Search PubMed⌕ Search

Biomedical subjects

Y Xie

Publications and source records attributed to Y Xie.

At least 199 records · Page 11Linked to original sources
PubMed2000

The study on the expression of keratin proteins in pterygial epithelium.

PURPOSE: To evaluate the expression patterns of several keratin proteins in pterygial epithelium. METHODS: The proteins of K8, K10, K14, K16 and AE3 in the epithelium of 8 pterygia and 4 normal conjunctiva were detected using immunofluorescent staining. RESULTS: In pterygial epithelium, the staining patterns of 5 keratin proteins were different with normal conjunctiva. No staining of K8, K10 and K16 was detected in normal conjunctival epithelium, but in pterygial epithelium, K8 and K16 were present in full thickness and K10 was present in superficial cells. In normal conjunctiva, only base layer of epithelium showed positive staining with antibody of K14 and AE3 proteins, but they were present in the full thickness in pterygial epithelium and the antibody of AE3 protein stained the superficial cells heavily comparing with base cells. CONCLUSION: The abnormal expression of keratin proteins (K8, K10, K14, K16 and AE3) in pterygia indicates that the epithelial cells in pterygia are in the state of hyperproliferation and keratinization, which may be the cause of the abnormal tear function in patients with pterygia.

Adult↗
PubMed2000

Excitatory connections between spinal motoneurons in the adult rat.

OBJECTIVES: Dendro-dendritic and dendro-somatic projections are common between spinal motoneurons. We attempted to clarify whether there are functional connections through these projections. METHODS: Motoneurons were antidromically stimulated by the muscle nerve and recorded intracellularly to examine the direct interaction between them after the related dorsal roots had been cut. RESULTS: Excitatory connections, demonstrated by depolarizing potentials in response to muscle nerve stimulation, were found between motoneurons innervating the same muscle or synergistic muscles, but never between motoneurons innervating antagonistic muscles. These potentials were finely graded in response to a series of increasing stimuli and resistant to high frequency (50Hz) stimulation. CONCLUSIONS: These results indicate that excitatory connections, with certain specificity of spatial and temporal distribution, occur in the spinal motoneurons. It is also suggested that electrical coupling should be involved in these connections and this mechanism should improve the excitability of the motoneurons in the same column.

Action Potentials↗
PubMed2000

[Two-dimensional surface Raman imaging of a roughened iron electrode in saline solution].

By using a confocal microprobe Raman system and proper surface roughening procedure for iron, the pit corrosion behavior of bare iron electrode in 3.4% NaCl (saline solution) solution has been investigated. The surface-enhanced Raman scattering (SERS) spectra of the corrosion products due to the pit corrosion at positive potential was obtained with high ratio of signal to noise. The application of SERS technique has been extended successfully to the study of iron corrosion. The two-dimensional surface Raman imaging acquired at 660 cm-1 was obtained also with the utility of surface Raman image technique. Results show that different iron oxides should coexist in the pit corrosion region and the distribution of the corrosion products was not uniform.

Chemical Phenomena↗
PubMed2000

[Application of confocal microprobe Raman spectroscopy in the analysis of interfaces].

Confocal microprobe Raman spectroscopy has been applied to the study of liquid/gas and solid/liquid interfaces. With the help of the resonance Raman effect, the aggregation process of TSPP has been monitored at the liquid/gas interface using Raman spectroscopy, which is shown to have very different behavior compared with that in the bulk. The solution layer analysis has been performed in the interfacial region above a Pt electrode under reaction, and the solution composition is monitored in situ during the electrochemecial reaction. Taking the advantage of high spatial resolution of the confocal microscope, the surface enhanced Raman imaging has been performed on the electrodeposited gold surface.

Electrochemistry↗
PubMed1999

The E2-E3 interaction in the N-end rule pathway: the RING-H2 finger of E3 is required for the synthesis of multiubiquitin chain.

We dissected physical and functional interactions between the ubiquitin-conjugating (E2) enzyme Ubc2p and Ubr1p, the E3 component of the N-end rule pathway in Saccharomyces cerevisiae. The binding of the 20 kDa Ubc2p by the 225 kDa Ubr1p is shown to be mediated largely by the basic residue-rich (BRR) region of Ubr1p. However, mutations of the BRR domain that strongly decrease the interaction between Ubr1p and Ubc2p do not prevent the degradation of N-end rule substrates. In contrast, this degradation is completely dependent on the RING-H2 finger of Ubr1p adjacent to the BRR domain. Specifically, the first cysteine of RING-H2 is required for the ubiquitylation activity of the Ubr1p-Ubc2p complex, although this cysteine plays no detectable role in either the binding of N-end rule substrates by Ubr1p or the physical affinity between Ubr1p and Ubc2p. These results defined the topography of the Ubc2p-Ubr1p interaction and revealed the essential function of the RING-H2 finger, a domain that is present in many otherwise dissimilar E3 proteins of the ubiquitin system.

