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Biomedical subjects

Yan Liu

Publications and source records attributed to Yan Liu.

At least 271 records · Page 15Linked to original sources
PubMed2004

Protein phosphatase 1 associates with the integrin alphaIIb subunit and regulates signaling.

Regulation of integrin activation occurs by specific interactions among cytoplasmic proteins and integrin alpha and beta cytoplasmic tails. We report that the catalytic subunit of protein phosphatase 1 (PP1c) constitutively associates with the prototypic integrin alphaIIbbeta3 in platelets and in cell lines overexpressing the integrin. PP1c binds directly to the cytoplasmic domain of integrin alphaIIb subunit containing a conserved PP1c binding motif 989KVGF992. Anchored PP1c is inactive, while thrombin-induced platelet aggregation or fibrinogen-alphaIIbbeta3 engagement caused PP1c dissociation and concomitant activation as revealed by dephosphorylation of PP1c substrate, myosin light chain. Inhibition of ligand binding to activated alphaIIbbeta3 blocks PP1c dissociation and represses PP1c activation. These studies reveal a previously unrecognized role for integrins whereby the alpha subunit cytoplasmic tail localizes the machinery for initiating and temporally maintaining the regulatory signaling activity of a phosphatase.

Amino Acid Sequence↗
PubMed2004

The mammalian exocyst, a complex required for exocytosis, inhibits tubulin polymerization.

The exocyst is a 734-kDa complex essential for development. Perturbation of its function results in early embryonic lethality. Extensive investigation has revealed that this complex participates in multiple biological processes, including protein synthesis and vesicle/protein targeting to the plasma membrane. In this article we report that the exocyst may also play a role in modulating microtubule dynamics. Using monoclonal antibodies, we observed that endogenous exocyst subunits co-localized with microtubules and mitotic spindles in normal rat kidney cells. To test for a functional relationship between the exocyst complex and microtubules, we established an in vitro exocyst reconstitution assay and studied exocyst effect on microtubule dynamics. We found that the exocyst complex reconstituted from eight recombinant exocyst subunits inhibited tubulin polymerization in vitro. Deletion of exocyst subunit sec5, sec6, sec15, or exo70 diminished its tubulin polymerization inhibition activity. Surprisingly, exocyst subunit exo70 itself was also capable of inhibiting tubulin polymerization, although exocyst complex with exo70 deletion did not lose its activity completely. Overexpression of exo70 in NRK cells resulted in microtubule network disruption and the formation of filopodia-like plasma membrane protrusions. The formation of these membrane protrusions was greatly hampered by stabilizing microtubules with taxol. Overexpression of exo84, an exocyst subunit that did not show tubulin polymerization inhibition activity, did not cause this phenotype. Results shown in this article, along with a previous report that localized microtubule instability induces plasma membrane addition, implicates a novel role for the exocyst in modulating microtubule dynamics underlying exocytosis.

Animals↗
PubMed2004

Cloning and identification of NS5ATP2 gene and its spliced variant transactivated by hepatitis C virus non-structural protein 5A.

AIM: To clone, identify and study new NS5ATP2 gene and its spliced variant transactivated by hepatitis C virus non-structural protein 5A. METHODS: On the basis of subtractive cDNA library of genes transactivated by NS5A protein of hepatitis C virus, the coding sequence of new gene and its spliced variant were obtained by bioinformatics method. Polymerase chain reaction (PCR) was conducted to amplify NS5ATP2 gene. RESULTS: The coding sequence of a new gene and its spliced variant were cloned and identified successfully. CONCLUSION: A new gene has been recognized as the new target transactivated by HCV NS5A protein. These results brought some new clues for studying the biological functions of new genes and pathogenesis of the viral proteins.

Antigens, Polyomavirus Transforming↗
PubMed2004

Transactivating effect of hepatitis C virus core protein: a suppression subtractive hybridization study.

