclei frequencies observed from the root meristems were used to determine the degree of genotoxicity. Micronuclei frequencies of the contaminated soil samples show linear dose responses to chromium contents in the soil, which were inversely proportional to the distance from the source.

Biological Assay↗

PubMed1999

The interferon-inducible nucleolar p204 protein binds the ribosomal RNA-specific UBF1 transcription factor and inhibits ribosomal RNA transcription.

p204, a member of the interferon-inducible p200 family of murine proteins, is primarily nucleolar. We generated cell lines in which p204 was inducible by muristerone. This induction resulted in retardation of cell proliferation and inhibition of rRNA transcription in vivo. Interferon treatment, resulting in p204 induction and retardation of proliferation, also caused inhibition of rRNA transcription in vivo. p204 also inhibited rRNA transcription in vitro. This inhibition was overcome by addition of UBF1, the rRNA-specific transcription factor. A direct interaction between p204 and UBF1 was revealed in vitro in pull-down assays, and in vivo by co-immunoprecipitation from cell extracts. UBF1 bound strongly to at least two regions of p204: the N-terminal segment linked to the conserved 200 amino acid a segment, and the conserved 200 amino acid b segment. Cleavage of the a or b segments into two segments (encoded by single exons) resulted in a strong decrease or loss of binding. The inhibition of rRNA transcription by p204 may be due to the inhibition by p204 of the specific DNA binding of UBF1. This was revealed in electrophoretic mobility shift, magnetic bead and footprinting assays. Thus, p204 serves as a mediator of the inhibition of rRNA transcription by interferon.

Animals↗

PubMed1999

Concentration-Dependent Sedimentation of Stable Magnetic Dispersions.

The concentration dependence of the sedimentation coefficient has been studied theoretically for a stable magnetic colloidal system under the influence of an external homogeneous magnetic field. The physical model of the magnetic colloid given by Donselaar et al. (1997, Langmuir 13, 6018) was adopted. It was found that the magnetic interaction accelerated the sedimentation of the particles. The stronger the external magnetic field is, the quicker the sedimentation of the particles. For sterically stabilized particles frequently used in experiments to simulate hard spheres, the combined influence of the magnetic attraction and van der Waals attraction on the sedimentation is also analyzed. Copyright 1999 Academic Press.

Journal Article↗

PubMed1999

A general method for producing bioaffinity MALDI probes.

A bioaffinity probe based on the idea of immobilizing avidin on the probe surface to extract biotinylated oligosaccharide is described. The probe is produced by taking advantage of the natural affinity of proteins for hydrophobic polymer films. The avidin is immobilized by simply drying the solution on a polymer film surface. This produces a bioaffinity probe that shows enhanced activity for biotin-labeled oligosaccharides. The probe is produced in a matter of minutes but is highly effective for concentrating biotinylated oligosaccharide on the surface. The best matrix for the analysis is DHB, and the best film for the probe is a polyester material commonly used for transparency film. The efficacy of the probe is illustrated with neutral and anionic oligosaccharides. Oligosaccharides derivatized with biotin are retained while those that are unlabeled are washed away. No trace of the unlabeled oligosaccharide is observed in the mass spectrum.

Affinity Labels↗

PubMed1999

Mechanisms of nasal tolerance induction in experimental autoimmune myasthenia gravis: identification of regulatory cells.

Autoantigen administration via nasal mucosal tissue can induce systemic tolerance more effectively than oral administration in a number of experimental autoimmune diseases, including Ab-mediated experimental autoimmune myasthenia gravis, a murine model of myasthenia gravis. The mechanisms underlying nasal tolerance induction are not clear. In this study, we show that nasal administration of acetylcholine receptor (AChR) in C57BL/6 mice, before immunizations with AChR in adjuvant, results in delayed onset and reduced muscle weakness compared with control mice. The delayed onset and reduced muscle weakness were associated with decreased AChR-specific lymphocyte proliferation and decreased levels of anti-AChR Abs of the IgG2a and IgG2b isotypes in serum. The clinical and immunological changes in the AChR-pretreated C57BL/6 wild-type (wt) mice were comparable with those observed in AChR-pretreated CD8-/- mice, indicating that CD8+ T cells were not required for the generation of nasal tolerance. AChR-pretreated wt and CD8-/- mice showed augmented TGF-beta and reduced IFN-gamma responses, whereas levels of IL-4 were unaltered. Splenocytes from AChR-pretreated wt and CD8-/- mice, but not from CD4-/- mice, suppressed AChR-specific lymphocyte proliferation. This suppression could be blocked by Abs against TGF-beta. Thus, our results demonstrate that the suppression induced in the present model is independent of CD8+ T cells and suggest the involvement of Ag-specific CD4+ Th3 cells producing TGF-beta.

