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Y Chen

Publications and source records attributed to Y Chen.

At least 325 records · Page 18Linked to original sources
PubMed2001

Rapid activation of ERK1/2 mitogen-activated protein kinase by corticosterone in PC12 cells.

Although the nongenomic effects of glucocorticoids have been well acknowledged, its precise intracellular signal transduction pathway remains to be elucidated. The present study using Western immunoblot and protein kinase activity assay, for the first time, showed that corticosterone (B) can induce a rapid activation of Erk1/2 mitogen-activated protein kinase (MAPK) in PC12 cells. The dose-response curve was bell shaped, with the maximal activation at 10(-9) M in 15 min. The results from immunofluorescence staining also revealed that the activated Erk1/2 MAPK was translocated from cytoplasm to nucleus of PC12 cells in 15 min. Activation of Erk1/2 MAPK by B was apparently not mediated by the classical cytosolic steroid receptors, for B-BSA can induce the phosphorylation of Erk1/2 MAPK, but the antagonist (RU38486) cannot block the phosphorylation of Erk1/2 MAPK induced by B. Phosphorylation of Erk1/2 MAPK induced by B was not affected by a tyrosine kinase inhibitor (genistein), suggesting that the pathway did not involve the tyrosine kinase activity. On the other hand, protein kinase C activator (PMA) can activate and protein kinase C inhibitor (Gö6976) can block the activation of Erk1/2 MAPK induced by B. Taken together, these data clearly demonstrated that B might act via putative membrane receptor and rapidly activate Erk1/2 MAPK through protein kinase C alpha in PC12 cells.

Active Transport, Cell Nucleus↗
PubMed2001

New lattice-Boltzmann model for magnetic fluids.

A new type of two-dimensional lattice-Boltzmann model is developed in order to study the rheological properties of magnetic fluids. The appropriate extension of the lattice-Boltzmann scheme for magnetohydrodynamics makes it possible to deal with the rotation of the magnetic moment without losing the advantage of its simple algorithm. This model is suitable for simulating various behaviors of magnetic fluids influenced by the internal angular momentum.

Journal Article↗
PubMed2001

Characterization of molecularly imprinted polymers with the Langmuir-Freundlich isotherm.

The majority of binding models that have been applied to molecularly imprinted polymers (MIPs) have been homogeneous models. MIPs, on the other hand, are heterogeneous materials containing binding sites with a wide array of binding affinities and selectivities. Demonstrated is that the binding behavior of MIPs can be accurately modeled by the heterogeneous Langmuir-Freundlich (LF) isotherm. The applicability of the LF isotherm to MIPs was demonstrated using five representative MIPs from the literature, including both homogeneous and heterogeneous MIPs. Previously, such comparisons required the use of several different binding models and analyses, including the Langmuir model, the Freundlich model, and numerical approximation techniques. In contrast, the LF model enabled direct comparisons of the binding characteristics of MIPs that have very different underlying distributions and were measured under different conditions. The binding parameters can be calculated directly using the LF fitting coefficients that yield a measure of the total number of binding sites, mean binding affinity, and heterogeneity. Alternatively, solution of the Langmuir adsorption integral for the LF model enabled direct calculation of the corresponding affinity spectrum from the LF fitting coefficients from a simple algebraic expression, yielding a measure of the number of binding sites with respect to association constant Finally, the ability of the LF isotherm to model MIPs suggests that a unimodal heterogeneous distribution is an accurate approximation of the distribution found in homogeneous and heterogeneous MIPs.

Adsorption↗
PubMed2001

The signal transfer regions of G alpha(s).

