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J Chen

Publications and source records attributed to J Chen.

At least 1,153 records · Page 64Linked to original sources
PubMed1999

[Malignant transformation of HPV-18 immortalized human bronchial epithelial cells induced by tobacco-specific nitrosamine NNK].

The malignant transformation of HPV-18 immortalized human bronchial epithelial cell(BEP2D) induced by tobacco-specific nitrosamine NNK and its biological characteristics were investigated. BEP2D cells treated with NNK at the concentration of 500 micrograms/ml for 24 hours could be subcultured continuously in vitro. The 15th passage cells in soft agar (0.038%) increased 11 fold compared with that of control cells (0.0033%). The 25th passage cells could grow into tumor in nude mice. The tumor was a squamous cell carcinoma in morphology confirmed by histopathological examination. The results indicated that the malignant transformation induced by NNK was a sequential process. This culture system provides a potential tool for the study of cell and molecular mechanism in the multistage carcinogenesis of human bronchial epithelial cells.

Animals↗
PubMed1999

Functional differences between memory and naive CD8 T cells.

To determine how murine memory and naive T cells differ, we generated large numbers of long-lived memory CD8(+) T cells and compared them to naive cells expressing the same antigen-specific receptor (T cell receptor; TCR). Although both populations expressed similar levels of TCR and CD8, on antigen stimulation in vitro memory T cells down-regulated their TCR faster and more extensively and secreted IFN-gamma and IL-2 faster than naive T cells. Memory cells were also larger, and when freshly isolated from mice they contained perforin and killed target cells without having to be restimulated. They further differed from naive cells in requiring IL-15 for proliferation and in having a greater tendency to undergo apoptosis in vitro. On antigen stimulation in vivo, however, they proliferated more rapidly than naive cells. These findings suggest that, unlike naive T cells, CD8 memory T cells are intrinsically programmed to rapidly express their effector functions in vivo without having to undergo clonal expansion and differentiation.

Animals↗
PubMed1999

The use of a fluorescent bacteriophage assay for detection of Escherichia coli O157:H7 in inoculated ground beef and raw milk.

The objective of this study was to develop a fluorescent bacteriophage assay (FBA) for the detection of E. coli O157:H7 in ground beef and raw milk. The FBA is a two step assay that combines immunomagnetic separation, to separate the target organism from mixed culture, with a highly specific fluorescently stained bacteriophage to label the E. coli O157:H7 cells. When used in conjunction with flow cytometry, the FBA was able to detect 2.2 CFU/g of artificially contaminated ground beef following a 6 h enrichment. Between 10(1) and 10(2) CFU/ml of artificially contaminated raw milk were detectable after a 10 h enrichment step. The results show that the FBA is potentially useful as a rapid technique for the preliminary detection of E. coli O157:H7 in food.

Animals↗
PubMed1999

Induction of specific tolerance to allografts in rats by therapy with non-mitogenic, non-depleting anti-CD3 monoclonal antibody: association with TH2 cytokines not anergy.

BACKGROUND: Anti-CD3 monoclonal antibodies (mAb) are potent immunosuppressives in transplantation but most do not induce tolerance. They induce anergy in Th1 cells but, if they bind to Fc receptors on antigen presenting cells, they activate T cells to release cytokines. METHODS: This study examined the mechanisms of transplant tolerance induction to PVG fully allogeneic grafts in dark agouti rats by G4.18, a mouse immunoglobulinG3 anti-rat CD3 mAb that does not bind rat Fc receptors. Evidence of T cell activation was assayed by flow cytometry, reverse transcription (RT)-polymerase chain reaction (PCR) for cytokine mRNA, and responsiveness in mixed lymphocyte culture. RESULTS: G4.18 treatment modulated T cell receptor/CD3 and CD2 and depleted T cells by <20% but did not induce activation surface markers. mRNA for interleukin (IL)-2, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and IL-4 in the lymph node, spleen, and thymus was not increased, and IFN-gamma mRNA was reduced. G4.18-treated and naive rat cells had similar proliferation and expression of IL-2, IFN-gamma, and IL-4 in vitro. G4.18-treated allograft recipients had no induction of mRNA for IL-2, IFN-gamma, TNF-alpha, TNF-beta, IL-4, IL-5, IL-10, perforin, and granzyme A & B in the spleen or grafts, with levels similar to those in isografts. The IL-4 and IL-5 mRNA levels in the spleen but not the graft of G4.18-treated recipients were higher than in rejecting and naive animals. Cells from G4.18-treated graft recipients proliferated more rapidly to the donor than to the third party and had increased IL-4 expression. CONCLUSIONS: G4.18 induced transplant tolerance by a combination of modulation and blocking of the TCR/CD3, associated with increased Th2 cytokines, without depletion, induction of anergy, or nonspecific activation of T cells.

