PubMed Health⌕ Search

Biomedical subjects

Hao Li

Publications and source records attributed to Hao Li.

At least 73 records · Page 4Linked to original sources
PubMed2005

PDMS microfludic device for optical detection of protein immunoassay using gold nanoparticles.

A simple but highly specific immunoassay system for goat anti-human IgG has been developed using gold nanoparticles and microfluidic techniques. The assay is based on the deposition of gold nanoparticles that are coated with protein antigens in the presence of their corresponding antibodies to microfluidic channel surface. The effects of time accumulation, the flow velocity, and the concentration of antibodies to the red light absorption percentage (RAP) of deposition were investigated with an ordinary optical microscope. By controlling the reaction time and flow velocity, a dynamic range of 3 orders of magnitude and a detection sensitivity of 10 ng ml(-1) of goat anti-human IgG were achieved. Because of its simplicity and flexibility, this new technique should be useful for fast, highthroughput screening of antibodies in clinical diagnostic applications.

Animals↗
PubMed2005

Enantioselective organocatalytic Mukaiyama-Michael addition of silyl enol ethers to alpha,beta-unsaturated aldehydes.

[reaction: see text] A highly enantioselective, organocatalytic Mukaiyama-Michael addition reaction of silyl ethers and alpha,beta-unsaturated aldehydes has been developed. The process, catalyzed by MacMillan's chiral imidazolidinone, affords delta-keto aldehydes in high yields (56-87%) and high enantioselectivities (85-97% ee). Moreover, the reaction is applicable to a wide range of silyl ethers and alpha,beta-unsaturated aldehydes and, as such, provides access to a range of important synthetic building blocks.

Journal Article↗
PubMed2005

Further characterization of human DNA polymerase delta interacting protein 38.

Polymerase delta interacting protein 38 (PDIP38) was identified as a human DNA polymerase (pol) delta interacting protein through a direct interaction with p50, the small subunit of human pol delta. PDIP38 was also found to interact with proliferating cell nuclear antigen, which suggested that it might play a role in vivo in the processes of DNA replication and DNA repair in the nucleus. In order to characterize further this novel protein, we have examined its subcellular localization by the use of immunochemical and cellular fractionation techniques. These studies show that PDIP38 is a novel mitochondrial protein and is localized mainly to the mitochondria. PDIP38 was shown to possess a functional mitochondrial targeting sequence that is located within the first 35 N-terminal amino acid residues. The mature PDIP38 protein is about 50 amino acid residues smaller than the full-length precursor PDIP38 protein, consistent with it being processed by cleavage of the mitochondrial targeting sequence during entry into the mitochondria. His-tagged mature PDIP38 inhibited pol delta activity in vitro and interacted with human papillomavirus 16 E7 oncoprotein, suggesting that PDIP38 might play a role in the pol delta-mediated viral DNA replication. Although the localization of PDIP38 to the mitochondria suggests that it serves functions within the mitochondria, we cannot eliminate the possibility that it may be involved in pol delta-mediated DNA replication or DNA repair under certain conditions such as viral infection.

Cell Line↗
PubMed2005

Identification of transcriptional regulatory elements in chemosensory receptor genes by probabilistic segmentation.

Genome sequencing has allowed many gene regulatory elements to be identified through cross-species comparisons . However, the expression of genes in multigene families can diverge rapidly between related species . An alternative approach to characterizing multigene families utilizes the fact that genes within the group are likely to share aspects of their regulation. Here, we use a statistical approach, probabilistic segmentation , to identify sequences that are overrepresented in the regions upstream of C. elegans chemosensory receptor genes. Although each of these elements is present in only a subset of the genes, their distribution across and within the promoters of chemosensory receptor genes makes it possible to detect them. Many of the motifs show positional preference with respect to the translational start site and correspond to the binding sites of known families of transcription factors. We verified one motif, the E-box sequence WWYCACSTGYY, by showing that it directs expression of reporter genes to the ADL chemosensory neurons. Thus, probabilistic segmentation can be used to identify functional regulatory elements with no previous knowledge of gene expression or regulation. This approach may be of particular value for rapidly evolving genes in the immune system and the nervous system.

Amino Acid Motifs↗
PubMed2005

A novel pyrrolidine imide catalyzed direct formation of alpha,beta-unsaturated ketones from unmodified ketones and aldehydes.

