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X Du

Publications and source records attributed to X Du.

At least 19 recordsLinked to original sources
PubMed2001

Crystal structure and mechanism of catalysis of a pyrazinamidase from Pyrococcus horikoshii.

Bacterial pyrazinamidase (PZAase)/nicotinamidase converts pyrazinamide (PZA) to ammonia and pyrazinoic acid, which is active against Mycobacterium tuberculosis. Loss of PZAase activity is the major mechanism of pyrazinamide-resistance by M. tuberculosis. We have determined the crystal structure of the gene product of Pyrococcus horikoshii 999 (PH999), a PZAase, and its complex with zinc ion by X-ray crystallography. The overall fold of PH999 is similar to that of N-carbamoylsarcosine amidohydrolase (CSHase) of Arthrobacter sp. and YcaC of Escherichia coli, a protein with unknown physiological function. The active site of PH999 was identified by structural features that are also present in the active sites of CSHase and YcaC: a triad (D10, K94, and C133) and a cis-peptide (between V128 and A129). Surprisingly, a metal ion-binding site was revealed in the active site and subsequently confirmed by crystal structure of PH999 in complex with Zn(2+). The roles of the triad, cis-peptide, and metal ion in the catalysis are proposed. Because of extensive homology between PH999 and PZAase of M. tuberculosis (37% sequence identity), the structure of PH999 provides a structural basis for understanding PZA-resistance by M. tuberculosis harboring PZAase mutations.

Amidohydrolases↗
PubMed2001

Mizoroki-Heck type reaction of organoboron reagents with alkenes and alkynes. A Pd(II)-catalyzed pathway with Cu(OAc)2 as an oxidant.

[reaction: see text]. In contrast to the Pd(0)-catalyzed mechanism by Uemura, Mizoroki-Heck type reaction of boronic acids is found to proceed under a Pd(II)-mediated pathway using a catalytic amount of Pd(OAc)2 in the presence of Cu(OAc)2 as an oxidant. Treatment of a variety of alkenes with boronic acids, boronates, and sodium tetraphenylborate furnishes beta-arylated and alkenylated products in good to excellent yields. The reactions with norbornene, norbornadiene, and diphenylacetylene are also performed to give 1:2 or 2:1 coupling products.

Journal Article↗
PubMed2001

A mitogen-activated protein kinase-dependent signaling pathway in the activation of platelet integrin alpha IIbbeta3.

We have recently shown that the platelet integrin alpha(IIb)beta(3) is activated by von Willebrand factor (vWF) binding to its platelet receptor, glycoprotein Ib-IX (GPIb-IX), via the protein kinase G (PKG) signaling pathway. Here we show that GPIb-IX-mediated activation of integrin alpha(IIb)beta(3) is inhibited by dominant negative mutants of Raf-1 and MEK1 in a reconstituted integrin activation model in Chinese hamster ovary (CHO) cells and that the integrin-dependent platelet aggregation induced by either vWF or low dose thrombin is inhibited by MEK inhibitors PD98059 and U0126. Thus, mitogen-activated protein kinase (MAPK) pathway is important in GPIb-IX-dependent activation of platelet integrin alpha(IIb)beta(3). Furthermore, vWF binding to GPIb-IX induces phosphorylation of Thr-202/Tyr-204 of extracellular signal-regulated kinase 2 (ERK2). GPIb-IX-induced ERK2 phosphorylation is inhibited by PKG inhibitors and enhanced by overexpression of recombinant PKG. PKG activators also induce ERK phosphorylation, indicating that activation of MAPK pathway is downstream from PKG. Thus, our data delineate a novel integrin activation pathway in which ligand binding to GPIb-IX activates PKG that stimulates MAPK pathway, leading to integrin activation.

Animals↗
PubMed2001

Increase of chemotherapy use in older women with breast carcinoma from 1991 to 1996.

BACKGROUND: There is little population-based information available on the actual use of chemotherapy and how closely this use mirrors consensus recommendations. The authors hypothesized that given the relative stability of consensus conference recommendations on chemotherapy use during the period 1991-1996 the patterns of use would more closely approximate consensus recommendation over time. METHODS: The authors studied women who received a diagnosis of Stage I-IV (American Joint Committee on Cancer staging) breast carcinoma at age 65 years and older from 1991 through 1996, using the SEER cancer registry cases linked with Medicare claims. RESULTS: Overall, women whose disease was diagnosed in 1996 had a 30% higher chance of receiving chemotherapy than those in 1991, after controlling for changes in tumor size, stage, and other factors. The use of chemotherapy was strongly influenced by age, with women age 65-69 years more than twice as likely to receive it as were women 70 years and older. The increase over time in chemotherapy depended on both tumor stage and patient age. For Stage I tumor, there was no increase in chemotherapy for any age. For Stage II, the increase was limited to younger women, whereas for Stage III and IV it was observed in women age 70 years and older. CONCLUSIONS: There was a significant increase of chemotherapy use over time from 1991 to 1996 in women age 65 years and older with breast carcinoma. The increase was limited to younger women and those with advanced stage at diagnosis. Thus, consensus recommendations and community practice seemed to mirror each other over time.

