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Biomedical subjects

L Yu

Publications and source records attributed to L Yu.

At least 577 records · Page 32Linked to original sources
PubMed1995

[Attachment of bacillus Calmette-Guerin to bladder cancer cells and the expression of interleukin-6 biological activity].

In order to elucidate the mechanisms of antitumor efforts of bacillus Calmette-Guerin (BCG), the effects of attachment of BCG to bladder carcinoma cell line EJ and the role of fibronectin in the in vitro experiment were studied. At the same time, the IL-6 biological activity in the medium of EJ cells was determined and the IL-6 biological activity in presence of BCG compared. The results indicated that BCG attached strongly to EJ cells, and the maximal attachment to the cells with BCG occurred 48 hours after culture. Fibronectin could significantly increase the attachment and not acclerate the proliferation of EJ cells. In the presence of fibronectin-conditioned medium, the maximal percentage of the tumor cells with attached BCG was 74.22%. Under this condition of experiment, there was IL-6 biological activity in the medium of EJ cells. The treatment of EJ cells with BCG did not regulate the expression of IL-6.

Cell Adhesion↗
PubMed1995

Effects of gypenosides on mouse splenic lymphocyte transformation and DNA polymerase II activity in vitro.

AIM: To study the effects of gypenosides (Gyp) on lymphocyte transformation and DNA polymerase II activity. METHODS: Lymphocyte transformation response was induced by concanavalin A and lipopolysaccharides respectively. The activity of DNA polymerase II and DNA synthesis were assayed with TTP and [3H]TdR incorporation respectively in mixed lymphocyte culture test. RESULTS: Gyp 2.5-20 mg L-1 enhanced splenic T- and B- cell transformation, increased the DNA synthesis and potentiated the activity of DNA polymerase II. However, Gyp > 40 mg L-1 showed contrary effects. CONCLUSION: Gyp regulated lymphocyte transformation and DNA synthesis by regulating DNA polymerase II activity.

Animals↗
PubMed1995

[Image analysis for intercellular adhesion molecule-1 expression in MRI/lpr mice: effects of Chinese herb medicine].

To clarify the role of intercellular adhesion molecule-1 (ICAM-1) on pathogenesis of autoimmune lupus nephritis in MRL/lpr mice and the effects of Chinese herb medicine (stragalin), a computer image analysis system was used to study immunodepositions of ICAM-1, immunoglobulins and C3 in renal tissue sections of the mice. ICAM-1 was found in the mesangial area and deposited along the glomerular capillary walls in MRL/lpr mice. The distribution intensity of ICAM-1, immunoglobulins and C3 were significantly decreased after treatment with stragalin in form of decoction per os in the mice. We found that ICAM-1 might play an important role in pathogenesis of autoimmune lupus nephritis in MRL/lpr mice and Chinese herb medicine has some inhibition effects on immunodepositions in renal tissue of MRL/lpr mice.

Animals↗
PubMed1995

Characterization of the cloned human mu opioid receptor.

Opioid drugs exert a wide spectrum of physiological and behavioral effects, including effects on pain perception, mood, motor control and autonomic functions. The effects of opioids are mediated via a family of membrane-bound receptors, of which the most extensively characterized are the mu, delta and kappa receptors. We have now cloned the human homolog of the mu opioid receptor and, in the present study, we have examined its pharmacological profile. The human mu receptor has high affinities for several alkaloids of high abuse potential as well as a variety of peptide and nonpeptide drugs characterized previously as mu-selective, but not delta- or kappa-selective. Most importantly, the human mu receptor has higher affinity for morphine and methadone than does the rat mu receptor, despite the fact that these receptors are 95% identical at the amino acid level. The labeling of the receptor by agonist was decreased by nonhydrolyzable GTP analogs and by pertussis toxin treatment of cells expressing the human mu receptor, consistent with the coupling of the receptor to guanine nucleotide binding proteins. The human mu receptor functionally couples to the inhibition of adenylyl cyclase in a stereospecific and naloxone-reversible manner. We have also investigated the distribution of mRNAs encoding the mu receptor in human brain by Northern analysis, which demonstrates the existence of multiple transcripts of 13.5, 11, 4.3 and 2.8 kb, which were highly expressed in the hypothalamus, thalamus and subthalamic nucleus, more moderately expressed in the amygdala and caudate nucleus and which demonstrated lowest levels of expression in the hippocampus, substantia nigra and corpus callosum.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

The human mu opioid receptor: modulation of functional desensitization by calcium/calmodulin-dependent protein kinase and protein kinase C.

