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S Chen

Publications and source records attributed to S Chen.

At least 793 records · Page 44Linked to original sources
PubMed1998

The role of 12-lipoxygenase in pancreatic -cells (Review).

Leukocyte type 12-lipoxygenase (12-LO) catalyzes the conversion of arachidonic acid (AA; C20:4) to 12-hydroperoxyeicosatetraenoic acid (12-HPETE) and linoleic acid (LA; C18:2) to 13-hydroperoxyoctadecadienoic acid (13-HPODE). Previous studies have demonstrated that 12-LO, but not 5- or 15-lipoxygenase (5-LO, 15-LO respectively), is specifically expressed in pancreatic -cells and is involved in regulating glucose-stimulated insulin secretion. Lipoxygenase products also have been linked with inflammatory pathways in endothelial cells, kidney mesangial cells, inflammatory bowel disease, and corneal epithelial cells. Therefore, 12-LO may play a role in cytokine mediated inflammation in pancreatic beta-cells (i.e. beta -cell dysfunction and cytotoxicity). Cytokines such as IL-1 stimulate both de novo 12-LO protein synthesis and enzyme activity in pancreatic beta-cells. The products generated by 12-LO may ultimately be involved in cellular events that lead to lipid peroxidation. Hydroperoxide and free radical production in beta-cells can activate intracellular signaling pathways that lead to cell death or may directly damage mitochondrial and plasma membranes. Increased 12-LO expression has also been found in islets from prediabetic Zucker fatty rats, a model that demonstrates insulin secretory defects similar to human type 2 diabetes. In this review, we present an overview of the 12-LO pathway in regulating glucose-stimulated insulin secretion in beta-cells as well as more recent data which supports the hypothesis that the 12-LO pathway participates in cytokine mediated beta-cell dysfunction and cytotoxicity.

Animals↗
PubMed1998

Piecewise exponential survival trees with time-dependent covariates.

Survival trees methods are nonparametric alternatives to the semiparametric Cox regression in survival analysis. In this paper, a tree-based method for censored survival data with time-dependent covariates is proposed. The proposed method assumes a very general model for the hazard function and is fully nonparametric. The recursive partitioning algorithm uses the likelihood estimation procedure to grow trees under a piecewise exponential structure that handles time-dependent covariates in a parallel way to time-independent covariates. In general, the estimated hazard at a node gives the risk for a group of individuals during a specific time period. Both cross-validation and bootstrap resampling techniques are implemented in the tree selection procedure. The performance of the proposed survival trees method is shown to be good through simulation and application to real data.

Biometry↗
PubMed1997

Advantage of yttrium-90-labeled over iodine-131-labeled monoclonal antibodies in the treatment of a human lung carcinoma xenograft.

BACKGROUND: The purpose of this investigation was to compare the therapeutic effectiveness of yttrium-90 (90Y)-labeled monoclonal antibodies (MoAbs) with iodine-131 (131I)-labeled MoAbs delivered to human tumor xenografts at their maximum tolerated doses (MTD). METHODS: Nude mice bearing size-matched human lung adenocarcinoma xenografts (Calu-3) with mean tumor dimensions of approximately 0.8 cm received intravenous injections of the MTD of either 90Y- or 131I-labeled MoAbs. The mice received 125 microCi of 90Y-RS11 or 90Y-RS7, or 300 microCi of 131I-RS11 or 131I-RS7. Tumor size was measured weekly. Body weight and blood counts were monitored to measure toxicity. RESULTS: The calculated average radiation doses delivered to tumors in mice treated with 90Y-RS11 and 90Y-RS7 were 3578 and 3787 centigray (cGy), respectively, versus 1264 and 1368 cGy for 131I-RS11 and 131I-RS7, respectively. These values were calculated taking into consideration the tumor size-dependent absorbed fractions for the beta particles of both radioisotopes. The calculated radiation doses absorbed in the tumor correlated with the tumor responses observed. Mean tumor volume decreases at nadir were 66% and 87% after 90Y-RS11 and 90Y-RS7 therapy, respectively, with 15 of 30 mice treated with either MoAb having complete regression of their tumors. In contrast, only mean stable disease was observed with the 131I MoAb treatments. CONCLUSIONS: The results demonstrate the superiority of 90Y-labeled MoAbs over conventionally labeled 131I-labeled MoAbs for therapy in this model. The fact that a substantial percentage of complete remissions was achieved with 90Y-labeled MoAbs suggests a considerable radiosensitivity of the tumor studied, and supports the suitability of choosing this tumor type as an attractive target for future clinical radioimmunotherapy.

