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Biomedical subjects

C Sun

Publications and source records attributed to C Sun.

At least 127 records · Page 7Linked to original sources
PubMed1998

Partial purification of heparanase activities in Chinese hamster ovary cells: evidence for multiple intracellular heparanases.

Heparanases are mammalian endoglycosidases that cleave heparan sulphate glycosaminoglycans from proteoglycan core proteins and degrade them into shorter chains. The enzymes have been proposed to act in a variety of cellular processes, including proteoglycan catabolism, remodelling of basement membranes and release of heparan sulphate-binding ligands from their extracellular storage sites. Additional functions for heparanases may be to generate short heparan sulphate chains that stabilize or activate other proteins. While heparanase activities have been described in a number of tissues and cell lines, it is not known how many different enzymes are responsible for these activities. Our recent studies characterizing the short glycosaminoglycans produced in Chinese hamster ovary (CHO) cells suggested that multiple heparanases are necessary for the formation of the short heparan sulphate chains [Bame and Robson (1997) J. Biol. Chem. 272, 2245-2251]. We examined whether this is the case by purifying heparanase activity from CHO cell homogenates. Based on their ability to bind ion-exchange resins and their elution from gel-filtration columns, four separate heparanase activities were partially purified. All four activities cleave free glycosaminoglycans over a broad pH range of 3.5-6.0 or 6. 5, suggesting that they act in the endosomal/lysosomal pathway. The sizes of the short heparan sulphate chains generated by the partially purified heparanases ranged from 6 to 9 kDa, and for two of the activities the product size is pH-dependent. Three of the four activities degrade proteoglycans as well as the free glycosaminoglycan chain. Interestingly, all four enzymes generate short glycosaminoglycans with a sulphate-rich, modified domain at the non-reducing end of the newly formed chain. Since our previous studies showed that in CHO cells there is also a population of short heparan sulphates with a modified domain at the reducing end of the chain, this suggests that there may be another heparanase in CHO cells that was not purified. Alternatively, our findings suggest that the formation of short heparan sulphate glycosaminoglycans inside CHO cells may be a result of the concerted action of multiple heparanases, and may depend on the proportions of the different enzymes and the environment in which the chains are degraded.

Animals↗
PubMed1998

The NMR solution structure of human glutaredoxin in the fully reduced form.

The determination of the nuclear magnetic resonance (NMR) solution structure of fully reduced human glutaredoxin is described. A total of 1159 useful nuclear Overhauser effect (NOE) upper distance constraints and 187 dihedral angle constraints were obtained as the input for the structure calculations for which the torsion angle dynamics program DYANA has been utilized followed by energy minimization in water with the AMBER force field as implemented in the program OPAL. The resulting 20 conformers have an average root-mean-square deviation value relative to the mean coordinates of 0.54 A for all the backbone atoms N, Calpha and C', and of 1.01 A for all heavy atoms. Human glutaredoxin consists of a four-stranded mixed beta-sheet composed of residues 15 to 19, 43 to 47, 72 to 75 and 78 to 81, and five alpha-helices composed of residues 4 to 9, 24 to 34, 54 to 65, 83 to 91, and 94 to 100. Comparisons with the structures of Escherichia coli glutaredoxin-1, pig liver glutaredoxin and human thioredoxin were made. Electrostatic calculations on the human glutaredoxin structure and that of related proteins provide an understanding of the variation of pKa values for the nucleophilic cysteine in the active site observed among these proteins. In addition, the high-resolution NMR solution structure of human glutaredoxin has been used to model the binding site for glutathione and for ribonucleotide reductase B1 by molecular dynamics simulations.

Glutaredoxins↗
PubMed1998

Overexpression, purification, and biophysical characterization of the heterodimerization domain of the core-binding factor beta subunit.

