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Biomedical subjects

Li Zheng

Publications and source records attributed to Li Zheng.

At least 37 records · Page 2Linked to original sources
PubMed2005

Experimental tooth movement upregulates preproenkephalin mRNA in the rat trigeminal nucleus caudalis and oralis.

Levels of preproenkephalin mRNA expression in trigeminal subnucleus complex by noxious tooth movement stimuli were examined using in situ hybridization. At 24 h, preproenkephalin mRNA expression was significantly upregulated in the ipsilateral trigeminal subnucleus caudalis (P<0.05), and in the subnucleus oralis (P<0.05). These findings suggested that enkephalinergic inhibitory systems could be activated during tooth movement, and that subnucleus oralis may be involved in modulation of the nociception, as well as the subnucleus caudalis.

Afferent Pathways↗
PubMed2005

Human 3-methyladenine-DNA glycosylase: effect of sequence context on excision, association with PCNA, and stimulation by AP endonuclease.

Human 3-methyladenine-DNA glycosylase (MPG protein) is involved in the base excision repair (BER) pathway responsible mainly for the repair of small DNA base modifications. It initiates BER by recognizing DNA adducts and cleaving the glycosylic bond leaving an abasic site. Here, we explore several of the factors that could influence excision of adducts recognized by MPG, including sequence context, effect of APE1, and interaction with other proteins. To investigate sequence context, we used 13 different 25 bp oligodeoxyribonucleotides containing a unique hypoxanthine residue (Hx) and show that the steady-state specificity of Hx excision by MPG varied by 17-fold. If APE1 protein is used in the reaction for Hx removal by MPG, the steady-state kinetic parameters increase by between fivefold and 27-fold, depending on the oligodeoxyribonucleotide. Since MPG has a role in removing adducts such as 3-methyladenine that block DNA synthesis and there is a potential sequence for proliferating cell nuclear antigen (PCNA) interaction, we hypothesized that MPG protein could interact with PCNA, a protein involved in repair and replication. We demonstrate that PCNA associates with MPG using immunoprecipitation with either purified proteins or whole cell extracts. Moreover, PCNA binds to both APE1 and MPG at different sites, and loading PCNA onto a nicked, closed circular substrate with a unique Hx residue enhances MPG catalyzed excision. These data are consistent with an interaction that facilitates repair by MPG or APE1 by association with PCNA. Thus, PCNA could have a role in short-patch BER as well as in long-patch BER. Overall, the data reported here show how multiple factors contribute to the activity of MPG in cells.

Base Pairing↗
PubMed2005

Multiple but dissectible functions of FEN-1 nucleases in nucleic acid processing, genome stability and diseases.

Flap EndoNuclease-1 (FEN-1) is a multifunctional and structure-specific nuclease involved in nucleic acid processing pathways. It plays a critical role in maintaining human genome stability through RNA primer removal, long-patch base excision repair and resolution of dinucleotide and trinucleotide repeat secondary structures. In addition to its flap endonuclease (FEN) and nick exonuclease (EXO) activities, a new gap endonuclease (GEN) activity has been characterized. This activity may be important in apoptotic DNA fragmentation and in resolving stalled DNA replication forks. The multiple functions of FEN-1 are regulated via several means, including formation of complexes with different protein partners, nuclear localization in response to cell cycle or DNA damage and post-translational modifications. Its functional deficiency is predicted to cause genetic diseases, including Huntington's disease, myotonic dystrophy and cancers. This review summarizes the knowledge gained through efforts in the past decade to define its structural elements for specific activities and possible pathological consequences of altered functions of this multirole player.

Amino Acid Motifs↗
PubMed2005

Organization and developmental expression of an amphibian vascular smooth muscle alpha-actin gene.

A gene encoding a putative homologue of the avian and mammalian vascular smooth muscle alpha-actin was isolated from an amphibian, Rana catesbeiana, and characterized in terms of its sequence, organization, and expression pattern. To assess the expression of this gene during amphibian embryonic development, a cDNA encoding the Xenopus homologue of this mRNA was isolated and characterized by in situ hybridization. The expression of this gene was not detected in the enteric smooth muscle cells or, unlike its avian and mammalian homologues, in the somites/skeletal muscle of the Xenopus embryos/tadpoles. Its initial expression coincides with the onset of cardiac muscle differentiation and is coincidental with the expression of the cardiac alpha-actin mRNAs in the heart-forming region of the stage 26/27 embryo. As development proceeds, transcripts from this gene are expressed throughout the developing heart until the formation of the heart chambers is completed and, thereafter, its expression becomes restricted to the outflow tract of the tadpole heart. The subsequent restricted expression of this gene to the vascular system in both of these amphibians identifies it as the amphibian homologue of the avian and mammalian vascular smooth muscle alpha-actin.