Opioids are some of the most efficacious analgesics used in humans. Prolonged administration of opioids, however, often causes the development of drug tolerance, thus limiting their effectiveness. To explore the molecular basis of those mechanisms that may contribute to opioid tolerance, we have isolated a cDNA for the human mu opioid receptor, the target of such opioid narcotics as morphine, codeine, methadone, and fentanyl. The receptor encoded by this cDNA is 400 amino acids long with 94% sequence similarity to the rat mu opioid receptor. Transient expression of this cDNA in COS-7 cells produced high-affinity binding sites to mu-selective agonists and antagonists. This receptor displays functional coupling to a recently cloned G-protein-activated K+ channel. When both proteins were expressed in Xenopus oocytes, functional desensitization developed upon repeated stimulation of the mu opioid receptor, as observed by a reduction in K+ current induced by the second mu receptor activation relative to that induced by the first. The extent of desensitization was potentiated by both the multifunctional calcium/calmodulin-dependent protein kinase and protein kinase C. These results demonstrate that kinase modulation is a molecular mechanism by which the desensitization of mu receptor signaling may be regulated at the cellular level, suggesting that this cellular mechanism may contribute to opioid tolerance in humans.

Adolescent↗
PubMed1995

Soluble transferrin receptor as an index of iron status in Zaïrian children with malaria.

This study was designed to evaluate soluble transferrin receptor (sTfR) as an index of iron status in 0.5-16-year-old Zaïrian children: 17 with symptomatic malaria, 8 with asymptomatic malaria, and 15 controls. sTfR was also measured in 20 plasma samples obtained from iron sufficient laboratory employees. sTfR, haemoglobin and ferritin were measured by enzyme-immunoassay, cyanmethaemoglobin method, and radioimmunoassay respectively. Mean haemoglobin levels were lower and ferritin higher (P < 0.001) in children with clinical symptoms of malaria than in those without malaria, and they were intermediate in those with asymptomatic malaria. Mean sTfR concentrations were similar among the three groups of children and laboratory controls. There was a considerable overlap in sTfR concentrations between the three groups of children (1.8-10.2, 2.9-11.6 and 2.97-8.95 mg 1(-1) in symptomatic malaria, asymptomatic malaria and control groups, respectively) as well as laboratory controls (1.2-7.30 mg l-1). Despite the overlap, 6 children with malaria (24%) and one control child (6.7%) had sTfR concentrations above the highest concentration found in laboratory controls. No child had serum ferritin < 12 micrograms l-1 (suggestive of iron deficiency). As expected, sTfR negatively correlated with ferritin (r = -0.230) in the overall study population of children, and with haemoglobin in children with asymptomatic malaria (r = -0.943, P < 0.05), as well as in control children (r = -0.363). All children with sTfR above normal were also anaemic. Although the upper limit of normal sTfR concentration in healthy children is unknown, using the cut-off value of adults, we conclude that sTfR might be a more sensitive index of iron deficiency than serum ferritin in patients with malaria.

Adolescent↗
PubMed1995

A biochemical study on combined treatment of experimental silicosis with tetradrine-PVNO and tetradrine-QOHP in rats.

A better understanding is needed to explain the mechanism of therapeutic effect of combined use of tetradrine-PVNO and tetradrine-QOHP which play very important roles in treatment of silicosis. Blood prolidase (PLD), monamine oxidase (MAO) and plasminogen (PLG) in silicotic rats after treatment with tetradrine-PVNO or tetradrine-QOHP were measured. The values obtained were compared with the untreated silicotic rats. It was found that the silicotic rats that received tetradrine-PVNO showed significant increase in PLD and decrease in PLG, but no significant change in MAO. The PLD in plasma of silicotic rats that received tetradrine-QOHP were elevated significantly, but PLG and MAO did not change appreciably. These findings suggest that the combined use of tetradrine-PVNO and tetradrine-QOHP can accelerate the degradation of collagen in silicotic rats.

Alkaloids↗
PubMed1995

Study on nude mice inoculated with Mycobacterium leprae by multiple routes.

