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N Xu

Publications and source records attributed to N Xu.

At least 55 records · Page 3Linked to original sources
PubMed1999

NMR structure and mutagenesis of the inhibitor-of-apoptosis protein XIAP.

The inhibitor-of-apoptosis (IAP) family of proteins, originally identified in baculoviruses, regulate programmed cell death in a variety of organisms. IAPs inhibit specific enzymes (caspases) in the death cascade and contain one to three modules of a common 70-amino-acid motif called the BIR domain. Here we describe the nuclear magnetic resonance structure of a region encompassing the second BIR domain (BIR2) of a human IAP family member, XIAP (also called hILP or MIHA). The structure of the BIR domain consists of a three-stranded antiparallel beta-sheet and four alpha-helices and resembles a classical zinc finger. Unexpectedly, conserved amino acids within the linker region between the BIR1 and BIR2 domains were found to be critical for inhibiting caspase-3. The absence or presence of these residues may explain the differences in caspase inhibition observed for different truncated and full-length IAPs. Our data further indicate that these residues may bind to the active site and that the BIR domain may interact with an adjacent site on the enzyme.

Amino Acid Sequence↗
PubMed1999

Electrospray ionization-mass spectrometry study of the interaction of cisplatin-adducted oligonucleotides with human XPA minimal binding domain protein.

Nucleotide excision repair (NER) is the process responsible for eliminating most ultraviolet (UV) radiation damage from DNA, as well as base alterations caused by a variety of mutagens. The xeroderma pigmentosum group A complementing protein (XPA) is believed to be involved in the early step of NER by recognizing and binding damaged DNA. Recent work has suggested that electrospray ionization-mass spectrometry (ESI-MS) can be an effective tool for the study of protein-DNA complexes. We have used ESI-Fourier transform ion cyclotron resonance (FTICR) mass spectrometry to examine the cisplatin-adducted oligonucleotide and its interaction with the human XPA minimal binding domain (XPA-MBD). High-resolution FTICR experiments of the binding products showed that both double-stranded damaged 20-mer and double-stranded undamaged 20-mer formed 1:1 noncovalent complexes with XPA-MBD. A 2:1 binding stoichiometry complex was also observed between XPA-MBD and double-stranded damaged 20-mer. Competitive binding experiments indicated only slightly preferential binding of XPA-MBD with the double-stranded damaged 20-mer compared to the undamaged 20-mer. The results demonstrate that ESI-FTICR mass spectrometry provides a fast and efficient approach for characterizing weak protein-DNA interactions such as the binding between XPA-MBD and a 20-mer oligonucleotide system.

Base Sequence↗
PubMed1999

Inhibition of cardiovascular activity following microinjection of novel opioid-like neuropeptide nociceptin (orphanin FQ) into the rat rostral ventrolateral medulla.

Nociceptin (orphanin FQ), the newly discovered endogenous ligand for the novel opioid receptor-like 1 receptor, has been initially found to participate in pain modulation. In this study, centrally mediated cardiovascular actions of this peptide were investigated in the alpha-chloralose/urethane-anesthetized rats. We found that bilateral injection of nociceptin (10 nmol) into the rostral ventrolateral medulla (RVLM), wherein injection of excitatory amino acid dl-homocysteic acid (3 nmol) induced typical pressor responses, significantly reduced arterial blood pressure and heart rate by -32% and -15%, respectively. Reduction of blood pressure and heart rate in response to intra-RVLM injection of nociceptin was dose-dependent with a threshold dose being 3 nmol. Pretreatment with the selective nociceptin receptor antagonist, [Phe1psi(CH2-NH)Gly2]NC(1-13)NH2 (10 nmol), into the RVLM abolished the nociceptin-induced cardiovascular inhibition. In contrast, non-selective opioid receptor antagonist, naloxone (10 nmol), did not modify the hypotension and bradycardia induced by nociceptin, even though naloxone at the same dose prevented reduction of blood pressure and heart rate induced by intra-RVLM injection of methionine-enkephalin (3 nmol). Both [Phe1psi(CH2-NH)Gly2]NC(1-13)NH2 and naloxone injection alone had no significant effect on baseline blood pressure and heart rate. These data suggest that the newly discovered opioid-like neuropeptide nociceptin in the CNS exert powerful influence on hemodynamic activity by affecting the RVLM neurons. This influence is inhibitory in nature, which may not be active in normal physiological conditions. Moreover, the cardiovascular effects of nociceptin were mediated by activation of specific nociceptin receptors rather than typical naloxone-sensitive opioid receptors.

