Biomedical subjects

Hai Lu

Publications and source records attributed to Hai Lu.

11 recordsLinked to original sources

PubMed2005

Compositional modulation in In(x)Ga(1-x)N: TEM and X-ray studies.

Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) have been used to study compositional modulation in In(x)Ga(1-x) N layers grown with compositions close to miscibility gap. The samples (0.34 < x < 0.8) were deposited by molecular beam epitaxy using either a 200 nm thick AlN or GaN buffer layer grown on a sapphire substrate. Periodic compositional modulation leads to extra electron diffraction spots and satellite reflections in XRD in the theta-2theta coupled geometry. The ordering period delta measured along c-axis was about delta = 45 A for x = 0.5 and delta = 66 A for x = 0.78 for samples grown on AlN buffer layer. TEM and XRD determinations of delta were in good agreement. Compositional modulation was not observed for the sample with x = 0.34 grown on a GaN buffer layer. Larger values of delta were observed for layers with higher In content and for those having larger mismatch with the underlying AlN buffer layer. The possibility that the roughness of the AlN growth surface promotes strong In segregation on particular crystallographic planes leading to compositional modulation is considered.

Journal Article↗

PubMed2005

Certification of the cadmium content in certified reference materials for Cd rice flour.

The materials used to prepare the certified reference materials (CRMs) for Cd rice flour described here were taken from Cd-contaminated rice samples, round-grained and non-sticky rice grown in different provinces throughout China. The Cd rice materials were first blown to remove dust and husk, and then were successively ground, sieved, dried and mixed to form homogeneous rice flour. The Cd rice flour was packed in glass bottles, each bottle containing 40 g. All bottled CRMs were subjected to 60Co radiation (2.5 megarads) for long-term preservation. Atomic absorption spectrometry was used to determine the homogeneity of the cadmium content in each material. The certification of the cadmium content for the three CRMs was performed using isotope dilution mass spectrometry.

Cadmium↗

PubMed2005

Absolute isotopic composition and atomic weight of neodymium using thermal ionization mass spectrometry.

Synthetic mixtures prepared gravimetrically from highly enriched isotopes of neodymium in the form of oxides of well-defined purity were used to calibrate a thermal ionization mass spectrometer. A new error analysis was applied to calculate the final uncertainty of the atomic weight value. Measurements on natural neodymium samples yielded an absolute isotopic composition of 27.153(19) atomic percent (at.%) 142Nd, 12.173(18) at.% 143Nd, 23.798(12) at.% 144Nd, 8.293(7) at.% 145Nd, 17.189(17) at.% 146Nd, 5.756(8) at.% 148Nd, and 5.638(9) at.% 150Nd, and the atomic weight of neodymium as 144.2415(13), with uncertainties given on the basis of 95% confidence limits. No isotopic fractionation was found in terrestrial neodymium materials.

Hot Temperature↗

PubMed2005

Molecular characterization of a glutathione transferase from Pinus tabulaeformis (Pinaceae).

Glutathione transferases (GSTs) play important roles in stress tolerance and detoxification metabolism in plants. To date, studies on GSTs in higher plants have focused largely on agricultural plants. In contrast, there is virtually no information on the molecular characteristics of GSTs in gymnosperms. The present study reports for the first time the cloning, expression and characteristics of a GST gene (PtGSTU1) from a pine, Pinus tabulaeformis, which is widely distributed from northern to central China covering cold temperate and drought regions. The PtGSTU1 gene encodes a protein of 228 amino acid residues with a calculated molecular mass of 26.37 kDa. Reverse transcription PCR revealed that PtGSTU1 was expressed in different tissues, both above and below ground, of P. tabulaeformis. The over-expressed recombinant PtGSTU1 showed high activity towards the substrates 1-chloro-2,4-dinitrobenzene (CDNB) and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl). Kinetic analysis with respect to CDNB as substrate revealed a Km of 0.47 mM and Vmax of 169.1 micromol/min per mg of protein. The recombinant PtGSTU1 retained more than 60% of its maximum enzymatic activity from 15 degrees C to 45 degrees C with a broad optimum Tm range of 25 degrees C - 35 degrees C. The enzyme had a maximum activity at approximately pH 8.5 - 9.0. Site-directed mutagenesis revealed that Ser13 in the N-terminal domain is a critical catalytic residue, responsible for stabilisation of the thiolate anion of enzyme-bound glutathione. Based on comparative analyses of its amino acid sequence, phylogeny and predicted three-dimensional structure, the PtGSTU1 should be classified as a tau class GST.

