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Biomedical subjects

Z Xu

Publications and source records attributed to Z Xu.

At least 559 records · Page 31Linked to original sources
PubMed1993

[Immunohistochemical localization of the epidermal growth factor receptor in mouse testes].

Immunohistochemical localization of the epidermal growth factor (EGF) receptor in mouse testes was studied. The biotin-avidin DCS system indirect immunofluorescent technique was used with mouse anti-human A431 cell EGF receptor monoclonal antibody 176 in vivo. Punctate fluorescence was detected in the cytoplasm of spermatogonia and Sertoli cells in the seminiferous tubules, while no fluorescence was observed in other seminiferous epithelial cells. Strong fluorescence was seen in Sertoli cells in vitro. These results suggest that spermatogonia and Sertoli cells are the target cells of epidermal growth factor.

Animals↗
PubMed1993

Detection of tumor suppressor gene and oncogene in So-Rb50 human retinoblastoma cell line.

Retinoblastoma (Rb) is the most common malignant cancer of eye. So-Rb50 is the first Rb cell line established in China in 1988. It has passed to the 387th passage now. We collected cells of the 327th passage of SO-Rb50, purified its genomic DNA and detected it with Rb and c-myc cDNA probes respectively (normal human white blood cells DNA was the control). We found the Rb gene was deleted while c-myc gene was amplified three times. This provides a basis for further study of the regulation of tumor development and tumor reversal with this cell line in vitro.

Eye Neoplasms↗
PubMed1992

Marked increase in nitric oxide synthase mRNA in rat dorsal root ganglia after peripheral axotomy: in situ hybridization and functional studies.

Using in situ hybridization, we studied nitric oxide (NO) synthase (EC 1.14.23.-) mRNA in lumbar dorsal root ganglia after peripheral transection of the sciatic nerve in rats. The effect of the NO synthase inhibitor N omega-nitro-L-arginine methyl ester on the nociceptive flexor reflex was also studied in axotomized rats. Nerve section induced a dramatic increase in number of NO synthase mRNA-positive cells in the ipsilateral dorsal root ganglia. In some of these cells the peptides galanin and/or vasoactive intestinal polypeptide and/or neuropeptide Y were also strongly up-regulated. Intravenous administration of nitro-L-arginine methyl ester blocked spinal hyperexcitability at much lower dosages in axotomized than in normal animals. The results suggest involvement of NO in the function of lumbar sensory neurons, especially after axotomy, perhaps preferentially at peripheral sites.

Amino Acid Oxidoreductases↗
PubMed1992

Evidence for upregulation of galanin synthesis in rat glial cells in vivo after colchicine treatment.

The localization of galanin (GAL) and GAL mRNA was studied in rat brain after colchicine or vinblastine treatment using in situ hybridization and immunohistochemistry. GAL-like immunoreactivity was found in glial cells, presumably activated microglia, in the cortex, caudate nucleus and septum, mainly on the injection side. GAL mRNA expression was found in small cells in the same areas with an overlapping distribution, including the adjacent white matter. The results suggest that the glial cells initiate synthesis of the peptide GAL in response to intraventricular injection of high doses of the 2 mitosis inhibitors.

Animals↗
PubMed1992

Structure of polymerizable lipid bilayers. V. Synthesis, bilayer structure and properties of diacetylenic ether and ester lipids.

