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Li Liu

Publications and source records attributed to Li Liu.

At least 91 records · Page 5Linked to original sources
PubMed2006

Identification of open reading frames unique to a select agent: Ralstonia solanacearum race 3 biovar 2.

An 8x draft genome was obtained and annotated for Ralstonia solanacearum race 3 biovar 2 (R3B2) strain UW551, a United States Department of Agriculture Select Agent isolated from geranium. The draft UW551 genome consisted of 80,169 reads resulting in 582 contigs containing 5,925,491 base pairs, with an average 64.5% GC content. Annotation revealed a predicted 4,454 protein coding open reading frames (ORFs), 43 tRNAs, and 5 rRNAs; 2,793 (or 62%) of the ORFs had a functional assignment. The UW551 genome was compared with the published genome of R. solanacearum race 1 biovar 3 tropical tomato strain GMI1000. The two phylogenetically distinct strains were at least 71% syntenic in gene organization. Most genes encoding known pathogenicity determinants, including predicted type III secreted effectors, appeared to be common to both strains. A total of 402 unique UW551 ORFs were identified, none of which had a best hit or >45% amino acid sequence identity with any R. solanacearum predicted protein; 16 had strong (E < 10(-13)) best hits to ORFs found in other bacterial plant pathogens. Many of the 402 unique genes were clustered, including 5 found in the hrp region and 38 contiguous, potential prophage genes. Conservation of some UW551 unique genes among R3B2 strains was examined by polymerase chain reaction among a group of 58 strains from different races and biovars, resulting in the identification of genes that may be potentially useful for diagnostic detection and identification of R3B2 strains. One 22-kb region that appears to be present in GMI1000 as a result of horizontal gene transfer is absent from UW551 and encodes enzymes that likely are essential for utilization of the three sugar alcohols that distinguish biovars 3 and 4 from biovars 1 and 2.

Arginine↗
PubMed2006

EST analysis of cDNA libraries from the entomopathogenic fungus Beauveria (Cordyceps) bassiana. I. Evidence for stage-specific gene expression in aerial conidia, in vitro blastospores and submerged conidia.

The entomopathogenic fungus Beauveria (Cordyceps) bassiana holds much promise as a pest biological control agent. B. bassiana produces at least three in vitro single cell infectious propagules, including aerial conidia, vegetative cells termed blastospores and submerged conidia, that display different morphological, biochemical and virulence properties. Populations of aerial conidia, blastospores and submerged conidia were produced on agar plates, rich liquid broth cultures and under conditions of nutrient limitation in submerged cultures, respectively. cDNA libraries were generated from mRNA isolated from each B. bassiana cell type and approximately 2,500 5' end sequences were determined from each library. Sequences derived from aerial conidia clustered into 284 contigs and 963 singlets, with those derived from blastospores and submerged conidia forming 327 contigs with 788 singlets, and 303 contigs and 1,079 contigs, respectively. Almost half (40-45 %) of the sequences in each library displayed either no significant similarity (e value >10(-4)) or similarity to hypothetical proteins found in the NCBI database. The expressed sequence tag dataset also included sequences representing a significant portion of proteins in cellular metabolism, information storage and processing, transport and cell processes, including cell division and posttranslational modifications. Transcripts encoding a diverse array of pathogenicity-related genes, including proteases, lipases, esterases, phosphatases and enzymes producing toxic secondary metabolites, were also identified. Comparative analysis between the libraries identified 2,416 unique sequences, of which 20-30 % were unique to each library, and only approximately 6 % of the sequences were shared between all three libraries. The unique and divergent representation of the B. bassiana transcriptome in the cDNA libraries from each cell type suggests robust differential gene expression profiles in response to environmental conditions.

Animals↗
PubMed2006

A bipartite system for the constitutive and inducible expression of high levels of foreign proteins in plants.

