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S Chen

Publications and source records attributed to S Chen.

At least 667 records · Page 37Linked to original sources
PubMed1998

Amyloid beta-peptide possesses a transforming growth factor-beta activity.

Amyloid beta-peptide (Abeta) of 39-42 amino acid residues is a major constituent of Alzheimer's disease neurite plaques. Abeta aggregates (fibrils) are believed to be responsible for neuronal damage and dysfunction, as well as microglia and astrocyte activation in disease lesions by multiple mechanisms. Since Abeta aggregates possess the multiple valencies of an FAED motif (20th to 23rd amino acid residues), which resembles the putative transforming growth factor-beta (TGF-beta) active site motif, we hypothesize that Abeta monomers and Abeta aggregates may function as TGF-beta antagonists and partial agonists, analogous to previously described monovalent and multivalent TGF-beta peptide antagonists and agonists (Huang, S. S., Liu, Q., Johnson, F. E., Konish, Y., and Huang, J. S. (1997) J. Biol. Chem. 272, 27155-27159). Here, we report that the Abeta monomer, Abeta-(1-40) and its fragment, containing the motif inhibit radiolabeled TGF-beta binding to cell-surface TGF-beta receptors in mink lung epithelial cells (Mv1Lu cells). Abeta-(1-40)-bovine serum albumin conjugate (Abeta-(1-40)-BSA), a multivalent synthetic analogue of Abeta aggregates, exhibited cytotoxicity toward bovine cerebral endothelial cells and rat post-mitotic differentiated hippocampal neuronal cells (H19-7 cells) and inhibitory activities of radiolabeled TGF-beta binding to TGF-beta receptors and TGF-beta-induced plasminogen activator inhibitor-1 expression, that were approximately 100-670 times more potent than those of Abeta-(1-40) monomers. At less than micromolar concentrations, Abeta-(1-40)-BSA but not Abeta-(1-40) monomers inhibited proliferation of Mv1Lu cells. Since TGF-beta is an organizer of responses to neurodegeneration and is also found in neurite plaques, the TGF-beta antagonist and partial agonist activities of Abeta monomers and aggregates may play an important role in the pathogenesis of the disease.

Amino Acid Sequence↗
PubMed1998

Glutamatergic neurotransmission involves structural and clinical deficits of schizophrenia.

BACKGROUND: Phencyclidine and ketamine induce a syndrome closely resembling schizophrenia due to their blockade of N-methyl-D-aspartate (NMDA) receptor. These findings suggested that some aspects of schizophrenia are associated with decreased NMDA--glutamatergic function. We hypothesized that structural and symptomatic deficits in schizophrenia are related to glutamatergic neurotransmission. METHODS: We studied the relationships among cerebrospinal fluid (CSF) glutamatergic markers, clinical presentation of schizophrenia, and CT parameters of brain structure in drug-free schizophrenics. RESULTS: We found no significant differences between patients with schizophrenia and controls in CSF glutamatergic markers. When patients with schizophrenia were considered as a group, significant negative correlations between glutamatergic markers and brain structural measures as well as clinical measures were observed. Cluster analysis reveals a group of lower indices of glutamatergic neurotransmission, and more prominent thought disorder as well as ventricular enlargement, and a group with increased glutamate level. CONCLUSIONS: The findings support the hypothesis that altered glutamatergic neurotransmission plays a role in the brain structure and the clinical symptoms of schizophrenia.

Adult↗
PubMed1998

The kinetics and shear threshold of transient and rolling interactions of L-selectin with its ligand on leukocytes.

The kinetics of rolling and transient adhesions through selectins may depend on the kinetics and mechanical properties of the selectin:ligand bond, as well as on cellular properties including receptor-anchoring to the cell membrane and cytoskeleton. Kinetics are known to depend on the selectin and may also be ligand dependent. Here, we study the kinetics of transient and rolling interactions of leukocytes with L-selectin immobilized on a substrate. Remarkably, all properties examined are similar to those seen when the sidedness is opposite, i.e., when the L-selectin ligand is on the substrate and when the ligand is isolated from HEV rather than present on leukocytes. The similar properties include rolling velocity, a threshold shear stress above 0.4 dyn/cm2 required to support rolling, a k degreesoff of 7.0 to 6.8 s-1 for the L-selectin tether bond, and a mechanical bond length of 0.24 to 0.20 A. Our results argue against a model in which L-selectin shedding mediates rolling. Furthermore, the fast and force-resistant kinetic properties suggest that L-selectin is specialized dynamically for tethering leukocytes to vessel walls and adherent leukocytes.

