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L Yuan

Publications and source records attributed to L Yuan.

At least 73 records · Page 4Linked to original sources
PubMed2000

Rab6c, a new member of the rab gene family, is involved in drug resistance in MCF7/AdrR cells.

A new Rab6 homolog cDNA, Rab6c, was discovered by a hypermethylated DNA fragment probe that was isolated from a human multidrug resistant (MDR) breast cancer cell line, MCF7/AdrR, by the methylation sensitive-representational difference analysis (MS-RDA) technique. Rab6c was found to be under-expressed in MCF7/AdrR and MES-SA/Dx5 (a human MDR uterine sarcoma cell line) compared with their non-MDR parental cell lines. MCF7/AdrR cells expressing the exogenous Rab6c exhibited less resistance to several anti-cancer drugs, such as doxorubicin (DOX), taxol, vinblastine, and vincristine, than the control cells containing the empty vector. Flow cytometry experiments confirmed that the transfectants' diminished resistance to DOX was caused by increased drug accumulation induced by the exogenous Rab6c. These results indicate that Rab6c is involved in drug resistance in MCF7/AdrR cells.

Amino Acid Sequence↗
PubMed2000

Expanding the epidemiologic profile: risk factors for active tuberculosis in people immigrating to Ontario.

BACKGROUND: Many people immigrating to Canada come from countries with a high burden of tuberculosis. The aim of this study was to develop a detailed epidemiologic profile of foreign-born people with tuberculosis living in Ontario. METHODS: In this population-based case-control study, cases of tuberculosis diagnosed in 1994-1995 were identified from the database of the Ontario Reportable Disease Information Service and were considered eligible for analysis if a record of landing (receipt of permission to establish residence in Canada) from the period 1986-1995 was found in the Citizenship and Immigration Canada (CIC) database, if the person was at least 11 years of age at the time their visa was issued, and if the person had not been diagnosed with tuberculosis before becoming legally landed in Canada. Control subjects, who met the same criteria as the case subjects but who did not have tuberculosis in 1994-1995, were identified from a CIC database for landed immigrants. RESULTS: A total of 1341 cases of tuberculosis in foreign-born people were reported in Ontario in 1994-1995. A record of landing was found in CIC databases for 1099 of these people, 224 of whom were not legally landed at the time of diagnosis. In total, 602 cases met the inclusion criteria. The 2 strongest determinants of risk among those who had become landed within the preceding 10 years were referral for medical surveillance by immigration officials (odds ratio [OR] 3.8, 95% confidence interval [CI] 2.6-6.0) and world region of origin (Somalia [OR 67.7, 95% CI 31.3-154.9], Vietnam [OR 25.0, 95% CI 12.5-50.0], the Philippines [OR 11.9, 95% CI 6.0-23.3], other sub-Saharan African countries [OR 11.6, 95% CI 5.7-23.2], India [OR 9.7, 95% CI 4.9-18.9], China [OR 6.1, 95% CI 3.1-12.1], other Asian countries [OR 4.7, 95% CI 2.4-9.1], the Middle East [OR 4.1, 95% CI 2.0-8.3], Latin America [OR 1.9, 95% CI 0.9-3.8), and the former socialist countries of Europe [OR 1.8, 95% CI 0.8-3.8]; the reference category was countries with established market economies). Low socioeconomic status was an independent risk factor. INTERPRETATION: The risk of tuberculosis in groups of people migrating to Ontario is highly variable and is influenced by several factors. Successful population-based tuberculosis prevention strategies will need to accommodate this variability.

Adolescent↗
PubMed2000

Intraspecific differences in physiological response of 20 wheat cultivars to enhanced ultraviolet-B radiation under field conditions.

Field studies were conducted to determine the potential for alterations in physiology and the intraspecific variation in sensitivity of 20 wheat (Triticum aestivum) cultivars to enhanced ultraviolet-B (UV-B, 280-315 nm) radiation. The supplemental UV-B radiation was 5 kJ m(-2), simulating a depletion of 20% stratospheric ozone. Out of 20 wheat cultivars (from South China, North China and Mexico) tested, 13 showed significant changes in total chlorophyll content. In most of these sensitive species, chlorophyll a content was strongly reduced, and chlorophyll b content decreased in a lesser extent, leading to a decrease in chlorophyll a/b ratio. However, some species had an increased chlorophyll a/b ratio under enhanced UV-B. The effect of UV-B on flavonoid content also showed intraspecific differences, a significant increase for one cultivar, decreases in 12 cultivars and no effect on the other seven cultivars. Superoxide dismutase (SOD) activity of five cultivars was significantly increased, and that of six cultivars significantly decreased. Membrane permeability of 12 cultivars significantly increased, while only that of Dali 905 was significantly decreased. Malonaldehyde (MDA) contents of eight cultivars were increased significantly, while that of three cultivars was significantly decreased. Although large intraspecific differences were found for the different parameters measured, there was no clear correlation between them under UV-B radiation.