4-Chloro-7-nitrobenzofurazan↗

PubMed2005

Overexpression of mtlD gene in transgenic Populus tomentosa improves salt tolerance through accumulation of mannitol.

The mtlD gene encoding mannitol-1-phosphate dehydrogenase, which catalyzes the biosynthesis of mannitol from fructose, was cloned from Escherichia coli and transferred to poplar (Populus tomentosa Carr.) through Agrobacterium-mediated transformation. The transgenic plants were screened and selected on Murashige and Skoog (MS) medium containing 30-50 mg l(-1) kanamycin and verified by polymerase chain reaction (PCR) and Southern blotting. Expression of the gene led to synthesis and accumulation of mannitol in the transgenic plants. Gas chromatography and mass spectrometry (GC/MS) and capillary gas chromatography (GC) showed that transgenic plants accumulated much more mannitol in their tissues than the wild-type plants, whether cultured in vitro, or grown hydroponically or in the field. Increased salt tolerance of transgenic plants was observed both in vitro and in hydroponic culture. The transgenic buds rooted normally on MS medium containing 50 mM NaCl, whereas wild-type buds did not. In the 40-day hydroponic experiments, transgenic poplar plants survived in a 75-mM NaCl treatment, whereas the wild-type poplar plants tolerated only 25 mM NaCl. Under the same NaCl stress, stomatal conductance, transpiration rates and photosynthetic rates were all higher in transgenic plants than in wild-type plants, whereas cellular relative conductivity was lower. We demonstrated that the mtlD gene was expressed in transgenic poplar plants, resulting either directly or indirectly in mannitol accumulation and improved salt tolerance. The constant mannitol concentrations in transgenic plants during the NaCl treatments indicated that mannitol accumulation caused by the mtlD gene was not a consequence of NaCl stress. Height growth was reduced by about 50% in the transgenic plants compared with the wild-type plants in the absence of salt; however, relative growth rate was much less influenced by salt stress in transgenic plants than in wild-type plants. The stunted growth of the transgenic plants may in part explain their improved salt tolerance.

Escherichia coli↗

PubMed2005

[TNF-alpha mRNA expression in lung cancer cell lines induced by ionizing radiation].