The crystal structure of soluble functional fragments of adenylyl cyclase complexed with G alpha(s) and forskolin, shows three regions of G alpha(s) in direct contact with adenylyl cyclase. The functions of these three regions are not known. We tested synthetic peptides encoding these regions of G alpha(s) on the activities of full-length adenylyl cyclases 2 and 6. A peptide encoding the Switch II region (amino acids 222-247) stimulated both adenylyl cyclases 2- to 3-fold. Forskolin synergized the stimulation. Addition of peptides in the presence of activated G alpha(s) partially inhibited G alpha(s) stimulation. Corresponding Switch II region peptides from G alpha(q) and G alpha(i) did not stimulate adenylyl cyclase. A peptide encoding the Switch I region (amino acids 199-216) also stimulated AC2 and AC6. The stimulatory effects of the two peptides at saturating concentrations were non-additive. A peptide encoding the third contact region (amino acids 268-286) located in the alpha 3-beta 5 region, inhibits basal, forskolin, and G alpha(s)-stimulated enzymatic activities. Since this region in G alpha(s) interacts with both the central cytoplasmic loop and C-terminal tail of adenylyl cyclases this peptide may be involved in blocking interactions between these two domains. These functional data in conjunction with the available structural information suggest that G alpha(s) activation of adenylyl cyclase is a complex event where the alpha 3-beta 5 loop of G alpha(s) may bring together the central cytoplasmic loop and C-terminal tail of adenylyl cyclase thus allowing the Switch I and Switch II regions to function as signal transfer regions to activate adenylyl cyclase.

Adenylyl Cyclases↗
PubMed2001

Mechanisms for increased levels of phosphorylation of elongation factor-2 during hibernation in ground squirrels.

Previously, eEF-2 phosphorylation has been identified as a reversible mechanism involved in the inhibition of the elongation phase of translation. In this study, an increased level of phosphorylation of eukaryotic elongation factor-2 (eEF-2) was observed in the brains and livers of hibernating ground squirrels. In brain and liver from hibernators, eEF-2 kinase activity was increased relative to that of active animals. The activity of protein phosphatase 2A (PP2A), a phosphatase that dephosphorylates eEF-2, was also decreased in brain and liver from hibernators. This was associated with an increase in the level of inhibitor 2 of PP2A (I(2)(PP2A)), although there was an increase in the level of the catalytic subunit of PP2A (PP2A/C) in hibernating brains and livers. These results indicate that eEF-2 phosphorylation represents a specific and previously uncharacterized mechanism for inhibition of the elongation phase of protein synthesis during hibernation. Increased levels of eEF-2 phosphorylation in hibernators appear to be a component of the regulated shutdown of cellular functions that permits hibernating animals to tolerate severe reductions in cerebral blood flow and oxygen delivery capacity.

Animals↗
PubMed2001

[The clinical and pathological manifestations of aristolochic acid nephropathy--the report of 58 cases].

OBJECTIVE: To realize and classify the aristolochic acid nephropathy (AAN) according to its clinical and pathological manifestations. METHODS: Fifty eight cases in our Division during October 1998 to August 2001 were reviewed, and their clinical, laboratory and pathological manifestations as well as the response of therapy were analyzed. The aristolochic acid (AA) component in some Chinese traditional drugs taken by our patients was detected with thin-layer chromatography (TLC) scan. RESULTS: AAN might be divided the following three types: (1) acute AAN (n = 4): acute tubular necrosis and acute renal failure were its pathological and clinical characters, respectively. (2) tubular dysfunctional AAN (n = 7): tubular degradation with atrophy, and renal tubular acidosis and/or Fanconi syndrome were its main pathological and clinical manifestations, respectively. (3) chronic AAN (n = 47): renal interstitial fibrosis with few infiltrated mononuclear cells, and chronically progressive renal failure were its dominant pathological and clinical findings, respectively. Steroid therapy was tried to treat some patients with AAN, and a few patients in the first two types obtained some good effects. AA component was demonstrated by the TLC scan in the drugs taken by our patients. CONCLUSION: Chinese traditional drugs containing AA are able to cause a special tubulointerstitial nephropathy which may be classified three types with different outcome. To definite effects of steroid on AAN still need to be proved by further studies.

Adult↗
PubMed2001

IkappaBbeta, but not IkappaBalpha, functions as a classical cytoplasmic inhibitor of NF-kappaB dimers by masking both NF-kappaB nuclear localization sequences in resting cells.