Antibodies, Monoclonal↗
PubMed1998

Role for neuronally derived fractalkine in mediating interactions between neurons and CX3CR1-expressing microglia.

A recently identified chemokine, fractalkine, is a member of the chemokine gene family, which consists principally of secreted, proinflammatory molecules. Fractalkine is distinguished structurally by the presence of a CX3C motif as well as transmembrane spanning and mucin-like domains and shows atypical constitutive expression in a number of nonhematopoietic tissues, including brain. We undertook an extensive characterization of this chemokine and its receptor CX3CR1 in the brain to gain insights into use of chemokine-dependent systems in the central nervous system. Expression of fractalkine in rat brain was found to be widespread and localized principally to neurons. Recombinant rat CX3CR1, as expressed in Chinese hamster ovary cells, specifically bound fractalkine and signaled in the presence of either membrane-anchored or soluble forms of fractalkine protein. Fractalkine stimulated chemotaxis and elevated intracellular calcium levels of microglia; these responses were blocked by anti-CX3CR1 antibodies. After facial motor nerve axotomy, dramatic changes in the levels of CX3CR1 and fractalkine in the facial nucleus were evident. These included increases in the number and perineuronal location of CX3CR1-expressing microglia, decreased levels of motor neuron-expressed fractalkine mRNA, and an alteration in the forms of fractalkine protein expressed. These data describe mechanisms of cellular communication between neurons and microglia, involving fractalkine and CX3CR1, which occur in both normal and pathological states of the central nervous system.

Amino Acid Sequence↗
PubMed1998

Methylprednisolone inhibition of TNF-alpha expression and NF-kB activation after spinal cord injury in rats.

Post-traumatic inflammatory reaction has been implicated in the secondary injury after SCI. TNF-alpha is a key inflammatory mediator, which plays a pathogenetic role in cell death in inflammatory disorders and traumatic brain injury. TNF-alpha exerts its effector actions, at least partially, through the activation of a pro-inflammatory transcription factor, NF-kB, which in turn upregulates such genes as iNOS, cytokines, adhesive molecules, and others. Consistent with a post-traumatic inflammatory reaction after SCI, we noted an increase in TNF-alpha expression by Western blotting (4.5-fold increase at 1 day after SCI, P<0.01) and immunohistochemistry in a rat SCI model. Post-traumatic TNF-alpha expression was accompanied by an increase in NF-kB binding activity in nuclear proteins isolated from the injured cord (3.9-fold increase, P<0.01). MP is the only drug proven effective in improving neurological function in patients with acute SCI. The mechanism of action of MP is not fully understood, but is thought to be related to its antioxidant effects. MP is also a potent anti-inflammatory agent, which has been recently shown to inhibit NF-kB binding activity. MP (30 mg/kg, i.v.) given immediately after SCI reduced TNF-alpha expression by 55% (P<0.01) and NF-kB binding activity. These findings suggest that post-traumatic inflammatory activity that is mediated by the TNF-alpha-NF-kB cascade can be suppressed by MP.

Animals↗
PubMed1998

Retinoic acid uses divergent mechanisms to activate or suppress mitogenesis in rat aortic smooth muscle cells.

In different experimental models, retinoid has been shown to stimulate or suppress mitogenesis in cultured cells. The mechanisms underlying this seemingly paradoxical activity remain only partially understood. We have examined the ability of all-trans retinoic acid (ATRA), as well as a number of synthetic retinoids, either alone or in the presence of a mitogenic stimulus (i.e., endothelin), to regulate DNA synthesis and cell replication in cultured rat aortic smooth muscle cells. ATRA alone stimulates [3H]thymidine incorporation (approximately twofold) and increases cell number (approximately twofold) in these cultures but suppresses [3H]thymidine incorporation and reduces cell number in cultures treated with endothelin. The reduction in endothelin-stimulated DNA synthesis correlates closely with the ability of ATRA to inhibit endothelin-stimulated extracellular signal-regulated kinase but not c-Jun NH2-terminal kinase activity. Activation of mitogenesis, seen in the presence of ATRA alone, was independent of extracellular signal-regulated kinase activation but correlated well with increased expression of cyclin D1 mRNA and protein. Concomitant activation of the cdk inhibitor p21 led to truncation of ATRA's mitogenic activity at higher doses of ligand. Collectively, these data indicate that the role of retinoids in the regulation of mitogenesis in vascular smooth muscle is complex. Under quiescent conditions they activate mitogenesis, while in the presence of growth stimulation, as is frequently seen with vasculopathic conditions, they suppress mitogenesis. It appears that independent circuitry is involved in signaling each of these effects.