Animals↗
PubMed1999

The FKBP12-rapamycin-binding domain is required for FKBP12-rapamycin-associated protein kinase activity and G1 progression.

The immunosuppressant rapamycin, in complex with its cellular receptor FKBP12, targets the cellular protein FKBP12-rapamycin-associated protein/mammalian target of rapamycin/rapamycin and FKBP12 target 1 (FRAP/mTOR/RAFT1) and inhibits/delays G1 cell cycle progression in mammalian cells. As a member of the novel phosphatidylinositol kinase-related kinase family, FRAP's kinase activity is essential for its signaling function. The FKBP12-rapamycin binding (FRB) domain in FRAP is also speculated to play an important role in FRAP function and signaling. However, the biochemical and physiological functions of FRB, as well as the mechanism for rapamycin inhibition, have been unclear. The present study focuses on investigation of FRB's role and the functional relationship between FRB domain and kinase domain in FRAP. Microinjection of purified FRB protein into human osteosarcoma MG63 cells results in a drastic blockage of the G1 to S cell cycle progression; such a dominant negative effect is reversed by a point mutation (Trp2027 --> Phe). The same mutation also abolishes kinase activity of FRAP without affecting ATP binding, and truncation studies suggest that upstream sequences including FRB are required for kinase activity in vitro. Given these data, we propose a model for FRAP function, in which the FRB domain is required for activation of the kinase domain, possibly through the interaction with an upstream activator. In addition, our observations provide direct evidence linking FRAP function to G1 cell cycle progression.

Amino Acid Sequence↗
PubMed1999

[Detection of insertion/deletion polymorphism of angiotensin converting enzyme gene in preeclampsia].

OBJECTIVE: To establish a method for sensitive, specific and rapid detection of the angiotensin converting enzyme(ACE) genotypes and to study the relationship between the ACE gene polymorphism and preeclampsia. METHODS: Sixty patients with preeclampsia and 76 normal pregnant women as controls were investigated. A pair of primers, for the intron 16 of ACE gene was designed. A sensitive and specific method for detecting the ACE polymorphism of the insertion/deletion was established. Determined by polymerase chain reaction (PCR),a 490bp(I) and 190bp(D) PCR product was identified,corresponding to the PCR amplification of the allele with or without the insertion. RESULTS: The subjects were classified, according to the presence or absence of a 287bp insertion in intron 16 of the ACE gene, as II, DD, or heterozygotes for deletion/insertion (DI). The frequency of allele gene (0.75) and the percentage of the ACE DD genotype (65%) in the preeclampsia group were significantly higher as compared with the frequency 10.308 and the percentage (10.5%) in the control group respectively. CONCLUSION: Genotype II of ACE is a marker for reduced risk for preeclampsia and DD is a risk gene.

Female↗
PubMed1999

Protein-protein recognition: exploring the energy funnels near the binding sites.

We present a rapidly executable minimal binding energy model for molecular docking and use it to explore the energy landscape in the vicinity of the binding sites of four different enzyme inhibitor complexes. The structures of the complexes are calculated starting with the crystal structures of the free monomers, using DOCK 4.0 to generate a large number of potential configurations, and screening with the binding energy target function. In order to investigate possible correlations between energy and variation from the native structure, we introduce a new measure of similarity, which removes many of the difficulties associated with root mean square deviation. The analysis uncovers energy gradients, or funnels, near the binding site, with decreasing energy as the degree of similarity between the native and docked structures increases. Such energy funnels can increase the number of random collisions that may evolve into productive stable complex, and indicate that short-range interactions in the precomplexes can contribute to the association rate. The finding could provide an explanation for the relatively rapid association rates that are observed even in the absence of long-range electrostatic steering.