Immune-deficient nude mice were inoculated with nude mouse derived Mycobacterium leprae by multiple routes (intravenously, subcutaneously at the foot pads and ears). The results showed that these inoculated animals were capable of producing a great number of Mycobacterium leprae to a level 10 per gram of tissue and were detected histopathologically to have heavy lepromatous lesions. The dissemination of the infection was found particularly in sites with lower body temperature. The organisms have a partiality to striated muscles and peripheral nerves. The authors suggest that experimental leprosy in nude mice is a very useful tool for leprosy research, especially in countries without armadillos. Compared with the single-route inoculation reported previously, multiple-route inoculation is more available.

Animals↗
PubMed1995

Coordination of transcription factors, NF-Y and C/EBP beta, in the regulation of the mdr1b promoter.

The expression of mdr genes that encode P-glycoprotein, an integral membrane drug transporter, has been associated with the emergence of the multidrug resistance phenotype during treatment with cancer chemotherapeutic drugs. To understand the regulation of the mdr genes, the murine mdr1b promoter has been isolated and characterized in our laboratory. Three nuclear protein binding sites that interact with nuclear proteins present in both drug-sensitive and -resistant murine macrophage-like 1774.2 cells have been localized to the promoter. In this report, transcription factor NF-Y has been identified as binding to the Y-box sequence in site 1 and as a major factor in the regulation of the murine mdr1b promoter in the mouse adrenal cell line, Y-1, that endogenously expresses the mdr1b gene. The expression of CCAAT/enhancer binding protein beta (C/EBP beta) in Y-1 cells augmented mdr1b promoter activity and resulted in an increased level of mdr1b mRNA. The effect of C/EBP beta expression on mdr1b promoter activity was sensitive to mutations in the Y-box, suggesting that coordination of NF-Y with C/EBP beta is required for further activation of the mdr1b promoter. Our studies have indicated that NF-Y is a critical factor for the mdr1b promoter, and its coordination with other factors, such as C/EBP beta, could be an important mechanism involved in mdr1b gene expression.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

The major protein of GLUT4-containing vesicles, gp160, has aminopeptidase activity.

A glycoprotein of M(r) 160,000 (gp160) represents the major protein component of GLUT4-containing vesicles other than GLUT4 itself. These vesicles are the tissue-specific secretory-like microsomal structures that are responsible for insulin-dependent translocation of GLUT4 to the cell surface in fat and muscle cells. Our previous studies demonstrated that the expression of gp160 is also limited to fat and muscle tissues, where it is localized exclusively in GLUT4-containing vesicles, and thus, it represents a marker protein for insulin-activated glucose transport. We demonstrate here that gp160 has structural homology to aminopeptidase N and possesses aminopeptidase activity in vitro. Since aminopeptidase activity has also been found in a variety of secretory type vesicles from other tissues, it may be essential for the organization and functioning of secretory machinery in different cell types.

Adipocytes↗
PubMed1994

Differential binding domains of peptide and non-peptide ligands in the cloned rat kappa opioid receptor.

This study was to identify specific regions in kappa opioid receptors that accounted for binding selectivity of kappa ligands. Six chimeric mu/kappa receptors were constructed from cloned rat kappa and mu opioid receptors and transiently expressed in COS-1 cells. All six chimeric mu/kappa receptors bound [3H] diprenorphine with high affinities, indicating that these chimeras retain opioid receptor conformation. Binding affinities of three peptide ligands (dynorphin A, alpha-neo-endorphin, and dynorphin B) and three nonpeptide ligands (norbinaltorphimine, U50,488H, and U69,593) for chimeras were determined and compared to those for mu and kappa opioid receptors. The second extracellular loop and the adjoining C-terminal portion of the fourth transmembrane helix were essential for the high affinity binding of dynorphin A, alpha-neo-endorphin, and dynorphin B to the kappa receptor. The third extracellular loop and the sixth and seventh transmembrane helices played an important role in determining the selectivity of nor-binaltorphimine for the kappa over the mu receptor. U50,488H and U69,593 appeared to require the whole kappa receptor except the second extracellular loop to attain high affinity binding. Thus, the kappa opioid receptor has differential binding domains for peptide and non-peptide ligands.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1994

The secondary structure of the ets domain of human Fli-1 resembles that of the helix-turn-helix DNA-binding motif of the Escherichia coli catabolite gene activator protein.

