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Biomedical subjects

Xiang Yu

Publications and source records attributed to Xiang Yu.

At least 19 recordsLinked to original sources
PubMed2006

Nrf2-mediated induction of cytoprotective enzymes by 15-deoxy-Delta12,14-prostaglandin J2 is attenuated by alkenal/one oxidoreductase.

NADPH-dependent alkenal/one oxidoreductase (Aor) was discovered to be highly inducible in rat liver following treatment with the cancer chemopreventive agent 3H-1, 2-dithiole-3-thione. Aor was further characterized as an Nrf2-regulated antioxidative enzyme that reduces carbon-carbon double bonds in a variety of alpha, beta-unsaturated aldehydes and ketones. 15-Deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) is a reactive membrane lipid metabolite that activates multiple pathways, including Nrf2-mediated induction of cytoprotective enzymes. Physiologically, it is postulated that 15d-PGJ2 alkylates key regulatory proteins via the electrophilic carbon centers found in two alpha, beta-unsaturated ketone moieties. This current study addresses the metabolism of 15d-PGJ2 by rat Aor (rAor) and subsequent deactivation of the Nrf2 signaling pathway by both rat and human AOR. We demonstrate that induction of NADPH-dependent quinone oxidoreductase activity by 15d-PGJ2 is markedly attenuated in mouse embryonic fibroblasts that overexpress rAor. Luciferase reporter assay and quantitative real-time PCR confirmed these findings. Concentrations required for doubling the NADPH-dependent quinone oxidoreductase response are increased from 1.8 microm in wild-type to >10 microm in rat Aor transgenic fibroblasts. 15d-PGJ2 is metabolized by recombinant rAor with a Km of 9.6 microm and k(cat) of 18.5 min(-1). The major product is 12,13-dihydro-15-deoxy-Delta12,14-prostaglandin J2 (dihydro-15d-PGJ2). The reduction of C=C by Aor yielding dihydro-15d-PGJ2 abolishes the inducibility in an antioxidant response element-driven luciferase assay. Collectively, these results demonstrate that 15d-PGJ2 can be catabolized by Aor, thereby attenuating subsequent Nrf2 signaling and possibly inflammatory and apoptotic processes also influenced by 15d-PGJ2.

Alcohol Oxidoreductases↗
PubMed2006

Investigating the role of stereochemistry in the activity of anticancer acylfulvenes: synthesis, reductase-mediated bioactivation, and cellular toxicity.

Acylfulvenes comprise a family of semisynthetic natural product derivatives with potent antitumor activities. Previous studies indicated that acylfulvenes are bioactivated by NADPH-dependent alkenal/one reductase (AOR), presumably generating intermediates with the capacity to alkylate cellular targets, such as DNA, proteins, and glutathione. This process is thought to induce apoptosis, and the chemical and biochemical pathways involved are topics of current investigation. In this study, four acylfulvene analogues were synthesized: (-)-acylfulvene, (+)-acylfulvene, (-)-(hydroxymethyl)acylfulvene, and (+)-(hydroxymethyl)acylfulvene. These compounds were synthesized by a chiral-resolution method, described for the first time in this report, and by asymmetric synthesis using a method formally demonstrated previously. Cell toxicity studies indicate a positive correlation between AOR level and acylfulvene sensitivity. The absolute configuration of acylfulvene analogues has a significant influence on cytotoxicity. (-)-(Hydroxymethyl)acylfulvene is 25 times more potent than (+)-(hydroxymethyl)acylfulvene in cells transfected with an AOR overexpression vector. Based on kinetic parameters, the rates of AOR-mediated activation are more strongly dependent on acylfulvene substitution than on absolute stereochemistry. These data support the role of AOR-mediated metabolism and indicate the involvement of other stereochemically dictated pathways, such as transport and biomolecule binding, in contributing to the cytotoxicity of acylfulvenes.

Alcohol Oxidoreductases↗
PubMed2006

Eukaryotic translation initiation factor 5B activity regulates larval growth rate and germline development in Caenorhabditis elegans.

