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W J Liu

Publications and source records attributed to W J Liu.

At least 19 recordsLinked to original sources
PubMed2006

Arsenic sequestration in iron plaque, its accumulation and speciation in mature rice plants (Oryza sativa L.).

A compartmented soil-glass bead culture system was used to investigate characteristics of iron plaque and arsenic accumulation and speciation in mature rice plants with different capacities of forming iron plaque on their roots. X-ray absorption near-edge structure spectra and extended X-ray absorption fine structure were utilized to identify the mineralogical characteristics of iron plaque and arsenic sequestration in plaque on the rice roots. Iron plaque was dominated by (oxyhydr)oxides, which were composed of ferrihydrite (81-100%), with a minor amount of goethite (19%) fitted in one of the samples. Sequential extraction and XANES data showed that arsenic in iron plaque was sequestered mainly with amorphous and crystalline iron (oxyhydr)oxides, and that arsenate was the predominant species. There was significant variation in iron plaque formation between genotypes, and the distribution of arsenic in different components of mature rice plants followed the following order: iron plaque > root > straw > husk > grain for all genotypes. Arsenic accumulation in grain differed significantly among genotypes. Inorganic arsenic and dimethylarsinic acid (DMA) were the main arsenic species in rice grain for six genotypes, and there were large genotypic differences in levels of DMA and inorganic arsenic in grain.

Absorptiometry, Photon↗
PubMed2004

Medication compliance among renal transplant patients: a Hospital Kuala Lumpur experience.

This survey aims to identify prevalence, reasons and predictors of noncompliance among renal transplant patients followed up in Hospital Kuala Lumpur (HKL). All adult renal transplant patients who were at least 6 months post transplant were recruited from 10/2001 till 5/2002. Patients who consented were interviewed by a medical doctor or research assistant based on questionnaire. Noncompliers were defined as those who missed or self adjusted any dose of immunosuppressant within the preceding 4 weeks. Inter-rater agreement was assessed prior by Kappa (K) scores and they were acceptable. Out of 304 patients, 246 patients volunteered; of whom 144 (58.5%) were males. Twenty-one (9.3%) were noncompliers. Reasons for noncompliance included forgetfulness (n=8), financial constraints (n=1), fear of rejection (n=1), side effects (n=9), decision not to take (n=6), difficulty in breaking medication into correct dosages (n=1). Significant predictors of noncompliance were longer duration of transplant noncompliance to other drugs, regular use of nonprescription drugs; the lack of symptoms of fat facial cheeks and infection. Surveillance for noncompliance should not be relaxed as its predictors are diverse and persistent, especially in those who are at high risks.

Adult↗
PubMed2003

Effects of icariin on cGMP-specific PDE5 and cAMP-specific PDE4 activities.

AIM: To clarify the mechanism of the therapeutic action of icariin on erectile dysfunction (ED). METHODS: PDE5 was isolated from the human platelet and PDE4 from the rat liver tissue using the FPLC system (Pharmacia, Milton Keynes, UK) and the Mono Q column. The inhibitory effects of icariin on PDE5 and PDE4 activities were investigated by the two-step radioisotope procedure with [(3)H]-cGMP/[(3)H]-cAMP. Papaverine served as the control drug. RESULTS: Icariin and papaverine showed dose-dependent inhibitory effects on PDE5 and PDE4 activities. The IC(50) of Icariin and papaverine on PDE5 were 0.432 micromol/L and 0.680 micromol/L, respectively and those on PDE4, 73.50 micromol/L and 3.07 micromol/L, respectively. The potencies of selectivity of icariin and papaverine on PDE5 (PDE4/PDE5 of IC(50)) were 167.67 times and 4.54 times, respectively. CONCLUSION: Icariin is a cGMP-specific PDE5 inhibitor that may be developed into an oral effective agent for the treatment of ED.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2001

Polynucleotide viral vaccines: codon optimisation and ubiquitin conjugation enhances prophylactic and therapeutic efficacy.

Papillomavirus infection is a major antecedent of anogenital malignancy. We have previously established that the L1 and L2 capsid genes of papillomavirus have suboptimal codon usage for expression in mammalian cells. We now show that the lack of immunogenicity of polynucleotide vaccines based on the L1 gene can be overcome with codon modified L1, which induces strong immune responses, including conformational virus neutralising antibody and delayed type hypersensitivity. Conjugation of a ubiquitin gene to a hybrid gene incorporating L1 and the E7 non-structural papillomavirus protein improved E7 specific CTL responses, and induced protection against an E7 expressing tumour, but induced little neutralising antibody. However, a mixture of ubiquitin conjugated and non-ubiquitin conjugated polynucleotides induced virus neutralising antibody and E7 specific CD8 T cells. An optimal combined prophylactic/therapeutic viral vaccine might therefore comprise ubiquitin conjugated and non-ubiquitinated genes, to induce prophylactic neutralising antibody and therapeutic cell mediated immune responses.

