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N Xu

Publications and source records attributed to N Xu.

At least 73 records · Page 4Linked to original sources
PubMed1998

Profound inhibition of cardiomotor neurons in the rat rostral ventrolateral medulla by nociceptin (orphanin FQ).

Nociceptin (orphanin FQ), the newly discovered endogenous ligand for the opioid receptor like-1 receptor, profoundly inhibited spontaneous discharges of neurons in the rostral ventrolateral medulla (RVLM) in rat brain slices. This inhibition was concentration-dependent (0.3, 1, 3 and 10 nM) and insensitive to pharmacological blockade of traditional opioid receptors by naloxone. Moreover, nociceptin injected into the RVLM (10 nM, 0.1 microliter) in anesthetized rats decreased arterial blood pressure and heart rate by 31% and 15%, respectively. The data obtained in vitro and in vivo suggest that nociceptin has powerful effects on the RVLM neurons involving central control of cardiovascular activity. The negative regulation of cardiovascular activity by nociceptin is not mediated through typical naloxone-sensitive opioid receptors.

Animals↗
PubMed1998

Hetero-oligomerization-dependent binding of pig oocyte zona pellucida glycoproteins ZPB and ZPC to boar sperm membrane vesicles.

The zona pellucida surrounding the pig oocyte contains two Mr 55,000 glycoproteins, pZPB and pZPC, which are orthologues of mouse zona proteins ZP1 and ZP3, respectively. We previously reported that isolated boar sperm membrane vesicles possess high affinity binding sites for partially purified pZPB, but not pZPC. Interestingly, co-incubation experiments also implicated pZPB-pZPC complexes as potential ligands. We now report that when depleted of a minor pZPC contaminant by size exclusion chromatography, pZPB lacks independent binding activity. In solid phase binding assays employing immobilized boar sperm membranes, pZPB failed to compete with biotin-(pZPB+pZPC) probe, and biotin-labeled pZPB yielded negligible binding. However, when co-incubated with pZPC prior to the binding assays, pZPB acted as a potent competitor, and biotin-labeled pZPB exhibited high affinity, saturable binding. Binding activity was attributed to pZPB-pZPC heterocomplexes, which were detected in co-incubation mixtures by size exclusion chromatography and Western blot analysis. In the pig, therefore, sperm membranes possess a zona-binding protein with high affinity sites for pZPB-pZPC heterocomplexes, but not free glycoprotein subunits. Consequently, associative interactions between zona molecules can contribute toward both the assembly of the zona matrix and generation of ligands important for sperm-zona interactions.

Animals↗
PubMed1998

A broader role for AU-rich element-mediated mRNA turnover revealed by a new transcriptional pulse strategy.

The widespread occurrence of AU-rich elements (AREs) in mRNAs encoding proteins with diversified functions and synthesized under a vast variety of physiological conditions suggests that AREs are involved in finely tuned and stringent control of gene expression. Thus it is important to investigate the regulation of ARE-mediated mRNA decay in a variety of mammalian cells in different physiological states. The tetracycline (Tet)-regulatory promoter system appears appropriate for these investigations. However, we found that efficient degradation of mRNAs bearing different AREs cannot be observed simply by blocking constitutive transcription from the Tet-regulated promoter with Tet, possibly due to saturation of the cellular decay machinery. In addition, deadenylation kinetics and their relationship to mRNA decay cannot be adequately measured under these conditions. To overcome these obstacles we have developed a new strategy that employs the Tet-regulated promoter system to achieve a transient burst of transcription that results in synthesis of a population of cytoplasmic mRNAs fairly homogeneous in size. Using this new system we show that ARE-destabilizing function, necessary for down-regulating mRNAs for cytokines, growth factors and transcription factors, is maintained in quiescent or growth-arrested cells as well as in saturation density-arrested NIH 3T3 cells. We also demonstrate that the ARE-mediated decay pathway is conserved between NIH 3T3 fibroblasts and K562 erythroblasts. These in vivo observations support a broader role for AREs in the control of cell growth and differentiation. In addition, we observed that there is a significant difference in deadenylation and decay rates for beta-globin mRNA expressed in these two cell lines. Deadenylation and decay of beta-globin mRNA in K562 cells is extraordinarily slow compared with NIH 3T3 cells, suggesting that the increased stability gained by beta-globin mRNA in K562 cells is mainly controlled at the deadenylation step. Our strategy for studying mammalian mRNA turnover now permits a more general application to different cell lines harboring the Tet-regulated system under various physiological conditions.