We have developed combined transgene/virus vector systems for the expression of heterologous proteins in plants. The systems are based on the bipartite RNA plant virus, cowpea mosaic virus (CPMV), and involve the amplification of integrated copies of either full-length or deleted versions of RNA-2 carrying a foreign gene. In the case of plants transgenic for full-length versions of RNA-2 carrying the green fluorescent protein (GFP), amplification can be achieved by supplying RNA-1 either exogenously or by crossing. This allows either inducible or constitutive expression of the foreign gene and results in an infection that can be passaged to further plants. Replication of deleted versions of RNA-2 harbouring GFP requires the presence of both RNA-1 and a suppressor of gene silencing, a function which we show can be supplied by HcPro from potato virus Y. Replication of the deleted versions of RNA-2 can be achieved by supplying the suppressor and RNA-1 either exogenously or by crossing, showing that this system can also be used in an inducible and constitutive format. The use of deleted forms of RNA-2 has the advantage that no infectious virus is produced, providing an effective method of biocontainment. The CPMV-based systems have advantages over existing plant expression systems in terms of the expression levels obtainable and the simplicity and flexibility of use, and should be of great practical benefit in the development of plants as bioreactors.

Comovirus↗
PubMed2006

Attenuation of MPTP-induced neurotoxicity and locomotor dysfunction in Nucling-deficient mice via suppression of the apoptosome pathway.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity is one of the experimental models most commonly used to study the pathogenesis of Parkinson's disease (PD). Although the biochemical mechanisms underlying the cell death induced by MPTP remain to be clarified, it has been found that the mitochondrial apoptotic signaling pathway plays an important role in the neurotoxicity of MPTP. Nucling is a novel type of apoptosis-associated molecule, essential for cytochrome c, apoptosis protease activating factor 1 (Apaf-1), pro-caspase-9 apoptosome induction and caspase-9 activation following pro-apoptotic stress. Here we found that Nucling-deficient mice treated with MPTP did not exhibit locomotor dysfunction in an open-field test. The substantia nigra dopaminergic neurons of Nucling-deficient mice were resistant to the damaging effects of the neurotoxin MPTP. Up-regulated expression of apoptosome was attenuated in Nucling-deficient mice treated with MPTP. These results indicate an important role for Nucling in MPTP-induced neuronal degeneration and suggest that the suppression of Nucling would be of therapeutic benefit for the treatment of neurodegeneration in PD.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed2006

Detection of Helicobacter pylori DNA in peripheral blood from patients with peptic ulcer or gastritis.

Cases of Helicobacter bacteremia have been reported from time to time. Helicobacter pylori is the most important representative of Helicobacterium, yet whether it can result in bacteremia has rarely been studied. In this study, we examined H. pylori DNA in peripheral blood and gastric mucosa of patients with peptic ulcer or chronic gastritis by polymerase chain reaction (PCR). We found H. pylori DNA in 15 of 20 gastric samples, and 9 of these specimens were positive for H. pylori culture. H. pylori DNA amplified by PCR was positive in the peripheral blood of three patients, who all had duodenal ulcers. Gastric biopsy specimens from these three patients were all positive for H. pylori genes and H. pylori was isolated from these specimens. After the 16S rRNA gene sequences of three specimens from the same patient were obtained, we found that they were identical, which suggested that they are the same strain. Our findings suggest that H. pylori exists not only in gastric mucosa but also in peripheral blood, and it is possible that H. pylori can result in bacteremia.

Adolescent↗
PubMed2006

Second intron of mouse nestin gene directs its expression in pluripotent embryonic carcinoma cells through POU factor binding site.

Nestin, an intermediate filament protein, is expressed in the neural stem cells of the developing central nervous system. This tissue-specific expression is driven by the neural stem cell-specific enhancer in the second intron of the nestin gene. In this study, we showed that the mouse nestin gene was expressed in pluripotent embryonic carcinoma (EC) P19 and F9 cells, not in the differentiated cell types. This cell type-specific expression was conferred by the enhancer in the second intron. Mutation of the conserved POU factor-binding site in the enhancer abolished the reporter gene expression in EC cells. Oct4, a Class V POU factor, was found to be coexpressed with nestin in EC cells. Electrophoretic mobility-shift assays and supershift assays showed that a unique protein-DNA complex was formed specifically with nuclear extracts of EC cells, and Oct4 protein was included. Together, these results suggest the functional relevance between the conserved POU factor-binding site and the expression of the nestin gene in pluripotent EC cells.

Animals↗
PubMed2006

Processing halftone color images by vector space methods.

