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S Li

Publications and source records attributed to S Li.

At least 577 records · Page 32Linked to original sources
PubMed1999

Interferon beta induces T-helper 2 immune deviation in MS.

OBJECTIVE: To define the in vitro effects of interferon beta la (IFN-beta1a) on myelin basic protein (MBP)-reactive T cells and to determine its regulatory mechanism on cytokine networks in patients with MS. METHODS: The proliferation and cytokine production of MBP-reactive T-cell clones were measured in thymidine uptake assays and ELISA respectively. The precursor frequency of MBP-reactive T cells was estimated in a microwell culture system. RESULTS: IFN-beta inhibited the proliferation of established MBP-reactive T-cell clones, which correlated with enhanced production of anti-inflammatory interleukin (IL)-4 and IL-10, and a decrease in tumor necrosis factor alpha (TNF-alpha) and IFN-gamma. When examined with peripheral blood mononuclear cells (PBMCs), IFN-beta was found to reduce the in vitro T-cell responses to MBP, as indicated by the significantly decreased frequency of MBP-reactive T cells. The decreased frequency of MBP-reactive T cells corresponded to an augmented production of IL-4 and IL-10. Although the level of TNF-alpha and IFN-gamma was generally unaltered or decreased, IFN-beta appeared to enhance the production of IFN-gamma in PBMCs derived from some individuals with MS. CONCLUSION: Interferon beta la (IFN-beta) suppresses myelin basic protein (MBP)-reactive T cells and induces immune deviation toward the production of T-helper 2 cytokines, which may contribute to its therapeutic benefit in MS. The study also suggests some heterogeneity in MBP-reactive T-cell responses to IFN-beta in different individuals with MS.

Cell Division↗
PubMed1999

Cell-type-specific activation of p38 protein kinase cascades by the novel tumor promoter palytoxin.

Palytoxin is a potent non-12-O-tetradecanoylphorbol-13-acetate (TPA)-type skin tumor promoter. We used COS7 and HeLa cells to investigate the protein kinase cascades by which palytoxin activates the mitogen-activated protein kinase (MAPK) p38. Three p38 kinases have been identified: stress-activated protein kinase/extracellular signal-regulated kinase kinase-1 (SEK1), MAPK kinase 3 (MKK3), and MKK6. SEK1 phosphorylates and activates both p38 and c-Jun NH(2)-terminal kinase (JNK), whereas MKK3 and MKK6 selectively phosphorylate and activate p38. Although transiently overexpressed SEK1 activates p38 in cells, the importance of endogenous SEK1 for the activation of p38 by specific types of stimuli is unclear because some agents, such as sorbitol, can activate p38 in cells derived from SEK1 knockout mice. Because we previously showed that palytoxin activates JNK through an SEK1-dependent pathway, we investigated whether SEK1 also mediates the activation of p38 by palytoxin. The results presented here demonstrate that endogenous SEK1 does play an important role in the activation of p38 by palytoxin in specific cell types. In COS7 cells, palytoxin stimulated the phosphorylation of SEK1 and MKK6, and expression of dominant negative mutants of either SEK1 or MKK6 inhibited palytoxin-stimulated p38 activation. In HeLa cells, palytoxin stimulated the phosphorylation of MKK3 in addition to SEK1 and MKK6. In contrast to COS7 cells, in HeLa cells expression of a dominant negative mutant of SEK1 did not inhibit palytoxin-stimulated activation of p38, although expression of dominant negative mutants of either MKK3 or MKK6 did inhibit palytoxin-stimulated p38 activation in this cell type. These studies indicate that the importance of SEK1 in the activation of p38 by palytoxin depends on the ability of palytoxin to activate MKK3 and MKK6.

Acrylamides↗
PubMed1999

A new subdivision of mammalian neostriatum with functional implications to learning and memory.