3T3 Cells↗
PubMed1998

Corrosion behavior of copper in a copper bearing intrauterine device in the presence of indomethacin.

As an improvement to the use of the copper bearing intrauterine device, indomethacin has been introduced to reduce the incidence of bleeding after insertion of the device. The effects of indomethacin on copper corrosion were studied in vitro in simulated uterine fluid. Electrochemical polarization resistance measurements indicated that indomethacin powder slightly increased the corrosion rate of copper if pH of the fluid was not under control and it did not change the corrosion rate if pH was adjusted daily to maintain some constancy. The experimental results for medication by indomethacin-releasing Silastic were basically the same as those with powdered indomethacin. X-ray diffraction showed that only cuprous oxide was formed on the copper substrated surface and that indomethacin did not affect the corrosion products. As scanning electron microscopy demonstrated, however, in the presence of indomethacin the oxide particles formed were found to be more coarse and dense than in the absence of indomethacin.

Body Fluids↗
PubMed1998

Effect of stainless steel on corrosion behavior of copper in a copper-bearing intrauterine device.

Some copper-bearing intrauterine devices (Cu-IUDs) consist of pure copper and stainless steel. Corrosion of copper in the Cu-IUD was anticipated to be affected by galvanic action due to electrical contact between these two metals. Electrochemical measurements were carried out in physiological saline with or without indomethacin, which was introduced for bleeding control. In the copper/stainless steel couple, the open-circuit potential of stainless steel was found to play a decisive role. In most cases, when stainless steel was in the passive state and acted as the cathode, the contact accelerated copper corrosion. In addition, the area ratio of stainless steel to copper altered copper corrosion behavior. The larger the area of stainless steel, the greater the acceleration of copper corrosion. It was noted that the stainless steel surface might be activated due to improper handling of the IUD. In this case, copper became the cathode of the couple and its corrosion was suppressed.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1998

Association of vitamin K-dependent coagulation proteins and C4b binding protein with triglyceride-rich lipoproteins of human plasma.

The triglyceride (TG) concentration in plasma is an independent risk factor for coronary heart disease. There is evidence that TG-rich lipoprotein (TGRLP), ie, chylomicrons (CMs), chylomicron remnants (CMRs), and VLDLs associate with factor VII and prothrombin and that the association enhances a platelet factor Xa-mediated prothrombin activation when the CM-prothrombin complex is exposed to platelets. In this study, we examined the association of the vitamin K-dependent coagulation factors VII, IX, X, and prothrombin, as well as the anticoagulation protein C and its cofactor protein S, in plasma lipoproteins obtained from human fasting and postprandial plasma. We also analyzed some other proteins that are related to the coagulation system but not to vitamin K-dependent proteins, including factor V, serum amyloid P component (SAP), C4b binding protein (C4BP), and thrombomodulin (TM), and as a control, Ig G. Human TGRLP (d < 1.006 kg/L), LDL (d = 1.006 to 1.063 kg/L), and HDL (d = 1.063 to 1.210 kg/L) were separated from normal subjects both in fasting and 2 to 3 hours after the ingestion of a meal containing 100 g fat. The different coagulation proteins, SAP, C4BP, TM, and Ig G were determined by SDS-polyacrylamide gel electrophoresis combined with Western blotting, using specific polyclonal or monoclonal antibodies, and were visualized by peroxidase staining. All the vitamin K-dependent proteins associate with TGRLP in both fasting and postprandial plasma, but not with LDL or HDL. Factor V, SAP, TM, and Ig G were not found in any lipoprotein classes. C4BP, which is a regulatory protein of the classic pathway of the complement system and which binds protein S in vivo to regulate blood coagulation, was present in TGRLP, especially postprandial, but not in LDL or HDL. The amounts of prothrombin, protein S, and C4BP in postprandial TGRLP were larger than those in fasting TGRLP. Vitamin K-dependent procoagulation and anticoagulation proteins, as well as C4BP, could be associated with TGRLP in vivo. If the association enhances prothrombin activation, this effect may thus be counteracted by simultaneous binding of protein S.

Adult↗
PubMed1998

[The relation between DNA replication error and clinicopathological features of colorectal carcinoma].