The reproduction of color images by color halftoning can be characterized by the Neugebauer model/equation. However, the Neugebauer equation is not easy to solve because of the highly nonlinear relationship between the underlying Neugebauer primaries and the colorants. We attempt to solve the Neugebauer equation by vector space methods. The proposed method of solution is applicable to any number of colorants, although our experimental results are confined to the CMY and CMYK cases. Among the constraints we consider are those related to a bound on the permissible amount of total ink and a bound on the total cost of applying colorants to achieve a satisfactory level of color reproduction. Our results demonstrate that the vector space method is a feasible approach for solving for the required amounts of colorants in the constrained color halftoning problem.

Algorithms↗
PubMed2006

Dominance of HIV-1 subtype CRF01_AE in sexually acquired cases leads to a new epidemic in Yunnan province of China.

BACKGROUND: Dating back to the first epidemic among injection drug users in 1989, the Yunnan province has had the highest number of human immunodeficiency virus type 1 (HIV-1) infections in China. However, the molecular epidemiology of HIV-1 in Yunnan has not been fully characterized. METHODS AND FINDINGS: Using immunoassays, we identified 103,015 accumulated cases of HIV-1 infections in Yunnan between 1989 and 2004. We studied 321 patients representing Yunnan's 16 prefectures from four risk groups, 11 ethnic populations, and ten occupations. We identified three major circulating subtypes: C/CRF07_BC/CRF08_BC (53%), CRF01_AE (40.5%), and B (6.5%) by analyzing the sequence of p17, which is part of the gag gene. For patients with known risk factors, 90.9% of injection drug users had C/CRF07_BC/CRF08_BC viruses, whereas 85.4% of CRF01_AE infections were acquired through sexual transmission. No distinct segregation of CRF01_AE viruses was found among the Dai ethnic group. Geographically, C/CRF07_BC/CRF08_BC was found throughout the province, while CRF01_AE was largely confined to the prefectures bordering Myanmar. Furthermore, C/CRF07_BC/CRF08_BC viruses were found to consist of a group of viruses, including C, CRF08_BC, CRF07_BC, and new BC recombinants, based on the characterization of their reverse transcriptase genes. CONCLUSIONS: This is the first report of a province-wide HIV-1 molecular epidemiological study in Yunnan. While C/CRF07_BC/CRF08_BC and CRF01_AE are codominant, the discovery of many sexually transmitted CRF01_AE cases is new and suggests that this subtype may lead to a new epidemic in the general Chinese population. We discuss implications of our results for understanding the evolution of the HIV-1 pandemic and for vaccine development.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Lentivirus-mediated silencing of Tiam1 gene influences multiple functions of a human colorectal cancer cell line.

T lymphoma invasion and metastasis 1 (Tiam1) is a metastasis-related gene of T lymphoma that is also involved in the metastasis of a variety of other cancers. In this study, we tested the hypothesis that Tiam1 is a determinant of proliferation and metastasis in colorectal cancer, and we examined the effect of the inhibition of Tiam1 expression on proliferation and metastasis. We succeeded in establishing the Tiam1 knockdown colorectal cancer cell line using human immunodeficiency virus lentivirus-mediated RNA interference (RNAi) and found that the silencing of Tiam1 resulted in the effective inhibition of in vitro cell growth and of the invasive ability of colorectal cancer cells. Using an orthotopic xenograft model in nude mice, we confirmed that Tiam1 silencing could reduce tumor growth by subcutaneous injection and could suppress lung and liver metastases of colorectal cancer cells. Our results suggest that Tiam1 truly plays a causal role in the metastasis of colorectal cancer and that RNAi-mediated silencing of Tiam1 may provide an opportunity to develop a new treatment strategy for colorectal cancer.

Animals↗
PubMed2006

Increased expression of heat shock protein 72 protects renal proximal tubular cells from gentamicin-induced injury.