In C. elegans, a population of proliferating germ cells is maintained via GLP-1/Notch signaling; in the absence of GLP-1 signaling, germ cells prematurely enter meiosis and differentiate. We previously identified ego (enhancer of glp-1) genes that promote germline proliferation and interact genetically with the GLP-1 signaling pathway. Here, we report that iffb-1 (initiation factor five B) is an ego gene. iffb-1 encodes the sole C. elegans isoform of eukaryotic translation initiation factor 5B, a protein essential for translation. We have used RNA interference and a deletion mutation to determine the developmental consequences of reduced iffb-1 activity. Our data indicate that maternal iffb-1 gene expression is sufficient for embryogenesis, and zygotic iffb-1 expression is required for development beyond late L1/early L2 stage. Partial reduction in iffb-1 expression delays larval development and can severely disrupt proliferation and differentiation of germ cells. We hypothesize that germline development is particularly sensitive to iffb-1 expression level.

3' Untranslated Regions↗
PubMed2006

In vitro activity of novel rifamycins against rifamycin-resistant Staphylococcus aureus.

We describe novel rifamycin derivatives (new chemical entities [NCEs]) that retain significant activity against a comprehensive collection of Staphylococcus aureus strains that are resistant to rifamycins. This collection of resistant strains contains 21 of the 26 known single-amino-acid alterations in RpoB, the target of rifamycins. Some NCEs also demonstrated a lower frequency of resistance development than rifampin and rifalazil in S. aureus as measured in a resistance emergence test. When assayed for activity against the strongest rifamycin-resistant mutants, several NCEs had MICs of 2 microg/ml, in contrast to MICs of rifampin and rifalazil, which were 512 microg/ml for the same strains. The properties of these NCEs therefore demonstrate a significant improvement over those of earlier rifamycins, which have been limited primarily to combination therapy due to resistance development, and suggest a potential use of these NCEs for monotherapy in several clinical indications.

Drug Resistance, Bacterial↗
PubMed2005

A focused microarray to assess dopaminergic and glial cell differentiation from fetal tissue or embryonic stem cells.

We designed oligonucleotide gene-specific probes to develop a focused array that can be used to discriminate between neural phenotypes, identify biomarkers, and provide an overview of the process of dopaminergic neuron and glial differentiation. We have arrayed approximately 100 genes expressed in dopaminergic neurons, oligodendrocytes, and astrocytes, an additional 200 known cytokines, chemokines, and their respective receptors, as well as markers for pluripotent and progenitor cells. The gene-specific 60-mer 3' biased oligonucleotides for these 281 genes were arrayed in a 25 x 12 format based on function. Using human adult brain substantia nigra, human embryonic stem cells (ESCs), and the differentiated progeny of pluripotent cells, we showed that this array was capable of distinguishing dopaminergic neurons, glial cells, and pluripotent cells by their gene expression profiles in a concentration-dependent manner. Using linear correlation coefficients of input RNA with output intensity, we identified a list of genes that can serve as reporting genes for detecting dopaminergic neurons, glial cells, and contaminating ESCs and progenitors. Finally, we monitored NTera2 differentiation toward dopaminergic neurons and have shown the ability of this array to distinguish stages of differentiation and provide important clues to factors regulating differentiation, the degree of contaminating populations, and stage of cell maturity. We suggest that this focused array will serve as a useful complement to other large-scale arrays in routine assessment of cell properties prior to their therapeutic use.

Base Sequence↗
PubMed2005

Differential response of dendritic cells to human metapneumovirus and respiratory syncytial virus.