AIM: To investigate the transactivating effect of hepatitis C virus (HCV) core protein and to screen genes transactivated by HCV core protein. METHODS: pcDNA3.1(-)-core containing full-length HCV core gene was constructed by insertion of HCV core gene into EcoRI/BamHI site. HepG2 cells were cotransfected with pcDNA3.1(-)-core and pSV-lacZ. After 48 h, cells were collected and detected for the expression of beta-gal by an enzyme-linked immunosorbent assay (ELISA) kit. HepG2 cells were transiently transfected with pcDNA3.1(-)-core using Lipofectamine reagent. Cells were collected and total mRNA was isolated. A subtracted cDNA library was generated and constructed into a pGEM-Teasy vector. The library was amplified with E. coli strain JM109. The cDNAs were sequenced and analyzed in GenBank with BLAST search after polymerase chain reaction (PCR). RESULTS: The core mRNA and protein could be detected in HepG2 cell lysate which was transfected by the pcDNA3.1(-)-core. The activity of beta-galactosidase in HepG2 cells transfected by the pcDNA3.1(-)-core was 5.4 times higher than that of HepG2 cells transfected by control plasmid. The subtractive library of genes transactivated by HCV core protein was constructed successfully. The amplified library contained 233 positive clones. Colony PCR showed that 213 clones contained 100-1 000 bp inserts. Sequence analysis was performed in 63 clones. Six of the sequences were unknown genes. The full length sequences were obtained with bioinformatics method, accepted by GenBank. It was suggested that six novel cDNA sequences might be target genes transactivated by HCV core protein. CONCLUSION: The core protein of HCV has transactivating effects on SV40 early promoter/enhancer. A total of 63 clones from cDNA library were randomly chosen and sequenced. Using the BLAST program at the National Center for Biotechnology Information, six of the sequences were unknown genes. The other 57 sequences were highly similar to known genes.

Gene Expression Regulation, Viral↗
PubMed2004

Heme oxygenase-1 in cholecystokinin-octapeptipe attenuated injury of pulmonary artery smooth muscle cells induced by lipopolysaccharide and its signal transduction mechanism.

AIM: To study the effect of cholecystokinin-octapeptide (CCK-8) on lipopolysaccharide (LPS) -induced pulmonary artery smooth muscle cell (PASMCs) injury and the role of heme oxygenase-1 (HO-1), and to explore the regulation mechanism of c-Jun N-terminal kinase (JNK) and activator protein-1 (AP-1) signal transduction pathway in inducing HO-1 expression further. METHODS: Cultured PASMCs were randomly divided into 4 or 6 groups: normal culture group, LPS (10 mg/L), CCK-8 (10(-6) mol/L) plus LPS (10 mg/L) group, CCK-8 (10(-6) mol/L) group, zinc protoporphyrin 9 (ZnPPIX) (10(-6) mol/L) plus LPS (10 mg/L) group, CCK-8 (10(-6) mol/L) plus ZnPPIX and LPS (10 mg/L) group. Seven hours after LPS administration, ultrastructural changes and content of malondialdehyde (MDA) of PASMCs in each group were investigated by electron microscopy and biochemical assay respectively. HO-1 mRNA and protein of PASMCs in the former 4 groups were examined by reverse transcriptase polymerase chain reaction (RT-PCR) and immunocytochemistry staining. Changes of c-fos expression and activation of JNK of PASMCs in the former 4 groups were detected with immunocytochemistry staining and Western blot 30 min after LPS administration. RESULTS: The injuries of PASMCs and the increases of MDA content induced by LPS were alleviated and significantly reduced by CCK-8 (P<0.05). The specific HO-1 inhibitor- ZnPPIX could worsen LPS-induced injuries and weaken the protective effect of CCK-8. The expressions of c-fos, p-JNK protein and HO-1 mRNA and protein were all slightly increased in LPS group, and significantly enhanced by CCK-8 further (P<0.05). CONCLUSION: HO-1 may be a key factor in CCK-8 attenuated injuries of PASMCs induced by LPS, and HO-1 expression may be related to the activation of JNK and activator protein (AP-1).

Animals↗
PubMed2004

Highly-efficient DNA photocleavers with long wavelength absorptions: thio-heterocyclic fused naphthalimides containing aminoalkyl side chains.

