Biomedical subjects

N Chen

Publications and source records attributed to N Chen.

At least 55 records · Page 3Linked to original sources

PubMed2001

A calcium-dependent feedback mechanism participates in shaping single NMDA miniature EPSCs.

NMDA receptors (NMDARs) are highly calcium-permeable and are negatively regulated by intracellular calcium during prolonged exposure to agonist. We have investigated whether calcium-mediated feedback occurs during transient exposure to glutamate during single synaptic events. Examination of miniature EPSCs (mEPSCs) indicated that the decay kinetics of the NMDAR component was markedly slowed by the intracellular perfusion of exogenous calcium buffers (BAPTA or Fluo-3). In contrast, the AMPA receptor component of the miniature EPSC was unaffected. Slow on-rate calcium buffers, such as EGTA, did not alter kinetics of the NMDAR component of the mEPSC. Addition of exogenous fast calcium buffers did not slow the decay kinetics of glutamate-evoked currents mediated by NR1/NR2A heteromers expressed in HEK 293 cells, suggesting that the effect we observed in neurons may be specific to processes associated with synaptically activated receptors. Trial-to-trial amplitude variability of miniature calcium transients mediated by NMDARs increased with the injection of exogenous calcium buffers, suggesting that the amplitude of synaptic calcium transients are maintained at a rather constant level by a calcium-mediated feedback mechanism.

Aniline Compounds↗

PubMed2001

Inositol hexaphosphate inhibits ultraviolet B-induced signal transduction.

Inositol hexaphosphate (InsP6) has an effective anticancer action in many experimental models in vivo and in vitro. Ultraviolet B (UVB) radiation is believed to be responsible for many of the carcinogenic effects related to sun exposure, and alteration in UVB-induced signal transduction is associated with UVB-induced carcinogenesis. Here we report the effects of InsP6 on UVB-induced signal transduction. InsP6 strongly blocked UVB-induced activator protein-1 (AP-1) and NF-kappaB transcriptional activities in a dose-dependent manner. InsP6 also suppressed UVB-induced AP-1 and nuclear factor kappaB (NF-kappaB) DNA binding activities and inhibited UVB-induced phosphorylation of extracellular signal-regulated protein kinases (Erks) and c-Jun NH2-terminal kinases (JNKs). Phosphorylation of p38 kinases was not affected. InsP6 also blocked UVB-induced phosphorylation of IkappaB-alpha, which is known to result in the inhibition of NF-kappaB transcriptional activity. InsP6 does not block UVB-induced phosphotidylinositol-3' (PI-3) kinase activity, suggesting that the inhibition of UVB-induced AP-1 and NF-kappaB activities by InsP6 is not mediated through PI-3 kinase. Because AP-1 and NF-kappaB are important nuclear transcription factors that are related to tumor promotion, our work suggests that InsP6 prevents UVB-induced carcinogenesis by inhibiting AP-1 and NF-kappaB transcription activities.

Androstadienes↗

PubMed2001

Mutant huntingtin enhances excitotoxic cell death.

Evidence suggests overactivation of NMDA-type glutamate receptors (NMDARs) contributes to selective degeneration of medium-sized spiny striatal neurons in Huntington's disease (HD). Here we determined whether expression of huntingtin containing the polyglutamine expansion augments NMDAR-mediated excitotoxicity. HEK293 cells coexpressing mutant huntingtin (htt-138Q) and either NR1A/NR2A- or NR1A/NR2B-type NMDARs exposed to 1 mM NMDA showed a significant increase in excitotoxic cell death compared to controls (cells coexpressing htt-15Q or GFP), but the difference was larger for NR1A/NR2B. Moreover, agonist-dependent cell death showed apoptotic features for cells coexpressing htt-138Q and NR1A/NR2B, but not for cells expressing htt-138Q and NR1A/NR2A. Further, NR1A/NR2B-mediated apoptosis was not seen with coexpression of an N-terminal fragment of mutant htt. Since NR1A/NR2B is the predominant NMDAR subtype in neostriatal medium-sized spiny neurons, enhancement of NMDA-induced apoptotic death in NR1A/NR2B-expressing cells by full-length mutant htt may contribute to selective neurodegeneration in HD.

