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N Zhang

Publications and source records attributed to N Zhang.

At least 37 records · Page 2Linked to original sources
PubMed2001

MEK (MAPKK) inhibitors. Part 2: structure-activity relationships of 4-anilino-3-cyano-6,7-dialkoxyquinolines.

A series of 4-anilino-3-cyano-6,7-dialkoxyquinolines with different substituents attached to the 4-anilino group has been prepared that are potent MEK (MAP kinase kinase) inhibitors. The best activity is obtained when a phenyl or a thienyl group is attached to the para-position of the aniline through a hydrophobic linker, such as an oxygen, a sulfur, or a methylene group. The most active compounds show low nanomolar IC(50)'s against MEK (MAP kinase kinase), and have potent growth inhibitory activity in LoVo cells (human colon tumor line).

Aniline Compounds↗
PubMed2001

Functional Analysis of six novel ORFs on the left arm of Chromosome XII of Saccharomyces cerevisiae reveals three of them responding to S-starvation.

Six novel Open Reading Frames (ORFs) located on the left arm of the chromosome XII (YLL061w, YLL060c, YLL059c, YLL058w, YLL057c and YLL056c) have been analysed using either short-flanking homology (SFH) or long-flanking homology (LFH) gene replacement. Sporulation and tetrad analysis showed none of these ORFs to be essential for vegetative growth. The standard EUROFAN growth tests failed to reveal any obvious phenotypes resulting from deletion of each of the ORFs. Bioinformatic analysis revealed that YLL061w is probably an amino acid permease for S-methylmethionine and that YLL060c encodes a glutathione transferase which is involved in cellular detoxification, while YLL058w may play a role in sulphur-containing amino-acid metabolism, YLL057c in sulphonate catabolism and YLL056c in stress response. The transcription of three ORFs (YLL061w, YLL057c and YLL056c) has been shown to increase more than 10-fold under sulphate starvation. Replacement cassettes, comprising the kanMX marker flanked by each ORF's promoter and terminator regions, were cloned into pUG7. All the cognate clones, were generated using direct PCR products amplified from genomic DNA or using gap-repair. All clones and strains produced have been deposited in the EUROFAN genetic stock centre (EUROSCARF, Frankfurt).

Amino Acid Transport Systems↗
PubMed2001

Synthesis and Src kinase inhibitory activity of a series of 4-phenylamino-3-quinolinecarbonitriles.

Screening of a directed compound library in a yeast-based assay identified 4-[(2,4-dichlorophenyl)amino]-6,7-dimethoxy-3-quinolinecarbonitrile (2a) as a Src inhibitor. An enzymatic assay established that 2a was an ATP-competitive inhibitor of the kinase activity of Src. We present here SAR data for 2a which shows that the aniline group at C-4, the carbonitrile group at C-3, and the alkoxy groups at C-6 and C-7 of the quinoline are crucial for optimal activity. Increasing the size of the C-2 substituent of the aniline at C-4 of 2a from chloro to bromo to iodo resulted in a corresponding increase in Src inhibition. Furthermore, replacement of the 7-methoxy group of 2a with various 3-heteroalkylaminopropoxy groups provided increased inhibition of both Src enzymatic and cellular activity. Compound 25, which contains a 3-morpholinopropoxy group, had an IC(50) of 3.8 nM in the Src enzymatic assay and an IC(50) of 940 nM for the inhibition of Src-dependent cell proliferation.

Aniline Compounds↗
PubMed2001

Relationships involving metastable equilibrium solubility, surface complexes, and crystallite disorder with carbonated apatites.

Previous studies have shown that the metastable equilibrium solubility (MES) behavior of carbonated apatites (CAPs) may be described by a surface complex with the hydroxyapatite (HAP) stoichiometry in the absence of solution fluoride and by that with the fluorapatite (FAP) stoichiometry when appreciable solution fluoride is present. Studies have also shown that the magnitude of the MES is directly related to the crystallinity of the CAP. The aim of the present investigation was to examine the relationship between the CAP MES determined in the presence of solution fluoride and CAP crystallinity and to examine the effect of the change in the stoichiometry of the surface complex (from that of HAP to that of FAP) upon the relationship of the CAP MES to crystallinity. CAP samples were prepared by methods based on the precipitation of CAP from calcium phosphate solutions and the hydrolysis of dicalcium phosphate dihydrate in bicarbonate solutions. From X-ray diffraction experiments, the crystallite microstrain, and the full width at half maximum (FWHM) of the 002 reflection were determined for the CAPs. From CAP MES experiments conducted in the presence of solu tion fluoride, linear plots of the mean MES (i.e., mean pK(FAP)) values vs the crystallinity parameter (i.e., microstrain and FWHM) were obtained that yielded slopes that were essentially the same as those obtained in the absence of solution fluoride (i.e., mean pK(HAP) values vs crystallinity). This parallel finding suggests that the CAP crystallite disorder affects the energetics of the two surface complexes essentially to the same extent and provides new insight into the nature of CAP surface complexes.