A new subdivision with distinctive morphological and functional attributes has been identified at the caudomedial margin of the neostriatum and surrounding the rostrolateral border of the globus pallidus in the brains of the rat, cat, monkey, and human. The subdivision is termed marginal division (MrD) based on its location. It is readily distinguishable from the rest of striatum by consisting of spindle-shaped neurons, special connections, and intensely expressed immunoreactivities of many neuropeptides and some monoamines in the fibers, terminals, and neuronal somata. Three-dimensional reconstruction from Nissl-stained sections of the rat brain revealed that the MrD is a flat, pan-shaped zone between the neostriatum and globus pallidus. Functional neuronal connections were delineated by chemical-induced c-Fos expression between the MrD and hippocampus, amygdala, as well as the basal nucleus of Meynert. In rats with chemical lesions of bilateral MrD, learning and memory functions were severely impaired as demonstrated by double blind Y-maze test. Our results thus suggested that the MrD is a distinct part and a universal structure in the neostriatum of the mammalian brain and might play an important role in the mechanism of learning and memory.

Animals↗
PubMed1999

The human papilloma virus (HPV)-18 E6 oncoprotein physically associates with Tyk2 and impairs Jak-STAT activation by interferon-alpha.

We have examined the effects of human papilloma virus (HPV) E6 proteins on interferon (IFN) signaling. Here we show that expression of the 'malignant' HPV-18 E6 in human HT1080 cells results in inhibition of Jak-STAT activation in response to IFN-alpha but not IFN-gamma. This inhibitory effect is not shared by the 'benign' HPV-11 E6. The DNA-binding and transactivation capacities of the transcription factor ISGF3 are diminished in cells expressing HPV-18 E6 after IFN-alpha treatment as a result of decreased tyrosine phosphorylation of Tyk2, STAT2 and STAT1. However, HPV-18 E6 does not affect the induction of tyrosine phosphorylation and DNA-binding of STAT1 by IFN-gamma. In addition, HPV E6 proteins physically interact with Tyk2. This interaction takes place preferably with HPV-18 E6 and to a lesser extent with HPV-11 E6. The E6/Tyk2 interaction requires the JH6-JH7 domains of Tyk2, which are important for Tyk2 binding to the cytoplasmic portion of IFN-alpha receptor 1 (IFNAR1). These findings demonstrate an inhibitory role of HPV-18 E6 in the IFN-alpha-induced Jak-STAT pathway, which may be explained, at least in part, by the ability of E6 to interact with and impair Tyk2 activation.

Cell Line↗
PubMed1999

[Effect of zinc on the growth of cerebral cortex neurons of human fetus].

With the primary cultured cerebral cortex neurons of human fetus, studies were made to investigate the effect of zinc on the growth of neurons by using immunohistochemical stain and image analysis. The main results were as follows: (1) The growth of neurons of zinc group was the most prosperous at the 10-14 day of primary culture. The number of survival neurons was increased at the 1-28 day of culture (P < 0.01). (2) In the presence of zinc, the number and the length of neurites as well as the soma areas were all increased remarkably(P < 0.01). It was concluded that zinc could promote the growth of neurons.

Cell Count↗
PubMed1999

[Studies on 14 functional foods labelled with tumor inhibition effects].

Tumor inhibition effects of 14 functional foods were measured. Test items included sarcoma 180(S180) inhibiting test, Ehrlich ascites carcinoma (EAC) inhibiting test, phagocyte phagocytosis test and NK cell activity test. The results showed dose-response tendencies in all indices. But the tumor inhibition rate and survival time were decreased in high dose groups and even lower than those of control group (P < 0.05) in some samples. Correlation analysis showed a positive correlation between tumor inhibition rate and survival time, phagocytic percentage and phagocytic index, phagocytic percentage and NK activity, phagocytic index and NK activity (P < 0.01). Tumor inhibition rate and phagocytic percentage appeared negative correlation (P < 0.05). It is suggested that the present methods should be modified. The new and better methods needed to be established. The judge criterion for functional food should be strictly enacted. More Studies needed to be repeated for some foods with significant tumor inhibition functions.

