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Xiang Li

Publications and source records attributed to Xiang Li.

At least 37 records · Page 2Linked to original sources
PubMed2006

RGS2 determines short-term synaptic plasticity in hippocampal neurons by regulating Gi/o-mediated inhibition of presynaptic Ca2+ channels.

RGS2, one of the small members of the regulator of G protein signaling (RGS) family, is highly expressed in brain and regulates G(i/o) as well as G(q)-coupled receptor pathways. RGS2 modulates anxiety, aggression, and blood pressure in mice, suggesting that RGS2 regulates synaptic circuits underlying animal physiology and behavior. How RGS2 in brain influences synaptic activity is unknown. We therefore analyzed the synaptic function of RGS2 in hippocampal neurons by comparing electrophysiological recordings from RGS2 knockout and wild-type mice. Our study provides a general mechanism of the action of the RGS family containing RGS2 by demonstrating that RGS2 increases synaptic vesicle release by downregulating the G(i/o)-mediated presynaptic Ca(2+) channel inhibition and therefore provides an explanation of how regulation of RGS2 expression can modulate the function of neuronal circuits underlying behavior.

Animals↗
PubMed2006

Over-expression of hypoxia-inducible factor-1alpha increases the invasive potency of LNCaP cells in vitro.

OBJECTIVE: To evaluate the effect of hypoxia-inducible factor-1alpha (HIF-1alpha) over-expression on the invasion-associated proteins in human prostate cancer cells, as HIF-1alpha is a transcriptional factor that could activate genes involved in the response to hypoxia, but might also enhance the invasive potency of prostate cancer cells. MATERIALS AND METHODS: Prostate cancer (LNCaP) cells were transfected with recombinant plasmid pcDNA3.1(-)/HIF-1alpha and pcDNA3.1(-) control vector using a commercial system, designated as LNCaP/HIF-1alpha and LNCaP/pcDNA3.1, respectively. The positive clones were selected with G418 and confirmed by Western blot and indirect immunofluorescence labelling. A polycarbonate filter, coated with a matrix gel, was used to analyse the invasive potency. The expression of E-cadherin, vimentin, cathepsin D, matrix metalloproteinase (MMP2) and urokinase plasminogen activator receptor (uPAR) was detected by Western blot. RESULTS: The expression level of HIF-1alpha in LNCaP/HIF-1alpha was distinctly higher than that in LNCaP/pcDNA3.1 and LNCaP. Many more cells of LNCaP/HIF-1alpha penetrated through the polycarbonate filter than those of LNCaP/pcDNA3.1 and LNCaP. Compared with the LNCaP/pcDNA3.1 and LNCaP cells, the expression of vimentin, cathepsin D, MMP-2 and uPAR were up-regulated in LNCaP/HIF-1alpha, whereas the expression of E-cadherin was down-regulated. CONCLUSION: These results show that over-expression of HIF-1alpha directly stimulates the invasive potency of human prostate carcinoma LNCaP cells through the matrix gel. The expression of E-cadherin, vimentin, cathepsin D, MMP-2 and uPAR, which are proteins with established roles in the pathophysiology of invasion, could be regulated by HIF-1alpha in human prostate cancer cells.

Blotting, Western↗
PubMed2006

[Over-expression of Hypoxia-inducible factor 1alpha increases invasive potency of LNCaP cells in vitro].

