Search PubMed⌕ Search

Biomedical subjects

Q Y Liu

Publications and source records attributed to Q Y Liu.

At least 19 recordsLinked to original sources
PubMed2006

Oxidative stress regulated expression of ubiquitin Carboxyl-terminal Hydrolase-L1: role in cell survival.

The ubiquitin Carboxyl-terminal Hydrolase-L1 gene (UCHL1) is a key enzyme in the protein degradation pathway; however, its precise role in protecting cells under stress conditions is unclear. In the present study we investigated the activity of this gene in human NT2/D1 embryonal carcinoma cells subjected to oxygen-glucose deprivation (OGD) and reoxygenation. OGD/reoxygenation cause global metabolic changes due to energy withdrawal and the subsequent generation of reactive oxygen species which initiates either a stress-adaptation-survival response or cell death, depending on the severity of the insult. A bi-phasic change in UCHL1 expression was observed by Q-PCR, Western blotting and flow cytometry. Down regulation of UCHL1 was detected immediately after OGD treatment and its expression was subsequently restored and increased 6 h after OGD treatment as well as during reoxygenation. Furthermore, flow cytometry analysis detected a lower level of UCHL1 only in apoptotic cells that had severe loss of mitochondrial membrane potential. Accordingly, down-regulation of endogenous UCHL1 by antisense cDNA in mouse N2a neuroblastoma cells increased the cell's sensitivity to OGD treatment. This down-regulation of endogenous UCHL1 led to the accumulation of p27, suggesting that UCHL1 is an essential gene to maintain cell homeostasis under normal growth and oxidative stress conditions.

Cell Line, Tumor↗
PubMed2005

S/MAR-binding properties of Sox2 and its involvement in apoptosis of human NT2 neural precursors.

DNA fragmentation in apoptosis, especially in lymphocytic cells, is initiated at scaffold/matrix attachment regions (S/MARs) and is preceded by the degradation of nuclear proteins. The present study was performed to establish whether the same mechanism occurred in human NT2 cells subjected to oxygen and glucose deprivation (OGD). We analyzed the integrity of c-myc S/MAR containing a base-unpairing region (BUR)-like element, which we established to be a binding site of the transcription factor Sox2. An accumulation of DNA breaks in close proximity to this element and a degradation of Sox2 were observed early in the OGD-induced apoptotic response. Identification of Sox2 as a novel c-myc BUR-binding protein was achieved through yeast one-hybrid screening and the Sox2/DNA interaction was confirmed by electrophoretic mobility shift assay and immunoprecipitation with Sox2 antibody. Our data support the notion that early proteolysis of unique BUR-binding proteins might represent a universal mechanism that renders these DNA sites vulnerable to endonucleolysis.

Apoptosis↗
PubMed2004

An autosomal genomic scan for loci linked to type 2 diabetes in northern Han Chinese.

We report the results of a genome-wide scan conducted in 219 individuals from 34 large multiplex nuclear pedigrees from the northern Han Chinese population at an average resolution of about 10 cM. Nonparametric two-point and multipoint linkage analyses were performed to detect evidence of linkage with type 2 diabetes in this study. On chromosome 1 four regions showed evidence of linkage with type 2 diabetes in northern Han Chinese. Of these regions a marker D1S193 (73 cM) showed evidence of linkage (two-point nonparametric linkage 2.409), and another region (around 190 cM) was a replication of several other studies performed in different ethnic populations. Evidences of linkage have been confirmed by typing additional markers (average distance 1-5 cM) flanking these two positive regions on chromosome 1. We also found indication of linkage with type 2 diabetes on chromosomes 2, 10, 12, 18, 20, and 22 by two-point linkage analyses.

Adult↗
PubMed2004

Regulation of DNaseY activity by actinin-alpha4 during apoptosis.