Aged↗
PubMed2001

Fatty acids inhibit growth-factor-induced diacylglycerol kinase alpha activation in vascular smooth-muscle cells.

We have previously shown that unsaturated fatty acids amplify platelet-derived-growth-factor (PDGF)-induced protein kinase C (PKC) activation in vascular smooth-muscle cells (VSMCs). Diacylglycerol-induced PKC activation is normally terminated by diacylglycerol kinases (DGKs). We thus hypothesized that fatty acids act by inhibiting a DGK. Fractionation of VSMC extracts demonstrated that the DGK alpha isoform was the major DGK activity present. PDGF markedly increased the DGK activity of cultured cells. An inhibitor selective for the DGK alpha isoform, R59949 [3-[2-[4-(bis-(4-fluorophenyl)methylene]piperidin-1-yl)ethyl]-2,3-dihydro-2-thioxo-4(1H)-quinazolinone], abolished the growth-factor-induced increase in DGK activity, but had little effect on basal activity. PDGF thus selectively activates DGKalpha. Epidermal growth factor and alpha-thrombin stimulated total DGK activity similarly to PDGF. Activation by epidermal growth factor was sensitive to R59949, again suggesting involvement of DGKalpha. However, the alpha-thrombin-induced activity was unaffected by this agent. Unsaturated fatty acids inhibited growth-factor-induced DGKalpha activation, but had no effect on basal activity. Fatty acids also amplified the PDGF-induced increase in cell diacylglycerol content. These results indicate that inhibition of DGKalpha contributes to fatty-acid-induced amplification of PKC activation. Increased levels of fatty acids in diabetes may thus contribute to chronic PKC activation associated with this disorder.

Animals↗
PubMed2001

Bowman-Birk protease inhibitor and its palmitic acid conjugate prevent 7,12-dimethylbenz[a]anthracene-induced transformation in cultured mouse mammary glands.

The chemopreventive effects of Bowman-Birk protease inhibitor (BBI), a soybean polypeptide, and its palmitic acid conjugate, Pal-BBI, on 7,12-dimethylbenz[a]anthracene (DMBA)-induced transformation were investigated by using an in vitro whole organ culture system of mouse mammary glands. The transformation incidence was measured as the number of glands containing nodule-like alveolar lesions (NLAL). Both BBI and Pal-BBI were effective in preventing DMBA-induced transformation, especially when added to the medium during the developing period after the exposure of mammary glands to DMBA, i.e. 35.9 and 53.4% prevention, respectively. However, when only present in the medium before the promotion period, Pal-BBI was effective in decreasing the transformation incidence (32.2%) while BBI was not (10.3%). This difference could possibly be due to the high lipophilicity and tissue retention of Pal-BBI in mammary gland cultures.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed2001

Patterns of use of chemotherapy for breast cancer in older women: findings from Medicare claims data.

PURPOSE: There is little population-based information available on the use of chemotherapy in women with breast cancer. This study describes the use of chemotherapy through analysis of Medicare claims and determines the correlates of chemotherapy use. PATIENTS AND METHODS: We used the merged Surveillance, Epidemiology, and End Results-Medicare database and identified women > or = 65 years of age diagnosed with breast cancer in 1991 and 1992. Chemotherapy was ascertained from Medicare claims through procedure codes for chemotherapy made within 24 months of the diagnosis. RESULTS: In women with stages I, II, III, and IV breast cancer, the percentage receiving chemotherapy within 24 months of diagnosis was 5.1%, 19.5%, 33.9%, and 35.2%, respectively. Most women receiving chemotherapy had two to 12 claims; the median number was eight. Use of chemotherapy decreased significantly with age across all tumor stages; eg, in women with stage III cancer, the use of chemotherapy declined from 49% in those aged 65 to 69 years to 10% in those > or = 80 years old. In a multivariate analysis, there was little variation by ethnicity. Chemotherapy use was highest (70%) in women aged 65 to 69 years with node-positive and estrogen receptor-negative tumors and lowest (5%) in those with node-negative and estrogen receptor-positive tumors. Compared with those without comorbid diseases, patients with a comorbidity score of 2 had significantly lower use of chemotherapy. CONCLUSION: Medicare claims data seem to provide valuable information on the use of chemotherapy for breast cancer in older women. However, external validation of the accuracy and completeness of these data is required before any firm conclusion can be drawn.