OBJECTIVE: To study the relationship between DNA replication error and development of colorectal carcinoma (CRC). METHODS: Silver staining PCR-SSCP and denatured polyacrylamide gel electrophoresis methods were used to detect microsatellites instability (MSI) at 4 loci on chromosome 2, 5, 17 in paraffin embedded specimens of 60 CRC and their paired normal tissue. If replication errors (RER) were found at 2 or more loci, then a diagnosis of RER+ was made. RESULTS: RER+ was observed in 19/60 CRC, among which 7 cases had CRC family history. According to Amsterdam criteria, 4 were diagnosed as HNPCC(hereditary nonpolyposis colorectal cancer), of which 3 cases were RER+. The ratio of RER+ in HNPCC (75%) was significantly higher than that among sporadic CRC (28.5%). Most RER+ CRC have features of poorly differentiated adenocarcinoma (P < 0.01), tendency for right side involvement of the colon (P < 0.05) and a higher proportion with family history (P < 0.05). Rate of Dukes A and B stage higher than C and D stage (P < 0.05). CONCLUSION: RER+ is a relatively common molecular event in CRC. RER+ CRC and RER- CRC have different clinicopathological features and behavior.

Adenocarcinoma↗
PubMed1997

Tissue uptake and interconversion of plasma unesterified 14C linoleic acid in the guinea pig.

Part of the arachidonic acid (20:4, n - 6) pools in the gastrointestinal tract and blood forming tissues may be formed by local interconversion of linoleic acid (18:2, n - 6) taken up as a free fatty acid from blood. This study examined the rate of uptake and interconversion of unesterified 14C-18:2 by different tissues in young guinea pigs. The clearance rate of 14C-18:2 was fast, and the initial half-life was 6.3 s. The retention of 14C in tissue lipids was 1.6-1.8% g-1 in the liver, 0.4% g-1 in stomach, 0.7% g-1 in small intestine, 0.2% g-1 in colon, 0.4% g-1 in bone marrow and 0.7% g-1 in spleen. Autoradiographic localization of 3H-18:2 under light microscope demonstrated that most of the 3H radioactivity of the gastrointestinal tract was in the mucosa, in both villus and crypt cells. In bone marrow smears, a high density of silver grains was found in megakaryocytes. The percent of 14C in delta6 desaturase products was higher in gastrointestinal tract, heart, lung, bone marrow and spleen than in liver. The ratio of 14C-20:3/14C-20:4 formation in most tissues was high, and a notable finding being a lower rate of 20:4 formation from plasma free 18:2 in the liver, (170 pmol min-1) than in the gastrointestinal tract (428 pmol min-1) and bone marrow (1203 pmol min-1). The local interconversion of 18:2 into delta6 desaturase products is thus an important source of 20:4 in these organs in guinea pigs.

Animals↗
PubMed1997

Structural characterization of an abnormally cross-linked muropeptide dimer that is accumulated in the peptidoglycan of methicillin- and cefotaxime-resistant mutants of Staphylococcus aureus.

Laboratory mutants of Staphylococcus aureus strain ATCC 8325 (27S) selected for increased minimal inhibitory concentration (MIC) values to methicillin and cefotaxime showed increased rates of cell wall turnover and detergent-induced autolysis in virtual parallel with the increasing MIC for the antibiotic. Also in parallel with the increasing MICs for the particular antibiotic used in the selection was the gradual accumulation of an unusual muropeptide in the peptidoglycan of the mutants, muropeptide 12, which is a minor component of the cell wall of the parental strain. Analysis of muropeptide 12, its peptide derivative, and its lysostaphin degradation products by high pressure liquid chromatography, Edman degradation, and mass spectrometry suggests that muropeptide 12 is a dimer in which the two monomeric components are interlinked by two pentaglycyl cross-bridges, thus generating a 14-member macrocyclic ring structure. This unusual cross-linked structure may be the product of the abnormal activity of penicillin-binding protein 2 which has grossly reduced antibiotic binding capacity in the mutant staphylococci.

Amino Acid Sequence↗
PubMed1997

The small GTP-binding protein Rho links G protein-coupled receptors and Galpha12 to the serum response element and to cellular transformation.