OBJECTIVE: To evaluate the effect of hypoxia-inducible factor-1alpha (HIF1alpha) over-expression on the invasive potency of human prostate cancer cell. METHODS: Human prostate cancer cells of the line LNCaP were cultured and transfected by the recombinant plasmid pcDNA3.1(-)-HIF-1alpha containing the gene HIF1alpha with Lipofectamine 2000 system. The positive clone cells were selected by G418 and confirmed by Western blotting and immunofluorescence staining (LNCaP/HIF1alpha cells). Transwell chambers with polycarbonate filter were coated by 100 microl Matrigel at 1:20 dilution in serum-free medium. LNCaP cell suspension and LNCaP/HIF1alpha cell suspension were inoculated into the Transwell chambers respectively for 24 hours to analyze the invasive potency. Western blotting was used to detect the expression of E-cadherin, vimentin, matrix metalloproteinase-2 (MMP-2), cathepsin D, and urokinase-type plasminogen activator receptor (uPAR). RESULTS: The expression level of HIF1alpha in the LNCaP/HIF1alpha cells was distinctly higher than that in the LNCaP cells. The numbers of LNCaP-HIF1alpha cells penetrating through the Transwell polycarbonate filter was 4.6 +/- 0.4 x 10(4), significantly higher than that of the LNCaP cells (3.2 +/- 0.3 x 10(4), P < 0.01). The expressions of vimentin, MMP-2, cathepsin D, and uPAR were all up-regulated in LNCaP-HIF1alpha cells than those of the LNCaP cells. Whereas, the expression of E-cadherin was down-regulated in the LNCaP-HIF1alpha cells. CONCLUSION: Over-expression of HIF-1alpha stimulates the invasion potency of human prostate carcinoma cell. The expression of E-cadherin, vimentin, MMP-2, cathepsin D, and uPAR, all playing an established role in the invasion of tumor, can be regulated by HIF-1 in human prostate cancer cell.

Cell Line, Tumor↗
PubMed2006

Scanning peptide array analyses identify overlapping binding sites for the signalling scaffold proteins, beta-arrestin and RACK1, in cAMP-specific phosphodiesterase PDE4D5.

The cAMP-specific phosphodiesterase PDE4D5 can interact with the signalling scaffold proteins RACK (receptors for activated C-kinase) 1 and beta-arrestin. Two-hybrid and co-immunoprecipitation analyses showed that RACK1 and beta-arrestin interact with PDE4D5 in a mutually exclusive manner. Overlay studies with PDE4D5 scanning peptide array libraries showed that RACK1 and beta-arrestin interact at overlapping sites within the unique N-terminal region of PDE4D5 and at distinct sites within the conserved PDE4 catalytic domain. Screening scanning alanine substitution peptide arrays, coupled with mutagenesis and truncation studies, allowed definition of RACK1 and beta-arrestin interaction sites. Modelled on the PDE4D catalytic domain, these form distinct well-defined surface-exposed patches on helices-15-16, for RACK1, and helix-17 for beta-arrestin. siRNA (small interfering RNA)-mediated knockdown of RACK1 in HEK-293 (human embryonic kidney) B2 cells increased beta-arrestin-scaffolded PDE4D5 approx. 5-fold, increased PDE4D5 recruited to the beta2AR (beta2-adrenergic receptor) upon isoproterenol challenge approx. 4-fold and severely attenuated (approx. 4-5 fold) both isoproterenol-stimulated PKA (protein kinase A) phosphorylation of the beta2AR and activation of ERK (extracellular-signal-regulated kinase). The ability of a catalytically inactive form of PDE4D5 to exert a dominant negative effect in amplifying isoproterenol-stimulated ERK activation was ablated by a mutation that blocked the interaction of PDE4D5 with beta-arrestin. In the present study, we show that the signalling scaffold proteins RACK1 and beta-arrestin compete to sequester distinct 'pools' of PDE4D5. In this fashion, alterations in the level of RACK1 expression may act to modulate signal transduction mediated by the beta2AR.

Amino Acid Sequence↗
PubMed2006

Solution structure of GOPC PDZ domain and its interaction with the C-terminal motif of neuroligin.

GOPC (Golgi-associated PDZ and coiled-coil motif-containing protein) represents a PDZ domain-containing protein associated with the Golgi apparatus, which plays important roles in vesicular trafficking in secretory and endocytic pathways. GOPC interacts with many other proteins, such as the Wnt receptors Frizzled 8 and neuroligin via its PDZ domain. Neuroligin is a neural cell-adhesion molecule of the post-synapse, which binds to the presynapse molecule neurexin to form a heterotypic intercellular junction. Here we report the solution structure of the GOPC PDZ domain by NMR. Our results show that it is a canonical class I PDZ domain, which contains two alpha-helices and six beta-strands. Using chemical shift perturbation experiments, we further studied the binding properties of the GOPC PDZ domain with the C-terminal motif of neuroligin. The observations showed that the ensemble of the interaction belongs to fast exchange with low affinity. The 3D model of the GOPC PDZ domain/neuroligin C-terminal peptide complex was constructed with the aid of the molecular dynamics simulation method. Our discoveries provide insight into the specific interaction of the GOPC PDZ domain with the C-terminal peptide of Nlg and also provide a general insight about the possible binding mode of the interaction of Nlg with other PDZ domain-containing proteins.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Cytokinin-mediated cell cycling arrest of pericycle founder cells in lateral root initiation of Arabidopsis.