Apatites↗
PubMed2001

Involvement of apoptosis in neurological injury after hypothermic circulatory arrest: a new target for therapeutic intervention?

BACKGROUND: This study was undertaken to evaluate the role of apoptosis in neurological injury after hypothermic circulatory arrest (HCA). METHODS: Twenty-one pigs (27 to 31 kg) underwent 90 minutes of HCA at 20 degrees C and were electively sacrificed at 6, 24, 48, and 72 hours, and at 7, 10, and 12 days after HCA, and compared with unoperated controls. In addition, 3 animals that had HCA at 10 degrees C, and 3 treated with cyclosporine A (CsA) in conjunction with HCA at 20 degrees C, were examined 72 hours after HCA. After selective perfusion and cryopreservation, all brains were examined to visualize apoptotic DNA fragmentation and chromatin condensation on the same cryosection of the hippocampus: fluorescent in situ end labeling (ISEL) was combined with staining with a nucleic acid-binding cyanine dye (YOYO). RESULTS: In addition to apoptosis, which was seen at a significantly higher level (p = 0.05) after HCA than in controls, two other characteristic degenerative morphological cell types (not seen in controls) were characterized after HCA. Cell death began 6 hours after HCA and reached its peak at 72 hours, but continued for at least 7 days. Compared with the standard protocol at 20 degrees C, HCA at 10 degrees C and CsA treatment both significantly reduced overall cell death after HCA, but not apoptosis. CONCLUSIONS: The data establish that significant neuronal apoptosis occurs as a consequence of HCA, but at 20 degrees C, other pathways of cell death, probably including necrosis, predominate. Although preliminary results suggest that the neuroprotective effects of lower temperature and of CsA are not a consequence of blockade of apoptotic pathways, inhibition of apoptosis nevertheless seems promising as a strategy to protect the brain from the subtle neurological injury that is associated with prolonged HCA at clinically relevant temperatures.

Animals↗
PubMed2001

Expression of Deltex1 during mouse embryogenesis: comparison with Notch1, 2 and 3 expression.

The Notch signalling pathway defines a phylogenetically conserved cell-cell communication process that enables cell-fate specification in multicellular organisms. Deltex is a component of the Notch signalling network that physically interacts with the ankyrin repeats of Notch. Here, we report on the expression pattern of the Deltex1 gene during mouse embryonic development and, furthermore, we compare its expression with that of the Notch1, 2 and 3 genes. Complementary and combinatorial expression patterns between Deltex1 and the three Notch genes were observed throughout embryogenesis since Deltex1 expression was related either to cytodifferentiation (i.e. neuronal tissues) or to cell proliferation events (i.e. eye, vascular structures, hematopoiesis).

Animals↗
PubMed2001

Cyclosporine A as a potential neuroprotective agent: a study of prolonged hypothermic circulatory arrest in a chronic porcine model.

OBJECTIVE: To assess whether Cyclosporine A (CsA) or cycloheximide (CHX) can reduce ischemia-induced neurological damage by blocking apoptotic pathways, we assessed their effects on cerebral recovery in a chronic animal model of hypothermic circulatory arrest (HCA). METHODS: Twenty-eight pigs (28-33 kg) underwent 90 min of HCA at 20 degrees C. In this blinded study, animals were randomized to placebo (n=12), 5 mg/kg CsA (n=8), given intravenously before and subcutaneously for 7 days after HCA, or a single dose of 1 mg/kg CHX (n=8), given after weaning from cardiopulmonary bypass. Hemodynamics, intracranial pressure (ICP) and neurophysiological data (EEG, SSEP) were assessed for 3 h after HCA; early behavioral recovery was scored, and neurological/behavioral evaluation (9=normal) was carried out daily until elective sacrifice on postoperative day (POD) 7. Brains were selectively perfused and evaluated histopathologically for apoptosis. RESULTS: Basic hemodynamic data revealed no differences between CsA or CHX and control groups. ICP was significantly lower throughout rewarming (P=0.009) and reperfusion (P=0.05) in the CsA group. EEG recovery 3 h after HCA was observed in four of eight CsA animals but in only 1 of 12 controls (P=0.11) and one of eight CHX animals; cortical SSEP recovery also seemed faster in CsA animals, but failed to reach significance. Some early recovery scores were significantly better in the CsA group, and daily behavioral scores were consistently and significantly higher in the CsA-treated animals from POD1 through POD4. CONCLUSIONS: The data indicate that treatment with Cyclosporine A but not cycloheximide has a positive effect on cerebral recovery following HCA. Whether CsA results in inhibition of neuronal apoptosis, and/or inhibits release of cytokines and thereby reduces postischemic cerebral edema remains to be elucidated. The neuroprotective effect of CsA, if confirmed in further studies, would make its clinical application conceivable.

