Biomedical subjects

Jun Xu

Publications and source records attributed to Jun Xu.

At least 37 records · Page 2Linked to original sources

PubMed2006

C-terminal HERG (LQT2) mutations disrupt IKr channel regulation through 14-3-3epsilon.

Beta-adrenergic receptor-mediated cAMP or protein kinase A (PKA)-dependent modulation of cardiac potassium currents controls ventricular action potential duration (APD) at faster heart rates. HERG (KCNH2) gene mutations are associated with congenital long-QT syndrome (LQT2) and affect IKr activity, a key determinant in ventricular repolarization. Physical activity or emotional stress often triggers lethal arrhythmias in LQT2 patients. Beta-adrenergic stimulation of HERG channel activity is amplified and prolonged in vitro by the adaptor protein 14-3-3epsilon. In LQT2 families, we identified three novel heterozygous HERG mutations (G965X, R1014PfsX39, V1038AfsX21) in the C-terminus that led to protein truncation and loss of a PKA phosphorylation site required for binding of 14-3-3epsilon. When expressed in CHO cells, the mutants produced functional HERG channels with normal kinetic properties. We now provide evidence that HERG channel regulation by 14-3-3epsilon is of physiological significance in humans. Upon co-expression with 14-3-3epsilon, mutant channels still bound 14-3-3epsilon but did not respond with a hyperpolarizing shift in voltage dependence as seen in wild-type channels. Co-expression experiments of wild-type and mutant channels revealed dominant-negative behavior of all three HERG mutations. Simulations of the effects of sympathetic stimulation of HERG channel activity on the whole-cell action potential suggested a role in rate-dependent control of APD and an impaired ability of mutant cardiac myocytes to respond to a triggered event or an ectopic beat. In summary, the attenuated functional effects of 14-3-3epsilon on C-terminally truncated HERG channels demonstrate the physiological importance of coupling beta-adrenergic stimulation and HERG channel activity.

14-3-3 Proteins↗

PubMed2006

Genomewide expression profiling in the zebrafish embryo identifies target genes regulated by Hedgehog signaling during vertebrate development.

Hedgehog proteins play critical roles in organizing the embryonic development of animals, largely through modulation of target gene expression. Little is currently known, however, about the kinds and numbers of genes whose expression is controlled, directly or indirectly, by Hedgehog activity. Using techniques to globally repress or activate Hedgehog signaling in zebrafish embryos followed by microarray-based expression profiling, we have discovered a cohort of genes whose expression responds significantly to loss or gain of Hedgehog function. We have confirmed the Hedgehog responsiveness of a representative set of these genes with whole-mount in situ hybridization as well as real time PCR. In addition, we show that the consensus Gli-binding motif is enriched within the putative regulatory elements of a sizeable proportion of genes that showed positive regulation in our assay, indicating that their expression is directly induced by Hedgehog. Finally, we provide evidence that the Hedgehog-dependent spatially restricted transcription of one such gene, nkx2.9, is indeed mediated by Gli1 through a single Gli recognition site located within an evolutionarily conserved enhancer fragment. Taken together, this study represents the first comprehensive survey of target genes regulated by the Hedgehog pathway during vertebrate development. Our data also demonstrate for the first time the functionality of the Gli-binding motif in the control of Hedgehog signaling-induced gene expression in the zebrafish embryo.

Animals↗

PubMed2006

V-cluster algorithm: a new algorithm for clustering molecules based upon numeric data.