Adjuvants, Immunologic↗
PubMed1999

A common TCR V-D-J sequence in V beta 13.1 T cells recognizing an immunodominant peptide of myelin basic protein in multiple sclerosis.

T cell responses to the immunodominant peptide (residues 83-99) of myelin basic protein are potentially associated with multiple sclerosis (MS). This study was undertaken to examine whether a common sequence motif(s) exists within the TCR complementarity-determining region (CDR)-3 of T cells recognizing the MBP83-99 peptide. Twenty MBP83-99-reactive T cell clones derived from patients with MS were analyzed for CDR3 sequences, which revealed several shared motifs. Some V beta 13.1 T cell clones derived from different patients with MS were found to contain an identical CDR3 motif, V beta 13.1-LGRAGLTY. Oligonucleotides complementary to the shared CDR3 motifs were used as specific probes to detect identical target CDR3 sequences in a large panel of T cell lines reactive to MBP83-99 and unprimed PBMC. The results revealed that, in contrast to other CDR3 motifs examined, the LGRAGLTY motif was common to T cells recognizing the MBP83-99 peptide, as evident by its expression in the majority of MBP83-99-reactive T cell lines (36/44) and PBMC specimens (15/48) obtained from randomly selected MS patients. The motif was also detected in lower expression in some PBMC specimens from healthy individuals, suggesting the presence of low precursor frequency of T cells expressing this motif in healthy individuals. This study provides new evidence indicating that the identified LGRAGLTY motif is preferentially expressed in MBP83-99-reactive T cells. The findings have important implications in monitoring and targeting MBP83-99-reactive T cells in MS.

Amino Acid Sequence↗
PubMed1999

Suppression of Raf-1 kinase activity and MAP kinase signalling by RKIP.

Raf-1 phosphorylates and activates MEK-1, a kinase that activates the extracellular signal regulated kinases (ERK). This kinase cascade controls the proliferation and differentiation of different cell types. Here we describe a Raf-1-interacting protein, isolated using a yeast two-hybrid screen. This protein inhibits the phosphorylation and activation of MEK by Raf-1 and is designated RKIP (Raf kinase inhibitor protein). In vitro, RKIP binds to Raf-1, MEK and ERK, but not to Ras. RKIP co-immunoprecipitates with Raf-1 and MEK from cell lysates and colocalizes with Raf-1 when examined by confocal microscopy. RKIP is not a substrate for Raf-1 or MEK, but competitively disrupts the interaction between these kinases. RKIP overexpression interferes with the activation of MEK and ERK, induction of AP-1-dependent reporter genes and transformation elicited by an oncogenically activated Raf-1 kinase. Downregulation of endogenous RKIP by expression of antisense RNA or antibody microinjection induces the activation of MEK-, ERK- and AP-1-dependent transcription. RKIP represents a new class of protein-kinase-inhibitor protein that regulates the activity of the Raf/MEK/ERK module.

3T3 Cells↗
PubMed1999

The inhibitory role of CpG immunostimulatory motifs in cationic lipid vector-mediated transgene expression in vivo.

We have previously reported that intravenous administration of cationic lipid-protamine-DNA complexes (LPD) induces production of large quantities of proinflammatory cytokines that are toxic and cause inhibition of transgene expression. Cytokine induction appears to be mediated by the unmethylated CpG sequences since methylation of plasmid DNA significantly decreases the cytokine levels. In this study, the inhibitory role of CpG in lipid-mediated gene transfer was further investigated using chemically well-defined, CpG-containing oligodeoxynucleotides (ODNs). Injection (intravenous) of ODNs formulated in LPD into mice triggered production of proinflammatory cytokines including interferon gamma and TNF-alpha. The potency of CpG-containing ODNs in cytokine induction was affected by its flanking sequences and was significantly reduced when CpG was methylated. Preinjection of ODN-containing LPD led to inhibition of transgene expression in lungs after a subsequent injection of LPD containing plasmid expression vector with luciferase gene. The degree of inhibition correlated with the levels of ODN-triggered cytokines. Finally, intraperitoneal injection of dexamethasone suppressed LPD-induced cytokine production, and led to significantly higher levels of transgene expression on both first and second injection. These studies suggest that mutation of potent CpG motifs in plasmid DNA together with the use of immune suppression agent may represent an effective approach to improve cationic lipid-mediated gene transfer to the lung.

