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Biomedical subjects

Q Zhou

Publications and source records attributed to Q Zhou.

At least 253 records · Page 14Linked to original sources
PubMed1997

Proteolytic cleavage of the beta1 subunit of platelet alpha2beta1 integrin by the metalloproteinase jararhagin compromises collagen-stimulated phosphorylation of pp72.

Early signaling events in the stimulation of platelets by collagen include the tyrosine phosphorylations of FcR gamma-chain, pp72(syk) and phospholipase Cgamma2. These events are dependent on the main platelet collagen receptor, alpha2beta1 integrin (glycoprotein Ia-IIa complex). We recently found that jararhagin, a 52-kDa snake venom metalloproteinase, selectively inhibits collagen-induced platelet secretion and aggregation in parallel with the cleavage of the beta1 subunit of the alpha2beta1 integrin. The present study demonstrates that jararhagin also interferes with collagen-induced phosphorylation of the protein-tyrosine kinase pp72(syk). This effect is not observed when the platelet aggregation response to collagen is inhibited by two venom RGD-containing disintegrins, contortrostatin and echistatin. These disintegrins inhibit platelet aggregation through their high affinity binding to the platelet alphaIIbbeta3 integrin (glycoprotein IIb-IIIa complex). We also show that mild stimulation by ADP of jararhagin-treated platelets, but not of platelets treated with the RGD-containing disintegrins, restores the collagen-induced platelet aggregation. ADP also restored both pp72(syk) and pleckstrin phosphorylation of jararhagin-treated platelets in response to collagen, presumably via interaction of collagen with ADP-activated alphaIIbbeta3 integrin. Thus, RGD-containing disintegrins do not interfere with agonist-induced pp72(syk) phosphorylation but inhibit aggregation through occupancy of the alphaIIbbeta3 integrin. Conversely, jararhagin affects early platelet signaling events in response to collagen through its effects on the alpha2beta1 integrin without interfering with the function of the alphaIIbbeta3 integrin. Our demonstration that the degradation of the beta1 subunit of alpha2beta1 by jararhagin results in the loss of pp72(syk) phosphorylation, suggests that this subunit is critically involved in collagen-induced platelet signaling.

Collagen↗
PubMed1997

Benzidine-DNA adduct levels in human peripheral white blood cells significantly correlate with levels in exfoliated urothelial cells.

In a cross-sectional study of 33 workers exposed to benzidine and benzidine dyes and 15 non-exposed controls, we previously reported that exposure status and internal dose of benzidine metabolites were strongly correlated with the levels of specific benzidine-DNA adducts in exfoliated urothelial cells. We also evaluated DNA adduct levels in peripheral white blood cells (WBC) of a subset of 18 exposed workers and 7 controls selected to represent a wide range of adducts in exfoliated urothelial cells. Samples were coded and then DNA was analyzed using 32P-postlabeling, along with n-butanol extraction. One adduct, which co-chromatographed with a synthetic N-(3'-phospho-deoxyguanosin-8-yl)-N'-acetylbenzidine standard, predominated in those samples with adducts present. The median level (range) of this adduct in WBC DNA was 194.4 (3.2-975) RAL x 10(9) in exposed workers and 1.4 (0.1-6.4) in the control subjects (p = 0.0002, Wilcoxon Rank Sum Test). There was a striking correlation between WBC and exfoliated urothelial cell adduct levels (Pearson r = 0.84, p < 0.001) among exposed subjects. In addition, the sum of urinary benzidine, N-acetylbenzidine and N,N'-diacetylbenzidine correlated with the levels of this adduct in both tissues. This is the first study in humans to show a relationship for a specific carcinogen adduct in a surrogate tissue and in urothelial cells, the target for urinary bladder cancer.

Adult↗
PubMed1997

Treadmill running increases phosphatidylinostol 3-kinase activity in rat skeletal muscle.