Animals↗
PubMed2001

Cloning, characterization, and phylogenetic analysis of a shrimp white spot syndrome virus gene that encodes a protein kinase.

An open reading frame (ORF) that encodes a 715-amino-acid polypeptide was found in an 8421-bp EcoRI fragment of the shrimp white spot syndrome virus (WSSV) genome. The polypeptide shows significant homology to eukaryotic serine/threonine protein kinase (PK) and contains the major conserved subdomains for eukaryotic protein kinases. Coupled in vitro transcription and translation generated a protein having an apparent molecular mass of about 87 kDa according to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. For transcriptional analysis of the pk gene, total RNA was isolated from WSSV-infected shrimp at different times after infection. Northern blot analysis with pk-specific riboprobe found a major and a minor transcript of 2.7 and 5.7 kb, respectively. Rapid amplification of the 5' cDNA ends of the major 2.7-kb pk transcript showed that there were two transcriptional initiation sites located at nucleotide residues -38(G) and -39(G) relative to the ATG translational start codon. Temporal expression analysis by RT-PCR indicated that the transcription of the pk gene started 2 h after infection and continued for at least 60 h. Phylogenetic analysis showed that WSSV protein kinase does not have any close relatives and does not fall into any of the major protein kinase groups.

3' Untranslated Regions↗
PubMed2001

Association of bovine papillomavirus type 1 with microtubules.

Transport of BPV-1 virus from the cell membrane to the nucleus was studied in vitro in CV-1 cells. At reduced temperature (4 degrees C), BPV-1 binding to CV-1 cells was unaffected but there was no transport of virions across the cytosol. Electron microscopy showed BPV-1 virions in association with microtubules in the cytoplasm, a finding confirmed by co-immunoprecipitation of L1 protein and tubulin. Internalization of virus was unimpaired in cells treated with the microtubule-depolymerizing drug nocodazole but virions were retained in cytoplasmic vesicles and not transported to the nucleus. We conclude that a microtubule transport mechanism in CV-1 cells moves intact BPV-1 virions from the cell surface to the nuclear membrane.

Active Transport, Cell Nucleus↗
PubMed2001

Cloning and characterization of ELL-associated proteins EAP45 and EAP20. a role for yeast EAP-like proteins in regulation of gene expression by glucose.

RNA polymerase II elongation factor ELL was recently purified from rat liver as a component of a multiprotein complex containing ELL and three ELL-associated proteins (EAPs) of approximately 45 (EAP45), approximately 30 (EAP30), and approximately 20 (EAP20) kDa (Shilatifard, A. (1998) J. Biol. Chem. 273, 11212-11217). Cloning of cDNA encoding the EAP30 protein revealed that it shares significant sequence similarity with the product of the Saccharomyces cerevisiae SNF8 gene (Schmidt, A. E., Miller, T., Schmidt, S. L., Shiekhattar, R., and Shilatifard, A. (1999) J. Biol. Chem. 274, 21981-21985), which is required for efficient derepression of glucose-repressed genes. Here we report the cloning of cDNAs encoding the EAP45 and EAP20 proteins. In addition, we identify the S. cerevisiae VPS36 and YJR102c genes as potential orthologs of EAP45 and EAP20 and show that they are previously uncharacterized SNF genes with properties very similar to SNF8.

Amino Acid Sequence↗
PubMed2001

Efficiency of delivery of DNA to cells by bovine papillomavirus type-1 L1/L2 pseudovirions.

To investigate the efficiency of encapsidation of plasmid by papillomavirus virus-like particles (PV VLPs), and the infectivity of the resultant PV pseudovirions, Cos-1 cells were transfected with an 8-kb plasmid incorporating a green fluorescent protein (GFP) reporter gene (pGSV), and infected with bovine PV (BPV-1) L1/L2 recombinant vaccinia virus to produce BPV1 pseudovirions. Approximately 1 in 1.5 x 10(4) of dense (1.35 g/ml) PV pseudovirions and 0.3 in 10(4) of less-dense (1.29 g/ml) pseudovirions packaged an intact pGSV plasmid. The majority (>75%) of packaged plasmids contained deletions, and the deletions affected all tested genes. After exposure of Cos-1 cells to BPV-1 pseudovirions at an MOI of 40,000:1, 6% of cells expressed GFP, giving a calculated efficiency of delivery of the pGSV plasmid, by pseudovirions which had packaged an intact plasmid, of approximately 5%. Plasmid delivery was not effected by purified pGSV plasmid, was blocked by antiserum against BPV-1, and was not blocked by DNase treatment of pseudovirions, confirming that delivery was mediated by DNA within the pseudovirion. We conclude that a major limitation to the use of PV pseudovirions as a gene delivery system is that intact plasmid DNA is not efficiently selected for packaging by VLPs in cell-based pseudovirions production systems.