OBJECTIVE: The aim of this study is to investigate the release of TNF-alpha mRNA in two lung cancer cell lines in vitro and the regulation of TNF-alpha mRNA expression by ionizing radiation. METHODS: Two lung cancer cell lines (A549 and NCI-H596) were investigated for their TNF-alpha mRNA expression before and after exposure to different irradiation doses (2, 5, 10, 20, 30 and 40 Gy) and at different time intervals (1, 3, 6, 12, 24, 48 and 72 hours after irradiation). The TNF-alpha mRNA expression was quantified by fluorescence-based real-time quantitative RT-PCR. Colony formation assays were performed after irradiation with a dose of 2, 4, 6, and 8 Gy to determine the clonogenic survival. RESULTS: Dependent on the dose given, irradiation was found to cause increasing induction of TNF-alpha mRNA expression of NCI-H596 cells, reaching maximal level after 40 Gy irradiation, which was 83 times higher than that of normal controls. On the other hand, dependent on the time after irradiation, TNF-alpha mRNA expression of NCI-H596 and A549 cells was increased, reaching maximal level at 6h for NCI-H596 cells, which was 568 times higher than that of normal control cells. TNF-alpha mRNA expression of A549 cells was increased to maximum at 1 h after irradiation and was 136 times higher than that of control cells. Colony formation efficiency (number of colonies divided by the number of inoculated cells) of unirradiated control A549 and NCI-H596 cells was 0.37-0.45 and 0.12-0.24, respectively. The survival fraction (SF) of A549 cells was 47.3% +/- 9.0% at 2 Gy, 18.0% +/- 3.0% at 4 Gy, 6.0% +/- 2.0% at 6 Gy, 1.4% +/- 0.3% at 8 Gy. The SF of NCI-H596 cells was 55.2% +/- 51.0% at 2 Gy, 15.9% +/- 9.2% at 4 Gy, 3.5% +/- 1.7% at 6 Gy; 0.9% +/- 0.6% at 8 Gy. The curves of TNF-alpha expression of the two tumor cell lines were nearly identical, therefore the radiosensitivity of these cell lines was similar. Statistically there was no significant difference for D(0) and D(q) (P > 0.05). CONCLUSION: The two lung cancer cell lines studied express TNF-alpha following irradiation in a time- and irradiation dose-dependent manner. Radiation-induced TNF-alpha production of tumor cells may be of paramount importance not only for tumor behaviour, but also in respect to potential damage to normal tissues and the clinical status of the host.

Adenocarcinoma↗

PubMed2004

Squamous cell carcinoma cell aggregates escape suspension-induced, p53-mediated anoikis: fibronectin and integrin alphav mediate survival signals through focal adhesion kinase.

Resistance to anoikis, or apoptosis triggered by detachment from the extracellular matrix (ECM), lengthens the survival of malignant cells, facilitating reattachment and colonization of secondary sites. To examine the molecular mechanisms underlying resistance to anoikis in human oral squamous cell carcinoma (SCC) cells, we cultured human squamous carcinoma (HSC-3) cells in suspension on plates coated with poly-2-hydroxyethyl methacrylate, which blocks access to the ECM. Cells in suspension that formed multicellular aggregates had significantly lower levels of apoptosis than single cells. Aggregates, but not single cells, had high levels of fibronectin. Preincubation with a cyclic arginine-glycine-aspartic acid peptide or fibronectin-blocking antibody significantly increased anoikis. Single cells had markedly lower expression of the integrin alpha(v) receptor than aggregates. Blocking alpha(v) function with a blocking antibody or by transfection with an antisense oligonucleotide increased apoptosis and inhibited aggregation. In single cells but not aggregates, phosphorylation of the integrin-associated focal adhesion kinase (FAK) at tyrosine 397 was reduced, and p53 levels were increased. Apoptosis was increased by blocking FAK with an antisense oligonucleotide and reduced by blocking p53. These findings show that SCC cells escape suspension-induced anoikis by forming multicellular aggregates that avail themselves of fibronectin survival signals mediated by integrin alpha(v). Single cells in suspension that do not form aggregates undergo anoikis because of decreased FAK phosphorylation and increased p53 levels. Thus, SCC cells appear to use neighboring cells and the ECM molecule FN to promote the metastatic phenotype.

Animals↗

PubMed2004

Functional differences between integrin alpha4 and integrins alpha5/alphav in modulating the motility of human oral squamous carcinoma cells in response to the V region and heparin-binding domain of fibronectin.

