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Biomedical subjects

F Ding

Publications and source records attributed to F Ding.

At least 19 recordsLinked to original sources
PubMed2005

Apoptosis-stimulating protein of p53-2 (ASPP2/53BP2L) is an E2F target gene.

The p53 pathway is a central apoptotic regulator. Deregulation of the Rb/E2F pathway occurs in a majority of tumors, resulting in both unrestrained proliferation and enhanced apoptosis sensitivity via p53-dependent and independent mechanisms. However, the mechanisms coupling the p53 and Rb/E2F pathways remain incompletely understood. We report that ASPP2/53BP2L, a p53/p73-binding protein that promotes p53/p73-dependent apoptosis, is an E2F target gene. The ASPP2/53BP2L promoter was identified and ectopic expression of transcription-competent E2F-1 (E2F-2 and E2F-3) stimulated an ASPP2/53BP2L promoter-luciferase reporter. Mutational analysis of the ASPP2/53BP2L promoter identified E2F-binding sites that cooperate for E2F-1 induction and basal repression of ASPP2/53BP2L. Moreover, endogenous ASPP2/53BP2L levels increased after E2F-1 expression, and E2F-1 bound the endogenous ASPP2/53BP2L promoter after chromatin immunoprecipitation. Typical for an E2F target, ASPP2/53BP2L expression was maximal in early S-phase. Thus, ASPP2/53BP2L is downstream of E2F, suggesting that it functions as a common link between the p53/p73 and Rb/E2F apoptotic pathways.

Apoptosis↗
PubMed2004

Discrete molecular dynamics simulations of peptide aggregation.

We study the aggregation of peptides using the discrete molecular dynamics simulations. Specifically, at temperatures above the alpha-helix melting temperature of a single peptide, the model peptides aggregate into a multilayer parallel beta-sheet structure. This structure has an interstrand distance of 4.8 A and an intersheet distance of 10 A, which agree with experimental observations. Our model explains these results as follows: hydrogen-bond interactions give rise to the interstrand spacing in beta sheets, while Gō interactions between side chains make beta strands parallel to each other and allow beta sheets to pack into layers. An important feature of our results is that the aggregates contain free edges, which may allow for further aggregation of model peptides to form elongated fibrils.

Amyloid beta-Peptides↗
PubMed2004

Molecular dynamics simulation of amyloid beta dimer formation.

Recent experiments with amyloid beta (Abeta) peptide indicate that formation of toxic oligomers may be an important contribution to the onset of Alzheimer's disease. The toxicity of Abeta oligomers depends on their structure, which is governed by assembly dynamics. Due to limitations of current experimental techniques, a detailed knowledge of oligomer structure at the atomic level is missing. We introduce a molecular dynamics approach to study Abeta dimer formation. 1), We use discrete molecular dynamics simulations of a coarse-grained model to identify a variety of dimer conformations; and 2), we employ all-atom molecular mechanics simulations to estimate thermodynamic stability of all dimer conformations. Our simulations of a coarse-grained Abeta peptide model predicts 10 different planar beta-strand dimer conformations. We then estimate the free energies of all dimer conformations in all-atom molecular mechanics simulations with explicit water. We compare the free energies of Abeta(1-42) and Abeta(1-40) dimers. We find that 1), dimer conformations have higher free energies compared to their corresponding monomeric states; and 2), the free-energy difference between the Abeta(1-42) and the corresponding Abeta(1-40) dimer conformation is not significant. Our results suggest that Abeta oligomerization is not accompanied by the formation of thermodynamically stable planar beta-strand dimers.

Amyloid beta-Peptides↗
PubMed2001

Determination of the molecular mass distribution of synthetic polymers by size-exclusion electrochromatography.

The performance of size-exclusion electrochromatography (SEEC) for the mass distribution analysis of synthetic polymers was studied and compared to conventional, pressure-driven size-exclusion chromatography (SEC). Electroosmotic flow control, within-day, day-to-day and column-to-column repeatability were determined for SEEC with respect to retention and separation efficiency. It was shown that by using the retention ratio instead of the migration time, the precision of the mass distribution calculations is sufficiently high, and that similar distributions were obtained for a sample analyzed by pressure-driven SEC and by SEEC. Furthermore, hexafluoroisopropanol was demonstrated to be a new and potent solvent for SEEC. It was used for the separation of narrow polymethylmethacrylate standards and several commercially important polymers such as polycarbonate, polycaprolactam and poly(ethylene terephthalate), using UV detection in the deep UV region (195-230 nm).

Chromatography, Gel↗
PubMed2001

Oscillatory electroosmosis-enhanced intra/inter-particle liquid transport and its primary applications in the preparative electrochromatography of proteins.