DNaseY, a Ca(2+)- and Mg(2+)-dependent endonuclease, has been implicated in apoptotic DNA degradation; however, the molecular mechanisms controlling its involvement in this process have not been fully elucidated. We have obtained evidence from yeast two-hybrid screening and coimmunoprecipitation experiments that DNaseY interacted physically with actinin-alpha4 and this interaction significantly enhanced its endonuclease activity. Accordingly, simultaneous overexpression of both proteins in PC12 cells dramatically increased the rate of apoptosis in response to teniposide' VM26. However, overexpression of DNaseY alone neither triggered apoptosis nor facilitated cell death in response to VM26 or serum deprivation. Instead, the overexpression of DNaseY increased the production of single-strand DNA breaks and evoked a profound upregulation of DNA repair pathways. Taken together, our results point to a novel regulatory mechanism of DNaseY activity and offer an explanation for why cells must first cleave key DNA repair and replication proteins before the successful execution of apoptosis.

Actinin↗
PubMed2003

Mapping the initial DNA breaks in apoptotic Jurkat cells using ligation-mediated PCR.

Apoptotic DNA degradation could be initiated by the accumulation of single-strand (ss) breaks in vulnerable chromatin regions, such as base unpairing regions (BURs), which might be preferentially targeted for degradation by both proteases and nucleases. We tested this hypothesis in anti-Fas-treated apoptotic Jurkat cells. Several nuclear proteins known for their association with both MARs and the nuclear matrix, that is, PARP, NuMA, lamin B and SATB1, were degraded, but the morphological rearrangement of the BUR-binding SATB1 protein was one of the earliest detected changes. Subsequently, we have identified several genes containing sequences homologous to the 25 bp BUR element of the IgH gene, a known SATB1-binding site, and examined the integrity of genomic DNA in their vicinity. Multiple ss breaks were found in close proximity to these sites relative to adjacent regions of DNA. Consistent with our prediction, the results indicated that the initiation of DNA cleavage in anti-Fas-treated Jurkat cells occurred within the BUR sites, which likely became accessible to endonucleases due to the degradation of BUR-binding proteins.

Base Sequence↗
PubMed2001

GABA expression dominates neuronal lineage progression in the embryonic rat neocortex and facilitates neurite outgrowth via GABA(A) autoreceptor/Cl- channels.

GABA emerges as a trophic signal during rat neocortical development in which it modulates proliferation of neuronal progenitors in the ventricular/subventricular zone (VZ/SVZ) and mediates radial migration of neurons from the VZ/SVZ to the cortical plate/subplate (CP/SP) region. In this study we investigated the role of GABA in the earliest phases of neuronal differentiation in the CP/SP. GABAergic-signaling components emerging during neuronal lineage progression were comprehensively characterized using flow cytometry and immunophenotyping together with physiological indicator dyes. During migration from the VZ/SVZ to the CP/SP, differentiating cortical neurons became predominantly GABAergic, and their dominant GABA(A) receptor subunit expression pattern changed from alpha4beta1gamma1 to alpha3beta3gamma2gamma3 coincident with an increasing potency of GABA on GABA(A) receptor-mediated depolarization. GABA(A) autoreceptor/Cl(-) channel activity in cultured CP/SP neurons dominated their baseline potential and indirectly their cytosolic Ca(2+) (Ca(2+)c) levels via Ca(2+) entry through L-type Ca(2+) channels. Block of this autocrine circuit at the level of GABA synthesis, GABA(A) receptor activation, intracellular Cl(-) ion homeostasis, or L-type Ca(2+) channels attenuated neurite outgrowth in most GABAergic CP/SP neurons. In the absence of autocrine GABAergic signaling, neuritogenesis could be preserved by depolarizing cells and elevating Ca(2+)c. These results reveal a morphogenic role for GABA during embryonic neocortical neuron development that involves GABA(A) autoreceptors and L-type Ca(2+) channels.

Action Potentials↗
PubMed2001

Population dynamics of phytophagous and predatory mites (Acari: Tetranychidae, Eriophyidae, Phytoseiidae) on bamboo plants in Fujian, China.