Animals↗
PubMed1997

Effectiveness of five-loop coils to occlude patent ductus arteriosus.

Coil occlusion of patent ductus arteriosus with 5-loop coils was undertaken in 10 patients without coil embolizations, and with 90% immediate occlusion and 100% occlusion at follow-up. We conclude that 5-loop coil occlusion of patent ductus arteriosus is safe and effective.

Adult↗
PubMed1997

Catalytic properties of NAD(P)H:quinone oxidoreductase-2 (NQO2), a dihydronicotinamide riboside dependent oxidoreductase.

Human NAD(P)H:quinone acceptor oxidoreductase-2 (NQO2) has been prepared using an Escherichia coli expression method. NQO2 is thought to be an isoform of DT-diaphorase (EC 1.6.99.2) [also referred to as NAD(P)H:quinone acceptor oxidoreductase] because there is a 49% identity between their amino acid sequences. The present investigation has revealed that like DT-diaphorase, NQO2 is a dimer enzyme with one FAD prosthetic group per subunit. Interestingly, NQO2 uses dihydronicotinamide riboside (NRH) rather than NAD(P)H as an electron donor. It catalyzes a two-electron reduction of quinones and oxidation-reduction dyes. One-electron acceptors, such as potassium ferricyanide, cannot be reduced by NQO2. This enzyme also catalyzes a four-electron reduction, using methyl red as the electron acceptor. The NRH-methyl red reductase activity of NQO2 is 11 times the NADH-methyl red reductase activity of DT-diaphorase. In addition, through a four-electron reduction reaction, NQO2 can catalyze nitroreduction of cytotoxic compound CB 1954 [5-(aziridin-1-yl)-2,4-dinitrobenzamide]. NQO2 is 3000 times more effective than DT-diaphorase in the reduction of CB 1954. Therefore, NQO2 is a NRH-dependent oxidoreductase which catalyzes two- and four-electron reduction reactions. NQO2 is resistant to typical inhibitors of DT-diaphorase, such as dicumarol, Cibacron blue, and phenindone. Flavones are inhibitors of NQO2. However, structural requirements of flavones for the inhibition of NQO2 are different from those for DT-diaphorase. The most potent flavone inhibitor tested so far is quercetin (3,5,7,3',4'-. 6pentahydroxyflavone). It has been found that quercetin is a competitive inhibitor with respect to NRH (Ki = 21 nM). NQO2 is 43 amino acids shorter than DT-diaphorase, and it has been suggested that the carboxyl terminus of DT-diaphorase plays a role in substrate binding (S. Chen et al., Protein Sci. 3, 51-57, 1994). In order to understand better the basis of catalytic differences between NQO2 and DT-diaphorase, a human NQO2 with 43 amino acids from the carboxyl terminus of human DT-diaphorase (i.e., hNQO2-hDT43) has been prepared. hNQO2-hDT43 still uses NRH as an electron donor. In addition, the chimeric enzyme is inhibited by quercetin but not dicumarol. These results suggest that additional region(s) in these enzymes is involved in differentiating NRH from NAD(P)H.

Amino Acid Sequence↗
PubMed1997

Design, synthesis, and biochemical evaluation of phosphonate and phosphonamidate analogs of glutathionylspermidine as inhibitors of glutathionylspermidine synthetase/amidase from Escherichia coli.

Three phosphapeptides designed to mimic two distinct tetrahedral intermediates formed during either the synthesis or hydrolysis of glutathionylspermidine (Gsp) were synthesized and evaluated as inhibitors of the bifunctional enzyme Gsp synthetase/amidase. While the polyamine-containing phosphapeptides were determined to be potent and selective inhibitors, they selectively inhibit the synthetase activity over the amidase domain. A phosphonate-containing tetrahedral mimic is a reversible mixed-type inhibitor of Gsp synthetase with an inhibition constant of 6 microM for the inhibitor binding to the free enzyme (Ki) and 14 microM for the inhibitor binding to the enzyme-substrate complex (Ki'). The corresponding phosphonamidate is a slow-binding inhibitor with a Ki of 24 microM and a Ki* (isomerization inhibition constant) of 0.88 microM. A non-polyamine-containing phosphonamidate exhibits no significant inhibition of the synthetase or amidase activity.

