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Biomedical subjects

Y Sun

Publications and source records attributed to Y Sun.

At least 577 records · Page 32Linked to original sources
PubMed1998

Serum-free culture of Pasteurella haemolytica optimized for leukotoxin production.

OBJECTIVE: To screen supernatants of Pasteurella haemolytica cultures grown in 4 serum-free culture media for maximal leukotoxin (LKT) production and minimal protein concentration as an optimal source of LKT for purification. SAMPLE POPULATION: One strain of P haemolytica biotype A serotype 1 originally isolated from the pneumonic lung of a calf. PROCEDURE: Pasteurella haemolytica was grown in brain-heart infusion (BHI) broth, yeast-tryptone broth, RPMI-1640 medium, and McCoy's modified 5A medium. Culture biomass and protein concentration, LKT activity, and LKT concentration in culture supernatants were measured. Effects of media pH and supplementation with metal cations and glucose on growth rate of P haemolytica and culture supernatant parameters were evaluated. RESULTS: Pasteurella haemolytica cultivated in BHI broth or RPMI-1640 medium containing 0.1 M phosphate (pH 6.8) produced the highest concentrations of LKT. Supplementation of RPMI-1640 medium with 0.36 mM FeCl3 or 1.0 mM MgSO4 further increased specific activity of LKT in culture supernatant, but addition of 1% glucose did not enhance LKT production. Leukotoxin production in MgSO4-supplemented RPMI-1640 medium was comparable to that in serum protein-supplemented medium. CONCLUSIONS: Although BHI broth was superior to RPMI-1640 medium for P haemolytica growth and LKT production, the higher protein concentration and lower LKT specific activity made BHI broth a less desirable medium, compared with RPMI-1640 medium. Growth rate and LKT production with minimal protein content was optimal in pH 6.8 phosphate-buffered MgSO4-supplemented RPMI-1640 medium. This medium can serve as a source of culture supernatant for purification of LKT.

Animals↗
PubMed1998

Technique for arterial-phase contrast-enhanced three-dimensional MR angiography of the carotid and vertebral arteries.

Our goal was to evaluate whether contrast-enhanced three-dimensional MR angiography using the MR Smartprep technique would enable us to obtain arterial-phase MR angiograms of the carotid and vertebral arteries. The study included 35 patients with suspected lesions of the neck in whom the MR Smartprep technique was used for MR angiography performed with a 1.5-T superconducting system. The tracker volume was placed primarily in the middle part of the right common carotid artery. The imaging volume was placed in a coronal direction to include the carotid and vertebral arteries from the aortic arch to the skull base. A centric phase-ordering scheme was used. Imaging times were 20 to 38 seconds for 14 patients and 11 to 16 seconds for 21 patients. By using a smaller tracker volume and an imaging time of less than 16 seconds, we were able to achieve a 100% successful triggering rate and to delineate selectively arterial-phase carotid and vertebral arteries with almost no venous contamination. Contract-enhanced 3-D MR angiography with the MR Smartprep technique was useful for showing arterial-phase carotid and vertebral arteries selectively.

Aorta, Thoracic↗
PubMed1998

Serum cholesterol and osteoarthritis. The baseline examination of the Ulm Osteoarthritis Study.

OBJECTIVE: To assess the association between serum cholesterol and osteoarthritis (OA). METHODS: OA patterns were studied in 809 patients with knee or hip joint replacement due to OA in 4 hospitals in southwest Germany. Participants had a standardized interview and examination. Radiographs of the contralateral joint as well as both hands and a blood sample were obtained. Serum cholesterol levels were divided into tertiles and hypercholesterolemia was defined as > or = 6.2 mmol/l or use of antihyperlipidemic drugs. According to the presence or absence of radiographic OA in the contralateral joint, participants were categorized as having bilateral or unilateral OA. If radiographic OA of different finger joints was present, participants were categorized as having generalized OA. Odds ratios and 95% confidence intervals for the association of serum cholesterol with OA patterns were calculated with logistic regression, adjusting for potential confounders. RESULTS: Eighty-five percent of participants with radiographs had bilateral OA and 26% generalized OA. No association was observed between hypercholesterolemia and bilateral OA. Hypercholesterolemia (OR 1.61; 95% CI 1.06-2.47) and high serum cholesterol levels (3rd versus 1st tertile: OR 1.73; 95% CI 1.02-2.92) were independently associated with generalized OA. This association was almost exclusively due to participants with knee OA. CONCLUSION: These data add to the evidence regarding the independent role of serum cholesterol as a systemic risk factor for OA. The discrepant associations observed for different OA patterns are likely due to the relative weight of other risk factors.