Age Factors↗
PubMed2001

Regulation of von Willebrand factor binding to the platelet glycoprotein Ib-IX by a membrane skeleton-dependent inside-out signal.

The platelet receptor for von Willebrand factor (vWF), glycoprotein Ib-IX (GPIb-IX), mediates initial platelet adhesion and activation. We show here that the receptor function of GPIb-IX is regulated intracellularly via its link to the filamin-associated membrane skeleton. Deletion of the filamin binding site in GPIb(alpha) markedly enhances ristocetin- (or botrocetin)-induced vWF binding and allows GPIb-IX-expressing cells to adhere to immobilized vWF under both static and flow conditions. Cytochalasin D (CD) that depolymerizes actin also enhances vWF binding to wild type GPIb-IX. Thus, vWF binding to GPIb-IX is negatively regulated by the filamin-associated membrane skeleton. In contrast to native vWF, binding of the isolated recombinant vWF A1 domain to wild type and filamin binding-deficient mutants of GPIb-IX is comparable, suggesting that the membrane skeleton-associated GPIb-IX is in a state that prevents access to the A1 domain in macromolecular vWF. In platelets, there is a balance of membrane skeleton-associated and free forms of GPIb-IX. Treatment of platelets with CD increases the free form and enhances vWF binding. CD also reverses the inhibitory effects of prostaglandin E1 on vWF binding to GPIb-IX. Thus, GPIb-IX-dependent platelet adhesion is doubly controlled by vWF conformation and a membrane skeleton-dependent inside-out signal.

Animals↗
PubMed2001

Comparison of nitrophenylethyl and hydroxyphenacyl caging groups.

Nitrophenylethyl (NPE)- and hydroxyphenacyl (HPA)-caged nucleotides were employed in a time-resolved Fourier transform IR spectroscopy study on Ras-catalyzed guanosine triphosphate (GTP) hydrolysis. A fast kinetic component was observed following the photolysis of NPE-caged nucleotides in the NPE-GTP-Ras complex. However, this kinetic component was not observed in the HPA-GTP-Ras experiment. This fast kinetic component was likely due to a chemical reaction between Ras and the detached caging group, nitrosoacetophenone. This communication serves as a note of caution in interpreting spectral changes and kinetic behavior of the enzymatic systems employing NPE-caged compounds.

Guanosine Triphosphate↗
PubMed2001

Increased cell death in the developing vestibulocochlear ganglion complex of the mouse after prenatal ethanol exposure.

BACKGROUND: Previous studies have demonstrated that excessive prenatal alcohol exposure can damage the auditory and vestibular systems, in particular, cochlear hair cells. However, the direct effect of ethanol on the peripheral neurons in these pathways has not been examined. To study the effects of prenatal ethanol exposure on the developing vestibulocochlear ganglion (VCG) complex and the peripheral sensory organs, we exposed pregnant mice to ethanol and examined the levels of cell death in the inner ear. METHODS: Pregnant C57BL/6J mice were administered one of three doses of either ethanol (3.0, 4.5, and 5.5 g/kg) or isocaloric maltose/dextrin via intragastric intubation on gestational day (GD) 12.5. Embryos were dissected out of the uterus 8 hr after the intubation. Dying cells in the inner ear were stained with Nissl stain and labeled by in situ terminal dUTP nick-end labeling (TUNEL), and the percentage of dying cells was quantified. RESULTS: Ethanol exposure produced region-specific effects, with ethanol-exposed embryos exhibiting enhanced cell death only in the VCG complex, and not in the primitive saccule, cochlea, semicircular canal, or endolymphatic sac. The effects of ethanol on cell death in the VCG are dose dependent, with a significant increase in the level of cell death found only at the higher doses. CONCLUSIONS: Ethanol has a selective cytotoxic dose-dependent effect on the VCG at GD 12.5 suggesting that loss of VCG neurons may contribute to hearing and /or vestibular abnormalities in FAS children. Furthermore, the presence of TUNEL-positive cells and DNA laddering is consistent with the cells undergoing apoptotic cell death.

Animals↗
PubMed2001

Flow-injection chemical vapor-generating procedure for the determination of Au by atomic absorption spectrometry.