Four diacetylenic phosphatidylcholines (PC's) have been synthesized and the structures of bilayers of these lipids have been determined at low resolution by low-angle X-ray diffraction. The PC's all have 18-carbon chains but differ with respect to the ether/ester linkage at the sn-1 and sn-2 positions and the relative position of the diacetylene moiety: diester-PC (1): 1,2-bis(octadeca-4',6'-diynoyl)-sn-glycero-3-phosphocholine diester-PC (2): 1-(octadeca-4',6'-diynoyl)-2-(octadeca-5',7'-diynoy l)-sn- glycero-3-phosphocholine diester-PC (3): 1,2-bis(octadeca-8',10'-diynoyl)-sn-glycerol-3-phosphocholin e diether-PC (4): 1-O-(octadeca-4',6'-diynyl)-2-O-(octadeca-5",7"-din yl)-sn- glycero-3-phosphocholine Only (1) exhibits the typical bilayer profile, whereas (2), (3) and (4) show evidence of interdigitation and/or significant disorder. Only (1) polymerized effectively upon illumination with 254 nm light, turning deep blue in seconds, indicating the formation of long, well-ordered polydiacetylenic structures. Liposomes of these derivatives were tested for permeability by osmotic swelling. Polymerized liposomes of (1) underwent osmotic swelling with urea, glycerol, and acetamide more rapidly than did liposomes of stearoyl-oleoyl-PC, but the initial rates of osmotic swelling of polymerized liposomes of (1) were 3-10-times lower than those of unpolymerized liposomes of (1). Blue polymerized multilayer samples of (1) exhibited an irreversible thermochromic transition to red at approx. 40 degrees C. Differential scanning calorimetry with liposome suspensions of (1) revealed an endotherm at 28.3 degrees C with a transition enthalpy of 40 J/g. PC (1) is a potentially useful diacetylenic lipid which exhibits facile, complete polymerization and a bilayer thickness comparable to that of biomembrane lipids.

Calorimetry, Differential Scanning↗
PubMed1992

Interactions of the heme-regulated eIF-2 alpha kinase with heat shock proteins in rabbit reticulocyte lysates.

Inhibition of protein synthesis in rabbit reticulocyte lysates occurs in response to a variety of conditions including heme deficiency, addition of oxidants, and heat stress. The inhibition of translation is due to the activation of a heme-regulated protein kinase (HRI) which specifically phosphorylates the alpha-subunit of the eukaryotic initiation factor eIF-2. In this report, immunoadsorption with monoclonal antibodies (mAbs) and Western blot analysis were used to investigate the interaction of HRI, the 90-kDa heat shock protein (hsp 90), hsp 70, and the EC1 antigen in rabbit reticulocyte lysates under protein synthesizing conditions. The data indicate that hsp 90, hsp 70, and the EC1 antigen interact with HRI in rabbit reticulocyte lysate. The EC1 antigen is a protein that has been demonstrated to be associated with several steroid hormone receptor-hsp 90 complexes and reacts with the KN 382/EC1 mAb (EC1). The association of HRI with hsp 90 and the EC1 antigen in the reticulocyte lysate was found to be dependent on the presence of hemin at a concentration of 5 microM or higher; little HRI was coadsorbed by the 8D3 anti-hsp 90 mAb or the EC1 mAb in the absence of hemin. Hsp 70 remains associated with HRI in the absence of hemin, suggesting that hsp 90 and 70 may bind to HRI at different sites. The immunological properties of the hsp 70 associated with HRI indicate that it may be the constitutively express heat shock cognate protein (hsc 73). The results suggest that the association of HRI with hsp 90 and the EC1 antigen may be in a dynamic equilibrium, in which complex formation is either facilitated or stabilized by the presence of hemin, and supports the notion that these proteins in conjunction with hsp 70 may play a role in regulating HRI activity or activation in situ.

Animals↗
PubMed1992

Polyunsaturated fatty acid incorporation into plasmalogens in plasma membrane of glioma cells is preceded temporally by acylation in microsomes.