Amide Synthases↗
PubMed1997

Polarized apical targeting directed by the signal/anchor region of simian virus 5 hemagglutinin-neuraminidase.

To examine the possibility of independent cytoplasmic/transmembrane domain-based apical sorting, we have investigated paramyxovirus SV5 hemagglutinin-neuraminidase (HN), a type II membrane protein with a small N-terminal signal/anchor region. In SV5-infected Madin-Darby canine kidney (MDCK) cells, >90% of HN is found on the apical surface. We have expressed chimeric proteins in which the N terminus of HN, including its signal/anchor region, is attached to a (normally cytosolic) reporter pyruvate kinase (PK). PK itself expressed immediately downstream from a cleavable signal peptide was converted to a 58-kDa N-linked glycosylated form, which was secreted predominantly (80%) to the basolateral surface of MDCK cells. By contrast, stably expressed PK chimeras, now anchored as type II membrane proteins with either the first 48 or 72 amino acids of HN, received similar N-linked glycosylation, yet exhibited polarized transport with a preferentially (75%) apical distribution. These results suggest that the N-terminal signal/anchor region of HN contains independent sorting information for apical specific targeting in MDCK cells.

Animals↗
PubMed1997

Cloning and functional expression of a swelling-induced chloride conductance regulatory protein, plCln, from rabbit ocular ciliary epithelium.

The cDNA encoding a swelling-induced chloride conductance regulatory protein, plcln, was cloned from rabbit ciliary epithelium by using a polymerase chain reaction (PCR)-based approach. The open reading frame encoding 236 amino acids possesses high amino acid identity (93/%) with the previously cloned plcln from human ciliary epithelium. Outwardly rectifying currents were recorded in Xenopus oocytes injected with plcln cRNA, a result consistent with plcln expression in ciliary epithelium. A widespread distribution and marked expression of plcln mRNA in both nonpigmented ciliary epithelial (NPE) cells and pigmented ciliary epithelial (PE) cells was found for the first time. In situ hybridization analysis showed that plcln expression is more abundant in NPE than PE. These findings are consistent with the idea that plcln may be an important regulatory element in these secretory cells.

Amino Acid Sequence↗
PubMed1997

Preparation and Characterization of Surface-Covered Nanometer-Sized Catalyst by Carboxylate Phase Transfer

Surface-covered nanometer-sized CuO/Al2O3, CuO-ZnO/Al2O3, and CuO/ZnO catalysts were prepared by phase transfer with carboxylate. The surface-covered structure was studied using XPS, XRD, TEM, and high-resolution electron microscope. The results indicated that amorphous CuO and ZnO were dispersed on the surface of nanometer-sized Al2O3 particles in catalysts CuO-ZnO/Al2O3 and CuO/Al2O3, respectively. The thickness of its surface layer is about several angstroms. No spinel structure was found in the catalyst. The particle size of the surface-covered CuO/Al2O3 catalyst was about 2-3 nm. Al2O3 in the catalyst was amorphous. Surface-covered material CuO in the catalyst with low CuO content was also armophous. A large amount of copper carboxylate resulted in crystalline CuO and Cu2O. The protective ability of carboxylate to sol particles differs from the metal element of carboxylate. Copyright 1997 Academic Press. Copyright 1997Academic Press

Journal Article↗
PubMed1997

Phenotypic knockout of HIV type 1 chemokine coreceptor CCR-5 by intrakines as potential therapeutic approach for HIV-1 infection.

A genetic defect in a CC-chemokine receptor (CCR)-5, the principal coreceptor for the macrophage-tropic HIV type 1 (HIV-1), recently was found to naturally protect CCR-5-defective, but healthy, individuals from HIV-1 infection. In this study, we mimic the natural resistance of the CCR-5-defective individuals by designing a strategy to phenotypically knock out CCR-5. The inactivation of the CCR-5 coreceptor is accomplished by targeting a modified CC-chemokine to the endoplasmic reticulum to block the surface expression of newly synthesized CCR-5. The lymphocytes transduced to express the intracellular chemokine, termed "intrakine," were found to be viable and resistant to macrophage-tropic HIV-1 infection. Thus, this gene-based intrakine strategy targeted at the conserved cellular receptor for the prevention of HIV-1 entry should have significant advantages over currently described approaches for HIV-1 therapy.

Acquired Immunodeficiency Syndrome↗
PubMed1997

CLARP, a death effector domain-containing protein interacts with caspase-8 and regulates apoptosis.