Clustering molecules based on numeric data such as, gene-expression data, physiochemical properties, or theoretical data is very important in drug discovery and other life sciences. Most approaches use hierarchical clustering algorithms, non-hierarchical algorithms (for examples, K-mean and K-nearest neighbor), and other similar methods (for examples, the Self-Organization Mapping (SOM) and the Support Vector Machine (SVM)). These approaches are non-robust (results are not consistent) and, computationally expensive. This paper will report a new, non-hierarchical algorithm called the V-Cluster (V stands for vector) Algorithm. This algorithm produces rational, robust results while reducing computing complexity. Similarity measurement and data normalization rules are also discussed along with case studies. When molecules are represented in a set of numeric vectors, the V-Cluster Algorithm clusters the molecules in three steps: (1) ranking the vectors based upon their overall intensity levels, (2) computing cluster centers based upon neighboring density, and (3) assigning molecules to their nearest cluster center. The program is written in C/C++ language, and runs on Window95/NT and UNIX platforms. With the V-Cluster program, the user can quickly complete the clustering process and, easily examine the results by use of thumbnail graphs, superimposed intensity curves of vectors, and spreadsheets. Multi-functional query tools have also been implemented.

Algorithms↗

PubMed2006

Langmuir-Blodgett monolayers of gold nanoparticles with amphiphilic shells from V-shaped binary polymer arms.

Gold nanoparticles functionalized with amphiphilic polybutadiene-poly(ethylene glycol) (PB-PEG) V-shaped arms formed stable Langmuir monolayers at the air-water and the air-solid interfaces. At these interfaces, the binary arms vertically segregated into a dense polymer corona, which surrounded the gold nanoparticles, preventing their large-scale agglomeration and keeping individual nanoparticles well-separated from each other and forming flattened, pancake nanostructures. The presence of both PEG and PB chains in the close proximity to the gold core was confirmed by surface enhanced Raman spectroscopy, whereas the AFM phase contrast images revealed the presence of 2 nm gold cores surrounded by the polymer shell with the diameter of 11 nm. We suggest that the amphiphilic shell drives their spontaneous organization into discrete 2D pancake-like hybrid structures that measured up to 10 microm in diameter and had a high packing density of gold clusters.

Journal Article↗

PubMed2006

Chronic daily administration of ethyl docosahexaenoate protects against gerbil brain ischemic damage through reduction of arachidonic acid liberation and accumulation.

Recently, we reported that dietary ethyl docosahexaenoate (Et-DHA) intake decreases the level of membrane arachidonic acid (AA), which reduces the generation of AA metabolites in ischemic gerbil brain. As an extended study, we further investigated the influence of the chronic administration of Et-DHA on free AA levels after ischemia. In addition, Na,K-ATPase activity, cation content, cerebral edema and brain damage were also evaluated. Weanling male gerbils were orally pretreated with either Et-DHA (200 mg/kg) or vehicle, once a day for 10 weeks, and subjected to transient forebrain ischemia by bilateral common carotid occlusion for 30 min. Time-course analyses revealed that pretreatment with Et-DHA, compared with pretreatment with the vehicle, significantly decreased the brain's free AA levels during ischemia (5, 15 and 30 min) and after reperfusion (5, 10, 15 and 30 min), and attenuated the decline of Na,K-ATPase activity at examined time points. Pretreatment with Et-DHA significantly prevented an increase in Na(+) concentration and a decrease in K(+) concentration after 24 h of reperfusion, which resulted in lower cerebral water content. Reduced brain infarct volume and low animal mortality were also observed in Et-DHA-treated animals. These data suggest that the reduction of ischemia-induced AA liberation and accumulation by Et-DHA pretreatment may be attributable to (a) protection against the decline of Na,K-ATPase activity, (b) postischemic cerebral edema and brain damage and (c) animal mortality.

Animals↗

PubMed2006

Simultaneous three-photon-excited violet upconversion luminescence of Ce3+:Lu2Si2O7 single crystals by femtosecond laser irradiation.

We found that Ce3+:Lu2Si2O7 single crystals could be excited at 800 nm by using a femtosecond Ti:sapphire laser. The emission spectra of Ce3+:Lu2Si2O7 crystals were the same for one-photon excitation at 267 nm as for excitation at 800 nm. The emission intensity of Ce3+:Lu2Si2O7 crystals was found to depend on the cube of the laser power at 800 nm, consistent with simultaneous absorption of three 800 nm photons. The measured value of the three-photon absorption cross section is sigma'3=2.44x10(-77) cm6 s2.