Algorithms↗
PubMed1999

[Application of gas chromatography-mass spectrometry for determination of the organochlorine pesticide residues in ginseng].

A gas chromatographic-electronionization-mass spectrometric method (GC-EIMS) was developed for the determination of organochlorine pesticide residues in Ginseng plants. The Ginseng samples were extracted with acetone, partioned using petroleum ester with sodium chloride saturated aqueous solution and clean-up with concentrated sulfuric acid. The organochlorine pesticide residues were analysed by GC-MS with monitoring selective mass ions. Ten organochlorine pesticides including alpha, beta, gamma and delta isomers of hexachlorocyclohexane (HCH), pp'-DDE, pp'-DDT, op'-DDT, pp'-DDT, pentachloronitrobenzene (Quintozene, PCNB), and hexachlorobenzene(HCB), were determined simultaneously. Targeted pesticide analytes were separated on DB-5 capillary column. The optimum chromatographic conditions and MS parameters were determined. The average recovery rates for those pesticide residues Ginseng were from 76.6% to 90.1% at 0.1 mg/kg of spiked level, except 58.3% for PCNB. The relative standard deviations were 9.3%-15.0%.

Drug Contamination↗
PubMed1999

Do "America's Best Hospitals" perform better for acute myocardial infarction?

BACKGROUND: "America's Best Hospitals," an influential list published annually by U.S. News and World Report, assesses the quality of hospitals. It is not known whether patients admitted to hospitals ranked at the top in cardiology have lower short-term mortality from acute myocardial infarction than those admitted to other hospitals or whether differences in mortality are explained by differential use of recommended therapies. METHODS: Using data from the Cooperative Cardiovascular Project on 149,177 elderly Medicare beneficiaries with acute myocardial infarction in 1994 or 1995, we examined the care and outcomes of patients admitted to three types of hospitals: those ranked high in cardiology (top-ranked hospitals); hospitals not in the top rank that had on-site facilities for cardiac catheterization, coronary angioplasty, and bypass surgery (similarly equipped hospitals); and the remaining hospitals (non-similarly equipped hospitals). We compared 30-day mortality; the rates of use of aspirin, beta-blockers, and reperfusion; and the relation of differences in rates of therapy to short-term mortality. RESULTS: Admission to a top-ranked hospital was associated with lower adjusted 30-day mortality (odds ratio, 0.87; 95 percent confidence interval, 0.76 to 1.00; P=0.05 for top-ranked hospitals vs. the others). Among patients without contraindications to therapy, top-ranked hospitals had significantly higher rates of use of aspirin (96.2 percent, as compared with 88.6 percent for similarly equipped hospitals and 83.4 percent for non-similarly equipped hospitals; P<0.01) and beta-blockers (75.0 percent vs. 61.8 percent and 58.7 percent, P<0.01), but lower rates of reperfusion therapy (61.0 percent vs. 70.7 percent and 65.6 percent, P=0.03). The survival advantage associated with admission to top-ranked hospitals was less strong after we adjusted for factors including the use of aspirin and beta-blockers (odds ratio, 0.94; 95 percent confidence interval, 0.82 to 1.08; P=0.38). CONCLUSIONS: Admission to a hospital ranked high on the list of "America's Best Hospitals" was associated with lower 30-day mortality among elderly patients with acute myocardial infarction. A substantial portion of the survival advantage may be associated with these hospitals' higher rates of use of aspirin and beta-blocker therapy.

Adrenergic beta-Antagonists↗
PubMed1999

Moe1, a conserved protein in Schizosaccharomyces pombe, interacts with a Ras effector, Scd1, to affect proper spindle formation.

In fission yeast, Scd1/Ral1 is a putative guanine nucleotide exchange factor for Cdc42sp and also acts as a Ras1 effector necessary for the regulation of cytoskeleton organization. In this study, we have characterized a protein, Moe1, that binds directly to Scd1. A moe1 null (Delta) mutant exhibits numerous phenotypes indicative of abnormal microtubule functioning, including an abnormality in the spindle. moe1Delta mutants are resistant to microtubule destabilizing agents; moreover, moe1Delta rescued the growth defects of tubulin mutants containing unstable microtubules. These results suggest that Moe1 induces instability in microtubules. Biochemical and subcellular localization studies suggest that Moe1 and Scd1 colocalize in the nucleus. Furthermore, loss of function in Scd1 or Ras1 also induced abnormality in the spindle and is synthetically lethal with moe1Delta producing cells that lack a detectable spindle. These data demonstrate that Moe1 is a component of the Ras1 pathway necessary for proper spindle formation in the nucleus. Human and nematode Moe1 both can substitute for yeast Moe1, indicating that the function of Moe1 in spindle formation has been conserved substantially during evolution.