Apoptosis↗

PubMed2001

A novel approach to antigen-specific deletion of CTL with minimal cellular activation using alpha3 domain mutants of MHC class I/peptide complex.

In this study, we have compared the effector functions and fate of a number of human CTL clones in vitro or ex vivo following contact with variant peptides presented either on the cell surface or in a soluble multimeric format. In the presence of CD8 coreceptor binding, there is a good correlation between TCR signaling, killing of the targets, and FasL-mediated CTL apoptosis. Blocking CD8 binding using alpha3 domain mutants of MHC class I results in much reduced signaling and reduced killing of the targets. Surprisingly, however, FasL expression is induced to a similar degree on these CTLs, and apoptosis of CTL is unaffected. The ability to divorce these events may allow the deletion of antigen-specific and pathological CTL populations without the deleterious effects induced by full CTL activation.

Apoptosis↗

PubMed2001

The role of conserved tryptophan and acidic residues in the human dopamine transporter as characterized by site-directed mutagenesis.

The human dopamine (DA) transporter (hDAT) contains multiple tryptophans and acidic residues that are completely or highly conserved among Na(+)/Cl(-)-dependent transporters. We have explored the roles of these residues using non-conservative substitution. Four of 17 mutants (E117Q, W132L, W177L and W184L) lacked plasma membrane immunostaining and were not functional. Both DA uptake and cocaine analog (i.e. 2beta-carbomethoxy-3beta-(4-fluorophenyl)tropane, CFT) binding were abolished in W63L and severely damaged in W311L. Four of five aspartate mutations (D68N, D313N, D345N and D436N) shifted the relative selectivity of the hDAT for cocaine analogs and DA by 10-24-fold. In particular, mutation of D345 in the third intracellular loop still allowed considerable [(3)H]DA uptake, but caused undetectable [(3)H]CFT binding. Upon anti-C-terminal-hDAT immunoblotting, D345N appeared as broad bands of 66-97 kDa, but this band could not be photoaffinity labeled with cocaine analog [(125)I]-3beta-(p-chlorophenyl)tropane-2beta-carboxylic acid ([(125)I]RTI-82). Unexpectedly, in this mutant, cocaine-like drugs remained potent inhibitors of [(3)H]DA uptake. CFT solely raised the K(m) of [(3)H]DA uptake in wild-type hDAT, but increased K(m) and decreased V(max) in D345N, suggesting different mechanisms of inhibition. The data taken together indicate that mutation of conserved tryptophans or acidic residues in the hDAT greatly impacts ligand recognition and substrate transport. Additionally, binding of cocaine to the transporter may not be the only way by which cocaine analogs inhibit DA uptake.

Amino Acid Sequence↗

PubMed2001

Induction of EGFR-dependent and EGFR-independent signaling pathways by ultraviolet A irradiation.

Most of the signal pathways involved in ultraviolet (UV)-induced skin carcinogenesis are thought to originate at plasma membrane receptors. However, UVA-induced signal transduction to downstream ribosomal protein S6 kinases, p70(S6K) and p90(RSK), is not well understood. In this report, we show that UVA stimulation of the epidermal growth factor receptor (EGFR) may lead to activation of p70(S6K)/p90(RSK) through phosphatidyl isositol (PI)-3 kinase and extracellular receptor-activated kinases (ERKs). Evidence is provided that phosphorylation and activation of p70(S6K)/p90(RSK) induced by UVA were prevented in Egfr(-/-) cells and were also markedly inhibited by the EGFR-specific tyrosine kinase inhibitors AG1478 and PD153035. Furthermore, EGFR tyrosine kinase inhibitors and EGFR deficiency significantly suppressed activation of PI-3 kinase and ERKs in regulating activation of p90(RSK)/p70(S6K) but had no effect on activation of c-Jun NH(2)-terminal kinases (JNKs) and p38 kinase in response to UVA. Thus, our results suggest that UVA-induced EGFR signaling may be required for activation of p90(RSK)/p70(S6K), PI-3 kinase, and ERKs but not JNKs or p38 kinase.