Core-binding factors (CBF) are heteromeric transcription factors essential for several developmental processes, including hematopoiesis. CBFs contain a DNA-binding CBF alpha subunit and a non-DNA binding CBF beta subunit that increases the affinity of CBF alpha for DNA. We have developed a procedure for overexpressing and purifying full-length CBF beta as well as a truncated form containing the N-terminal 141 amino acids using a novel glutaredoxin fusion expression system. Substantial quantities of the CBF beta proteins can be produced in this manner allowing for their biophysical characterization. We show that the full-length and truncated forms of CBF beta bind to a CBF alpha DNA complex with very similar affinities. Sedimentation equilibrium measurements show these proteins to be monomeric. Circular dichroism spectroscopy demonstrates that CBF beta is a mixed alpha/beta protein and NMR spectroscopy shows that the truncated and full-length proteins are structurally similar and suitable for structure determination by NMR spectroscopy.

Circular Dichroism↗
PubMed1998

Camptothecin analogues/cisplatin: an effective treatment of advanced bladder cancer in a preclinical in vivo model system.

OBJECTIVE: To evaluate the impact of the camptothecin analogs on human TCC xenograft, both as monotherapy and in combination with cisplatin (CDDP). MATERIALS AND METHODS: Human transitional cell carcinoma (TCC) xenograft tumor line (DU4184) tested by subrenal capsule assay in 112 nude mice(NM-SRCA). CDDP and the camptothecin analogs irinotecan (CPT-11) and 9-aminocamptothecin(9-AC) were evaluated. RESULTS: Both of the camptothecin analogs showed significant short term tumor inhibition which translated into enhanced survival. Maximal tumor inhibition (>95%) was achieved when either of the camptothecin analogs was combined with CDDP with minimal host toxicity. This translated into 400% increase in median survival. While all controls were dead 39 days following tumor implantation, none of the combination treated animals had died. CONCLUSION: The combination of CDDP with these camptothecin analogs is an effective therapy against this model of advanced TCC. These observations suggest potential clinical value.

Animals↗
PubMed1998

Dose profiles in the region of abutting photon and electron fields in the irradiation of head and neck tumors.

In the treatment of head and neck tumors, after excluding the spinal cord from the primary photon beam, en face electron fields are employed to boost the dose to the tissues overlying the spinal cord. The electron fields are "hot-matched" on skin with the posterior edges of the photon fields irradiating the primary tumor. The purpose of this study is to measure the dose distribution in the "hot" matched region between the photon and the en face electron fields. Using film dosimetry, we measured the dose distributions at depths of 1 cm and 3 cm in the junction of the abutting photon (4 MV) and electron (9 MeV) fields for a hot-match setup. Two photon field setups were studied: (1) laterally opposed and, (2) shallow (5 degrees) right and left anterior oblique fields, a configuration sometimes used to avoid treating through the shoulders. To investigate the changes in dose distributions due to setup uncertainties, we also measured dose profiles at the same two depths using a 2 mm overlap and a 2 mm gap between the electron and photon fields. For a perfect hot-match, the dose profile across the junction at 1 cm depth consists of "hot-spots" on both sides of the junction. The minimum and maximum doses across the junction are 15% and 58%, respectively, above the prescribed dose for a parallel opposed setup and 35% and 54%, respectively, for the angled setup. At 3 cm depth, a 10% "cold spot" is observed in the electron field proximal to the junction while a 50% 'hot spot' is observed in the photon field for the opposed lateral setup. With the lateral fields angled 5 degrees anteriorly, hot spots are observed on both sides of the junction. The minimum and maximum doses are 23% and 54%, respectively, above the prescribed dose. With the right and left anterior oblique fields, a 2 mm overlap of the en face electron field with the ipsilateral photon field resulted in a 72% and 65% hot spot at 1 cm and 3 cm depths, respectively, in the photon field adjacent to the junction. A 2 mm gap still resulted in about a 45% hot spot in the same region at both depths. Clinically, if dose to the overlying tissue of the spinal cord is of primary concern, our measurements suggest that 80% normalization in the electron boost, together with a slight angulation of the photon fields would ensure adequate dose to the overlying tissues. If dose inhomogeneity to the superficial tissues is critical in the electron irradiation, 90% dose normalization in the electron boost, together with laterally opposed photon fields would be preferred. The clinical decision can only be made on a patient-by-patient basis.