The high-affinity heparin-binding domain and the V region of fibronectin (FN) mediate invasion and migration of human oral squamous cell carcinoma (SCC) cells. We investigated the role of the alpha4, alpha5, and alphav integrin receptors--which are central to mediating interactions with these domains of FN--in regulating SCC cell migration. SCC cells expressed the alpha4, alpha5, and alphav integrin subunits on their surface, although alpha4 expression was low. Treatment with recombinant FN proteins containing an alternatively spliced V region (V+) and either an unmutated (H+) or a mutated, nonfunctional high-affinity heparin-binding domain (H-) increased expression of alpha5 and alphav and cell motility. Antisense alpha5 or alphav oligonucleotides inhibited cell motility stimulated by FN proteins, as did blocking antibodies to alpha5 or alphav. Blocking antibodies to alpha5 increased alphav and alpha4 levels, and blocking antibodies to alphav increased the levels of alpha5 and alpha4, without increasing cell motility. In contrast, an antisense alpha4 oligonucleotide and alpha4-blocking antibodies increased cell motility, especially migration stimulated by V+H+ and V+H- FN proteins. alpha4-Blocking antibodies alone increased motility, probably by inducing alpha5 and alphav expression. Transfection with alpha4 cDNA decreased cell motility and alpha5 and alphav expression. Thus, the increased motility induced by the FN protein is probably mediated by alphav and alpha5, whereas alpha4 downregulates this process in a transdominant fashion.

Base Sequence↗

PubMed2004

Application of laser capture microdissection to phage display peptide library screening.

OBJECTIVE: When identifying important regulatory genes using methods such as phage display peptide library screening it is critical to select such peptides from cells and tissues in their native state. Here, we report a novel approach to screen tumors using phage display and laser capture microdissection (LCM). STUDY DESIGN: A phage peptide library was screened directly on fresh oral tumor tissue, such that specifically bound peptides were selected from fresh tumor cells in the native tissue state. Tissue processing conditions were modified to ensure the survival of the bacteriophage. RESULTS: Our results demonstrate that live phage-peptide conjugates can be recovered from laser capture microdissected cells in a form suitable for additional cycles of amplification. CONCLUSION: Thus, LCM will be a valuable adjunct to phage display studies.

Animals↗

PubMed2004

Stable and specific expression of 4-coumarate:coenzyme A ligase gene (4CL1) driven by the xylem-specific Pto4CL1 promoter in the transgenic tobacco.

The ability of 4-coumarate:coenzyme A ligase promoter from Populus tomentosa (Pto4CL1p) to drive expression of the GUS reporter gene and 4-coumarate:coenzyme A ligase gene in tobacco has been studied using transgenic plants produced by Agrobacterium-mediated transformation. Intense GUS histochemical staining was detected in the xylem of stem in transgenic tobacco plants carrying the 1140 bp Pto4CL1p promoter. To further investigate the regulation function of the tissue-specific expression promoter, Pto4CL1p, a binary vector containing Pto4CL1p promoter fused with 4CL1 gene was transferred into tobacco. The activity of the 4CL1 enzyme doubled in the stems of transgenic tobacco but did not increase in the leaves. The content of lignin was increased 25% in the stem but there was no increase in the leaves of transgenic tobacco.

Base Sequence↗

PubMed2002

[Application of laser capture microdissection in screening phage-display peptide library from osteosarcoma tissues].

OBJECTIVE: To establish a novel approach by using laser capture microdissection (LCM) for phage-display peptide library screening and direct recovery of the peptides specifically bound to the cells from fresh human tissue. METHODS: Fresh human osteosarcoma (OS) tissue specimens obtained from biopsy were incubated in phage peptide library solution, followed by shaking at 4 degrees celsius and subsequent preparation of frozen sections. Immunohistochemistry was employed to examine the infiltration of the phage in the tissues. After modification to improve the viability of the phage during the operation, LCM was used to isolate the targeted tumor cells that specifically bound the phage peptides. The phage was then recovered by transfecting the host bacteria, and the specificity of the selected phage was assessed by calculating the recovered phage transfection unit on different tissue sections. RESULTS: Enough phages that specifically bound to tumor cells were recovered from the sections. After three rounds of screening, the eluted phage showed up to 16-fold selectivity for OS tissue. CONCLUSION: Application of LCM makes it possible to screen phage display peptide library directly from fresh human tissue. Specific cell-binding peptides can be selected directly from fresh human tumor cells in their native tissue environment at the single cell level.

Animals↗