The ets family of eukaryotic transcription factors is characterized by a conserved DNA-binding domain of approximately 85 amino acids for which the three-dimensional structure is not known. By using multidimensional NMR spectroscopy, we have determined the secondary structure of the ets domain of one member of this gene family, human Fli-1, both in the free form and in a complex with a 16-bp cognate DNA site. The secondary structure of the Fli-1 ets domain consists of three alpha-helices and a short four-stranded antiparallel beta-sheet. This secondary structure arrangement resembles that of the DNA-binding domain of the catabolite gene activator protein of Escherichia coli, as well as those of several eukaryotic DNA-binding proteins including histone H5, HNF-3/fork head, and the heat shock transcription factor. Differences in chemical shifts of backbone resonances and amide exchange rates between the DNA-bound and free forms of the Fli-1 ets domain suggest that the third helix is the DNA recognition helix, as in the catabolite gene activator protein and other structurally related proteins. These results suggest that the ets domain is structurally similar to the catabolite gene activator protein family of helix-turn-helix DNA-binding proteins.

Amino Acid Sequence↗
PubMed1994

Identification of the ubiquinol-binding site in the cytochrome bo3-ubiquinol oxidase of Escherichia coli.

The cytochrome bo3-ubiquinol oxidase, one of two ubiquinol oxidases in Escherichia coli, is a member of the heme-copper oxidase superfamily. The enzyme contains four protein subunits (I-IV) with apparent molecular masses of 58, 33, 22, and 17 kDa, respectively. Cytochrome bo3 catalyzes the 2-electron oxidation of ubiquinol and the reduction of molecular oxygen to water. Although the primary structures of all four subunits have been determined, the ubiquinol-binding site has not been investigated. The photoreactive radiolabeled azidoubiquinone derivative 3-[3H]azido-2-methyl-5-methoxy-6-geranyl-1,4-benzoquinone (azido-Q), which has been widely used in locating the ubiquinone-binding sites of other enzymes, was used to identify the subunit(s) involved in the binding of quinol to cytochrome bo3. When reduced by dithioerythritol, the azido-Q derivative functioned as a substrate with partial effectiveness, suggesting that azido-Q interacts with a legitimate quinol-binding site. When cytochrome bo3 was incubated with an 8-fold molar excess of azido-Q, illumination by UV light for 10 min resulted in a 50% loss of activity. The uptake of radiolabeled azido-Q by the oxidase complex upon illumination correlated with the photoinactivation. In the presence of the competitive inhibitor 2-heptyl-4-hydroxyquinoline or ubiquinol, the rate of azido-Q uptake and the loss of enzyme activity upon illumination decreased. Analysis of the distribution of radioactivity among the subunits after separation by SDS-polyacrylamide gel electrophoresis showed that subunit II was heavily labeled by azido-Q, but that the other subunits were not. This suggests that the ubiquinol-binding site of the cytochrome bo3 complex is located at least partially on subunit II.

Affinity Labels↗
PubMed1994

pH titration of the histidine residues of cyclophilin and FK506 binding protein in the absence and presence of immunosuppressant ligands.

Histidine residues in immunophilins, particularly His-126 of cyclophilin (CyP) and His-87 of the FK506 binding protein (FKBP), have been suggested to play important roles in ligand binding and peptidyl prolyl cis-trans isomerase (PPiase) catalysis. The charged states of the histidine residues in FKBP and CyP, which were characterized by their pKa values, have been determined in the absence and presence of the immunosuppressant ligands, ascomycin and cyclosporin A (CsA), respectively, by using a heteronuclear two-dimensional NMR method. Overall, the histidine residues in FKBP and CyP are very acidic with pKa values ranging from < or = 2.8 to 6.5, indicating that they are predominantly uncharged at physiological pH. To our knowledge, the pKa value of < or = 2.8 determined from this study is the lowest pKa reported for the free imidazole ring of the histidine residues in proteins. The abnormally acidic pKa's of His-25 in FKBP and His-54 in CyP could be explained by their highly positively charged environments. His-87 of FKBP, which is located in the FK506 binding pocket, was found to exist in two forms in free FKBP with pKa values of 5.9 and 6.5 for the major and minor forms, respectively. His-126, which is part of the CsA and substrate binding site, has a pKa of 6.3 in free CyP. The pKa values of these two histidine residues in the free proteins are higher than the pKa's obtained for the peptidyl prolyl cis-trans isomerase (PPiase) activity of these enzymes, indicating that the acid/base characters of His-87 of FKBP and His-126 of CyP are not essential in the PPiase catalysis. The hydrogen bonding of the histidine imidazole rings and the effect of hydrophobicity upon changes in pKa values are discussed.