Amino Acid Sequence↗
PubMed1999

Lentiviral delivery of HIV-1 Vpr protein induces apoptosis in transformed cells.

Most current anticancer therapies act by inducing tumor cell stasis followed by apoptosis. HIV-1 Vpr effectively induces apoptosis of T cells after arrest of cells at a G(2)/M checkpoint. Here, we investigated whether this property of Vpr could be exploited for use as a potential anticancer agent. As a potentially safer alternative to transfer of genes encoding Vpr, we developed a method to efficiently introduce Vpr protein directly into cells. Vpr packaged into HIV-1 virions lacking a genome induced efficient cell cycle arrest and apoptosis. Introduction of Vpr into tumor cell lines of various tissue origin, including those bearing predisposing mutations in p53, XPA, and hMLH1, induced cell cycle arrest and apoptosis with high efficiency. Significantly, apoptosis mediated by virion-associated Vpr was more effective on rapidly dividing cells compared with slow-growing cells, thus, in concept, providing a potential differential effect between some types of tumor cells and surrounding normal cells. This model system provides a rationale and proof of concept for the development of potential cancer therapeutic agents based on the growth-arresting and apoptotic properties of Vpr.

Apoptosis↗
PubMed1999

Effect of mutation at valine 61 on the three-dimensional structure, stability, and redox potential of cytochrome b5.

To elucidate the role played by Val61 of cytochrome b(5), this residue of the tryptic fragment of bovine liver cytochrome b(5) was chosen for replacement with tyrosine (Val61Tyr), histidine (Val61His), glutamic acid (Val61Glu), and lysine (Val61Lys) by means of site-directed mutagenesis. The mutants Val61Tyr, Val61Glu, Val61His, and Val61Lys exhibit electronic spectra identical to that of the wild type, suggesting that mutation at Val61 did not affect the overall protein structure significantly. The redox potentials determined by differential pulse voltammetry were -10 (wild type), -25 (Val61Glu), -33 (Val61Tyr), 12 (Val61His), and 17 mV (Val61Lys) versus NHE. The thermal stabilities and urea-mediated denaturation of wild-type cytochrome b(5) and its mutants were in the following order: wild type > Val61Glu > Val61Tyr > Val61His > Val61Lys. The kinetics of denaturation of cytochrome b(5) by urea was also analyzed. The first-order rate constants of heme transfer between cytochrome b(5) and apomyoglobin at 20 +/- 0.2 degrees C were 0.25 +/- 0.01 (wild type), 0.42 +/- 0.02 (Val61Tyr), 0.93 +/- 0.04 (Val61Glu), 2.88 +/- 0.01 (Val61His), and 3.88 +/- 0.02 h(-)(1) (Val61Lys). The crystal structure of Val61His was determined using the molecular replacement method and refined at 2.1 A resolution, showing that the imidazole side chain of His61 points away from the heme-binding pocket and extends into the solvent, the coordination distances from Fe to NE2 atoms of two axial ligands are approximately 0.6 A longer than the reported value, and the hydrogen bond network involving Val61, the heme propionates, and three water molecules no longer exists. We conclude that the conserved residue Val61 is located at one of the key positions, the "electrostatic potential" around the heme-exposed area and the hydrophobicity of the heme pocket are determinant factors modulating the redox potential of cytochrome b(5), and the hydrogen bond network around the exposed heme edge is also an important factor affecting the heme stability.

Animals↗
PubMed1999

Regulation of intestinal epithelial brush border Na(+)/H(+) exchanger isoforms, NHE2 and NHE3, in C2bbe cells.