Exercise has been shown to increase insulin-stimulated skeletal muscle glucose transport. Activation of phosphatidylinostol 3-kinase (PI 3-kinase) is required for insulin to stimulate glucose transport. The present study was designed to investigate whether treadmill running (60 min, 8% grade, 30 m/min) augments insulin-stimulated activation of PI 3-kinase. Insulin dramatically increased insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation (p < 0.05). Treadmill running did not induce IRS-1 tyrosine phosphorylation, not did it alter insulin-stimulated IRS-1 tyrosine phosphorylation. Insulin increased PI 3-kinase activity by 3.0-fold (over basal activity) in white muscle and 5.2-fold in red muscle (p < 0.05). Exercise did not alter basal PI 3-kinase activity in either white or red muscle. However, in response to exercise, insulin-stimulated PI 3-kinase activity was significantly increased in both muscle fibers (p < 0.05). These results suggest that increased insulin responsiveness induced by exercise may be due, in part, to enhanced insulin-stimulated PI 3-kinase activity.

Animals↗
PubMed1997

Molecular cloning of human plasma membrane phospholipid scramblase. A protein mediating transbilayer movement of plasma membrane phospholipids.

The rapid movement of phospholipids (PL) between plasma membrane leaflets in response to increased intracellular Ca2+ is thought to play a key role in expression of platelet procoagulant activity and in clearance of injured or apoptotic cells. We recently reported isolation of a approximately 37-kDa protein in erythrocyte membrane that mediates Ca2+-dependent movement of PL between membrane leaflets, similar to that observed upon elevation of Ca2+ in the cytosol (Bassé, F., Stout, J. G., Sims, P. J., and Wiedmer, T. (1996) J. Biol. Chem. 271, 17205-17210). Based on internal peptide sequence obtained from this protein, a 1,445-base pair cDNA was cloned from a K-562 cDNA library. The deduced "PL scramblase" protein is a proline-rich, type II plasma membrane protein with a single transmembrane segment near the C terminus. Antibody against the deduced C-terminal peptide was found to precipitate the approximately 37-kDa red blood cell protein and absorb PL scramblase activity, confirming the identity of the cloned cDNA to erythrocyte PL scramblase. Ca2+-dependent PL scramblase activity was also demonstrated in recombinant protein expressed from plasmid containing the cDNA. Quantitative immunoblotting revealed an approximately 10-fold higher abundance of PL scramblase in platelet ( approximately 10(4) molecules/cell) than in erythrocyte ( approximately 10(3) molecules/cell), consistent with apparent increased PL scramblase activity of the platelet plasma membrane. PL scramblase mRNA was found in a variety of hematologic and nonhematologic cells and tissues, suggesting that this protein functions in all cells.

Amino Acid Sequence↗
PubMed1997

Inhibition of cyclin D expression in human breast carcinoma cells by retinoids in vitro.

Transfection and transgenic mouse experiments supported an oncogenic role for cyclin D1 in breast cancer. We recently reported that noninvasive carcinoma in situ lesions of the human breast overexpress cyclin D, suggesting that this molecular event may represent a valuable target for chemoprevention. The purpose of the present series of investigations was to identify agents which could reduce the cyclin D expression of breast cells. We report that 9-cis retinoic acid (9-cis RA) and all trans retinoic acid (tRA) inhibited the cyclin D1 and D3 expression levels of human MCF-7, ZR-75 and T-47D breast carcinoma cells in vitro. Where detectable, similar trends were observed in the immortalized, HBL-100 and MCF-10A breast cell lines. Cyclin D2 was undetectable. The effect of retinoids was both dose- and time-dependent, and correlated with altered cell cycle kinetics and proliferative status. Retinoids were also found to inhibit the expression levels of other cell cycle related proteins, including Cdk2 and Cdk4, resulting in lower kinase activities. In contrast to other breast prevention studies, no synergistic effect was observed with retinoids and tamoxifen. The data indicate that retinoids can potently reduce cyclin D expression levels in a variety of breast cell lines in vitro, and suggest further consideration of this mechanism for the chemoprevention of breast cancer.

