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Biomedical subjects

D Tang

Publications and source records attributed to D Tang.

At least 19 recordsLinked to original sources
PubMed2004

CCAAT/Enhancer binding protein delta (c/EBPdelta) regulation and expression in human mammary epithelial cells: II. Analysis of activating signal transduction pathways, transcriptional, post-transcriptional, and post-translational control.

CCAAT/enhancer binding protein delta (C/EBPdelta) plays a key role in mammary epithelial cell G0 growth arrest. C/EBPdelta gene expression is down-regulated in rodent mammary tumorigenesis and in human breast cancer, suggesting that "loss of function" alterations in C/EBPdelta gene expression are common in mammary gland malignancies. The goal of this study was to systematically investigate the mechanisms controlling C/EBPdelta gene expression in MCF-10A and MCF-12A human mammary epithelial cell lines. The results demonstrate that G0 growth arrest conditions (i.e., serum and growth factor withdrawal or Oncostatin M (OSM) treatment) result in the activation of JAK1, JAK2, and Tyk 2, members of the Janus kinase family of non-receptor tyrosine kinases, in MCF-10A and MCF-12A cells. Growth arrest or OSM treatment also specifically increases activated (phosphorylated) signal transduction and activators of transcription 3 (STAT3) levels, demonstrating that STAT3, not STAT1 or STAT5, is the downstream target of the activated Janus kinases in MCF-10A and MCF-12A cells. Whole cell lysates from G0 growth arrested (GA) and OSM-treated MCF-12A cells exhibit increased acute phase response element (APRE) binding compared to lysates from growing (GR) MCF-12A cells. Transient transfection using C/EBPdelta promoter-luciferase constructs demonstrated that the APRE (STAT3) consensus binding site is essential for growth arrest or OSM induction of the C/EBPdelta promoter. Mutation of the C/EBPdelta promoter STAT3 site or expression of a dominant negative STAT3 construct (STAT3delta) reduces C/EBPdelta promoter activity in response to growth arrest conditions. The human C/EBPdelta promoter also contains an Sp1 site at -61 bp (relative to the transcriptional start site) which is required for basal transcriptional activation. Mutation or deletion of the Sp1 site decreases promoter activity in response to growth arrest conditions. Treatment with the transcriptional inhibitor actinomycin D demonstrated that the C/EBPdelta mRNA exhibits a relatively short half-life (approximately 40 min). Similarly, treatment with the translational inhibitor anisomysin demonstrated that the C/EBPdelta protein half-life was also relatively short (approximately 160 min). These results indicate that the human C/EBPdelta gene is controlled at multiple levels, consistent with a role for C/EBPdelta in cell cycle control and/or cell fate determination.

Animals↗
PubMed2002

A study on the position of boron atoms in (Y(0.6)Ca(0.4))(SrBa)(Cu(2.5)B(0.5))O(7-delta).

The position of boron atoms in minute crystals of (Y(0.6)Ca(0.4))(SrBa)(Cu(2.5)B(0.5))O(7-delta) was studied by means of image processing based on the combination of high-resolution electron microscopy and electron diffraction. The structure image was obtained from a single image by image deconvolution based on the principle of maximum entropy. Its resolution is limited by that of the electron microscope. Then the image resolution was enhanced to about 1 A by direct-methods phase extension in combination with an empirical method of electron diffraction intensity correction. To study the substitution of boron atoms for copper, in the second cycle of diffraction intensity correction two different structure models were proposed. The one corresponding to a more reasonable atomic shape in the derived projected potential map (PPM) was accepted. In this model, the boron atoms are located at the 'chain' Cu sites.

Journal Article↗
PubMed2002

A possible role of initial cell death due to mechanical stretch in the regulation of subsequent cell proliferation in experimental vein grafts.