Journal Article↗
PubMed2000

High-throughput protein expression of cDNA products as a tool in functional genomics.

A proteomics approach has been developed aimed to allow high throughput analysis of protein products expressed from cDNA fragments (expressed sequence tags, ESTs). The concept relies on expression of gene products to generate specific antibodies for protein analysis, such as immunolocalization of the proteins on cellular and subcellular level. To evaluate the system, 55 cDNA clones with predominantly unknown function were selected from a mouse testis cDNA-library. A bacterial expression system was designed that allowed robust expression and easy purification. Protein levels between 15 and 80 mg l(-1) were obtained for 49 of the clones. Five clones were selected for immunization and all yielded functional antibodies that gave specific staining in Western blot screening of samples from various cell types. Furthermore, extensive immunolocalization information on subcellular level was obtained for three of the five clones. All generated data were stored in a relational database, and are made available through a web-interface (http://www.biochem.kth.se/multiscale/), which also provides relevant links and allows homology searches from the original sequences. The possibility to allow analysis of gene products from whole genomes using this 'localization proteomics' approach is discussed.

Amino Acid Sequence↗
PubMed2000

Developmental expression of pim kinases suggests functions also outside of the hematopoietic system.

We have cloned a novel quail cDNA with strong homology to the pim family of proto-oncogenes. The deduced amino acid (aa) sequence of the cDNA, named qpim, is more closely related to Xenopus Pim and to the recently identified rat Pim-3 than to human or rodent Pim-1 or Pim-2. The protein encoded by the qpim cDNA can autophosphorylate itself and share substrates with murine Pim-1, suggesting functional redundancy to other Pim family serine/threonine kinases. We have compared the expression of qpim in avian embryos to mouse pim-1, -2 and -3 by in situ hybridization. qpim shows a highly dynamic expression pattern, particularly at early developmental stages. Surprisingly, its expression pattern is not identical to any of the murine pim genes, which show complementary and/or partially overlapping expression sites both in- and outside of the hematopoietic system. Altogether, our results suggest novel functions for Pim family kinases during embryonic development, in particular in epithelia and in the central nervous system.

Abdomen↗
PubMed2000

CD40-independent pathways of T cell help for priming of CD8(+) cytotoxic T lymphocytes.

In many cases, induction of CD8(+) CTL responses requires CD4(+) T cell help. Recently, it has been shown that a dominant pathway of CD4(+) help is via antigen-presenting cell (APC) activation through engagement of CD40 by CD40 ligand on CD4(+) T cells. To further study this three cell interaction, we established an in vitro system using dendritic cells (DCs) as APCs and influenza hemagglutinin (HA) class I and II peptide-specific T cell antigen receptor transgenic T cells as cytotoxic T lymphocyte precursors and CD4(+) T helper cells, respectively. We found that CD4(+) T cells can provide potent help for DCs to activate CD8(+) T cells when antigen is provided in the form of either cell lysate, recombinant protein, or synthetic peptides. Surprisingly, this help is completely independent of CD40. Moreover, CD40-independent CD4(+) help can be documented in vivo. Finally, we show that CD40-independent T cell help is delivered through both sensitization of DCs and direct CD4(+)-CD8(+) T cell communication via lymphokines. Therefore, we conclude that CD4(+) help comprises at least three components: CD40-dependent DC sensitization, CD40-independent DC sensitization, and direct lymphokine-dependent CD4(+)-CD8(+) T cell communication.

Animals↗
PubMed2000

Kinetics of cellular and cytokine responses in a chimeric mouse model for the study of staphylococcal enterotoxin B pathogenesis.