Animals↗
PubMed1999

Persistent delivery of factor IX in mice: gene therapy for hemophilia using implantable microcapsules.

Severe hemophilia B is a life-threatening, life long condition caused by absence of or defective coagulation factor IX. Gene therapy could provide an alternative treatment to repeated injection of plasma-derived concentrate or recombinant factor IX. We have previously described the use of implantable microcapsules containing recombinant myoblasts to deliver human factor IX in mice. This study reports the generation of improved myoblast-specific expression vectors. Mouse myoblast clones transfected with the various vectors secreted factor IX in vitro, at rates between 70 and 1000 ng/10(6) cells/day. The recombinant myoblast clones were then encapsulated and implanted into mice. Immunocompetent mice implanted with encapsulated myoblasts had up to 65 ng of factor IX per milliliter in their plasma for up to 14 days, after which antibodies to human factor IX became detectable, and this coincided with decreased factor IX in mouse plasma. In immunodeficient mice, however, factor IX delivery was maintained at a constant level for at least 6 weeks (end of experiment). Interestingly, the highest-secreting myoblast clone in vitro did not deliver the highest level of hFIX in vivo. This discrepancy observed between performance in vitro and in vivo may have important implications for the development of gene therapy protocols based on recombinant cells.

Animals↗
PubMed1999

The nociceptin receptor-mediated inhibition of the rat rostral ventrolateral medulla neurons in vitro.

The recently available antagonist selective for novel nociceptin receptor, [Phe1 psi(CH2-NH)Gly2]NC(1-13)NH2, was utilized in this study to verify specificity of nociceptin receptor in mediating the nociceptin-induced inhibition of electrical activity of neurons in the rostral ventrolateral medulla of rat brain slices. Perfusion of nociceptin (10 nM) considerably reduced spontaneously firing frequency of the medullary neurons. Co-perfusion of [Phe1 psi(CH2-NH)Gly2]NC(1-13)NH2 (10 microM) completely blocked the nociceptin-induced depression of the neuronal activity. Blocking effect of [Phe1 psi(CH2-NH)Gly2]NC(1-13)NH2 was concentration-dependent. However, the nociceptin antagonist did not modify basal, and opioid peptide enkephalin-depressed, firing rates of the neurons. In contrast to [Phe1 psi(CH2-NH)Gly2]NC(1-13)NH2, the non-selective opioid receptor antagonist naloxone (10 microM) failed to affect the nociceptin inhibition even though naloxone at a lower concentration (1 microM) readily blocked enkephalin-induced depression of the neuronal activity. These data indicate that the nociceptin-induced inhibition of spontaneous discharge of the rostral ventrolateral medulla neurons is specifically mediated by [Phe1 psi(CH2-NH)Gly2]NC(1-13)NH2-sensitive nociceptin receptors distinct from typical naloxone-sensitive opioid receptors.

Animals↗
PubMed1999

Accurate measurement of H(N)-H(alpha) residual dipolar couplings in proteins.

A method for accurately measuring H(N)-H(alpha) residual dipolar couplings is described. Using this technique, both the sign and magnitude of the coupling can be determined easily. Residual dipolar coupling between H(N)(i)-H(alpha)(i) and H(N)(i)-H(alpha)(i-1) were measured for the FK506 binding protein complexed to FK506. The experimental values were in excellent agreement with predictions based on an X-ray crystal structure of the protein/ligand complex, suggesting that these residual dipolar couplings will provide accurate structural constraints for the refinement of protein structures determined by NMR.