Animals↗
PubMed1999

Nucleotide excision repair in a constitutive and inducible gene of a yeast minichromosome in intact cells.

Repair of UV-induced cyclobutane pyrimidine dimers (CPDs) was measured in a yeast minichromosome, having a galactose-inducible GAL1:URA3 fusion gene, a constitutively expressed HIS3 gene and varied regions of chromatin structure. Transcription of GAL1:URA3 increased >150-fold, while HIS3 expression decreased <2-fold when cells were switched from glucose to galactose medium. Following galactose induction, four nucleosomes were displaced or rearranged in the GAL3-GAL10 region. However, no change in nucleosome arrangement was observed in other regions of the minichromosome following induction, indicating that only a few plasmid molecules actively transcribe at any one time. Repair at 269 cis-syn CPD sites revealed moderate preferential repair of the transcribed strand of GAL1:URA3 in galactose, consistent with transcription-coupled repair in a fraction of these genes. Many sites upstream of the transcription start site in the transcribed strand were also repaired faster upon induction. There is remarkable repair heterogeneity in the HIS3 gene and preferential repair is seen only in a short sequence immediately downstream of the transcription start site. Finally, a mild correlation of repair heterogeneity with nucleosome positions was observed in the transcribed strand of the inactive GAL1:URA3 gene and this correlation was abolished upon galactose induction.

Chromatin↗
PubMed1999

Evidence from a novel human cell clone that adult vascular smooth muscle cells can convert reversibly between noncontractile and contractile phenotypes.

Smooth muscle cells (SMCs) perform diverse functions that can be categorized as contractile and synthetic. A traditional model holds that these distinct functions are performed by the same cell, by virtue of its capacity for bidirectional modulation of phenotype. However, this model has been challenged, in part because there is no physiological evidence that an adult synthetic SMC can acquire the ability to contract. We sought evidence for this by cloning adult SMCs from human internal thoracic artery. One clone, HITB5, expressed smooth muscle alpha-actin, smooth myosin heavy chains, heavy caldesmon, and calponin and showed robust calcium transients in response to histamine and angiotensin II, which confirmed intact transmembrane signaling cascades. On serum withdrawal, these cells adopted an elongated and spindle-shaped morphology, random migration slowed, extracellular matrix protein production fell, and cell proliferation and [(3)H]thymidine incorporation fell to near 0. Cell viability was not compromised, however; in fact, apoptosis rate fell significantly. In this state, agonist-induced elevation of cytoplasmic calcium was even more pronounced and was accompanied by SMC contraction. Readdition of 10% serum completely returned HITB5 cells to a noncontractile, proliferative phenotype. Contractile protein expression increased after serum withdrawal, although modestly, which suggested that the switch to contractile function involved reorganization or sensitization of existing contractile structures. To our knowledge, the physiological properties of HITB5 SMCs provide the first direct demonstration that cultured human adult SMCs can convert between a synthetic, noncontracting state and a contracting state. HITB5 cells should be valuable for characterizing the basis of this critical transition.

Adult↗
PubMed1999

A partial conditioning approach to achieve mixed chimerism in the rat: depletion of host natural killer cells significantly reduces the amount of total body irradiation required for engraftment.