Until recently, studies to characterize the intestinal epithelial Na(+)/H(+) exchangers had to be done in nonepithelial, mutated fibroblasts. In these cells, detection of any Na(+)/H(+) exchange activity requires prior acid loading. Furthermore, most of these experiments used intracellular pH changes to measure NHE activity. Because changes in pH(i) only approximate Na(+)/H(+) exchange activity, and may be confounded by alterations in buffering capacity and/or non-NHE contributions to pH regulation, we have used (22)[Na] unidirectional apical to cell uptake to measure activities specific to NHE2 or NHE3. Furthermore, we performed these measurements under basal, nonacid-stimulated conditions to avoid bias from this nonphysiological experimental precondition. Both brush border NHEs, when expressed in the well-differentiated, intestinal villuslike Caco-2 subclone, C2bbe (C2), localize to the C2 apical domain and are regulated by second messengers in the same way they are regulated in vivo. Increases in intracellular calcium and cAMP inhibit both isoforms, while phorbol ester affects only NHE3. NHE2 inhibition by cAMP and Ca(++) involves changes to both K(Na) and V(max). In contrast, the same two second messengers inhibit NHE3 by a decrease in V(max) exclusively. Phorbol ester activation of protein kinase C alters both V(max) and K(Na) of NHE3, suggesting a multilevel regulatory mechanism. We conclude that NHE2 and NHE3, in epithelial cells, are basally active and are differentially regulated by signal transduction pathways.

Caco-2 Cells↗
PubMed1999

Expression of insulin-like growth factor-1 receptor in synovial sarcoma: association with an aggressive phenotype.

It is well known that insulin-like growth factor-1 receptor (IGF-1R) plays a crucial role in proliferation and survival of transformed cells. Overexpression of IGF-1R in certain tumors has been reported, but there is still little known about its importance in vivo. Here, we evaluated the IGF-1R levels in 35 human synovial sarcoma tumors by Western blot and reverse transcriptase-PCR. In 18 of these, IGF-1R was detectable by Western blot, whereas 17 were nondetectable. There was a significant association between the amount of receptor proteins and mRNA transcripts. Furthermore, we found that the IGF-1R Western blot-positive tumors were associated with a high incidence of lung metastases. Eleven of 18 (61%) developed metastases in the IGF-1R detectable group, compared to 3 of 17 (18%) in the nondetectable group (P = 0.01). Moreover, in the detectable group of IGF-1R, 12 of 18 (67%) exhibited a high tumor cell proliferative rate, compared to 5 of 16 (31%) in the nondetectable group (P = 0.04). On the other hand, no association was found between the IGF-1R and type of fusion gene transcript (SYT-SSX1 or SYT-SSX2). Our results suggest that expression of IGF-1R can underlie an aggressive phenotype in synovial sarcoma.

Adult↗
PubMed1999

The SYT-SSX1 variant of synovial sarcoma is associated with a high rate of tumor cell proliferation and poor clinical outcome.

Cytogenetically, synovial sarcoma (SS) is characterized by the translocation t(X;18)(p11.2;q11.2), resulting in a fusion between the SYT gene on chromosome 18 and SSX1 or SSX2 on the X chromosome and the formation of new chimeric genes, SYT-SSX1 or SYT-SSX2. We examined the potential clinical relevance of SYT-SSX1 and SYT-SSX2 fusion transcripts together with tumor proliferation. In a series of 33 patients with primary SS, the type of fusion transcript was assessed by reverse transcription-PCR and sequence analysis. The proliferation rate was analyzed using anti-Ki-67 antibodies. One case carrying an atypical transcript with a 57-bp insert was excluded, leaving 13 SYT-SSX1 and 19 SYT-SSX2 cases for analysis. The hazard ratio (with respect to metastasis-free survival for patients with SYT-SSX1 versus patients with SYT-SSX2 fusion transcripts was 7.4 (95% confidence interval, 1.5-36; log-rank P = 0.004). There was also an association with reduced overall survival for patients with SYT-SSX1 compared to patients with SYT-SSX2 (hazard ratio, 8.5; 95% confidence interval, 1.0-73; log-rank P = 0.02). The 5-year metastasis-free survival for patients with SYT-SSX1 was 42% versus 89% for patients with SYT-SSX2. There was a significant association between SYT-SSX1 and a high tumor proliferation rate (P = 0.02). We conclude that the findings suggest that the type of SYT-SSX fusion transcript determines the proliferation rate and is an important predictor of clinical outcome in patients with SS.

Adolescent↗
PubMed1999

gamma-Radiation Synthesis of the Nanocrystalline Semiconductors PbS and CuS.