Animals↗

PubMed1999

Choline modulates cardiac membrane repolarization by activating an M3 muscarinic receptor and its coupled K+ channel.

Choline is a necessary substrate of the lipid membrane and for acetylcholine synthesis. Accumulating evidence indicates that besides being a structural component, choline is also a functional modulator of the membrane. It has been shown to be a muscarinic acetylcholine receptor (mAChR) agonist and can induce a novel K+ current in cardiac cells. However, the potential role of choline in modulating cardiac functions remained unstudied despite that mAChRs are known to be important in regulating heart functions. With microelectrode techniques, we found that choline produced concentration-dependent (0.1 approximately 10 mm) decreases in sinus rhythm and action potential duration in isolated guinea pig atria. The effects were reversed by 2 nm 4DAMP (an M3-selective antagonist). Whole-cell patch-clamp recordings in dispersed myocytes from guinea pig and canine atria revealed that choline is able to induce a K+ current with delayed rectifying properties. The choline-induced current was suppressed by low concentrations of 4DAMP (2 approximately 10 nm). Antagonists toward other subtypes (M1, M2 or M4) all failed to alter the current. The affinity of choline (Kd) at mAChRs derived from displacement binding of [3H]-NMS in the homogenates from dog atria was 0.9 mm, consistent with the concentration needed for the current induction and for the HR and APD modulation. Our data indicate that choline modulates the cellular electrical properties of the hearts, likely by activating a K+ current via stimulation of M3 receptors.

Animals↗

PubMed1999

A recombinant prodrug type approach for triggered delivery of streptokinase.

A novel prodrug type approach for triggered delivery of thrombolytic drugs without their associated hemorrhagic effects has been proposed. Presented herein is a rapid communication of preliminary observations that suggest the feasibility of the approach. A hirulog-streptokinase fusion protein (termed "HSK") possessing active thrombolytic functions has been successfully produced using recombinant DNA technology. The prodrug and triggered release features of this approach have been demonstrated by the inhibition of the plasminogen-activating activity of HSK via binding with thrombin and reversal of this inhibition by hirudin.

Amino Acid Sequence↗

PubMed1999

Plasminogen is not required for neointima formation in a mouse model of vein graft stenosis.

Recent studies of mice that lack plasminogen have identified a critical role for this zymogen in arterial remodeling. To permit the use of these (and other) genetically modified mice in the analysis of venous injury, we developed a model in which a patch cut from the external jugular vein of a mouse is grafted to repair a surgically created defect in its carotid artery. In wild-type mice, the venous graft showed initial endothelial denudation and formation of a neointima that progressively and reproducibly expanded in a manner analogous to human vein graft disease, albeit at an accelerated pace. This neointima occupied 37+/-4.6% of the vessel lumen at day 7 and 66+/-5.7% at day 20. The proliferative index of neointimal cells assessed by proliferating cell nuclear antigen staining was 50.6+/-3. 6% at day 7 and 15.2+/-2.0% at day 20. CD45-positive leukocytes and alpha-actin-positive smooth muscle cells accounted for 9.5+/-1.0% and 9.9+/-1.1% of intimal area at day 7, respectively, with the latter increasing to 40.9+/-2.6% at day 20. Collagen accounted for 6.8+/-0.7% of intimal area at day 7 and 20.7+/-1.8% at day 20. Surprisingly, even though arterial neointima formation due to electrostatic and immune-mediated injury is impaired in plasminogen -/- mice, in our study vein graft neointima formation in these mice was not significantly different from that in controls (70.9+/-6.4 versus 65.6+/-4.4% luminal occlusion, P=NS). Thus, plasmin proteolysis, although critical in extracellular matrix degradation and cellular migration after arterial injury, does not appear to be so important in vein graft neointima formation, perhaps because of the relative lack of structural barriers to cellular migration in the normal vein wall. This novel model of vein graft injury should be useful for further studies of differences in the response to injury of arterial and venous tissues.

Animals↗

PubMed1999

Energy transduction in the sodium F-ATPase of Propionigenium modestum.

The F-ATPase of the bacterium Propionigenium modestum is driven by an electrochemical sodium gradient between the cell interior and its environment. Here we present a mechanochemical model for the transduction of transmembrane sodium-motive force into rotary torque. The same mechanism is likely to operate in other F-ATPases, including the proton-driven F-ATPases of Escherichia coli.

Bacterial Proteins↗

PubMed1999

Decreased expression of N-methyl-D-aspartate (NMDA) receptors in rat dorsal root ganglion following complete Freund's adjuvant-induced inflammation: an immunocytochemical study for NMDA NR1 subunit.