BACKGROUND: Mixed allogeneic bone marrow chimerism induces tolerance to solid organ grafts. Although we previously reported that partially ablative conditioning with 700 cGy of total body irradiation (TBI) is sufficient to allow for bone marrow engraftment in mice, we determined that a minimum of 1000 cGy was required in the rat. Because T cells and NK cells are critical in bone marrow graft rejection, our purpose was to examine whether targeting of radioresistant NK cells and/or T cells in the recipient hematopoietic microenvironment would reduce the TBI dose required for engraftment of allogeneic rat bone marrow. METHODS: Wistar Furth rats received either anti-NK3.2.3 monoclonal antibodies on days -3 and -2, anti-lymphocyte serum on day -5, a combination of both or no pretreatment. TBI was performed on day 0 and rats were reconstituted with 100x10(6) T cell-depleted bone marrow cells from ACI donors. RESULTS: Engraftment of T cell-depleted rat bone marrow was readily achieved in animals conditioned with 1000 cGy TBI alone (12/12) and the level of donor chimerism averaged 89%. At 900 cGy TBI alone only one of eight recipients engrafted. In striking contrast, 11 of 12 animals pretreated with anti-NK monoclonal antibodies and irradiated with 900 cGy showed donor chimerism at a mean level of 41%. No further enhancement of bone marrow engraftment could be achieved when recipients were pretreated with antilymphocyte serum alone or antilymphocyte serum plus anti-NK monoclonal antibodies. Mixed allogeneic chimeras exhibited stable multilineage chimerism and donor-specific tolerance to subsequent cardiac allografts. CONCLUSION: Specific targeting of radioresistant host NK cells allows for a significant reduction of the TBI dose required for allogeneic bone marrow engraftment.

Animals↗
PubMed1999

Effects of satratoxins and other macrocyclic trichothecenes on IL-2 production and viability of EL-4 thymoma cells.

The macrocyclic trichothecenes are a group of potent protein synthesis inhibitors that have been encountered in indoor air and food as a result of infestation by the fungus Stachybotrys. To evaluate the capacity of these mycotoxins to alter immune functions, the effects of satratoxin G, H, F, roridin A, and verrucarin A on interleukin 2 (IL-2) production and viability were evaluated in a murine T-cell model. EL-4 thymoma cells were stimulated with phorbol 12-myristate 13-acetate and ionomycin and concurrently exposed to various concentrations of the trichothecenes. Enzyme-linked immunosorbent assay (ELISA) of supernatants revealed that IL-2 concentrations at 24 and 72 h were significantly increased in cultures that were incubated in the presence of 0.5 to 1 ng/ml of satratoxin H, 1 to 5 ng/ml of isosatratoxin F, 0.1 to 0.5 ng/ml of roridin A, and 0.25 to 0.5 ng/ml of verrucarin A. However, IL-2 levels at these time points were significantly depressed when incubated in the presence of higher concentrations of satratoxin G (> or =2.5 ng/ml), satratoxin H and isosatratoxin F (> or =5 ng/ml), and roridin A and verrucarin A (> or =1 ng/ml). Cell viability, as measured by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, was depressed by each of the trichothecenes in a concentration-dependent manner. MTT responses were significantly decreased by as little as 0.5 ng/ml satratoxin G, roridin A, and verrucarin A and by 2.5 ng/ml of isosatratoxin F and satratoxin H. When these data were compared to those found in EL-4 cells for the 8-ketotrichothecene vomitoxin (deoxynivalenol), a common food contaminant, the macrocyclic trichothecenes were at least 100 times more potent. The results indicate that, at low concentrations, macrocyclic trichothecenes as a group could superinduce IL-2 production even while partially decreasing cell viability, whereas higher concentrations suppressed cytokine production and were markedly cytotoxic. The capacity of these compounds to dysregulate cytokine production in a biphasic fashion may play an etiologic role in outbreaks of human illnesses associated with indoor Stachybotrys contamination.