Animals↗
PubMed2001

Characterization of the regulatory function of the 46-kDa isoform of Rubisco activase from Arabidopsis.

Arabidopsis Rubisco activase was recently shown to be regulated by redox changes in the larger (46-kDa) isoform specifically mediated by thioredoxin-f [Zhang and Portis (1999) Proc Natl Acad Sci USA 96: 9438-9443]. Reduction greatly increases the activity of the 46-kDa isoform and the native protein at physiological ATP/ADP ratios. In this study we conducted additional experiments to characterize the regulation of Rubisco activase by thioredoxin-f. The K(m) for both ATP hydrolysis and Rubisco activation by the 46-kDa isoform was lowered by 4 to 5-fold after reduction, but the maximum activity was increased by only 10%. Only 0.35 muM thioredoxin-f was required for a half-maximal activity change after a 10 min preincubation and activation with 1 muM was complete after 10 min. Equal amounts of 46-kDa and 43-kDa isoforms were required for a complete inhibition of the Rubisco activation activity after a reduction-oxidation cycle and assay at an ATP/ADP ratio of 3:1, whereas activity was only inhibited by 50% at a 2:1 ratio (43-/46-kDa) of the isoforms. This requirement is consistent with the fact that Arabidopsis normally contains about a 1:1 ratio of the two isoforms at both the mRNA and protein levels. Redox titrations indicated a midpoint potential of -344 mV for the 46-kDa isoform as compared to -342 mV for spinach fructose 1,6-bisphosphatase at pH 7.9, consistent with previous reports indicating that these proteins are co-regulated by light intensity in a similar manner.

Journal Article↗
PubMed2001

The ties that bind what is known to the recognition of what is new.

Recognition success varies with how information is encoded (e.g., level of processing) and with what is already known as a result of past learning (e.g., word frequency). This article presents the results of experiments showing that preexisting connections involving the associates of studied words facilitate their recognition regardless of whether the words are intentionally encoded or are incidentally encoded under semantic or nonsemantic conditions. Words are more likely to be recognized when they have either more resonant connections coming back to them from their associates or more connections among their associates. Such results occur even though attention is never drawn to these associates. Regression analyses showed that these connections affect recognition independently of frequency, so the present results add to the literature showing that prior lexical knowledge contributes to episodic recognition. In addition, equations that use free-association data to derive composite strength indices of resonance and connectivity were evaluated. Implications for theories of recognition are discussed.

Adult↗
PubMed2001

A functional genomics strategy that uses metabolome data to reveal the phenotype of silent mutations.

A large proportion of the 6,000 genes present in the genome of Saccharomyces cerevisiae, and of those sequenced in other organisms, encode proteins of unknown function. Many of these genes are "silent, " that is, they show no overt phenotype, in terms of growth rate or other fluxes, when they are deleted from the genome. We demonstrate how the intracellular concentrations of metabolites can reveal phenotypes for proteins active in metabolic regulation. Quantification of the change of several metabolite concentrations relative to the concentration change of one selected metabolite can reveal the site of action, in the metabolic network, of a silent gene. In the same way, comprehensive analyses of metabolite concentrations in mutants, providing "metabolic snapshots," can reveal functions when snapshots from strains deleted for unstudied genes are compared to those deleted for known genes. This approach to functional analysis, using comparative metabolomics, we call FANCY-an abbreviation for functional analysis by co-responses in yeast.

Adenine Nucleotides↗
PubMed2001

Cerebral effects of cold reperfusion after hypothermic circulatory arrest.