Magnetic Resonance Spectroscopy↗
PubMed1999

Transcriptional pulsing approaches for analysis of mRNA turnover in mammalian cells.

Modulation of mRNA stability provides a powerful means for controlling gene expression during the cell cycle, cell differentiation, the immune response, as well as many other physiological transitions. Through the years, many different methods have been developed for measuring mRNA stability. Frequently mRNA stability is studied indirectly by analyzing the steady-state level of mRNA. Therefore by inference, changes in mRNA abundance are thought to affect only the stability of the mRNA, an assumption that is not always correct. Alternatively, direct measurements of mRNA decay are performed in a number of ways, including kinetic labeling techniques and administration of transcriptional inhibitors. Due to the nature of these techniques, they either are technically demanding or introduce a significant change in cell physiology. In addition, many critical mechanistic issues as to deadenylation kinetics, decay intermediates, and precursor-product relationships cannot be readily addressed by these methods. Here, we describe and discuss in detail two different transcriptional pulsing methods based on the c-fos serum-inducible promoter and the tetracycline-regulated promoter systems as an effort to better elucidate the mechanistic steps and regulation underlying differential and selective mRNA turnover in mammalian cells. Both systems allow unequivocal monitoring of deadenylation and decay kinetics as well as determination of precursor-product relationship. In addition, decay rate constants and half-lives are determined and used in both methods to quantitatively denote the mRNA stability. Thus, they provide a reliable way to determine subtle yet physiologically meaningful changes in mRNA stability. Application of one method or the other covers the study of mRNA turnover in most mammalian cell types under a wide range of physiological conditions.

3T3 Cells↗
PubMed1999

Characteristics of copper corrosion in simulated uterine fluid in the presence of protein.

In order to acquire more knowledge of the performance of copper-bearing intrauterine devices (Cu-IUDs), corrosion behavior of copper in a simulated uterine fluid was investigated in the presence of proteins. The proteins studied included serum albumin, gamma-globulin and hemoglobin. Electrochemical polarization resistance measurements indicated that, in all cases under study, the corrosion rate of copper declined with time and the proteins always increased the rate. Moreover, different kinds of protein showed different dependence of copper corrosion rate on protein level. Addition of serum albumin initially raised the copper corrosion rate; however, the higher albumin concentration resulted in less promotion of the corrosion. X-ray diffraction (XRD) of the specimen surface showed that, both in the presence and absence of serum albumin, cuprous oxide was the only corrosion product, even though at higher concentrations of albumin less cuprous oxide was formed. This implies that serum albumin does not alter the corrosion mechanism. Electrochemical cathodic reduction of the oxide film and chemical analysis of solution after corrosion testing proved that the proportion of soluble ionic copper in the whole corrosion products varied with the albumin level. The copper corrosion rate in the presence of gamma-globulin or hemoglobin increased monotonically with increasing concentration of the protein. These three proteins shifted the corrosion potential of copper towards negative. It could be inferred that the proteins accelerated the anodic dissolution process of copper and hence enhanced its corrosion.

Body Fluids↗
PubMed1999

Characterization of AT2 receptor expression in NIH 3T3 fibroblasts.

1. A high expression of angiotensin II receptors and of angiotensin-converting enzyme (ACE) activity was detected in confluent NIH 3T3 fibroblasts. 2. Characterization with selective ligands, dithiothreitol, and GTP gamma S, indicated that only the AT2 subtype was expressed. 3. AT2 receptors and ACE expression were strictly dependent on the cell density and growth phase of the cells, with AT2 receptors being expressed earlier than ACE. In contrast, high expression of AT2 receptors irrespective of their growth state was observed in NIH 3T3 cells lacking contact inhibition upon neoplastic transformation with ras. 4. Our results imply a possible relation of AT2 receptors to cell growth and cell-cell contact.

3T3 Cells↗
PubMed1999

Hypertension is associated with a high risk of cancer.