The nephrotoxicity of gentamicin (GM) has been widely recognized. Heat shock protein 72 (HSP72) has been reported to be a cytoprotectant. However, its cytoprotective effect against GM induced kidney injury has not yet been studied. In this study, we investigated the cytoprotective effect of HSP72 on GM-induced nephrotoxicity in vitro. Human Kidney tubular cell line, HK-2 cells were divided into four groups: control group, GM group (cells incubated with GM only), heat shock (HS) group (cells incubated at 43 degrees C for 30 min), and GM plus HS group, respectively. Lactate dehydrogenase (LDH) release increased time-dependently from 24 hr to 96 hr compared to the data of cells treated with GM only. Results of NAG activities, superoxide dismutase (SOD) activities and malondialdehyde (MDA) content were similar to that of the LDH release. The amount of HSP72 positive cells increased significantly at 72 hr after cells were treated with GM only. Both HSP72 protein and gene expression increased significantly at 72 hr when cells were treated with GM. On the other hand, HS induced HSP72 expression markedly. Pretreatment of HS inhibited HK-2 cells from GM-induced injury. It could reduce LDH release and NAG activity. HS also increased SOD activity, and decreased MDA content when cells were damaged by GM. These findings suggested that HS may protect kidney cells from GM-induced injury. Pre-induction of HSP72 may provide therapeutic strategies for nephrotoxicity induced by GM.

Cells, Cultured↗
PubMed2006

[On the role of liver-enriched transcription factors in regulating HBV transcription and replication].

OBJECTIVE: To investigate the effects of various liver-enriched transcription factors in regulating HBV transcription and replication, and to explore their potential roles in HBV hepatotropism. METHODS: The replication-competent HBV recombinant plasmid pHBV4.1 plus different liver-enriched transcription factor (HNF1, HNF3, HNF4, HNF6, C/EBP and RXRa/PPARa) expression plasmids were co-transfected into nonhepatic cell lines (NIH3T3, HeLa, 293T, SW1353, CV-1 and COS1). The transcription levels of 3.5 kb, 2.4/2.1 kb and 0.7 kb HBV RNA were analyzed by Northern blot hybridization, and the level of HBV DNA replication intermediates was detected by Southern blot hybridization analysis. RESULTS: In the absence of co-transfected liver enriched transcription factor expression vectors, the 3.5 kb HBV RNA is not transcribed and HBV DNA replication is not detected after transfecting of NIH 3T3 cells with pHBV4.1. Expression of the liver-enriched transcription factor HNF4 or RXRalpha/PPARalpha, stimulates the transcription of 3.5 kb HBV RNA and the replication of HBV DNA. In contrast, expression of HNF1, HNF3, HNF6 and C/EBP does not stimulate the transcription of 3.5 kb HBV RNA and therefore does not activate viral replication. HNF4 and RXRalpha/PPARalpha were also shown to activate the transcription of 3.5 kb HBV RNA and viral replication in divers cell types including HeLa, 293T, SW1353, CV-1 and COS1 cells. Mutation of the proximal nucleocapsid HNF4 binding site results in a greatly decreased level of HNF4 or RXRalpha/PPARalpha dependent HBV replication. CONCLUSION: This study demonstrated that the liver-enriched transcription factors HNF4 and RXRa/PPARa can support HBV transcription and replication in nonhepatic cells, indicating that liver-specific gene transcription is one of the determinants of HBV hepatotropism.

Animals↗
PubMed2006

[Construction of phage-displayed library by DNA shuffling and the screening of potent hirudin variants].

AIM: To directed promote the antithrombotic activity of hirudin in vitro with DNA family shuffling method. METHODS: PCR products of HV1, HV2 and HV3 genes of hirudin were combined and digested by DNase I. Then random fragments about 50 bp were purified and reassembled to the same size of hirudin gene by two amplifications of PCR with or without primers. The shuffled hirudin genes were inserted into phagemid pCANTAB5E vector and the hirudin mutants were displayed on the surface of bacteriophage M13. Mutants with increased specific activity of antithrombin were screened by affinity panning with decreased amounts of thrombin. RESULTS: After shuffling and selection, a clone (HV2-N47K) with high antithrombotic activity was obtained. CONCLUSION: Hirudin variants with improved properties could be hopefully aquired by DNA family shuffling and affinity panning.

Animals↗
PubMed2006

[Generation and preliminary application of rabbit anti-human polyclonal antibodies against NH2-terminal peptides of CXCR3-B].