The concept of generating an oscillatory electroosmotic flux inside the porous particle to enhance the intra-particle mass transport was presented and a new kind of electrochromatography carried out in a five-compartment electrolyzer were developed. The adsorbent was packed in the central compartment, while the neighboring compartments were used as the elution compartments and the electrode compartments, respectively. Chromatographic separations of human serum albumin on Blue Sepharose Fast Flow, bovine serum albumin (BSA) on DEAE-Sepharose Fast Flow, and BSA on hydroxyapatite were carried out, respectively. The adsorption isotherms were shown to be independent of electric field, while the increase in the electric field strength resulted in a linear increase in the magnitude of electroosmotic flux and the improvement of the breakthrough behavior in all cases. The experiment results have demonstrated the effectiveness of the oscillatory electroosmosis in enhancing intra- and inter-particle mass transport and its high potential to large-scale chromatography.

Adsorption↗
PubMed2001

Genomic imprinting disrupted by a maternal effect mutation in the Dnmt1 gene.

Maintenance of genomic methylation patterns in mammalian somatic cells depends on DNA methyltransferase-1 (Dnmt1). Mouse oocytes and preimplantation embryos lack Dnmt1 but express a variant of this protein called Dnmt1o. We eliminated Dnmt1o by deletion of the oocyte-specific promoter and first exon from the Dnmt1 locus. Homozygous animals were normal, but most heterozygous fetuses of homozygous females died during the last third of gestation. Although genomic methylation patterns were established normally in Dnmt1o-deficient oocytes, embryos derived from such oocytes showed a loss of allele-specific expression and methylation at certain imprinted loci. Transient nuclear localization of Dnmt1o in 8-cell embryos suggests that this variant of Dnmt1 provides maintenance methyltransferase activity specifically at imprinted loci during the fourth embryonic S phase.

Animals↗
PubMed2001

Overexpression of Na+/Ca2+ exchanger alters contractility and SR Ca2+ content in adult rat myocytes.

The functional consequences of overexpression of rat heart Na+/Ca2+ exchanger (NCX1) were investigated in adult rat myocytes in primary culture. When maintained under continued electrical field stimulation conditions, cultured adult rat myocytes retained normal contractile function compared with freshly isolated myocytes for at least 48 h. Infection of myocytes by adenovirus expressing green fluorescent protein (GFP) resulted in >95% infection as ascertained by GFP fluorescence, but contraction amplitude at 6-, 24-, and 48-h postinfection was not affected. When they were examined 48 h after infection, myocytes infected by adenovirus expressing both GFP and NCX1 had similar cell sizes but exhibited significantly altered contraction amplitudes and intracellular Ca2+ concentration ([Ca2+]i) transients, and lower resting and diastolic [Ca2+]i when compared with myocytes infected by the adenovirus expressing GFP alone. The effects of NCX1 overexpression on sarcoplasmic reticulum (SR) Ca2+ content depended on extracellular Ca2+ concentration ([Ca2+]o), with a decrease at low [Ca2+]o and an increase at high [Ca2+]o. The half-times for [Ca2+]i transient decline were similar, suggesting little to no changes in SR Ca2+-ATPase activity. Western blots demonstrated a significant (P < or = 0.02) threefold increase in NCX1 but no changes in SR Ca2+-ATPase and calsequestrin abundance in myocytes 48 h after infection by adenovirus expressing both GFP and NCX1 compared with those infected by adenovirus expressing GFP alone. We conclude that overexpression of NCX1 in adult rat myocytes incubated at high [Ca2+]o resulted in enhanced Ca2+ influx via reverse NCX1 function, as evidenced by greater SR Ca2+ content, larger twitch, and [Ca2+]i transient amplitudes. Forward NCX1 function was also increased, as indicated by lower resting and diastolic [Ca2+]i.

Adenoviridae↗
PubMed2001

[The application of air-lift loop column filling with porous carrier in wastewater treatment].

An air lift loop reactor filling with porous carrier particles was utilized as aeration column. Experiments were carried out in wide operating conditions. The experimental results showed that in the range of gas flow rate from 0.117 to 0.156 m3/(min.m3), a higher efficiency of removal of ammonium-N was achieved, and when the gas flow rate was above 0.039 m3/(min.m3), the COD was completely degraded in about 1 h. The filling ratio of the porous carriers in the column was an important factor for the removal of C and N compounds, and a filling ratio of 15% was proved to be most suitable in the operation ranges. The experimental results also indicated that the effect of aeration temperature on the removal efficiency was significant and the highest efficiency was obtained at around 25 degrees C.

Nitrogen↗
PubMed2001

[Apoptosis during placentation].