Breast Neoplasms↗
PubMed1997

Activation of pro-caspase-7 by serine proteases includes a non-canonical specificity.

As a model to investigate the mechanism of caspase activation we have analysed the processing of pro-caspase-7 by serine proteases with varied specificities. The caspase-7 zymogen was rapidly activated by granzyme B and more slowly by subtilisin and cathepsin G, generating active enzymes with similar kinetic properties. Significantly, cathepsin G activated the zymogen by cleaving at a Gln-Ala bond, indicating that the canonical cleavage specificity at aspartic acid is not required for activation.

Amino Acid Sequence↗
PubMed1997

Photostimulation with caged neurotransmitters using fiber optic lightguides.

'Caged' neurotransmitters are molecules that are transformed to a neuroactive state by exposure to light of an appropriate wavelength and intensity. Use of these substances has centered on in vitro bath application and subsequent activation using light from lasers or flashlamps that is delivered into the preparation through microscope optics. We have tested a new and simpler method, using finely tapered fiberoptic lightguides, that promises to expand the use of caged compounds for in vitro and in vivo experimentation. We demonstrated the feasibility and flexibility of this method for caged neurotransmitter delivery using a range of ex vitro, in vitro and in vivo approaches. The degree and timing of uncaging could be controlled by manipulating the wavelength, intensity and timing of the light projected into the optical fiber. Because of the small size of the light guide and the ability to control light exposure at the source, this new method promises greater control over the spatial and temporal delivery of neuroactive substances than simple bath or iontophoretic application, and enables delivery of conventional neurotransmitters with a spatial and temporal resolution closer to that of the natural neuronal circuitry. In addition, this new method allows the application of normally labile substances, such as the free radical gas nitric oxide, by the photoconversion of photosensitive precursors.

Animals↗
PubMed1997

Effects of an anabolic-androgenic steroid on the regulation of the NMDA receptor NR1, NR2A and NR2B subunit mRNAs in brain regions of the male rat.

The expression of the N-methyl-D-aspartate (NMDA) receptor subunits NR1, NR2A and NR2B mRNAs was examined in discrete areas of the male rat brain (including hippocampus, hypothalamus, nucleus accumbens and cortex) following 14 days daily intramuscular injections of high doses (5 and 15 mg/kg) of an anabolic-androgenic steroid (AAS) (nandrolone decanoate). The results indicated that the drug produced a significant decrease in the mRNA expression of the NR2A receptor subunit both in the hypothalamus and hippocampus. A decrease in the level of NR2B receptor mRNA was observed in hypothalamus at the lower dose of the AAS but in other areas examined, this receptor subunit mRNA was not affected. Except for a decreased expression in the nucleus accumbens at the higher dose of AAS the NR1 receptor subunit mRNA was not affected by the drug. The three subunit mRNAs in cortex were not significantly altered. The effects of the steroid on the mRNA expression for the NMDA receptor subunits in hippocampus and hypothalamus are suggested to be involved in the mechanism behind aggressive behaviour, a feature previously associated with AAS misuse. The downregulation of the mRNA for the NR1 receptor subunit in nucleus accumbens may relate to a mechanism involved in the recently suggested AAS-induced stimulation of the brain reward system.

Animals↗
PubMed1997

Target protease specificity of the viral serpin CrmA. Analysis of five caspases.

When ectopically expressed in animal cells, cytokine response modifier A (CrmA), a product of the cowpox virus, prevents programmed cell death initiated by a variety of stimuli. Since CrmA is a proteinase inhibitor, its target is probably a protease that promotes cell death. The identification of this target is crucial in delineating essential regulation points that modulate the apoptotic program. We have compared the kinetics of interaction of CrmA with five proteases that may play a role in apoptosis. Four of the proteases, all members of the caspase family, are inhibited with widely different rates and affinities ranging over 5 orders of magnitude. One is not inhibited at all under the experimental conditions. CrmA is quite selective in its ability to inhibit caspases, showing the highest affinity for interleukin-1beta-converting enzyme and the second highest for the caspase FLICE (Ki = 0.95 nM), identified as a component of the intracellular signaling complex recruited by ligation of the death receptor Fas. On the basis of comparative inhibitor kinetics, we propose that CrmA is unlikely to inhibit the caspases Yama, Mch2, or LAP3 in vivo but that its inhibition of FLICE is of a magnitude for this protease to be a key target of CrmA during Fas-mediated apoptosis. Therefore, our results support the hypothesis that FLICE catalyzes a crucial step in the promotion of cell death.