Actins↗
PubMed2005

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) from a large shallow, eutrophic lake of the subtropical China.

Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) were studied monthly in a large shallow, eutrophic lake of the subtropical China during June-November, 2003. Microcystins (MCs) were quantitatively determined by High-Performance Liquid Chromatography (HPLC) with a qualitative analysis by a Finnigan LC-MS system. On the average of the study period, hepatopancreas was the highest in MC contents (mean 4.14 and range 1.06-7.42 microg g(-1)DW), followed by digestive tracts (mean 1.69 and range 0.8-4.54 microg g(-1)DW) and gonad (mean 0.715 and range 0-2.62 microg g(-1)DW), whereas foot was the least (mean 0.01 and range 0-0.06 microg g(-1)DW). There was a positive correlation in MC contents between digestive tracts and hepatopancreas. A constantly higher MC content in hepatopancreas than in digestive tracts indicates a substantial bioaccumulation of MCs in the hepatopancreas of the snail. The average ratio of MC-LR/MC-RR showed a steady increase from digestive tracts (0.44) to hepatopancreas (0.63) and to gonad (0.96), suggesting that MC-LR was more resistant to degradation in the snail. Since most MCs were present in the hepatopancreas, digestive tracts and gonad with only a very small amount in the edible foot, the risk to human health may not be significant if these toxic parts are removed prior to snail consumption. However, the possible transference of toxins along food chains should not be a negligible concern.

Animals↗
PubMed2005

Comparative analysis of 87,000 expressed sequence tags from the fumonisin-producing fungus Fusarium verticillioides.

Fusarium verticillioides (teleomorph Gibberella moniliformis) is a pathogen of maize worldwide and produces fumonisins, a family of mycotoxins that have been associated with several animal diseases as well as cancer in humans. In this study, we sought to identify fungal genes that affect fumonisin production and/or the plant-fungal interaction. We generated over 87,000 expressed sequence tags from nine different cDNA libraries that correspond to 11,119 unique sequences and are estimated to represent 80% of the genomic complement of genes. A comparative analysis of the libraries showed that all 15 genes in the fumonisin gene cluster were differentially expressed. In addition, nine candidate fumonisin regulatory genes and a number of genes that may play a role in plant-fungal interaction were identified. Analysis of over 700 FUM gene transcripts from five different libraries provided evidence for transcripts with unspliced introns and spliced introns with alternative 3' splice sites. The abundance of the alternative splice forms and the frequency with which they were found for genes involved in the biosynthesis of a single family of metabolites as well as their differential expression suggest they may have a biological function. Finally, analysis of an EST that aligns to genomic sequence between FUM12 and FUM13 provided evidence for a previously unidentified gene (FUM20) in the FUM gene cluster.

Amino Acid Sequence↗
PubMed2005

Pharmacodynamics and pharmacokinetics of the insulin-mimetic agent vanadyl acetylacetonate in non-diabetic and diabetic rats.

The objectives of this study were to evaluate the pharmacodynamics and pharmacokinetics of vanadyl acetylacetonate (VAC) in rats. Pharmacodynamic study was carried out using non-diabetic and diabetic rats by subcutaneous (s.c.) and intragastric (i.g.) administrations at single dose or multiple doses. Pharmacokinetic study was performed using non-diabetic rats. Results showed that VAC resulted in a significant decrease of plasma glucose levels in diabetic rats in all dosing levels, and nearly restored hyperglycemic values to normal values after s.c. injection at a single dose of 2, 4, and 8 mg vanadium (V)/kg, or after i.g. administration at multiple doses of 3 and 6 mg V/kg once daily for seven consecutive days, respectively. The VAC could be rapidly absorbed and T(max) values ranged from 0.9 +/- 0.3 h for s.c. injection to 3.0 +/- 0.9 h for i.g. administration. The average absolute bioavailabilities for i.g. administrations at a single dose of 3, 6, and 10 mg V/kg were 34.7%, 28.1%, and 22.8%, respectively. After i.g. administration at a single dose of 10 mg V/kg, the average elimination half-lives obtained from non-diabetic rats were very long ranging from 144.7 +/- 8.7 h in plasma to 657.3 +/- 34.8 h in femur tissue. In conclusion, VAC widely distributed in various tissues and accumulated more in the femur tissue. The time to reach maximal vanadium level after s.c. injection or i.g. administration was not coincident with the time to reach maximal hypoglycemic effect. The accumulated vanadium in bone, kidney or other tissues may gradually release and exert a longer action. In present dosing levels and administration routes, VAC was effective for lowering plasma glucose levels in diabetic rats and could reverse the higher triglyceride and cholesterol levels to the normal ranges. VAC did not influence the insulin levels in plasma and not cause obvious toxic signs like diarrhea.