The seasonal cycle and population dynamics of Schizotetranychus nanjingensis Ma and Yuan, Aponychus corpuzae Rimando (Tetranychidae), Aculus hambusae Kuang (Eriophyidae) and their natural enemy Tvphlodromus bambusae Ehara (Phytoseiidae) were studied during 1996-1998 in moso bamboo forests in Nanping, Fujian, China. Damage to bamboo leaves was often caused by mixed populations of the three phytophagous species, which displayed different seasonal dynamics: S. nanjingensis fed actively and reproduced in May and from late July to late October (aestivating from June to mid July), Ap. corpuzae was active and reproduced from mid July to late November, and Ac. bambusae from July to next February. During Spring S. nanjingensis was the dominant species with the greatest niche width, but in Summer Ac. bambusae and Ap. corpuzae became dominant and had greater niche widths. In Autumn, Ac. bambusae decreased but both S. nanjingensis and Ap. corpuzae mites increased and the latter became dominant. In winter all species decreased sharply in number. The two spider mite species (S. nanjingensis and Ap. corpuzae) had high niche overlaps in all four seasons. Niche overlaps between the eriophyid Ac. bambusae and the two spider mites were similarly high except during the spring when Ac. bambusae was absent. The predatory mite (T. bambusae) had higher niche overlap with Ap. corpuzae than with others during Autumn and Winter, but during Spring and Summer niche overlap was higher with S. nanjingensis.

Animals↗
PubMed2001

Stimulation of cardiac L-type calcium channels by extracellular ATP.

The co-release of ATP with norepinephrine from sympathetic nerve terminals in the heart may augment adrenergic stimulation of cardiac Ca(2+) channel activity. To test for a possible direct effect of extracellular ATP on L-type Ca(2+) channels, single channels were reconstituted from porcine sarcolemma into planar lipid bilayers so that intracellular signaling pathways could be controlled. Extracellular ATP (2-100 microM) increased the open probability of the reconstituted channels, with a maximal increase of approximately 2.6-fold and an EC(50) of 3.9 microM. The increase in open probability was due to an increase in channel availability and a decrease in channel inactivation rate. Other nucleotides displayed a rank order of effectiveness of ATP > alpha,beta-methylene-ATP > 2-methylthio-ATP > UTP > adenosine 5'-O-(3-thiotriphosphate) >> ADP; adenosine had no effect. Several antagonists of P2 receptors had no impact on the ATP-dependent increase in open probability, indicating that receptor activation was not required. These results suggest that extracellular ATP and other nucleotides can stimulate the activity of cardiac L-type Ca(2+) channels via a direct interaction with the channels.

Adenosine↗
PubMed2000

Functional ionotropic glutamate receptors emerge during terminal cell division and early neuronal differentiation of rat neuroepithelial cells.

Ionotropic glutamate receptors mediate fast forms of excitatory synaptic transmission in mature neurons and may play critical roles in neuronal development. However, the developmental stage at which neuronal cells begin to express functional receptors and their roles in lineage progression remain unclear. In the present study, neural precursor cells were isolated from the cortical neuroepithelium of embryonic day 13 rats, and rapidly expanded in serum-free medium in response to basic fibroblast growth factor. RT-PCR revealed the presence of mRNAs encoding AMPA(A), AMPA(C), KA(1), KA(2), NMDA(1), and NMDA(2D) subunits after 3 days in culture. The functional expression of AMPA/kainate and NMDA receptors was investigated using Ca(2+) imaging and whole-cell patch-clamp recording techniques in cells pulse-labeled with bromodeoxyuridine (BrdU) for 1-4 hr. The recorded cells were then double-immunostained for BrdU incorporation and neuron-specific beta-tubulin (TuJ1). The results show that AMPA/kainate and NMDA induced increases in cytosolic Ca(2+) and inward currents only in differentiating neurons. In contrast, proliferating (BrdU(+)TuJ1(-)) cells failed to respond to any ionotropic glutamate receptor agonists. Interestingly, Ca(2+) imaging revealed that a subpopulation of BrdU(+)TuJ1(+) cells also responded to AMPA, indicating the emergence of functional ionotropic AMPA/kainate receptors during terminal cell division and the earliest commitment to neuronal cell lineage. These in vitro results were supported by flow cytometric sorting of AMPA-responsive cells pulse-labeled with BrdU for 1 hr in vivo, which revealed that functional AMPA receptors appear in BrdU(+)TuJ1(+) cells under physiological conditions and may play a role in terminal cell division.

Animals↗
PubMed2000

Organization and conservation of the GART/SON/DONSON locus in mouse and human genomes.