Thio-heterocyclic fused naphthalimides with aminoalkyl side chains were designed, synthesized and evaluated. These compounds have long wavelength absorptions and binding affinities to Calf thymus DNA. They could photodamage supercoiled pBR322 DNA from form I (closed) to II (nicked) at a concentration as low as 0.5 microM and to form III (linear) at a concentration of 50 microM. A possible mechanism of superoxide anion was provided.

Amines↗
PubMed2004

Convergence of depth from texture and depth from disparity in macaque inferior temporal cortex.

The visual system must reconstruct the three-dimensional structure of an object from two-dimensional retinal images. Previous research has shown that macaque inferior temporal (IT) neurons, although belonging to the ventral visual stream, code for depth defined by binocular disparity gradients. Here, we demonstrate that macaque IT neurons also code for depth defined by texture gradients, a monocular depth cue. Single IT neurons were selective for the tilt of texture-defined surfaces, and the tilt preferences of individual neurons remained the same, whether surfaces were defined by texture or disparity cues. Furthermore, the tilt preference was invariant over different types of textures and slants, suggesting an abstract representation of surface tilt in ventral visual cortex.

Animals↗
PubMed2004

Protein kinase C (PKC) betaII induces cell invasion through a Ras/Mek-, PKC iota/Rac 1-dependent signaling pathway.

Protein kinase C betaII (PKCbetaII) promotes colon carcinogenesis. Expression of PKCbetaII in the colon of transgenic mice induces hyperproliferation and increased susceptibility to colon cancer. To determine molecular mechanisms by which PKCbetaII promotes colon cancer, we established rat intestinal epithelial (RIE) cells stably expressing PKCbetaII. Here we show that RIE/PKCbetaII cells acquire an invasive phenotype that is blocked by the PKCbeta inhibitor LY379196. Invasion is not observed in RIE cells expressing a kinase-deficient PKCbetaII, indicating that PKCbetaII activity is required for the invasive phenotype. PKCbetaII induces activation of K-Ras and the Ras effector, Rac1, in RIE/PKCbetaII cells. PKCbetaII-mediated invasion is blocked by the Mek inhibitor, U0126, and by expression of either dominant negative Rac1 or kinase-deficient atypical PKCiota. Expression of constitutively active Rac1 induces Mek activation and invasion in RIE cells, indicating that Rac1 is the critical downstream effector of PKCbetaII-mediated invasion. Taken together, our results define a novel PKCbetaII --> Ras --> PKCiota /Rac1 --> Mek signaling pathway that induces invasion in intestinal epithelial cells. This pathway provides a plausible mechanism by which PKCbetaII promotes colon carcinogenesis.

Animals↗
PubMed2004

Simple and sensitive electrode design for microchip electrophoresis/electrochemistry.

A simple and sensitive electrode design for microchip capillary electrophoresis/electrochemistry (CE-EC) is presented. The system employs metal microwires as the working electrodes for electrochemical detection. Two general approaches for integration of electrodes in microchip CE-EC are commonly used, end-channel and microfabrication. The end-channel approach allows electrode cleaning and the use of chemically modified electrodes; however, the designs generally lack portability and the ability to incorporate multiple electrodes. Microfabrication allows the incorporation of multiple electrodes on-chip and is easily made portable; however, it requires the use of expensive metallization and clean room facilities, and integration of more than one electrode material is challenging. The reported approach aligns a solid metal microwire through the separation channel allowing integration of multiple electrodes and the use of different electrode materials without sacrificing the portability. A detection limit of 100 nM for dopamine was achieved without the use of a decoupler as a result of a higher collection efficiency with the new design.

Journal Article↗
PubMed2004

Semaphorin3D guides retinal axons along the dorsoventral axis of the tectum.