The changes in expression of NMDA NR1, an essential functional subunit of N-methyl-D-aspartate (NMDA) receptors, were examined in the rat lumbar dorsal root ganglion (DRG) by immunocytochemical technique following injection of complete Freund's adjuvant (CFA) into the unilateral hindpaw. The results showed that there appeared a significant and several days-lasting down-regulation in expression of NMDA NR1 in the lumbar DRG following CFA injection, and especially, this change mainly appeared in the small and medium sized DRG neurons. It is suggested that a long-lasting flow of nociceptive inputs in nociceptors will elicit a decreased expression of NMDA receptors on primary afferent neurons and this plastic change would act as a factor leading towards the hyposensitization for nociception at the nociceptor level.

Animals↗

PubMed1999

Interferon-gamma-mediated inhibition of cyclin A gene transcription is independent of individual cis-acting elements in the cyclin A promoter.

Interferons (IFNs) affect cellular functions by altering gene expression. The eukaryotic cell cycle is governed in part by the periodic transcription of cyclin genes, whose protein products associate with and positively regulate the cyclin-dependent kinases. To understand better the growth inhibitory effect of IFN-gamma on vascular smooth muscle cells (VSMCs), we compared the expression and activity of G1 and S phase cyclins in control and IFN-gamma-treated VSMCs. IFN-gamma treatment did not inhibit the G1 cyclins but did decrease cyclin A protein, mRNA, and associated kinase activity by 85, 90, and 90%, respectively. Nuclear run-on and mRNA stability determinations indicated that this decrease was the result of transcriptional inhibition. To investigate the molecular basis of this inhibition, we examined protein-DNA interactions involving the cyclin A promoter. Electromobility shift assays showed little change with IFN-gamma treatment in the binding of nuclear proteins to isolated ATF, NF-Y, and CDE elements. In vivo genomic footprinting indicated that IFN-gamma treatment changed the occupancy of chromosomal NF-Y and CDE sites slightly and did not affect occupancy of the ATF site. In a previous study of transforming growth factor-beta1-mediated inhibition of the cyclin A promoter, we mapped the inhibitory effect to the ATF site; in the present study of IFN-gamma treatment, functional analysis by transient transfection showed that inhibition of the cyclin A promoter persisted despite mutation of the ATF, NF-Y, or CDE elements. We hypothesize that IFN-gamma inhibits cyclin A transcription by modifying co-activators or general transcription factors within the complex that drives transcription of the cyclin A gene.

Animals↗

PubMed1999

Dual mechanisms of regulation of Na/H exchanger NHE-3 by parathyroid hormone in rat kidney.

Parathyroid hormone (PTH) is a potent inhibitor of mammalian renal proximal tubule sodium absorption via suppression of the apical membrane Na/H exchanger (NHE-3). We examined the mechanisms by which PTH inhibits NHE-3 activity by giving an acute intravenous PTH bolus to parathyroidectomized rats. Parathyroidectomy per se increased apical membrane NHE-3 activity and antigen. Acute infusion of PTH caused a time-dependent decrease in NHE-3 activity as early as 30 min. Decrease in NHE-3 activity at 30 and 60 min was accompanied by increased NHE-3 phosphorylation. In contrast to the rapid changes in NHE-3 activity and phosphorylation, decrease in apical membrane NHE-3 antigen was not detectable until 4-12 h after the PTH bolus. The decrease in apical membrane NHE-3 occurred in the absence of changes in total renal cortical NHE-3 antigen. Pretreatment of the animals with the microtubule-disrupting agent colchicine blocked the PTH-induced decrease in apical NHE-3 antigen. We propose that PTH acutely cause a decrease in NHE-3 intrinsic transport activity possibly via a phosphorylation-dependent mechanism followed by a decrease in apical membrane NHE-3 antigen via changes in protein trafficking.

Amino Acid Sequence↗

PubMed1999

ATP synthase: two motors, two fuels.

FoF1 ATPase is the universal protein responsible for ATP synthesis. The enzyme comprises two reversible rotary motors: Fo is either an ion 'turbine' or an ion pump, and F1 is either a hydrolysis motor or an ATP synthesizer. Recent biophysical and biochemical studies have helped to elucidate the operating principles for both motors.

Adenosine Triphosphate↗

PubMed1999

Plasma DNA microsatellites as tumor-specific markers and indicators of tumor progression in melanoma patients.

Multiple DNA microsatellites with frequent loss of heterozygosity (LOH) in melanomas have been demonstrated. The finding that free DNA is enriched in blood of melanoma patients prompted studies to determine whether tumor-specific DNA, such as DNA microsatellites exhibiting LOH, can be detected in blood and have clinical use. In this study, 57 advanced and 19 early clinically staged melanoma patients were assessed using 10 microsatellite markers on six chromosomes. Matched plasma and melanoma tissues from 40 patients showed significant concordance of LOH (P < 0.0001). The frequency of LOH microsatellite markers detected in plasma significantly increased in more advanced-staged patients. At locus D3S1293, LOH detection showed significant correlation to clinical disease progression (P = 0.02). Additionally, the combination of LOH microsatellite markers D9S157 and D3S1293 (P = 0.01), D9S157 and D1S228 (P = 0.05), and D11S925 and D3S1293 (P = 0.01) were significantly correlated to progression of different clinical stages of disease. These studies indicate that tumor-specific LOH markers in plasma have a potential clinical use as diagnostic and prognostic markers in melanoma patients.