Amino Acid Isomerases↗
PubMed1994

Protein ubiquinone interaction. Synthesis and biological properties of 5-alkyl ubiquinone derivatives.

For the investigation of the protein-ubiquinone interaction in the succinate-cytochrome c reductase region of the bovine heart mitochondrial electron transport chain, a series of 5-alkyl-substituted ubiquinone derivatives (5-R-Q0C10) were synthesized and characterized. Syntheses of 5-ethyl-Q0C10, 5-propyl-Q0C10, 5-isopropyl-Q0C10, and 5-butyl-Q0C10, were archived through radical coupling reactions between 2,3-dimethoxy-6-decyl-1,4-benzoquinone (5-H-Q0C10) and the corresponding alkanoyl peroxides. Although the spectral and redox properties of 5-R-Q0C10 are very similar to those of 5-methyl-2,3 dimethoxy-6-decyl-1,4-benzoquinone, the biological electron transfer efficiencies of these derivatives differ significantly. The reducibility of these derivatives by succinate, as measured with succinate-Q reductase and the oxidizability as measured by ubiquinol-cytochrome c reductase, decreased as the size of the substituents increased. 5-Ethyl-Q0C10 has about 50% of the activity of 5-methyl-2,3-dimethoxy-6-decyl-1,4-benzoquinone, whereas molecules with 5-alkyl groups of three or more carbon atoms are virtually inactive as electron acceptors for succinate-Q reductase. Reduced form of the derivative with no substituent at the 5-position, 5-H derivative is more effectively oxidized by ubiquinol-cytochrome c reductase than does the 5-methyl derivative, the native form. The oxidation of 5-H derivative is in a concentration-dependent manner at low concentrations but exhibits a substrate inhibition at higher concentrations. No such substrate inhibition is observed when other 5-substituted Q derivatives are used. 5-H derivative is a better electron acceptor for succinate-Q reductase than any other Q derivatives and does not show substrate inhibition, even at high concentrations. These results indicate that the binding environment of the benzoquinone ring in succinate-Q reductase is more specific than that of ubiquinol-cytochrome c reductase.

Alkylation↗
PubMed1994

Crystallization of mitochondrial cytochrome b-c1 complex from gel with or without reduced pressure.

Cytochrome b-c1 complex (ubiquinol-cytochrome c reductase) of beef heart mitochondria has been crystallized. Crystals grown in capillary tubes diffracted X-rays from a laboratory source to a resolution of 7 A and synchrotron radiation to a resolution of 4.5 A in the presence of mother liquor. However, the movement of crystals in the mother liquor makes data collection very difficult. Removal of the mother liquor from the crystals causes severe loss of diffraction quality. To circumvent these difficulties we have recently developed a method for crystallization of the cytochrome b-c1 complex from a gel. The sizes, shapes and diffraction qualities of crystals grown in gel approach those of crystals obtained from liquid. Preliminary experiments on a Xuong-Hamlin area detector indicate that these crystals have the symmetry of a body centered tetragonal space group with cell constants a = b = 157 A, c = 590 A. Assuming eight cytochrome b-c1 complex dimers per unit cell, the crystals have a solvent content of 70% (v/v). Under reduced pressure the crystallization time is significantly decreased. Although crystals obtained under reduced pressure are generally smaller, the shorter crystallization time provides an opportunity to explore more crystallization conditions.

Animals↗
PubMed1994

Functional coupling of the 5-HT2C serotonin receptor to G proteins in Xenopus oocytes.

The serotonin 2c (5-HT2C) receptor mediates its cellular effects by interacting with heterotrimeric guanine nucleotide binding proteins (G proteins). To characterize which G proteins are involved in functional coupling to the receptor, a mouse 5-HT2C receptor was expressed in Xenopus oocytes, and antisense oligoncleotides complementary to the mRNA sequence of the endogenous Xenopus G protein alpha subunits were used to inhibit G protein synthesis. Antisense oligonucleotide against the Xenopus G(o) alpha subunit inhibited the 5-HT2C receptor function, and coexpression of a rat G(o) alpha subunit reversed the inhibition by the anti-Xenopus G(o) oligonucleotide. Furthermore, antisense oligonucleotides against both the G(o) and Gi1 alpha subunits inhibited the electrophysiologic response induced by stimulation of the 5-HT2C receptor. These data suggest that both G(o) and Gi1 are involved in functional coupling of the 5-HT2C receptor to phospholipase C in Xenopus oocytes.

Animals↗