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Biomedical subjects

C Yu

Publications and source records attributed to C Yu.

At least 163 records · Page 9Linked to original sources
PubMed1999

Investigation of the structural stability of cardiotoxin analogue III from the Taiwan cobra by hydrogen-deuterium exchange kinetics.

The conformational stability of a small ( approximately 7 kDa), all beta-sheet protein, cardiotoxin analogue III (CTX III), from the venom of the Taiwan cobra has been investigated by hydrogen-deuterium (H/D) exchange using two-dimensional NMR spectroscopy. The H/D exchange kinetics of backbone amide protons in CTX III has been monitored at pD 3.6 and 6.6 (at 25 degrees C), for over 5000 h. Examination of H/D exchange kinetics in the protein showed that a number of slowly exchanging residues are in the hydrophobic core of the protein. The average protection factor of the amide protons of residues belonging to the triple-stranded beta-sheet domain is about 20 times greater than that of those in the double-stranded beta-sheet segment. The residues in the C-terminal tail of the molecule, though structureless, have been found to exhibit significant protection against H/D exchange. Comparison of the quenched-flow H/D exchange data on CTX III with those obtained in the present study reveals that the most slowly exchanging portion constitutes the folding core of the protein.

Amides↗
PubMed1999

Stable mixed hematopoietic chimerism in dog leukocyte antigen-identical littermate dogs given lymph node irradiation before and pharmacologic immunosuppression after marrow transplantation.

Stable mixed donor/host hematopoietic chimerism can be accomplished in dog leukocyte antigen (DLA)-identical littermate dogs given sublethal (200 cGy) total-body irradiation (TBI) before and immunosuppression with mycophenolate mofetil (MMF) and cyclosporine (CSP) after transplant (Blood 89:3048, 1997). Studies were based on the hypothesis that drugs that prevent graft-versus-host disease (GVHD) after transplant also suppress host-versus-graft (HVG) reactions and thereby enhance engraftment. Here, we asked whether pretransplant TBI provided marrow space for the graft to home or caused host immunosuppression. To address the questions, recipients were given pretransplant irradiation to cervical, thoracic, and abdominal lymph nodes (except pelvis), DLA-identical littermate marrow grafts, and MMF/CSP posttransplant. Six dogs that received 450 cGy irradiation showed initial engraftment. Two rejected their grafts after 8 and 18 weeks, 1 died with GVHD and engraftment, and 3 are alive as mixed chimeras after 57 to 97 weeks. Four dogs given 200 cGy irradiation also showed initial engraftment, but rejected their grafts after 10 to 18 weeks. Mixed chimerism was present in nonirradiated marrow and lymph node spaces and involved granulocytes, T cells, and monocytes. While other explanations are possible, results seem consistent with the hypothesis that pretransplant radiation provides host immunosuppression, and grafts can create their own marrow space. These data set the stage for the development of novel transplant regimens that substitute immunosuppressive for cytotoxic agents.

Animals↗
PubMed1999

Cloning and mapping of the XRN2 gene to human chromosome 20p11.1-p11.2.

The Dhm1 gene is the mouse homologue of the dhp1(+) gene of Schizosaccharomyces pombe, which is involved in homologous recombination and RNA metabolism, such as RNA synthesis and RNA trafficking, in S. pombe. Complementation analysis showed the Dhm1 gene on a multicopy plasmid can rescue the temperature-sensitivity mutation of dhp1(ts) and the lethality of the dhp1 null mutation. This finding suggests that Dhm1 has a function in mouse similar to that of dhp1(+). The human homologue of this gene, XRN2, has been identified. A 3.6-kb transcript of XRN2 was detected in 16 tissues examined and was more abundant in testis. By radiation hybrid panel mapping, the XRN2 gene was localized to chromosome 20p11.1-p11.2 between markers D20S180 and D20S871.

Adult↗
PubMed1999

GATA-1 and erythropoietin cooperate to promote erythroid cell survival by regulating bcl-xL expression.