Animals↗
PubMed1998

An ultrastructural study of p75 neurotrophin receptor-immunoreactive fiber terminals in the reticular thalamic nucleus of young rats.

The reticular thalamic nucleus (RT) receives cholinergic fibers from both the basal forebrain and the brainstem. Recent studies have shown that the p75 neurotrophin receptor (p75NTR) is synthesized in cholinergic neurons in the basal forebrain but not in those in the brainstem. In this study, to identify cholinergic fibers originating from the basal forebrain, we used a monoclonal antibody against p75NTR (192-IgG) and characterized the ultrastructure of the immunoreactive fiber terminals in the rostral part of the RT in 3-week-old rats. Light microscopy revealed that p75NTR-immunoreactive fine fibers and varicosities were distributed throughout the nucleus. From electron micrographs, three types of labeled terminals were identified. The first type of labeled fiber terminals (63 out of 106) was consistently small, contained densely packed vesicles, and established asymmetrical synaptic contacts with heavy and bushy postsynaptic thickening on distal dendritic profiles; the second type (18 out of 106) established asymmetrical synaptic contacts with very slight postsynaptic thickening; and the third type (25 out of 106) of labeled terminals contained pleomorphic vesicles and established symmetrical synaptic contacts with more proximal dendritic surfaces than the first two types. In addition to the above, labeled dendritic profiles receiving non-labeled asymmetrical and symmetrical synaptic contacts were identified. These findings suggest that the basal forebrain cholinergic system establishes a variety of synaptic connections in the RT and influences cortical activity indirectly via thalamocortical pathways, as well as via direct projections to the cortex.

Animals↗
PubMed1998

Aromatase and breast cancer.

Estrogens play an important role in breast cancer development. Aromatase (CYP19), a cytochrome P450, is the enzyme that synthesizes estrogens. Aromatase is expressed at a higher level in human breast cancer tissue than in normal breast tissue using enzyme activity measurement, immunocytochemistry, and RT-PCR analysis. Cell culture, animal experiments using aromatase-transfected breast cancer cells, and transgenic mouse studies have demonstrated that in situ produced estrogen plays a more important role than circulating estrogens in breast tumor promotion. In addition, tumor aromatase has been shown to stimulate breast cancer growth in both an autocrine and a paracrine manner. RT-PCR and gene transcriptional studies have revealed that aromatase promoter switches from a glucocorticoid-stimulated promoter, I.4, in normal tissue to cAMP-stimulated promoters, I.3 and II, in cancereous tissue. Suppression of in situ estrogen biosynthesis can be achieved by the prevention of aromatase expression or by the inhibition of aromatase activity in breast tumors. While the control mechanism of aromatase expression in breast cancer tissue is not yet fully understood, aromatase-inhibitor therapy is considered for second-line treatment in patients who fail anti-estrogen therapy. Twenty to thirty percent of the patients who fail anti-estrogen treatment respond to aromatase-inhibitor treatment. Several potent and selective aromatase inhibitors have been developed and used to treat breast cancer. The binding nature of various aromatase inhibitors has been examined by computer modeling, site-directed mutagenesis of aromatase, and inhibition kinetics. The enzyme structure-function studies have led to the development of a computer model of the active site region of human aromatase. The model is used to evaluate the interaction of phytoestrogens such as flavones and isoflavones with aromatase. The study provides a molecular basis as to why isoflavones are significantly poorer inhibitors of aromatase than flavones. The phytoestrogen studies will help to determine which fruits and vegetables (those containing the appropriate phytoestrogens) should be included in the diet of postmenopausal women in order to reduce the incidence for breast cancer by inhibiting estrogen biosynthesis in breast tissue.