We examined the role of Sema3D, a semaphorin of previously unknown function, in guiding retinal ganglion cell (RGC) axons to the optic tectum in the developing zebrafish. Sema3D is expressed more strongly in the ventral versus dorsal tectum, suggesting that it may participate in guiding RGC axons along the dorsoventral axis of the tectum. Ubiquitous misexpression of Sema3D in transgenic zebrafish inhibits ventral but not dorsal RGC axon growth. In addition, ventral RGC axons avoid or stop at individual cells misexpressing Sema3D along their pathway. Sema3D ubiquitous misexpression at later stages also causes ventral RGC axon arbors to spread more widely along the dorsoventral axis of the tectum. Knock-down of Sema3D with morpholino antisense causes ventral RGC axons to extend aberrantly into the ventral tectum. These results suggest that Sema3D in the ventral tectum normally acts to inhibit ventral RGCs from extending into ventral tectum, ensuring their correct innervation of dorsal tectum.

Animals↗
PubMed2004

[Induction of atherosclerotic plaque instability in rabbits after transfection of human wild-type p53 gene].

OBJECTIVE: To develop an animal model of unstable atherosclerotic plaques. METHODS: Sixty-four New Zealand white rabbits were randomly divided into two groups: group A (n = 54, undergoing balloon-induced abdominal aortic wall injury and then fed on a diet of 1% cholesterol) and group B (n = 10, fed on a diet of 1% cholesterol only). At the end of the eighth week, the rabbits in group A were randomly divided into two subgroups: group A1 (n = 27) and group A2 (n = 27). Recombinant adenovirus carrying human wild-type p53 gene and beta galactosidase (LacZ) genes were injected through a catheter into the aortic segments rich in plaques in group A1 and A2 respectively. Two weeks later, 10 rabbits each in group A1 and A2 were killed to observe the occurrence rate of spontaneous plaque rupture, and the remaining rabbits in group A1, A2 and B all underwent pharmacological triggering by Chinese Russell's viper venom injected subperitoneally and histamine injected intravenously two times with an interval of 24 hours. Twenty-four hours after the second pharmacological triggering the remaining rabbits were all killed and their abdominal aortae were taken out to undergo macropathologic observation, staining, and immunohistochemistry to examine the accumulation of macrophages and the expression of p53 protein, in the plaques with and without rupture respectively. At the beginning of the experiment and before being killed the serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein choloesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) were examined. RESULTS: Before the rabbits were killed the blood-lipid levels were significantly increased in comparison with the baseline levels (all P < 0.01), however, without significant differences among the three groups. The rate of cells positive in p53 transfection was 32.4% +/- 10.2% in the group A1, significantly higher than those in the group A2 and group B (15.8% +/- 3.6% and 16.2% +/- 6.7% respectively, both P < 0.001). The fibrous cap of the plaque was significantly thinner in the group A1 than in the other 2 groups (both P < 0.05). The apoptosis rate was 2.5% +/- 0.8% in the group A1, significantly higher than those in the group A2 and group B (1.0% +/- 0.3% and 0.9% +/- 0.4% respective, both P < 0.01). The accumulation of macrophages within the plaques was significantly remarkable and the number of vessel smooth muscle cells was much smaller in the group A1. Plaque rupture and thrombosis occurred in 12 rabbits, numbering 20 lesions, after pharmacological triggering in the group A1, and occurred in only 5 rabbits, numbering 7 lesions, in the group A2. None of the rabbits in group B showed any lesions after the pharmacological triggering. CONCLUSION: With transfection of human wild-type p53 genes and pharmacological triggering, plaque rupture and thrombosis may occur in most atherosclerotic lesions in rabbits, which offered a reliable model for the further study of unstable plaques.

Animals↗
PubMed2004

A new glucoceramide from the watermelon Begonia, Pellionia repens.

A new glucoceramide named pellioniareside (1) was isolated from the aqueous ethanolic extract of whole plants of Pellionia repens, together with lupeol (2), uracil (3), (22E,20S,24R)-5alpha,8alpha-epidioxyergosta-6,22-dien-3-beta-ol (4), and daucosterol (5). The structure and relative configurations of pellioniareside were identified as (2S,3S,4R,6E,8E)-1-O-beta-D-glucopyranosyl-2-[(2 R)-2-hydroxytetracosanoylamino]-1,3,4-octadecanetriol-6,8-diene by analysis of spectral data and by chemical evidence.