Animals↗
PubMed2001

Outcome of 235 renal transplant recipients followed up at ministry of health hospitals in the State of Johor.

Retrospective analysis was done on 235 recipients, 133 males and 102 females, who were transplanted between 25th September 1979 and 25th June 1999. 85.1% were Chinese, 7.7% were Indians and 7.2% Malays. 23% (54) were living related renal transplants (LRRT) all except 5 done at Hospital Kuala Lumpur. 60% (141) were living unrelated donor renal transplants (LURT) done in India. 17% (40) were cadaveric transplants (CADT) (all done in China except 2 at Hospital Kuala Lumpur and one in London). 97% (228) were first transplants. Primary renal disease was unknown in 69.4%, 17% (40) glomerulonephritis, 5.5% diabetic nephropathy and 8.1% 19 others. All were on prednisolone, 93.2% were on azathioprine and 96.6% were on cyclosporin A. The acute rejection rate was 23.4% (55 episodes). Patient survival was 88% at five years and patients alive with functioning graft was 84% at 5 years. LRRT had significantly better survival compared to LURT. 34 grafts were lost to chronic allograft nephropathy. 46 recipients died (33 died with functioning graft).

Adult↗
PubMed2001

[Molecular mechanisms involved in the regulation of telomerase activity].

The main components of telomerase include RNA subunit, hTERT catalytic subunit and hTEP1 regulatory protein. While telomerase plays an important role in maintenance of telomere structural stability, telomere is also involved in the regulation of telomerase activity. Some anticancer drugs inhibit the telomerase activity by breaking the structure of telomere. Activation of human telomerase requires de novo transcription of hTERT gene and correct incorporation of all subunits into holoenzyme. The expression of telomerase activity is likely to be regulated at multiple levels. Firstly, the expression and transcription of the hTERT gene is regulated by various factors; Secondly, various oncogenes and tumor suppressor genes are involved in regulation of telomerase activity by protein-protein interaction with telomere and telomerase proteins directly or indirectly. Thirdly, phosphorylation of hTERT and hTEP1 by protein kinase leads to significant up-regulation of telomerase activity, and conversely, the dephosphorylation result in down-regulation of telomerase activity.

Animals↗
PubMed2000

Papillomavirus virus-like particles for the delivery of multiple cytotoxic T cell epitopes.

Chimeric papillomavirus (PV) virus-like particles (VLPs) based on the bovine papillomavirus type 1 (BPV-1) L1 protein were constructed by replacing the 23-carboxyl-terminal amino acids of the BPV1 major protein L1 with an artificial "polytope" minigene, containing known CTL epitopes of human PV16 E7 protein, HIV IIIB gp120 P18, Nef, and reverse transcriptase (RT) proteins, and an HPV16 E7 linear B epitope. The CTL epitopes were restricted by three different MHC class I alleles (H-2(b), H-2(d), HLA-A*0201). The chimeric L1 protein assembled into VLPs when expressed in SF-9 cells by recombinant baculovirus. After immunization of mice with polytope VLPs in the absence of adjuvant, serum antibodies were detected which reacted with both polytope VLPs and wild-type BPV1L1 VLPs, in addition to the HPV16E7 linear B cell epitope. CTL precursors specific for the HPV16 E7, HIV P18, and RT CTL epitopes were also detected in the spleen of immunized mice. Polytope VLPs can thus deliver multiple B and T epitopes as immunogens to the MHC class I and class II pathways, extending the utility of VLPs as self-adjuvanting immunogen delivery systems.

Amino Acid Sequence↗
PubMed2000

BPV1 E2 protein enhances packaging of full-length plasmid DNA in BPV1 pseudovirions.

