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J Wu

Publications and source records attributed to J Wu.

At least 1,423 records · Page 79Linked to original sources
PubMed1992

[Preliminary studies of the relationship between micronucleus formation and cell cycle. IV. Micronucleus formation induced by chemical mutagens at G0, G1, S and G2 phases of human lymphocytes].

In this paper the authors studied quantitatively the micronucleus formation at various phases of interphase in human lymphocytes induced by chemical mutagens by means of control of cell culture intervals, autoradiography and block of metaphase cells etc. The results show that mutagenic anti-tumor drugs: bimolane (treatment in vitro) and thio-tepa etc. (treatment in vivo) can induce micronucleus formation at various phases of interphase in lymphocytes. The frequency of micronucleus (MNF) induced at G1 phase is significantly higher than that at G0 and G2 phase. The MNF at S phase of cells is obviously lower than at G1. This result suggests that most of the micronucleated cells at G1 phase do not enter S phase and micronucleus rarely form at S phase of cells.

Adolescent↗
PubMed1991

Autophosphorylation in vitro of recombinant 42-kilodalton mitogen-activated protein kinase on tyrosine.

Mitogen-activated protein kinase (MAP kinase) is a serine/threonine protein kinase that becomes enzymatically activated and phosphorylated on tyrosine and threonine following treatment of quiescent cells with a variety of stimulatory agonists. Phosphorylation on both tyrosine and threonine is necessary to maintain full activity, and these two regulatory phosphorylations occur close to each other, separated by a single glutamate. To study the mechanisms by which MAP kinase becomes phosphorylated and activated, we have cloned a full-length cDNA encoding MAP kinase and have expressed the enzyme in Escherichia coli as a soluble nonfusion protein. We find that the enzyme displays a basal, intramolecular autophosphorylation on tyrosine-185 that is accompanied by activation of the enzyme's kinase activity towards an exogenous substrate. The tyrosine-phosphorylated protein displays a small fraction of the activity seen with the fully activated, doubly phosphorylated enzyme isolated from mammalian cells but is activated 10- to 20-fold relative to the unphosphorylated enzyme. These findings raise the possibility that regulation of MAP kinase activity in response to agonist stimulation could occur in part through the enhancement of autophosphorylation on tyrosine.

Adenosine Triphosphatases↗
PubMed1991

Evidence for a factor required for transcriptional stimulation by the chimeric acidic activator GAL-VP16 in HeLa cell extracts.

We provide biochemical evidence for the existence of a transcriptional intermediary factor (TIF) in HeLa whole-cell extracts (WCE) that is distinct from the basic transcription factors and that is required for transcriptional stimulation by the chimeric acidic activator GAL-VP16. We have fractionated HeLa WCE by heparin-agarose chromatography. Of transcriptionally active fractions eluting in a step between 0.24 and 0.6 M KCl, the initial fractions are refractory to GAL-VP16 stimulation, whereas subsequent fractions are strongly stimulated by the activator. Aliquots of GAL-VP16-responsive fractions efficiently complement refractory fractions for transcriptional stimulation. Aliquots of responsive fractions are also far more efficient than those of refractory fractions in overcoming transcriptional inhibition that is brought about by high concentrations of GAL-VP16. Experiments performed with heat-treated WCE support the idea that HeLa cells contain a TIF that is essential for GAL-VP16 stimulation, but that is not required for basal transcription. Addition of recombinant yeast or human transcription factor TFIID (rTFIIDY and rTFIIDH, respectively) to a WCE heated at 48 degrees C for 15 min restores basal transcription, but in neither case is the reconstituted system activated by GAL-VP16. However, a 45 degrees C heat-treated WCE reconstituted with either rTFIIDH or rTFIIDY is stimulated by GAL-VP16, suggesting that a HeLa TIF can be selectively inactivated by heating at 48 degrees C, but not at 45 degrees C. Interestingly, a TFIID fraction partially purified from HeLa cell extracts, but not rTFIIDH, efficiently relieves transcriptional inhibition by GAL-VP16, suggesting that there may be an association between TIF(s) and TFIID and, moreover, that TIF(s) may be the direct target of the acidic domain of GAL-VP16. In summary, our results support the existence of a TIF that is not essential for basal transcription but that is required to mediate the stimulatory activity of the acidic activator GAL-VP16.