Aged↗
PubMed1998

Cardiac remodelling by fibrous tissue: role of local factors and circulating hormones.

Following myocardial infarction (MI), extensive fibrosis appears at and remote to the MI and is associated with diastolic dysfunction. Both circulating and tissue hormones contribute to the adverse structural remodelling of the myocardium and thereby influence the progressive nature of heart failure. In this review, factors contributing to the appearance of fibrous tissue will be considered, with special emphasis on the role of peptides produced within the diseased myocardium and on the circulating hormones of the renin-angiotensin-aldosterone system.

Aldosterone↗
PubMed1998

bcl-2/bax expression and p53 gene status in human bladder cancer: relationship to early recurrence with intravesical chemotherapy after resection.

PURPOSE: Studies have shown that the effects of chemotherapy depend on some biochemical mechanisms to induce apoptosis. Many genes are involved in apoptosis modulation, including p53, bcl-2 and bax. We determined the roles of p53 status and the ratio of bcl-2/bax proteins for predicting the recurrence of bladder superficial transitional cell carcinoma that had been treated with intravesical chemotherapy after resection. MATERIALS AND METHODS: We performed Western blot analysis to express bcl-2 and bax proteins, and PCR-SSCP to determine the alteration in the p53 gene in 43 patients with transitional cell carcinoma of the bladder treated with intravesical chemotherapy after tumor resection. RESULTS: The expression of bcl-2 or bax did not correlate with histological grade, clinical stage or relapse. In cases of relapse within 1 year after resection bcl-2/bax was greater than and less than 1 in 50 and 11%, respectively (p <0.01). Recurrence within 1 year after the initial operation was also more common in patients with than without p53 gene mutation (64 versus 22%, p <0.05). Furthermore, bcl-2/bax greater than and less than 1 was associated with p53 gene mutation in 38 and 11% of cases, respectively (p <0.05). CONCLUSIONS: A bcl-2/bax ratio greater than 1 and p53 gene mutation were closely associated with early relapse in patients with superficial transitional cell carcinoma of the bladder during intravesical chemotherapy after resection. This finding suggests that the relative levels of bcl-2 and bax, and p53 gene status may contribute to drug sensitivity and progression, and help to predict recurrence. Moreover, bcl-2/bax correlated with p53 status, which implies that cross talk among bcl-2, bax and p53 has a role in influencing drug induced apoptosis and regulating resistance to chemotherapy.

Carcinoma, Transitional Cell↗
PubMed1998

Linking multiple heterogeneous data sources to practice guidelines.

The BiliLIGHT system is a World Wide Web (Web) based system that integrates an interactive clinical practice guideline with real-time patient-data retrieval from remote heterogeneous data sources to help clinicians manage newborn jaundice at the point of care in three clinical settings. We briefly describe the system, how actual information exchange of medical data across institutional boundaries was achieved, and how the data were connected to a CPG. In particular, we examine the requirements for patient identification, exchange protocols, authentication, and a standard vocabulary.

Computer Systems↗
PubMed1997

p53CP, a putative p53 competing protein that specifically binds to the consensus p53 DNA binding sites: a third member of the p53 family?