Animals↗

PubMed2001

In Caenorhabditis elegans, the RNA-binding domains of the cytoplasmic polyadenylation element binding protein FOG-1 are needed to regulate germ cell fates.

FOG-1 controls germ cell fates in the nematode Caenorhabditis elegans. Sequence analyses revealed that FOG-1 is a cytoplasmic polyadenylation element binding (CPEB) protein; similar proteins from other species have been shown to bind messenger RNAs and regulate their translation. Our analyses of fog-1 mutations indicate that each of the three RNA-binding domains of FOG-1 is essential for activity. In addition, biochemical tests show that FOG-1 is capable of binding RNA sequences in the 3'-untranslated region of its own message. Finally, genetic assays reveal that fog-1 functions zygotically, that the small fog-1 transcript has no detectable function, and that missense mutations in fog-1 cause a dominant negative phenotype. This last observation suggests that FOG-1 acts in a complex, or as a multimer, to regulate translation. On the basis of these data, we propose that FOG-1 binds RNA to regulate germ cell fates and that it does so by controlling the translation of its targets. One of these targets might be the fog-1 transcript itself.

3' Untranslated Regions↗

PubMed2001

Changes in agonist concentration dependence that are a function of duration of exposure suggest N-methyl-D-aspartate receptor nonsaturation during synaptic stimulation.

Evidence suggests that N-methyl-D-aspartate receptors (NMDARs) have a relatively high affinity for agonist compared with non-NMDA receptors. Dose-response curves constructed with sustained agonist application suggest that the 50% effective concentration (EC(50)) for peak glutamate-evoked current at NMDARs is 1 to 10 microM, whereas that of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors is approximately 500 microM. Given estimates of synaptic cleft glutamate concentration in the millimolar range, it would be expected that NMDARs would be saturated with agonist. However, studies of synaptic NMDAR responses indicate that these receptors may not be saturated during single release events at many synapses. To address this apparent contradiction, we have compared the glutamate dose-response curve for the peak NMDAR current generated by sustained glutamate application with that obtained during brief synaptic-like pulses of agonist. Our results using both recombinant and native NMDARs indicate a marked reduction in glutamate potency with reduced agonist application duration (EC(50) = 100 to 200 microM with 1 ms application). A kinetic model suggested that the reduction in potency with shorter agonist application duration could be attributed to the relatively slow activation and deactivation rates of the NMDARs. Comparison of room temperature to 37 degrees C indicated that NMDAR activation and deactivation were strongly accelerated by increased temperature. However, at 37 degrees C, we still observed a significant increase in potency with longer agonist application duration. We propose that glutamate has a relatively lower potency at NMDARs than previously thought from agonist application under equilibrium conditions. This lower potency would account for data that shows nonsaturation of NMDARs during synaptic transmission.

Cells, Cultured↗

PubMed2001

The effects of olanzapine on the 5 dimensions of schizophrenia derived by factor analysis: combined results of the North American and international trials.

BACKGROUND: The choice of drug to treat a patient with schizophrenia is one of the most critical clinical decisions. Controversy exists on the differential efficacy of olanzapine. DATA SOURCES AND STUDY SELECTION: Raw data from all 4 registrational double-blind, random-assignment studies of olanzapine compared with placebo or haloperidol were obtained from Eli Lilly and Company for this meta-analysis. METHOD: Analysis of covariance of the intent-to-treat last-observation-carried-forward endpoint scores was used to assess efficacy on Brief Psychiatric Rating Scale (BPRS) and Positive and Negative Syndrome Scale (PANSS) total scores and the 5 factors derived by factor analysis (negative symptoms, positive symptoms, disorganized thoughts, impulsivity/hostility, and anxiety/depression). RESULTS: Olanzapine produced a statistically significantly greater reduction in schizophrenic symptoms than haloperidol (p < .05) on total scores on the BPRS and PANSS on each of the 5 factors as well as on almost all items. Olanzapine induced a response at a rate equal to that induced by haloperidol in the first few weeks, but by the end of the study produced a greater percentage of responders. Compared with haloperidol, olanzapine produced a somewhat greater response on symptoms responsive to haloperidol, but a markedly better response on symptoms unresponsive to haloperidol. This difference favoring olanzapine occurred to an equal degree in all subgroups examined. The incidence of parkinsonism or akathisia following olanzapine treatment was extremely low and not statistically distinguishable from placebo. CONCLUSION: Olanzapine produced a greater improvement than haloperidol particularly by benefiting a much larger number of items or factors. Extrapyramidal side effects and akathisia during olanzapine treatment were statistically indistinguishable from effects seen with placebo.

