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Biomedical subjects

K Du

Publications and source records attributed to K Du.

At least 19 recordsLinked to original sources
PubMed2006

Semi-nested PCR detection of Babesia orientalis in its natural hosts Rhipicephalus haemaphysaloides and buffalo.

Babesiosis has recently been recognized as an emerging infectious disease of buffalo in China. In order to investigate the epidemiology and enzootic potential of this parasite in Hubei province, we sought to develop a semi-nested PCR to detect Babesia orientalis in buffalo and the potential tick vector-Rhipicephalus haemaphysaloides by amplifying a specific 257bp fragment of B. orientalis 18S rRNA gene. The practical limit of detection showed that it had high sensitivity and an approximate parasitemia of 0.00000012% was detected by the PCR system. The blood samples of 121 asymptomatic buffaloes collected from four babesia endemic counties and that of 71 asymptomatic buffaloes collected from three babesia free counties in Hubei province of China were examined for the presence of B. orientalis using both Wright-Giemsa stained blood smear and semi-nested PCR. Microscopic examination revealed that 5/121 animals were positive, whereas 24/121 animals were positive by the semi-nested PCR assay. Of 378 ticks (R. haemaphysaloides) collected from buffaloes and examined by the semi-nested PCR, 35 were positive. The results showed that the semi-nested PCR was a useful method to investigate the epidemiology of buffalo babesiosis (B. orientalis), which is widely distributed in Hubei province, China.

Animals↗
PubMed2006

Quantitative comparison of image contrast and pattern between experimental and simulated high-resolution transmission electron micrographs.

Aiming to determine the contrast mismatch factor i.e. the Stobbs factor between the experimental and simulated high-resolution transmission electron micrographs, we have systematically compared the experimental images and simulations of a cleaved silicon sample for a series of focal settings and specimen thicknesses. For zero-loss energy filtered images, a mismatch factor of about 1.5-2.3 is measured for the image contrast, where the mismatch factor is focal dependent and higher mismatch appears around the focus value of 10nm. Attention is also given to the effects of the sample vibration and drift to the image contrast and pattern of the high-resolution micrographs.

Journal Article↗
PubMed2005

Demonstration of bulk acceleration of ions in ultraintense laser interactions with low-density foams.

Ion acceleration inside low-density foams irradiated by ultraintense laser pulses has been studied experimentally and theoretically. It is found that the ion generation is closely correlated with the suppressed hot electron transport inside the foams. Particle-in-cell simulations suggest that localized electrostatic fields with multi peaks around the surfaces of lamellar layers inside the foams are induced. These fields inhibit hot electron transport and meanwhile accelerate ions inside the foams, forming a bulk acceleration in contrast to the surface acceleration at the front and rear sides of a thin solid target.

Journal Article↗
PubMed2005

Measurement of crystal thickness and orientation from selected-area Fourier transformation of a high-resolution electron hologram.

Precise knowledge of crystal thickness and orientation is critical for reliable interpretation of high-resolution transmission electron micrographs. In this paper, we propose a criterion of S(2)(T, u, v), which measures the crystal thickness by intensity matching of the selected-area Fourier transform of experimental holograms with the calculated electron diffraction pattern at a series of trial thicknesses (T) and crystal tilts (u, v). This criterion has been demonstrated successfully for local thickness determination from a simulated high-resolution image of a wedge-shaped YBa(2)Cu(3)O(7-delta) and from an experimental hologram of a Si crystal.

Crystallization↗
PubMed2002

Correction of aberration for a high-resolution electron hologram by means of the amplitude contrast criterion of image wave.

In order to further improve the resolution for a high-resolution electron hologram, the aberration working on the hologram must be corrected. Since it is rather difficult to precisely control aberration coefficients in the experimental stage, we proposed an amplitude contrast D criterion of imaging wave to determine the working aberration from the hologram itself. In the determination or correction of the aberration, we assume a symmetrical aberration function is parameterized only by a spherical aberration coefficient and a defocus value. First, D is calculated from a holographically reconstructed imaging wave of YBa(2)Cu(3)O(7-x) for each combination of these parameters. The working aberration on the imaging wave is determined from the combination of the parameters by noting the maximum or minimum D of the imaging wave at some specifically chosen thickness regions. The theoretical validity for the D criterion is then proved with three-beam dynamical diffraction formula. Finally, the 'experimental' examination for the D criterion is successfully performed on the reconstructed image wave for the Sigma=9 interface structure of a wedge-shaped silicon sample.

Journal Article↗
PubMed2001

A transcriptional switch mediated by cofactor methylation.