Animals↗
PubMed1998

Pulsed ultrafiltration characterization of binding.

We describe a new method for measuring binding constants, pulsed ultrafiltration. In this technique, a single injection or "pulse" of ligand is passed through a cell containing macromolecules confined by a conventional ultrafiltration membrane. Any binding of the ligand to the macromolecule alters the elution profile of the ligand. We describe this interaction by a set of coupled differential equations whose solution allows us to extract the binding density as a function of free ligand concentration eluting from the cell. A method of comparing elution profile areas which leads to values for both binding affinity and stoichiometry is also presented. We show that the pulsed ultrafiltration method can generate an extensive binding isotherm with a dense set of data points over a wide range of binding densities. We apply the method to several model ligand-macromolecule binding systems to demonstrate the measurement of equilibrium association constants and binding stoichiometry, the accuracy and precision of the method, and temperature dependence of binding. In general, our results agree with those from the literature, and they show that the approach is a fast and flexible method for characterizing ligand-macromolecule binding.

Chromatography, High Pressure Liquid↗
PubMed1998

In vivo inhibition of CC and CX3C chemokine-induced leukocyte infiltration and attenuation of glomerulonephritis in Wistar-Kyoto (WKY) rats by vMIP-II.

Chemokines play a central role in immune and inflammatory responses. It has been observed recently that certain viruses have evolved molecular piracy and mimicry mechanisms by encoding and synthesizing proteins that interfere with the normal host defense response. One such viral protein, vMIP-II, encoded by human herpesvirus 8, has been identified with in vitro antagonistic activities against CC and CXC chemokine receptors. We report here that vMIP-II has additional antagonistic activity against CX3CR1, the receptor for fractalkine. To investigate the potential therapeutic effect of this broad-spectrum chemokine antagonist, we studied the antiinflammatory activity of vMIP-II in a rat model of experimental glomerulonephritis induced by an antiglomerular basement membrane antibody. vMIP-II potently inhibited monocyte chemoattractant protein 1-, macrophage inflammatory protein 1beta-, RANTES (regulated on activation, normal T cell expressed and secreted)-, and fractalkine-induced chemotaxis of activated leukocytes isolated from nephritic glomeruli, significantly reduced leukocyte infiltration to the glomeruli, and markedly attenuated proteinuria. These results suggest that molecules encoded by some viruses may serve as useful templates for the development of antiinflammatory compounds.

Animals↗
PubMed1998

Sustained gene expression in retrovirally transduced, engrafting human hematopoietic stem cells and their lympho-myeloid progeny.

Inefficient retroviral-mediated gene transfer to human hematopoietic stem cells (HSC) and insufficient gene expression in progeny cells derived from transduced HSC are two major problems associated with HSC-based gene therapy. In this study we evaluated the ability of a murine stem cell virus (MSCV)-based retroviral vector carrying the low-affinity human nerve growth factor receptor (NGFR) gene as reporter to maintain gene expression in transduced human hematopoietic cells. CD34(+) cells lacking lineage differentiation markers (CD34(+)Lin-) isolated from human bone marrow and mobilized peripheral blood were transduced using an optimized clinically applicable protocol. Under the conditions used, greater than 75% of the CD34(+) cell population retained the Lin- phenotype after 4 days in culture and at least 30% of these expressed a high level of NGFR (NGFR+) as assessed by fluorescence-activated cell sorter analysis. When these CD34(+)Lin-NGFR+ cells sorted 2 days posttransduction were assayed in vitro in clonogenic and long-term stromal cultures, sustained reporter expression was observed in differentiated erythroid and myeloid cells derived from transduced progenitors, and in differentiated B-lineage cells after 6 weeks. Moreover, when these transduced CD34(+)Lin-NGFR+ cells were used to repopulate human bone grafts implanted in severe combined immunodeficient mice, MSCV-directed NGFR expression could be detected on 37% +/- 6% (n = 5) of the donor-type human cells recovered 9 weeks postinjection. These findings suggest potential utility of the MSCV retroviral vector in the development of effective therapies involving gene-modified HSC.