In Arabidopsis, lateral root formation is a post-embryonic developmental event, which is regulated by hormones and environmental signals. In this study, via analyzing the expression of cyclin genes during lateral root (LR) formation, we report that cytokinins (CTKs) inhibit the initiation of LR through blocking the pericycle founder cells cycling at the G(2) to M transition phase, while the promotion by CTK of LR elongation is due to the stimulation of the G(1) to S transition. No significant difference was detected in the inhibitory effect of CTK on LR formation between wild-type plants and mutants defective in auxin response or transport. In addition, exogenously applied auxin at different concentrations could not rescue the CTK-mediated inhibition of LR initiation. Our data suggest that CTK and auxin might control LR initiation through two separate signaling pathways in Arabidopsis. The CTK-mediated repression of LR initiation is transmitted through the two-component signal system and mediated by the receptor CRE1.

Arabidopsis↗
PubMed2006

Simultaneous determination of three residual barbiturates in pork using accelerated solvent extraction and gas chromatography-mass spectrometry.

A new method was developed for the rapid extraction and unequivocal determination of barbital, amobarbital and phenobarbital residues in pork. The isolation of the analytes from pork samples was accomplished by utilizing an accelerated solvent extractor ASE 300. The procedure was automatically carried out in series for fat removing and extraction, respectively with n-hexane and acetonitrile pressurized constantly at 10.3 MPa for 30 min. After evaporation, the extracts were cleaned up on a C(18) solid phase extraction (SPE) cartridge and the barbiturates were eluted with hexane-ethyl acetate (7:3), evaporated on a rotary evaporator and derivatized with CH(3)I. The methylated barbiturates were separated on a HP-5MS capillary column and detected with a mass detector. Electron impact ion source (EI) operating in time program-selected ion monitoring mode (SIM) was used for identification and external standard method was used for quantification. Good linearity was obtained in the range from 0.5 microg/kg to 25 microg/kg. Average recoveries of the three barbiturates spiked in pork ranged from 84.0% to 103.0%, with relative standard deviations from 1.6% to 12%. The limit of detection (LOD) was 0.5 microg/kg for the three barbiturates (S/N>or=3). The quantification limit (LOQ) was 1 microg/kg for the three barbiturates (S/N>or=10).

Animals↗
PubMed2006

Pongamone A-E, five flavonoids from the stems of a mangrove plant, Pongamia pinnata.

Chemical investigation of stems of the mangrove plant, Pongamia pinnata, resulted in isolation and characterization of five structurally unusual flavonoids pongamones A-E, along with 16 known flavonoid metabolites. Their structures were determined on the basis of spectroscopic analyses and by comparison of their spectroscopic data with those of related compounds reported in the literature. Pongamones A-E were assayed against DHBV RCs DNAP and HIV-1 RT in vitro. A possible biogenetic pathway of the isolated compounds is also proposed.

Circular Dichroism↗
PubMed2006

The hpa1 mutant of Arabidopsis reveals a crucial role of histidine homeostasis in root meristem maintenance.

Histidine (His) is an essential ingredient for protein synthesis and is required by all living organisms. In higher plants, although there is considerable evidence that His is essential for plant growth and survival, there is very little information as to whether it plays any specific role in plant development. Here, we present evidence for such a role of this amino acid in root development in Arabidopsis (Arabidopsis thaliana) from the characterization of a novel Arabidopsis mutant, hpa1, which has a very short root system and carries a mutation in one of the two Arabidopsis histidinol-phosphate aminotransferase (HPA) genes, AtHPA1. We have established that AtHPA1 encodes a functional HPA and that its complete knockout is embryo lethal. Biochemical analysis shows that the mutation in hpa1 only resulted in a 30% reduction in free His content and had no significant impact on the total His content. It did not cause any known symptoms of His starvation. However, the mutant displayed a specific developmental defect in root meristem maintenance and was unable to sustain primary root growth 2 d after germination. We have demonstrated that the root meristem failure in the mutant is tightly linked to the reduction in free His content and could be rescued by either exogenous His supplementation or AtHPA1 overexpression. Our results therefore reveal an important role of His homeostasis in plant development.

