PubMed Health⌕ Search

Biomedical subjects

Y Yuan

Publications and source records attributed to Y Yuan.

At least 19 recordsLinked to original sources
PubMed2001

Cloning, expression, and characterization of a human inosine triphosphate pyrophosphatase encoded by the itpa gene.

ITP and dITP exist in all cells. dITP is potentially mutagenic, and the levels of these nucleotides are controlled by inosine triphosphate pyrophosphatase (EC ). Here we report the cloning, expression, and characterization of a 21.5-kDa human inosine triphosphate pyrophosphatase (hITPase), an enzyme whose activity has been reported in many animal tissues and studied in populations but whose protein sequence has not been determined before. At the optimal pH of 10.0, recombinant hITPase hydrolyzed ITP, dITP, and xanthosine 5'-triphosphate to their respective monophosphates whereas activity with other nucleoside triphosphates was low. K(m) values for ITP, dITP, and xanthosine 5'-triphosphate were 0.51, 0.31, and 0.57 mm, respectively, and k(cat) values were 580, 360, and 640 s(-1), respectively. A divalent cation was absolutely required for activity. The gene encoding the hITPase cDNA sequence was localized by radiation hybrid mapping to chromosome 20p in the interval D20S113-D20S97, the same interval in which the ITPA inosine triphosphatase gene was previously localized. A BLAST search revealed the existence of many similar sequences in organisms ranging from bacteria to mammals. The function of this ubiquitous protein family is proposed to be the elimination of minor potentially mutagenic or clastogenic purine nucleoside triphosphates from the cell.

Amino Acid Sequence↗
PubMed2001

Expression and permeation properties of the K(+) channel Kir7.1 in the retinal pigment epithelium.

Bovine Kir7.1 clones were obtained from a retinal pigment epithelium (RPE)-subtracted cDNA library. Human RPE cDNA library screening resulted in clones encoding full-length human Kir7.1. Northern blot analysis indicated that bovine Kir7.1 is highly expressed in the RPE. Human Kir7.1 channels were expressed in Xenopus oocytes and studied using the two-electrode voltage-clamp technique. The macroscopic Kir7.1 conductance exhibited mild inward rectification and an inverse dependence on extracellular K+ concentration ([K+]o). The selectivity sequence based on permeability ratios was K+ (1.0) approximately Rb+ (0.89) > Cs+ (0.013) > Na+ (0.003) approximately Li+ (0.001) and the sequence based on conductance ratios was Rb+ (9.5) >> K+ (1.0) > Na+ (0.458) > Cs+ (0.331) > Li+ (0.139). Non-stationary noise analysis of Rb+ currents in cell-attached patches yielded a unitary conductance for Kir7.1 of approximately 2 pS. In whole-cell recordings from freshly isolated bovine RPE cells, the predominant current was a mild inwardly rectifying K+ current that exhibited an inverse dependence of conductance on [K+]o. The selectivity sequence based on permeability ratios was K+ (1.0) approximately Rb+ (0.89) > Cs+ (0.021) > Na+ (0.003) approximately Li+ (0.002) and the sequence based on conductance ratios was Rb+ (8.9) >> K+ (1.0) > Na+ (0.59) > Cs+ (0.23) > Li+ (0.08). In cell-attached recordings with Rb+ in the pipette, inwardly rectifying currents were observed in nine of 12 patches of RPE apical membrane but in only one of 13 basolateral membrane patches. Non-stationary noise analysis of Rb+ currents in cell-attached apical membrane patches yielded a unitary conductance for RPE Kir of approximately 2 pS. On the basis of this molecular and electrophysiological evidence, we conclude that Kir7.1 channel subunits comprise the K+ conductance of the RPE apical membrane.

Animals↗
PubMed2001

A preliminary model for predicting heavy metal contaminant loading from an urban catchment.