NF-kappaB dimers, inhibitor IkappaB proteins, and NF-kappaB.IkappaB complexes exhibit distinct patterns in partitioning between nuclear and cytoplasmic cellular compartments. IkappaB-dependent modulation of NF-kappaB subcellular localization represents one of the more poorly understood processes in the NF-kappaB signaling pathway. In this study, we have combined in vitro biochemical and cell-based methods to elucidate differences in NF-kappaB regulation exhibited by the inhibitors IkappaBbeta and IkappaBalpha. We show that although both IkappaBalpha and IkappaBbeta bind to NF-kappaB with similar global architecture and stability, significant differences exist that contribute to their unique functional roles. IkappaBbeta derives its high affinity toward NF-kappaB dimers by binding to both NF-kappaB subunit nuclear localization signals. In contrast, IkappaBalpha contacts only one NF-kappaB NLS and employs its carboxyl-terminal proline, glutamic acid, serine, and threonine-rich region for high affinity NF-kappaB binding. We show that the presence of one free NLS in the NF-kappaB.IkappaBalpha complex renders it a dynamic nucleocytoplasmic complex, whereas NF-kappaB.IkappaBbeta complexes are localized to the cytoplasm of resting cells.

Animals↗
PubMed2001

Dimethyl sulphoxide enhances the effects of P(i) in myofibrils and inhibits the activity of rabbit skeletal muscle contractile proteins.

In the catalytic cycle of skeletal muscle, myosin alternates between strongly and weakly bound cross-bridges, with the latter contributing little to sustained tension. Here we describe the action of DMSO, an organic solvent that appears to increase the population of weakly bound cross-bridges that accumulate after the binding of ATP, but before P(i) release. DMSO (5-30%, v/v) reversibly inhibits tension and ATP hydrolysis in vertebrate skeletal muscle myofibrils, and decreases the speed of unregulated F-actin in an in vitro motility assay with heavy meromyosin. In solution, controls for enzyme activity and intrinsic tryptophan fluorescence of myosin subfragment 1 (S1) in the presence of different cations indicate that structural changes attributable to DMSO are small and reversible, and do not involve unfolding. Since DMSO depresses S1 and acto-S1 MgATPase activities in the same proportions, without altering acto-S1 affinity, the principal DMSO target apparently lies within the catalytic cycle rather than with actin-myosin binding. Inhibition by DMSO in myofibrils is the same in the presence or the absence of Ca(2+) and regulatory proteins, in contrast with the effects of ethylene glycol, and the Ca(2+) sensitivity of isometric tension is slightly decreased by DMSO. The apparent affinity for P(i) is enhanced markedly by DMSO (and to a lesser extent by ethylene glycol) in skinned fibres, suggesting that DMSO stabilizes cross-bridges that have ADP.P(i) or ATP bound to them.

Adenosine Triphosphate↗
PubMed2001

In silico cloning of mouse Muc5b gene and upregulation of its expression in mouse asthma model.

Using a BLAST-searching approach, we identified a mouse expressed sequence tag (EST) clone (AA038672) showing great similarity to the 3' end of the human MUC5B gene. The clone was named "3pmmuc5b-1" after complete nucleotide sequencing (Genbank Accession, AF369933). A subsequent search of the mouse genome database with the 3pmmuc5b-1 sequence identified two overlapping genomic clones (AC020817 and AC020794) that contained the sequence of both 3pmmuc5b-1 and the mouse Muc5ac gene. Like their human homologs, the genomic order of the mouse Muc genes is 5'-Muc5ac-Muc5b-3'. These results suggest that the newly identified EST clone, 3pmmuc5b-1, is part of the 3' portion of the mouse Muc5b gene. In situ hybridization demonstrated that this putative mouse Muc5b message was expressed in a restricted manner in the sublingual gland region of the tongue and the submucosal gland region of the mouse trachea in a normal animal. However, the gene expression was greatly enhanced in airway surface epithelium and the submucosal gland region in ovalbumin-induced asthmatic mice. These results were consistent with previous studies of human airway tissues. We therefore conclude that this newly cloned mouse Muc5b gene could be used as a marker for studying aberrant mucin gene expression in mouse models of various airway diseases.