Biological Factors↗
PubMed1991

Recent progress in characterization of protein kinase cascades for phosphorylation of ribosomal protein S6.

Ribosomal protein S6 is phosphorylated in response to mitogens by activation of one or more protein kinase cascades. Phosphorylation of S6 in vivo is catalyzed by (at least) two distinct mitogen-activated S6 kinase families distinguishable by size, the 70 kDa and 90 kDa S6 kinases. Both S6 kinases are activated by serine/threonine phosphorylation. Members of each family have been cloned. The 90 kDa S6 kinases are activated more rapidly than the 70 kDa S6 kinase, and may have other intracellular targets. The 70 kDa S6 kinase is relatively specific for 40 S ribosomal subunits. No kinase capable of activating the 70 kDa S6 kinase has been identified. Members of the 90 kDa S6 kinases are activated in vitro by 42 kDa and 44 kDa MAP kinases, which are in turn activated by mitogen-dependent activators. The pathways for mitogen-stimulated S6 phosphorylation are discussed.

Amino Acid Sequence↗
PubMed1991

Ring-opening kinetics of the D-pentofuranuronic acids.

The ring-opening reactions of the furanose forms of the penturonic acids D-arabinuronic acid (1), D-lyxuronic acid (2), D-riburonic acid (3), and D-xyluronic acid (4) in aqueous solution have been studied as a function of temperature and solution pH by 13C saturation-transfer n.m.r. (s.t.-n.m.r.) spectroscopy using 1-13C-substituted compounds. Unidirectional rate constants of ring-opening (kopen) have been determined for the cyclic forms of 1-4 in their protonated (pH 1.5) and ionized (pH 4.5) forms, and have been compared to the k-values measured previously for structurally related furanose sugars. At 50 degrees and pH 1.5, kopen values decrease as follows: alpha-xyluronic acid (2.57 s-1) greater than alpha-riburonic (1.65 s-1) greater than beta-arabinuronic (1.52 s-1) greater than beta-xyluronic (1.09 s-1) greater than beta-riburonic (0.76 s-1) greater than beta-lyxuronic (0.55 s-1) greater than alpha-arabinuronic (0.46 s-1) greater than alpha-lyxuronic (0.40 s-1). At 50 degrees and pH 4.5, this order changes significantly (e.g., beta-arabinuronate is most reactive); in general kopen values for beta anomers appear to be enhanced relative to those for corresponding alpha anomers, suggesting the involvement of intramolecular catalysis in which the carboxylate anion assists in abstracting the hydroxyl proton from O-1. Activation energies of ring-opening, determined for the alpha and beta anomers of 1-4, were found to depend on ring configuration and solution pH.

Kinetics↗
PubMed1991

Decreased seasonal mesor of platelet 3H-imipramine binding in depression.

Seasonal cycles of platelet 3H-imipramine binding were compared in 49 endogenous unipolar depressed patients and 20 normal volunteers. A significant sinusoidal component was detected in the Bmax of binding in both patients and controls with similar amplitudes and seasonal peaks. However, the yearly average (mesor) of the patient group was significantly lower (20.0%) than that of the normal controls. The results support earlier claims of a diminished platelet binding in endogenous depression and indicate that this decrease was still evident in the presence of a 48.2% (controls) to 65.8% (patients) seasonal variation. Control Bmax values were normally distributed about a best-fit mean (cosinor fit). In contrast, patient values appeared to be bimodally distributed with one mode that was similar to controls and one mode that was substantially lower. In general, psychiatric symptoms failed to distinguish between patients with high and low platelet binding and no correlation was found between Bmax and severity of illness (HAM-D).

Adolescent↗
PubMed1991

Proteolytic modification of neural cell adhesion molecule (NCAM) by the intracellular proteinase calpain.