OBJECTIVES: This study was undertaken to explore whether an interval of cold reperfusion can improve cerebral outcome after prolonged hypothermic circulatory arrest. METHODS: Sixteen pigs (27-30 kg) underwent 90 minutes of circulatory arrest at a brain temperature of 20 degrees C. Eight animals were rewarmed immediately after hypothermic circulatory arrest (controls), and 8 were reperfused for 20 minutes at 20 degrees C and then rewarmed (cold reperfusion). Electrophysiologic recordings, fluorescent microsphere determinations of cerebral blood flow, calculations of cerebral oxygen consumption, and direct measurements of intracranial pressure (millimeters of mercury) were obtained at baseline (37 degrees C), before hypothermic circulatory arrest, after discontinuing circulatory arrest at 37 degrees C deep brain temperature, and at 2, 4, and 6 hours thereafter. Histopathologic features and percent brain water were determined after the animals were sacrificed. RESULTS: Cerebral blood flow and oxygen consumption decreased during cooling: cerebral oxygen consumption returned to baseline levels after 4 hours, but cerebral blood flow remained depressed until 6 hours in both groups. Cold reperfusion failed to improve electrophysiologic recovery or to reduce brain weight, but median intracranial pressure increased significantly less after cold reperfusion than in controls (P =.02). Although no significant difference in the incidence of histopathologic abnormalities between groups was found, all 3 animals with an intracranial pressure of more than 15 mm Hg after immediate rewarming had histopathologic lesions, and high intracranial pressure was more prevalent among all animals with subsequent histopathologic lesions (P =.03). CONCLUSIONS: Cold reperfusion significantly inhibited the rise in intracranial pressure seen in control pigs after 90 minutes of circulatory arrest at 20 degrees C, suggesting that cold reperfusion may decrease cerebral edema and thereby improve outcome after prolonged hypothermic circulatory arrest.

Animals↗
PubMed2001

Retrograde cerebral perfusion provides negligible flow through brain capillaries in the pig.

OBJECTIVES: Although retrograde cerebral perfusion is being used clinically during aortic arch surgery, whether retrograde flow perfuses the brain effectively is still uncertain. METHODS: Fourteen pigs were cooled to 20 degrees C with cardiopulmonary bypass and perfused retrogradely via the superior vena cava for 30 minutes: 7 underwent standard retrograde cerebral perfusion and 7 underwent retrograde perfusion with occlusion of the inferior vena cava. Antegrade and retrograde cerebral blood flow were calculated by quantitating fluorescent microspheres trapped in brain tissue after the animals were put to death; microspheres returning to the aortic arch, the inferior vena cava, and the descending aorta were also analyzed during retrograde cerebral perfusion. RESULTS: Antegrade cerebral blood flow was 16 +/- 7.7 mL. min(-1). 100 g(-1) before retrograde cerebral perfusion and 22 +/- 6.3 mL. min(-1). 100 g(-1) before perfusion with caval occlusion (P =.14). During retrograde perfusion, calculations based on the number of microspheres trapped in the brain showed negligible flows (0.02 +/- 0.02 mL. min(-1). 100 g(-1) with retrograde cerebral perfusion and 0.04 +/- 0.02 mL. min(-1). 100 g(-1) with perfusion with caval occlusion; P =.09): only 0.01% and 0.02% of superior vena caval inflow, respectively. Less than 13% of retrograde superior vena caval inflow blood returned to the aortic arch with either technique. During retrograde cerebral perfusion, more than 90% of superior vena caval input was shunted to the inferior vena cava and was then recirculated, as indicated by rapid development of an equilibrium in microspheres between the superior and inferior venae cavae. With retrograde perfusion and inferior vena caval occlusion, less than 12% of inflow returned to the descending aorta and only 0.01% of microspheres. CONCLUSIONS: The paucity of microspheres trapped within the brain indicates that retrograde cerebral perfusion, either alone or combined with inferior vena caval occlusion, does not provide sufficient cerebral capillary perfusion to confer any metabolic benefit. The slightly improved outcome previously reported with retrograde cerebral perfusion during prolonged circulatory arrest in this model may be a consequence of enhanced cooling resulting from perfusion of nonbrain capillaries and from venoarterial and venovenous shunting.

Analysis of Variance↗
PubMed2001

Ggamma in dictyostelium: its role in localization of gbetagamma to the membrane is required for chemotaxis in shallow gradients.