To investigate the possible relationship between hypertension and cancer, a retrospective analysis was carried out using a database including 1225 cases, of which 552 were hypertensives and 673 normotensives. Seventy cases of cancers with different origins were found during a 17-year follow-up. Odds ratio (OR) for occurrence of cancer was calculated. It was shown that an age over 40 years, male sex, alcohol-taking, systolic and diastolic blood pressures (SBP/DBP) were the five risk factors for the occurrence of cancers, while occupation, smoking, body mass index, left ventricular hypertrophy, and antihypertensive medication had no effect on cancer incidence. Hypertensives were at a high risk of overall cancer incidence with OR 2.2 (P < 0.01). After stratification of age, OR for hypertensives aged 40-49 years old with SBP > or =140 mm Hg or DBP > or =90mm Hg was 3.18 and 2.98 (P < 0.01 respectively). The OR of cancer for non-alcohol taking male hypertensives with SBP < or =140 mm Hg or DBP > or =90 mm Hg were 3.6 (95%CI 1.37-9.68, P = 0.003) and 5.67 (95%CI 2.01-16.75, P < 0.001), 7.55 (95%CI 2.10-33.19, P < 0.001) and 7.80 (95%CI 2.14-33.79, P < 0.001) for non-alcohol taking female hypertensives with SBP > or =140 mm Hg or DBP > or =90 mm Hg. After adjustment of age, sex and alcohol taking, the OR of the cancer incidence was 3.45 (95%CI 1.30-9.01, P < 0.01) for male and 5.0 (95%CI 1.56-16.67, P < 0.01) for female hypertensives aged 40-49 years. Multiple logistic regression analysis shows that age over 40 years, male sex, alcohol-taking, and DBP were the four independent risk factors for cancers. It is concluded that hypertension is associated with a high risk of cancer.

Adult↗
PubMed1999

Bovine chromosome 4 workshop: consensus and comprehensive linkage maps.

The report of the bovine chromosome 4 (BTA4) workshop is presented. Six laboratories contributed a total of 30,168 informative meioses from 62 loci. Twenty-two loci were typed by at least two independent laboratories and were used to construct a consensus linkage map of BTA4. The remaining 40 loci were subsequently incorporated into a comprehensive map. The sex-averaged consensus map covered 131.4 cM. The female map was 124.3 cM in length, while the male map was 134.3 cM. The comprehensive sex-averaged map spanned 141.6 cM. The length of the female and male comprehensive maps were 123.1 cM and 156.4 cM, respectively. Average genetic distance between loci was 6 and 2.3 cM for the consensus and comprehensive linkage maps, respectively.

Animals↗
PubMed1999

Neutrophil inhibitory factor abrogates neutrophil adhesion by blockade of CD11a and CD11b beta(2) integrins.

We studied the basis of inhibition of polymorphonuclear leukocyte (PMN) adhesion induced by neutrophil inhibitory factor (NIF), a 41-kDa CD11/CD18 beta(2) integrin-binding protein isolated from the canine hookworm (Ancylostoma caninum). NIF blocked PMN adhesion in a concentration-dependent manner with complete blockade occurring at approximately 10 nM NIF. Because CD11a and CD11b beta(2) integrins are functionally active on stimulated PMNs, and yet NIF is postulated to inhibit only CD11b integrin by binding to its I domain, we evaluated the contributions of CD11a and CD11b beta(2) integrins in the mechanism of inhibition of PMN adhesion to endothelial cells. We observed an additive inhibitory effect (>90% inhibition) of PMN adhesion to endothelial cells when NIF was used in combination with anti-CD11b monoclonal antibodies, which alone at saturating concentrations reduced PMN adhesion by only 50%. NIF also prevented aggregation of phorbol ester-stimulated JY lymphoblastoid cells that expressed only the functionally active CD11a, suggesting that NIF also can inhibit CD11a-dependent response. We transduced the NIF cDNA into human dermal microvessel endothelial cells in which NIF synthesis and release prevented PMN adhesion to the transduced human dermal microvessel endothelial cells. These data indicated that the potent antiadhesive effect of NIF may be the result of inhibition of CD11a and CD11b beta(2) integrins on PMNs. Moreover, the strategy of NIF release from transduced endothelial cells suggests the feasibility of blocking the CD11a- and CD11b beta(2) integrin-dependent PMN adhesion and PMN migration responses specifically at sites of endothelial cell activation.