We describe a molecular switch based on the controlled methylation of nucleosome and the transcriptional cofactors, the CREB-binding proteins (CBP)/p300. The CBP/p300 methylation site is localized to an arginine residue that is essential for stabilizing the structure of the KIX domain, which mediates CREB recruitment. Methylation of KIX by coactivator-associated arginine methyltransferase 1 (CARM1) blocks CREB activation by disabling the interaction between KIX and the kinase inducible domain (KID) of CREB. Thus, CARM1 functions as a corepressor in cyclic adenosine monophosphate signaling pathway via its methyltransferase activity while acting as a coactivator for nuclear hormones. These results provide strong in vivo and in vitro evidence that histone methylation plays a key role in hormone-induced gene activation and define cofactor methylation as a new regulatory mechanism in hormone signaling.

Acetyltransferases↗
PubMed2001

A novel active L1 retrotransposon subfamily in the mouse.

Unlike human L1 retrotransposons, the 5' UTR of mouse L1 elements contains tandem repeats of approximately 200 bp in length called monomers. Multiple L1 subfamilies exist in the mouse which are distinguished by their monomer sequences. We previously described a young subfamily, called the T(F) subfamily, which contains approximately 1800 active elements among its 3000 full-length members. Here we characterize a novel subfamily of mouse L1 elements, G(F), which has unique monomer sequence and unusual patterns of monomer organization. A majority of these G(F) elements also have a unique length polymorphism in ORF1. Polymorphism analysis of G(F) elements in various mouse subspecies and laboratory strains revealed that, like T(F), the G(F) subfamily is young and expanding. About 1500 full-length G(F) elements exist in the diploid mouse genome and, based on the results of a cell culture assay, approximately 400 G(F) elements are potentially capable of retrotransposition. We also tested 14 A-type subfamily elements in the assay and estimate that about 900 active A elements may be present in the mouse genome. Thus, it is now known that there are three large active subfamilies of mouse L1s; T(F), A, and G(F), and that in total approximately 3000 full-length elements are potentially capable of active retrotransposition. This number is in great excess to the number of L1 elements thought to be active in the human genome.

3' Untranslated Regions↗
PubMed2001

Chromatin-dependent cooperativity between constitutive and inducible activation domains in CREB.

The cyclic AMP (cAMP)-responsive factor CREB induces target gene expression via constitutive (Q2) and inducible (KID, for kinase-inducible domain) activation domains that function synergistically in response to cellular signals. KID stimulates transcription via a phospho (Ser133)-dependent interaction with the coactivator paralogs CREB binding protein and p300, whereas Q2 recruits the TFIID complex via a direct association with hTAF(II)130. Here we investigate the mechanism underlying cooperativity between the Q2 domain and KID in CREB by in vitro transcription assay with naked DNA and chromatin templates containing the cAMP-responsive somatostatin promoter. The Q2 domain was highly active on a naked DNA template, and Ser133 phosphorylation had no additional effect on transcriptional initiation in crude extracts. Q2 activity was repressed on a chromatin template, however, and this repression was relieved by the phospho (Ser133) KID-dependent recruitment of p300 histone acetyltransferase activity to the promoter. In chromatin immunoprecipitation assays of NIH 3T3 cells, cAMP-dependent recruitment of p300 to the somatostatin promoter stimulated acetylation of histone H4. Correspondingly, overexpression of hTAFII130 potentiated CREB activity in cells exposed to cAMP, but had no effect on reporter gene expression in unstimulated cells. We propose that cooperativity between the KID and Q2 domains proceeds via a chromatin-dependent mechanism in which recruitment of p300 facilitates subsequent interaction of CREB with TFIID.

Animals↗
PubMed2001

[Effect of zinc on adrenocorticotropic hormone secretion in the pituitary cell line AtT-20].

The effect of zinc on adrenocorticotropic hormone (ACTH) secretion in the pituitary cell line AtT-20 was studied. Different concentrations of zinc(10(-8) to 1 mmol/L) were added to the medium and ACTH was determined 12 hours later. The findings revealed that zinc within certain concentrations could promote the secretion of ACTH in AtT-20 cells.

Adrenocorticotropic Hormone↗
PubMed2000

Stimulation of MCF-7 cell proliferation by low concentrations of Chinese domestic polychlorinated biphenyls.