The toxicity of heavy metals to biota in urban catchments has been regarded as a very important non-point source pollution issue. Numerous studies on heavy metal pollution in urban receiving waters have found that metal transport by surface runoff is closely correlated to the partitioning of the metal forms between dissolved and particulate phases, where sediment plays an important role in the transport process. Sediment cycling on urban streets, metal binding form, and rainfall character in the catchment area are considered to be the key factors for metal transport. A preliminary model is developed based on these considerations. Starting from classical build-up and wash-off processes for the suspended sediment (SS) on the urban impervious surface, the model links the transport of suspended sediment to the transport of metal species. Monitoring data from a small highway catchment were used in the model development. A total of 47 rain events over 1 year were monitored intensively at short time intervals (5-10 min) for hydrological data, rainfall intensity, and stormwater quality. In developing the model, lead was used for the metal load prediction, as it has been a common fuel additive for urban transportation. Agreement between model results and monitoring data indicates that the model can be used in predicting metal load from impervious urban areas, such as streets and roadways, on a long-term basis.

Animals↗
PubMed2001

Inhibition of breast and brain cancer cell growth by BCCIPalpha, an evolutionarily conserved nuclear protein that interacts with BRCA2.

BRCA2 is a tumor suppressor gene involved in mammary tumorigenesis. Although important functions have been assigned to a few conserved domains of BRCA2, little is known about the longest internal conserved domain encoded by exons 14-24. We identified a novel protein, designated BCCIPalpha, that interacts with part of the internal conserved region of human BRCA2. Human BCCIP represents a family of proteins that are evolutionarily conserved, and contain three distinct domains: an N-terminus acidic domain (NAD) of 30-60 amino acids, an internal conserved domain (ICD) of 180-220 amino acids, and a C-terminus variable domain (CVD) of 30-60 amino acids. The N-terminal half of the human BCCIP ICD shares moderate homology with regions of calmodulin and M-calpain, suggesting that BCCIP may also bind Ca. Human cells express both a longer, BCCIPalpha, and a shorter, BCCIPbeta, form of the protein, which differ in their CVD. BCCIP is a nuclear protein highly expressed in testis. Although BCCIPbeta expression is relatively consistent in cancer cells, the expression of BCCIPalpha varies in cancer cell lines. The BCCIPalpha gene is located at chromosome 10q25.3-26.2, a region frequently altered in brain and other cancers. Furthermore, expression of BCCIPalpha inhibits breast and brain cancer cell growth, but fails to inhibit HT1080 cells and a non-transformed human skin fibroblast. These results suggest that BCCIPalpha is an important cofactor for BRCA2 in tumor suppression.

Amino Acid Sequence↗
PubMed2001

Surface-renewable cobalt(II) hexacyanoferrate-modified graphite organosilicate electrode and its electrocatalytic oxidation of thiosulfate.

Cobalt(II) hexacyanoferrate (CoHCF) was deposited on graphite powder by an in situ chemical deposition procedure and then dispersed into methyltrimethoxysilane-derived gels to prepare a surface-renewable CoHCF-modified electrode. The electrochemical behavior of the modified electrode in different supporting electrolyte solutions was characterized by cyclic voltammetry. In addition, square-wave voltammetry was employed to investigate the pNa-dependent electrochemical behavior of the electrode. The CoHCF-modified electrode showed a high electrocatalytic activity toward thiosulfate oxidation and could thus be used as an amperometric thiosulfate sensor.

Journal Article↗
PubMed2001

The molecular basis of O2-sensing and hypoxia tolerance in pheochromocytoma cells.

Hypoxia is a common environmental stimulus. However, very little is known about the mechanisms by which cells sense and respond to changes in oxygen. Our laboratory has utilized the PC12 cell line in order to study the biophysical and molecular response to hypoxia. The current review summarizes our results. We demonstrate that the O2-sensitive K(+) channel, Kv1.2, is present in PC12 cells and plays a critical role in the hypoxia-induced depolarization of PC12 cells. Previous studies have shown that PC12 cells secrete a variety of autocrine/paracrine factors, including dopamine, norepinephrine, and adenosine during hypoxia. We investigated the mechanisms by which adenosine modulates cell function and the effect of chronic hypoxia on this modulation. Finally, we present results identifying the mitogen- and stress-activated protein kinases (MAPKs and SAPKs) as hypoxia-regulated protein kinases. Specifically, we show that p38 and an isoform, p38gamma, are activated by hypoxia. In addition, our results demonstrate that the p42/p44 MAPK protein kinases are activated by hypoxia. We further show that p42/p44 MAPK is critical for the hypoxia-induced transactivation of endothelial PAS-domain protein 1 (EPAS1), a hypoxia-inducible transcription factor. Together, these results provide greater insight into the mechanisms by which cells sense and adapt to hypoxia.