A method for direct, stereoselective preparation of (E)-alpha,beta-unsaturated ketones from ketones and aldehydes, promoted by a novel pyrrolidine imide organocatalyst, has been developed in moderate to high yields. Unlike the Claisen-Schmidt condensation and Lewis acid catalyzed tandem aldol-dehydration processes, this method provides mild reaction conditions to access alpha,beta-unsaturated ketones from simple, unmodified ketones. [reaction: see text]

Journal Article↗
PubMed2005

Functional specificity of shuttling hnRNPs revealed by genome-wide analysis of their RNA binding profiles.

Nab2, Npl3, and Nab4/Hrp1 are essential RNA binding proteins of the shuttling hnRNP class that are required for the efficient export of mRNA. To characterize the in vivo transcript specificity of these proteins, we identified their mRNA binding partners using a microarray-based assay. Each of the three proteins was coimmunoprecipitated with many different mRNA transcripts. Interestingly, each protein exhibits preferential associations with a distinct set of mRNAs. Notably, some of these appear to denote specific functional classes. For example, the ribosomal protein mRNAs and other highly expressed transcripts significantly favor association with Npl3 over Nab2, and Nab4/Hrp1 is strongly enriched with transcripts required for amino acid metabolism. Significantly, nab4 mutants showed a striking, desensitized growth phenotype when exposed to amino acid stress conditions suggesting a biological consequence to the associations we observed. Supporting the hypothesis that these proteins display transcript specificity, we identified a unique 7-nucleotide sequence overrepresented in the transcripts highly associated with Nab2 and Nab4/Hrp1 using the REDUCE algorithm. Validating our approach, our bioinformatics analysis correctly identified the known binding site for Nab4/Hrp1. These specialized associations of the hnRNP proteins of Saccharomyces cerevisiae suggest the opportunity to regulate the processing of particular transcripts between transcription and translation.

Genome, Fungal↗
PubMed2005

Inference of combinatorial regulation in yeast transcriptional networks: a case study of sporulation.

Decomposing transcriptional regulatory networks into functional modules and determining logical relations between them is the first step toward understanding transcriptional regulation at the system level. Modules based on analysis of genome-scale data can serve as the basis for inferring combinatorial regulation and for building mathematical models to quantitatively describe the behavior of the networks. We present here an algorithm called modem to identify target genes of a transcription factor (TF) from a single expression experiment, based on a joint probabilistic model for promoter sequence and gene expression data. We show how this method can facilitate the discovery of specific instances of combinatorial regulation and illustrate this for a specific case of transcriptional networks that regulate sporulation in the yeast Saccharomyces cerevisiae. Applying this method to analyze two crucial TFs in sporulation, Ndt80p and Sum1p, we were able to delineate their overlapping binding sites. We proposed a mechanistic model for the competitive regulation by the two TFs on a defined subset of sporulation genes. We show that this model accounts for the temporal control of the "middle" sporulation genes and suggest a similar regulatory arrangement can be found in developmental programs in higher organisms.

Algorithms↗
PubMed2005

Genome-wide regulatory complexity in yeast promoters: separation of functionally conserved and neutral sequence.

To gauge the complexity of gene regulation in yeast, it is essential to know how much promoter sequence is functional. Conservation across species can be a sensitive means of detecting functional sequences, provided that the significance of conservation can be accurately calibrated with the local neutral mutation rate. By analyzing yeast coding and promoter sequences, we find that neutral mutation rates in yeast are uniform genome-wide, in contrast to mammals, where neutral mutation rates vary along chromosomes. We develop an approach that uses this uniform rate to estimate the amount of promoter sequence under purifying selection. This amount is approximately 30%, corresponding to roughly 90 bp for a typical promoter. Furthermore, using a hidden Markov model, we are able to separate each promoter into distinct high and low conservation regions. Known regulatory motifs are strongly biased toward high conservation regions, while low conservation regions have mutation rates similar to that of the neutral background. Certain Gene Ontology groupings of genes (e.g., Carbohydrate Metabolism) have large amounts of high conservation sequence, suggesting complexity in their transcriptional regulation. Others (e.g., RNA Processing) have little high conservation sequence and are likely to be simply regulated. The separation of functionally conserved sequence from the neutral background allows us to estimate the complexity of cis-regulation on a genomic scale.