Animals↗
PubMed2005

Novel function of the flap endonuclease 1 complex in processing stalled DNA replication forks.

Restarting stalled replication forks partly depends on the break-induced recombination pathway, in which a DNA double-stranded break (DSB) is created on the stalled replication fork to initiate the downstream recombination cascades. Single-stranded DNA gaps accumulating on stalled replication forks are potential targets for endonucleases to generate DSBs. However, it is unclear how this process is executed and which nucleases are involved in eukaryotic cells. Here, we identify a novel gap endonuclease (GEN) activity of human flap endonuclease 1 (FEN-1), critical in resolving stalled replication fork. In response to replication arrest, FEN-1 interacts specifically with Werner syndrome protein for efficient fork cleavage. Replication protein A facilitates FEN-1 interaction with DNA bubble structures. Human FEN-1, but not the GEN-deficient mutant, E178A, was shown to rescue the defect in resistance to UV and camptothecin in a yeast FEN-1 null mutant.

Cell Extracts↗
PubMed2005

Bone morphogenetic protein 3 expression pattern in rat condylar cartilage, femoral cartilage and mandibular fracture callus.

Mandibular condylar cartilage differs from primary cartilage in morphological organization of the chondrocytes and in responses to biomechanical stress and humoral factors. For the first time, we describe the expression of Bmp3 mRNA in relation to types I, II and X collagen mRNA (as determined by in situ hybridization) in chondrocytes of the rat mandibular condylar cartilage, femoral articular cartilage, femoral growth plate cartilage, and temporal cartilage, which transiently appeared in the reparative response stage of mandibular ramus fracture healing. In all cartilages evaluated, Bmp3 was expressed in proliferating chondrocytes that expressed type I collagen in condylar cartilage, articular cartilage, and temporal cartilage appearing during fracture healing. Bmp3 was also found in hypertrophic chondrocytes that expressed type X collagen mRNA in all cartilages evaluated. Furthermore, in remodeling bone, Bmp3 mRNA was strongly expressed in active osteoblast cells in periosteal reaction layers formed after fracture. These findings suggest that Bmp3 expression in a special layer of typical articular cartilage may be regulated by mechanical stress stimulation. We also found that Bmp3 was expressed in the periosteal layers of the bone segments near the fracture site during fracture healing.

Animals↗
PubMed2005

Global regulation of gene expression by ArlRS, a two-component signal transduction regulatory system of Staphylococcus aureus.

Staphylococcus aureus expresses various cell wall-associated and extracellular virulence factors, coordinately controlled by different two-component signal transduction systems and transcriptional regulators. In this study, we used microarray technology to identify the genes regulated by ArlR. The microarray data indicate that ArlR functions as a positive regulator and also as a negative repressor to directly and/or indirectly mediate the expression of at least 114 genes involved in different functions, including autolysis, cell division, growth, and pathogenesis.

Bacterial Proteins↗
PubMed2005

Identification of a novel essential two-component signal transduction system, YhcSR, in Staphylococcus aureus.

Two-component signal transduction systems play an important role in the ability of bacteria to adapt to various environments by sensing changes in their habitat and by altering gene expression. In this study, we report a novel two-component system, YhcSR, in Staphylococcus aureus which is required for bacterial growth in vitro. We found that the down-regulation of yhcSR expression by induced yhcS antisense RNA can inhibit and terminate bacterial growth. Moreover, without complementary yhcS or yhcR, no viable yhcS or yhcR gene replacement mutant was recoverable. Collectively, these results demonstrated that the YhcSR regulatory system is indispensable for S. aureus growth in culture. Moreover, induced yhcS antisense RNA selectively increased bacterial susceptibility to phosphomycin. These data suggest that YhcSR probably modulates the expression of genes critical for bacterial survival and may be a potential target for the development of novel antibacterial agents.