Plasmalogens (1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine) are major phospholipids in many tissues and cells, particularly of neural origin. Using cultured C6 glioma cells and subcellular fractions isolated on Percoll gradients we investigated selectivity for esterification of several polyunsaturated fatty acids (PUFA) in the sn-2 position of plasmalogens compared to [1-14C]hexadecanol, representative of de novo synthesis of the ether-linked sn-1 position. In whole cells at a final concentration of 105 microM PUFA, 2-4 nmol plasmalogen/mg protein was labeled in 4 h and 10-14 nmol in 24 h, representing 8-15% and 35-50%, respectively, of initial plasmalogen mass. Incorporation of label from hexadecanol was lower than PUFA incorporation (20:5(n-3) greater than 20:4(n-6) greater than 18:3(n-3) much greater than 18:2(n-6)) suggesting deacylation-reacylation at the sn-2 position. Plasmalogens accounted for 50% of total cell ethanolamine phospholipids and 75% in plasma membrane. Using a novel, improved method for extraction of subcellular fractions containing Percoll, plasma membrane also was enriched in plasmalogen relative to microsomes (107.4 +/- 5.2 vs. 40.0 +/- 2.9 nmol/mg protein). Selectivity for esterification at the sn-2 position of plasmalogens with respect to chain length and unsaturation of the fatty acyl chain was similar in both subcellular fractions and reflected that of whole cells. Labeling of plasma membrane with PUFA and fatty alcohol lagged behind that of microsomes. Chase experiments in cells prelabeled with [1-14C]18:3(n-3) for 2 h showed no significant reduction of label in plasmalogen of any subcellular fraction although accumulation of label in the microsomal fraction was slowed initially. Reduction of plasmalogen label (40-50%) did occur in microsomes and plasma membrane when cells prelabeled for 24 h were switched to chase medium with or without chase fatty acid. Our data suggest that esterification of PUFA to plasmalogen may occur at the endoplasmic reticulum with subsequent translocation to plasma membrane resulting in accumulation of relatively stable pools of plasmalogen that are not readily accessible for deacylation-reacylation exchange with newly appearing PUFA. Alternatively, deacylation-reacylation may occur in a more stable phospholipid pool within the plasma membrane but would involve a slower process than at the endoplasmic reticulum.

Acylation↗
PubMed1992

Crystal structure of recombinant murine adipocyte lipid-binding protein.

Adipocyte lipid-binding protein (ALBP) is the adipocyte member of an intracellular hydrophobic ligand-binding protein family. ALBP is phosphorylated by the insulin receptor kinase upon insulin stimulation. The crystal structure of recombinant murine ALBP has been determined and refined to 2.5 A. The final R factor for the model is 0.18 with good canonical properties. Crystalline ALBP has a conformation which is essentially identical to that of intestinal fatty acid binding protein and myelin P2 protein. Although the crystal structure is of the apo- form, a cavity resembling that in other family members is present. It contains a number of bound and implied unbound water molecules and shows no large obvious portal to the external milieu. The cavity of ALBP, which by homology is the ligand-binding site, is formed by both polar and hydrophobic residues among which is tyrosine 19. Y19 is phosphorylated by the insulin receptor kinase as described in the accompanying paper [Buelt, M. K., Xu, Z., Banaszak, L. J., & Bernlohr, D. A. (1992) Biochemistry (following paper in this issue)]. By comparing ALBP with the earlier structural results on intestinal fatty acid binding protein, it is now possible to delineate conserved amino acids which help form the binding site in this family.

Amino Acid Sequence↗
PubMed1992

Structural and functional characterization of the phosphorylated adipocyte lipid-binding protein (pp15).