Adult↗

PubMed2001

An experimental study on drugs for improving blood circulation and removing blood stasis in treating mild chronic hepatic damage.

Large and small doses of drugs for improving blood circulation and removing blood stasis were used in model rats to treat mild chronic hepatic damage induced by carbon tetrachloride (CCl4). The results show that large dose of Dang Gui ([symbol: see text] Radix Angelicae Sinensis) and Dan Shen ([symbol: see text] Radix Salviae Miltiorrhizae) (drugs for regulating blood flow) and small dose of Yu Jin ([symbol: see text] Radix Curcumae) and Niu Xi ([symbol: see text] Radix Achyranthis Bidentatae) (drugs for activating blood flow) can significantly elevate the activity of SOD (P < 0.05) and/or lower the T/K ratio, markedly reduce the MDA content (P < 0.05 or P < 0.01) and significantly decrease the activities of ALT and AST (P < 0.05 or P < 0.01), demonstrating that these drugs are effective in combating oxygen free radicals (OFR) in chronic liver damage. On the contrary, large dose of Tu Bie Chong ([symbol: see text] Eupolyphaga seu Steleophaga) and E Zhu ([symbol: see text] Rhizoma Curcumae) (drugs for removing blood stasis) tend to increase the ALT and AST (P < 0.05) activities. The results suggest that the synergism of elevation of the SOD activity and reduction of T/K ratio contributes to the action of drugs for improving blood circulation and removing blood stasis in combating the liver damage induced by CCl4.

Alanine Transaminase↗

PubMed2001

[Clinical and pathologic analysis of Sjögren's syndrome with renal impairment: a report of 84 cases].

OBJECTIVE: To further study the renal damage of Sjögren's syndrome (SS) and its clinical and pathologic characteristics with biopsy and recent technology. METHODS: 84 patients of SS with renal impairment from 1993 to 1999 were analyzed by routine, immunoassay, tubular function and biopsy examination. RESULTS: 55 of the 84 cases presented with renal tubular acidosis (RTA), 5 with diabetes insipidus and 3 with hypokalemic paralysis. Glomerulopathy occurred in 22 cases (nephrotic syndrome 12, glomerulonephritis 10) and mild renal failure (RF) was found in 14. 69.1% of the patients had hypergamma-globulinemia. 64.3% and 44.1% of the patients showed positive anti SS-A and anti SS-B. In 37 renal biopsy specimens 21 showed chronic interstitial nephritis (CIN) with extensive lymphoplasmic cell infiltration and tubular atrophy. 10 of the 37 specimens revealed lupus nephritis (LN, type III and IV) and 5 mesangial proliferative glomerulonephritis (MsPGN). With immunofluorescence tests, no positive findings were seen in most of the specimens, but deposition of IgA, IgM or C(3) was seen in some patients. IgG deposits in the interstitial lymphoplasmic cells were found in 1 patient. 25 patients were treated with prednisone combined with cytoxan (CTX). In 14 patients with renal failure, serum creatinine level returned to normal after treatment. CONCLUSION: Renal impairment may be the presenting or predominant feature in SS. The major clinical manifestations are RTA and GN. Treatment with prednisone may decrease the infiltration of lymphoplasmic cells in the interstitium, improve the renal function and correct RTA.

Adolescent↗

PubMed2001

Traumatic extradural hematoma in the middle cranial fossa base: clinical analysis of 14 cases.

OBJECTIVE: To explore clinical characteristics, CT manifestation and operative indications of traumatic extradural hematoma in the middle cranial fossa base (EHMCFB). METHODS: A total of 14 cases with traumatic EHMCFB from January 1997 to May 2000 were retrospectively analyzed. RESULTS: Of 14 cases, 12 cases (85.7%) maintained form chan ge of cisterna ambiens for being pressed; 11 cases who received operations were all cured; 3 received conservative therapy, of whom 2 became better and 1 died. CONCLUSIONS: In traumatic EHMCFB, the form change of cisterna ambiens occurs easily. Therefore, if there appears progressively aggravated form change of cisterna ambiens after the cisterna ambiens being pressed, an early a nd active operation is necessary and crucial.