Animals↗
PubMed1998

Nop5p is a small nucleolar ribonucleoprotein component required for pre-18 S rRNA processing in yeast.

We have identified a novel nucleolar protein, Nop5p, that is essential for growth in Saccharomyces cerevisiae. Monoclonal antibodies B47 and 37C12 recognize Nop5p, which has a predicted size of 57 kDa and possesses a KKX repeat motif at its carboxyl terminus. Truncations that removed the KKX motif were functional and localized to the nucleolus, but conferred slow growth at 37 degreesC. Nop5p shows significant sequence homology with yeast Sik1p/Nop56p, and putative homologues in archaebacteria, plants, and human. Depletion of Nop5p in a GAL-NOP5 strain lengthened the doubling time about 5-fold, and selectively reduced steady-state levels of 40 S ribosomal subunits and 18 S rRNA relative to levels of free 60 S subunits and 25 S rRNA. Northern blotting and primer extension analyses showed that Nop5p depletion impairs processing of 35 S pre-rRNA at the A0 and A2 cleavage sites. Nop5p is associated with the small nucleolar RNAs U3, snR13, U14, and U18. Depletion of Nop5p caused the nucleolar protein Nop1p (yeast fibrillarin) to be localized to the nucleus and cytosol. Also, 37C12 co-immunoprecipitated Nop1p. These results suggest that Nop5p functions with Nop1p in the execution of early pre-rRNA processing steps that lead to formation of 18 S rRNA.

Amino Acid Sequence↗
PubMed1998

Involvement of de novo ceramide biosynthesis in tumor necrosis factor-alpha/cycloheximide-induced cerebral endothelial cell death.

Cytokines, including tumor necrosis factor-alpha (TNF-alpha), may elicit cytotoxic response through the sphingomyelin-ceramide signal transduction pathway by activation of sphingomyelinases and the subsequent release of ceramide: the universal lipid second messenger. Treatment of bovine cerebral endothelial cells (BCECs) with TNF-alpha for 16 h followed by cycloheximide (CHX) for 6 h resulted in an increase in ceramide accumulation, DNA fragmentation, and cell death. Application of a cell permeable ceramide analogue C2 ceramide, but not the biologically inactive C2 dihydroceramide, also induced DNA laddering and BCEC death in a concentration- and time-dependent manner. TNF-alpha/CHX-mediated ceramide production apparently is not a result of sphingomyelin hydrolysis because sphingomyelin content does not decrease in this death paradigm. In addition, an acidic sphingomyelinase inhibitor, desipramine, had no effect on TNF-alpha/CHX-induced cell death. However, addition of fumonisin B1, a selective ceramide synthase inhibitor, attenuated TNF-alpha/CHX-induced intracellular ceramide elevation and BCEC death. Together, these findings suggest that ceramide plays at least a partial role in this paradigm of BCEC death. Our results show, for the first time, that ceramide derived from de novo synthesis is an alternative mechanism to sphingomyelin hydrolysis in the BCEC death process initiated by TNF-alpha/CHX.

Animals↗
PubMed1998

Gold nanoelectrodes of varied size: transition to molecule-like charging

A transition from metal-like double-layer capacitive charging to redox-like charging was observed in electrochemical ensemble Coulomb staircase experiments on solutions of gold nanoparticles of varied core size. The monodisperse gold nanoparticles are stabilized by short-chain alkanethiolate monolayers and have 8 to 38 kilodaltons core mass (1.1 to 1.9 nanometers in diameter). Larger cores display Coulomb staircase responses consistent with double-layer charging of metal-electrolyte interfaces, whereas smaller core nanoparticles exhibit redox chemical character, including a large central gap. The change in behavior is consistent with new near-infrared spectroscopic data showing an emerging gap between the highest occupied and lowest unoccupied orbitals of 0.4 to 0.9 electron volt.

Journal Article↗
PubMed1998

Transient c-fos gene expression in cerebellar development and functional stimulation.