Amino Acid Sequence↗
PubMed1997

Suckling and sucrose ingestion suppress persistent hyperalgesia and spinal Fos expression after forepaw inflammation in infant rats.

Sweet taste and nonnutritive suckling produce analgesia to transient noxious stimuli in infant rats and humans. The present study evaluated the pain-modulating effects of sucrose and suckling in a rat model of persistent pain and hyperalgesia that mimics the response to tissue injury in humans. Fore- and hindpaw withdrawal latencies from a 30 degrees or 48 degrees C brass stylus were determined in 10-day-old rats following paw inflammation induced by complete Freund's adjuvant (CFA; 1:1 injected s.c. in a 0.01 ml volume). CFA markedly decreased escape latencies to both 48 degrees and 30 degrees C stimulation, thereby demonstrating thermal hyperalgesia and mechanical allodynia. The combination of nonnutritive suckling and sucrose (7.5%, 0.01-0.06 ml/min) infusion markedly increased escape latencies to forepaw stimulation in both CFA-treated and control rats. In contrast, intraoral sucrose and suckling did not increase hindpaw withdrawal latencies in either control or CFA-inflamed rats. The effect was specific to sweet taste because neither water nor isotonic saline infusion affected forepaw escape latencies. Parallel findings were obtained for CFA-induced Fos-like immunoreactivity (Fos-LI), a marker of neuronal activation. Fos-LI was selectively induced in cervical and lumbar regions ipsilateral to forepaw and hindpaw inflammation, respectively. Suckling-sucrose treatment significantly reduced Fos-LI at the cervical but not at the lumbar regions. These findings demonstrate: (i) the development of persistent pain and hyperalgesia in 10-day-old rats that can be attenuated by endogenous pain-modulating systems activated by taste and nonnutritive suckling; (ii) the mediation of the sucrose-suckling analgesia and antihyperalgesia at the spinal level; and (iii) a differential rostrocaudal maturation of descending pain-modulating systems to the spinal cord of 10-day-old rats. These findings may provide new clinical approaches for engaging endogenous analgesic mechanisms in infants following tissue injury and inflammation.

Animals↗
PubMed1997

Homotypic interaction of the heat-stable antigen is not responsible for its co-stimulatory activity for T cell clonal expansion.

The heat-stable antigen (HSA) is an important co-stimulatory molecule on antigen-presenting cells (APC). However, the receptor on T cells that receives the co-stimulatory signal from HSA has not been identified. Because the HSA is transiently expressed on T cells after the T cell receptor/CD3 complex is engaged, and because it can bind to itself in a homotypic fashion, it has been proposed that homotypic interaction of HSA is responsible for its co-stimulatory activity. Here we test this hypothesis using mice that have a targeted mutation of the HSA gene, as well as novel transgenic mice that constitutively express HSA on T cells. We show that HSA-deficient T cells remain responsive to co-stimulation by HSA. Furthermore, constitutive expression of HSA does not enhance T cell response to co-stimulatory by HSA. Taken together, our results demonstrate that homotypic interaction of HSA is not responsible for co-stimulation mediated by HSA expressed on APC.

Animals↗
PubMed1997

Chronic, topical administration of 4-aminobiphenyl induces tissue-specific DNA adducts in mice.