Dendritic cells (DCs) play a pivotal role in shaping antiviral immune responses in the respiratory tract. Human metapneumovirus (hMPV) is a recently identified pathogen and like its better known relative, respiratory syncytial virus (RSV), has been increasingly recognized as a major cause of respiratory morbidity in infants and in elderly persons. In the present study, we examined susceptibility as well as cellular responses of human DCs to hMPV compared with RSV. Monocyte-derived DCs (moDCs) were susceptible to infection by both viruses, but only RSV was able to induce a productive infection with release of viral progeny. Despite the fact that viral infection resulted in phenotypic maturation of moDCs, as shown by the upregulation of cell surface markers and antigen-presenting molecules (MHC I and II, CD80, CD83, CD86, CD38), RSV-infected moDCs showed a severely impaired capacity to stimulate CD4+ T cell proliferation. Compared with hMPV, RSV was a more potent inducer of inflammatory and immunomodulatory cytokines, including TNF-alpha, IL-6, IL-1beta, IL-10, and IL-12p70 in both moDCs and plasmacytoid dendritic cells (pDCs). On the other hand, hMPV, but not RSV, was able to trigger production of IFN-alpha by moDCs, while both viruses strongly induced IFN-alpha in pDCs. Finally, both viruses strikingly suppressed IFN-alpha production by moDCs or pDCs stimulated with synthetic dsRNA and CpG-ODN, respectively. The findings provide novel evidence that RSV and hMPV differentially activate human DCs and may use distinct mechanisms to interfere with the host innate and adaptive immune responses.

Antigen Presentation↗
PubMed2005

IL-1 receptor antagonist-mediated therapeutic effect in murine myasthenia gravis is associated with suppressed serum proinflammatory cytokines, C3, and anti-acetylcholine receptor IgG1.

In myasthenia gravis (MG), TNF and IL-1beta polymorphisms and high serum levels of these proinflammatory cytokines have been observed. Likewise, TNF and IL-1beta are critical for the activation of acetylcholine receptor (AChR)-specific T and B cells and for the development of experimental autoimmune myasthenia gravis (EAMG) induced by AChR immunization. We tested the therapeutic effect of human recombinant IL-1 receptor antagonist (IL-1ra) in C57BL/6 mice with EAMG. Multiple daily injections of 0.01 mg of IL-1ra administered for 2 wk following two AChR immunizations decreased the incidence and severity of clinical EAMG. Furthermore, IL-1ra treatment of mice with ongoing clinical EAMG reduced the clinical symptoms of disease. The IL-1ra-mediated suppression of clinical disease was associated with suppressed serum IFN-gamma, TNF-alpha, IL-1beta, IL-2, IL-6, C3, and anti-AChR IgG1 without influencing total serum IgG. Therefore, IL-1ra could be used as a nonsteroidal drug for the treatment of MG.

Animals↗
PubMed2005

Nrf2 as a target for cancer chemoprevention.

Chemical insults, whether of endogenous or exogenous origins, play major roles in the etiopathogenesis of many cancers. As such, strategies to blunt their formation and limit their damage to biomolecules are a central aspect of chemoprevention. Cellular defenses against such insults are regulated in part by the transcription factor Nrf2. Nrf2, in turn, regulates gene expression through interactions with the ARE (antioxidant-response-element) found in the promoter regions of many cytoprotective genes. Under basal conditions, Nrf2 is tethered in the cytoplasm to an actin binding protein Keap1. Pharmacological and food-derived agents such as dithiolethiones and isothiocyanates trigger the release of Nrf2 from Keap1, allowing it to translocate into the nucleus and stimulate gene transcription. Studies using nrf2-deficient mice have revealed that Nrf2 regulates basal and inducible expression of multiple categories of genes, including xenobiotic-metabolizing enzymes, antioxidant enzymes, molecular chaperones/stress response proteins, as well as proteasome subunits, that collectively reflect the complex and important role Nrf2 plays in the cellular defense against carcinogens. Nrf2 knockout mice are greatly predisposed to chemical-induced DNA damage and exhibit higher susceptibility towards cancer development in several models of chemical carcinogenesis. Nrf2 also mediates protection against oxidative stress and influences inflammatory processes, both of which contribute to carcinogenesis. Observations that nrf2-deficient mice are refractory to the protective actions of some chemopreventive agents highlight the importance of the Keap1-Nrf2-ARE signaling pathway as a molecular target for prevention.