Animals↗
PubMed2001

Novel and transient populations of corticotropin-releasing hormone-expressing neurons in developing hippocampus suggest unique functional roles: a quantitative spatiotemporal analysis.

Robust physiological actions of the neuropeptide corticotropin-releasing hormone (CRH) on hippocampal pyramidal neurons have been demonstrated, which may contribute to synaptic efficacy and to learning and memory processes. These excitatory actions of the peptide, as well as the expression of the CRH receptor type that mediates them, are particularly prominent during early postnatal life, suggesting that endogenous CRH may contribute to processes involved in maturation of hippocampal circuitry. To further elucidate the function(s) of endogenous CRH in developing hippocampus, we used neurochemical and quantitative stereological methods to characterize in detail CRH-expressing neuronal populations during postnatal hippocampal differentiation. These experiments revealed progressively increasing numbers of CRH-expressing neurons in developing hippocampus that peaked on postnatal day 11-18 and then declined drastically to adult levels. These cells belonged to several discrete populations, distinguished by GAD67 mRNA expression, morphology, and distinct spatiotemporal distribution profiles. Importantly, a novel population of Cajal-Retzius-like CRH-expressing neurons was characterized that exists only transiently in early postnatal hippocampus and is positioned to contribute to the establishment of hippocampal connectivity. These findings suggest novel, age-specific roles for CRH in regulating early developmental events in the hippocampal formation.

Aging↗
PubMed2001

Sulfide-mediated dehydrative glycosylation.

The development of a new method for glycosylation with 1-hydroxy glycosyl donors employing dialkyl sulfonium reagents is described. The process employs the reagent combination of a dialkyl sulfide and triflic anhydride to effect anomeric bond constructions. This controlled dehydrative coupling of various C(1)-hemiacetal glycosyl donors and nucleophilic acceptors proceeds by way of a sulfide-to-sulfoxide oxidation process in which triflic anhydride serves as the oxidant.

Glycoconjugates↗
PubMed2001

Apolipoprotein E inhibits serum-stimulated cell proliferation and enhances serum-independent cell proliferation.

Independently of its role in lipid homeostasis, apolipoprotein E (apoE) inhibits cell proliferation. We compared the effects of apoE added to media (exogenous apoE) with the effects of stably expressed apoE (endogenous apoE) on cell proliferation. Exogenous and endogenous apoE increased population doubling times by 30-50% over a period of 14 days by prolonging the G(1) phase of the cell cycle. Exogenous and endogenous apoE also decreased serum-stimulated DNA synthesis by 30-50%. However, apoE did not cause cell cycle arrest; both apoE-treated and control cells achieved equivalent saturation densities at 14 days. Further analyses demonstrated that exogenous and endogenous apoE prevented activation of MAPK but not induction of c-fos expression in response to serum growth factors. Endogenous (but not exogenous) apoE altered serum concentration-dependent effects on proliferation. Whereas control (non-apoE-expressing) cell numbers increased with increasing serum concentrations (1.6-fold for every 2-fold increase in serum), apoE-expressing cell numbers did not differ as serum levels were raised from 2.5 to 10%. In addition, in low serum (0.1%), apoE-expressing cells had elevated DNA synthesis levels compared with control cells. We conclude that apoE does not simply inhibit cell proliferation; rather, the presence of apoE alters the response to and requirement for serum mitogens.

Animals↗
PubMed2001

Characterization of the DNA-binding property of Smad5.