The proliferation of vascular cells contributes to the formation of neointima and hypertrophy of the blood vessel wall. Here we show that mechanical stretch possibly regulates the proliferation of vascular cells via the mediation of cell death in a rat vein graft model. The wall of vein grafts is subject to a suddenly increased mechanical stretch due to exposure to arterial blood pressure. Such a stretch induces rapid cell death with a reduction in cell density by approximately 60% within the first day after surgery. The initial cell death was followed by an increase in the percentage of proliferating cells, as shown by a BrdU incorporation assay (1.55 +/- 1.27%, 8.48 +/- 2.27%, 11.93 +/- 2.36%, 6.36 +/- 1.77%, and 5.60 +/- 1.46% at days 1, 5, 10, 20, and 30, respectively). When mechanical stretch was reduced by restraining the vein graft using a polytetrafluoroethylene sheath, the percentage of proliferating cells reduced significantly (0.76 +/- 0.76%, 1.70 +/- 0.46%, 1.29 +/- 0.56%, 0.99 +/- 0.83%, and 0.47+/-0.52% at days 1, 5, 10, 20, and 30, respectively). A further reduction in cell density, induced by local administration of a cell death inducer ceramide to experimental vein grafts (without sheath), enhanced subsequent cell proliferation. In contrast, a prevention of cell death, induced by local administration of a cell death inhibitor tetrapeptide-aldehyde DEVD-CHO to experimental vein grafts (without sheath), significantly reduced subsequent cell proliferation. These results suggest that mechanical stretch induces cell death, which possibly mediates subsequent cell proliferation in the present model.

Adaptation, Physiological↗
PubMed2001

Association between carcinogen-DNA adducts in white blood cells and lung cancer risk in the physicians health study.

In this matched case-control study nested within the prospective Physicians' Health Study, we evaluated whether DNA damage in blood samples collected at enrollment significantly predicted risk, consistent with our hypothesis that cases have greater biological susceptibility to polycyclic aromatic hydrocarbons and other aromatic tobacco carcinogens. The subjects were 89 cases of primary lung cancer and 173 controls, all males, matched on smoking, age, and duration of follow-up. Aromatic-DNA adducts were measured in WBCs by the nuclease P1-enhanced (32)P-postlabeling method that primarily detects smoking-related adducts. Among current smokers, but not former or nonsmokers, there was a significant increase in mean adduct levels of cases compared with controls (11.04 versus 5.63; P = 0.03). "Healthy" current smokers who had elevated levels of aromatic DNA adducts in WBCs were approximately three times more likely to be diagnosed with lung cancer 1-13 years later than current smokers with lower adduct concentrations (odds ratio, 2.98; 95% confidence interval, 1.05-8.42; P = 0.04). We were not able to discern case-control differences in former smokers and nonsmokers. The findings are of interest because they suggest that individuals who become cases have greater biological susceptibility to tobacco carcinogens, a biological difference, which manifests most clearly while exposure is ongoing.

Carcinogens↗
PubMed2001

Akt is activated in response to an apoptotic signal.

Akt is a serine-threonine kinase known to exert antiapoptotic effects through several downstream targets. Akt is cleaved during mitochondrial-mediated apoptosis in a caspase-dependent manner. The reason for this is not clear, however, because Akt has not been demonstrated to be activated in response to mitochondrial apoptotic stimuli. Accordingly, we explored whether the well described mitochondrial apoptotic stimuli staurosporine (STS) and etoposide activate Akt and whether such activation impacts apoptosis. Both STS and etoposide activated Akt in NIH 3T3 cells, maximally at 8 and 2 h, respectively, preceding the onset of apoptosis and poly(ADP-ribose) polymerase cleavage. The overexpression of Akt delayed STS-induced apoptosis with an even more pronounced delay observed with overexpression of constitutively active Akt. Akt activation by proapoptotic stimuli lay upstream of mitochondria, because neither caspase inhibitors nor overexpression of Bcl-2 or Bcl-x(L) could prevent it. Activation depended on phosphatidylinositol 3-kinase activity, however. Conversely, inhibition of phosphatidylinositol 3-kinase with wortmannin sensitized cells to apoptosis initiated by STS. These data demonstrate that mitochondrial apoptotic stimuli also activate Akt and such activation modulates apoptosis in this setting.

3T3 Cells↗
PubMed2001

Phosphorylation of vimentin head domain inhibits interaction with the carboxyl-terminal end of alpha-helical rod domain studied by surface plasmon resonance measurements.

The amino-terminal head domain of vimentin is the target site for several protein kinases and phosphorylation induces disassembly of the vimentin intermediate filaments in vivo and in vitro. To better understand molecular mechanisms involved in phosphorylation-dependent disassembly, we examined domain interactions involving the head domain and the effect of phosphorylation on the interaction, using surface plasmon resonance. We observed that the head domain binds to the carboxyl-terminal helix 2B in the rod domain, under physiological ionic strength. This interaction was interfered with by A-kinase phosphorylation of the head domain. Deletion of the carboxyl-terminal 20 amino acids of helix 2B resulted in loss of the interaction. Furthermore, peptide representing the carboxyl-terminal 20 residues of helix 2B had a substantial affinity with the head domain but not with the phosphorylated one. These findings support the idea that the interaction between the head domain and the last 20 residues of helix 2B is essential for association of vimentin tetramers into the intermediate filaments and that the phosphorylation-dependent disassembly is the result of loss of the interaction.