The SON gene, which maps to human chromosome 21q22.1-q22.2, encodes a novel regulatory protein. Here we describe the organization of the Son locus in the mouse genome. The mouse Son gene spans a region of approximately 35 kb. The coding region is more than 8 kb in length and has been completely sequenced. The gene is organized into 11 coding exons and 1 noncoding 3'UTR exon, with over 70% of the coding region residing in one 5.7-kb exon. The gene contains at least one alternative exon, N/C exon 1, which can be used, by splicing, to generate a truncated form of the SON protein. Further investigation of the mouse Son locus has identified the genes directly flanking Son. The glycinamide ribonucleotide formyltransferase gene, Gart, is encoded 5' of Son in a head-to-head arrangement, with the start of both genes lying within 899 bp. Sequence comparison with the expressed sequence tagged database identified a novel gene within 65 bp of the 3' end of Son, which we have named Donson. In this unusually compact gene cluster, we have found overlap in the pattern of expression between Gart, Son, and Donson. However, at least two of these genes have very different functions. While GART is involved in purine biosynthesis, we find that SON shows the characteristics of "SR- type" proteins, which are involved in mRNA processing and gene expression.

Amino Acid Sequence↗
PubMed2000

Effects of neoplastic transformation and teniposide (VM26) on protein kinase C isoform expression in rodent fibroblasts.

This study examined changes in protein kinase C (PKC) isoforms in rodent fibroblasts (rat F111 and mouse NIH3T3), transformed by the polyoma virus middle T antigen (mT) and undergoing apoptosis in response to teniposide (VM26). The mT-transformed cells up-regulated PKC delta and down-regulated both PKC epsilon and PKC lambda expression, and were more sensitive to the drug than their non-transformed counterparts. The drug treatment further lowered the expression of PKC epsilon, triggered nuclear translocation of PKC delta and its site-specific proteolysis, consistent with the notion that changes in specific PKC isoforms play a role not only in the neoplastic transformation of fibroblasts, but also in their apoptotic response.

3T3 Cells↗
PubMed2000

Synaptic connectivity in hippocampal neuronal networks cultured on micropatterned surfaces.

Embryonic rat hippocampal neurons were grown on patterned silane surface in order to organize synapse formations in a controlled manner. The surface patterns were composed of trimethoxysilylpropyl-diethylenetriamine (DETA) lines separated by tridecafluoro-1,1,2,2-tetrahydrooctyl-1-dimethylchlorosilane (13F) spaces. Pre- and post-synaptic specializations were identified by immunostaining for synapsin I and microtubule-associated protein-2 (MAP-2). Functional synaptic connections were examined by recording simultaneously from pairs of neurons using the whole-cell configuration of the patch-clamp technique. Spontaneous and evoked synaptic currents were recorded in neurons cultured for 2-14 days. The formation of functional connections was accompanied by the appearance of spontaneous synaptic currents (SSCs), which could be detected after approximately 3 days in culture in the absence of evoked synaptic currents (ESCs). ESCs were detected only after approximately 7 days in culture, mostly in the form of unidirectional synaptic connections. Other forms of synaptic connectivity, such as bidirectional and autaptic connections, were also identified. Both transient GABAergic and glutamatergic signals mediated the transmissions between communicating cells. These results demonstrate the combination of various types of synaptic connections forming simple and complex networks in neurons cultured on line (DETA)-space (13F) patterns. Finally, precisely synchronized SSCs were recorded in neuron pairs cultured on pattern indicating the existence of a fast-acting feedback mechanism mediated by pre-synaptic GABA(A) receptors.

Alkanes↗
PubMed2000

Effects of cis-unsaturated fatty acids on doxorubicin sensitivity in P388/DOX resistant and P388 parental cell lines.