The neural cell adhesion molecule, NCAM, is concentrated in synaptic regions and thus may contribute to the formation and maintenance of connections between brain cells. We present evidence that the cytoplasmic domain of NCAM can be experimentally modified by the intracellular calcium-dependent proteinase, calpain. This degradation could provide a mechanism for rapidly uncoupling and reorganizing synaptic contacts.

Animals↗
PubMed1991

Temporal and hippocampal metabolic rate during an olfactory memory task assessed by positron emission tomography in patients with dementia of the Alzheimer type and controls. Preliminary studies.

Positron emission tomography with fludeoxyglucose F 18 was used to assess cortical metabolic rate during an olfactory memory task in six patients with dementia of the Alzheimer type. Metabolic activity was compared with that of both age-matched controls performing the olfactory task and controls resting with their eyes closed. Patients had lower metabolic rates in the anterior portion of the medial-temporal cortex than did controls, and the difference was greatest between patients and the controls performing the memory task. This region is known to receive a large olfactory input and has been implicated in the encoding of human memory. Normal controls resting with their eyes closed had significantly lower metabolic rates in this area when compared with normal controls performing the task. Our results are consistent with those of earlier reports of temporal lobe decreases in metabolic rate and extend them through the examination of areas salient to the behavioral loss.

Aged↗
PubMed1991

Conserved beta-tubulin binding domain for the microtubule-associated motors underlying sperm motility and fast axonal transport.

An antiserum against tubulin, NS20, has been previously shown to inhibit anterograde and retrograde axonal transport by 50% in vivo and in vitro. We report here that Protein A purified NS20 antibodies also attenuate sperm motility by 50% in demembranated sea urchin sperm. This inhibition is absorbed out by preincubating the NS20 antibodies with a biochemically purified porcine microtubule preparation, with recombinant Trypanosoma beta- (but not alpha-) tubulin and most specifically, with a 37 amino acid (a.a.) synthetic peptide corresponding to a domain near (but not including) the porcine beta-tubulin C terminus. Furthermore, addition of this beta-tubulin peptide alone is sufficient to attenuate motility by 50% in demembranated sperm, indicating that this critical 37a.a. NS20 antigen is a motor binding domain. Together, the results suggest that at least two phenotypically distinct forms of microtubule-based motility, axonal transport and flagellar beating, are homologous at the fundamental level of the microtubule domains (the beta-tubulin peptide and we suggest a distinct but similarly located alpha-tubulin domain) mediating the attachment of tubulin-associated motors.

Amino Acid Sequence↗
PubMed1991

Emetine allows identification of origins of mammalian DNA replication by imbalanced DNA synthesis, not through conservative nucleosome segregation.

In the presence of emetine, an inhibitor of protein synthesis, nascent DNA on forward arms of replication forks in hamster cell lines containing either single or amplified copies of the DHFR gene region was enriched 5- to 7-fold over nascent DNA on retrograde arms. This forward arm bias was observed on both sides of the specific origin of bidirectional DNA replication located 17 kb downstream of the hamster DHFR gene (OBR-1), consistent with at least 85% of replication forks within this region emanating from OBR-1. However, the replication fork asymmetry induced by emetine does not result from conservative nucleosome segregation, as previously believed, but from preferentially inhibiting Okazaki fragment synthesis on retrograde arms of forks to produce 'imbalanced DNA synthesis'. Three lines of evidence support this conclusion. First, the bias existed in long nascent DNA strands prior to nuclease digestion of non-nucleosomal DNA. Second, the fraction of RNA-primed Okazaki fragments was rapidly diminished. Third, electron microscopic analysis of SV40 DNA replicating in the presence of emetine revealed forks with single-stranded DNA on one arm, and nucleosomes randomly distributed to both arms. Thus, as with cycloheximide, nucleosome segregation in the presence of emetine was distributive.

Animals↗
PubMed1991

Compartmentation and glycoprotein substrates of calpain in the developing rat brain.