Adolescent↗

PubMed2001

[Some spectrum methods on the structures of metal phthalocyanine].

The recent progress in some spectrum methods on the structures of metal phthalocyanine was introduced. IR and UV/Vis spectral properties of phthalocyanine were presented systematically, especially the effect of the types, numbers and positions of the peripheral substituted groups as well as the different aggregation states in solution on the UV/Vis spectra, the characterization method of the isomers of tetra-substituted metal-phthalocyanine by NMR was also discussed.

Indoles↗

PubMed2000

Huntingtin interacting protein 1 induces apoptosis via a novel caspase-dependent death effector domain.

Huntington disease is a devastating neurodegenerative disease caused by the expansion of a polymorphic glutamine tract in huntingtin. The huntingtin interacting protein (HIP-1) was identified by its altered interaction with mutant huntingtin. However, the function of HIP-1 was not known. In this study, we identify HIP-1 as a proapoptotic protein. Overexpression of HIP-1 resulted in rapid caspase 3-dependent cell death. Bioinformatics analyses identified a novel domain in HIP-1 with homology to death effector domains (DEDs) present in proteins involved in apoptosis. Expression of the HIP-1 DED alone resulted in cell death indistinguishable from HIP-1, indicating that the DED is responsible for HIP-1 toxicity. Furthermore, substitution of a conserved hydrophobic phenylalanine residue within the HIP-1 DED at position 398 eliminated HIP-1 toxicity entirely. HIP-1 activity was found to be independent of the DED-containing caspase 8 but was significantly inhibited by the antiapoptotic protein Bcl-x(L), implicating the intrinsic pathway of apoptosis in HIP-1-induced cell death. Co-expression of a normal huntingtin fragment capable of binding HIP-1 significantly reduced cell death. Our data identify HIP-1 as a novel proapoptotic mediator and suggest that HIP-1 may be a molecular accomplice in the pathogenesis of Huntington disease.

Amino Acid Sequence↗

PubMed2000

The angiogenic factors Cyr61 and connective tissue growth factor induce adhesive signaling in primary human skin fibroblasts.

The angiogenic inducers cysteine-rich angiogenic protein 61 (Cyr61) and connective tissue growth factor (CTGF) are structurally related, extracellular matrix-associated heparin-binding proteins. Both can stimulate chemotaxis and promote proliferation in endothelial cells and fibroblasts in culture and induce neovascularization in vivo. Encoded by inducible immediate early genes, Cyr61 and CTGF are synthesized upon growth factor stimulation in cultured fibroblasts and during cutaneous wound healing in dermal fibroblasts. Recently, we have shown that adhesion of primary human fibroblasts to immobilized Cyr61 is mediated through integrin alpha(6)beta(1) and cell surface heparan sulfate proteoglycans (HSPGs) (Chen, N., Chen, C.-C., and Lau, L.F. (2000) J. Biol. Chem. 275, 24953-24961), providing the first demonstration of an absolute requirement for HSPGs in integrin-mediated cell attachment. We show in this study that CTGF also mediates fibroblast adhesion through the same mechanism and demonstrate that fibroblasts adhesion to immobilized Cyr61 or CTGF induces distinct adhesive signaling responses consistent with their biological activities. Compared with fibroblast adhesion to fibronectin, laminin, or type I collagen, cell adhesion to Cyr61 or CTGF induces 1) more extensive and prolonged formation of filopodia and lamellipodia, concomitant with formation of integrin alpha(6)beta(1)-containing focal complexes localized at leading edges of pseudopods; 2) activation of intracellular signaling molecules including focal adhesion kinase, paxillin, and Rac with similar rapid kinetics; 3) sustained activation of p42/p44 MAPKs lasting for at least 9 h; and 4) prolonged gene expression changes including up-regulation of MMP-1 (collagenase-1) and MMP-3 (stromelysin-1) mRNAs and proteins sustained for at least 24 h. Together, these results establish Cyr61 and CTGF as bona fide adhesive substrates with specific signaling capabilities, provide a molecular basis for their activities in fibroblasts through integrin alpha(6)beta(1) and HSPG-mediated signaling during attachment and indicate that these proteins may function in matrix remodeling through the activation of metalloproteinases during angiogenesis and wound healing.