While current human exposure to 4-aminobiphenyl (4-ABP) is mainly through inhalation, historically, occupational exposure occurred most often through the skin. 4-ABP targets the urinary bladder in humans, dogs, and rats and the liver and urinary bladder in mice. This study examines the time course of DNA adduct levels in mouse target tissues, liver and urinary bladder, and nontarget tissues, lung and skin, after repeated dermal exposure to subcarcinogenic doses of 4-ABP. It was found that, in female mice dermally treated with 50 nmol of 4-ABP twice weekly for 21 weeks, DNA adduct levels measured by 32P-postlabeling increased over time in target and nontarget tissues, but the greatest rate of accumulation occurred in urinary bladder. At 21 weeks liver, urinary bladder, and skin reached their highest median adduct levels of 55, 82, and 58, respectively. Median adduct levels in lung reached a maximum of 3.2 at 3 weeks of exposure. An adduct which had similar chromatographic properties to a standard previously identified as N-(deoxyguanosin-8-yl)-4-aminobiphenyl was the primary adduct detected in all tissues. There were significant correlations in adduct levels between liver and urinary bladder and liver and skin, but not between skin and urinary bladder. These data suggest that urinary bladder adducts are the result of hepatic and not dermal activation. However, adducts were detected at relatively high levels in skin but not in lung, suggesting that skin may have the metabolic capacity to activate 4-ABP when it is applied topically.

Administration, Cutaneous↗
PubMed1997

Anabolic androgenic steroids increase beta-endorphin levels in the ventral tegmental area in the male rat brain.

The levels of beta-endorphin and Met-enkephalin-Arg-Phe (MEAP) immunoreactivity in various brain regions (including amygdala, cortex, hippocampus, hypothalmus, nucleus accumbens, pituitary and ventral tegmental area) were studied in male rats subjected to daily intramuscular injections during 14 days of high doses (5 and 15 mg/kg) of the anabolic androgenic steroid (AAS), nandrolone decanoate. At the nandrolone dose of 15 mg/kg a significant (about 20-fold) increase in beta-endorphin levels in the ventral tegmental area (VTA) was observed. The steroid did not significantly affect the concentration of the peptide at any dose in other brain areas examined. The levels of MEAP remained unaltered in all studied regions. A slight increase in serum concentrations of both peptides was also found but this elevation was not statistically significant. The observed increase in beta-endorphin in VTA was suggested to be involved in a mechanism by which the steroid may influence the reward system in the brain. An opioid mediated stimulation of the reward system following injection of AAS supports a previous hypothesis that AAS may induce psychological dependence.

Anabolic Agents↗
PubMed1997

Polyamine derivatives as inhibitors of trypanothione reductase and assessment of their trypanocidal activities.

Trypanothione reductase (TR) occurs exclusively in trypanosomes and leishmania, which are the etiological agents of many diseases. TR plays a vital role in the antioxidant defenses of these parasites and inhibitors of TR have potential as antitrypanosomal agents. We describe the syntheses of several spermine and spermidine derivatives and the inhibiting effects of these compounds on T. cruzi TR. All of the inhibiting compounds displayed competitive inhibition of TR-mediated reduction of trypanothione disulfide. The three most effective compounds studied were N4,N8-bis(3-phenylpropyl)spermine (12), N4,N8-bis(2-naphthylmethyl)spermine (14), and N1,N8-bis(2-naphthylmethyl)spermidine (21), with Ki values of 3.5, 5.5 and 9.5 microM, respectively. Compounds 12, 14, and 21 were found to be potent trypanocides in vitro with IC50 values ranging from 0.19 to 0.83 microM against four T. brucei ssp. strains. However, these compounds did not prolong the lives of mice infected with trypanosomes. This work indicates that certain polyamine derivatives which target a unique pathway in Trypanosomatidae have potential as antitrypanosomal agents.

Animals↗
PubMed1997

The contractile mechanism of sodium metavanadate in isolated rat aortae.