Begoniaceae↗
PubMed2004

A novel immunosensor based on immobilization of hepatitis B surface antibody on platinum electrode modified colloidal gold and polyvinyl butyral as matrices via electrochemical impedance spectroscopy.

Hepatitis B surface antibody (HBsAb) was immobilized to the surface of platinum electrode modified with colloidal gold and polyvinyl butyral (PVB) as matrices to detect hepatitis B surface antigen (HBsAg) via electrochemical impedance spectroscopy (EIS). The electrochemical measurements of cyclic voltammetry and impedance spectroscopy showed that K(4)[Fe(CN)(6)]/K(3)[Fe(CN)(6)] reactions on the platinum electrode surface were blocked due to the procedures of self-assembly of HBsAb-Au-PVB. The binding of a specific HBsAb to HBsAg recognition layer could be detected by measurements of the impedance change. A new strategy was introduced for improving the sensitivity of impedance measurements via the large specific surface area and high surface free energy of Au nanoparticles and the encapsulated effect of polyvinyl butyral. The results showed that this strategy caused dramatic improvement of the detection sensitivity of HBsAg and had good linear response to detect HBsAg in the range of 20-160 ng.ml(-1) with a detection limit of 7.8 ng.ml(-1). Moreover, the studied immunosensor exhibited high sensitivity and long-term stability.

Biosensing Techniques↗
PubMed2004

Optimizing dilute acid hydrolysis of hemicellulose in a nitrogen-rich cellulosic material--dairy manure.

Effective dilute acid hydrolysis of dairy manure which contains roughly 12% hemicellulose on a dry matter basis can produce a variety of mono-sugars such as arabinose, xylose and galactose, as well as to further benefit utilization of cellulose in the manure. To enhance the effectiveness of this dilute acid hydrolysis, the effect of manure nitrogen content was studied because some reactions such as the browning reaction between amino acids and reducing sugars and acid-base reactions involving ammonia and acid interfere with the hydrolysis. Two dairy manure samples were used to study this nitrogen effect; the original manure and the pretreated manure derived from a solid/liquid separation pretreatment. The pretreated manure had a total nitrogen content of 1.3% dry matter (DM) while the original dairy manure had twice that amount with a total nitrogen content of 2.6% DM. Results found that the optimal conditions for hydrolysis of manure hemicellulose were 2 h reaction time, 1% sulfuric acid concentration, 135 degrees C, and 10% sample concentration using the pretreated dairy manure as raw material. Under these conditions the corresponding sugar yield from hemicellulose was 111% and sugar concentration in the solution reached 16.5 g/l. At the same time, the hydrolyzed solid had 43% DM of cellulose, which was much higher than both the original manure containing 22% and the pretreated manure with 32%.

Acids↗
PubMed2004

Human alphaA- and alphaB-crystallins prevent UVA-induced apoptosis through regulation of PKCalpha, RAF/MEK/ERK and AKT signaling pathways.

AlphaA- and alphaB-crystallins are distinct antiapoptotic regulators. Regarding the antiapoptotic mechanisms, we have previously demonstrated that under staurosporine treatment, HalphaA- and HalphaB-crystallins can interact with Bax and Bcl-XS, proapoptotic members of the Bcl-2 family, to sequester their translocation into mitochondria, and thus prevent the staurosporine-induced apoptosis. In the present study, we further compared the anti-apoptotic mechanisms of HalphaA- and HalphaB-crystallin in preventing human lens epithelial cells from UVA-induced apoptosis. UVA-irradiation of human lens epithelial cells turned on the apoptotic death program. Moreover, associated with the activation of the death program, UVA also activated the RAF/MEK/ERK signaling pathway. In contrast, p38 kinase and JNK1/2 signaling pathways were not activated. Inhibition of the RAF/MEK/ERK pathway by a dominant negative mutant RAF1 greatly attenuated UVA-induced apoptosis. Expression of the exogenous human alphaB-crystallin prevented UVA-induced activation of RAF/MEK/ERK pathway and thus substantially abrogated UVA-induced apoptosis. In contrast, expression of the exogenous human alphaA-crystallin did not prevent UVA-induced activation of RAF/MEK/ERK pathway. Instead, it activated AKT kinase pathway to promote survival and thus counteracted the UVA-induced apoptosis. Together, our results for the first time reveal that by regulating multiple signaling pathways the two alpha-crystallins can prevent stress-induced apoptosis through different mechanisms.

