Search PubMed⌕ Search

Biomedical subjects

L Zheng

Publications and source records attributed to L Zheng.

At least 235 records · Page 13Linked to original sources
PubMed1997

[Homology analysis of RubisCO gene of Thiobacillus versutus with extremelly acidophilic thiobacilli].

The chromosomal DNA of Thiobacillus thiooxidans and T. versutus was digested with restriction enzymes, blotted to nylon membrane by the way of Southern, and hybridized with the gene probe of ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) from T. ferrooxidans. The result showed that T. thiooxidans exhibited high homology with the probe anc T. versutus was less homology with it. However T. versutus can hybridize with the gene probe of RubisCO from Rhodobacter sphaeroides, which indicated that they had high homology with each other. As RubisCO was highly reserved in the evolutionary, they should be divided into different group.

DNA, Bacterial↗
PubMed1996

Cytokine expression by human peripheral blood dendritic cells stimulated in vitro with HIV-1 and herpes simplex virus.

Dendritic cells are potent stimulators of Ag-specific T cell responses and have been implicated in the pathogenesis of HIV-1 and other viral infections. Although cytokines may be involved in both of these processes, there is little information on the expression of cytokines by human blood dendritic cells. We characterized cytokine gene and protein expression in dendritic cells that were purified from normal human PBMC by flow cytometry and stimulated in vitro for up to 24 h with HIV-1 or herpes simplex virus (HSV). The unstimulated, uncultured dendritic cells were defined by their phenotype (HLA DR+ CD3- CD19- CD16- CD56- CD14-) and distinct morphology, lack of mRNA expression for CD3, CD14 and CD19, and presence of mRNA for CD4 and CD83. The purified dendritic cells also expressed CD4 (70-90%), CD33 (36-48%), and CD11c (44-54%); lacked CD1a expression (<1%); and were potent stimulators of an allogeneic MLR. The stimulated dendritic cells expressed mRNA for IFN-alpha, IL-1alpha, IL-1beta, IL-6, IL-10, IL-12, GM-CSF, and TNF-alpha within 4 to 12 h as determined by reverse transcription-PCR, with higher levels induced by HSV compared with HIV-1 strains IIIb or BaL. In contrast, the dendritic cells produced detectable protein only for IFN-alpha and IL-6 in response to HIV-1 or HSV, and IL-1beta in response to HSV within 24 h. There were no differences in expression of CD80 and CD86 surface molecules by dendritic cells that were either mock stimulated or stimulated with HIV-1 or HSV for 24 h. Production of IFN-alpha, IL-1beta, and IL-6 by dendritic cells may be important to the immunologic function of these cells and their role in the pathogenesis of HIV-1 and HSV infections.

Antigens, CD↗
PubMed1996

A slight asymmetry in the transbilayer distribution of lysophosphatidylcholine alters the surface properties and poly(ethylene glycol)-mediated fusion of dipalmitoylphosphatidylcholine large unilamellar vesicles.

Large, unilamellar vesicles (LUV) composed of dipalmitoylphosphatidylcholine (DPPC) were made asymmetric in L-alpha-lysopalmitoylphosphatidylcholine (LPC) either by adding a small amount (total mole fraction = 0.003) of LPC to their outer leaflets (LUV-LPCout) or by extracting a small amount from outer leaflets which already contained 0.0015 mol fraction LPC (LUV-LPCin). The slow rate of the transbilayer redistribution of LPC allowed the asymmetric vesicles to be characterized with regard both to their physical properties and to their ability to fuse in the presence of poly(ethylene glycol) (PEG). The fraction of LPC extractable with bovine serum albumin was taken as a measure of LPC transbilayer asymmetry. The ratio of LPC available to that unavailable to BSA extraction was 6 for LUV-LPCout and 0.3 for LUV-LPCin. These asymmetries could not be enhanced significantly by increasing the vesicle LPC content. Measurements of the mixing and leakage of vesicle contents showed that LUV-LPCin fused in the presence of 15% (w/w) PEG without loss of contents but that LUV-LPCout did not fuse in the presence of up to 35% PEG. Vesicles prepared from palmitoyloleoylphosphatidylcholine could also be made asymmetric in LPC, but did not fuse even in the presence of 30% PEG. Quasi-elastic light scattering revealed that LUV-LPCin aggregated at 25 degrees C except when swollen by an osmotic gradient while LUV-LPCout were much less likely to aggregate. Trapped volume determinations suggested that neither type of vesicle was perfectly spherical in shape, but no correlation was found between fusogenicity and vesicle shape. Measurements of the fluorescence properties of TMA-DPH and of C6-NBD-PC suggested that the interface region of the outer leaflet of LUV-LPCin was slightly less ordered and less well packed than that of LUV-LPCout. This slight perturbation of the external vesicle surface correlated with the ability of juxtaposed vesicle bilayers to fuse.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1996

Antibody-induced engagement of beta 2 integrins on adherent human neutrophils triggers activation of p21ras through tyrosine phosphorylation of the protooncogene product Vav.

