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Biomedical subjects

C Y Peng

Publications and source records attributed to C Y Peng.

At least 19 recordsLinked to original sources
PubMed2001

Speciation of As in the blackfoot disease endemic area.

Speciation of arsenic (As) in well water and contaminated soil in the blackfoot disease endemic area has been studied by extended X-ray absorption fine structural (EXAFS) spectroscopy in the present work. Experimentally, we found that arsenic in the well water possessed an As-O bond distance of 1.72 A with a coordination number (CN) of 4.3. In the blackfoot disease area, arsenic with a high oxidation state (As(V)) was also observed in the contaminated soil. In the early stage (after 90 minutes) of the electrokinetic remediation (EKR) of the contaminated soil, the in-situ EXAFS data indicated that the CN of As-O (1st shell) decreased slightly, that may be due to the perturbation of the incompact As atoms in the outer shells by EKR.

Arsenic↗
PubMed2001

Aging and development in social insects with emphasis on the honey bee, Apis mellifera L.

Honey bee colonies typically consist of about 20-40 thousand workers, zero to few thousand males (drones), depending on the time of year, and a single queen, the mother of the colony. Workers typically live 3-6 weeks during the spring and summer and can live about 4months during the winter. Queens are longer lived. Anecdotes of queens living 2-3years are not unusual, though they normally live less than a year in commercial hives. Little is known about the life span of drones. Queens develop from fertilized eggs that are not different from the eggs that develop into workers. Queens are, however, twice as large, have specialized anatomy, live much longer, and develop faster from egg to adult. All of these differences are derived from differences in larval rearing environment, primarily nutrition. The developmental trajectory of a female larva from worker into a queen can be determined as late as the third day of larval development, after this time the developmental pathway is fixed for a worker phenotype. The total time of larval development is only 5-6 days, therefore, just 2-3 days of differential feeding can lead to profound differences in development, and longevity. Workers undergo age development after they become adults. Workers usually initiate foraging behavior when they are 2-3 weeks old. The age at which a worker initiates foraging is a strong determinant of her length of life. This is presumed to be a result of the hazards of foraging, but natural senescence also occurs. Some bees remain in the nest and are never observed to forage, thereby outliving their forager sisters. Corresponding to this behavioral development are changes in the sizes of glands and the production of glandular products, increases in biogenic amine titers within the brain, an increase in the volume of specific regions of the brain, and changes in the neural system that affect perception of stimuli, and learning and memory. These age-related changes in behavior are regulated by intrinsic and extrinsic factors. Genetic variation has been demonstrated for many of these life history and behavioral traits. Selection and genome mapping studies have demonstrated relationships between the neural system, behavior, and life history traits.

Aging↗
PubMed2000

The tumour-suppressor genes lgl and dlg regulate basal protein targeting in Drosophila neuroblasts.

Drosophila neuroblasts are a model system for studying asymmetric cell division: they divide unequally to produce an apical neuroblast and a basal ganglion mother cell that differ in size, mitotic activity and developmental potential. During neuroblast mitosis, an apical protein complex orients the mitotic spindle and targets determinants of cell fate to the basal cortex, but the mechanism of each process is unknown. Here we show that the tumour-suppressor genes lethal giant larvae (lgl) and discs large (dlg) regulate basal protein targeting, but not apical complex formation or spindle orientation, in both embryonic and larval neuroblasts. Dlg protein is apically enriched and is required for maintaining cortical localization of Lgl protein. Basal protein targeting requires microfilament and myosin function, yet the lgl phenotype is strongly suppressed by reducing levels of myosin II. We conclude that Dlg and Lgl promote, and myosin II inhibits, actomyosin-dependent basal protein targeting in neuroblasts.

Amino Acid Sequence↗
PubMed2000

Aberrant transcripts of the cyclin-dependent kinase-associated protein phosphatase in hepatocellular carcinoma.