The transcription factor GATA-1 is essential for normal erythropoiesis. By examining in vitro-differentiated embryonic stem cells, we showed previously that in the absence of GATA-1, committed erythroid precursors fail to complete maturation and instead undergo apoptosis. The mechanisms by which GATA-1 controls cell survival are unknown. Here we report that in erythroid cells, GATA-1 strongly induces the expression of the anti-apoptotic protein bcl-xL, but not the related proteins bcl-2 and mcl-1. Consistent with a role for bcl-xL in mediating GATA-1-induced erythroid cell survival, in vitro-differentiated bcl-xL-/- embryonic stem cells fail to generate viable mature definitive erythroid cells, a phenotype resembling that of GATA-1 gene disruption. In addition, we show that erythropoietin, which is also required for erythroid cell survival, cooperates with GATA-1 to stimulate bcl-xL gene expression and to maintain erythroid cell viability during terminal maturation. Together, our data show that bcl-xL is essential for normal erythroid development and suggest a regulatory hierarchy in which bcl-xL is a critical downstream effector of GATA-1 and erythropoietin-mediated signals.

Animals↗
PubMed1999

Secondary structure formation is the earliest structural event in the refolding of an all beta-sheet protein.

The refolding kinetics of cobrotoxin (CBTX), a small-molecular-weight ( approximately 7 kDa) all beta-sheet protein, has been monitored using a variety of biophysical techniques. The secondary structure formation and hydrophobic collapse occur as distinct events during the refolding of the protein. Complete secondary structure formation occurs prior to the clustering of the hydrophobic residues. The late stage(s) of the refolding pathway of CBTX is characterized by change(s) in the local environment and optical asymmetry of the indole ring of the sole tryptophan residue. The results obtained in the present study, to our knowledge, represent the first unambiguous experimental support for the framework model of protein folding.

Cobra Neurotoxin Proteins↗
PubMed1999

Cellular expression of alpha-gustducin and the A blood group antigen in rat fungiform taste buds cross-reinnervated by the IXth nerve.

Although taste buds are trophically dependent on their innervation, cross-reinnervation experiments have shown that their gustatory sensitivities are determined by the local epithelium. Both the gustatory G-protein, alpha-gustducin, and the cell-surface carbohydrate, the A blood group antigen, are expressed by significantly fewer fungiform than vallate taste cells in the rat. In these experiments, one side of the anterior portion of the tongue was cross-reinnervated by the IXth nerve in order to determine whether the molecular expression of taste bud cells is determined by the epithelium from which they arise or by the nerve on which they are trophically dependent. The proximal portion of the IXth nerve was anastomosed to the distal portion of the chorda tympani (CT) nerve using fibrin glue (IX-CT rats). Control animals had the CT cut and reanastomosed using the same technique (CT-CT rats), or had the CT avulsed from the bulla and resected to prevent regeneration (CTX rats). The animals survived for 12 weeks postoperatively, and the tongues were removed, stained with methylene blue, and the fungiform taste pores counted on both sides. Tissue from the anterior 5 mm of the tongue was cut into 50-microm sections, which were incubated with antibodies against alpha-gustducin and the human blood group A antigen. In both CT-CT and IX-CT rats, there was regeneration of fungiform taste buds, although in both groups there were significantly fewer taste buds on the operated side of the tongue. The normal vallate papilla had a mean of 8.37 alpha-gustducin-expressing cells and 5.22 A-expressing cells per taste bud, whereas the fungiform papillae contained 3.06 and 0.23 cells per taste bud, respectively. In both CT-CT and IX-CT rats there was a normal number of cells expressing alpha-gustducin or the A antigen in regenerated taste buds; in the CTX animals there was a significant decrease in the expression of these markers. These results demonstrate that the molecular phenotype of taste bud cells is determined by the local epithelium from which they arise and not by properties of the innervating nerve.

ABO Blood-Group System↗
PubMed1999

Binding of nucleotide triphosphates to cardiotoxin analogue II from the Taiwan cobra venom (Naja naja atra). Elucidation of the structural interactions in the dATP-cardiotoxin analogue ii complex.