Animals↗
PubMed2005

Generation of silent synapses by acute in vivo expression of CaMKIV and CREB.

The transcription factor CREB is critical for several forms of experience-dependent plasticity in a range of species and is commonly activated in neurons by calcium/calmodulin-dependent protein kinase IV (CaMKIV). Surprisingly, little is known about the neural circuit adaptations caused by activation of CaMKIV and CREB. Here, we use viral-mediated gene transfer in vivo to examine the consequences of acute expression of constitutively active forms of CaMKIV and CREB on synaptic function in the rodent hippocampus. Acute expression of active CaMKIV or CREB caused an enhancement of both NMDA receptor-mediated synaptic responses and long-term potentiation (LTP). This was accompanied by electrophysiological and morphological changes consistent with the generation of "silent synapses," which provide an ideal substrate for further experience-dependent modifications of neural circuitry and which may also be important for the consolidation of long-term synaptic plasticity and memories.

Animals↗
PubMed2004

Formation and photoluminescence of silver nanoparticles stabilized by a two-armed polymer with a crown ether core.

Silver nanoparticles were synthesized by the use of a two-armed polymer with a crown ether core [poly(styrene)]-dibenzo-18-crown-6-[poly(styrene)] based on the flexibility of the polymer chains and the complex effect of crown ether with Ag(+) and Ag. The size of silver nanoparticles could be tailored by controlling the initial concentrations of the polymer and Ag(+), and the molecular weight of the polymer. The emission of silver nanoparticles was blue-shifted, and the intensity of the photoluminescence of silver nanoparticles stabilized by the polymer was significantly increased due to the complex effect between the crown ether embedded in the polymer and the silver nanoparticles.

Journal Article↗
PubMed2004

A mixed model approach to identify yeast transcriptional regulatory motifs via microarray experiments.

A genome-wide location analysis method has been introduced as a means to simultaneously study protein-DNA binding interactions for a large number of genes on a microarray platform. Identification of interactions between transcription factors (TF) and genes provide insight into the mechanisms that regulate a variety of cellular responses. Drawing proper inferences from the experimental data is key to finding statistically significant TF-gene binding interactions. We describe how the analysis and interpretation of genome-wide location data can be fit into a traditional statistical modeling framework that considers the data across all arrays and formulizes appropriate hypothesis tests. The approach is illustrated with data from a yeast transcription factor binding experiment that illustrates how identified TF-gene interactions can enhance initial exploration of transcriptional regulatory networks. Examples of five kinds of transcriptional regulatory structure are also demonstrated. Some stark differences with previously published results are explored.

Journal Article↗
PubMed2004

NADPH alkenal/one oxidoreductase activity determines sensitivity of cancer cells to the chemotherapeutic alkylating agent irofulven.

Illudins S and M are extremely cytotoxic products of the fungus Omphalotus illudens. They were evaluated as possible anticancer chemotherapeutic agents but displayed unfavorable therapeutic indices. Irofulven (6-hydroxymethylacylfulvene), a less toxic, synthetic derivative of illudin S, has proven very effective in many preclinical and clinical studies. It has been postulated that metabolism via hydrogenation of the 8,9-double bonds of these molecules would unmask the electrophilic, and thus, the toxic nature of their cyclopropyl moieties. Illudins S and M were found to be rapidly metabolized by NADPH-dependent alkenal/one oxidoreductase (AOR) with maximal rates of 115.9 and 44.1 micromol x min(-1) mg(-1), and K(m)s of 308 and 109 microM, respectively. Irofulven was reduced at a much slower rate: V(max) 275 nmol min(-1) mg(-1) and K(m) 145 microM. Human 293 cells transfected with an AOR overexpression vector were 100-fold more sensitive than control cells to irofulven, but displayed little differential sensitivity to illudin M. Addition of glutathione to the alpha,beta-unsaturated ketone moiety of illudin M, but not irofulven, occurred readily at physiological concentrations. Electrophilic intermediates of irofulven and illudin M that were activated by AOR were trapped with glutathione and identified by high performance liquid chromatography with tandem mass spectrometry. Samples of the 60 human tumor cell line panel used by the National Cancer Institute to evaluate potential chemotherapeutic compounds were assayed for AOR activity, which correlated positively with previously determined growth inhibitory measures for irofulven, but not illudin M or S. Collectively, these data indicate that bioactivation of irofulven by AOR plays a predominant role in its chemotherapeutic activity.