The mechanisms by which superantigens, such as staphylococcal enterotoxin B (SEB), contribute to microbial pathogenicity have been poorly defined. The study of such pathogenic processes has been hampered by the lack of an adequate animal model. We utilized a previously described murine chimeric model to determine the cytokines and cell populations that might be involved in SEB toxicity. In the absence of bone marrow transplantation (BMT), all total body irradiated (TBI) mice died, while all transplanted mice survived up to 6 months. Compared with non-TBI and non-BMT mice, chimeric mice had an increased percentage of CD11b (Mac-1)-positive splenocytes (17 vs. 59%, P < 0.05) and decreased CD45R-positive (B) cells (33 vs. 6%, P < 0.05) at 6 weeks after BMT. The relative numbers of splenocyte CD4 and CD8 cells were similar in chimeric and normal mice. Susceptibility of chimeric animals to 10 or 100 microg SEB was time-dependent: no mice challenged at 2 weeks post-BMT died, but 15% of mice challenged at 4 weeks and 50% of those challenged at 6-8 weeks died. Compared with TBI and non-BMT C3H/HeJ mice, SEB-challenged chimeric mice at 6-8 weeks had (1) increased splenocyte mRNA expression for: IFN-gamma (3.5 x optimally at 1 h), TNF-alpha (6.5 x at 2 h), IL-6 (4.8 x at 4 h), IL-1beta (8.4 x at 4 h), IL-2 (4.7 x at 4 h), and IL-10 (3 x at 16 h), and (2) increased and earlier peak serum levels of IFN-gamma, IL-6, IL-1beta and IL-2, but no increase in serum TNF-alpha or IL-4. These data support the hypothesis that the decreased percentage of B cells and increased macrophages in chimeric mice lead to enhanced T cell-macrophage interactions after SEB administration and a lethal burst of T cell and macrophage cytokine release. This model will provide insight into cell populations and mechanisms that mediate superantigen-induced toxicity.

Animals↗
PubMed2000

The murine SCP3 gene is required for synaptonemal complex assembly, chromosome synapsis, and male fertility.

During meiosis, the homologous chromosomes pair and recombine. An evolutionarily conserved protein structure, the synaptonemal complex (SC), is located along the paired meiotic chromosomes. We have studied the function of a structural component in the axial/lateral element of the SC, the synaptonemal complex protein 3 (SCP3). A null mutation in the SCP3 gene was generated, and we noted that homozygous mutant males were sterile due to massive apoptotic cell death during meiotic prophase. The SCP3-deficient male mice failed to form axial/lateral elements and SCs, and the chromosomes in the mutant spermatocytes did not synapse. While the absence of SCP3 affected the nuclear distribution of DNA repair and recombination proteins (Rad51 and RPA), as well as synaptonemal complex protein 1 (SCP1), a residual chromatin organization remained in the mutant meiotic cells.

Animals↗
PubMed2000

Differential responsiveness of MCF-7 human breast cancer cell line stocks to the pineal hormone, melatonin.

The estrogen receptor (ER)-positive MCF-7 human breast cancer cell line has been used extensively for the study of estrogen-responsive human breast cancer. However, various levels of estrogen responsiveness have been described in different stocks of MCF-7 cells. Because we have previously shown that the pineal hormone, melatonin, inhibits proliferation of MCF-7 cells and can modulate ER expression and transactivation, we investigated if various stocks of MCF-7 cells exhibit a differential responsiveness to the anti-proliferative effects of melatonin and the possible mechanisms involved. The MCF-7 stocks (M, O, H) were examined for: (1) mitogenic response to estradiol; (2) steady-state ER mRNA levels; (3) expression of the mt1 melatonin membrane receptor; (4) growth inhibition by melatonin; and (5) melatonin's modulation of expression of the ER and the estrogen-regulated genes, PgR, TGFbeta and pS2. For all of these parameters, there was a stock-specific response which showed: MCF-7M > MCF-7O > MCF-7H. These results demonstrate that there are significant differences in the responsiveness of various stocks of MCF-7 breast cancer cells to the growth-inhibitory effects of melatonin which can be correlated with both the level of ER mRNA expression and the degree of estrogen-responsiveness. These findings suggest that not only may these differences have some impact on the cells' estrogen-response pathway, but also that the primary growth-inhibitory effects of melatonin are transduced through the membrane-associated G-protein coupled mt1 melatonin receptor.

Blotting, Northern↗
PubMed2000

The impact of educational videotapes on water contact behaviour of primary school students in the Dongting Lakes region, China.

Multimedia has become increasingly important in educational programmes in schools in all societies, and has potential value for health education. We developed a video and a comic book on the transmission and prevention of schistosomiasis for use in primary schools in endemic areas of China. The material was designed to increase children's knowledge of schistosomiasis as an environmental disease and to encourage them to reduce their contact with unsafe water sources. To test the effectiveness of the video and booklet, a quasi-experimental study was conducted among 1,739 children in 50 primary schools in the Dongting Lake region. A self-administered questionnaire pre- and post-intervention showed a significant increase in knowledge about schistosomiasis in the intervention schools. Significantly, this change was associated with a decrease in contact with unsafe water sources, as established from water contact observations. This behavioural change suggests the value of short, targeted educational interventions to decrease risk of infection.