Electrons↗
PubMed1998

The two genes encoding starch-branching enzymes IIa and IIb are differentially expressed in barley.

The sbeIIa and sbeIIb genes, encoding starch-branching enzyme (SBE) IIa and SBEIIb in barley (Hordeum vulgare L.), have been isolated. The 5' portions of the two genes are strongly divergent, primarily due to the 2064-nucleotide-long intron 2 in sbeIIb. The sequence of this intron shows that it contains a retro-transposon-like element. Expression of sbeIIb but not sbeIIa was found to be endosperm specific. The temporal expression patterns for sbeIIa and sbeIIb were similar and peaked around 12 d after pollination. DNA gel-blot analysis demonstrated that sbeIIa and sbeIIb are both single-copy genes in the barley genome. By fluorescence in situ hybridization, the sbeIIa and sbeIIb genes were mapped to chromosomes 2 and 5, respectively. The cDNA clones for SBEIIa and SBEIIb were isolated and sequenced. The amino acid sequences of SBEIIa and SBEIIb were almost 80% identical. The major structural difference between the two enzymes was the presence of a 94-amino acid N-terminal extension in the SBEIIb precursor. The (beta/alpha)8-barrel topology of the alpha-amylase superfamily and the catalytic residues implicated in branching enzymes are conserved in both barley enzymes.

1,4-alpha-Glucan Branching Enzyme↗
PubMed1998

[Treatment of avascular necrosis of femoral head by periosteal cell transplantation: an experimental study].

OBJECTIVE: To investigate the effect of periosteal cell transplantation on the repair of avascular necrosis of femoral head (ANFH). On the basis of successful culture of periosteal cells in vitro. METHODS: The tibial periostea of new born dog were excised and cultured under aseptic conditions. Eight adult dogs were used and divided into 2 groups: experimental group and control group. The animal model of ANFH was made by transferring the freed femoral head into the muscle under the ilium on one side in each dog. Two weeks after the establishment of ANFH, the cultured periosteal cells were collected and transplanted into the necrotic femoral heads in the experimental group, and the femoral heads without periosteal cell transplantation served as the control. Six weeks after cell transplantation, the femoral heads were taken out and histological examination was made. RESULTS: There was active bone formation in the experimental group. The new bone was arranged into bone trabeculae, most of which were covered by a monolayer of osteoblasts. Between bone trabeculae were fibrous tissue rich in blood vessels. In the control group, the bone trabeculae withered and remained necrotic. There were fibrous tissues with few blood vessels between bone trabeculae. CONCLUSION: Periosteal cell transplantation can improve the repair of ANFH.

Animals↗
PubMed1998

[Proliferative effect of low energy laser and colony stimulating factor on human umbilical cord blood hematopoietic cells].

OBJECTIVE: To study the proliferative effect of low energy laser on human cord blood hematopoietic cells in vitro and the relationship between the effect of low energy laser and colony stimulating factor (CSF). METHODS: Human umbilical cord blood hematopoietic cells were irradiated with copper vapour laser and cultured in vitro. The number of colony and cells was calculated. RESULTS: Laser irradiation synergized with CSF in expansion of cord blood hematopoietic cell. The GM-CFUc number from the group treated with irradiation plus CSF increased significantly as compared with that from other groups including laser irradiation or CSF treatment alone or control (P < 0.01). Reincubation of cord blood cells in the soft agar medium revealed that secondary colonies were formed and the absolute number of colony was obviously increased as compared with that before liquid culture. The number of colony in irradiation group was more than these of non-irradiation group. CONCLUSION: Low energy laser irradiation for cord blood stem cells is effective in vitro expansion of cord blood stem cells.