G-protein-mediated signal transduction pathways play an essential role in the developmental program of the simple eukaryotic organism Dictyostelium discoideum. Database searches have yielded 11 Galpha-subunits, a single Gbeta-subunit, but no Ggamma-subunits. We report here the purification, cDNA isolation, and functional analysis of a Ggamma-subunit. Like Gbeta, the Ggamma appears to be unique and hybridization studies show that Ggamma and Gbeta are expressed in parallel during development. Species-wide sequence comparisons of Ggamma-subunits and gamma-like domains of RGS proteins reveal short stretches of highly conserved residues as well as the common CXXL motif at the COOH-terminal of Ggammas that target Gbetagammas to plasma membrane. Overexpression of a CSVL-deleted Ggamma (GgammaDelta) in wild-type cells shifts Gbetagamma to the cytosol and selectively impairs certain G-protein-mediated signal transduction pathways. These cells are able to respond to increments in the stimulus, but are unable to sense chemoattractant gradients. They neither move directionally nor recruit PH-domains to their leading edge. Thus, a full complement of membrane-tethered Gbetagamma is required for sensing shallow gradients, but is not essential for responses to increments in extracellular stimuli.

Animals↗
PubMed2001

Tumor-specific proteolytic processing of cyclin E generates hyperactive lower-molecular-weight forms.

Cyclin E is a G(1) cyclin essential for S-phase entry and has a profound role in oncogenesis. Previously this laboratory found that cyclin E is overexpressed and present in lower-molecular-weight (LMW) isoforms in breast cancer cells and tumor tissues compared to normal cells and tissues. Such alteration of cyclin E is linked to poor patient outcome. Here we report that the LMW forms of cyclin E are hyperactive biochemically and they can more readily induce G(1)-to-S progression in transfected normal cells than the full-length form of the protein can. Through biochemical and mutational analyses we have identified two proteolytically sensitive sites in the amino terminus of human cyclin E that are cleaved to generate the LMW isoforms found in tumor cells. Not only are the LMW forms of cyclin E functional, as they phosphorylate substrates such as histone H1 and GST-Rb, but also their activities are higher than the full-length cyclin E. These nuclear localized LMW forms of cyclin E are also biologically functional, as their overexpression in normal cells increases the ability of these cells to enter S and G(2)/M. Lastly, we show that cyclin E is selectively cleaved in vitro by the elastase class of serine proteases to generate LMW forms similar to those observed in tumor cells. These studies suggest that the defective entry into and exit from S phase by tumor cells is in part due to the proteolytic processing of cyclin E, which generates hyperactive LMW isoforms whose activities have been modified from that of the full-length protein.

Amino Acid Sequence↗
PubMed2001

[mRNA expression of matrix metalloproteinase-2 and membrane type matrix metalloproteinase in pulmonary fibroblasts and macrophages of rat pulmonary fibrosis model].

OBJECTIVE: To study the changes and significance of MMP-2 and MT1-MMP mRNA expressions in fibroblasts and macrophages of rat pulmonary fibrosis model. METHODS: Fifty pathogen-free Sprague-Dawley rats were randomly divided into ten groups. Five groups were instillated with bleomycin A5 (BLM A5) intratracheally, while 5 control groups with normal saline instead. Pulmonary interstitial fibroblasts and alveolar macrophages were isolated at day 1,3,7,14,28th after BLM exposure. The mRNA expression of MMP-2 and MT1-MMP was evaluated by RT-PCR quantitative analysis. RESULTS: (1) The MMP-2 gene expression of fibroblasts increased 2.05 times(t = 10.667, P < 0.01) higher than that of control in 24 hours after bleomycin instillation and remained at the high level until the 28th day after exposure. It was only slightly increased in macrophages at the first day (t = 3.27, P < 0.05) and dropped down to the level of control during pulmonary fibrosis. (2) The mRNA expressions of MT1-MMP were enhanced both in fibroblasts and macrophages of fibrosis groups. They were 2.1 times(t = 4.823, P < 0.01) higher than that of control at the 14th day and 1.8 times(t = 4.016, P < 0.01) at the 28th day, respectively, in fibroblasts, while it was 2.4 times(t = 5.851, P < 0.01) higher than that of control at the 28th day in macrophages. CONCLUSIONS: (1) Fibroblasts not only were the target cells but also involved in the damage of the pulmonary basement membrane and in the initiation of pulmonary fibrosis mediated by up-regulation of the mRNA expression of MMP-2. (2) The highly expressed MT1-MMP of fibroblasts and macrophages in the late stage of pulmonary fibrosis participated in the activation of pro-MMP-2 to promote the progression of pulmonary fibrosis.

Animals↗