Base Sequence↗
PubMed2005

Crosslinked hyaluronan hydrogels containing mitomycin C reduce postoperative abdominal adhesions.

OBJECTIVE: To evaluate the efficacy of crosslinked hyaluronan (HA) hydrogels that contained covalently-bound mitomycin C (MMC) in reducing postoperative adhesions in a rat uterine horn model. DESIGN: Two independent parameters were investigated: [1] the quantity of MMC in preformed crosslinked hydrogel films and [2] the efficacy of intraperitoneal injection of in situ crosslinkable solutions. SETTING: University animal research facility. ANIMAL(S): Female Wistar rats. INTERVENTION(S): Injuries (3 x 10 mm) were made to contacting serosal surfaces of the medial uterine wall musculature in female rats. Two treatment protocols were used. In the first, sterile crosslinked HA films that contained different MMC loadings (0, 0.5%, and 2%) were applied to two injured uterine horns; control animals received no films. In the second protocol, MMC-loaded crosslinked HA gels that contained different MMC loadings (0.31%, 0.625%, and 1.25%) were spread on the site of uterine horn injury (1 mL); then, an additional 4 mL of the same formulation was injected into the peritoneal cavity after abdominal closure. Control animals were injected with 5 mL of buffer only. MAIN OUTCOME MEASURE(S): Extent of postoperative adhesions between uterine horns and with surrounding tissues and organs. RESULT(S): Mitomycin C-loaded crosslinked HA films and in situ crosslinked gels were more effective in reducing postoperative adhesion formation than were buffer controls or crosslinked HA films without MMC. CONCLUSION(S): Mitomycin C-loaded crosslinked HA films and gels reduced formation of postoperative intraperitoneal adhesions.

Abdomen↗
PubMed2005

Molecular, anatomical, and biochemical events associated with neurodegeneration in mice with Niemann-Pick type C disease.

In Niemann-Pick type C (NPC) disease, cholesterol associated with either apoE or apoB100 is taken up by cells in all tissues, including the central nervous system, through clathrin-coated pits and becomes trapped in late endosomes and lysosomes. This study defines the functional, biochemical, and molecular events that ensue as nerve cell death occurs. In mice homozygous for a mutation in NPC1, neuromuscular dysfunction begins at 5 weeks and death occurs at 13 weeks of age. Cholesterol accumulates in every tissue in the body. Purkinje cell loss in the cerebellum begins at 3 to 4 weeks of age and is nearly complete by 11 weeks. This neurodegeneration in the cerebellum is associated with increases in the levels of mRNA for caspase 1, caspase 3, NPC2, LipA, apoE, apoD, glial fibrillary acidic protein, and tumor necrosis factor-alpha, but not for most target genes of the LXR nuclear receptors. The level for apoER2 is significantly reduced. These studies show there is a compensatory increase in NPC2 and LipA in an attempt to overcome the physiological defect caused by the mutation. Nevertheless, neurodegeneration proceeds utilizing apoptosis with activation of glial cells, increased apoE and apoD synthesis, and increased cholesterol turnover across the CNS.

Animals↗
PubMed2005

Regulation of cellular plasticity in Drosophila imaginal disc cells by the Polycomb group, trithorax group and lama genes.

Drosophila imaginal disc cells can switch fates by transdetermining from one determined state to another. We analyzed the expression profiles of cells induced by ectopic Wingless expression to transdetermine from leg to wing by dissecting transdetermined cells and hybridizing probes generated by linear RNA amplification to DNA microarrays. Changes in expression levels implicated a number of genes: lamina ancestor, CG12534 (a gene orthologous to mouse augmenter of liver regeneration), Notch pathway members, and the Polycomb and trithorax groups of chromatin regulators. Functional tests revealed that transdetermination was significantly affected in mutants for lama and seven different PcG and trxG genes. These results validate our methods for expression profiling as a way to analyze developmental programs, and show that modifications to chromatin structure are key to changes in cell fate. Our findings are likely to be relevant to the mechanisms that lead to disease when homologs of Wingless are expressed at abnormal levels and to the manifestation of pluripotency of stem cells.

Animals↗
PubMed2005

Uptake and metabolism of ginsenoside Rh2 and its aglycon protopanaxadiol by Caco-2 cells.