It has been reported that several cis-unsaturated fatty acids (c-UFAs) could increase doxorubicin (DOX) accumulation in cancer cells and hence elevate its cytotoxicity. However, some researchers showed that c-UFA pretreatment did not affect its cytotoxicity in special cell lines. It is possible that the different results occurred due to different cellular characteristics. We hypothesized that c-UFA treatment might modulate the activities of some antioxidant enzymes to affect the resistance of cells to DOX. In the present study, we examined how c-UFA pretreatment affected DOX cytotoxicity on mouse leukemia cell line, P388, and its resistant subline, P388/DOX, which we found to have significantly higher glutathione peroxidase (GPx) activity as well as P-glycoprotein (p-gp) overexpression. We chose two c-UFAs, gamma-linolenic acid (GLA) (18:3n-6) and docosahexaenoic acid (DHA) (22:6n-3). Cytotoxicity was measured by MTT (3-(4.5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and trypan blue exclusion assays. DOX accumulation and p-gp expression were measured by flow cytometry. The activities of catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), and GPx were determined for both cell lines with and without treatment with GLA or DHA. Significant DOX accumulation occurred in both cell lines with GLA or DHA pretreatment, but without any change in p-gp expression in either cell line. Sensitivity to DOX cytotoxicity was improved by GLA or DHA pretreatment in P388/DOX in which only SOD activity was significantly increased, but not in the parental cell line P388 in which both SOD and CAT were significantly increased by the pretreatment. However, combined pretreatment of GLA or DHA with antioxidants, pyrrolidinedithiocarbamate (PDTC) or Vitamin C, could sensitize not only P388/DOX but also P388 cells to DOX. We conclude that the effects of c-UFA pretreatment on the sensitivity of cancer cells to DOX not only depend on the change in drug accumulation but also the change in the levels of antioxidant enzyme activities, and suggest that combined administration of c-UFAs, antioxidants, and DOX may be more effective in treating leukemia.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Acetylcholine stimulates cortical precursor cell proliferation in vitro via muscarinic receptor activation and MAP kinase phosphorylation.

Increasing evidence has shown that some neurotransmitters act as growth-regulatory signals during brain development. Here we report a role for the classical neurotransmitter acetylcholine (ACh) to stimulate proliferation of neural stem cells and stem cell-derived progenitor cells during neural cell lineage progression in vitro. Neuroepithelial cells in the ventricular zone of the embryonic rat cortex were found to express the m2 subtype of the muscarinic receptor. Neural precursor cells dissociated from the embryonic rat cortical neuroepithelium were expanded in culture with basic fibroblast growth factor (bFGF). reverse transcriptase-polymerase chain reaction (RT-PCR) revealed the presence of m2, m3 and m4 muscarinic receptor subtype transcripts, while immunocytochemistry demonstrated m2 protein. ACh and carbachol induced an increase in cytosolic Ca2+ and membrane currents in proliferating (BrdU+) cells, both of which were abolished by atropine. Exposure of bFGF-deprived precursor cells to muscarinic agonists not only increased both cell number and DNA synthesis, but also enhanced differentiation of neurons. These effects were blocked by atropine, indicating the involvement of muscarinic ACh receptors. The growth-stimulating effects were also antagonized by a panel of inhibitors of second messengers, including 1,2-bis-(O-aminophenoxy)-ethane-N,N,N', N'-tetraacetic acid (BAPTA-AM) to chelate cytosolic Ca2+, EGTA to complex extracellular Ca2+, pertussis toxin, which uncouples certain G-proteins, the protein kinase C inhibitor H7 and the mitogen-activated protein kinase (MAPK) inhibitor PD98059. Muscarinic agonists activated MAPK, which was significantly inhibited by atropine and the same panel of inhibitors. Thus, muscarinic receptors expressed by neural precursors transduce a growth-regulatory signal during neurogenesis via pathways involving pertussis toxin-sensitive G-proteins, Ca2+ signalling, protein kinase C activation, MAPK phosphorylation and DNA synthesis.

Acetylcholine↗
PubMed2000

Ionic basis for action potential prolongation by phenylephrine in canine epicardial myocytes.