Receptors coupled to heterotrimeric G proteins can effectively stimulate growth promoting pathways in a large variety of cell types, and if persistently activated, these receptors can also behave as dominant-acting oncoproteins. Consistently, activating mutations for G proteins of the Galphas and Galphai2 families were found in human tumors; and members of the Galphaq and Galpha12 families are fully transforming when expressed in murine fibroblasts. In an effort aimed to elucidate the molecular events involved in proliferative signaling through heterotrimeric G proteins we have focused recently on gene expression regulation. Using NIH 3T3 fibroblasts expressing m1 muscarinic acetylcholine receptors as a model system, we have observed that activation of this transforming G protein-coupled receptors induces the rapid expression of a variety of early responsive genes, including the c-fos protooncogene. One of the c-fos promoter elements, the serum response element (SRE), plays a central regulatory role, and activation of SRE-dependent transcription has been found to be regulated by several proteins, including the serum response factor and the ternary complex factor. With the aid of reporter plasmids for gene expression, we observed here that stimulation of m1 muscarinic acetylcholine receptors potently induced SRE-driven reporter gene activity in NIH 3T3 cells. In these cells, only the Galpha12 family of heterotrimeric G protein alpha subunits strongly induced the SRE, while Gbeta1gamma2 dimers activated SRE to a more limited extent. Furthermore, our study provides strong evidence that m1, Galpha12 and the small GTP-binding protein RhoA are components of a novel signal transduction pathway that leads to the ternary complex factor-independent transcriptional activation of the SRE and to cellular transformation.

3T3 Cells↗
PubMed1997

Multiple isoforms of GAGA factor, a critical component of chromatin structure.

The GAGA transcription factor of Drosophila melanogaster is ubiquitous and plays multiple roles. Characterization of cDNA clones and detection by domain- specific antibodies has revealed that the 70-90 kDa major GAGA species are encoded by two open reading frames producing GAGA factor proteins of 519 amino acids (GAGA-519) and 581 amino acids (GAGA-581), which share a common N-terminal region that is linked to two different glutamine-rich C-termini. Purified recombinant GAGA-519 and GAGA-581 proteins can form homomeric complexes that bind specifically to a single GAGA sequence in vitro. The two GAGA isoforms also function similarly in transient transactivation assays in tissue culture cells and in chromatin remodeling experiments in vitro . Only GAGA-519 protein accumulates during the first 6 h of embryogenesis. Thereafter, both GAGA proteins are present in nearly equal amounts throughout development; in larval salivary gland nuclei they colocalize completely to specific regions along the euchromatic arms of the polytene chromosomes. Coimmunoprecipitation of GAGA-519 and GAGA-581 from crude nuclear extracts and from mixtures of purified recombinant proteins, indicates direct interactions. We suggest that homomeric complexes of GAGA-519 may function during early embryogenesis; both homomeric and heteromeric complexes of GAGA-519 and GAGA-581 may function later.

Amino Acid Sequence↗
PubMed1997

The p53 tumor suppressor targets a novel regulator of G protein signaling.

Heterotrimeric G proteins transduce multiple growth-factor-receptor-initiated and intracellular signals that may lead to activation of the mitogen-activated or stress-activated protein kinases. Herein we report on the identification of a novel p53 target gene (A28-RGS14) that is induced in response to genotoxic stress and encodes a novel member of a family of regulators of G protein signaling (RGS) proteins with proposed GTPase-activating protein activity. Overexpression of A28-RGS14p protein inhibits both Gi- and Gq-coupled growth-factor-receptor-mediated activation of the mitogen-activated protein kinase signaling pathway in mammalian cells. Thus, through the induction of A28-RGS14, p53 may regulate cellular sensitivity to growth and/or survival factors acting through G protein-coupled receptor pathways.

Amino Acid Sequence↗
PubMed1997

Cancer risk after renal transplantation in Japan.

Excess of cancer in patients receiving renal transplantation is well-known in Western countries, but information in Japan remains limited. Our study examined whether excess risk is found in patients receiving renal transplantation in Japan. Between 1970 and 1995, 1155 males and 589 females underwent renal transplantation in 6 hospitals, and a total of 12,982 person-years of observation was accumulated. Malignancies developed in 2.6% of patients; O/E ratio was 2.78. Median interval from renal transplantation to tumor development was 58 months. The interval in the patients receiving medication with cyclosporine-A (CyA) (median, 42.5 months) was significantly shorter than that with non-CyA (median, 95.5 months). Median age at the diagnosis of malignancy was 40 years, which is much younger than that in the general population. Relative risk was highest in renal cancer, followed by thyroid cancer, malignant lymphoma and uterine cancer. A distribution of malignancies was different from that reported from Western countries. These findings showed the excess risk of malignancies in Japan with renal transplants, especially in male patients, similar to that observed in Western countries, though the types of malignancy were different.

Adolescent↗
PubMed1997

Structural characterization of peptidoglycan muropeptides by matrix-assisted laser desorption ionization mass spectrometry and postsource decay analysis.