p53 tumor suppressor protein negatively regulates cell growth, mainly through the transactivation of its downstream target genes. As a sequence-specific DNA binding transcription factor, p53 specifically binds to a 20-bp consensus motif 5'-PuPuPuC(A/T) (T/A)GPyPyPyPuPuPuC(A/T)(T/A)GPyPyPy-3'. We have now identified, partially purified, and characterized an additional approximately 40-kDa nuclear protein, p53CP (p53 competing protein), that specifically binds to the consensus p53 binding sites found in several p53 downstream target genes, including Waf-1, Gadd45, Mdm2, Bax, and RGC. The minimal sequence requirement for binding is a 14-bp motif, 5'-CTTGCTTGAACAGG-3' [5'-C(A/T)(T/A)GPyPyPyPuPuPuC(A/T)(T/A)G-3'], which includes the central nucleotides of the typical p53 binding site with one mismatch. p53CP and p53 (complexed with antibody) showed a similar binding specificity to Waf-1 site but differences in Gadd45 and T3SF binding. Like p53, p53CP also binds both double- and single-stranded DNA oligonucleotides. Important to note, cell cycle blockers and DNA damaging reagents, which induce p53 binding activity, were found to inhibit p53CP binding in p53-positive, but not in p53-negative, cells. This finding suggested a p53-dependent coordinate regulation of p53 and p53CP in response to external stimuli. p53CP therefore could be a third member of the p53 family, in addition to p53 and p73, a newly identified p53 homolog. p53CP, if sequestering p53 from its DNA binding sites through competitive binding, may provide a novel mechanism of p53 inactivation. Alternatively, p53CP may have p53-like functions by binding and transactivating p53 downstream target genes. Cloning of the p53CP gene ultimately will resolve this issue.

Animals↗
PubMed1997

Phosphoenolpyruvate carboxykinase (GTP) gene transcription and hyperglycemia are regulated by glucocorticoids in genetically obese db/db transgenic mice.

The molecular mechanisms underlying increased hepatic phosphoenolpyruvate carboxykinase (PEPCK) gene transcription and gluconeogenesis in type II diabetes are largely unknown. To examine the involvement of glucocorticoids and the cis-acting insulin response sequence (IRS, -416/-407) in the genetically obese db/db mouse model, we generated crosses between C57BL/KsJ-db/+ mice and transgenic mice that express -460 or -2000 base pairs of the rat PEPCK gene promoter containing an intact or mutated IRS, linked to a reporter gene. Transgenic mice expressing the intact PEPCK(460)-CRP (C-reactive protein) transgene bred to near homozygosity at the db locus were obese, hyperinsulinemic, and developed fasting hyperglycemia (389 +/- 26 mg/100 ml) between 4 and 10 weeks of age. Levels of CRP reporter gene expression were increased 2-fold despite severe hyperinsulinemia compared with non-diabetic non-obese transgenic mice. Reporter gene expression was also increased 2-fold in transgenic obese diabetic db/db mice bearing a mutation in the IRS, -2000(IRS)-hGx, compared with non-obese non-diabetic transgenic 2000(IRS)-hGx mice. Treatment of obese diabetic db/db transgenic mice with the glucocorticoid receptor blocker RU 486 decreased plasma glucose by 50% and reduced PEPCK, GLUT2, glucose-6-phosphatase, tyrosine aminotransferase, CRP, and hGx reporter gene expression to levels similar to those of non-obese normoglycemic transgenic mice. Taken together, these results establish that -460 bp of 5'-flanking sequence is sufficient to mediate the induction of PEPCK gene transcription in genetically obese db/db mice during the development of hyperglycemia. The results further demonstrate that the mechanism underlying increased expression of gluconeogenic enzymes in the db/db mouse requires the action of glucocorticoids and occurs independently of factors acting through the PEPCK IRS (-416/-407) promoter binding site.

Animals↗
PubMed1997

RNA minihelices as model substrates for ATP/CTP:tRNA nucleotidyltransferase.

Twenty-one RNA minihelices, resembling the coaxially stacked acceptor- /T-stems and T-loop found along the top of a tRNA's three-dimensional structure, were synthesized and used as substrates for ATP/CTP:tRNA nucleotidyltransferases from Escherichia coli and Saccharomyces cerevisiae. The sequence of nucleotides in the loop varied at positions corresponding to residues 56, 57 and 58 in the T-loop of a tRNA. All minihelices were substrates for both enzymes, and the identity of bases in the loop affected the interaction. In general, RNAs with purines in the loop were better substrates than those with pyrimidines, although no single base identity absolutely determined the effectiveness of the RNA as substrate. RNAs lacking bases near the 5'-end were good substrates for the E. coli enzyme, but were poor substrates for that from yeast. The apparent Km values for selected minihelices were 2-3 times that for natural tRNA, and values for apparent Vmax were lowered 5-10-fold.