The nanocrystalline semiconductors PbS and CuS were prepared by gamma-irradiation at room temperature in an ethanol system for the first time. Carbon disulfide was used as the sulfur source; lead acetate and copper chloride were used as metal ion sources. X-ray Powder Diffraction was used to characterize the products and Transmission Electron Microscopy to determine their morphology. The purity and compositions of the products were examined by X-ray photoelectron spectra. The photoluminescence property of as-prepared PbS was studied. A blue shift was observed in the PL spectra, indicating the quantum size effect on nanocrystalline PbS. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Structure of the agonist-binding sites of the Torpedo nicotinic acetylcholine receptor: affinity-labeling and mutational analyses identify gamma Tyr-111/delta Arg-113 as antagonist affinity determinants.

Photoaffinity labeling of the Torpedo nicotinic acetylcholine receptor (nAChR) with [3H]d-tubocurarine (dTC) has identified a residue within the gamma-subunit which, along with the analogous residue in delta-subunit, confers selectivity in binding affinities between the two agonist sites for dTC and alpha-conotoxin (alpha Ctx) MI. nAChR gamma-subunit, isolated from nAChR-rich membranes photolabeled with [3H]dTC, was digested with Staphylococcus aureus V8 protease, and a 3H-labeled fragment was purified by reversed-phase high-performance liquid chromatography. Amino-terminal sequence analysis of this fragment identified 3H incorporation in gamma Tyr-111 and gamma Tyr-117 at about 5% and 1% of the efficiency of [3H]dTC photoincorporation at gamma Trp-55, the primary site of [3H]dTC photoincorporation within gamma-subunit [Chiara, D. C., and Cohen, J. B. (1997) J. Biol. Chem 272, 32940-32950]. The Torpedo nAChR delta-subunit residue corresponding to gamma Tyr-111 (delta Arg-113) contains a positive charge which could confer the lower binding affinity seen for some competitive antagonists at the alpha-delta agonist site. To test this hypothesis, we examined by voltage-clamp analysis and/or by [125I]alpha-bungarotoxin competition binding assays the interactions of acetylcholine (ACh), dTC, and alpha Ctx MI with nAChRs containing gamma Y111R or delta R113Y mutant subunits expressed in Xenopus oocytes. While these mutations affected neither ACh equilibrium binding affinity nor the concentration dependence of channel activation, the gamma Y111R mutation decreased by 10-fold dTC affinity and inhibition potency. Additionally, each mutation conferred a 1000-fold change in the equilibrium binding of alpha Ctx MI, with delta R113Y enhancing and gamma Y111R weakening affinity. Comparison of these results with previous results for mouse nAChR reveals that, while the same regions of gamma- (or delta-) subunit primary structure contribute to the agonist-binding sites, the particular amino acids that serve as antagonist affinity determinants are species-dependent.

Amino Acid Sequence↗
PubMed1999

Synthesis, structural characterization and antitumor activity evaluations of copper complex with tetraazamacrocyclic ligand.

Cu (II) complex with 1,4,7,10-tetrakis(2-cyanoethyl-)-1,4,7,10-tetraazacyclododecane was prepared and characterized by X-ray diffraction. Four nitrogen atoms of macrocyclic ligand and oxygen atom of water molecule defined a tetragonal pyramidal polyhedron surrounding the central copper atom. Preliminary pharmacological tests showed that it had antitumor activity against P388 and BEL-7404 cell lines in vitro. Also it exhibited perturbation effects to K562 tumor cell lines at G0-G1 stage and further studies showed that it can cleave supercoiled DNA (pBR 322) to nicked and linear DNA in aerobic condition.

Antineoplastic Agents↗
PubMed1999

Regulatory role of mevalonate and N-linked glycosylation in proliferation and expression of the EWS/FLI-1 fusion protein in Ewing's sarcoma cells.