Journal Article↗

PubMed2006

Increased expression of ribosome recycling factor is responsible for the enhanced protein synthesis during the late growth phase in an antibiotic-overproducing Streptomyces coelicolor ribosomal rpsL mutant.

K88E mutation within rpsL, which encodes the S12 ribosomal protein, enhanced the protein synthetic activity of Streptomyces coelicolor during the late growth phase, resulting in overproduction of the deep blue-pigmented polyketide antibiotic actinorhodin. In vitro cross-mixing experiments using the ribosomal and S-150 fractions derived from wild-type and K88E mutant strains suggested that one or more translation factors are enriched in the mutant's S-150 fraction, while Western analysis using antibodies against various translation factors revealed ribosome recycling factor (RRF) to be one of the enriched mediators. RRF purified from overexpressing cells stimulated mRNA-directed green fluorescent protein (GFP) synthesis in an in vitro protein synthesis system. GFP synthesis rates were complemented by RRF addition into wild-type cell's S-150 fraction, eliminating the difference between wild-type and mutant S-150 fractions. The frr gene encoding RRF was found to be transcribed from two distinct start points (frrp1 and frrp2), and increased expression from frrp1 could account for the elevated level of RRF in the K88E mutant during the late growth phase. Moreover, introduction of a plasmid harbouring a high copy number of frr gene into wild-type S. coelicolor induced remarkable overproduction of antibiotic, demonstrating that the increased levels of RRF caused by the K88E mutation is responsible for an aberrant stationary-phase event: overproduction of antibiotic.

Anthraquinones↗

PubMed2006

New progesterone receptor antagonists: phosphorus-containing 11beta-aryl-substituted steroids.

A new series of phosphorus-containing 11beta-aryl-substituted steroids have been synthesized in an eight-step sequence involving a palladium-catalyzed coupling reaction to introduce a phosphorus group onto the aromatic ring. The compounds were evaluated for progesterone receptor (PR) antagonist activity in a T47D cell-based assay and for glucocorticoid receptor (GR) antagonist activity in an A549 cell-based assay. The structure-activity relationships of these compounds are discussed. Selected compounds were tested in vivo in a rat complement C3 assay.

Alkaline Phosphatase↗

PubMed2006

Extraction of biologic particles by pumping effect in a pi-shaped ultrasonic actuator.

This paper presents a new method of extracting biologic particles from a mixture of particles. The method is based on the pumping effect in a pi-shaped ultrasonic actuator, which has a gap between its two vibrating metal plates. An adhesive tape is placed at a proper position in the gap. Due to the pumping effect which is induced by the sound field in the gap, the particles with smaller mass and radius in the mixture can be pumped up to reach the adhesive tape; while the ones with larger mass cannot. Therefore, the particles with smaller mass and radius can be extracted from the mixture. A theoretical model which can well explain the operation principle and experimental phenomena is developed. By the experimental results and the theoretical analyses based on the model, the validity of the method in extracting small particles from a mixture of solid particles in air is confirmed, and the effects of the actuator's vibration, adhesive tape height, contents of the mixture and viscosity of fluid on the extraction are clarified. Also, it is theoretically predicted that the method will work under the microgravity condition in air.

Biopolymers↗

PubMed2006

Studies on a new carrier of trimethylsilyl-modified mesoporous material for controlled drug delivery.