3T3 Cells↗
PubMed2001

Repression of the HSP70B promoter by NFIL6, Ku70, and MAPK involves three complementary mechanisms.

We have studied mechanisms of HSP70 gene regulation at 37 degrees C by the cellular factors NF-IL6 and Ku70. As both factors repress HSF1, we first examined whether phosphorylation on serine 303 and 307 of HSF1 by MAPK and GSK3, which has known to inhibit HSF1, was involved in the repression. However, repression by NF-IL6 was found using HSF1 mutants S303G and S307G refractory to the effects of MAPK and GSK3. We then examined whether NF-IL6 repressed HSP70B by a mechanism resembling Ku proteins. However, in Ku-deficient cells, NF-IL6 was still able to displace HSF1 from heat shock element (HSE) and repressed HSF1 activation. In addition, activation of the HSP 70B promoter by wild type, S303G, or S307G HSF1 was observed to be much more pronounced in Ku-deficient cells. In vitro translated Ku70 interacted with HSF1 by binding to and displacing it from HSE. These data indicate that the repression of the HSP70B promoter by NF-IL6, Ku70, and MAPK occurs independently of each other and involves three complementary mechanisms.

Amino Acid Substitution↗
PubMed2001

Comparison of photovoltaic behaviors for horseradish peroxidase and its mimicry by surface photovoltage spectroscopy.

Surface photovoltage spectroscopy (SPS) was chosen to study the photovoltaic behavior of horseradish peroxidase (HRP), hemin and immobilized hemin (poly(NIPAAm/MBA/hemin)). Different photovoltaic behaviors were observed in these three systems. In air, similar SPS curves were found for HRP and poly(NIPAAm/MBA/hemin) with different response intensities. However, poly(NIPAAm/MBA/hemin) showed a wider changing range upon increasing the positive and negative bias to 1.0 V. The SPS of hemin showed a total different behavior when an external positive potential was applied. In vacuum, clearly different photovoltaic behaviors were found. Moreover, the response value decreased when HRP was exposed to O2, the SPS intensity was different from that in air, and could be altered by changing the external biases. On the other hand, the SPS could not be changed before and after poly(NIPAAm/MBA/hemin) was exposed to O2. These differences may result from different chemical microenvironments for hemin in HRP versus that in poly(NIPAAm/MBA/hemin). It could be concluded that H2O and O2 were important factors affecting the photovoltage response in HRP, but only H2O played this important role in poly(NIPAAm/MBA/hemin).

Horseradish Peroxidase↗
PubMed2001

Negative regulation of defense responses in plants by a conserved MAPKK kinase.

The enhanced disease resistance 1 (edr1) mutation of Arabidopsis confers resistance to powdery mildew disease caused by the fungus Erysiphe cichoracearum. Resistance mediated by the edr1 mutation is correlated with induction of several defense responses, including host cell death. Double mutant analysis revealed that all edr1-associated phenotypes are suppressed by mutations that block salicylic acid (SA) perception (nim1) or reduce SA production (pad4 and eds1). The NahG transgene, which lowers endogenous SA levels, also suppressed edr1. In contrast, the ein2 mutation did not suppress edr1-mediated resistance and associated phenotypes, indicating that ethylene and jasmonic acid-induced responses are not required for edr1 resistance. The EDR1 gene was isolated by positional cloning and was found to encode a putative MAP kinase kinase kinase similar to CTR1, a negative regulator of ethylene responses in Arabidopsis. Taken together, these data suggest that EDR1 functions at the top of a MAP kinase cascade that negatively regulates SA-inducible defense responses. Putative orthologs of EDR1 are present in monocots such as rice and barley, indicating that EDR1 may regulate defense responses in a wide range of crop species.

Amino Acid Sequence↗
PubMed2001

Timing cell-cycle exit and differentiation in oligodendrocyte development.