Amino Acid Sequence↗
PubMed2006

[Glucose metabolism status and angiographic features of coronary artery in patients undergoing their first coronary angiography: study of 553 cases].

OBJECTIVE: To investigate the correlation between glucose metabolism status and coronary artery lesion in the patients undergoing their first coronary angiography (CAG). METHODS: Oral glucose tolerance test (OGTT) and CAG were performed in 553 patients with suspected or confirmed coronary artery disease (CAD), aged 60.1 +/- 9.7. The anthroposomatologic parameters, blood pressure, HbA1c, and lipid profile of these patients were collected. Their glucose metabolism status was assessed based on the WHO diagnostic criteria of diabetes mellitus 1999 and American Heart Association's grading standards for evaluating coronary artery stenosis and Gensini score were applied to analyze the coronary artery lesion. According to the CAG results the patients were divided into CAD group and non-CAD group and then the glucose metabolic characteristics in both groups were analyzed by comparison based on the glycometabolic status. The patients were also grouped into diabetic and non-diabetic groups and the coronary artery angiographic features in both groups were compared. RESULTS: Among the 533 patients 277 (50.1%) had normal OGTT, 127 (23.0%) were diagnosed as with impaired glucose regulation, 61 (11%) were newly diagnosed as with type 2 diabetes mellitus, and the other 88 patients (15.9%) were already known diabetics. The prevalence of abnormal glycometabolism in the CAD group was 56.4%, significantly higher than that in the non-CAD group (34.5%, P < 0.05). The prevalence of multiple branches involvement in the diabetic group was 63.8%, significantly higher than that of the non-diabetic group (44.1%, P < 0.05), and the Gensini score in the diabetic group was 15 (30.5), significantly higher than that of the [20 (27), P < 0.05]. CONCLUSION: Abnormal glycometabolism is common in the population undergoing coronary angiography. Both the prevalence of multiple branches involvement and the degree of stenosis of coronary in the diabetics are higher than that in those without diabetes.

Aged↗
PubMed2006

A novel antioxidant agent, astragalosides, prevents shock wave-induced renal oxidative injury in rabbits.

Extracorporeal shock-wave lithotripsy (ESWL)-induced renal damage can occur as a result of multiple mechanisms, including small vessel injury and free radical formation. Our previous studies have demonstrated that Astragalus membranaceus (AM), a traditional Chinese herb, could significantly alleviate shock wave-induced renal oxidative injury, and its renoprotective effects were superior to those of varapamil, a calcium antagonist, which were considered to be a powerful agent in treating renal damage during ESWL. However, the effective antioxidant ingredient of this herb in the setting of lithotripsy remains unclear. Astragalosides, the major components of AM, was demonstrated to have superior antioxidation properties both in vitro and in vivo. Therefore, in this study we further investigate the potential effects of astragalosides on the shock wave-induced oxidative stress in rabbit kidney. Thirty male rabbits were randomly assigned to two groups, each consisting of 15 rabbits: (1) control group, (2) astragaloside-treated group. Each group of animals underwent 1,500 shock waves to the right kidney. Peripheral blood, urine and kidney tissue samples were collected pre- and post-ESWL. The level of urinary N-acetyl-beta-glucosaminidase (NAG), serum creatinine, serum or homogenates malondialdehyde (MDA) and superoxide dismutase (SOD), respectively, were detected. Histological alterations were also examined through light microcopy and transmission electron microscopy. In the control group, shock wave significantly increased the level of MDA and decreased SOD activity in both blood and renal homogenates (P<0.05, respectively). The comparison between the control and astragalosides group demonstrated that astragalosides could significantly decrease the level of MDA (P<0.05) and inhibit the decline of SOD activity (P<0.05). After exposure to shock waves, the activity of urinary NAG increased significantly in the control group (P<0.05). However, the concentration of serum creatinine did not change significantly. The comparison between the control and astragalosides group demonstrated that astragalosides significantly reduced the shock wave-induced leakage of NAG into the urine (P<0.05). Histological examination also showed that renal morphological impairments were much milder in astragaloside-treated rabbits than those of the control group. Our results indicated that astragaloside treatment provided significant protection against shock wave-induced renal oxidative injury.