The cyclin-dependent kinase (Cdk)-associated protein phosphatase (KAP) is a human dual specificity protein phosphatase that dephosphorylates Cdk2 on threonine 160 in a cyclin-dependent manner. To investigate whether mutations of this enzyme occur in hepatocellular carcinoma (HCC), KAP mRNA was analyzed by reverse transcription-PCR (RT-PCR), followed by cloning and sequencing. Eight of 14 biopsy tissues obtained from advanced HCC, 6 of 13 surgically removed HCC tissues, and 2 of the adjacent noncancerous tissues contained aberrant KAP transcripts. Using the yeast two-hybrid system, five of seven representative KAP mutants were shown to be defective in interacting with Cdk2. These data suggest a possible role of KAP mutations in multiple-step hepatocarcinogenesis.

Amino Acid Sequence↗
PubMed2000

Activation of nuclear factor kappaB in hepatitis C virus infection: implications for pathogenesis and hepatocarcinogenesis.

The hepatitis C virus (HCV) core protein is a multifunctional protein. It may bind to the death domain of tumor necrosis factor receptor 1 (TNFR1) and to the cytoplasmic tail of lymphotoxin-beta receptor, implying that it may be involved in the apoptosis and anti-apoptosis signaling pathways. In vitro studies have been inconclusive regarding its ability to inhibit or enhance TNF-alpha-induced apoptosis. To address this issue, electrophoretic mobility shift assay (EMSA) and immunohistochemical studies were used to show the activation of nuclear factor kappaB (NF-kappaB) in HCV-infected liver tissues and in HCV core-transfected cells. The activation of NF-kappaB was correlated with the apoptosis assays. The results showed that NF-kappaB activation could be shown in HCV-infected livers and HCV core-transfected cells. The data of EMSA correlated with those of immunohistochemical studies, which revealed a higher frequency of NF-kappaB nuclear staining in HCV-infected than in normal livers. NF-kappaB activation conferred resistance to TNF-alpha-induced apoptosis in HCV core-transfected cells. Inhibition of NF-kappaB activation by pyrrolidine dithiocarbamate sensitized them to TNF-alpha-induced apoptosis. These findings suggest that HCV infection may cause anti-apoptosis by activation of NF-kappaB and implicate a mechanism by which HCV may evade the host's immune surveillance leading to viral persistence and possibly to hepatocarcinogenesis.

Adult↗
PubMed2000

Performance evaluation of a sorbent tube sampling method using short path thermal desorption for volatile organic compounds.

Air sampling, using sorbents, thermal desorption and gas chromatography, is a versatile method for identifying and quantifying trace levels of volatile organic compounds (VOCs). Thermal desorption can provide high sensitivity, appropropriate choices of sorbents and method parameters can accommodate a wide range of compounds and high humidity, and automated short-path systems can minimize artifacts, losses and carry-over effects. This study evaluates the performance of a short-path thermal desorption method for 77 VOCs using laboratory and field tests and a dual sorbent system (Tenax GR, Carbosieve SIII). Laboratory tests showed that the method requirements for ambient air sampling were easily achieved for most compounds, e.g., using the average and standard deviation across target compounds, blank emissions were < or = 0.3 ng per sorbent tube for all target compounds except benzene, toluene and phenol; the method detection limit was 0.05 +/- 0.08 ppb, reproducibility was 12 +/- 6%, linearity, as the relative standard deviation of relative response factors, was 16 +/- 9%, desorption efficiency was 99 +/- 28%, samples stored for 1-6 weeks had recoveries of 87 +/- 9%, and high humidity samples had recoveries of 102 +/- 12%. Due to sorbent, column and detector characteristics, performance was somewhat poorer for phenol groups, ketones, and nitrogen containing compounds. The laboratory results were confirmed in an analysis of replicate samples collected in two field studies that sampled ambient air along roadways and indoor air in a large office building. Replicates collected under field conditions demonstrated good agreement except for very low concentrations or large (> 41 volume) samples of high humidity air. Overall, the method provides excellent performance and satisfactory throughput for many applications.

Adsorption↗
PubMed1999

Enhanced decomposition of NO on the alkalized PdO/Al2O3 catalyst.