Activation of TGF-beta superfamily receptors leads to phosphorylation of Smad proteins which function as transcription factors to regulate gene expression. Previous studies have indicated that Smad5, together with Smad1 and Smad8, participates in signaling downstream of BMP receptors. To characterize the DNA-binding characteristics of Smad5, we used the GST-Smad5 N-terminal fusion protein to select for random oligonucleotide sequences that were able to binds the protein. As a result, we found that Smad5 is able to bind a consensus sequence TGTGC. We further used the Smad7 promoter sequence that contains a Smad-binding element (SBE), GTCTAGAC to determine how mutations in each nucleotide in the SBE affects the binding with Smad5, compared with the binding with Smad1, Smad2, Smad3, Smad4, and Smad8. Interestingly, Smad5, but not Smad1 and Smad8, was able to bind the SBE, at a level similar to the binding by Smad3 and Smad4. However, mutations at the SBE had different effect on the binding with Smad5, compared to that with Smad3 and Smad4. These studies suggest that even though Smad5 falls into the same subfamily with Smad1 and Smad8 in mediating the signaling by BMP receptors, it has an unique DNA-binding property that is similar to Smad3, which specifically transduces signaling for TGF-beta and activin receptors.

Animals↗
PubMed2001

A hepatocellular carcinoma-specific adenovirus variant, CV890, eliminates distant human liver tumors in combination with doxorubicin.

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death in the world. Tumor resection remains the only curative treatment but is often not possible because of advanced stage and frequently unsuccessful because of intrahepatic or distant tumor recurrence. alpha-Fetoprotein (AFP), a tumor marker currently used for the diagnosis and management of HCC, is an oncofetal protein expressed in a majority of HCCs but rarely in normal hepatocytes. Because AFP gene expression is tightly regulated at the level of transcription, AFP transcriptional regulatory elements (TRE) are excellent candidates for generating HCC-specific oncolytic adenoviruses. We devised a new strategy for the AFP TRE to control an artificial E1A-IRES-E1B bicistronic cassette in an adenovirus 5 vector (Ad5) and constructed an HCC-specific oncolytic virus, CV890. In vitro, CV890 expression of the E1A and E1B genes, virus replication, and cytopathic effects were examined by Northern blot, Western blot, virus yield assay, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay in AFP-producing cell lines (HepG2, Huh7, Hep3B, PLC/PRF/5, and SNU449), non-AFP-producing cell lines (Sk-Hep-1, Chang liver cell, LNCaP, HBL-100, PA-1, UM-UC-3, SW 780, Colo 201, and U118 MG), and non-AFP-producing human primary cells (lung fibroblast, bladder smooth muscle, and mammary epithelial). CV890 efficiently replicates in and destroys AFP-producing HCC cells as well as wild-type Ad5, but replication is highly attenuated in non-AFP-producing HCC cells or non-HCC cells. CV890 produced 5,000-100,000-fold less virus than wild-type Ad5 in non-AFP-producing cells. CV890 was attenuated 100-fold more than CV732, a virus containing the AFP TRE driving the E1A gene alone, in non-AFP-producing cells. These studies demonstrated that expression of both E1A and E1B genes under the control of a bicistronic AFP-E1A-IRES-E1B cassette yielded improvements in virus specificity equivalent to driving the E1A and E1B genes with two independent TREs yet requires only one TRE thereby conserving genomic space within the virus. Significantly, CV890 produced nearly the same yield of virus in cells that produced AFP over a 75-fold range, from a low of 60 ng AFP/10(6) cells/10 days to as high as 4585 ng AFP/10(6) cells/10 days. In vivo, antitumor efficacy of CV890 was examined in BALB/c-nu/nu mice containing large s.c. HepG2 or Hep3B tumor xenografts. Tumor volume of distant xenografts dropped below baseline 4 weeks after a single i.v. injection. Combination of CV890 with doxorubicin demonstrated synergistic antitumor efficacy, yielding complete elimination of distant Hep3B tumors 4 weeks after a single i.v. administration of both compounds. Our results support the clinical development of CV890 as an antineoplastic agent for the treatment of localized or metastatic HCC.

Adenoviridae↗
PubMed2001

Apoptotic signaling in polyamine analogue-treated SK-MEL-28 human melanoma cells.