The Ewing's sarcoma cell line RD-ES, which carries the EWS/FLI-1 fusion gene, responded to the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor lovastatin with growth arrest. Replenishment of mevalonate (MVA) to the arrested cells restored cell growth. However, if tunicamycin (TM), which is an inhibitor of N-linked glycosylation, was present together with MVA the cells remained arrested, indicating that N-linked glycosylation is of importance for growth of Ewing's sarcoma cells. Inhibition of the biosynthesis of EWS/FLI-1 fusion protein by treatment with antisense oligonucleotides also led to growth arrest, suggesting that this protein is of importance for cell growth. We investigated whether MVA synthesis and N-linked glycosylation could be involved in regulation of the expression of the EWS/FLI-1 fusion protein, which in fact contains four potential sites for N-linked glycosylation. We found that inhibition of both HMG-CoA reductase and N-linked glycosylation drastically decreased the expression of the fusion protein, which mainly appears in the cell nuclei. There was no significant difference in the inhibitory effect on the fusion protein between the cytoplasm and the cell nuclei, indicating that the transport of the fusion protein to the cell nucleus is not affected. The fusion protein did not exhibit any gel electrophoretic mobility shift after treatment of the cells with lovastatin or TM, and it did not incorporate [3H]glucosamine. Therefore we can conclude that the fusion protein is not a glycoprotein. The decreased expression of the fusion protein following lovastatin or TM treatment was found to be due to a lowered stability of de novo-synthesized fusion protein. The down-regulation of the fusion protein was correlated to growth arrest. Furthermore, the kinetics between the expression of EWS/FLI-1 fusion protein and the initiation of DNA synthesis in MVA-stimulated cells were similar. Taken together, our data suggest that the regulatory role of N-linked glycosylation in the expression of the EWS/FLI-1 fusion protein is important for growth of Ewing's sarcoma cells. Possible mechanisms underlying TM-induced decrease in EWS/FLI-1 expression may involve the breaking of growth factor receptor pathways.

Amino Acid Sequence↗
PubMed1999

Structure, interaction and electron transfer between cytochrome b5, its E44A and/or E56A mutants and cytochrome c.

Site-directed mutagenesis has been used to produce variants of a tryptic fragment of bovine liver cytochrome b5 in which Glu44 and Glu56 are mutated to alanine. The reduction potentials measured by spectroelectrochemical titration (in the presence of 1 mM (Ru(NH3)6)3+, pH 7.0 and I=0.1 M) are 4.5, 6.0, 6.0 and 7.5 mV versus the standard hydrogen electrode (SHE) for the wild-type and E44A, E56A and E44/56A mutants of cytochrome b5, respectively. A comparative two-dimensional NMR study of cytochrome b5 and its E44/56A mutant in water solution has been achieved. Resonance assignments of side-chains have been completed successfully. The NMR results suggest that the secondary structures and global folding of the E44/56A mutant remain unchanged, but the mutation of both Glu44 and Glu56 to hydrophobic alanine may lead to the two helices containing mutated residues contracting towards the heme center. The inner mobility of the Gly42 approximately Glu44 segment in cytochrome b5 may be responsible for the difference of the binding mode between Glu44 and Glu56 with cytochrome c. The binding between cytochrome c and cytochrome b5 was studied by optical difference spectra of cytochrome c and variants of cytochrome b5. The association constants (KA) for the wild-type, E44A, E56A, and E44/56A mutants of cytochrome b5 with cytochrome c, are 4.70(+/-0. 10)x10(6) M-1, 1.88(+/-0.03)x10(6) M-1, 2.70(+/-0.13)x10(6) M-1, and 1.14(+/-0.05)x10(6) M-1, respectively. This is indicative that both Glu44 and Glu56 are involved in the complex formation between cytochrome b5 and cytochrome c. The reduction of horse heart ferricytochrome c by recombinant ferrocytochrome b5 and its mutants has been studied. The rate constant of the electron transfer reaction between ferricytochrome c and wild-type ferrocytochrome b5 (1.074(+/-0.49)x10(7) M-1 s-1) is higher than those of the mutant protein E44A (8.98(+/-0.20)x10(6) M-1 s-1), E56A (8.76(+/-0. 39)x10(6) M-1 s-1), and E44/56A (8.02(+/-0.38)x10(6) M-1 s-1) at 15 degreesC, pH 7.0, I=0.35 M. The rate constants are strongly dependent on ionic strength and temperature. These studies, by means of a series of techniques, provide conclusive results that the interaction between cytochrome b5 and cytochrome c is electrostatically guided, and, more importantly, that both Glu44 and Glu56 participate in the electron transfer reaction.

Alanine↗
PubMed1999

Estimating unobserved reflection intensities in Laue diffraction by the maximum-entropy method.

In protein crystallography, the use of low-resolution reflections is important in defining the molecular mask and polypeptide backbone. However, in Laue data collection, the loss of low-resolution reflection data (>2dmin) can be as high as 40-50%, even after the deconvolution of multiples. To estimate the reflection intensities that are not recorded in data collection, a new method is presented based on maximizing the entropy of the Patterson function subject to the constraints imposed by the intensities of the observed reflections. The method has been tested with Laue diffraction data from hen egg-white lysozyme. All unobserved reflections within 5 A resolution were estimated, and their inclusion in the electron-density-map calculation significantly improved the connectivity. This method could also be applied to improve the completeness of monochromatic data.

Animals↗