Volatile Au species in an acidified medium were generated at room temperature by reduction with NaBH4 in acidified aqueous medium using a flow-injection chemical vapor-generation atomic absorption spectrometric (FI-CVG-AAS) system in the presence of micro amounts of sodium diethyldithiocarbamate (DDTC). Precision of 2.0% RSD (n = 11, 2.0 mg L(-1) level) was obtained at a sample throughput of 180 h(-1). A detection limit of 24 ng mL(-1) (3sigma) was obtained with 300 microL sample solution. The method was used for the determination of gold in ore sample digests, and the results obtained agreed well with those obtained by flame AAS.

Journal Article↗
PubMed2001

Nature of cerium(III)- and lanthanum(III)-induced aggregation of human erythrocyte membrane proteins.

To clarify the nature of the aggregation of membrane proteins (MP) induced by lanthanide cations (Lns), the interaction of cerium(III) (Ce3+) and lanthanum(III)(La3+) with erythrocyte membrane proteins was studied by means of SDS-PAGE, light scattering measurement, fluorescence, CD and FTIR spectra. The results showed that Ce3+ and La3+ induce protein aggregation not only by Lns non-covalent binding and cross-linking, but also by oxidative cross-linking through disulfide bond formation. As demonstrated by intrinsic fluorescence, CD and FTIR spectra studies, the aggregation was accompanied by the conformation changes with tryptophane residues exposing to more hydrophobic environment and the decreasing alpha-helix and beta-sheet contents. By stopped-flow studies, protein aggregation was shown to be a slow change, which is initiated by rapid Lns binding and then followed by subsequent conformational changes.

Blood Proteins↗
PubMed2001

The adipocyte-secreted protein Acrp30 enhances hepatic insulin action.

Acrp30 is a circulating protein synthesized in adipose tissue. A single injection in mice of purified recombinant Acrp30 leads to a 2-3-fold elevation in circulating Acrp30 levels, which triggers a transient decrease in basal glucose levels. Similar treatment in ob/ob, NOD (non-obese diabetic) or streptozotocin-treated mice transiently abolishes hyperglycemia. This effect on glucose is not associated with an increase in insulin levels. Moreover, in isolated hepatocytes, Acrp30 increases the ability of sub-physiological levels of insulin to suppress glucose production. We thus propose that Acrp30 is a potent insulin enhancer linking adipose tissue and whole-body glucose metabolism.

Adipocytes↗
PubMed2001

Enhancement of biodegradability of polychlorinated dibenzo-p-dioxins.

Enhancement of biodegradability of polychlorinated dibenzo-p-dioxins (PCDDs) was studied with new isolated bacterial strains from soil and oxic-sediments contaminated by PCDDs. The results indicated that mono- and di-chlorinated dibenzo-p-dioxins could be utilized as a sole carbon source and degraded by isolated bacterial strains, but tri-chlorinated dibenzo-p-dioxin (TrCDD) was hardly degraded. The biodegradability of TrCDD and tetra-chlorinated dibenzo-p-dioxin (TCDD) by the strain Pseudomonas sp. EE41, a new isolated one, could be enhanced through primary nutrient of co-metabolism of o-dichlorobenzene (o-DCB). In this case, TrCDD (1.2mg/l for 3 weeks) was degraded by 33.1% and the degradation rate enhanced more than 2 fold; also TCDD (0.1 mg/l for 3 weeks) biodegraded by 37.8%. Most highly chlorinated, Penta-, Hexa-, Hepta-, and Octa-chlorinated, dibenzo-p-dioxins (P-CDD, H6, H7-CDD and OCDD) tested in this study could not be degraded while accumulated in bacterial cells.

Biodegradation, Environmental↗
PubMed2001

Methylation of the protein phosphatase 2A catalytic subunit is essential for association of Balpha regulatory subunit but not SG2NA, striatin, or polyomavirus middle tumor antigen.

Binding of different regulatory subunits and methylation of the catalytic (C) subunit carboxy-terminal leucine 309 are two important mechanisms by which protein phosphatase 2A (PP2A) can be regulated. In this study, both genetic and biochemical approaches were used to investigate regulation of regulatory subunit binding by C subunit methylation. Monoclonal antibodies selectively recognizing unmethylated C subunit were used to quantitate the methylation status of wild-type and mutant C subunits. Analysis of 13 C subunit mutants showed that both carboxy-terminal and active site residues are important for maintaining methylation in vivo. Severe impairment of methylation invariably led to a dramatic decrease in Balpha subunit binding but not of striatin, SG2NA, or polyomavirus middle tumor antigen (MT) binding. In fact, most unmethylated C subunit mutants showed enhanced binding to striatin and SG2NA. Certain carboxy-terminal mutations decreased Balpha subunit binding without greatly affecting methylation, indicating that Balpha subunit binding is not required for a high steady-state level of C subunit methylation. Demethylation of PP2A in cell lysates with recombinant PP2A methylesterase greatly decreased the amount of C subunit that could be coimmunoprecipitated via the Balpha subunit but not the amount that could be coimmunoprecipitated with Aalpha subunit or MT. When C subunit methylation levels were greatly reduced in vivo, Balpha subunits were found complexed exclusively to methylated C subunits, whereas striatin and SG2NA in the same cells bound both methylated and unmethylated C subunits. Thus, C subunit methylation is critical for assembly of PP2A heterotrimers containing Balpha subunit but not for formation of heterotrimers containing MT, striatin, or SG2NA. These findings suggest that methylation may be able to selectively regulate the association of certain regulatory subunits with the A/C heterodimer.