Carrier Proteins↗
PubMed1999

Conformational Structure of Triblock Copolymers by FT-Raman and FTIR Spectroscopy.

Fourier transform Raman (FT-Raman) and Fourier transform infrared (FTIR) spectra of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers as pure solids or liquids and in aqueous solutions have been examined. The qualitative features in Raman and FTIR spectra of these copolymers have been presented. The Raman and FTIR spectra of PEO-PPO-PEO triblock copolymers are very sensitive to the structural and conformational changes. It shows that the relative intensities of several peaks in Raman spectra are dependent on the PPO/PEO ratios and the conformation of the copolymers. From Raman and FTIR spectra, Pluronic F68 and F88 assume helical structures with a few trans conformers. Other block copolymers exhibit that the disordered structure increases with increasing PPO/PEO ratio. Comparison of Raman spectra of PEO-PPO-PEO triblock copolymers as pure solids or liquids with those in aqueous solutions has been presented. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Psychological stress in the workplace and menstrual function.

The relation between psychological stress at work and menstrual function was examined for 276 healthy, working, premenopausal women who participated in the California Women's Reproductive Health Study in 1990-1991. Subjects collected daily urine samples and completed a daily diary for an average of five menstrual cycles. Metabolites of estrogen and progesterone were measured in the urine, and computer algorithms were developed to characterize each cycle as ovulatory or anovulatory and to select a probable day of ovulation. A telephone interview collected information about psychological stress at work as well as other occupational, demographic, lifestyle, and environmental factors. Logistic regression was used to model stressful work and risk of anovulation (> or = 36 days without ovulating) and measures of within-woman cycle variability. Repeated measures analyses were performed on other menstrual cycle parameters. Stressful work (high demand in combination with low control) was not strongly related to an increased risk for anovulation or cycle variability or to any of the following cycle endpoints: short luteal phase (< or = 10 days), long follicular phase (> or = 24 days), long menses (> or = 8 days), or long cycle (> or = 36 days). However, women in stressful jobs had a more than doubled risk for short cycle length (< or = 24 days) compared with women not working in stressful jobs (adjusted odds ratio = 2.24, 95% confidence interval 1.09-4.59).

Adolescent↗
PubMed1999

T lymphocyte development in the absence of CD3 epsilon or CD3 gamma delta epsilon zeta.

CD3 gamma, delta, epsilon, and zeta proteins together with the pre-TCR alpha-chain (pT alpha) and a rearranged TCR beta-chain assemble to form the pre-TCR that controls the double negative (DN) to double positive (DP) stages of thymopoiesis. The CD3 proteins are expressed before pT alpha and TCR beta-chains in prothymocytes and are expressed intracellularly in precursor NK cells, suggesting that the CD3 complex may function independent of pT alpha and TCR beta. In this report, both the role of CD3 epsilon exclusively, and the role of CD3 proteins collectively, in thymocyte and NK cell development were examined. In a mouse strain termed E delta P, a neomycin cassette inserted within the CD3 epsilon promoter abolishes CD3 epsilon and delta expression and also abolishes CD3 gamma expression in all but a small minority (< or =1%) of prothymocytes. These prothymocytes became deficient in CD3 epsilon alone upon reconstitution of CD3 delta expression and were severely, but not completely, arrested at the DN stage, as small numbers of double positive thymocytes were detected. In de facto CD3 gamma delta epsilon zeta(null) mice generated by crossing the epsilon delta P mice with CD3 zeta-/- mice, thymopoiesis were arrested at the CD44-CD25+ DN stage as observed in RAG-/- mice, DJ and VDJ recombination at the TCR beta locus was functional, and normal numbers of NK cells were detected. Together, the findings demonstrate that during thymocyte development, the CD3 complex collectively is not essential until the critical CD44-CD25+ DN stage in which pre-TCR begins to function, whereas CD3 epsilon is critical for the assembly of pre-TCR. Moreover, CD3 proteins are dispensable for NK cell development.