An activated form of calpain I associates with telencephalic membranes in a developmentally regulated fashion during early postnatal ontogeny. During this period, the cytoskeletal component spectrin is available and appears to be differentially susceptible to calpain-mediated cleavage. Lectin blotting techniques demonstrated that the leupeptin-sensitive action of calpain is primarily directed toward large proteins which are glycoconjugate in nature; neuronal cell adhesion molecules are among the glycoproteins whose associations with the telencephalic membranes decrease due to calpain activity. These data suggest that cytoplasmic calpain is translocated to the membrane during early brain development in order to act on the cytoskeletal and adhesive structures responsible in part for neuronal shape and function.

Animals↗
PubMed1991

Chronobiologic approach to beat-to-beat variations of cultured murine myocardial cells.

An earlier demonstration of a circadian rhythm in rat atria by others is complemented herein by observations in culture: A single murine myocardial cell and two sets of grouped cells beating in culture for several days reveal several features of an anticipated, presumably built-in spectrum of multifrequency rhythms and trends, the chronome. Circadian and about 12-h (circasemidian) components are modulated by an approximately 84-h (circasemiseptan) component, which cannot be separated from trends in view of the brevity of the series. The circumstance under which the culture is aging and in which fibroblasts proliferate is a further complication that limits the findings to a single cycle reproduced in three separate cultures. Whether it is a rhythm that repeats itself of a response to placement into culture, an approximately 3.5-d component in the beating of myocardial cells in culture is to be aligned with a very prominent similar component found in the incidence of 85,819 human myocardial infarctions.

Animals↗
PubMed1991

Effects of noise and salicylate on auditory evoked-response thresholds in the chinchilla.

The combined effects of noise and sodium salicylate on auditory sensitivity were examined in the chinchilla. Sensitivity was monitored by recording the evoked response recorded with an electrode implanted in the inferior colliculus. Sodium salicylate (300 mg/kg/day), an octave band of noise centered at 500 Hz (80 or 105 dB SPL), or both of these agents were delivered for 15 days. Threshold testing was performed at 7 frequencies before, during, and after exposure to the ototraumatic agent(s). The salicylate alone caused an average temporary threshold shift of less than 10 dB and essentially no permanent shift. Animals exposed to noise alone had temporary and permanent threshold shifts which were not significantly different from those observed in animals exposed to noise plus salicylate. The data suggest that a single daily injection of sodium salicylate, resulting in peak serum salicylate concentrations of 28 to 34 mg% 2 to 4 hours after delivery, does not exacerbate the temporary or permanent threshold shifts induced by 15-day, 24-hour-per day exposure to either a moderate- or high-level, low-frequency noise. A second series of experiments utilizing a higher dose of salicylate (450 mg/kg/day) was not completed due to a high mortality rate among subjects that received salicylate and were exposed to noise. This result was consistent with other recent examinations of the interaction of these agents.

Animals↗
PubMed1991

Microscopic model for selective permeation in ion channels.

Ionic permeation in the selectivity filter of ion channels is analyzed by a microscopic model based on molecular kinetic theory. The energy and flux equations are derived by assuming that: (a) the selectivity filter is formed by a symmetrical array of carbonyl groups; (b) ion movement is near the axis of the channel; (c) a fraction of water molecules is separated from the ion while it moves across the selectivity filter; (d) the applied voltage drops linearly across the selectivity filter; (e) ions move independently. Energy profiles, single channel conductances, and the degree of hydration of K+ in a hypothetical K+ channel are examined by varying the following microscopic parameters: ion radius and mass, channel radius, number of effective water dipoles, and number of carbonyl groups. The i-V curve is linear up to +/- 170 mV. If the positions of energy maxima and minima are fixed, this linear range is reduced to +/- 50 mV. Channel radius and ion-water interactions are found to be two major channel structural determinants for selectivity sequences. Both radius and mass of an ion are important in selectivity mediated by these interactions. The theory predicts a total of 15 possible kinetic selectivity sequences for alkali cations in ion channels with a single selectivity filter.

Animals↗