Cell Division↗
PubMed1998

[PTA1 monoclonal antibody induces human platelet aggregation and intra-cytoplasmic Ca2+ elevation].

OBJECTIVE: To explore the mechanism of PTA1 monoclonal antibody (McAb) induced human platelet aggregation and its effect on intra-cytoplasmic Ca2+ level. METHODS: Platelet aggregation, ATP releasing assay and Pollock's test were used. RESULTS: PTA1 McAb induced human platelet aggregation in vitro, which could be completely inhibited by EGTA and PGI2. F(ab')2 of PTA1 McAb had no effect on CD9 or CD41 induced platelet activation and aggregation. PTA1 McAb enhanced platelet intra-cytoplasmic Ca2+ elevation. CONCLUSION: PTA1 McAb inducing platelet aggregation is related to platelet Fc receptor and CD41/CD61 (II b/III a) complex, and the induced platelet intra-cytoplasmic Ca2+ elevation is resulted from Ca2+ influx and releasing of intracytoplasmic Ca2+ storage.

Antibodies, Monoclonal↗
PubMed1998

[Diagnosis and treatment of thoracic outlet syndrome].

OBJECTIVE: Thoracic outlet syndrome (TOS) is clinically common, but liable to be misdiagnosed. We would like to emphasize the recognition of TOS, and through thorough examination for a complete relief from indicated operation. METHODS: 13 cases receiving surgical operations in PUMC hospital from 1982 to 1996 are reported and discussed the cause of misdiagnosis, investigate the various kinds of abnormalities and compare the result of operation. RESULTS: 92% of the patients had experence of being misdiagnosed for other diseases, the history may be as long as 10 years. In the operations we found 8 kinds of anatomic abnormalities that cause the symptoms and complete relief is satisfactory. CONCLUSIONS: We have to emphasize the recognition of TOS. The thorough physical examination is important to diagnosis. Patients with typical and apparent symptoms need an operation to relieve the thoracic outlet through the transaxillary approach.

Adolescent↗
PubMed1998

[Direct determination of zinc in polymerized rosin by flame atomic absorption spectrometry].

Using 95% ethanol as the solvent, we directly determined zinc in polymerized rosin by flame atomic absorption spectrometry. The recovery rate is from 100 to 103 percent. The relative standard deviation (RSD) of the determination is between 1.1-4.1%. The sensitivity is high and the characteristic concentration reaches 0.0077 microg x mL(-1)/1%. The method is quite significant in forestry chemical works with its simplicity and efficiency.

English Abstract↗
PubMed1997

The yeast nucleolar protein Nop4p contains four RNA recognition motifs necessary for ribosome biogenesis.

The Saccharomyces cerevisiae nucleolar protein Nop4p is necessary for processing of rRNA and assembly of 60 S ribosomal subunits. Nop4p is unusual in that it contains four RNA recognition motifs (RRMs) including one noncanonical RRM, as well as several auxiliary motifs, two acidic regions between the RRMs, and a carboxyl-terminal domain rich in lysines and arginines. To examine the functional importance of these motifs, we isolated random and site-directed mutations in NOP4 and assayed Nop4p function in vivo. Our results indicate that each RRM is essential for Nop4p function; mutations in conserved aromatic residues of Nop4p cause a temperature-sensitive lethal phenotype and diminished 60 S ribosomal subunit production. The carboxyl-terminal 68 amino acids are important but apparently not essential; carboxyl-terminal truncation of Nop4p causes slow growth, decreased ribosome production, and mislocalization of Nop4p. Deletion of both acidic motifs is lethal but replacement of most of the acidic residues with alanine has no apparent phenotype. These acidic residues may serve as spacers or tethers to separate the RRMs.

Amino Acid Sequence↗
PubMed1997

Complete 1H, 13C, and 15N NMR resonance assignments and secondary structure of human glutaredoxin in the fully reduced form.