To better control drug delivery rate, a simple and effective approach has been developed for controlled drug delivery carrier system through one-step surface modification of the ibuprofen-impregnated silica MCM-41 with 1, 1, 1, 3, 3, 3-hexamethyldisilazane (HMDS). The 29Si MAS NMR characterization demonstrated that different contents of trimethylsilyl (TMS) groups were successfully grafted onto the samples modified with different silylation times. The results obtained from in vitro tests exhibited that the introduction of TMS groups greatly retarded the ibuprofen release rate. Even after in vitro test for 48 h, only 75% of the impregnated ibuprofen could be released from the modified sample with TMS groups content of 14.5% (related to the total silicon atoms). However, the release of ibuprofen could be completed just after about 1 h from the pure silica MCM-41 under the same release conditions. Furthermore, the release rate of ibuprofen could be well modulated by changing the grafted content of TMS groups, and was found to decrease with increasing grafted amount of TMS groups.

Biological Availability↗

PubMed2006

Acidity of mesoporous MoO(x)/ZrO2 and WO(x)/ZrO2 materials: a combined solid-state NMR and theoretical calculation study.

The acidity of mesoporous MoO(x)/ZrO2 and WO(x)/ZrO2 materials was studied in detail by multinuclear solid-state NMR techniques as well as DFT quantum chemical calculations. The 1H MAS NMR experiments clearly revealed the presence of two different types of strong Brønsted acid sites on both MoO(x)/ZrO2 and WO(x)/ZrO2 mesoporous materials, which were able to prontonate adsorbed pyrine-d5 (resulting in 1H NMR signals at chemical shifts in the range 16-19 ppm) as well as adsorbed trimethylphosphine (giving rise to 31P NMR signal at ca. 0 ppm). The 13C NMR of adsorbed 2-(13)C-acetone indicated that the average Brønsted acid strength of the two mesoporous materials was stronger than that of zeolite HZSM-5 but still weaker than that of 100% H2SO4, which was in good agreement with theoretical predictions. The quantum chemical calculations revealed the detailed structures of the two distinct types of Brønsted acid sites formed on the mesoporous MoO(x)/ZrO2 and WO(x)/ZrO2. The existence of both monomer and oligomer Mo (or W) species containing a Mo-OH-Zr (or W-OH-Zr) bridging OH group was confirmed with the former having an acid strength close to zeolite HZSM-5, with the latter having an acid strength similar to sulfated zirconia. On the basis of our NMR experimental and theoretical calculation results, a possible mechanism was proposed for the formation of acid sites on these mesoporous materials.

Journal Article↗

PubMed2006

High-throughput screening for the discovery of inhibitors of fatty acid amide hydrolase using a microsome-based fluorescent assay.

Fatty acid amide hydrolase (FAAH) is a membrane-associated enzyme that catalyzes the hydrolysis of several endogenous bioactive lipids, including anandamide (AEA), N-palmitoylethanolamine (PEA), oleamide, and N-oleoylethanolamine (OEA). These fatty acid amides participate in many physiological activities such as analgesia, anxiety, sleep modulation, anti inflammatory responses, and appetite suppression. Because FAAH plays an essential role in controlling the tone and activity of these endogenous bioactive lipids, this enzyme has been implicated to be a drug target for the therapeutic management of pain, anxiety, and other disorders. In an effort to discover FAAH inhibitors, the authors have previously reported the development of a novel fluorescent assay using purified FAAH microsomes as an enzyme source and a fluorogenic substrate, arachidonyl 7-amino, 4-methyl coumarin amide (AAMCA). Herein, the authors have adapted this assay to a high-throughput format and have screened a large library of small organic compounds, identifying a number of novel FAAH inhibitors. These data further verify that this fluorescent assay is sufficiently robust, efficient, and low-cost for the identification of FAAH inhibitory molecules and open this class of enzymes for therapeutic exploration.

Amidohydrolases↗

PubMed2006

Role of Bmi1 in H2A ubiquitylation and Hox gene silencing.