Adolescent↗
PubMed2000

Blockade of the alpha(v)beta(3) integrin adversely affects implantation in the mouse.

The role of endometrial and embryonic integrins during implantation remains unresolved although work in animal models and in humans supports their involvement in this process. Temporal and spatial distribution of the alpha(v)beta(3) integrin on both embryo and endometrium in women and mice coincides with the time of initial attachment during implantation. In mice, the endometrial and embryonic alpha(v)beta(3) integrin is present at the time of implantation, as shown by reverse transcription-polymerase chain reaction and immunohistochemistry. In situ hybridization demonstrates the presence of the alpha(v)beta(3) integrin on the subluminal stromal cells of the uterus. Functional blockade of this integrin on the day of implantation by intrauterine injection of neutralizing monoclonal antibodies against alpha(v) or beta(3) integrin subunits, arg-gly-asp (RGD)-containing peptides, or of the disintegrin echistatin, reduced the number of implantation sites compared to controls receiving BSA. These studies demonstrate that, like the human, the murine alpha(v)beta(3) integrin is expressed at the time of implantation in the endometrium and on the blastocyst, and may play a critical role in the cascade of events leading to successful implantation.

Animals↗
PubMed2000

Effects of opsonization and gamma interferon on growth of Brucella melitensis 16M in mouse peritoneal macrophages in vitro.

Entry of opsonized pathogens into phagocytes may benefit or, paradoxically, harm the host. Opsonization may trigger antimicrobial mechanisms such as reactive oxygen or nitric oxide (NO) production but may also provide a safe haven for intracellular replication. Brucellae are natural intramacrophage pathogens of rodents, ruminants, dogs, marine mammals, and humans. We evaluated the role of opsonins in Brucella-macrophage interactions by challenging cultured murine peritoneal macrophages with Brucella melitensis 16M treated with complement- and/or antibody-rich serum. Mouse serum rich in antibody against Brucella lipopolysaccharide (LPS) (aLPS) and human complement-rich serum (HCS) each enhanced the macrophage uptake of brucellae. Combinations of suboptimal levels of aLPS (0. 01%) and HCS (2%) synergistically enhanced uptake. The intracellular fate of ingested bacteria was evaluated with an optimal concentration of gentamicin (2 microg/ml) to control extracellular growth but not kill intracellular bacteria. Bacteria opsonized with aLPS and/or HCS grew equally well inside macrophages in the absence of gamma interferon (IFN-gamma). Macrophage activation with IFN-gamma inhibited replication of both opsonized and nonopsonized brucellae but was less effective in inhibiting replication of nonopsonized bacteria. IFN-gamma treatment of macrophages with opsonized or nonopsonized bacteria enhanced NO production, which was blocked by N(G)-monomethyl L-arginine (MMLA), an NO synthesis inhibitor. MMLA also partially blocked IFN-gamma-mediated bacterial growth inhibition. These studies suggest that primary murine macrophages have limited ability to control infection with B. melitensis, even when activated by IFN-gamma in the presence of highly opsonic concentrations of antibody and complement. Additional cellular immune responses, e.g., those mediated by cytotoxic T cells, may play more important roles in the control of murine brucellosis.

Animals↗
PubMed2000

Intranasal administration of 2/6-rotavirus-like particles with mutant Escherichia coli heat-labile toxin (LT-R192G) induces antibody-secreting cell responses but not protective immunity in gnotobiotic pigs.