Human glutaredoxin is a member of the glutaredoxin family, which is characterized by a glutathione binding site and a redox-active dithiol/disulfide in the active site. Unlike Escherichia coli glutaredoxin-1, this protein has additional cysteine residues that have been suggested to play a regulatory role in its activity. Human glutaredoxin (106 amino acid residues, M(r) = 12,000) has been purified from a pET expression vector with both uniform 15N labeling and 13C/15N double labeling. The combination of three-dimensional 15N-edited TOCSY, 15N-edited NOESY, HNCA, HN(CO)CA, and gradient sensitivity-enhanced HNCACB and HNCO spectra were used to obtain sequential assignments for residues 2-106 of the protein. The gradient-enhanced version of the HCCH-TOCSY pulse sequence and HCCH-COSY were used to obtain side chain 1H and 13C assignments. The secondary structural elements in the reduced protein were identified based on NOE information, amide proton exchange data, and chemical shift index data. Human glutaredoxin contains five helices extending approximately from residues 4-10, 24-36, 53-64, 83-92, and 94-104. The secondary structure also shows four beta-strands comprised of residues 15-19, 43-48, 71-75, 78-80, which form a beta-sheet almost identical to that found in E. coli glutaredoxin-1. Complete 1H, 13C, and 15N assignments and the secondary structure of fully reduced human glutaredoxin are presented. Comparison to the structures of other glutaredoxins is presented and differences in the secondary structure elements are discussed.

Amino Acid Sequence↗
PubMed1997

Serum basic fibroblast growth factor in pediatric Crohn's disease. Implications for wound healing.

Basic fibroblast growth factor is a heparin-binding protein known to stimulate angiogenesis and promote wound healing in tissues. Since Crohn's disease is characterized in part by submucosal vascular proliferation, we sought to determine whether serum basic fibroblast growth factor is elevated in children with Crohn's disease and whether serum levels reflect disease activity. Sera were obtained from 64 children with Crohn's disease, 44 children with ulcerative colitis, 20 children with functional abdominal pain, and 29 from children with documented inflammatory disease evaluated in our gastroenterology program. Disease activity indices and clinical data were gathered prospectively for the inflammatory bowel disease patients. Serum basic fibroblast growth factor levels were measured by enzyme-linked immunosorbent assay. Although the mean basic fibroblast growth factor level did not significantly differ between children with Crohn's disease and other conditions, there was a strong (r = 0.53, P < 0.001) correlation between basic fibroblast growth factor level and disease activity. The relationship of basic fibroblast growth factor with disease activity persisted even after adjusting for other covariates (including age, sex, hematocrit, albumin, and sedimentation rate) in a multivariate linear regression model. There was also a statistically significant, although less strong correlation (r = 0.33, P = 0.03) between basic fibroblast growth factor level and disease activity in ulcerative colitis. While basic fibroblast growth factor is not a specific marker for Crohn's disease, serum levels reflect disease activity. Therefore, basic fibroblast growth factor release may be important in mediating the angiogenesis and wound healing seen in Crohn's disease.

Adolescent↗
PubMed1997

The use of comparative 137Cs body burden estimates from environmental data/models and whole body counting to evaluate diet models for the ingestion pathway.