The uptake and metabolism profiles of ginsenoside Rh2 and its aglycon protopanaxadiol (ppd) were studied in the human epithelial Caco-2 cell line. High-performance liquid chromatography-mass spectrometry was applied to determine Rh2 and its aglycon ppd concentration in the cells at different pH, temperature, concentration levels and in the presence or absence of inhibitors. Rh2 uptake was time and concentration dependent, and its uptake rates were reduced by metabolic inhibitors and influenced by low temperature, thus indicating that the absorption process was energy-dependent. Drug uptake was maximal when the extracellular pH was 7.0 for Rh2 and 8.0 for ppd. Rh2 kinetic analysis showed that a non-saturable component (Kd 0.17 nmol x h(-1) x mg(-1) protein) and an active transport system with a Km of 3.95 micromol x l(-1) and a Vmax of 4.78 nmol x h(-1) x mg(-1)protein were responsible for the drug uptake. Kinetic analysis of ppd showed a non-saturable component (Kd 0.78 nmol x h(-1) x mg(-1) protein). It was suggested that active extrusion of P-glycoprotein and drug degradation in the intestine may influence Rh2 bioavailability.

Caco-2 Cells↗
PubMed2005

[Study on the long-time effect on allitridum and selenium in prevention of digestive system cancers].

OBJECTIVE: To evaluate the long-time effect on allitridum and selenium in preventing cancer of digestive system. METHODS: Persons who were recruited into the intervention group and took allitridum and selenium to prevent gastric cancer in Qixia county of China from 1989-1991 were followed up to 2001 and data of deaths was collected. The long effect on allitridum and selenium in preventing cancer of digestive system was analysed. RESULTS: Data were compared to placebo group five years (1992-1996) after the termination of intervention to have found that the accumulative mortality rate of all cancer, digestive system cancer and gastric cancer had decreased 45.5%, 41.2% and 63.3% in the intervention group respectively. By stratum analysis, accumulative mortality rate of all cancer, digestive system cancer and gastric cancer had decreased 51.5%, 51.5% and 67.7% in males of the intervention group, respectively. Relative risks for males in the intervention group were 0.48, 0.47 and 0.30 times more than the placebo group, respectively. All of them were statistically significant. Relative risks for females in the intervention group were 0.74, 0.92 and 0.70 times more than placebo group. Six to ten years later after the termination of intervention, the accumulative mortality rate and relative risk of all cancers in two groups became similar. CONCLUSION: Allitridum and selenium had the effect of decreasing the incidence risk of digestive cancer with a protective rate more than 50% for five years after the termination of intervention program.

Adult↗
PubMed2005

[Expression of cyclins in hepatocellular carcinoma and its correlation to tumor cell apoptosis].

BACKGROUND & OBJECTIVE: Cyclins overexpress in various tumors, but its expression in hepatocellular carcinoma (HCC) and its correlation to cell proliferation and apoptosis are unclear. This study was to determine the expression of Cyclins, proliferating cell nuclear antigen (PCNA), and cell apoptosis in HCC, and to analyze their interrelations. METHODS: Tissue microarray technology and SP immunohistochemistry were used to detect expressions of Cyclins A, B1, D1, E, and PCNA in 122 specimens of HCC. In situ terminal deoxyribonucleotide transferase labeling was used to detect cell apoptosis. RESULTS: In the 122 HCC specimens, positive rate of Cyclin A was 50.0%, of Cyclin B1 was 47.5%, of Cyclin D1 was 42.6%, of Cyclin E was 35.2%. Cyclins levels were significantly higher in HCC tissues of grade II, III, and IV than in HCC tissues of grade I(P 0.05). Densities of apoptotic cells were significantly lower in HCC tissues of grade II, III, and IV than in HCC tissues of grade I(P 0.05); PCNA scores were significantly higher in HCC tissues of grade II, III, and IV than in HCC tissues of grade I(P 0.01). The poorer differentiation, the lower density of apoptotic cells in HCC, the higher PCNA score in HCC. Cyclins levels were negatively related to density of apoptotic cells (r=-0.686, P < 0.01), and positively related to PCNA score (r=0.599, P < 0.01); density of apoptotic cells was negatively related to PCNA score (r=-0.701, P < 0.01). CONCLUSION: Cyclins overexpress in HCC, which may shorten tumor cell cycle phase, accelerate cell proliferation and decrease apoptosis, and result in increased malignant phenotypes.