Snake venom cardiotoxins have been recently shown to block the enzymatic activity of phospholipid protein kinase and Na+,K+-ATPase. To understand the molecular basis for the inhibitory effects of cardiotoxin on the action of these enzymes, the nucleotide triphosphate binding ability of cardiotoxin analogue II (CTX II) from the Taiwan cobra (Naja naja atra) venom is investigated using a variety of spectroscopic techniques such as fluorescence, circular dichroism, and two-dimensional NMR. CTX II is found to bind to all the four nucleotide triphosphates (ATP, UTP, GTP, and CTP) with similar affinity. Detailed studies of the binding of dATP to CTX II indicated that the toxin molecule is significantly stabilized in the presence of the nucleotide. Molecular modeling, based on the NOEs observed for the dATP.CTX II complex, reveals that dATP binds to the CTX II molecule at the groove enclosed between the N- and C-terminal ends of the toxin molecule. Based on the results obtained in the present study, a molecular mechanism to account for the inhibition of the enzymatic activity of the phospholipid-sensitive protein kinase and Na+,K+-ATPase is also proposed.

Circular Dichroism↗
PubMed1999

Activation of topoisomerase II-mediated excision of chromosomal DNA loops during oxidative stress.

Hydrogen peroxide (H2O2), a reactive oxygen species (ROS), is known to induce oxidative stress and apoptosis. U937 cells treated with H2O2 were shown to produce high molecular weight (HMW) DNA fragments approximately 50 to 100 kb in size in <1 min. The formation of these HMW DNA fragments is reversible and shown to be mediated by DNA topoisomerase II (TOP2). Following this initial event, formation of irreversible HMW DNA fragments and nucleosomal ladders occurs. Our results thus demonstrate a potential role of TOP2 in oxidative damage of DNA and apoptotic cell death.

DNA Damage↗
PubMed1999

Cloning of an L-3-hydroxyacyl-CoA dehydrogenase that interacts with the GLUT4 C-terminus.

Evidence indicates that the carboxy-terminal cytoplasmic domain of glucose transporter 4 (GLUT4) is important for the regulation of GLUT4 in muscle and adipocytes. We cloned from a human skeletal muscle cDNA library a 34-kDa protein which interacts with GLUT4 C-terminal cytoplasmic domain in a two-hybrid system and also with GLUT4 C-terminus synthetic peptide in an in vitro binding assay. This protein, called YP10, showed a high degree (>90%) of sequence homology with l-3-hydroxyacyl-CoA dehydrogenase (HAD) and had a dehydrogenase activity similar to pig heart HAD, which was inhibited by GLUT4 C-terminus synthetic peptide. An antiserum raised against pig heart HAD also reacted with YP10. Western blot analysis using this antiserum revealed abundant immunoreactivity only in the mitochondria- and plasma membrane-enriched fractions of rat adipocytes. Northern blots revealed that YP10 mRNA is most abundant in skeletal and heart muscle. These findings suggest that YP10, a HAD isoform, interacts with GLUT4 at the plasma membrane and may play a role in cross-talk between glucose transport and fatty acid metabolism.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1999

Structurally homologous toxins isolated from the Taiwan cobra (Naja naja atra) differ significantly in their structural stability.

Cardiotoxin and neurotoxin analogues isolated from snake venom sources are highly homologous proteins (>50% homology) with similar three-dimensional structures but exhibit drastically different biological properties. In the present study, we compare the conformational stability of cardiotoxin analogue III (CTX III) and cobrotoxin (CBTX), a neurotoxin analogue, from the Taiwan cobra (Naja naja atra), using circular dichroism spectroscopy and hydrogen-deuterium (H/D) exchange techniques in conjunction with two-dimensional NMR methods. Contrary to expectations, it is found that CTX III and CBTX differ significantly in their structural stabilities. The three-dimensional structure of CBTX is less stable than that of CTX III. The amide protons of residues at the N- and C-terminal ends of the CTX III molecule are strongly protected against H/D exchange, implying that the terminal ends of the molecule are bridged together by significant numbers of hydrogen bonds. However, in CBTX, amide protons at the terminal ends of the molecule do not exhibit an significant protection against H/D exchange. Comparison of the protection factors of the various amide protons in CTX III and CBTX reveals that the extraordinary stability of CTX III stems from the strong network of interactions among the residues at the N- and C-terminal ends and also due to the tight and ordered packing of the nonpolar residues involved in the triple-stranded, anti-parallel, beta-sheet segment of the molecule.