It is known that beta 2 integrins are crucial for leukocyte cell-cell and cell-matrix interactions, and accumulating evidence now suggests that integrins serve not only as a structural link but also as a signal-transducing unit that controls adhesion-induced changes in cell functions. In the present study, we plated human neutrophils on surface-bound anti-beta 2 (CD18) antibodies and found that the small GTP-binding protein p21ras is activated by beta 2 integrins. Pretreatment of the cells with genistein, a tyrosine kinase inhibitor, led to a complete block of p21ras activation, an effect that was not achieved with either U73122, which abolishes the beta 2 integrin-induced Ca2+ signal, or wortmannin, which totally inhibits the phosphatidylinositol 3-kinase activity. Western blot analysis revealed that antibody-induced engagement of beta 2 integrins causes tyrosine phosphorylation of several proteins in the cells. One of these tyrosine-phosphorylated proteins had an apparent molecular mass of 95 kDa and was identified as the protooncogene product Vav, a p21ras guanine nucleotide exchange factor that is specifically expressed in cells of hematopoietic lineage. A role for Vav in the activation of p21ras is supported by the observations that antibody-induced engagement of beta 2 integrins causes an association of Vav with p21ras and that the effect of genistein on p21ras activation coincided with its ability to inhibit both the tyrosine phosphorylation of Vav and the Vav-p21ras association. Taken together, these results indicate that antibody-induced engagement of beta 2 integrins on neutrophils triggers tyrosine phosphorylation of Vav and, possibly through its association, a downstream activation of p21ras.

Antigen-Antibody Reactions↗
PubMed1996

Ca2+ signalling mechanisms of the beta 2 integrin on neutrophils: involvement of phospholipase C gamma 2 and Ins(1,4,5)P3.

Engagement of beta 2 integrins triggers a tyrosine kinase-dependent intracellular mobilization and influx of Ca2+ in human neutrophils. However, the transduction pathway involved in generating this Ca2+ signal is obscure. In the present study we identified phospholipase C gamma 2 (PLC gamma 2) as one of the major proteins that was phosphorylated on tyrosine in response to beta 2 integrin activation. This beta 2 integrin-induced phosphorylation of PLC gamma 2 occurred in parallel with an increased accumulation of Ins(1,4,5)P3. The relevance of these observations for the beta 2 integrin-induced Ca2+ signal was investigated using an inhibitor of PLC signalling pathways, 1-(6-{[17 beta-3-methoxyoestra-1,3.5(10)-trien-17-yl] amino}hexyl)-1H-pyrrole-2,5-dione(U73122). U73122 dose-dependently (IC50, approx. 0.15 microM) inhibited both the beta 2 integrin-induced release of Ca2+ from intracellular stores and the subsequent influx of Ca2+ across the plasma membrane. These effects were not observed with the inactive analogue 1-(6-{[17 beta-3-methoxyoestra-1,3,5(10)-trien-17-yl] amino}hexyl)-pyrrolidine-2,5-dione (U73343). To gain further support for an involvement of PLC-induced Ins(1,4,5)P3 formation in the beta 2 integrin-induced Ca2+ signal, we searched for the molecular event(s) underlying the effects of U73122. Our experiments revealed that U73122 had no effect on either beta 2 integrin-induced tyrosine phosphorylation of PLC gamma 2 (or any of the other proteins) or on the formation of Ins(1,4,5)P3, but it reduced the Ins(1,4,5)P3-induced release of 45Ca2+ from intracellular stores of electropermeabilized cells. Taken together, the present data suggest that the beta 2 integrin-induced Ca2+ signal in human neutrophils is generated through activation of a PLC gamma 2-dependent pathway.

CD18 Antigens↗
PubMed1996

Leukotriene D4-induced mobilization of intracellular Ca2+ in epithelial cells is critically dependent on activation of the small GTP-binding protein Rho.