Experimentally, decomposition of NO on the alkalized Pd/Al2O3 catalyst is remarkably enhanced at 825-1000 K. The enhancement in N2 yield may be due to the additional basic sites on the alkalized catalyst that can trap NO molecules. However, at T > 1000 K, due to the fact that the absorbed oxygen in subsurface or bulk of Pd was involved in the formation and desorption of oxygen molecules, yield of oxygen was enhanced.

Adsorption↗
PubMed1998

Biochemical analysis of ++Prospero protein during asymmetric cell division: cortical Prospero is highly phosphorylated relative to nuclear Prospero.

Drosophila neuroblasts are a model system for studying asymmetric cell division. Neuroblasts bud off a series of smaller progeny, called ganglion mother cells (GMCs). An essential regulator of GMC development is the Prospero homeodomain transcription factor: Prospero is asymmetrically localized to the basal cortex of the mitotic neuroblast and partitioned into the newborn GMC. Prospero is translocated into the GMC nucleus, where it is necessary to establish GMC-specific gene expression. Cortical localization of Prospero protein is observed only during mitosis; cortical localization requires entry into mitosis and cortical delocalization requires exit from mitosis. The tight correlation and functional requirement between mitosis and cortical Prospero localization suggests that mitosis-specific posttranslational modifications may be involved in regulating Prospero subcellular localization. Here we use monoclonals recognizing the N-terminal or C-terminal region of Prospero to explore its posttranslational regulation. One- and two-dimensional Western analysis reveal a complex pattern of Prospero isoforms; phosphatase assays show that there are several phosphoisoforms of Prospero. Developmental 2D Western blots, cell fractionation assays, and analysis of a missense prospero mutation show that cortical Prospero protein is highly phosphorylated compared to nuclear Prospero protein. Our results are consistent with two functions of Prospero phosphorylation: (i) phosphorylation may be required for Prospero cortical localization; or (ii) phosphorylation may be a consequence of Prospero cortical localization, in which case it may facilitate subsequent events, such as Prospero cortical release or nuclear localization.

Animals↗
PubMed1998

Identification of Miranda protein domains regulating asymmetric cortical localization, cargo binding, and cortical release.

An important question in cellular and developmental biology is how a cell divides to produce daughter cells with different fates. Drosophila neuroblasts are a model system for studying asymmetric cell division: at each division, neuroblasts retain stem cell-like features, whereas their sibling ganglion mother cell (GMC) has a more restricted fate. Establishing neuroblast/GMC differences involves the asymmetric localization of proteins (Inscuteable, Miranda, Prospero, and Staufen) and RNA (prospero). All of these factors are apically localized during interphase, and all except Inscuteable move to the basal cortex at mitosis prior to being partitioned solely into the GMC. In this study, we show that Miranda is colocalized with Staufen and Prospero in neuroblasts, and is required for the asymmetric cortical localization of both proteins. Analysis of miranda mutants reveals three functional domains within the Miranda protein: (1) an N-terminal domain (1-290 aa) sufficient for association of Miranda with the cell cortex and basal localization in mitotic neuroblasts; (2) a central domain (446-727 aa) necessary for apical localization in interphase neuroblasts as well as for "cargo binding" of Prospero, Staufen, and prospero mRNA; and (3) a C-terminal domain (727-830 aa) necessary for the timely degradation of Miranda and release of its cargo from the cortex of the newborn GMC. In addition, Miranda is asymmetrically localized in epithelial cells that lack Inscuteable and divide symmetrically; thus the mechanism regulating Miranda localization is common to epithelial cells and neuroblasts, and Inscuteable is not an obligate component. Finally, we define a C-terminal domain of Staufen sufficient for Miranda-dependent cortical localization in neuroblasts.

Amino Acid Sequence↗
PubMed1998

C-TAK1 protein kinase phosphorylates human Cdc25C on serine 216 and promotes 14-3-3 protein binding.