The simple and sensitive in vitro MCF-7 human breast cancer cell proliferation assay was used to examine the proliferation abilities of two Chinese commercial polychlorinated biphenyl (PCB) mixtures made in the 1960s. Chinese PCB3 and Chinese PCB5 were compared with 17 beta-estradiol (E2). All of the positive activities of these types of Chinese PCBs were significantly different compared to controls with respect to MCF-7 cell doubling time. At lower levels of 7.8 pg/ml and 182 pg/ml, the Chinese PCB3 showed 94% and 86% of relative proliferation effects compared to 17 beta-estradiol, respectively. Chinese PCB5, also showed higher cell proliferation activity at lower level of 8.3 pg/ml, with relative proliferation effect as high as 107% in comparison to 17 beta-estradiol. Thus, both PCBs seem to be different from corresponding Aroclor mixtures. However, Chinese PCBs did not express cell proliferation effects at higher levels of 9.1 ng/ml for Chinese PCB3 and 166 pg/ml and 8.3 ng/ml for Chinese PCB3. This may be due to cytotoxicity and/or antiestrogenic compounds in the mixtures.

Breast Neoplasms↗
PubMed2000

Critical loads of acidity for surface waters in China.

For further control of acid rain and sulphur dioxide pollution, the Chinese government has designated the Acid Rain Control Zone and the Sulphur Dioxide Pollution Control Zone for those areas that are, or could become, affected by acid deposition or ambient sulphur dioxide concentrations. One of the most important principles for designating the Acid Rain Control Zone is that the critical load is exceeded by the sulphur deposition. Through the steady-state water chemistry method (SSWC), critical loads of acidity for surface waters were mapped based on available data. Results show that surface waters sensitive to acid deposition, i.e. surface waters with low critical loads, are mainly found in north-east China, on the Tibetan Plateau, and in north-west China. Compared with the critical loads of soils, critical loads of surface waters are usually higher in almost all areas in China. The reason for very low critical loads of surface waters in some regions dominated by soils geologically not sensitive to acid deposition may be attributed to the low temperature, high altitude and low runoff. In contrast, surface waters in south China are not susceptible to acid deposition, and so far acidification of surface water has not been found in spite of the heavy acid rain. As can be seen from the critical load exceedance map, nearly 10% of the surface waters are subject to risk of acidification in 1995.

Acid Rain↗
PubMed2000

Synthesis and cytotoxicity of 2,4-disubstituted and 2,3,4-trisubstituted brominated pyrroles in murine and human cultured tumor cells.

The 2,4-disubstituted and 2,3,4-trisubstituted brominated pyrroles were successfully prepared and demonstrated potent cytotoxicity against the growth of suspended murine and human tumors, i.e. leukemia and lymphomas, acute monocytic leukemia, and HeLa-S3 uterine carcinoma. The brominated compounds were more selective in inhibiting the growth of tumors derived from human solid tumors. Nevertheless, activity with some of the derivatives occurred in the human KB nasopharynx, SW-480 colon, and HCT ileum adenocarcinoma, and lung A549 carcinoma screens. In Tmolt4 T cell leukemia cells DNA synthesis was reduced over 60 min from 25 to 100 microM followed by RNA synthesis reduction. De novo purine synthesis was retarded with the regulatory enzyme PRPP-amido transferase being markedly inhibited with less effects on the activities of IMP dehydrogenase, dihydrofolate reductase,, and the nucleoside kinases. After 60 min incubations d[TTP] and d[GTP] pools were marginally reduced. In vitro ct-DNA studies suggest that the agents may affect the DNA molecule itself with increased DNA viscosity and the Tmolt4 studies suggest that DNA cross-linking of DNA strands may be present.

Antineoplastic Agents↗
PubMed2000

Characterization of a CREB gain-of-function mutant with constitutive transcriptional activity in vivo.

The cyclic AMP (cAMP)-responsive factor CREB promotes cellular gene expression, following its phosphorylation at Ser133, via recruitment of the coactivator paralogs CREB-binding protein (CBP) and p300. CBP and p300, in turn, appear to mediate target gene induction via their association with RNA polymerase II complexes and via intrinsic histone acetyltransferase activities that mobilize promoter-bound nucleosomes. In addition to cAMP, a wide variety of stimuli, including hypoxia, UV irradiation, and growth factor addition, induce Ser133 phosphorylation with stoichiometry and kinetics comparable to those induced by cAMP. Yet a number of these signals are incapable of promoting target gene activation via CREB phosphorylation per se, suggesting the presence of additional regulatory events either at the level of CREB-CBP complex formation or in the subsequent recruitment of the transcriptional apparatus. Here we characterize a Tyr134Phe CREB mutant that behaves as a constitutive activator in vivo. Like protein kinase A (PKA)-stimulated wild-type CREB, the Tyr134Phe polypeptide was found to stimulate target gene expression via the Ser133-dependent recruitment of CBP and p300. Biochemical studies reveal that mutation of Tyr134 to Phe lowers the K(m) for PKA phosphorylation and thereby induces high levels of constitutive Ser133 phosphorylation in vivo. Consistent with its constitutive activity, Tyr134Phe CREB strongly promoted differentiation of PC12 cells in concert with suboptimal doses of nerve growth factor. Taken together, these results demonstrate that Ser133 phosphorylation is sufficient for cellular gene activation and that additional signal-dependent modifications of CBP or p300 are not required for recruitment of the transcriptional apparatus to the promoter.