This study examined the temporal appearance of c-fos expression in rat cerebella from birth to postnatal day 21 (P21) and following systemic kainic acid administration in adults. During development, Fos positive granule cells appeared first at P3 in caudal lobules and extended to all folia by P9. These reactive cells occurred in clusters throughout the granular layer and reached their highest reactivity by P15. In addition, Fos positive basket and stellate cells were seen in the molecular layer at this time. A steep decline in Fos protein labeling of the cerebellum began by P18 and was barely detectable in adulthood. In adult rats, systemic injection of kainic acid induced c-fos expression in granule cells and stellate/basket interneurons within 1 h of treatment. Fos reactive granule cells appeared in clusters with some forming distinct parasagittal bands in caudal folia. One day after unilateral cerebellar lesioning, a limited number of reactive cells were found on the lesion margins. A combination of lesioning and systemic kainic acid produced a strong, c-fos expression throughout the ipsilateral granular layer as well as in Purkinje cell nuclei. Contralateral to the lesion, the pattern of granule cell reactivity appeared the same but slightly stronger than those with kainate alone. We conclude that c-fos gene expression occurs transiently in granule cells during postnatal development and can be rapidly re-induced in the adult following systemic injection of glutamate agonists. The c-fos expression patterns suggest that subpopulations of granule cells are clustered and related to the parasagittal compartments of Purkinje cells.

Age Factors↗
PubMed1998

Characterization of a silencer element in the human aromatase gene.

Aromatase, a cytochrome P450, catalyzes three consecutive hydroxylation reactions converting C19 androgens to aromatic C18 estrogens. The control of human aromatase expression is complex in that several promoters drive aromatase expression in a tissue-specific manner. Promoters I.3 and II are situated within the 700-bp region immediately upstream of exon II of the human aromatase gene, and these promoters have been shown to drive aromatase expression in breast tumors. This paper reports the characterization of a negative regulatory element that is situated between promoters I.3 and II and down regulates the action of these promoters. This negative regulatory element is thought to be a silencer element (S1) because it acts in an orientation- and promoter-independent manner. The position of S1 (5'-CCAAGGTCAGAAATGCTGCAATTCAAGCCA-3') was mapped by DNase I footprinting and DNA deletion analyses. The region contains three pairs of inverted repeats, as indicated by an underline, probably explaining why S1 functions in both orientations. Chloramphenicol acetyltransferase functional analyses indicated that the transcriptional activity of promoter I.3 was suppressed two- to three-fold by S1. Mutations of two inverted repeat segments (i.e., TTC and CC) in S1 destroyed its silencing action and modified the protein binding patterns in DNA mobility shift analysis. UV cross-linking experiments with 32P-labeled bromodeoxyuridine-substituted S1 as the probe and nuclear extracts from MCF-7 breast cancer cells and skin fibroblasts revealed that four major nuclear proteins, with molecular masses of approximately 150, 45, 30, and 25 kDa, bound to this element. Interestingly, two smaller proteins could be competed by an unlabeled fragment which contains promoter I.3. In addition, mutation of S1 at the region CC destroyed the ability to compete with the wild-type S1 for the binding of 30- and 25-kDa proteins. These results led us to propose that S1 down regulates the action of promoter I.3, and the 30- and 25-kDa proteins present in the nuclear extract of MCF-7 cells and skin fibroblasts are involved in the silencer action.

Aromatase↗
PubMed1998

RICK, a novel protein kinase containing a caspase recruitment domain, interacts with CLARP and regulates CD95-mediated apoptosis.

Signaling through the CD95/Fas/APO-1 death receptor plays a critical role in the homeostasis of the immune system. RICK, a novel protein kinase that regulates CD95-mediated apoptosis was identified and characterized. RICK is composed of an N-terminal serine-threonine kinase catalytic domain and a C-terminal region containing a caspase-recruitment domain. RICK physically interacts with CLARP, a caspase-like molecule known to bind to Fas-associated protein with death domain (FADD) and caspase-8. Expression of RICK promoted the activation of caspase-8 and potentiated apoptosis induced by Fas ligand, FADD, CLARP, and caspase-8. Deletion mutant analysis revealed that both the kinase domain and caspase-recruitment domain were required for RICK to promote apoptosis. Significantly, expression of a RICK mutant in which the lysine of the putative ATP-binding site at position 38 was replaced by a methionine functioned as an inhibitor of CD95-mediated apoptosis. Thus, RICK represents a novel kinase that may regulate apoptosis induced by the CD95/Fas receptor pathway.

Adenosine Triphosphate↗