Animals↗
PubMed1999

[Effects of hyperbaric oxygen therapy on the changes in serum sIL-2R and Fn in severe burn patients].

OBJECTIVE: Many reports showed that level of soluble interleukin 2 receptor (sIL-2R) in sera was obviously increased in burn patients, while plasma fibronectin (Fn) was markedly decreased, and they had close relation with the occurrence and development of burn infection. The purpose of this study was to verify the significance of hyperbaric oxygen therapy (HBOT) in the prevention and treatment of burn infections by observing its effect on the levels of serum sIL-2R and Fn in severe burn patients. METHODS: Forty two burn patients(with more than 30% body surface area or three degree more than 10%) were selected and divided into two groups at random: HBOT group(25 cases) and non-HBOT group(17 cases); forty healthy blood donors were selected as normal control. The venous blood samples were drawn from 42 patients at 1/3, 1, 2, 3, 5, 7, 10, 14, 17, 21, 28 and 35 days postburn, the levels of serum sIL-2R and Fn were measured by ELISA and rocket electrophoresis techniques respectively, meanwhile, the incidences of sepsis of two groups were compared. RESULTS: 1. In non-HBOT group: the levels of serum sIL-2R were remarkably increased, while serum Fn were markedly decreased at all periods postburn (compared with normal control: P < 0.05 or P < 0.01); 2. In HBOT group: the levels of serum sIL-2R were not obviously increased at all periods except 21 days postburn, and Fn were not decreased at all periods except 8 h postburn (compared with normal control: P > 0.05). Compared with non-HBOT group, however, the levels of serum sIL-2R were profoundly reduced, while Fn was significantly enhanced at all periods postburn(P < 0.05 or P < 0.01), and the incidence of sepsis was obviously lowered (P < 0.05). CONCLUSION: HBOT can significantly reduce the level of serum sIL-2R but enhance Fn in severe burn patients, so it may have a positive effect on the prevention and treatment of burn infections.

Adolescent↗
PubMed1999

[Relationship between use of antibiotics and chronic diarrhoea in infants and young children].

OBJECTIVE: To study the relationship between use of antibiotics and chronic diarrhea in infants and young children. METHODS: A matched case-control study was carried out in Fuzhou City, Fujian Province during April to October 1997, with a total of 32 cases, (aged 1 - 19 months), with chronic diarrhea (with a length > 2 months), and 128 cases of acute diarrhea (as control group I) and 94 cases of acute respiratory tract infection (as control group II), from the Department of Pediatrics, the First Affiliated Hospital of Fujian Medical University during January 1987 to December 1996. RESULTS: Unconditional multiple logistic regression analysis showed that unreasonable use of antibiotics in treatment for acute diarrhea was the major risk factor for chronic diarrhea (OR = 5.61, 95% CI of OR = 1.15 - 27.36 with control group I, and OR = 16.92, 95% CI of OR = 2.67 - 107.32 with control group II). Chi-square test for trend showed that odds ratio of the use of antibiotics in the cases to the controls increased with the number of antibiotics used in treatment. CONCLUSION: Unreasonable use of antibiotics in treatment for acute diarrhea was an important factor contributing to chronic diarrhea in infants and young children. Early pathogenic diagnosis for diarrhea and reasonable use of antibiotics played important roles in prevention form chronicity of diarrheal diseases.

Anti-Bacterial Agents↗
PubMed1998

A microfabricated dialysis device for sample cleanup in electrospray ionization mass spectrometry.