Animals↗
PubMed2006

Bioremediation of environmental endocrine disruptor di-n-butyl phthalate ester by Rhodococcus ruber.

In this study DBP-degradation strain CQ0301 was isolated from rubbish landfill soil. According to the biophysical, biochemical characteristics and analysis of 16S rRNA, the strain was identified as Rhodococcus ruber. Three new protein bands could be fractioned after DBP-inducing, which were suspected to participate the process of DBP-degrading. Catechol was suspected to be an intermediate product of DBP and cleaving the benzene ring was catalyzed by catechol 1,2-dioxygenase, because a highly activity of catechol 1,2-dioxygenase could be detected after DBP-inducing. The results of this study also showed the optimal pH value, optimal temperature which influenced the degradation rate in soil: pH 7.0-8.0, 30-35 degrees C. Kinetics of degradation reaction had been performed at different initial concentration and different time. Analyzed with SPSS10.0 software, the DBP degradation can be described as the same exponential model when the initial DBP concentration was lower than 50 mg/kg. The kinetics equation was lnC=-0.1332t + A, with the degradation half-life of DBP in soil (5.20 d). Inoculating CQ0301 could relieve DBP content in plant. We also found that adding nutrient materials into soil was useful for decreasing the DBP content in plant. In summary, we isolated a bacterium capable of degrading DBP and decreasing DBP content in plant. We also explored the mechanism of biodegradation and characterized the environmental factors influencing the degradation process in contaminated soil. Based on this work, we hope that these findings can provide some information for applying of bioremediation of DBP contaminated soil.

Biodegradation, Environmental↗
PubMed2006

Risk factors for prostatic inflammation extent and infection in benign prostatic hyperplasia.

AIM: To investigate the risk factors for prostatic inflammation extent and infection in patients with benign prostatic hyperplasia (BPH) so as to manage prostatic inflammation more efficiently. METHODS: Sixty patients with BPH undergoing TURP between September 2005 and December 2005 in West China Hospital of Sichuan University were studied. Prostate fluid (PF) was collected for the measurement of secretory IgA (SIgA) and complement 3 (C3). Prostate tissue were collected for testing bacterial 16S rDNA by real-time PCR, examining SIgA in the tissue and examining the inflammation. The possible clinical and immune risk factors for prostatic inflammation or infection were analyzed by using the logistic regression method. RESULTS: Abnormal white blood cell count in urinalysis, prostatic infection and a high concentration of C3 in PF are the risk factors for prostatic inflammation extent (P = 0.025, 0.034 and 0.035, respectively and odds ratio [OR] = 18.269, 8.284 and 1.508, respectively). Risk factors for prostatic infection include the C3 concentration and the concentration of SIgA in PF (P = 0.003 and 0.013, respectively, and OR=1.645 and 0.993, respectively). CONCLUSION: The present study suggests that prostatic inflammation is associated with urinary tract infection, prostatic infection and the activated complement and that prostatic infection is associated with the activated complement and downregulated mucosal immunity in prostates of the patients with BPH. It is also suggested that individual immune regulation should be considered in the treatment of prostatic inflammation and infection of patients with BPH.

Bacteria↗
PubMed2006

Peptides of aminoxy acids as foldamers.

This Feature Article summarizes our efforts in developing a new family of foldamers from alpha-, beta- and gamma-aminoxy acids. From a series of conformational studies, we demonstrate that peptides consisting of aminoxy acids adopt several well-defined secondary structures, such as alpha N-O turns (which feature an eight-membered-ring hydrogen bond), beta N-O turns (a nine-membered-ring hydrogen bond), gamma N-O turns (a ten-membered-ring hydrogen bond), 1.8(8) helices (consecutive homochiral alpha N-O turns), 7/8 helices (alternating alpha N-O turns and gamma-turns), 1.7(9) helices (consecutive beta N-O turns), reverse turns (consecutive heterochiral alpha N-O turns) and sheet-like structures.