We have identified and characterized CLARP, a caspase-like apoptosis-regulatory protein. Sequence analysis revealed that human CLARP contains two amino-terminal death effector domains fused to a carboxyl-terminal caspase-like domain. The structure and amino acid sequence of CLARP resemble those of caspase-8, caspase-10, and DCP2, a Drosophila melanogaster protein identified in this study. Unlike caspase-8, caspase-10, and DCP2, however, two important residues predicted to be involved in catalysis were lost in the caspase-like domain of CLARP. Analysis with fluorogenic substrates for caspase activity confirmed that CLARP is catalytically inactive. CLARP was found to interact with caspase-8 but not with FADD/MORT-1, an upstream death effector domain-containing protein of the Fas and tumor necrosis factor receptor 1 signaling pathway. Expression of CLARP induced apoptosis, which was blocked by the viral caspase inhibitor p35, dominant negative mutant caspase-8, and the synthetic caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-(OMe)-fluoromethylketone (zVAD-fmk). Moreover, CLARP augmented the killing ability of caspase-8 and FADD/MORT-1 in mammalian cells. The human clarp gene maps to 2q33. Thus, CLARP represents a regulator of the upstream caspase-8, which may play a role in apoptosis during tissue development and homeostasis.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Leukemia-associated retinoic acid receptor alpha fusion partners, PML and PLZF, heterodimerize and colocalize to nuclear bodies.

In acute promyelocytic leukemia (APL), the typical t(15;17) and the rare t(11;17) translocations express, respectively, the PML/RARalpha and PLZF/RARalpha fusion proteins (where RARalpha is retinoic acid receptor alpha). Herein, we demonstrate that the PLZF and PML proteins interact with each other and colocalize onto nuclear bodies (NBs). Furthermore, induction of PML expression by interferons leads to a recruitment of PLZF onto NBs without increase in the levels of the PLZF protein. PML/RARalpha and PLZF/RARalpha localize to the same microspeckled nuclear domains that appear to be common targets for the two fusion proteins in APL. Although PLZF/RARalpha does not affect the localization of PML, PML/RARalpha delocalizes the endogenous PLZF protein in t(15;17)-positive NB4 cells, pointing to a hierarchy in the nuclear targeting of these proteins. Thus, our results unify the molecular pathogenesis of APL with at least two different RARalpha gene translocations and stress the importance of alterations of PLZF and RARalpha nuclear localizations in this disease.

Animals↗
PubMed1997

The effects of total lymphocyte deficiency on the extent of atherosclerosis in apolipoprotein E-/- mice.

Activated T lymphocytes are present in human atherosclerotic lesions and autoantibodies to antigens within lesions have been detected in serum, but the roles of the cellular and humoral immune systems in atherogenesis have not been determined. The effect of total lymphocyte deficiency on atherogenesis was investigated by crossing apo E-deficient mice (which develop atherosclerosis resembling human disease) with mice deficient in RAG2 (which is required for normal B and T lymphocyte development). Mice were placed on a fat- and cholesterol-enriched diet for 12 wk. RAG2-deficient mice had no serum autoantibodies, in contrast to the high titers in RAG2+/- littermates. There were no T lymphocytes and a markedly reduced number of MHC class II-positive macrophages in atherosclerotic lesions of RAG2-deficient mice. Despite these differences, RAG2-deficient mice developed atherosclerosis similar in extent to that in immunocompetent littermates, based on quantification by two independent methods. In conclusion, the absence of autoantibodies and T lymphocytes did not influence the extent of aortic atherosclerotic lesions in apo E-deficient mice.

Animals↗
PubMed1997

The kinetics of L-selectin tethers and the mechanics of selectin-mediated rolling.

Two mechanisms have been proposed for regulating rolling velocities on selectins. These are (a) the intrinsic kinetics of bond dissociation, and (b) the reactive compliance, i.e., the susceptibility of the bond dissociation reaction to applied force. To determine which of these mechanisms explains the 7.5-11.5-fold faster rolling of leukocytes on L-selectin than on E- and P-selectins, we have compared the three selectins by examining the dissociation of transient tethers. We find that the intrinsic kinetics for tether bond dissociation are 7-10-fold more rapid for L-selectin than for E- and P-selectins, and are proportional to the rolling velocities through these selectins. The durations of pauses during rolling correspond to the duration of transient tethers on low density substrates. Moreover, applied force increases dissociation kinetics less for L-selectin than for E- and P-selectins, demonstrating that reactive compliance is not responsible for the faster rolling through L-selectin. Further measurements provide a biochemical and biophysical framework for understanding the molecular basis of rolling. Displacements of tethered cells during flow reversal, and measurements of the distance between successive pauses during rolling provide estimates of the length of a tether and the length of the adhesive contact zone, and suggest that rolling occurs with as few as two tethers per contact zone. Tether bond lifetime is an exponential function of the force on the bond, and the upper limit for the tether bond spring constant is of the same order of magnitude as the estimated elastic spring constant of the lectin-EGF unit. Shear uniquely enhances the rate of L-selectin transient tether formation, and conversion of tethers to rolling adhesions, providing further understanding of the shear threshold requirement for rolling through L-selectin.