During animal development many cells permanently stop dividing and terminally differentiate. For the most part, the mechanisms that control when the cells exit the cell cycle and differentiate are not known. We have been studying the mechanisms in the oligodendrocyte cell lineage. Studies of oligodendrocyte precursor cells (OPCs) in culture suggest that each OPC has a built-in timing mechanism that helps determine when the cell stops dividing and differentiates. This intrinsic timer consists of at least two components--a timing component, which measures elapsed time, and an effector component, which stops cell division and initiates differentiation at the appropriate time. The timer seems to involve both transcriptional and posttranscriptional mechanisms, with some proteins progressively increasing and others progressively decreasing over time.

Animals↗
PubMed2001

Glutathione transport in human retinal pigment epithelial (HRPE) cells: apical localization of sodium-dependent gsh transport.

The study was undertaken to identify and localize GSH transport in non-transformed cultured human retinal pigmented epithelial cells (HRPE). In confluent monolayers exhibiting high transepithelial resistance (TER 700-1000 Omega cm(-2)), apical and basolateral GSH uptake were determined after introducing(35)S-GSH (+ 1 m M GSH) to the apical side or basal side in NaCl (Na+ -containing) or choline chloride (Na+ -free) buffers. Cells in growth medium or in incubation buffers were pretreated with acivicin to inhibit gamma-glutamyltranspeptidase (GGT). GSH efflux was measured after labelling the intracellular GSH pool by incubation overnight with 35 S-cysteine and quantitating the release of labelled GSH into the medium. Uptake of GSH was found at both the apical and basolateral membranes of HRPE cells. Inhibition of gamma-glutamyltranspeptidase (GGT) with acivicin did not alter mean GSH uptake (nmol per million cells per 30 min) significantly at the apical (1.63 +/- 0.32 vs 1.45 +/- 0.30; with and without acivicin respectively) or the basolateral (1.17 +/- 0.21 vs 1.44 +/- 0.38) membranes. Transport was verified to be in the form of intact GSH by HPLC. Uptake was unaffected by the removal of Na+ at the basolateral membrane while apical uptake exhibited partial but significant (approximately 40%) Na+ -dependency. Net GSH efflux (nmol per million cells per min) to the apical side of HRPE cells was higher than to the basolateral side in the presence of sodium. Transepithelial flux in the basolateral to apical direction was approximately 17-fold higher than the apical to basolateral direction resulting in a net flux of GSH to the apical side. In conclusion, HRPE cells exhibit GSH transport by Na+ -dependent and Na+ -independent mechanisms. The Na+ -dependent GSH transporter is localized to the apical membrane of HRPE cells.

Biological Transport↗
PubMed2001

Expressional profiling of genes related to pollination and fertilization in rice.

Pollination and fertilization are key steps leading to seed and fruit formation. To obtain genes involved in pollination and fertilization in rice, an RNA fingerprinting technique, cDNA-AFLP (amplified fragment length polymorphism), was used to generate transcript profiles related to pollination. Of 15,000 cDNA fragments inspected, 2,100 showed altered expression in the pollinated pistil, of which about 1/5 were up-regulated (URP) and the rest down-regulated (DRP), suggesting that gene repression is a predominant mode of gene regulation in the pollinated pistil. Over 200 URP genes were sequenced and databank searches revealed that 70% of them represented previously unnoticed rice genes. DNA blot analysis of 20 URP genes detected no restriction fragment length polymorphisms (RFLP) between two relatively distant rice varieties, suggesting that the URP genes are highly conserved and likely play important roles in pollination and fertilization. Furthermore, two genes, URP47 and URP63, probably encoding an ADP-ribosylation factor and a membrane transporter, respectively, in relation to pollination were discussed.

DNA, Plant↗
PubMed2001

Steady flow and wall compression in stenotic arteries: a three-dimensional thick-wall model with fluid-wall interactions.

Severe stenosis may cause critical flow and wall mechanical conditions related to artery fatigue, artery compression, and plaque rupture, which leads directly to heart attack and stroke. The exact mechanism involved is not well understood. In this paper a nonlinear three-dimensional thick-wall model with fluid-wall interactions is introduced to simulate blood flow in carotid arteries with stenosis and to quantify physiological conditions under which wall compression or even collapse may occur. The mechanical properties of the tube wall were selected to match a thick-wall stenosis model made of PVA hydrogel. The experimentally measured nonlinear stress-strain relationship is implemented in the computational model using an incremental linear elasticity approach. The Navier-Stokes equations are used for the fluid model. An incremental boundary iteration method is used to handle the fluid-wall interactions. Our results indicate that severe stenosis causes considerable compressive stress in the tube wall and critical flow conditions such as negative pressure, high shear stress, and flow separation which may be related to artery compression, plaque cap rupture, platelet activation, and thrombus formation. The stress distribution has a very localized pattern and both maximum tensile stress (five times higher than normal average stress) and maximum compressive stress occur inside the stenotic section. Wall deformation, flow rates, and true severities of the stenosis under different pressure conditions are calculated and compared with experimental measurements and reasonable agreement is found.