N(1),N(11)-Diethylnorspermine (DENSPM) is a polyamine analogue with clinicalrelevance as an experimental anticancer agent and the ability to elicit a profound apoptotic response in certain cell types. Here, we characterize the polyamine effects and apoptotic signaling events initiated by treatment of SK-MEL-28 human melanoma with 10 microM DENSPM. Maximal induction of the polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase (SSAT) and polyamine pool depletion were seen by 16 h, whereas early apoptosis was first apparent at 36 h. Intermediate events related to apoptotic signaling were sought between 16 and 36 h. A loss of mitochondrial transmembrane potential (Deltapsi(m)) beginning at 24 h was followed by the release of cytochrome c into the cytosol at 30 h. Loss of mitochondrial integrity was accompanied by caspase-3 activation and poly(ADP-ribose) polymerase digestion from 30 to 36 h. The caspase inhibitor Z-Asp-2,6-dichlorobenzoyloxymethylketone rendered cells resistant to analogue-induced caspase-3 activation and reduced the apoptotic response in a dose-dependent manner. Because polyamine reduction achieved by inhibitors of polyamine biosynthesis inhibited growth but did not cause apoptosis, we looked for alternative polyamine-related events, focusing on induction of SSAT. Three DENSPM analogues that differentially induced SSAT activity but similarly depleted polyamine pools revealed a close correlation between enzyme induction and cytochrome c release, caspase activation, and apoptosis. Dose-dependent inhibition of polyamine oxidase, an enzyme that oxidizes acetylated polyamines generated by SSAT and releases toxic by-products such as H(2)O(2) and aldehydes, prevented cytochrome c release, caspase activation, and apoptosis. Taken together, the findings indicate that DENSPM-induced apoptosis is at least partially initiated via massive induction of SSAT and related oxidative events and subsequently mediated by the mitochondrial apoptotic signaling pathway as indicated by cytochrome c release and caspase activation.

Acetyltransferases↗
PubMed2001

[Estimation of internal hemorrhage in tubal pregnancy with ultrasonography].

OBJECTIVE: To investigate the correlation between the free fluid area detected with ultrasonography and the internal hemorrhage volume observed during operation in tubal pregnancy. METHODS: The correlation between the size of free fluid area measured by ultrasound and the volume of internal hemorrhage collected during operation among 201 cases of tubal pregnancy was analyzed. The difference of internal hemorrhage between tubal abortion and tubal pregnant rupture was analyzed too. RESULTS: A positive correlation was observed between the size of free fluid area measured by ultrasound and the internal hemorrhage volume (r = 0.7712). A statistically significant difference of internal hemorrhage volume was found between tubal abortion and tubal pregnant rupture with a free fluid area in the range of 0.1-10.0 cm. CONCLUSION: The volume of internal hemorrhage caused by tubal pregnancy can be estimated according to the free fluid area detected with ultrasonography.

Adult↗
PubMed2001

Novel purinergic sensitivity develops in injured sensory axons following sciatic nerve transection in rat.

Teased fibers were made from 153 spontaneous A afferents ending in sciatic nerve end neuromas of 3-14 days standing, 21 A afferents from intact sensory endings in the contralateral sciatic nerve, and 50 intact A afferents from the sciatic nerve in intact rats. Ninety-two percent of the injured fibers responded to adenosine 5'-triphosphate (ATP) (i.v.). However, few fibers from the contralateral nerve or nerves from intact animals responded to ATP. P2 receptor antagonist suramin or reactive blue 2 blocked the ATP-induced response in 76% of the fibers tested, whereas the P1 receptor antagonist aminophylline blocked the ATP-evoked effect in only 18% of the fibers tested. Sympathectomy did not affect the ATP-induced effects in injured axons. Close-arterial injection of ATP caused similar results as i.v. injection of ATP. The present study suggests that a novel purinergic sensitivity is developed at the injury site after sciatic nerve transection in rats, which may play a role in neuropathic pain under some conditions such as sympathetic activation.

Action Potentials↗