Anti-Bacterial Agents↗
PubMed2005

[Effects of culture condition on fatty acids in Pseudcarbomonas sp].

The investigation on the growth of Pseudomonas sp. and the dynamics of its fatty acids under various culture conditions indicated that the optimum temperature for its growth was 30 degrees C, and the best carbon source was starch. 13 kinds of fatty acids were detected, among which, c16:1(n-7), c15:0, c16:0, c17:0, c18:1(n-6), c18:1 (n-9), 9, 10-cp-c17:0 and iso9, 10-cp-c17:0 were the major ones. When cultured at 30 degrees C, the relative content of unsaturated fatty acids decreased significantly. Carbon source in the media was the crucial factor affecting the contents of odd- and cyclopropane fatty acids. Cluster analysis revealed that temperature had a more obvious effect than carbon source.

Cell Membrane↗
PubMed2004

Enriched accumulation and biotransformation of selenium in the edible seaweed Laminaria japonica.

Accumulations of selenium in kelp Laminaria japonica cultured in seawater was achieved by adding selenite (Na2SeO3) with or without N-P (NaNO3 + NaH2PO4) nutrients at different concentrations. Biotransformation of selenium in the kelp was investigated through measuring the selenium of biological samples and different biochemical fractionations. The results showed that the optimal selenite-enrichment concentration is 200 mg L(-1), which can allow the kelp to accumulate a total selenium content from 0.51 +/- 0.15 to 26.23 +/- 3.12 microg g(-1) of fresh weight (fw). Selenium composition analysis of kelp (control group) showed that selenium is present as organic selenium, which is up to 86.22% of the total selenium, whereas inorganic selenium is barely 4.85%. When L. japonica was exposed for 56 h in seawater containing 200 mg L(-1) Na2SeO3, the organic selenium was 16.70 microg g(-1) of fw (68.23%) and inorganic selenium was 4.71 microg g(-1) of fw (19.26%). The capability of accumulation of selenium was further enhanced by adding N-P nutrients to the selenite-enriched medium. Total selenium is increased to be 33.65 microg g(-1) of fw at optimal concentration of N-P nutrient (150 mg L(-1) NaNO3 and 25 mg L(-1) NaH2PO4), whereas the inorganic selenium was not increased and remained at 4.597 microg g(-1) of fw (13.36%), and the increased part of selenium was organic selenium. This implied that kelp L. japonica could effectively transform inorganic selenium into organic selenium through metabolism.

Laminaria↗
PubMed2004

Co-administration of a DNA vaccine encoding the prostate specific membrane antigen and CpG oligodeoxynucleotides suppresses tumor growth.

BACKGROUND: Prostate-specific membrane antigen (PSMA) is a well characterized prostate-specific tumor associated antigen. Its expression is elevated in prostate carcinoma, particularly in metastatic and recurrent lesions. These observations suggest that PSMA can be used as immune target to induce tumor cell-specific recognition by the host and, consequently tumor rejection. We utilized a DNA-based vaccine to specifically enhance PSMA expression. An immune modulator, such as CpG oligodeoxynucleotides which promote Th1-type immune responses was combined to increase the efficacy of tumor recognition and elimination. METHODS: A eukaryotic expression plasmid pCDNA3.1-PSMA encoding full-length PSMA was constructed. C57BL/6 mice were immunized with endotoxin-free pCDNA3.1-PSMA alone or in combination with CpG oligodeoxynucleotides by intramuscular injection. After 4 immunizations, PSMA specific antibodies and cytotoxic T lymphocyte reactivity were measured. Immunized C57BL/6 mice were also challenged subcutaneously with B16 cells transfected with PSMA to evaluate suppression of tumor growth. RESULTS: Vaccine-specific cytotoxic T lymphocytes reactive with B16 cells expressing PSMA could be induced with this treatment schedule. Immune protection was observed in vaccinated mice as indicated by increased tumor growth in the control group (100%) compared with the groups vaccinated with DNA alone (66.7%) or DNA plus CpG oligodeoxynucleotides (50%) respectively. Average tumor volume was smaller in vaccinated groups and tumor-free survival time was prolonged by the vaccination. CONCLUSION: The current findings suggest that specific anti-tumor immune response can be induced by DNA vaccines expressing PSMA. In addition, the suppression of in vivo growth of tumor cells expressing PSMA was augmented by CpG oligodeoxynucleotides. This strategy may provide a new venue for the treatment of carcinoma of prostate after failure of standard therapy.