Amino Acids↗
PubMed2006

Generalized local-world models for weighted networks.

Based on the weighted scale-free network model proposed by Barrat, Barthélemy, and Vespignani [Phys. Rev. Lett. 92, 228701 (2004)] and enlightened by our local-world concept [Li and Chen, Physica A 328, 274 (2003)], we propose two generalized local-world (GLW) models for weighted complex networks. Theoretical analysis and numerical simulations show that the GLW models generate weighted networks as a crossover between exponential and scale-free weighted networks, and exhibit an alteration from assortative networks to disassortative networks.

Journal Article↗
PubMed2006

Hypoxia-inducible factor-1alpha induces the epithelial-mesenchymal transition of human prostatecancer cells.

BACKGROUND: Hypoxia-inducible factor-1alpha (HIF-1alpha) is a transcriptional factor that could improve the stimulation of angiogenesis and the metabolic adaptation of tumor cells to hypoxia. A recent study showed that HIF-1alpha could induce colon cancer cells epithelial-mesenchymal transition (EMT). However, no evidence indicates a similar correlation in human prostate cancer cells. This study was designed to evaluate the effect of HIF-1alpha over-expression on the EMT in human prostate cancer cells. METHODS: We selected the appropriate cell line for HIF-1alpha induction from those EMT negative prostate cell lines through vimentin gene detection by RT-PCR. As the result, LNCaP cell line is the best one for further experiment. LNCaP cells were transfected with recombinant plasmid pcDNA3.1 (-)/HIF-1alpha and pcDNA3.1 (-) control vector by Lipofectamine 2000 system. The positive cell colonies were confirmed by indirect immunofluorescence labeling. Then Transwell polycarbonate filter was used to analyze the invasive potency. The expression of EMT associated proteins, E-cadherin and vimentin, was detected by Western blotting. RESULTS: Among four of the EMT negative cell lines, LNCaP was the only one expressed the vimentin gene but not the associated protein. The expression level of HIF-1alpha in LNCaP/HIF-1alpha was distinctly higher than that in LNCaP/pcDNA3.1 and LNCaP. The cell numbers of LNCaP/HIF-1alpha that penetrated through the Transwell filter were higher than that of LNCaP/pcDNA3.1 and LNCaP. Compared with the LNCaP/pcDNA3.1 and LNCaP cells, the expression of vimentin was up-regulated in LNCaP/HIF-1alpha, whereas the expression of E-cadherin was down-regulated. CONCLUSIONS: Over-expression of HIF-1alpha stimulates the invasion potency of human prostate carcinoma cells through EMT pathway. The expression of E-cadherin and vimentin, playing established roles in EMT, could be regulated by HIF-1alpha in human prostate cancer cell line.

Cadherins↗
PubMed2006

Semiclassical calculation of nonadiabatic thermal rate constants: application to condensed phase reactions.

The nonadiabatic transition state theory proposed recently by Zhao et al. [J. Chem. Phys. 121, 8854 (2004)] is extended to calculate rate constants of complex systems by using the Monte Carlo and umbrella sampling methods. Surface hopping molecular dynamics technique is incorporated to take into account the dynamic recrossing effect. A nontrivial benchmark model of the nonadiabatic reaction in the condensed phase is used for the numerical test. It is found that our semiclassical results agree well with those produced by the rigorous quantum mechanical method. Comparing with available analytical approaches, we find that the simple statistical theory proposed by Straub and Berne [J. Chem. Phys. 87, 6111 (1987)] is applicable for a wide friction region although their formula is obtained using Landau-Zener [Phys. Z. Sowjetunion 2, 46 (1932); Proc. R. Soc. London, Ser. A 137, 696 (1932)] nonadiabatic transition probability along a one-dimensional diffusive coordinate. We also investigate how the nuclear tunneling events affect the dependence of the rate constant on the friction.

Journal Article↗