Aortic Valve Stenosis↗
PubMed2001

Modeling of bottom backscattering from three-dimensional volume inhomogeneities and comparisons with experimental data.

In this paper, backscattering from 3D volume inhomogeneities in the seabed is modeled and the results compared with experimental data at 250-650 Hz. The experiment was part of the Acoustic Reverberation Special Research Program (ARSRP) and the data were obtained in a sediment pond on the western flank of the Mid-Atlantic Ridge. A volume scattering model based on first-order perturbation theory is developed incorporating contributions from both sound speed and density fluctuations. With the propagators, i.e., the Green's functions, handled accurately through numerical wave number integration and random fluctuations generated effectively by a new scheme modified from the spectral method, the model is capable of simulating monostatic, backscattered fields in the frequency domain as well as in the time domain owing to 3D volumetric sediment inhomogeneities. The model compares favorably and consistently with the ARSRP backscattering data over the entire frequency band, with the fluctuations of sound speed and density in two irregular sediment layers, identified from the data analysis, described by a power-law type of power spectrum.

Journal Article↗
PubMed2001

Anthropophobia: its meaning and concomitant experiences.

This study investigated the essential feature and concomitant experiences of anthropophobia, a culturally specific phobic disorder in China and Japan. One hundred and fifty subjects, including 50 anthropophobic, 50 neurasthenic and 50 normal subjects, were recruited from hospitals and downtown residential areas in Beijing. Measures of anthropophobic symptoms and DSM-III-R depressive and anxiety symptoms were administered to all subjects. Nonparametric analysis of variance, analysis of variance (ANOVA and MANOVA) and Fisher's exact test were performed to examine group differences on each symptomatic item of the three measures. Results indicate that the core anthropophobic symptoms include a fear of making eye contact with others and a fear of being watched by others, which essentially express fears of others' judgement or opinion of oneself. Anxiety and depression are associated features of anthropophobia. However, these concomitants are experienced more cognitively and less somatically in the case of anthropophobia than neurasthenia.

Adult↗
PubMed2001

[Acidity and acid buffering capacity of aerosols during sand-dust storm weather in Beijing].

In the spring of 2000, there were 12 sand-dust storms in Beijing. 2 sand-dust storms were experienced in time and mass concentrations, elementary concentrations acidity and acidic buffering capacity of TSP(Total Suspended Particulate, < 100 microns) and PM10(Inhalable particulate, < 10 microns) were sampled and analyzed. Results showed that pollution level of aerosols was extremely high. However, the acidity of aerosols was relatively low and the aerosols had very strong acid buffering capacity for acidification. Therefore, the aerosols brought about by the sand-dust storms could avoid the occurrence of acidic precipitation to some extent.

Acids↗
PubMed2001

Neuronal cdc-2 like kinase in developing kindling rat hippocampus.

OBJECTIVE: To test the hypothesis that neuronal cdc2-like kinase (Cdk5/p35nck5a) plays an important role in neuronal maturation and sprouting. METHODS: Changes kinase activity, expression levels and subcellular localizations of Cdk5 and p35nck5a in the rat hippocampus were studied during kindling progression by Western blot analysis, immunohistochemistry, immunoprecipitation and kinase assay. RESULTS: Kinase activity in kindling rats was significantly higher than that in normal adult rats. The kinase activity at stage 3 was most prominent among all stages of kindling progression. The changes in kinase activity coincided with those of p35nck5a expression in kindling rats. In contrast, the expression of Cdk5 was constant throughout the progression of kindling stages. However, subcellular localization of Cdk5 dramatically changed in the hippocampal neurons of kindling rats. Cdk5 was translocated from axon to soma when kinase activity was high. p35nck5a was always localized in the soma throughout kindling progression. CONCLUSIONS: Neuronal cdc2-like kinase plays an important role in synaptic reorganization, and the translocation of Cdk5 to the soma from the axon may be a novel regulatory mechanism to control kinase activity.

Animals↗