AIM: To generate and identify the rabbit polyclonal antibodies against NH(2)-terminal peptides of CXCR3-B. METHODS: Three peptides (aa. 1 to 19, aa. 17 to 35, and aa. 33 to 51) of human CXCR3-B NH(2)-terminus were synthesized by using standard Fmoc. The synthesized peptides were purified by reversed phase high-performance liquid chromatography (RP-HPLC), and cross-linked with keyhole limpet hemocyanin (KLH) by sodium metaperiodate. Rabbits were immunized with conjugated peptides for 3 times (400 microg/rabbit). The polyclonal antibodies were purified by Protein G from the collected antiserum. RESULTS: NH(2)-terminal peptides of human CXCR3-B with the purity of 98%, 88.54%, and 80%, respectively, were prepared. The titers of purified polyclonal antibodies were 1:32,000 (0.1 mg/L), 1:4,000 (3 mg/L), and 1:1,000 (10 mg/L), respectively. Western blot results showed that the antibodies could recognize the protein with molecular weight of 50,000 in the total lysates of human fetal heart, whereas the antibodies against the peptides of No.1-19 amino acids could also recognize an additional protein (40,000). The antigens recognized by the antibodies were localized in the vascular endothelial cells of human fetal heart tissues. CONCLUSION: The polyclonal antibodies against NH(2)-terminal peptides generated and identified in the present work are specific to CXCR3-B protein and therefore can be useful tools for the functional study of human CXCR3-B.

Animals↗
PubMed2006

[Cytotoxicity of pentoxifylline and its effect on human hepatoma cell line Hep3b radiosensitivity].

OBJECTIVE: To investigate the effects of pentoxifylline (PTX) on radiation induced-cell cycle redistribution and radiosensitivity of human hepatocellular carcinoma cell line Hep3b. METHODS: MTT assay was performed to evaluate the cytotoxicity of PTX on p53-defective human hepatocellular carcinoma cell line Hep3b and clonogenic assay employed to observe its effects on the radiosensitivity of the cells quantified by calculating the sensitive enhancement ratio (SER). Flow cytometry was performed to observe the cell cycle changes of Hep3b cells in response to X-ray irradiation and the interventional effect of PTX. RESULTS: The cytotoxicity of PTX on the cells increased in a dose-dependent manner following a 48-hour treatment, with the optimal dose range of 1-5 mmol/L. A sub-toxic dose of PTX at 2 mmol/L was then used in subsequent experiments. Clonogenic survival assays up to 12 Gy demonstrated that p53-defective Hep3b cells (SER of 2.68+/-0.24) were sensitized by PTX (2 mmol/L). PTX (2 mmol/L) treatment following exposure to irradiation (6 Gy) resulted in abrogation of radiation-induced G(2)/M arrest of Hep3b cells, and the proportions of Hep3b cells in G(2)/M phase were 86.8% and 14.8% after exposure to 6 Gy alone and 6 Gy plus 2 mmol/L PTX, respectively. CONCLUSION: Radiosensitization by PTX is possibly associated with the abrogation of G(2)/M arrest in Hep3b cells following radiation exposure, suggesting that potential clinical application of PTX may enhance the efficacy of radiotherapy against hepatocellular carcinoma.

Carcinoma, Hepatocellular↗
PubMed2006

[Study on seed dormancy mechanisms of Changium smyrnioides and its geminating conditions].

OBJECTIVE: To study the seed dormancy mechanisms and the optimal seed germinating conditions, so as to provide basis for the seed testing of Changium smyrnioides. METHOD: Put the seeds into wettish sand under temperature of 25, 20, 15, 10, 5 degrees C, observe the shape changing of embryo and measure its length every other 10 days. Carry on experiments of seed germination under temperature of 25,20, 15, 10, 5 degrees C on the paper bed and sand bed, determine the time of germination starting, time of germination lasting, germination rate and germination energy. RESULT: Embryo grew the most quickly under 15 degrees C. The seed germination was largely prohibited when the temperature is higher than 20 degrees C. The mildew rate was very high under 25, 20, 15, 10 degrees C. Put the seeds under 5 degrees C for 45 days could quickly break off its dormancy, and its mildew rate was lower. The seeds germinate fastest under the condition of 15-10 degrees C on the paper bed, and its germination rate was the highest. CONCLUSION: The morphological post-maturation seems the major dormancy mechanism of C. smyrnioides. Temperature is a major factor that affect seed germination of C. smymioides. The best pretreatment method is to put the seeds into 5 degrees C of wettish sand for 45 days. The best germination bed is the paper bed, and the best germination temperature is 15-10 degrees C.

Apiaceae↗