INTRODUCTION: In canine ventricle, alpha-adrenergic agonists prolong action potential duration (APD) without any effect on the action potential notch, suggesting that, in this species, the effect on repolarization might be independent of inhibition of I(to). The present study investigated the action of the alpha-adrenergic agonist phenylephrine on the action potential and the repolarizing currents I(to) and I(K) in isolated canine epicardial myocytes. METHODS AND RESULTS: Isolated cells from canine epicardial tissue, and Purkinje fibers, were studied with the whole cell, voltage clamp method. Phenylephrine 0.1 microM increased APD by 13% +/- 4% at 90% repolarization without affecting the notch or amplitude. Under voltage clamp, concentrations of phenylephrine as high as 10 microM had no effect on I(to) in canine epicardial myocytes. However, I(to) of isolated canine Purkinje myocytes was reduced to 69% +/- 7% of control by 1 microM phenylephrine. Further studies in canine epicardial myocytes revealed an action of phenylephrine to inhibit I(K), and in particular I(Ks). Using a voltage protocol that included a two-step repolarization to separate I(Ks) and I(Kr) tail components, the largely I(Kr) component was not significantly affected by 1 microM phenylephrine, whereas the largely I(Ks) component was reduced to 81% +/- 5% of control value. CONCLUSION: Alpha-adrenergic prolongation of repolarization in canine epicardium does not result from inhibition of I(to). Rather, it appears that reduction of I(Ks) contributes to the action of phenylephrine. The unresponsiveness of epicardial I(to) is not a general characteristic of the canine heart, because Purkinje myocyte I(to) was inhibited, suggesting regional differences in the molecular basis of I(to) and/or alpha-adrenergic signaling in the canine heart.

Action Potentials↗
PubMed2000

Persistent activation of GABA(A) receptor/Cl(-) channels by astrocyte-derived GABA in cultured embryonic rat hippocampal neurons.

Whole cell patch-clamp recordings using Cl(-)-filled pipettes revealed more negative levels of baseline current and associated current variance in embryonic rat hippocampal neurons co-cultured on a monolayer of astrocytes than those cultured on poly-D-lysine. These effects were mimicked by culturing neurons on poly-D-lysine in astrocyte-conditioned medium (ACM). The baseline current and variance decreased immediately in all cells after either local perfusion with saline or exposure to bicuculline, an antagonist of GABA at GABA(A) receptor/Cl(-) channels. Baseline current and variance in all cells reached a nadir at approximately 0 mV, the calculated equilibrium potential for Cl(-). Perfusion of ACM rapidly induced a sustained current in neurons, which also reversed polarity at approximately 0 mV. Bicuculline attenuated or eliminated the ACM-induced current at a concentration that completely blocked micromolar GABA-induced current. Quantitative analyses of spontaneously occurring fluctuations superimposed on the ACM-induced current revealed estimated unitary properties of the underlying channel activity similar to those calculated for GABA's activation of GABA(A) receptor/Cl(-) channels. Bicuculline-sensitive synaptic-like transients, which reversed at approximately 0 mV, were also detected in neurons cultured in ACM, and these were immediately eliminated along with the negative baseline current and superimposed current fluctuations by perfusion. Furthermore bicuculline-sensitive synaptic-like transients were rapidly and reversibly triggered when ACM was acutely applied. ACM induced an increase in cytoplasmic Ca(2+) in cultured embryonic hippocampal neurons that was completely blocked by bicuculline and strychnine. We conclude that astrocytes release diffusible substances, most likely GABA, that persistently activate GABA(A) receptor/Cl(-) channels in co-cultured neurons.

3-Mercaptopropionic Acid↗
PubMed2000

[Inhibitory effect of paeonol on lipid peroxidational reaction and oxidational decorate of low density lipoprotein].

OBJECTIVE: To observe the effects of paeonol(Pae) on lipid peroxidational reaction and oxidational decorate of low density lipoprotein(LDL). METHOD: The rat model of hyperlipidaemia was established by feeding high lipid diet with cholesterol for 6 weeks. The contents of malondialdehyde(MDA) and oxidized low density lipoprotein(OX-LDL) were measured by thiobarbituric acid reactive substance(TBA) method and sandwich method of enzyme-linked immunosorbent assay for detection of polyclone antibody. LDL of serum in healthy person was separated by improve precipitate method. RESULTS: Pae(300, 150 mg.kg-1) could reduce significantly the levels of MDA of serum, aorta and liver; Pae(300 mg.kg-1) decreased obviously the content of OX-LDL of plasma; Pae(1,000, 200, 40 micrograms.ml-1) refrained markedly the course of oxidational decorate of LDL of serum in healthy person. CONCLUSION: Pae could reduce the levels of MDA and OX-LDL in hyperlipidaemia rats, and refrain the oxidational decorates of LDL of serum in healthy person.

Acetophenones↗