We studied determinants of efficient encapsidation of circular DNA, incorporating a PV early region DNA sequence (nt 584-1978) previously shown to enhance packaging of DNA within papillomavirus (PV)-like particles (VLPs). Insect coelomic cells (Sf-9) and cultured monkey kidney cells (Cos-1) were transfected with an 8-kb reporter plasmid incorporating the putative BPV packaging sequence and infected with BPV1 L1 and L2 recombinant baculovirus or vaccinia virus. Heavy (1.34 g/ml) and light (1.30 g/ml) VLPs were produced, and each packaged some of the input plasmid. In light VLPs, truncated plasmids, which nevertheless incorporated the PV-derived DNA packaging sequence, were more common than full-length plasmids. Packaging efficiency of the plasmid was estimated at 1 plasmid per 10(4) VLPs in both Cos-1 and Sf-9 cells. In each cell type, expression of the BPV1 early region protein E2 in trans doubled the quantity of heavy but not light VLPs and also increased the packaging efficiency of full-length circular plasmids by threefold in heavy VLPs. The resultant pseudovirions incorporated significant amounts of E2 protein. Pseudovirions, comprising plasmids packaged within heavy VLPs, mediated the delivery of packaged plasmid into Cos-1 cells, whereby "infectivity" was blocked by antisera to BPV1 L1, but not antisera to BPV1 E4. We conclude that (a) packaging of DNA within PV L1+L2 pseudovirions is enhanced by BPV1 E2 acting in trans, (b) E2 may be packaged with the pseudovirion, and (c) E2-mediated enhancement of packaging favors 8-kb plasmid incorporation over incorporation of shorter DNA sequences.

Animals↗
PubMed2000

Regulation of lymphocyte proliferation by uterine serpin: interleukin-2 mRNA production, CD25 expression and responsiveness to interleukin-2.

During pregnancy, the endometrium of the ewe secretes large amounts of a progesterone-induced protein of the serpin superfamily of serine proteinase inhibitors called ovine uterine serpin (OvUS). This protein inhibits lymphocyte proliferation in response to concanavalin A (ConA), phytohemagglutinin (PHA), or mixed lymphocyte reaction. The purpose of these experiments was to characterize the mechanism by which OvUS inhibits lymphocyte proliferation. Ovine US caused dose-dependent inhibition of lymphocyte proliferation induced by phorbol myristol acetate (PMA), an activator of protein kinase C. The PHA-induced increase in CD25 expression was inhibited in peripheral blood mononuclear leukocytes (PBML) by OvUS. However, no effect of OvUS on Con A-induced expression of CD25 was observed. Further analysis using two-color flow cytometry revealed that OvUS inhibited ConA-induced expression of CD25 in gammadelta-TCR- cells but not gammadelta-TCR+ cells. Stimulation of PBML for 14 hr with ConA resulted in an increase in steady state amounts of interleukin-2 (IL-2) mRNA that was not inhibited by OvUS. Ovine US was also inhibitory to lymphocyte proliferation induced by human IL-2. Results suggest that OvUS acts to inhibit lymphocyte proliferation by blocking the upregulation of the IL-2 receptor and inhibiting IL-2-mediated events. Lack of an effect of OvUS on ConA-stimulated CD25 expression in gammadelta-TCR+ cells may reflect a different mechanism of activation of these cells or insensitivity to inhibition by OvUS.

Animals↗
PubMed2000

[Establishment and its application of a reporter-based screening model for discovering new ligands of estrogen receptor alpha subtypes].

AIM: To establish a sensitive and efficient reporter gene based screening model and use it to screen compounds for discovering new ligands of estrogen receptor alpha subtype. METHODS: A recombinant Epstein-Barr virus episomal vector (pMT/ERE-CAT) was constructed by inserting a synthetic sequence composed of five estrogen response elements upstream of promoter and a chloramphenicol acetyltransferase (CAT) gene downstream of promoter. pMT/ERE-CAT was transfected into HepG2 cells expressing estrogen receptor alpha subtype (ER +HepG2). Hygromycin (200 micrograms.mL-1) was added 48 h after transfection for selection. One stably transfected clone was isolated and used to screen compounds for activity of stimulating CAT gene expression using colorimetric CAT assay. RESULTS: In the ER +HepG2 cells, the expression of CAT gene was induced by estradiol. A dose-dependent expression of CAT gene with half-maximal induction at 0.07 nmol.L-1 was observed. The ER +HepG2 cell was used to screen compounds for activity of stimulating CAT gene expression. Resveratrol was found to produce a maximal level of induction (1.75 times of estradiol). In vitro radiation survival experiment showed that the radioprotection activity of resveratrol (D0 = 3.18 Gy) is stronger than that of estradiol (D0 = 2.59 Gy). CONCLUSION: Vector pMT/ERE-CAT was used to generate stably transfected ER +HepG2 cell lines. The cell lines can be used to screen compounds for estrogen activity by testing extracts of cells grown in microtiter wells directly using colorimetric CAT assay. This system should provide an efficient method for screening and analyzing the activity of large numbers of ligands of estrogen receptor.