Animals↗
PubMed1999

Arf proteins bind to mitotic kinesin-like protein 1 (MKLP1) in a GTP-dependent fashion.

Arf proteins comprise a family of 21-kDa GTP-binding proteins with many proposed functions in mammalian cells, including the regulation of several steps of membrane transport, maintenance of organelle integrity, and activation of phospholipase D. We performed a yeast two-hybrid screen of human cDNA libraries using a dominant activating allele, [Q71L], of human Arf3 as bait. Eleven independent isolates contained plasmids encoding the C-terminal tail of mitotic kinesin-like protein-1 (MKLP1). Further deletion mapping allowed the identification of an 88 amino acid Arf3 binding domain in the C-terminus of MKLP1. This domain has no clear homology to other Arf binding proteins or to other proteins in the protein databases. The C-terminal domain of MKLP1 was expressed and purified from bacteria as a GST fusion protein and shown to bind Arf3 in a GTP-dependent fashion. A screen for mutations in Arf3 that specifically lost the ability to bind MKLP1 identified 10 of 14 point mutations in the GTP-sensitive switch I or switch II regions of Arf3. Two-hybrid assays of the C-terminal domain of MKLP1 with each of the human Arf isoforms revealed strong interaction with each. Taken together, these data are all supportive of the conclusion that activated Arf proteins bind to the C-terminal "tail" domain of MKLP1.

ADP-Ribosylation Factors↗
PubMed1999

Short-term aerobic training response in chronic myopathies.

We have previously demonstrated that patients with mitochondrial myopathies can benefit from short-term aerobic exercise training. In this study, we compared the responses to short-term aerobic training of patients with mitochondrial myopathies, patients with nonmetabolic myopathies, and sedentary normal subjects. Training consisted of 8 weeks of treadmill exercise at 70% to 85% of estimated maximum heart rate reserve. All groups showed significant improvements in estimated aerobic capacity as well as heart rate and blood lactate at submaximal exercise intensities. The increase in estimated aerobic capacity was greater in the mitochondrial myopathy patients than in the other two groups. Phosphorus magnetic resonance spectroscopy demonstrated increased oxidative capacity of muscle in patients with mitochondrial myopathies in response to this training but not in patients with other, nonmetabolic myopathies or sedentary control subjects. A self-assessed measurement of functional status (SF-36) suggested improved quality of life associated with the training. This study demonstrates that short-term aerobic training at low intensity can benefit patients with nonmetabolic myopathies but to a lesser extent than patients with mitochondrial myopathies.

Adolescent↗
PubMed1999

Synthesis of superporous hydrogels: hydrogels with fast swelling and superabsorbent properties.

We have been interested in the synthesis of hydrogels with fast swelling kinetics and superabsorbent properties. To increase the water absorption rate, interconnected pores were introduced to the hydrogels. Since the pore size in the dried hydrogels is in the order of hundreds of micrometers, these hydrogels are called "superporous" hydrogels. Superporous hydrogels were synthesized by crosslinking polymerization of various vinyl monomers in the presence of gas bubbles formed by the chemical reaction of acid and NaHCO3. The polymerization process was optimized to capture the gas bubbles inside the synthesized hydrogels. The use of the NaHCO3/acid system allowed easy control of timing for gelation and foam formation. We found that PF127 was the best foam stabilizer for most of the monomer systems used in our study. Scanning electron microscope (SEM) pictures showed interconnected pores forming capillary channels. The capillary channels, which were critical for fast swelling, were preserved during drying by dehydrating water-swollen hydrogels with ethanol before drying. The ethanol-dehydrated superporous hydrogels reached equilibrium swelling within minutes. The equilibrium swelling time could be reduced to less than a minute with the use of a wetting agent. In our study, water moisture was used as a wetting agent since the amount of moisture content in the dried hydrogels easily could be controlled. Preparation of superporous hydrogels using the right blowing system, foam stabilizer, drying method, and wetting agent makes it possible to reduce the swelling time to less than a minute regardless of the size of the dried gels. The superporous hydrogels can be used where fast swelling and superabsorbent properties are critical.

Absorption↗