Cell Adhesion↗

PubMed2000

Human glioma cell BT325 expresses a proteinase that converts human plasminogen to kringle 1-5-containing fragments.

Angiostatin, a specific angiogenesis inhibitor, is an internal fragment of plasminogen, and can be generated in many systems mediated by different enzymes in vitro. The mechanism of angiostatin generation in vivo has not been well defined. Here we demonstrated that human glioma cell line BT325 can express an enzyme that can convert purified plasminogen to angiostatin-like fragments with molecular masses of 65, 60, and 58 kDa, respectively. These fragments have an identical N-terminal as KVYLS, which starts from Lys(98) of the plasminogen precusor. According to their molecular mass, the three fragments should comprise kringle domain 1 to kringle domain 5 (kringle 1-5). The proteolytic fragments obtained as above can inhibit the growth of bovine aortic endothelial (BAE) cells specifically. The proteolysis process can be completely inhibited by serine proteinase inhibitors, and partially inhibited by EDTA. The molecular weight of the peptide, which contains an enzymatic activity responsible for the proteolysis, was 13 kD determined by gel filtration and SDS-PAGE. The present data suggest that glioma cell BT325 can produce a novel proteinase to generate kringle 1-5 of plasminogen as an angiogenesis inhibitor.

Amino Acid Sequence↗

PubMed2000

Structure-activity relationships of a series of pyrrolo[3,2-d]pyrimidine derivatives and related compounds as neuropeptide Y5 receptor antagonists.

Neuropeptide Y (NPY) has been shown to play an important role in the regulation of food intake and energy balance. Pharmacological data suggests that the Y5 receptor subtype contributes to the effects of NPY on appetite, and therefore a Y5 antagonist might be a useful therapeutic agent for the treatment of obesity. In attempts to identify potential Y5 antagonists, a series of pyrrolo[3, 2-d]pyrimidine derivatives was prepared and evaluated for their ability to bind to Y5 receptors in vitro. We report here the synthesis and initial structure-activity relationship investigations for this class of compounds. The target compounds were prepared by a variety of synthetic routes designed to modify both the substitution and the heterocyclic core of the pyrrolo[3,2-d]pyrimidine lead 1. In addition to identifying several potent Y5 antagonists for evaluation as potential antiobesity agents, a pharmacophore model for the human Y5 receptor is presented.

Anti-Obesity Agents↗

PubMed2000

NSAID treatment suppresses VSV propagation in mouse CNS.

Cyclooxygenase (COX) is the key enzyme in the conversion of arachidonic acid to prostaglandins. COX has two isoforms: COX-1, the constitutively expressed form, and COX-2, the inducible form. Prostaglandins are mediators of many critical physiological and inflammatory responses, but little is known about their roles during a viral infection in the central nervous system (CNS). We used non-selective inhibitors of COX, aspirin and indomethacin, and a selective antagonist of COX-2, celecoxib, to study the role of prostaglandins in Vesicular Stomatitis Virus (VSV) induced encephalitis. We found that the inhibition of COX antagonizes VSV propagation both in vitro and in vivo. In addition, aspirin and celecoxib both prevented the disruption of the blood brain barrier in VSV-infected mice. In vitro experiments showed that the effect of COX inhibition was at least partially mediated by increased production of Nitric Oxide (NO), a molecule known to inhibit VSV replication. When NO production was inhibited by N(omega)-nitro-L-methyl-arginine-ester (L-NAME), a nitric oxide synthase (NOS) inhibitor, the difference in viral titer between aspirin (or celecoxib)-treated and the control cells was abolished. VSV-infected mice treated with celecoxib expressed more NOS-1 and produced more NO in their CNS compared to the controls. Our data suggest that the product(s) of COX have antagonistic effect(s) on NO production in the mouse CNS.

Animals↗