A substrate for the insulin receptor kinase in 3T3-L1 adipocytes has previously been identified as the adipocyte lipid-binding protein (ALBP, also known as aP2 or p15). We have characterized the effect of tyrosyl phosphorylation on ALBP structure and ligand-binding properties. Phosphorylated ALBP (phospho-ALBP) was isolated by a combination of gel filtration, anion exchange chromatography, and immunoaffinity chromatography on anti-phosphotyrosine agarose. Circular dichroic spectroscopy indicated that the phosphoprotein was similar in structure to native ALBP. Phospho-ALBP exhibited a slight decrease in calculated alpha-helical content which was compensated for by an increase in beta-sheet structure. The wavelength yielding maximum tryptophan fluorescence was unaltered by phosphorylation (334 +/- 1 nm). However, the concentration of guanidine HCl yielding 50% denaturation was 1.43 M for ALBP and 0.92 M for phospho-ALBP. The delta Goapp was 3.87 and 3.25 kcal mol-1 for ALBP and phospho-ALBP, respectively, suggesting that phosphorylation destabilized the protein. To assess the binding characteristics of the phosphoprotein, a long-chain fatty acid affinity column was synthesized to which native ALBP specifically bound. In contrast, phospho-ALBP showed little or no affinity for the column. Furthermore, phosphorylation virtually abolished binding of the fluorescent fatty acid analogue 12-(9-anthroyloxy)oleic acid. Fatty acid binding activity was recovered (approximately 60%) upon dephosphorylation with protein tyrosine phosphatase. The structural studies, coupled with the crystal structure of the apoprotein, indicate that the dramatic reduction in binding affinity is likely a result of steric hindrance in the binding cavity or of electrostatic interactions of the phosphoryl group with the fatty acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Micronucleus formation in peripheral-blood lymphocytes from smokers and the influence of alcohol- and tea-drinking habits.

In recent years, studies on the genotoxic effects of smoking and its modifying factors have been widely followed with interest. In this report, frequencies of micronuclei (MNF) in peripheral-blood lymphocytes in 220 healthy smokers have been detected by the micronucleus test by finger-skin puncture, which needs only 1 to 2 drops of peripheral blood. On the basis of analysis of matched-pair data, the modifying effects of alcohol and tea are discussed. Our results show that (I) smoking significantly increases MNF in lymphocytes as compared with healthy non-smokers (p less than 0.01); (2) alcohol significantly increases MNF in smokers (p less than 0.01); (3) tea decreases MNF induced by smoking (p less than 0.01). Therefore, the anti-carcinogenic role of tea merits further study.

Adult↗
PubMed1992

Polymerase chain reaction-based comprehensive procedure for the analysis of the mutation spectrum at the hypoxanthine-guanine phosphoribosyltransferase locus in Chinese hamster cells.

We have established a comprehensive procedure based on the polymerase chain reaction (PCR) to analyze the molecular spectrum of mutations at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in Chinese hamster cells. The procedure includes direct sequencing of PCR-amplified hprt cDNA for locating point mutations in the expressed coding sequences, multiplex PCR amplification of the hprt exons for screening large deletions, and direct sequencing of PCR-amplified hprt exons and their flanking regions for detecting intronic mutations resulting in mRNA splicing errors. Using this procedure, we have identified different types of mutations among a representative collection of spontaneous and induced HPRT-deficient Chinese hamster cell mutants. This procedure is simple, rapid, accurate, and practical for a comprehensive study of the mutation spectrum in a large number of HPRT-deficient Chinese hamster cell mutants.

Animals↗
PubMed1992

Virus-reactive and autoreactive T cells are accumulated in cerebrospinal fluid in multiple sclerosis.

Elevated numbers of B cells--plasma cells secreting antibodies to measles and mumps virus, and to myelin associated glycoprotein (MAG), one of several putative myelin autoantigens--have previously been reported in cerebrospinal fluid (CSF) from patients with multiple sclerosis (MS), while it is unknown if corresponding T cell reactivities occur. We have defined the T cell reactivities to measles and mumps virus and to MAG in an immunospot assay which is based on the detection of secretion of interferon-gamma (IFN-gamma) by single cells upon stimulation with specific antigen in short term cultures. Patients with MS had higher numbers of MAG-reactive T cells in blood compared to controls, while no differences were observed for measles or mumps virus-reactive T cells. In CSF, elevated numbers of MAG-reactive T cells and also of measles- and mumps-reactive T cells were found in patients with MS compared to other neurological diseases. A strong accumulation of antigen-reactive T cells was observed in the MS patients' CSF compared to blood. The magnitude of these T cell reactivities did not correlate with clinical MS variables. The T cell repertoire in MS thus includes, besides myelin basic protein, proteolipid protein and myelin oligodendrocyte glycoprotein, also MAG and, in addition, measles and mumps virus. It is not clear whether these T cell reactivities accumulated in the CSF have importance for the pathogenesis of MS or reflect phenomena secondary to myelin damage, or result from both these alternatives.