Animals↗
PubMed2001

Identification of hypoxia-responsive genes in a dopaminergic cell line by subtractive cDNA libraries and microarray analysis.

Transplantation of dopamine-secreting cells harvested from fetal mesencephalon directly into the striatum has had limited success as a therapy for Parkinson's disease. A major problem is that the majority of the cells die during the first 3 weeks following transplantation. Hypoxia in the tissue surrounding the graft is a potential cause of the cell death. We have used subtractive cDNA libraries and microarray analysis to identify the gene expression profile that regulates tolerance to hypoxia. An improved understanding of the molecular basis of hypoxia-tolerance may allow investigators to engineer cells that can survive in the hypoxic environment of the brain parenchyma following transplantation.

Journal Article↗
PubMed2001

Reduction of functional N-methyl-D-aspartate receptors in neurons by RNase P-mediated cleavage of the NR1 mRNA.

One approach to studying the functional role of individual NMDA receptor subunits involves the reduction in the abundance of the protein subunit in neurons. We have pursued a strategy to achieve this goal that involves the use of a small guide RNA which can lead to the destruction of the mRNA for a specific receptor subunit. We designed a small RNA molecule, termed 'external guide sequence' (EGS), which binds to the NR1 mRNA and directs the endonuclease RNase P to cleave the target message. This EGS has exquisite specificity and directed the RNase P-dependent cleavage at the targeted location within the NR1 mRNA. To improve the efficiency of this EGS, an in vitro evolution strategy was employed which led to a second generation EGS that was 10 times more potent than the parent molecule. We constructed an expression cassette by flanking the EGS with self-cleaving ribozymes and this permitted generation of the specified EGS RNA sequence from any promoter. Using a recombinant Herpes simplex virus (HSV), we expressed the EGS in neurons and showed the potency of the EGS to reduce NR1 protein within neurons. In an excitotoxicity assay, we showed that expression of the EGS in cortical neurons is neuroprotective. Our results demonstrate the utility of EGSs to reduce the expression of any gene (and potentially any splice variant) in neurons.

Animals↗
PubMed2001

In vitro uptake of SCH 27899 (evernimicin) by rat alveolar macrophages.

The in vitro uptake of [(14)C]evernimicin ([(14)C]SCH 27899) by primary cultures of rat alveolar macrophages and hepatocytes was determined. Both cell populations exhibited linear rates of uptake. However, the initial rate of drug uptake by alveolar macrophages was about threefold higher than that by hepatocytes. These findings demonstrate that [(14)C]evernimicin is taken up by rat alveolar macrophages, supporting the likelihood that the drug is able to reach sites of infection.

Aminoglycosides↗
PubMed2001

FPL-64176 modifies pore properties of L-type Ca(2+) channels.

In addition to its known effects on Ca(2+) and Ba(2+) currents, the L-type Ca(2+) channel agonist FPL-64176 was found to affect channel function in isolated rat ventricular myocytes in the absence of Ca(2+), with other ions as current carriers through the channel. FPL-64176 induced Cd(2+) current through the L-type Ca(2+) channel, suggesting that certain selectivity properties had changed, perhaps indicative of a small change in pore structure. FPL-64176 slightly but significantly decreased the effectiveness of Co(2+) as a blocker of the channel. FPL-64176 also increased conductance through single L-type Ca(2+) channels recorded in the cell-attached configuration, from 71.9 +/- 11.6 to 94.1 +/- 8.3 pS, with Na(+) carrying the current at pH 9.0. At present it is uncertain whether FPL-64176 produces small alterations of a sole open state of the channel or whether it increases the prevalence of a second, higher conductance open state. These changes, particularly the conversion of Cd(2+) from a pure blocker to a permeant ion, may be of eventual help in discriminating among different models for Ca(2+) channel selectivity.