We investigated the immunogenicity of recombinant double-layered rotavirus-like particle (2/6-VLPs) vaccines derived from simian SA11 or human (VP6) Wa and bovine RF (VP2) rotavirus strains. The 2/6-VLPs were administered to gnotobiotic pigs intranasally (i.n.) with a mutant Escherichia coli heat-labile toxin, LT-R192G (mLT), as mucosal adjuvant. Pigs were challenged with virulent Wa (P1A[8],G1) human rotavirus at postinoculation day (PID) 21 (two-dose VLP regimen) or 28 (three-dose VLP regimen). In vivo antigen-activated antibody-secreting cells (ASC) (effector B cells) and in vitro antigen-reactivated ASC (derived from memory B cells) from intestinal and systemic lymphoid tissues (duodenum, ileum, mesenteric lymph nodes [MLN], spleen, peripheral blood lymphocytes [PBL], and bone marrow lymphocytes) collected at selected times were quantitated by enzyme-linked immunospot assays. Rotavirus-specific immunoglobulin M (IgM), IgA, and IgG ASC and memory B-cell responses were detected by PID 21 or 28 in intestinal and systemic lymphoid tissues after i.n. inoculation with two or three doses of 2/6-VLPs with or without mLT. Greater mean numbers of virus-specific ASC and memory B cells in all tissues prechallenge were induced in pigs inoculated with two doses of SA11 2/6-VLPs plus mLT compared to SA11 2/6-VLPs without mLT. After challenge, anamnestic IgA and IgG ASC and memory B-cell responses were detected in intestinal lymphoid tissues of all VLP-inoculated groups, but serum virus-neutralizing antibody titers were not significantly enhanced compared to the challenged controls. Pigs inoculated with Wa-RF 2/6-VLPs (with or without mLT) developed higher anamnestic IgA and IgG ASC responses in ileum after challenge compared to pigs inoculated with SA11 2/6-VLPs (with or without mLT). Three doses of SA 11 2/6-VLP plus mLT induced the highest mean numbers of IgG memory B cells in MLN, spleen, and PBL among all groups postchallenge. However, no significant protection against diarrhea or virus shedding was evident in any of the 2/6-VLP (with or without mLT)-inoculated pigs after challenge with virulent Wa human rotavirus. These results indicate that 2/6-VLP vaccines are immunogenic in gnotobiotic pigs when inoculated i.n. and that the adjuvant mLT enhanced their immunogenicity. However, i.n. inoculation of gnotobiotic pigs with 2/6-VLPs did not confer protection against human rotavirus challenge.

Animals↗
PubMed2000

Tumor necrosis factor-alpha: a potentially neurodestructive cytokine produced by glia in the human glaucomatous optic nerve head.

Tumor necrosis factor-alpha (TNF-alpha) mediates a range of cellular responses, which have potentially detrimental consequences that affect multiple cell types. To determine whether TNF-alpha contributes to glaucomatous optic neuropathy, we have studied the expression of this cytokine and its receptor, tumor necrosis factor receptor-1 (TNF- R1), in human glaucomatous optic nerve heads from patients with different stages of disease using double labeling fluorescence immunohistochemistry. We have also investigated the ability of this cytokine to induce nitric oxide synthase (NOS-2) in cultured human optic nerve astrocytes by immunocytochemistry and immunoblot. Normal tissue showed constitutive expression of TNF-R1 in the vasculature of the optic nerve heads but no positive labeling for TNF-alpha. In the glaucomatous optic nerve heads, the expression of both TNF-alpha and TNF-R1 were apparently upregulated, primarily in glial fibrillary acidic protein (GFAP)-positive astrocytes, and appeared to parallel the progression of optic nerve degeneration. In eyes with severe glaucomatous damage, some HLA-DR positive microglia also contained TNF-alpha and TNF-R1. In the most severely damaged optic nerve heads, the axons of the retinal ganglion cells contained TNF-R1 and, therefore, are direct targets for neurodegeneration caused by TNF-alpha. In vitro astrocytes constitutively express TNF-R1 and TNF-alpha stimulation induces expression of NOS-2. We hypothesize that TNF-alpha contributes to the progression of optic nerve degeneration in glaucoma by both a direct effect on the axons of the retinal ganglion cells and by inducing NOS-2 in astrocytes.

Aged↗
PubMed2000

[Antifungal effect of three natural products on the genetic substance of Saccharomyces cerevisiae GL7 and Prototheca wickerhamii].

AIM: To investigate the antifungal effect of three natural products on the genetic substance of Saccharomyces cerevisiae GL7 and Prototheca wickerhamii. METHODS: The normal and treated cells were observed by confocal laser scanning microscope (CLSM) and image analysis to quantitatively described the cell morphology, area, DNA and RNA content. RESULTS: The morphology, area, DNA and RNA contents were changed greatly in the treated cells. CONCLUSION: Solasodine, 4'-hydroxy-3, 5-dimethoxystilbene and dictamnine directly or indirectly interfered the synthesis and function of genetic substance in S. cerevisiae and P. wickerhamii.

Alkaloids↗
PubMed2000

[Wind-damage effects on quality of heartwood of Lignum Santali Albi].

OBJECTIVE: To evaluate the wind-damage effects on quality of heartwood of Lignum Santali Albi. METHOD: GC-MS, TLC and pharmacodynamic test. RESULTS: The content of volatile oil from heartwood of Wind-damaged Lignum Santali Albi is 1.42%; the content of various components in the oil and the chromatography of different extracts are similar to those of reference drug and 25 years old trees. CONCLUSION: Wind-damage should accelerate the formation of heartwood of Lignum Santali Albi without influence on its quality.

Animals↗