Posttranslational histone modifications play a crucial role in the regulation of chromatin structure and gene activity. In previous studies, we identified the histone H2A ubiquitin ligase as Ring2, together in a complex with Ring1, Bmi1, and HPH2 (human polyhomeotic 2). We report here that the oncogene Bmi1 stimulates H2A ubiquitylation both in vitro and in vivo and that Bmi1-regulated H2A ubiquitylation is required for Hox gene silencing and normal cell growth. Our studies indicate that Bmi1 maintains the integrity of the complex through simultaneous interactions with the other subunits. We reconstituted the functional human H2A ubiquitin ligase complex and a panel of subcomplexes of different subunits. Comparisons of the H2A ubiquitin ligase activities of these different complexes revealed that Bmi1 stimulates the H2A ubiquitin ligase activity of Ring2 (and Ring1). Additionally, we demonstrated that the HoxC5 gene is regulated by ubiquitylated H2A in HeLa cells and that ubiquitylated H2A is localized on 5' regulatory regions of the HoxC5 gene. The role of Bmi1 in H2A ubiquitylation and HoxC5 gene expression in vivo was analyzed by RNA interference experiments. Knockdown of Bmi1 causes a global and loci-specific loss of H2A ubiquitylation, up-regulation of the HoxC5 gene, and slower cell growth. Intriguingly, Ring2 binds to its target regions in Bmi1 knockdown cells. Therefore, our studies reveal that Bmi1 is required for H2A ubiquitylation and suggest that H2A ubiquitylation regulates Bmi1-mediated gene expression.

Animals↗

PubMed2006

Histone H3 and H4 ubiquitylation by the CUL4-DDB-ROC1 ubiquitin ligase facilitates cellular response to DNA damage.

Posttranslational histone modifications play important roles in transcription and other chromatin-based processes. Compared to acetylation, methylation, and phosphorylation, very little is known about the function of histone ubiquitylation. Here, we report the purification and functional characterization of a histone H3 and H4 ubiquitin ligase complex, CUL4-DDB-ROC1. We demonstrate that CUL4-DDB-ROC1-mediated H3 and H4 ubiquitylation occurs both in vitro and in vivo. Importantly, CUL4-DDB-ROC1-mediated H3 and H4 ubiquitylation is regulated by UV irradiation. Reduction of histone H3 and H4 ubiquitylation by knockdown of CUL4A impairs recruitment of the repair protein XPC to the damaged foci and inhibits the repair process. Biochemical studies indicate that CUL4-DDB-ROC1-mediated histone ubiquitylation weakens the interaction between histones and DNA and facilitates the recruitment of repair proteins to damaged DNA. Thus, our studies uncover CUL4-DDB-ROC1 as a histone ubiquitin ligase and demonstrate that histone H3 and H4 ubiquitylation participates in the cellular response to DNA damage.

Carrier Proteins↗

PubMed2006

A novel scintillation proximity assay for fatty acid amide hydrolase compatible with inhibitor screening.

A binding assay for human fatty acid amide hydrolase (FAAH) using the scintillation proximity assay (SPA) technology is described. This SPA uses the specific interactions of [3H]R(+)-methanandamide (MAEA) and FAAH expressing microsomes to evaluate the displacement activity of FAAH inhibitors. We observed that a competitive nonhydrolyzed FAAH inhibitor, [3H]MAEA, bound specifically to the FAAH microsomes. Coincubation with an FAAH inhibitor, URB-597, competitively displaced the [3H]MAEA on the FAAH microsomes. The released radiolabel was then detected through an interaction with the SPA beads. The assay is specific for FAAH given that microsomes prepared from cells expressing the inactive FAAH-S241A mutant or vector alone had no significant ability to bind [3H]MAEA. Furthermore, the binding of [3H]MAEA to FAAH microsomes was abolished by selective FAAH inhibitors in a dose-dependent manner, with IC50 values comparable to those seen in a functional assay. This novel SPA has been validated and demonstrated to be simple, sensitive, and amenable to high-throughput screening.

Amidohydrolases↗

PubMed2006

Amphiphilic gold nanoparticles with V-shaped arms.