Cdc25C is a dual-specificity protein kinase that controls entry into mitosis by dephosphorylating Cdc2 on both threonine 14 and tyrosine 15. Cdc25C is phosphorylated on serine 216 throughout interphase but not during mitosis. Serine 216 phosphorylation mediates the binding of 14-3-3 protein to Cdc25C, and Cdc25C/14-3-3 complexes are present throughout interphase but not during mitosis. Here we report the cloning of a human kinase denoted C-TAK1 (for Cdc twenty-five C associated protein kinase) that phosphorylates Cdc25C on serine 216 in vitro. C-TAK1 is ubiquitously expressed in human tissues and cell lines and is distinct from the DNA damage checkpoint kinase Chk1, shown previously to phosphorylate Cdc25C on serine 216. Cotransfection of Cdc25C with C-TAK1 resulted in enhanced phosphorylation of Cdc25C on serine 216. In addition, a physical interaction between C-TAK1 and Cdc25C was observed upon transient overexpression in COS-7 cells. Finally, coproduction of Cdc25C and C-TAK1 in bacteria resulted in the stoichiometric phosphorylation of Cdc25C on serine 216 and facilitated 14-3-3 protein binding in vitro. Taken together, these results suggest that one function of C-TAK1 may be to regulate the interactions between Cdc25C and 14-3-3 in vivo by phosphorylating Cdc25C on serine 216.

14-3-3 Proteins↗
PubMed1998

Neural stem cells: from fly to vertebrates.

Our goal in this review is to explore the relationship between Drosophila and vertebrate neural stem cell development by comparing progress in each system with the aim of answering several central questions in stem cell biology: (a) How are stem cells formed? (b) Do stem cells divide symmetrically or asymmetrically? (c) How is stem cell fate maintained? (d) How is stem cell differentiation initiated? (e) How are different stem cell fates determined? (f) How "plastic" are different neural stem cell fates? (g) How do neural stem cells produce different progeny? and (h) What regulates stem cell proliferation versus quiescence? Not surprisingly, research in Drosophila and vertebrate systems each have their own biases, strengths, and weaknesses; we hope that by directly comparing progress in each field, new experiments and interpretations in both vertebrate and Drosophila research will become apparent. It has become increasingly clear that vertebrates and Drosophila share many fundamental mechanisms of neurogenesis, validating a comparative approach.

Animals↗
PubMed1997

Mitotic and G2 checkpoint control: regulation of 14-3-3 protein binding by phosphorylation of Cdc25C on serine-216.

Human Cdc25C is a dual-specificity protein phosphatase that controls entry into mitosis by dephosphorylating the protein kinase Cdc2. Throughout interphase, but not in mitosis, Cdc25C was phosphorylated on serine-216 and bound to members of the highly conserved and ubiquitously expressed family of 14-3-3 proteins. A mutation preventing phosphorylation of serine-216 abrogated 14-3-3 binding. Conditional overexpression of this mutant perturbed mitotic timing and allowed cells to escape the G2 checkpoint arrest induced by either unreplicated DNA or radiation-induced damage. Chk1, a fission yeast kinase involved in the DNA damage checkpoint response, phosphorylated Cdc25C in vitro on serine-216. These results indicate that serine-216 phosphorylation and 14-3-3 binding negatively regulate Cdc25C and identify Cdc25C as a potential target of checkpoint control in human cells.

14-3-3 Proteins↗
PubMed1996

Laboratory and field studies on the effects of the antibiotic tylosin on honey bee Apis mellifera L. (Hymenoptera: Apidae) development and prevention of American foulbrood disease.

Laboratory and field studies were conducted to determine the effectiveness of the antibiotic tylosin in preventing and controlling infections of American foulbrood disease (AFB) of honey bees. Studies conducted on immature worker bees maintained in the laboratory revealed that honey bee larvae could tolerate quite a range of doses of antibiotic in their diet. Intermediate doses of tylosin protected very young larvae from becoming infected by Bacillus larvae at a concentration of 1.5 x 10(8) spores/ml of diet. Antibiotic treatment had no measurable effects on larval or pupal developmental rates until the dose reached a lethal level. Bees in field colonies readily consumed tylosin in powered sugar, up to a level of 800 mg/7 g sugar. No negative colony effects were noted at any dosage rates. Protection against infection by American foulbrood was compared to results obtained with 200 mg Terramycin, the standard dose of the only substance currently registered for foulbrood control. Both 200 mg Terramycin and 100 mg tylosin protected the colonies for up to 3 weeks. A 200-mg dose of tylosin protected the colony for an additional week. Doses of 100 mg or more of tylosin were adequate to eliminate signs of AFB infection in overtly diseased colonies.