Alcohol Oxidoreductases↗
PubMed2004

Multiple functions for the cadherin/catenin complex during neuronal development.

The cadherin/catenin complex is a major transmembrane signaling complex through which extracellular signals can influence the cytoskeleton. It is present in neuronal processes during early development (J. Neurosci. 18 (1998) 6892) and appears to play multiple roles during neural circuit formation and maturation (Nat. Neurosci. 7 (2004) 357; Neuron 35 (2002) 77; Nat. Neurosci. 6 (2003) 1169). In previous work (Nat. Neurosci. 6 (2003) 1169), we showed that molecular manipulation of the cadherin/catenin complex has significant effects on the dendritic aborization of cultured hippocampal neurons at 9 days in vitro (d.i.v.). Here we extend these observations by examining the effects of over-expression of beta-catenin (fused to GFP; GFP-beta-cat(*)) or sequestering endogenous beta-catenin [using the intracellular domain of N-cadherin; Ncad(intra)] in cultured hippocampal neurons at different developmental stages. When transfected at 1 d.i.v. and assayed 48 h later, over-expression of GFP-beta-cat(*) increased axonal length and complexity, while sequestering endogenous beta-catenin had the opposite effect. Dendritic aborization was also enhanced by GFP-beta-cat(*) expression throughout early development although the magnitude of this effect decreased as neurons matured from 3 to 12 d.i.v. Finally, at 12 d.i.v., GFP-beta-cat(*) expression increased the density of dendritic spines although not the relative proportion of different subtypes of spines. These results demonstrate that the cadherin/catenin complex plays multiple roles in the development of neuronal morphology and that these roles change as neurons mature.

Animals↗
PubMed2004

Loss of alpha-hemoglobin-stabilizing protein impairs erythropoiesis and exacerbates beta-thalassemia.

Hemoglobin (Hb) A production during red blood cell development is coordinated to minimize the deleterious effects of free alpha- and beta-Hb subunits, which are unstable and cytotoxic. The alpha-Hb-stabilizing protein (AHSP) is an erythroid protein that specifically binds alpha-Hb and prevents its precipitation in vitro, which suggests that it may function to limit free alpha-Hb toxicities in vivo. We investigated this possibility through gene ablation and biochemical studies. AHSP(-/-) erythrocytes contained hemoglobin precipitates and were short-lived. In hematopoietic tissues, erythroid precursors were elevated in number but exhibited increased apoptosis. Consistent with unstable alpha-Hb, AHSP(-/-) erythrocytes contained increased ROS and evidence of oxidative damage. Moreover, purified recombinant AHSP inhibited ROS production by alpha-Hb in solution. Finally, loss of AHSP worsened the phenotype of beta-thalassemia, a common inherited anemia characterized by excess free alpha-Hb. Together, the data support a model in which AHSP binds alpha-Hb transiently to stabilize its conformation and render it biochemically inert prior to Hb A assembly. This function is essential for normal erythropoiesis and, to a greater extent, in beta-thalassemia. Our findings raise the possibility that altered AHSP expression levels could modulate the severity of beta-thalassemia in humans.

Animals↗
PubMed2003

Array synthesis of novel lipodepsipeptide.

Synthetic array technology was utilized to rapidly synthesize and analyze a diverse set of reductive alkylation analogues of daptomycin. Analysis of the array suggested the use of polar functionality such as sulfonamides or amide or polar spaces such as piperazine would beneficially affect activity.

Alkylation↗