Air Microbiology↗
PubMed1999

Association of BRCA1 with the hRad50-hMre11-p95 complex and the DNA damage response.

BRCA1 encodes a tumor suppressor that is mutated in familial breast and ovarian cancers. Here, it is shown that BRCA1 interacts in vitro and in vivo with hRad50, which forms a complex with hMre11 and p95/nibrin. Upon irradiation, BRCA1 was detected in discrete foci in the nucleus, which colocalize with hRad50. Formation of irradiation-induced foci positive for BRCA1, hRad50, hMre11, or p95 was dramatically reduced in HCC/1937 breast cancer cells carrying a homozygous mutation in BRCA1 but was restored by transfection of wild-type BRCA1. Ectopic expression of wild-type, but not mutated, BRCA1 in these cells rendered them less sensitive to the DNA damage agent, methyl methanesulfonate. These data suggest that BRCA1 is important for the cellular responses to DNA damage that are mediated by the hRad50-hMre11-p95 complex.

Acid Anhydride Hydrolases↗
PubMed1999

Cell migration and chick limb development: chemotactic action of FGF-4 and the AER.

Experiments have been carried out to investigate the role of the apical ectodermal ridge (AER) and FGF-4 on the control of cell migration during limb bud morphogenesis. By coupling DiI cell labeling with ectopic implantation of FGF-4 microcarrier beads we have found that FGF-4 acts as a potent and specific chemoattractive agent for mesenchymal cells of the limb bud. The response to FGF-4 is dose dependent in both the number of cells stimulated to migrate and the distance migrated. The cell migration response to FGF-4 appears to be independent of the known inductive activity of FGF-4 on Shh gene expression. We investigated the role of the AER in controlling cell migration by characterizing the migration pattern of DiI-labeled subapical cells during normal limb outgrowth and following partial AER removal. Subapical cells within 75 micrometer of the AER migrate to make contact with the AER and are found intermingled with nonlabeled cells. Thus, the progress zone is dynamic with cells constantly altering their neighbor relationships during limb outgrowth. AER removal studies show that cell migration is AER dependent and that subapical cells redirect their path of migration toward a functional AER. These studies indicate that the AER has a chemoattractive function and regulates patterns of cell migration during limb outgrowth. Our results suggest that the chemoattractive activity of the AER is mediated in part by the production of FGF-4.

Animals↗
PubMed1999

Novel injury mechanism in anoxia and trauma of spinal cord white matter: glutamate release via reverse Na+-dependent glutamate transport.

Spinal cord injury is a devastating condition, with much of the clinical disability resulting from disruption of white matter tracts. Recent reports suggest a component of glutamate excitotoxicity in spinal cord injury. In this study, the role of glutamate and mechanism of release of this excitotoxin were investigated in rat dorsal column slices subjected to 60 min of anoxia or 15 sec of mechanical compression at a force of 2 gm in vitro. The broad-spectrum glutamate antagonist kynurenic acid (1 mm) and the selective AMPA antagonist GYKI52466 (30 microm) were protective against anoxia (compound action potential amplitude recovered to 56 vs 27% without drug). GYKI52466 was also effective against trauma (65 vs 35%). Inhibition of Na(+)-dependent glutamate transport with dihydrokainate or l-trans-pyrrolidine-2,4-dicarboxylic acid (1 mm each) protected against anoxia (65-75 vs 25%) and trauma (70 vs 35%). The depletion of cytosolic glutamate in axon cylinders and oligodendrocytes by anoxia was completely prevented by glutamate transport inhibition. Immunohistochemistry revealed that a large component of injury occurred in the myelin sheath and was prevented by AMPA receptor blockade or glutamate transport inhibitors. We conclude that release of glutamate by reversal of Na(+)-dependent glutamate transport with subsequent activation of AMPA receptors is an important mechanism in spinal cord white matter anoxic and traumatic injury.

ATP-Binding Cassette Transporters↗