Apoptosis is a normal physiological phenomenon. During the process of implantation, there are a large number of cells at the implantation site undergoing apoptosis, which has been suggested to play an important role in the regulation of endometrium decidulization and trophoblast invasion. Apoptosis mediated by Fas/FasL system may also be associated with maternal immunotolerance to the fetus. In this review, the common pathway of apoptosis and the regulation in the placenta are described.

Apoptosis↗
PubMed2000

Synergetic effect of dialyzer membrane and lipopolysaccharide on peripheral blood mononuclear cell cytokine production in uremic patients.

OBJECTIVE: To investigate the effect of lipopolysaccharide(LPS) and dialyzer membrane on cytokine gene expression and protein production in uremic patients on continuous ambulatory peritoneal dialysis (CAPD) and regular hemodialysis(HD). METHODS: Interleukin-1 beta (IL-1 beta) and interleukin-1 receptor antagonist (IL-1Ra) produced by cultured peripheral blood mononuclear cells (PBMC) after exposure to cuprammonium (Cup) membrane, polysulfone (PS) membranes or endotoxin were detected using enzyme-linked immunoabsorbent assay. mRNA expression was determined simultaneously by in situ hybridization. RESULTS: In the absence of endotoxin, a small amount of IL-1 beta and IL-1 Ra was produced by PBMC harvested from HD and CAPD patients after incubation with Cup or PS during subsequent 24-hour culture. For healthy controls, IL-1 beta was barely detectable just above the detection limit. Although no differences could be found in protein synthesis between Cup and PS, in situ hybridization showed that Cup induced markedly higher level mRNA coding for IL-1 beta and IL-1Ra. In contrast, when subsequently stimulated with endotoxin, PBMC incubated with Cup could produce significantly larger amount of IL-1 beta and IL-1Ra compared with either unstimulated cells or post-incubation PBMC with PS. LPS-stimulated PBMC in healthy subjects produced similar amount of IL-1 beta and markedly lower IL-1Ra as compared with uremic patients on HD and CAPD. CONCLUSIONS: Two steps are required in healthy control for IL-1 beta and IL-1Ra production: induction of mRNA transcription by membrane contact, followed by LPS-induced translation, while in uremic patients on HD or CAPD bioincompatibility-membrane and LPS have a synergetic effect on IL-1 beta and IL-1Ra production. There exists an unbalance between IL-1 beta and its specific inhibitor in maintenance dialysis patients.

Adult↗
PubMed1999

Experimental studies on affinity chromatography in an electric field.

A multicompartment electrolyzer, which has been used for preparative electrophoresis [Z. Liu, Z. Huang, J.-Y. Cong, et al., Sep. Sci. Technol. 31 (1996) 427], is applied for carrying out affinity chromatography in an alternating electric field. The effect of electric field strength on the adsorption and desorption characteristics is experimentally examined with human serum albumin and Blue Sepharose Fast Flow as a model system. It is shown that the existence of an electric field leads to a significant change in the adsorption capacity of the blue dye, which may be used for establishing a preferential adsorption to achieve a high resolution. The adsorption speed increases slightly with respect to the increase of electric field strength, while adsorption capacity in the presence of an electric field is independent of the electric field strength. Different elution behavior is observed as function of adsorption condition and a high recovery of the adsorbed protein is obtained when the adsorption is carried out in the presence of an electric field.

Buffers↗
PubMed1999

Identification of a protein component of a mammalian tRNA(Sec) complex implicated in the decoding of UGA as selenocysteine.

This report describes a novel RNA-binding protein, SECp43, that associates specifically with mammalian selenocysteine tRNA (tRNA(Sec)). SECp43, identified from a degenerate PCR screen, is a highly conserved protein with two ribonucleoprotein-binding domains and a polar/acidic carboxy terminus. The protein and corresponding mRNA are generally expressed in rat tissues and mammalian cell lines. To gain insight into the biological role of SECp43, affinity-purified antibody was employed to identify its molecular partners. Surprisingly, the application of native HeLa cell extracts to a SECp43 antibody column results in the purification of a 90-nt RNA species identified by direct sequencing and Northern blot analysis as tRNA(Sec). The purification of tRNA(Sec) by the antibody column is striking, based on the low abundance of this tRNA species. Using recombinant SECp43 as a probe for interacting protein partners, we also identify a 48-kDa interacting protein, which is a possible component of the mammalian selenocysteine insertion (SECIS) pathway. To our knowledge, SECp43 is the first cloned protein demonstrated to associate specifically with eukaryotic tRNA(Sec).

Amino Acid Sequence↗
PubMed1999

[Frequent loss of fragile histidine triad gene transcripts in lung cancer].