Chloramphenicol O-Acetyltransferase↗
PubMed2000

Regulation of telomerase activity in camptothecin-induced apoptosis of human leukemia HL-60 cells.

AIM: To explore the regulation of telomerase activity in camptothecin induced apoptosis of human leukemia HL-60 cells. METHODS: Apoptosis of HL-60 cells was induced by camptothecin (1 mg/L) for 2, 4, and 6 h. Apoptosis was determined by agarose electrophoresis and flow cytometry analysis. To assess telomerase activity, a PCR-based telomeric repeat amplification protocol assay (TRAP) was used. RT-PCR was performed to examine the mRNA levels of hTR (human telomerase RNA component), hEST2/hTERT (human telomerase reverse transcriptase), TLP1/TP1 (telomerase association protein 1), and bcl-2 (B cell leukemia/lymphoma 2 gene) in HL-60 cells before and after camptothecin treatment. RESULTS: Telomerase activity was decreased in a time-dependent manner during the camptothecin induced apoptosis of HL-60 cells. However, no difference in expression of each telomerase subunit was detected, while expression of bcl-2 was progressively down-regulated. CONCLUSION: These lines of evidences indicated that down-regulation of the telomerase activity in HL-60 cells was closely related to camptothecin-induced apoptosis, and the telomerase activity was not blocked at the transcriptional levels of the genes of the known ribonucleoprotein (RNP) complex components. We also found that bcl-2 did not regulate the mRNA expressions of telomerase subunits directly.

Apoptosis↗
PubMed1999

Studies on effective PCR screening strategies for white spot syndrome virus (WSSV) detection in Penaeus monodon brooders.

We re-tested stored (frozen) DNA samples in 5 independent polymerase chain reaction (PCR) replicates and confirmed that equivocal test results from a previous study on white spot syndrome virus (WSSV) in brooders and their offspring arose because amounts of WSSV DNA in the test samples were near the sensitivity limits of the detection method. Since spawning stress may trigger WSSV replication, we also captured a fresh batch of 45 brooders for WSSV PCR testing before and after spawning. Replicates of their spawned egg batches were also WSSV PCR tested. For these 45 brooders, WSSV prevalence before spawning was 67% (15/45 1-step PCR positive, 15/45 2-step PCR positive and 15/45 2-step PCR negative). Only 27 (60%) spawned successfully. Of the successful spawners, 56% were WSSV PCR positive before spawning and 74% after. Brooders (15) that were heavily infected (i.e. 1-step PCR positive) when captured mostly died within 1 to 4 d, but 3 (20%) did manage to spawn. All their egg batch sub-samples were 1-step PCR positive and many failed to hatch. The remaining 30 shrimp were divided into a lightly infected group (21) and a 2-step PCR negative group (9) based on replicate PCR tests. The spawning rates for these 2 groups were high (81 and 78%, respectively). None of the negative spawners (7) became WSSV positive after spawning and none gave egg samples positive for WSSV. In the lightly infected group (21), 6 brooders were 2-step WSSV PCR negative and 15 were 2-step WSSV PCR positive upon capture. However, all of them were WSSV PCR positive in replicate tests and after spawning or death. Four died without spawning. The remaining 17 spawned but only 2 gave egg samples PCR negative for WSSV. The other 15 gave PCR positive egg samples, but they could be divided into 2 spawner groups: those (7) that became heavily infected (i.e. 1-step PCR positive) after spawning and those (8) that remained lightly infected (i.e. became or remained 2-step PCR positive only). Of the brooders that became heavily infected after spawning, almost all egg sample replicates (91 %) tested 2-step PCR positive. One brooder even gave heavily infected (i.e. 1-step PCR positive) egg samples. For the brooders that remained lightly infected after spawning, only 27% of the egg sample replicates were 2-step PCR positive. Based on these results, we recommend that to avoid false negatives in WSSV PCR brooder tests screening tests should be delayed until after spawning. We also recommend, with our PCR detection system, discarding all egg batches from brooders that are 1-step PCR positive after spawning. On the other hand, it may be possible with appropriate monitoring to use eggs from 2-step PCR positive brooders for production of WSSV-free or lightly infected postlarvae. These may be used to stock shrimp ponds under low-stress rearing conditions.

Animals↗