Animals↗
PubMed2000

Synergistic adhesive interactions and signaling mechanisms operating between platelet glycoprotein Ib/IX and integrin alpha IIbbeta 3. Studies in human platelets ans transfected Chinese hamster ovary cells.

This study investigates three aspects of the adhesive interaction operating between platelet glycoprotein Ib/IX and integrin alpha(IIb)beta(3). These include the following: 1) examining the sufficiency of GPIb/IX and integrin alpha(IIb)beta(3) to mediate irreversible cell adhesion on immobilized von Willebrand factor (vWf) under flow; 2) the ability of the vWf-GPIb interaction to induce integrin alpha(IIb)beta(3) activation independent of endogenous platelet stimuli; and 3) the identification of key second messengers linking the vWf-GPIb/IX interaction to integrin alpha(IIb)beta(3) activation. By using Chinese hamster ovary cells transfected with GPIb/IX and integrin alpha(IIb)beta(3), we demonstrate that these receptors are both necessary and sufficient to mediate irreversible cell adhesion under flow, wherein GPIb/IX mediates cell tethering and rolling on immobilized vWf, and integrin alpha(IIb)beta(3) mediates cell arrest. Moreover, we demonstrate direct signaling between GPIb/IX and integrin alpha(IIb)beta(3). Studies on human platelets demonstrated that vWf binding to GPIb/IX is able to induce integrin alpha(IIb)beta(3) activation independent of endogenous platelet stimuli under both static and physiological flow conditions (150-1800 s(-)(1)). Analysis of the key second messengers linking the vWf-GPIb interaction to integrin alpha(IIb)beta(3) activation demonstrated that the first step in the activation process involves calcium release from internal stores, whereas transmembrane calcium influx is a secondary event potentiating integrin alpha(IIb)beta(3) activation.

Adenosine Diphosphate↗
PubMed2000

Cytoskeletal regulation of the platelet glycoprotein Ib/V/IX-von willebrand factor interaction.

Shear-induced binding of von Willebrand factor (vWf) to the platelet glycoprotein (GP) Ib/V/IX complex plays a key role in initiating platelet adhesion and aggregation at sites of vascular injury. This study demonstrated that pretreating human platelets with inhibitors of actin polymerization, cytochalasin D or latrunculin B, dramatically enhances platelet aggregation induced by vWf. The effects of these inhibitors were specific to the vWf-GPIbalpha interaction because they enhanced vWf-induced aggregation of Glanzmann thrombasthenic platelets and Chinese hamster ovary (CHO) cells transfected with GPIb/V/IX. Moreover, cytochalasin D enhanced the extent of platelet aggregation induced by high shear stress (5000 s(-1)) and also lowered the shear threshold required to induce aggregation from 3000 s(-1) to as low as 500 s(-1). Studies of CHO cells expressing GPIbalpha cytoplasmic tail truncation mutants that failed to bind actin-binding protein-280 (deletion of residues 569-610 or 535-568) demonstrated that the linkage between GPIb and actin-binding protein-280 was not required for vWf-induced actin polymerization, but was critical for the enhancing effects of cytochalasin D on vWf-induced cell aggregation. Taken together, these studies suggest a fundamentally important role for the cytoskeleton in regulating the adhesive function of GPIb/V/IX.

Actin Cytoskeleton↗
PubMed2000

Complete genome sequence of Pseudomonas aeruginosa PAO1, an opportunistic pathogen.

Pseudomonas aeruginosa is a ubiquitous environmental bacterium that is one of the top three causes of opportunistic human infections. A major factor in its prominence as a pathogen is its intrinsic resistance to antibiotics and disinfectants. Here we report the complete sequence of P. aeruginosa strain PAO1. At 6.3 million base pairs, this is the largest bacterial genome sequenced, and the sequence provides insights into the basis of the versatility and intrinsic drug resistance of P. aeruginosa. Consistent with its larger genome size and environmental adaptability, P. aeruginosa contains the highest proportion of regulatory genes observed for a bacterial genome and a large number of genes involved in the catabolism, transport and efflux of organic compounds as well as four potential chemotaxis systems. We propose that the size and complexity of the P. aeruginosa genome reflect an evolutionary adaptation permitting it to thrive in diverse environments and resist the effects of a variety of antimicrobial substances.