A laser microfabricated device was constructed for rapid microdialysis cleanup of biological samples for analysis by electrospray ionization mass spectrometry (ESI-MS) in both off-line and on-line modes. A microdialysis membrane was sandwiched between two chips having micromachined serpentine channels. The total volume of the sample serpentine channel used for the microdialysis was 1 microL. Efficient desalting was demonstrated for both DNA and protein samples using ESI with an ion trap mass spectrometer after microdialysis against a counter flow of ESI-compatible buffer. Signal-to-noise ratios were also greatly enhanced compared to direct infusion of the original nondialyzed samples. Importantly, the microfabricated device allowed use of sample flow rates 1 order of magnitude smaller than previous designs based on a microdialysis fiber, allowing reduced sample utilization and improved sensitivity with ESI-MS. The effectiveness of the cleanup was attributed to the size difference between the sample channel and the buffer channel and the fact that the sample is continuously refreshed by the buffer counterflow. The results indicate substantial potential for construction of highly compact and rugged devices enabling field applications of ESI-MS.

DNA↗
PubMed1998

RNA stabilization by the AU-rich element binding protein, HuR, an ELAV protein.

An important paradigm for post-transcriptional regulation is the control of cytoplasmic mRNA stability mediated by AU-rich elements (AREs) in the 3' untranslated region of transcripts encoding oncoproteins, cytokines and transcription factors. While many RNA-binding proteins have been shown to bind to AREs in vitro, neither the functional consequences nor the physiological significance of their interactions are known. Here we demonstrate a role for the embryonic lethal abnormal visual (ELAV) RNA-binding protein HuR in mRNA turnover in vivo. The ELAV family of RNA-binding proteins is highly conserved in vertebrates. In humans, there are four members; HuR is expressed in all proliferating cells, whereas Hel-N1, HuC and HuD are expressed in terminally differentiated neurons. We show that elevation of cytoplasmic HuR levels inhibits c-fos ARE-mediated RNA decay but has little effect on rapid decay directed by c-jun ARE. It appears that HuR has little effect on deadenylation but delays onset of decay of the RNA body and slows down its subsequent decay. We also show that HuR can be induced to redistribute from the nucleus to the cytoplasm and that this redistribution is associated with an altered function. Modulation of the ARE-mediated decay pathway through controlling distribution of the ELAV proteins between nucleus and cytoplasm may be a mechanism by which cell growth and differentiation is regulated.

3T3 Cells↗
PubMed1998

In vivo expression of neutrophil inhibitory factor via gene transfer prevents lipopolysaccharide-induced lung neutrophil infiltration and injury by a beta2 integrin-dependent mechanism.

The binding of beta2 (CD18) integrins on PMN cell membrane to intercellular adhesion molecule (ICAM) counter-receptors on the surface of vascular endothelial cells mediates PMN adhesion to endothelial cells. Neutrophil inhibitory factor (NIF), a 41-kD glycoprotein isolated from the canine hookworm (Ancylostoma caninum), is a beta2 integrin antagonist that inhibits PMN adhesion to endothelial cells. We transferred the NIF gene into CD1 mouse lungs by intravenous injection of cationic liposomes to study the effects of in vivo NIF expression on LPS-induced lung PMN sequestration and the development of lung injury. RT-PCR and Northern blot analysis indicated the lung-selective expression of the NIF transgene, and immunocytochemistry showed prominent NIF expression in pulmonary microvessel endothelial cells. NIF staining was also observed in intraluminal leukocytes present in pulmonary microvessels. This may be the result of NIF binding to leukocytes after its secretion from the transduced lung cells, since there was no evidence of NIF gene expression in circulating leukocytes. Pulmonary vascular NIF expression abrogated the lung tissue PMN uptake and airspace migration of PMN and prevented lung vascular injury (as measured by the lung tissue uptake of [125I]labeled albumin) after the intraperitoneal LPS challenge (200 microg/mouse). Expression of a control protein, chloramphenicol acetyltransferase (CAT), by the same strategy, had no effect on these responses. In vitro studies showed that NIF prevented mouse PMN adhesion consistent with the inhibition of lung uptake after LPS challenge in NIF transgene-expressing mice. We conclude that pulmonary vascular expression of NIF, a specific beta2 integrin- binding protein, is a potentially useful gene transfer strategy in modulating the infiltration of PMN across the alveolar-capillary epithelial barrier and in preventing lung vascular endothelial injury.

Animals↗