3T3 Cells↗
PubMed2001

Vitamin D deficiency and associated factors in adolescent girls in Beijing.

BACKGROUND: Several locally published reports indicate a high prevalence of vitamin D deficiency among adolescents in China, but no systematic population-based survey has been conducted. OBJECTIVE: The objective was to determine the prevalence of vitamin D deficiency and to study associated factors in adolescent girls in Beijing. DESIGN: A cross-sectional study was conducted in a random sample of 1248 Beijing girls aged 12-14 y. Nutrient intakes, ultraviolet light exposure, anthropometric characteristics, physical activity, signs and symptoms of rickets, and plasma concentrations of 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, and calcium were measured and X-rays of the hand and wrist were taken. RESULTS: The prevalence of clinical vitamin D and calcium deficiency (plasma 25-hydroxyvitamin D <12.5 nmol/L, plasma calcium <2.25 mmol/L, and muscle spasm at least once per week) was 9.4% in winter. The prevalence of subclinical vitamin D deficiency (25-hydroxyvitamin D <12.5 nmol/L) was 45.2% in winter and 6.7% in summer (P < 0.0005). Logistic regression analysis showed that subclinical and clinical vitamin D deficiency in winter were associated with low plasma 25-hydroxyvitamin D concentrations (<12.5 nmol/L) in summer, low calcium intake ( x +/- SD: 280 +/- 48 compared with 440 +/- 61 mg/d), and low plasma calcium concentrations (<2.25 mmol/L) in winter. The odds ratios for these associations were 3.1, 1.5, and 1.5, respectively. CONCLUSIONS: Subclinical vitamin D deficiency was widespread among Beijing adolescent girls in winter. Low plasma 25-hydroxyvitamin D concentrations in summer, low calcium intake, and low plasma calcium concentrations in winter were the main risk factors for vitamin D deficiency in winter.

Adolescent↗
PubMed2001

Down-regulation of glycosylphosphatidylinositol-specific phospholipase D induced by lipopolysaccharide and oxidative stress in the murine monocyte- macrophage cell line RAW 264.7.

Serum glycosylphosphatidylinositol-specific phospholipase D (GPI-PLD) activity is reduced over 75% in systemic inflammatory response syndrome. To investigate the mechanism of this response, expression of the GPI-PLD gene was studied in the mouse monocyte-macrophage cell line RAW 264.7 stimulated with lipopolysaccharide (LPS; 0.5 to 50 ng/ml). GPI-PLD mRNA was reduced approximately 60% in a time- and dose-dependent manner. Oxidative stress induced by 0.5 mM H(2)O(2) or 50 microM menadione also caused a greater than 50% reduction in GPI-PLD mRNA. The antioxidant N-acetyl-L-cysteine attenuated the down-regulatory effect of H(2)O(2) but not of LPS. Cotreatment of the cells with actinomycin D inhibited down-regulation induced by either LPS or H(2)O(2). The half-life of GPI-PLD mRNA was not affected by LPS, or decreased slightly with H(2)O(2), indicating that the reduction in GPI-PLD mRNA is due primarily to transcriptional regulation. Stimulation with tumor necrosis factor alpha (TNF-alpha) resulted in approximately 40% reduction in GPI-PLD mRNA in human A549 alveolar carcinoma cells but not RAW 264.7 cells, suggesting that alternative pathways could exist in different cell types for down-regulating GPI-PLD expression during an inflammatory response and the TNF-alpha autocrine signaling mechanism alone is not sufficient to recapitulate the LPS-induced reduction of GPI-PLD in macrophages. Sublines of RAW 264.7 cells with reduced GPI-PLD expression exhibited increased cell sensitivity to LPS stimulation and membrane-anchored CD14 expression on the cell surface. Our data suggest that down-regulation of GPI-PLD could play an important role in the control of proinflammatory responses.

Animals↗