Adolescent↗
PubMed1992

Spatial buffering of extracellular potassium by Müller (glial) cells in the toad retina.

We examined the role of Müller (glial) cells in buffering light-evoked changes in extracellular K+ concentration, [K+]o, in the isolated retina of the toad, Bufo marinus. We found evidence for two opposing Müller cell current loops that are generated by a light-evoked increase in [K+]o in the inner plexiform layer. These current loops, which are involved in the generation of the M-wave of the electroretinogram (ERG), prevent the accumulation of K+ in the inner plexiform layer by transporting K+ both to vitreous and to distal retina. In addition, under dark-adapted conditions, we found evidence for a Müller cell current loop that is generated by a light-evoked decrease in [K+]o in the receptor layer. This current loop, which is involved in the generation of the slow PIII component of the ERG, helps to buffer the light-evoked decrease in [K+]o throughout distal retina by transporting K+ from vitreous. The spatial buffering fluxes of K+ can be abolished by blocking Müller cell K+ conductance with 200 microM Ba2+. The separate contributions of the M-wave and slow PIII currents to Müller cell spatial buffering were isolated by various pharmacological treatments that were designed to enhance or suppress light-evoked activity in specific retinal neurons. Our results show that Müller cell K+ currents not only buffer light-evoked increases in [K+]o, but also buffer light-evoked decreases in [K+]o, and thereby diminish any deleterious effects upon neuronal function that could arise in response to large changes in [K+]o in the plexiform layers. Moreover, our results emphasize that spatial buffering currents generate many components of the electroretinogram.

Animals↗
PubMed1992

PII component of the toad electroretinogram.

1. The PII component of the electroretinogram (ERG) is comprised of the b-wave and the DC component and is thought to reflect bipolar cell activity. Although the b-wave is generated in large part by a K+/Müller cell mechanism, the origin of the DC component is unclear. In this paper we detail our investigation of the origin of the DC component. We hypothesize that the DC component is generated by a K+/Müller cell mechanism identical to that involved in b-wave generation. 2. We studied the ERG in the dark-adapted, isolated retina preparation of the toad, Bu fo marinus. We used K+ ion-sensitive microelectrodes (K+ISM), as well as conventional intra- and extracellular microelectrodes, to record [K+]o changes, the vitreal ERG, and Müller cell responses. 3. We used the excitatory amino acid receptor agonist N-methyl-DL-aspartate (NMDLA) to inhibit light responses of third-order neurons and thereby eliminate most of the ERG M-wave. In the absence of the M-wave, the ERG consisted of PII and PIII. We then superfused the retina with a solution containing both kynurenic acid (KYN) and 2-amino-4-phosphonobutyric acid (APB), which together inhibit all retinal responses proximal to the photoreceptors. In the presence of KYN and APB, the ERG consisted only of PIII. Using digital subtraction, we reconstructed PII. To our knowledge, this is the first report of the isolation of a PII component in the ERG of a nonmammalian species. 4. Using K+ISMs, we recorded the distal K+ changes in the outer plexiform layer (OPL).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

[Immunogold dot assay for diagnosis of early pregnancy].

Two monoclonal antibodies anti-HCG were prepared. One anti-alpha HCG was directly labeled with colloidal gold, and the other, anti-beta HCG was coated on nitrocellulose membrane as dot. After determination of optimal conditions of the system, an immunogold dot blot assay for testing HCG in urine sample was established. The sensitivity of the assay was 50 mIU HCG/ml, corresponding to the content of HCG in the urine of women about 30 days after last menstruation. The assay has been evaluated in clinical trial. All the testing results accorded with clinical diagnosis. No false positive results appeared. This simple, rapid and stable assay is ideal for women to diagnose early pregnancy at home.

Antibodies, Monoclonal↗