Antigens, Surface↗
PubMed1997

Mechanism of the synergistic end-product regulation of Bacillus subtilis glutamine phosphoribosylpyrophosphate amidotransferase by nucleotides.

De novo purine nucleotide synthesis is regulated, at least in part, by end-product inhibition of glutamine PRPP amidotransferase. An important feature of this inhibition is the fact that certain synergistic nucleotide pairs give more than additive inhibition. The physiological importance of synergism is in amplifying regulation by the adenine and guanine nucleotide end products of de novo synthesis. Using a new method to quantitate synergism, ADP plus GMP were confirmed [Meyer, E., and Switzer, R. L. (1978) J. Biol. Chem. 254, 5397-5402] to give strong synergistic inhibition of Bacillus subtilis glutamine PRPP amidotransferase. An X-ray structure of the ternary enzyme.ADP.GMP complex established that ADP binds to the allosteric A site and GMP to the catalytic C site. GMP increased the binding affinity of ADP for the A site by approximately 20-fold. Synergism results from a specific nucleotide-nucleotide interaction that is dependent upon a nucleoside diphosphate in the A site and a nucleoside monophosphate in the C site. Furthermore, synergism is enhanced by the competition between nucleotide inhibitor and PRPP substrate for the C site. Purine base specificity results from a backbone carbonyl interaction of Lys305' with the 6-NH2 group of adenine in the A site and a Ser347 Ogamma interaction with the 2-NH2 group of guanine in the C site. Steric considerations favor binding of the nucleoside diphosphate to the A site. Site-directed replacements of key residues increased the nucleotide concentrations needed for 50% inhibition and in some cases perturbed synergism. Mutations in either of the nucleotide sites perturbed function at both sites, supporting the important role of synergism.

Adenosine Diphosphate↗
PubMed1997

The development of a model for the homing of multiple myeloma cells to human bone marrow.

Prior in vitro studies have suggested a role of adhesion molecules, bone marrow stromal cells (BMSCs), and cytokines in the regulation of human multiple myeloma (MM) cell growth and survival. Although in vivo models have been developed in severe combined immunodeficient (SCID) mice that support the growth of human MM within the murine BM microenvironment, these xenograft models do not permit a study of the role of adhesion proteins in human MM cell-human BMSC interactions. We therefore established an in vivo model of human MM using SCID mice implanted with bilateral human fetal bone grafts (SCID-hu mice). For the initial tumor innoculum, human MM derived cell lines (1 x 10(4) or 5 x 10(4) ARH-77, OCI-My5, U-266, or RPMI-8226 cells) were injected directly into the BM cavity of the left bone implants in irradiated SCID-hu mice. MM cells engrafted and proliferated in the left human fetal bone implants within SCID-hu mice as early as 4 weeks after injection of as few as 1 x 10(4) MM cells. To determine whether homing of tumor cells occurred, animals were observed for up to 12 weeks after injection and killed to examine for tumor in the right bone implants. Of great interest, metastases to the right bone implants were observed at 12 weeks after the injection of 5 x 10(4) MM cells, without spread of human MM cells to murine BM. Human MM cells were identified on the basis of characteristic histology and monoclonal human Ig. Importantly, monoclonal human Ig and human interleukin-6 (IL-6), but not human IL-1beta or tumor necrosis factor-alpha, were detectable in sera of SCID-hu mice injected with MM cells. In addition, specific monoclonal Ig light chain deposition was evident within renal tubules. This in vivo model of human MM provides for the first time a means for identifying adhesion molecules that are responsible for specific homing of human MM cells to the human, as opposed to murine, BM microenvironment. Moreover, induction of human IL-6 suggests the possibility that regulation of MM cell growth by this cytokine might also be investigated using this in vivo model.

Animals↗