We have previously shown that the leukotriene D4 (LTD4)-induced mobilization of intracellular Ca2+ in epithelial cells is mediated by a G-protein that is distinctly different from the pertussis toxin-sensitive G-protein that regulates the subsequent influx of Ca2+. In the present study, we attempted to gain further knowledge about the mechanisms involved in the LTD4-induced mobilization of intracellular Ca2+ in epithelial cells by investigating the effects of compactin, an inhibitor of the isoprenylation pathway, on this signalling event. In cells preincubated with 10 microM compactin for 48 h, the LTD4-induced mobilization of intracellular Ca2+ was reduced by 75% in comparison with control cells. This reduction was reversed by co-administration of mevalonate (1 mM). The effect of compactin occurred regardless of whether or not Ca2+ was present in the extracellular medium, suggesting that isoprenylation must occur before Ca2+ is released from intracellular stores. In accordance with this, we also found that both the LTD4-induced formation of inositol 1,4,5-trisphosphate and the LTD4-induced phosphorylation of phospholipase C gamma 1 (PLC gamma 1) on tyrosine residues were significantly reduced in compactin-pretreated cells. These results open up the possibility that the activation of PLC gamma 1 is related to a molecule that is sensitive to impaired activity of the isoprenylation pathway, such as a small monomeric G-protein. This idea was supported by the observation that Clostridium botulinum C3 exoenzyme-induced inhibition of Rho proteins abolished the LTD4-induced intracellular mobilization of Ca2+. A regulatory role of Rho proteins in the LTD4-induced activation of PLC gamma 1 is unlikely to be indirectly mediated via an effect on the cytoskeleton, since cytochalasin D had no major effect on the LTD4-induced mobilization of Ca2+. Although the mechanism of interaction remains to be elucidated, the present findings indicate an important role of an isoprenylated protein such as Rho in the LTD4-induced Ca2+ signal.

ADP Ribose Transferases↗
PubMed1996

Reliability of self-reported human immunodeficiency virus risk behaviors in a residential drug treatment population.

This study examined test-retest reliabilities of self-reported human immunodeficiency virus (HIV) sexual and drug injection behaviors among 246 prior drug users admitted to either of two residential drug treatment programs in Westborough, Massachusetts, and Providence, Rhode Island, between June 1990 and September 1992. Participants, selected by their date of admission, were administered admission and reliability questionnaires pertaining to HIV risk behaviors, the latter at approximately 2 weeks after admission. Estimated reliabilities (kappa coefficients) of the sexual behaviors ranged from 0.72 to 0.91; those for the drug injection variables ranged from 0.63 to 0.98. These results were consistent across groups defined by sex and injection of drugs. The consistently good reliabilities are significant to the design of independent studies of drug treatment populations utilizing self-report measures of sexual and drug behaviors.

Female↗
PubMed1996

Increased serotonin in the developing superior colliculus does not alter the number or distribution of retinotectal ganglion cells.

Administration of a single subcutaneous dose of 5,7-dihydroxytryptamine (5,7-DHT) to newborn hamsters results in a significant increase in the density of serotoninergic (5-HT) fibers in the superficial layers of the superior colliculus (SC) and marked abnormalities in both the crossed and uncrossed retinotectal projections when these animals reach adulthood (R. Rhoades, C. Bennett-Clarke, R. Lane, M. Leslie, and R. Mooney, 1993, J. Comp. Neurol. 334:397-409). The present study was undertaken to determine whether changes in the retinotectal projection of 5,7-DHT-treated animals were associated with alterations in the number or distribution of retinal ganglion cells in these animals. Nissl staining of retinae from normal adult and 5,7-DHT-treated hamsters revealed no differences between them in the number or average diameter of cells in the retinal ganglion cell layer. Retrograde labeling with horseradish peroxidase (HRP) demonstrated no effect of 5,7-DHT treatment on the number or distribution of ipsilaterally or contralaterally projecting ganglion cells. Neonatal 5,7-DHT administration also had no effect on the distribution of soma diameters for HRP-labeled retinal ganglion cells. Electron microscopic analysis demonstrated no significant difference between the number of optic nerve fibers in the normal and 5,7-DHT-treated hamsters. The results are consistent with the conclusion that the effect of 5,7-DHT on the retinotectal projection may primarily be a function of this toxin, or the increase in 5-HT it induces, on the terminal arbors of retinotectal axons rather than on their parent cells.

5,7-Dihydroxytryptamine↗
PubMed1996

Structure and analysis of phospholipase D gene from Ricinus communis L.