The mechanism of contractile effect of vanadate was investigated in rat aortae. Sodium metavanadate (NaVO3; 10(-5)-3 x 10(-3) M) induced contractile responses in a concentration-dependent manner. Removal of endothelium did not affect the response to NaVO3. The response to NaVO3 was inhibited by nifedipine, a voltage-operated Ca2+ channel (VOC) inhibitor; NCDC, a phospholipase C inhibitor; and H-7, a protein kinase C inhibitor, but not by prazosin, an alpha1-adrenoceptor antagonist; methysergide, a serotonin-receptor antagonist; tripelennamine, a histamine-receptor antagonist; glibenclamide, an adenosine triphosphate (ATP)-dependent K+-channel inhibitor; or iberiotoxin, a large-conductance Ca2+-activated K+-channel inhibitor. In addition, genistein or tyrphostin A48, tyrosine kinase inhibitors, did not affect the contraction induced by NaVO3. Mg2+ removal or antimycin A, a Ca2+-ATPase inhibitor, did not cause any contraction. Ouabain, a Na+, K+-ATPase inhibitor, or K+-free medium caused the contraction of the aortae. The maximal contraction induced by NaVO3 plus ouabain was similar to that induced by NaVO3 alone. In addition, the response to NaVO3 was inhibited by AA861, a 5-lipoxygenase inhibitor, and RHC-80267, a diacylglycerol (DAG) lipase inhibitor. In the presence of AA861, either H-7 or nifedipine further inhibited the residual response to NaVO3. In the presence of NCDC, however, AA861 failed further to affect the residual response to NaVO3. In rat aortae, NaVO3 increased the levels of inositol monophosphate (IP) and prostaglandin F2alpha (PGF2alpha). AA861 and NCDC inhibited the IP increase. In addition, NCDC inhibited the PGF2alpha increase. These results suggest that the response to NaVO3 in rat aortae may be mainly the result of the increased phosphoinositide metabolism.

Animals↗
PubMed1997

Visualization of calcium influx through channels that shape the burst and tonic firing modes of thalamic relay cells.

Thalamic neurons have two firing modes: "tonic" and "burst." During burst mode, both low-threshold (LT) and high-threshold (HT) calcium channels are activated, while in tonic mode, only the HT-type of calcium channel is activated. The calcium signals associated with each firing mode were investigated in rat thalamic slices using whole cell patch clamping and confocal calcium imaging. Action potentials were induced by direct current injection into thalamic relay cells loaded with a fluorescent calcium indicator. In both tonic and burst firing modes, large calcium signals were recorded throughout the soma and proximal dendrites. To map the distribution of the channels mediating these calcium fluxes, LT and HT currents were independently activated using specific voltage-clamp protocols. We focused on the proximal region of the cell (up to 50 microm from the soma) because it appeared to be well clamped. For a voltage pulse of a given size, the largest calcium signals were observed in the proximal dendrites with smaller signals occurring in the soma and nucleus. This was true for both LT and HT signals. Rapid imaging, using one-dimensional linescans, was used to more precisely localize the calcium influx. For both LT and HT channels, calcium influx occurred simultaneously throughout all imaged regions including the soma and proximal dendrites. The presence of sizable calcium signals in the dendrites, soma, and nucleus during both firing modes, and the presence of LT calcium channels in the proximal dendrite where sensory afferents synapse, have implications for both the electrical functioning of relay cells and the transmission of sensory information to cortex.

Action Potentials↗
PubMed1997

[A non-invasive method for detecting endothelium-dependent dilation].

Using high resolution ultrasound, we measured the diameter of brachial arteries at rest, during reactive hyperemia and after glyceryl trinitrate (GTN) taking in 22 healthy persons. The results showed that brachial artery dilation was present both in reactive hyperemia and response to GTN. The mean flow-mediated dilation was 13.8 +/- 3.9% increment. The mean increment of dilation in response to GTN was 24.9 +/- 9.7%. The diameters of brachial arteries during reactive hyperemia and after sublingual GTN had significant difference compared with that in baseline (P < 0.01). It indicates that increased flow may mediate endothelium-dependent vessel dilatation and GTN cause endothelium-independent vessel dilatation in normal subjects. This paper presents a new non-invasive method of detecting endothelium-dependent dilation, which is proved to be simple, secure and practical.

Adult↗