Adult↗
PubMed2005

Effects of exogenous Ca2+ on the membrane permeability, MDA and SH group content of Alexandrium sp. LC3 under surfactant stress.

The effect of Ca2+ on the removal of Alexandrium sp. LC3 under HDTMAB stress was investigated. The results showed that the toxic effect of HDTMAB on Alexandrium sp. LC3 was significantly reduced in the presence of Ca2 , especially under 4 mmol/L of Ca2+. To understand the underlying mechanism, the SH group and MDA content of the cell membrane and membrane permeability were measured. It was found that the SH content of cell member increased, the MDA content and membrane permeability decreased when Alexandrium sp. was treated with Ca2+ and HDTMAB complex, compared with using HDTMAB only. The data suggested that Ca2+ might promote HDTMAB stress resistance of Alexandrium sp. LC3 by reducing the permeability and increasing the stability of cell membrane.

Animals↗
PubMed2005

[Human bone marrow multipotent adult progenitor cells differentiate into hepatocyte-like cells with hepatocyte growth factor plus fibroblast growth factor-4 in vitro].

OBJECTIVE: To investigate the possibility of the human bone marrow multipotent adult progenitor cells (hMAPCs) to differentiate into hepatocytes with hepatocyte growth factor (HGF)/ fibroblast growth factor-4 (FGF-4) in vitro. METHODS: (1) Obtaining the hMAPCs. Bone marrow was obtained from volunteers and then centrifuged through density gradient centrifugation methods. The collected mononuclear cells were cultured through adheret culture to get mesenchymal stem cells (MSCs). The hMAPCs were obtained through collecting and isolating the MSCs by magnetic activated cell sorting (MACS) through depletion selection by use of CD45 and GlyA microbeads. (2) Differentiation of the hMAPCs with HGF+FGF-4. Group A: HGF (20 ng/ml) + FGF-4 (10 ng/ml) induced hMAPCs; group B (positive control group): L-02 human hepatocytes(cell lines); and group C (negative control group): the undifferentiated hMAPCs. (3) The expressions of albumin (Alb), alpha fetoprotein (AFP), cytokeratin-18 (CK-18), and cytokeratin-19 (CK-19) were detected with immunocytochemistry to identify the characteristics of the differentiated cells at different times and the ratio of the positive cells was determined. (4) ALB, AFP, CK-18, and CK-19 expressions of the differentiated cells were detected by RT-PCR assay to investigate the mRNA transcriptions of characteristic hepatic proteins. (5) Alb expressions of the differentiated cells at different times were detected by Western blot on the 21st and 35th days. RESULTS: (1) The results of immunocytochemistry. The staining of Alb, CK18 were essentially positive in group A. As an early marker of immature hepatocytes, AFP staining was positive on the 7th day but negative in later differentiating periods in group A. (2) The results of RT-PCR. On the 7th day, the differentiated hMAPCs expressed AFP mRNA but were negative in later differentiating periods. On the contrary, the mRNA of Alb and CK-18 were positive at all times. (3) The results of Western blot assay. Alb protein was positive on the 21st day and 35th day. CONCLUSIONS: Under some definite inducing conditions hMAPCs can differentiate into hepatocyte-like cells. They may serve as a potential cell source for liver engineering.

Bone Marrow Cells↗
PubMed2005

Cloning, expression and characterization of the Ste6 gene encoding a UDP-glucose dehydrogenase in Streptomyces.

Streptomyces sp. 139 was identified to produce a new exopolysaccharide Ebosin (139A) with antirheumatic arthritis activity in vivo. The Ebosin biosynthesis gene cluster(31.3 kb; GenBank Accession Number: AY131229) containing 22 ORFs (ste1-ste22) of Streptomyces sp. 139 had been reported previously. In this paper,we present experimental evidence for the identity of the ste6 gene product as a UDP-glucose dehydrogenase (UDPGDH). With pET-30a as vector,the gene was cloned and expressed in Escherichia coli BL21 (DE3). The expressed protein was purified to homogeneity by His-Bind resin affinity chromatograpy and it was able to catalyze UDP-glucose to UDP-glucuronic acid. To evaluate the function of ste6, the gene was disrupted by a single-crossover homologous recombination event and the result showed that ste6 is required in Ebosin biosynthesis.

Amino Acid Sequence↗