Journal Article↗
PubMed2004

Evidence for and characterization of Ca2+ binding to the catalytic region of Arabidopsis thaliana phospholipase Dbeta.

Most types of plant phospholipase D (PLD) require Ca(2+) for activity, but how Ca(2+) affects PLD activity is not well understood. We reported previously that Ca(2+) binds to the regulatory C2 domain that occurs in the N terminus of the Ca(2+)-requiring PLDs. Using Arabidopsis thaliana PLDbeta and C2-deleted PLDbeta (PLDbetacat), we now show that Ca(2+) also interacts with the catalytic regions of PLD. PLDbetacat exhibited Ca(2+)-dependent activity, was much less active, and required a higher level of Ca(2+) than the full-length PLDbeta. Ca(2+) binding of the proteins was stimulated by phospholipids; phosphatidylserine was the most effective among those tested. Scatchard plot analysis of Ca(2+) binding data yielded an estimate of 3.6 high affinity (K(d) = 29 mum) binding sites on PLDbeta. The Ca(2+)-PLDbetacat interaction increased the affinity of the protein for the activator, phosphatidylinositol 4,5-bisphosphate, but not for the substrate, phosphatidylcholine. This is in contrast to the effect of Ca(2+) binding to the C2 domain, which stimulates phosphatidylcholine binding but inhibits phosphatidylinositol 4,5-bisphosphate binding of the domain. These results demonstrate the contrasting and complementary effects of the Ca(2+)- and lipid-binding properties of the C2 and catalytic domains of plant PLD and provide insight into the mechanism by which Ca(2+) regulates PLD activity.

Arabidopsis↗
PubMed2004

Human papillomavirus 16 E6 oncoprotein interferences with insulin signaling pathway by binding to tuberin.

Tuberous sclerosis complex (TSC) is a genetic disorder caused by mutations in either TSC1 or TSC2 tumor suppressor gene. TSC1 and TSC2 products, Harmatin and Tuberin, form the functional complex to serve as the negative regulator for insulin-induced phosphorylation of S6 kinase and elF4E-binding protein 1. High-risk human papillomavirus (HPV) infection is the necessary cause for cervical cancer. E6 oncoprotein encoded by HPV plays a pivotal role in carcinogenesis by interference with the host intracellular protein functions. In this study, we show that HPV16 E6 interacts with tumor suppressor gene TSC2 product, Tuberin, and results in the phosphorylation of S6 kinase and S6 even in the absence of insulin. The overexpression of Tuberin overcomes the effect of E6 on S6 kinase phosphorylation. Binding with HPV16 E6 causes the proteasome-mediated degradation of Tuberin. A DILG motif and an ELVG motif located in the carboxyl-terminal of Tuberin are required for E6 binding. In addition, the Tuberin interaction region in E6 has been mapped in the amino-terminal portion of HPV16 E6, which is different from the binding domain with p53. These results provide a possible link between E6-induced oncogenesis and the insulin-stimulated cell proliferation signaling pathway.

Animals↗
PubMed2004

[Transmission-blocking vaccine candidate of Plasmodium vivax Pvs25 is highly conservative among Chinese isolates].

OBJECTIVE: To investigate the genetic diversity of Plasmodium vivax transmission-blocking vaccine candidate antigen (TBV) Pvs25, with P. vivax isolates from Hubei and Zhejiang Provinces, and to compare the genetic polymorphism of Pvs25 with that from Bangladesh. METHODS: The parasite DNA used for the genetic polymorphism assay was obtained from dried filter paper blood spots. The genes were PCR amplified and the products were purified and sequenced directly. RESULTS: 45 complete new sequences were analyzed. Only 3 nucleotide changes were found that would result in amino acid substitutions in Pvs25 in comparison with the sequence from P. vivax Sal-I strain. The measurement of nucleotide diversity (pi) was remarkably similar for the two populations, indicating that DNA sequences and deduced amino acid sequences were highly homologous among the geographically dispersed isolates or isolates from the same geographical region. CONCLUSION: The results suggest that Pvs25 has limited antigenic polymorphism, especially compared with candidate antigens expressed by hepatic and erythrocytic stage, which may support the development and application of Pvs25-based transmission-blocking vaccine in China.

Amino Acid Sequence↗