Animals↗
PubMed2000

[Simultaneous determination of magnolol and honokiol in serum and urine by high performance liquid chromatography].

A reversed-phase high performance liquid chromatographic method for simultaneous determination of magnolol and honokiol in serum and urine of rat has been established. Two drugs were determined within 15 minutes by the method on the column with spherisorb C18, by using a mobile phase consisted of methanol-water-glacial acetic acid (70:30:1, V/V) at 1 mL/min, monitored at 294 nm and with a sensitivity of 0.005 AUFS. After 0.25, 1 and 8 hour of administration of the drugs, protein in serum and urine of Wistar rat was precipitated by methanol and magnolol and honokiol in acidified body fluid were determined after being extracted by a mixture of ethyl acetate and ether. Good linear relationship between concentration in serum and urine and peak area in the ranges of 0.05-2 mg/L for magnolol and 0.025-1 mg/L for honokiol was obtained. Good precision and reproducibility were found too. The average recoveries of the two drugs were 95.6% (RSD = 3.85%), 93.8% (RSD = 3.95%) in serum and 96.0% (RSD = 3.83%), 94.9% (RSD = 3.54%) for urine respectively. The lower limit of the method was 0.02 mg/L of magnolol and 0.04 mg/L of honokiol respectively. The results showed that this method is suitable for the determination of magnolol and honokiol in body fluids.

Animals↗
PubMed1999

Mitogenic up-regulation of the PRL-1 protein-tyrosine phosphatase gene by Egr-1. Egr-1 activation is an early event in liver regeneration.

The cellular signals that initiate cell growth are incompletely understood. Insight could be provided by understanding the signals regulating the transcriptional induction of immediate-early genes which occurs within minutes of the growth stimulus. The expression of the PRL-1 gene, which encodes a unique nuclear protein-tyrosine phosphatase, is rapidly induced in regenerating liver and mitogen-treated cells. Transcription of the PRL-1 gene increased in the rat liver remnant within a few minutes after partial hepatectomy and largely explained the increase in steady-state PRL-1 mRNA in the first few hours posthepatectomy. Egr-1 (early growth response factor) specifically bound a region of the proximal PRL-1 promoter P1 (-99). Egr-1 binding activity was more rapidly induced in regenerating liver than mitogen-treated H35 and NIH 3T3 cells, remained elevated through 4 h posthepatectomy, and appeared to be dependent not only on new Egr-1 protein synthesis but on post-translational regulation of Egr-1. Egr-1 efficiently transactivated a PRL-1 promoter reporter construct containing an intact not mutant Egr-1 site, and the Egr-1 site largely accounted for PRL-1 gene up-regulation in response to mitogen stimulation. These data predict that Egr-1 activation is an early event in liver regeneration and mitogen-activated cells that provides a regulatory stimulus for a subset of immediate-early genes.

3T3 Cells↗
PubMed1998

Transcriptional up-regulation of the delayed early gene HRS/SRp40 during liver regeneration. Interactions among YY1, GA-binding proteins, and mitogenic signals.

Arg-Ser-rich domain-containing proteins (SR proteins), a family of splicing factors, can regulate pre-mRNA alternative splicing in a concentration dependent manner. Thus, the relative expression of various SR proteins may play an important role in alternative splicing regulation. HRS/SRp40, an SR protein and delayed early gene in liver regeneration, can mediate alternative splicing of fibronectin mRNA. Here we determined that transcription of the HRS/SRp40 gene is induced about 5-fold during liver regeneration, similar to the level of steady-state mRNA. We found that both mouse and human HRS promoters lack TATA and CAAT boxes. The mouse promoter region from -130 to -18, which contains highly conserved GA-binding protein (GABP) and YY1 binding sites, conferred high transcriptional activity. While GABPalpha/GABPbeta heterodimer transactivated the HRS promoter, YY1 functioned as a repressor. During liver regeneration, the relative amount of GABPalpha/GABPbeta heterodimer increased 3-fold, and YY1 changed little, which could partially account for the increase in HRS gene transcription. Interleukin-6, a critical mitogenic component of liver regeneration, was able to relieve the repressive activity of the YY1 site within the HRS promoter. The combined effect of small changes in the level of existing transcription factors and mitogenic signals may explain the transcriptional activation of the HRS gene during cell growth.

Alternative Splicing↗