OBJECTIVE: To investigate the significance of the fragile histidine triad (FHIT) gene in evaluation of early diagnosis and metastasis in lung cancer. METHODS: 47 lung cancer samples and 16 matched metastatic hilar lymph nodes of lung cancer patients were examined for abnormalities of the gene by using RT-PCR and RT-PCR-SSCP. RESULTS: 32 of 47 (68%) lung cancer samples and 15 of 16 metastatic hilar lymph nodes showed loss of FHIT gene transcripts (exon5-9 or exon1-4). RT-PCR-SSCP reveal no variants. CONCLUSIONS: These data indicate that loss of FHIT gene transcript is frequent in lung cancer and may be an early event in lung tumorigenesis and FRA3B may be involved in the development and progression of the lung cancer.

Acid Anhydride Hydrolases↗
PubMed1999

[The effects of lead poisoning on expression of nerve growth factor gene of submandibular gland in mice].

OBJECTIVE: To study the toxicity of lead poisoning to submandibular gland and its effects on nerve growth factor (NGF) gene expression in mice. METHODS: An experimental model with lead poisoning was established and its histopathological changes in the submandibular gland of mice were observed under light and electronic microscopes. Effects of lead poisoning on expression of NGF mRNA in submandibular gland were analyzed quantitatively by human NGF DNA probe labelled with digoxin with in situ hybridization. RESULTS: Body weight of the mice with experimental lead poisoning reduced, and their lead levels in blood and submandibular gland increased. Lobular atrophy, fibrous hypertrophy, angiectasis of the stroma and enlargement of lobule interstitial in mouse submandibular gland with lead poisoning could be found under light and electron microscopes. Their rough surfaced endoplasmic reticulum was extended and mitochondrion swollen. Graphic analysis showed that diameters of the secretory striate ducts and granular tubules decreased in the mice with lead poisoning. Results of in situ hybridization indicated that hybridized signals in the granular and secretory striate ducts and granular tubules reduced significantly, and NGF mRNA expression decreased. CONCLUSION: Lead is toxic to the submandibular gland of mice and can affect their NGF gene expression.

Animals↗
PubMed1998

Electrophoretic affinity chromatography: method validation.

A new method for preparative-scale separation of biomolecules, electrophoretic affinity chromatography (EAC), is proposed in this paper. Separation by EAC is carried out in a long and ribbon-like multicompartment electrolyser separated by membranes, in which the two central compartments are used for packing the gel matrix and for sample loading respectively. Next to the central compartments are the elution compartments and electrode compartments. The electric field is applied perpendicular to the fluid flow in the compartments. Adsorption and desorption steps may both be carried out in the presence of an electric field, which transports the target components into the gel compartment for adsorption and the impurities into the elution compartments for washing. After the adsorption step an elution solution is introduced and the product is released from the gel matrix and washed out. Separation of human serum albumin (HSA) from human serum gives HSA product of high purity, as demonstrated by isoelectric focusing analysis. The characteristics of electrophoretic binding of HSA on Blue Sepharose Fast Flow are examined. The preliminary results show that this new method has advantages in terms of high rate of mass transfer and ease of scaling up, which are of particular interest when large-scale separation of biomolecules is considered.

Adsorption↗
PubMed1998

[Effect of herbs 814 on tumor necrosis factor a production from alveolar macrophages in vitro].

OBJECTIVE: To study the influence of herbs 814 on the secretion of tumor necrosis factor alpha (TNF-alpha) from hamster alveolar macrophages (AMs) in vitro and elucidate mechanism of herbs 814's prevention of emphysema. METHODS: AMs of hamster were collected by bronchial alveolar lavage (BAL). The lung lavage cells were adjusted to 5 x 10(5)/ml and seeded in each well of a 24-well tissue culture plates. The herbs 814 was added into these wells before or after lipopolysaccharide (LPS) stimulation and then cultured supernatants were collected. TNF-alpha production in the supernatants was tested by ELISA, TNF-alpha cytotoxicity was assayed using L929 cells which were susceptible to TNF-alpha and a monoclonal antibody (MAb) that neutralizes rhTNF-alpha was utilized to identify the cytotoxicity of cultured TNF-alpha. RESULTS: ELISA showed that TNF-alpha production in the supernatants with 814 added was lower than those either in LPS-stimulated or non LPS-stimulated supernatants and there was a significant decrease in the supernatants of higher concentration (1:5) of herbs 814. Cytotoxicity test showed that TNF-alpha cytotoxic activity in the supernatants into which herbs 814 was added was lower than one in the LPS-stimulated supernatants and there was a significant decrease in the supernatants of higher concentration (1:5) of herbs 814. Meanwhile, MAb significantly reduced cytotoxicity of LPS-stimulated culture supernatants. CONCLUSIONS: Herbs 814 could inhibit the secretion of TNF-alpha and prevent the lung damage mediated by TNF-alpha.

Animals↗