Animals↗
PubMed1994

Cell cycle regulation of the p34cdc2 inhibitory kinases.

In cells of higher eukaryotic organisms the activity of the p34cdc2/cyclin B complex is inhibited by phosphorylation of p34cdc2 at two sites within its amino-terminus (threonine 14 and tyrosine 15). In this study, the cell cycle regulation of the kinases responsible for phosphorylating p34cdc2 on Thr14 and Tyr15 was examined in extracts prepared from both HeLa cells and Xenopus eggs. Both Thr14- and Tyr15- specific kinase activities were regulated in a cell cycle-dependent manner. The kinase activities were high throughout interphase and diminished coincident with entry of cells into mitosis. In HeLa cells delayed in G2 by the DNA-binding dye Hoechst 33342, Thr14- and Tyr15-specific kinase activities remained high, suggesting that a decrease in Thr14- and Tyr15- kinase activities may be required for entry of cells into mitosis. Similar cell cycle regulation was observed for the Thr14/Tyr15 kinase(s) in Xenopus egg extracts. These results indicate that activation of CDC2 and entry of cells into mitosis is not triggered solely by activation of the Cdc25 phosphatase but by the balance between Thr14/Tyr15 kinase and phosphatase activities. Finally, we have detected two activities capable of phosphorylating p34cdc2 on Thr14 and/or Tyr15 in interphase extracts prepared from Xenopus eggs. An activity capable of phosphorylating Tyr15 remained soluble after ultracentrifugation of interphase extracts whereas a second activity capable of phosphorylating both Thr14 and Tyr15 pelleted. The pelleted fraction contained activities that were detergent extractable and that phosphorylated p34cdc2 on both Thr14 and Tyr15. The Thr14- and Tyr15-specific kinase activities co-purified through three successive chromatographic steps indicating the presence of a dual-specificity protein kinase capable of acting on p34cdc2.

Animals↗
PubMed1994

Cyclin A/CDK2 binds directly to E2F-1 and inhibits the DNA-binding activity of E2F-1/DP-1 by phosphorylation.

E2F-1, a member of the E2F transcription factor family, contributes to the regulation of the G1-to-S phase transition in higher eukaryotic cells. E2F-1 forms a heterodimer with DP-1 and binds to several cell cycle regulatory proteins, including the retinoblastoma family (RB, p107, p130) and cyclin A/CDK2 complexes. We have analyzed E2F-1 phosphorylation and its interaction with cyclin A/CDK2 complexes both in vivo and in vitro. In vitro, E2F-1 formed a stable complex with cyclin A/CDK2 but not with either subunit alone. DP-1 did not interact with cyclin A, CDK2, or the cyclin A/CDK2 complex. While the complex of cyclin A/CDK2 was required for stable complex formation with E2F-1, the kinase-active form of CDK2 was not required. However, E2F-1 was phosphorylated by cyclin A/CDK2 in vitro and was phosphorylated in vivo in HeLa cells. Two-dimensional tryptic phosphopeptide mapping studies demonstrated an overlap in the phosphopeptides derived from E2F-1 labeled in vitro and in vivo, indicating that cyclin A/CDK2 may be responsible for the majority of E2F-1 phosphorylation in vivo. Furthermore, an active DNA-binding complex could be reconstituted from purified E2F-1/DP-1 and cyclin A/CDK2. Binding studies conducted both in vitro and in vivo demonstrated that the cyclin A/CDK2-binding region resided within the N-terminal 124 amino acids of E2F-1. Because the stable association of E2F-1 with cyclin A/CDK2 in vitro and in vivo did not require a DP-1- or RB-binding domain and because the interactions could be reconstituted from purified components in vitro, we conclude that the interactions between cyclin A/CDK2 and E2F-1 are direct. Finally, we report that the DNA-binding activity of the E2F-1/DP-1 complex is inhibited following phosphorylation by cyclin A/CDK2.

CDC2-CDC28 Kinases↗