Adult↗

PubMed1999

Mutations in immunodominant T cell epitopes derived from the nonstructural 3 protein of hepatitis C virus have the potential for generating escape variants that may have important consequences for T cell recognition.

One of the most disturbing features of hepatitis C virus (HCV) is its long-term persistence in the host. One hypothesis to explain this phenomenon is that HCV escapes immune recognition through its intrinsic hypermutability. To determine whether immunodominant T cell epitopes derived from HCV nonstructural 3 (NS3) protein might be subject to sequence variations leading to escape mutants, we examined sequence variations of one IL-2-producing epitope, NS3358-375, and one IL-10-producing epitope, NS3505-521. By PCR amplification, cloning, and sequencing, we observed significant sequence variations in the two epitopes, although the selection intensity for each epitope was different. For NS3358-375, more variants were observed, and for NS3505-521, fewer mutations were observed. Moreover, functional studies revealed that three NS3358-375 and one NS3505-521 variants failed to stimulate T cell proliferation, and two other NS3358-375 and NS3505-521 variants weakly stimulated T cell responses. Our results are consistent with immune selection of viral variants at the epitope level, which may enable HCV to evade host defenses over time.

Amino Acid Sequence↗

PubMed1999

Telomerase extends the lifespan of virus-transformed human cells without net telomere lengthening.

Human fibroblasts whose lifespan in culture has been extended by expression of a viral oncogene eventually undergo a growth crisis marked by failure to proliferate. It has been proposed that telomere shortening in these cells is the property that limits their proliferation. Here we report that ectopic expression of the wild-type reverse transcriptase protein (hTERT) of human telomerase averts crisis, at the same time reducing the frequency of dicentric and abnormal chromosomes. Surprisingly, as the resulting immortalized cells containing active telomerase continue to proliferate, their telomeres continue to shorten to mean lengths below those in control cells that enter crisis. These results provide evidence for a protective function of human telomerase that allows cell proliferation without requiring net lengthening of telomeres.

Antigens, Viral, Tumor↗

PubMed1999

DRC1, DNA replication and checkpoint protein 1, functions with DPB11 to control DNA replication and the S-phase checkpoint in Saccharomyces cerevisiae.

In addition to DNA polymerase complexes, DNA replication requires the coordinate action of a series of proteins, including regulators Cdc28/Clb and Dbf4/Cdc7 kinases, Orcs, Mcms, Cdc6, Cdc45, and Dpb11. Of these, Dpb11, an essential BRCT repeat protein, has remained particularly enigmatic. The Schizosaccharomyces pombe homolog of DPB11, cut5, has been implicated in the DNA replication checkpoint as has the POL2 gene with which DPB11 genetically interacts. Here we describe a gene, DRC1, isolated as a dosage suppressor of dpb11-1. DRC1 is an essential cell cycle-regulated gene required for DNA replication. We show that both Dpb11 and Drc1 are required for the S-phase checkpoint, including the proper activation of the Rad53 kinase in response to DNA damage and replication blocks. Dpb11 is the second BRCT-repeat protein shown to control Rad53 function, possibly indicating a general function for this class of proteins. DRC1 and DPB11 show synthetic lethality and reciprocal dosage suppression. The Drc1 and Dpb11 proteins physically associate and function together to coordinate DNA replication and the cell cycle.

Amino Acid Sequence↗

PubMed1999

[Effect of deoxynivalenol and aflatoxin G1 on apoptosis of human blood lymphocytes in vitro].

Effect of deoxynivalenol (DON) and aflatoxin G1 (AFG1) on human blood lymphocytes in culture were studied with flow cytometric DNA content analyses and DNA agarose gel electrophoresis. DON and AFG1 are two of the predominant mycotoxins contaminating foodstuffs or residents in a high incidence of esophageal cancer in Cixian County, Hebei province. A typical sub-diploid apoptosis peak was demonstrated in lymphocytes treated with DON and AFG1. A significant dose-effect response and time-effect correlation could be found between apoptosis rates and mycotoxin concentrations (DON: 50-2000 micrograms/L and AFG1: 3.12-2000 micrograms/L) and the treated time (DON: 2-72 hours and AFG1: 2-24 hours). The lymphocytes treated with DON and AFG1 showed characteristic 'ladder' pattern in agarose gel electrophoresis. All results confirmed that DON and AFG1 could induce and accelerate apoptosis in human peripheral blood lymphocytes.

Aflatoxins↗