Bacterial Proteins↗
PubMed2000

A small-molecule nitroimidazopyran drug candidate for the treatment of tuberculosis.

Mycobacterium tuberculosis, which causes tuberculosis, is the greatest single infectious cause of mortality worldwide, killing roughly two million people annually. Estimates indicate that one-third of the world population is infected with latent M. tuberculosis. The synergy between tuberculosis and the AIDS epidemic, and the surge of multidrug-resistant clinical isolates of M. tuberculosis have reaffirmed tuberculosis as a primary public health threat. However, new antitubercular drugs with new mechanisms of action have not been developed in over thirty years. Here we report a series of compounds containing a nitroimidazopyran nucleus that possess antitubercular activity. After activation by a mechanism dependent on M. tuberculosis F420 cofactor, nitroimidazopyrans inhibited the synthesis of protein and cell wall lipid. In contrast to current antitubercular drugs, nitroimidazopyrans exhibited bactericidal activity against both replicating and static M. tuberculosis. Lead compound PA-824 showed potent bactericidal activity against multidrugresistant M. tuberculosis and promising oral activity in animal infection models. We conclude that nitroimidazopyrans offer the practical qualities of a small molecule with the potential for the treatment of tuberculosis.

Animals↗
PubMed2000

Kinetics of two-liquid-phase Taxus cuspidata cell culture for production of Taxol.

The effects of different organic solvents (paraffin, organic acid, alcohol and ester) and their volumetric fractions on the cell growth and Taxol production were studied in two-liquid-phase and the two-stage culture. A kinetic model, incorporated the effects of the toxicity of organic solvents was developed for two-liquid-phase culture of Taxus cuspidata in the two-stage Taxol production. The results showed that the proposed kinetic model could fit the experimental data satisfactorily. The results also showed that Taxol production could reach the optimal value when 10-logP was in the range of 2 to 5 and the volumetric fraction of the organic solvents at the corresponding the highest Taxol production should be lower when 10-logP was high.

Journal Article↗
PubMed2000

DNA repair and recombination factor Rad51 is over-expressed in human pancreatic adenocarcinoma.

Molecular processes that could contribute to differences in chemo- and radioresistance include variations in DNA repair mechanisms. In mammalian cells, the product of the rad51 gene mediates DNA repair via homologous recombination. We describe that in contrast to conventional monolayer cell systems Rad51 protein accumulates to high-levels in three-dimensional cell culture models as well as in orthotopic xeno-transplants of human pancreatic cancer cells. Strikingly, over-expression of wild-type Rad51 was also found in 66% of human pancreatic adenocarcinoma tissue specimens. Functional analysis revealed that Rad51 over-expression enhances survival of cells after induction of DNA double strand breaks. These data suggest that perturbations of Rad51 expression contribute to the malignant phenotype of pancreatic cancer. Oncogene (2000).

Adenocarcinoma↗
PubMed2000

Adsorbed Layers of Ferritin at Solid and Fluid Interfaces Studied by Atomic Force Microscopy.

The adsorption of the iron storage protein ferritin was studied by liquid tapping mode atomic force microscopy in order to obtain molecular resolution in the adsorbed layer within the aqueous environment in which the adsorption was carried out. The surface coverage and the structure of the adsorbed layer were investigated as functions of ionic strength and pH on two different charged surfaces, namely chemically modified glass slides and mixed surfactant films at the air-water interface, which were transferred to graphite substrates after adsorption. Surface coverage trends with both ionic strength and pH indicate the dominance of electrostatic effects, with the balance shifting between intermolecular repulsion and protein-surface attraction. The resulting behavior is more complex than that seen for larger colloidal particles, which appear to follow a modified random sequential adsorption model monotonically. The structure of the adsorbed layers at the solid surfaces is random, but some indication of long-range order is apparent at fluid interfaces, presumably due to the higher protein mobility at the fluid interface. Copyright 2000 Academic Press.

Journal Article↗