In this study we report the development of matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS)-based methods for the structural characterization of muropeptides derived from peptidoglycan. Prior to analysis, peptidoglycan samples were subjected to enzymatic digestion with muramidase and the resulting muropeptides were purified by HPLC. A new matrix, 5-chloro-2-mercaptobenzothiazole, was employed for the MALDI-MS analysis. The results have demonstrated that sub-picomole to femtomole detection can be achieved in both positive mode and negative mode, allowing unambiguous determination of the molecular masses of monomeric and oligomeric muropeptides. Structural information from monomeric muropeptides was obtained by further postsource decay (PSD) analysis. Fragmentation patterns in positive mode and negative mode PSD were complementary for the elucidation of the peptide chain sequence. Lysostaphin digestion was also incorporated with MALDI mass mapping analysis for determination of peptide chain cross-linking patterns of muropeptide oligomers from Staphylococcus aureus strains.

Amino Acid Sequence↗
PubMed1997

Accumulation of sulfoquinovosyl-1-O-dihydroxyacetone in a sulfolipid-deficient mutant of Rhodobacter sphaeroides inactivated in sqdC.

The biosynthesis of the sulfolipid sulfoquinovosyl diacylglycerol in the purple bacterium Rhodobacter sphaeroides requires at least four genes:sqdA, sqdB, sqdC, and sqdD. As part of our strategy aimed at the elucidation of the function of the different sqd gene products, we insertionally inactivated sqdC of R. sphaeroides. The resulting sqdC null mutant showed only a 90% reduction in sulfolipid content. Apparently, the sqdC gene product is required for optimal sulfolipid biosynthesis, but either catalyzes no essential reaction in the pathway or can be functionally replaced to a certain extent by a different protein. The mutant accumulated a 35S-labeled compound that was purified to homogeneity from cell extracts. Matrix-assisted laser desorption mass spectrometry and nuclear magnetic resonance spectroscopy provided conclusive structural evidence to identify the compound as alpha-D-sulfoquinovosyl-1-O-dihydroxyacetone that exists in two interconvertible, keto and hemiacetal forms. Incubation of wild-type protein extracts with the labeled compound did not result in the incorporation into sulfolipid as would be expected for an intermediate of the pathway. Based on our results we propose that the sqdC gene product mediates the substrate specificity of the UDP-sulfoquinovose:diacylglycerol sulfoquinovosyltransferase that is encoded by sqdD and that catalyzes the final reaction of sulfolipid biosynthesis.

Bacterial Proteins↗
PubMed1997

Intralipid rapidly attenuates the agonist-induced activation of rat platelets in vitro.

This study examines the uptake of Intralipid by rat platelets and the effect of Intralipid on platelet activation and platelet lipid composition in vitro. 3H-cholesteryl hexadecyl ether labeled Intralipid (3H-Intralipid) was incubated with rat platelets for up to 4 hours. A significant uptake of 3H-Intralipid occurred as indicated by the increase of 3H in platelets with time. Addition of unlabelled Intralipid or chyle chylomicrons decreased the uptake of labeled Intralipid by the platelets, whereas Intralipid had less effect on the uptake of 14C linoleic acid labeled chylomicrons. Incubation of rat platelets with Intralipid caused a dose dependent inhibition of ADP, collagen and thrombin induced platelet aggregation and serotonin release. Both an attenuated response and a reduction of platelet cholesterol contents was seen within 10 minutes. Intralipid thus causes a rapid, dose- dependent inhibition of agonist-induced activation of rat platelets in vitro. This inhibition is linked to a loss of cholesterol and to an uptake of Intralipid particles by the platelets.

Animals↗
PubMed1997

The pathway connecting m2 receptors to the nucleus involves small GTP-binding proteins acting on divergent MAP kinase cascades.

m1 and m2 receptors are traditionally linked to tissue specific functions performed by fully differentiated cells. However, these receptors have been also implicated in growth stimulation. The mechanisms whereby these receptors regulate proliferative signaling pathways are still poorly understood. Furthermore, pharmacological evidence suggest that many growth promoting agents act on Gi coupled receptors, but there is no formal proof that induction of DNA-synthesis results from decreased intracellular levels of cAMP. In our laboratory, we have used the expression of ml and m2 receptors as a model for studying proliferative signaling through G protein-coupled receptors. Currently available evidence suggest that these receptors signal to distinct members of the MAP kinase superfamily, MAP kinase and JNK, through betagamma subunits of heterotrimeric G proteins acting, respectively, on a Ras and Rac1 dependent pathway.

Animals↗