Here we describe a very efficient method to produce well-defined amphiphilic gold nanoparticles (Au NPs) with an equal number of hydrophobic and hydrophilic arms which are distributed along the surface of a 2-nm gold core in an alternating fashion. The strategy involves direct coupling of V-shaped block copolymer amphiphile 2 with a carboxylic group at its junction point to mercaptophenol-terminated Au NPs. The reaction proceeds under mild esterification conditions and yields the product with a molecular weight of 40 kDa, high grafting density (2.9 chains/nm2), and extremely low polydispersity (1.07). The big advantage of this approach is the opportunity to avoid the use of expensive and often inaccessible polymeric thiols. The method described here is applicable to any carboxyl-terminated molecules and can be used for the preparation of complex, yet well-defined, macromolecular hybrid structures such as 1 (Au(PB-PEG)n). The new product, which was characterized by a combination of SEC, NMR, UV-vis, DLS, and TEM, represents a unique example of gold nanoparticles soluble in any conventional solvent.

Journal Article↗

PubMed2006

[Intraoperative angiography in treatment of neurovascular disorders].

OBJECTIVE: To investigate the value of intraoperative angiography in treatment of cerebrovascular disorders. METHODS: Between July 2003 and July 2005, 38 consecutive patients of cerebrovascular disorders, 21 males and 17 females, aged 33.7, 27 with arteriovenous malformations (AVMs) with a nidus 2 - 8 cm in diameter among which 7 had a diameter >or= 6 cm, and 11 cases with aneurysms among which 3 cases being with an aneurysm >or= 2.5 cm in diameter, and 4 being at the Hunt-Hess grade 1, 4 at the grade 2, and 3 at the grade 3 preoperatively, underwent cerebrovascular surgery assisted with intraoperative angiography. After intubation was achieved and general anesthesia was administrated, a catheter was inserted into the right femoral artery to the intracranial artery related to the surgery. When the lesion was managed, such as the AVMs were resected or the aneurysm was clipped, intraoperative angiography was performed so as to monitor the surgical process. RESULTS: Nine of the 38 patients underwent emergency operation because of acute intracranial hemorrhage without preoperative angiography and intraoperative angiography conformed the diagnosis of AVM in 7 of them and the diagnosis of aneurysms in the other 2 patients. Intraoperative angiography showed that satisfying management was achieved in 36 of the 38 patients (94.7%), and residue of ophthalmic artery aneurysm was seen in 1 patient which underwent clip adjustment later. Only 1 patient with posterior fossa AVM had residual AVM that was resected later. There was no operation mortality, no unexpected major artery occlusion, and no complication attributable to angiography. Intraoperative angiography lasted 53.4 minutes (20 - 125 minutes). CONCLUSION: Intraoperative angiography is able to detect unexpected residual aneurysm, AVM nidus, and major artery occlusion, helps modify the technical faults, thus preventing re-operation, and decreases the complication rate in cerebrovascular surgery.

Adolescent↗

PubMed2006

Acid sites and oxidation center in molybdena supported on tin oxide as studied by solid-state NMR spectroscopy and theoretical calculation.

Solid-state NMR spectroscopy and density functional theory (DFT) calculations were employed to study the structure and properties, especially the solid acidity, of molybdenum oxide supported on tin oxide. As demonstrated by solid-state NMR experiments, Mo species are mainly dispersed on the surface of SnO(2) support rather than significantly dissolved into the SnO(2) structure and Brønsted as well as Lewis acid sites are present on the MoO(3)/SnO(2) catalyst. Acid strength of the supported metal oxide is stronger than those of zeolites, e.g., HY and HZSM-5, though the concentration of acid sites is relatively lower. The DFT calculated (13)C chemical shift for acetone adsorbed on MoO(3)/SnO(2) is in good agreement with the experimental value, which confirms our proposed structure of -Mo-(OH)-Sn- for the Brønsted acid site. Reducibility of the supported metal oxide is also demonstrated by solid-state NMR experiments and an active oxidation center of this catalyst is proposed as well.

Acids↗