Rongelap and Utirik Atolls were contaminated on 1 March 1954, by a U.S. nuclear test at Bikini Atoll code named BRAVO. The people at both atolls were removed from their atolls in the first few days after the detonation and were returned to their atolls at different times. Detailed studies have been carried out over the years by Lawrence Livermore National Laboratory (LLNL) to determine the radiological conditions at the atolls and estimate the doses to the populations. The contribution of each exposure pathway and radionuclide have been evaluated. All dose assessments show that the major potential contribution to the estimated dose is 137Cs uptake via the terrestrial food chain. Brookhaven National Laboratory (BNL) has carried out an extensive whole body counting program at both atolls over several years to directly measure the 137Cs body burden. Here we compare the estimates of the body burdens from the LLNL environmental method with body burdens measured by the BNL whole body counting method. The combination of the results from both methods is used to evaluate proposed diet models to establish more realistic dose assessments. Very good agreement is achieved between the two methods with a diet model that includes both local and imported foods. Other diet models greatly overestimate the body burdens (i.e., dose) observed by whole body counting. The upper 95% confidence limit of interindividual variability around the population mean value based on the environmental method is similar to that calculated from direct measurement by whole body counting. Moreover, the uncertainty in the population mean value based on the environmental method is in very good agreement with the whole body counting data. This provides additional confidence in extrapolating the estimated doses calculated by the environmental method to other islands and atolls.

Body Burden↗
PubMed1997

Dbp3p, a putative RNA helicase in Saccharomyces cerevisiae, is required for efficient pre-rRNA processing predominantly at site A3.

In Saccharomyces cerevisiae, ribosomal biogenesis takes place primarily in the nucleolus, in which a single 35S precursor rRNA (pre-rRNA) is first transcribed and sequentially processed into 25S, 5.8S, and 18S mature rRNAs, leading to the formation of the 40S and 60S ribosomal subunits. Although many components involved in this process have been identified, our understanding of this important cellular process remains limited. Here we report that one of the evolutionarily conserved DEAD-box protein genes in yeast, DBP3, is required for optimal ribosomal biogenesis. DBP3 encodes a putative RNA helicase, Dbp3p, of 523 amino acids in length, which bears a highly charged amino terminus consisting of 10 tandem lysine-lysine-X repeats ([KKX] repeats). Disruption of DBP3 is not lethal but yields a slow-growth phenotype. This genetic depletion of Dbp3p results in a deficiency of 60S ribosomal subunits and a delayed synthesis of the mature 25S rRNA, which is caused by a prominent kinetic delay in pre-rRNA processing at site A3 and to a lesser extent at sites A2 and A0. These data suggest that Dbp3p may directly or indirectly facilitate RNase MRP cleavage at site A3. The direct involvement of Dbp3p in ribosomal biogenesis is supported by the finding that Dbp3p is localized predominantly in the nucleolus. In addition, we show that the [KKX] repeats are dispensable for Dbp3p's function in ribosomal biogenesis but are required for its proper localization. The [KKX] repeats thus represent a novel signaling motif for nuclear localization and/or retention.

Amino Acid Sequence↗
PubMed1997

High-efficiency entrapment of superoxide dismutase into cationic liposomes containing synthetic aminoglycolipid.

A monofatty acid ester of glucosamine (PGlcN) was synthesized to provide liposomal membranes with a positive charge, and the trapping efficiency of negatively charged substances (superoxide dismutases, SODs) into cationic liposomes containing PGlcN or stearylamine (SA) prepared by various methods was compared to find the most efficient trapping methods. We demonstrated that cationic liposomes, which were prepared in a buffer of low ionic strength containing sorbitol by a simple hydration method, could entrap a large amount of negatively charged SODs which retained their activity, as compared with cationic liposomes prepared in a buffer of high ionic strength. We also showed a reverse-phase evaporation method entrapped a large amount of SODs. However, SODs were inactivated during the preparation; therefore, this method was not suitable to entrap the enzyme. Freeze-thaw method induced the formation of cationic liposomes which were smaller than extruded liposomes and could entrap the SODs in a buffer of low ionic strength. Dehydration-rehydration method with a buffer of low ionic strength also entrapped a large amount of SODs, indicating that the integrity of liposomes was lost in the lipid bilayer after freeze-drying and the SODs were entrapped in the reconstruction of liposomes during rehydration. These findings showed that the hydration method based on electrostatic attraction with a buffer of low ionic strength was simple and the most effective for entrapping SODs without loss of their activity.

Cations↗