Autoradiography↗
PubMed1997

Calmodulin regulation of Drosophila light-activated channels and receptor function mediates termination of the light response in vivo.

Calmodulin (CAM) participates in a variety of intracellular transduction processes by modulating signaling molecules in response to calcium changes. We report the characterization of Drosophila Cam mutants and the role of CAM in photoreceptor cell function. Contrary to current models of excitation and TRP channel function, we demonstrate that the transient phenotype of trp mutants can be explained by CAM regulation of the TRPL channel rather than by the loss of a store-operated conductance leading to depletion of the internal stores. We also analyzed light responses in a variety of mutant and transgenic backgrounds and demonstrate the importance of calmodulin in mediating calcium-dependent negative regulation of phototransduction. Our results show that CAM coordinates termination of the light response by modulating receptor and ion channel activity.

Animals↗
PubMed1997

Structural determinants in AUF1 required for high affinity binding to A + U-rich elements.

AUF1 is an RNA-binding protein that contains two nonidentical RNA recognition motifs (RRMs). AUF1 binds to A + U-rich elements (AREs) with high affinity. The binding of AUF1 to AREs is believed to serve as a signal to an mRNA-processing pathway that degrades mRNAs encoding many cytokines, oncoproteins, and G protein-coupled receptors. Because the ARE binding activity of AUF1 appears central to the regulation of many important genes, we analyzed the domains of the protein that are important for this activity. Examination of the RNA binding affinity of various AUF1 mutants suggests that both RRMs may be required for binding to the human c-fos ARE. However, the two RRMs together are not sufficient. Highest affinity binding of AUF1 to an ARE requires an alanine-rich region of the N terminus and a short glutamine-rich region in the C terminus. In addition, the N terminus is required for dimerization of AUF1. However, AUF1 binds an ARE as a hexameric protein. Thus, protein-protein interactions are important for high affinity ARE binding activity of AUF1.

Adenine↗
PubMed1997

Regulation of gliogenesis in the central nervous system by the JAK-STAT signaling pathway.

A mechanism by which members of the ciliary neurotrophic factor (CNTF)-leukemia inhibitory factor cytokine family regulate gliogenesis in the developing mammalian central nervous system was characterized. Activation of the CNTF receptor promoted differentiation of cerebral cortical precursor cells into astrocytes and inhibited differentiation of cortical precursors along a neuronal lineage. Although CNTF stimulated both the Janus kinase-signal transducer and activator of transcription (JAK-STAT) and Ras-mitogen-activated protein kinase signaling pathways in cortical precursor cells, the JAK-STAT signaling pathway selectively enhanced differentiation of these precursors along a glial lineage. These findings suggest that cytokine activation of the JAK-STAT signaling pathway may be a mechanism by which cell fate is controlled during mammalian development.

Animals↗
PubMed1997

Transforming growth factor beta-induced phosphorylation of Smad3 is required for growth inhibition and transcriptional induction in epithelial cells.

Drosophila Mad proteins are intracellular signal transducers of decapentaplegic (dpp), the Drosophila transforming growth factor beta (TGF-beta)/bone morphogenic protein (BMP) homolog. Studies in which the mammalian Smad homologs were transiently overexpressed in cultured cells have implicated Smad2 in TGF-beta signaling, but the physiological relevance of the Smad3 protein in signaling by TGF-beta receptors has not been established. Here we stably expressed Smad proteins at controlled levels in epithelial cells using a novel approach that combines highly efficient retroviral gene transfer and quantitative cell sorting. We show that upon TGF-beta treatment Smad3 becomes rapidly phosphorylated at the SSVS motif at its very C terminus. Either attachment of an epitope tag to the C terminus or replacement of these three serine residues with alanine abolishes TGF-beta-induced Smad3 phosphorylation; these proteins act in a dominant-negative fashion to block the antiproliferative effect of TGF-beta in mink lung epithelial cells. A Smad3 protein in which the three C-terminal serines have been replaced by aspartic acids is also a dominant inhibitor of TGF-beta signaling, but can activate plasminogen activator inhibitor 1 (PAI-1) transcription in a ligand-independent fashion when its nuclear localization is forced by transient overexpression. Phosphorylation of the three C-terminal serine residues of Smad3 by an activated TGF-beta receptor complex is an essential step in signal transduction by TGF-beta for both inhibition of cell proliferation and activation of the PAI-1 promoter.