Apoptosis↗
PubMed2004

Biological actions and mechanism of action of calbindin in the process of apoptosis.

Although it was originally proposed that the major role of calbindin is to facilitate the vitamin D dependent movement of calcium through the cytosolic compartment of the intestinal or renal cell, we found that calbindin also has a major role in different cell types in protecting against apoptotic cell death. Calbindin, which buffers calcium, can inhibit apoptosis induced by different proapoptotic stimuli. Expression of calbindin-D(28k) in neural cell suppressed the proapoptotic actions of presenilin-1, which is causally linked to familial Alzheimer's disease, by preventing calcium mediated mitochondrial damage and the subsequent release of cytochrome c. Calbindin, by buffering intracellular calcium can also protect HEK 293 kidney cells from parathyroid hormone induced apoptosis that was found to be mediated by a phospholipase C dependent increase in intracellular calcium. In addition, cytokine mediated destruction of pancreatic beta cells can be prevented by calbindin. Induction by cytokines of nitric oxide, peroxynitrite and lipid hydroperoxide production was significantly decreased in calbindin expressing beta cells. Thus, calbindin-D(28k), by inhibiting free radical formation, can protect islet beta cells from autoimmune destruction in type 1 diabetes. Calbindin-D(28k) can also protect against apoptosis in bone cells. Calbindin was found to block apoptosis in osteocytic and osteoblastic cells. Our findings suggest that calbindin is capable of directly inhibiting the activity of caspase-3, a common downstream effector of multiple apoptotic signaling pathways, and that this inhibition results in an inhibition of tumor necrosis factor (TNFalpha) and glucocorticoid induced apoptosis in bone cells. Thus, while part of calbindin's protective effect may result from buffering rises in intracellular calcium, other mechanisms of action, such as inhibition of caspase activity, also play a significant role in the prevention of apoptosis by calbindin-D(28k). These findings have implications for the prevention of degeneration in different cell types and therefore could prove important for the therapeutic intervention of many diseases, including diabetes and osteoporosis.

Apoptosis↗
PubMed2004

Effect of adenovirus-mediated p27 gene expression on the proliferation and apoptosis of HL-60 and Raji cell lines.

OBJECTIVE: To explore the possible effect of p27 gene expression on the proliferation and apoptosis of HL-60 and Raji cell lines. METHODS: The infections of HL-60 and Raji cells were performed by the adenovirus-mediated p27 gene transfection approach. The efficiency of Adp27 infection and the expression of p27 mRNA and protein were evaluated by X-gal staining, RT-PCR and flow cytometry. The proliferation and apoptosis of HL-60 and Raji cells were estimated by using trypan blue staining, MTT assay, Annexin V/PI and DNA ladder electrophoresis. RESULTS: The infection efficiency of HL-60 and Raji cells were 40.3 and 32%, respectively; RT-PCR and flow cytometry showed that there were significant expressions of p27 mRNA and protein of HL-60 and Raji cells infected by Adp27, while HL-60 cells themselves showed only faint p27 mRNA and protein, and Raji cells hardly presented p27 mRNA and protein. The strong proliferation inhibitions, which were in a time-dependent manner for HL-60 and Raji cells infected by Adp27, were indicated by cell growth curve and MTT assay. After 72 h infection of HL-60 and Raji cells by Adp27, the Annexin V+/PI- apoptotic cell rates were 46.9 and 35.7% respectively, which were significantly increased compared with control group (4.7 and 5.6% respectively). The typical DNA ladder bands were detectable in HL-60 and Raji cells after 48 h of Adp27 infection. CONCLUSION: The infection of HL-60 and Raji cells by means of adenoviral vector-mediated p27 gene could evidently inhibit cellular proliferation and promote cell apoptosis, which would provide experimental evidence for gene therapy of leukemia/lymphoma using adenovirus-mediated p27 gene approach.

Adenoviridae↗