Phospholipase D (PLD; EC 3.1.4.4) has been proposed to play a pivotal role in various cellular processes, but molecular understanding of this enzyme is rather limited. This report describes the nucleotide sequence, structure, and genomic organization of a PLD gene from castor bean (Ricinus communis L. cv. Hale). The PLD gene was isolated from a castor bean genomic library using the PLD cDNA as a hybridization probe. Sequence comparison with the PLD cDNA revealed that the PLD gene consisted of four exons and three introns, one of which interrupts the 5'-untranslated region. Southern blot analysis indicated that the cloned PLD gene was present as a single-copy gene, and yet there were other PLD or PLD-related sequences in the castor bean genome.

Ricinus communis↗
PubMed1996

Synaptic organization of damaged infraorbital nerve axons in perinatal rats: demonstration by galanin immunocytochemistry.

Neonatal transection of the infraorbital nerve (ION; the trigeminal, V, branch that supplies the mystacial vibrissae follicles) results in an upregulation of galanin in the central arbors of primary afferent axons. The present study was undertaken to evaluate the synaptic organization of these galanin-positive primary afferents and compare it with that of normal neurobiotin/biocytin-labeled primary afferent axons from animals of the same age. Examination of 1200 neurobiotin/biocytin-labeled profiles in V nucleus principalis (PrV) of rats killed on postnatal day (P-) 7 indicated that 23.3% (n = 279) of these profiles made synaptic contacts: 87.4% were axodendritic, 8.9% were axoaxonic, 2.8% were axosomatic, and 0.7% were axospinous. Evaluation of 1200 galanin-positive profiles in PrV from rats that sustained transection of the ION on P-0 and were killed on P-7 indicated that only 64 (5.3%) of these profiles made synaptic contacts (P < 0.05 compared with the intact animals). Of the galanin-positive profiles that did make synapses in PrV, 81.2% (n = 52) were axodendritic and 18.8% (n = 12) were axoaxonic. These results indicate that galanin released by damaged ION primary afferents in PrV is likely to affect the activity of second-order V neurons by a paracrine action rather than by acting at specific synapses.

Afferent Pathways↗
PubMed1996

Paralytic shellfish poisoning in southern China.

The rapidly expanding mariculture and commercial region along the southern coast of China has experienced sporadic outbreaks of paralytic shellfish poisoning for nearly 30 years, yet virtually nothing is known of the nature of that toxicity or of the causative organisms. This study presents the first direct comparisons of the high performance liquid chromatography toxin composition profiles of shellfish implicated in paralytic shellfish poisoning outbreaks in Daya Bay with Alexandrium tamarense cultures established from those waters. The three cultures that were analyzed produced an unusually high proportion of the low potency N-sulfocarbamoyl toxins C1 and C2 (nearly 90% of the total), and only trace quantities of the other saxitoxin derivatives. Total toxicity was thus very low with mild acid extraction, ranging between 7.2 and 12.7 fmole cell-1, or 0.7-0.9 pg saxitoxin equiv. cell-1. Following acid hydrolysis using the standard AOAC extraction method, the dominant toxins in the cultures were gonyautoxins 2 and 3 and decarbamoyl gonyautoxins 2 and 3. Total potency increased fourfold to 2.6-3.4 pg saxitoxin equiv. cell-1 following acid hydrolysis. These cultures are thus at the low end of the range of toxicities recorded for members of the A. tamarense species complex. Two scallop samples and one mussel sample collected from Daya Bay during paralytic shellfish poisoning episodes in 1990 and 1991 were also analyzed following the AOAC extraction procedure. The toxin profiles were similar for the three shellfish samples, in that the same suite of toxins were present in each, but the relative proportion of those toxins varied. The dominant toxins were gonyautoxins 2 and 3 and toxins C1-C4. Total toxicity was 336 and 654 micrograms saxitoxin per 100 g meat for the scallop samples, and 723 for the mussels. Toxins C3,4 were present in the shellfish at up to 22 mole%, but were not detected in cultures, even when mild acid was used for extraction. Despite the otherwise similar nature of the culture versus the shellfish toxin signatures, the presence of C3,4 indicates that another strain or species of Alexandrium, or possibly a paralytic shellfish poisoning-producing species of another genus was responsible for the 1990 and 1991 paralytic shellfish poisoning outbreaks in Daya Bay. Since the cultures analyzed were of low intrinsic toxicity, A. tamarense may be more widespread along the south coast of China than is suggested by the sporadic pattern of past paralytic shellfish poisoning outbreaks. Blooms with high cell density are required to generate sufficient toxin to be dangerous. The alarming increase in algal blooms in Chinese waters due to persistent and growing pollution may make these low toxicity populations more problematic in the future.

Animals↗