Amino Acid Sequence↗
PubMed1997

Neuregulin-3 (NRG3): a novel neural tissue-enriched protein that binds and activates ErbB4.

We describe the identification of Neuregulin-3 (NRG3), a novel protein that is structurally related to the neuregulins (NRG1). The NRG1/neuregulins are a diverse family of proteins that arise by alternative splicing from a single gene. These proteins play an important role in controlling the growth and differentiation of glial, epithelial, and muscle cells. The biological effects of NRG1 are mediated by receptor tyrosine kinases ErbB2, ErbB3, and ErbB4. However, genetic studies have suggested that the activity of ErbB4 may also be regulated in the central nervous system by a ligand distinct from NRG1. NRG3 is predicted to contain an extracellular domain with an epidermal growth factor (EGF) motif, a transmembrane domain, and a large cytoplasmic domain. We show that the EGF-like domain of NRG3 binds to the extracellular domain of ErbB4 in vitro. Moreover, NRG3 binds to ErbB4 expressed on cells and stimulates tyrosine phosphorylation of this receptor. The expression of NRG3 is highly restricted to the developing and adult nervous system. These data suggest that NRG3 is a novel, neural-enriched ligand for ErbB4.

Amino Acid Sequence↗
PubMed1997

Alternative splicing of cyclin transcripts in maize endosperm.

Cyclins are the regulatory subunits of cyclin-dependent protein kinases. In investigations of the expression of a cyclin gene during maize endosperm development, we detected a cyclin transcript with a 63-bp deletion in the region encoding the conserved 'cyclin box' where cyclin interacts with p34cdc2, the catalytic domain of the cyclin-dependent protein kinase. Analysis of cDNA and genomic sequences, and other observations, indicated that the deletion was caused by alternative splicing of a retained intron in the normally spliced transcript. Whereas the normally spliced cyclin RNA was mitotically functional, as indicated by its ability to promote maturation of Xenopus oocytes, the alternatively spliced transcript was unable to promote maturation. In addition to maize endosperm, the alternatively spliced cyclin was detected in apical meristem, mature leaf, root tip and mature root.

Alternative Splicing↗
PubMed1997

Scavenger receptor BI promotes high density lipoprotein-mediated cellular cholesterol efflux.

Scavenger receptor BI (SR-BI) binds high density lipoproteins (HDL) with high affinity and mediates the selective uptake of HDL cholesteryl ester. We examined the potential role of SR-BI in mediating cellular cholesterol efflux. In Chinese hamster ovary cells stably transfected with murine SR-BI, overexpression of SR-BI resulted in a 3-4-fold stimulation of initial cholesterol efflux rates. Efflux rates correlated with SR-BI expression in cells and HDL concentration in the medium. When incubated with synthetic cholesterol-free HDL, SR-BI-transfected cells showed approximately 3-fold increases in initial rates of efflux compared with control cells, indicating that SR-BI expression enhances net cholesterol efflux mediated by discoidal HDL. In six different cell types, including cultured macrophages, the rate of efflux of cholesterol mediated by HDL or serum was well correlated with cellular SR-BI expression level. In addition, in situ hybridization experiments revealed that SR-BI mRNA was expressed in the thickened intima of atheromatous aorta of apolipoprotein E knockout mice. Thus, SR-BI is an authentic HDL receptor mediating cellular cholesterol efflux. SR-BI may facilitate the initial steps of HDL-mediated cholesterol efflux in the arterial wall as well as later steps of reverse cholesterol transport involving uptake of HDL cholesterol in the liver.

Animals↗