Animals↗
PubMed1999

Design of antineoplastic agents based on the "2-phenylnaphthalene-type" structural pattern. 4. Synthesis and biological activity of 2-chloro-3-(substituted phenoxy)-1, 4-naphthoquinones and related 5,8-dihydroxy-1,4-naphthoquinones.

The intermediate in the preparation of 1,3,7, 10-tetrahydroxybenzo[b]naphtho[2,3-d]furan-6,11-dione (2), 2-chloro-5,8-dimethoxy-3-(3,5-dimethoxyphenoxy)-1,4-naphthoquinone (8h), and corresponding hydroxyl, methoxyl, and acetoxyl analogues was found to possess interesting inhibitory activities in a number of cytotoxic test systems. Activities were also noticed in some 5, 8-dihydroxy-1,4-naphthoquinone derivatives. A structure-activity discussion of compounds of this series is presented. The newly uncovered biological activity of 2-chloro-3-(substituted phenoxyl)-1, 4-naphthoquinones and 2,3-bis(substituted phenoxy)-1, 4-naphthoquinones may suggest an approach for the development of new classes of antineoplastic agents.

Antineoplastic Agents↗
PubMed1999

Echo-enhancing sonography of a large-vessel hemangioma of the neck.

Because of the slow flow in the venous spaces of large-vessel hemangiomas, demonstration of color flow signals with conventional color Doppler or power Doppler sonography may be difficult. We report the case of a 22-year-old female patient with a soft tissue tumor containing multiple fluid-filled spaces in the right supraclavicular region. Gray-scale, color, and power Doppler sonography could not differentiate between cystic lymphangioma and large-vessel hemangioma. The intravenous echo-enhancing contrast agent Levovist was administered, and a significant echo-enhancing effect on color and power Doppler imaging was demonstrated in the fluid-filled spaces and lasted for about 3 minutes. Histopathologic study of the excised tumor confirmed the sonographic diagnosis of hemangioma. Levovist appears useful in depicting slow flow in a large-vessel hemangioma.

Adult↗
PubMed1999

c-kit<low Pluripotent hemopoietic stem cells form CFU-S on day 16.

Using Ly5 congenic mice, we characterized the early differentiation step of pluripotent hemopoietic stem cells. Lineage- (Lin-)/CD71- cells in the bone marrow cells were separated into major histocompatibility complex (MHC) class I(high)/c-kit(low) and MHC class I(high)/c-kit<low populations from C57BL/6 Ly5.1 male mice. These two populations (1,000 cells) were transplanted into lethally irradiated (5.5 Gy x 2) C57BL/6 Ly5.2 female mice. Colony-forming unit in spleen (CFU-S) assays were carried out on days 10, 12, 14, 16, and 20. In the mice that received c-kit(low) cells, CFU-S were first detected on day 12, and the CFU-S counts gradually increased. In contrast, no visible colony was detected until day 14 in the mice that received c-kit<low cells; CFU-S were first observed on day 16. Donor-derived (Ly5.1+) cells, such as B cells, T cells, and myeloid cells, were detected by fluorescence-activated cell sorter analyses, and donor-derived erythroid cells were detected by polymerase chain reaction analyses using Y-chromosome-specific primers. Donor-derived cells in the recipients of c-kit(low) cells were detected in the spleen, bone marrow, and peripheral blood on day 12 after transplantation, while they were detected on day 16 in the mice that received c-kit<low cells. Therefore, c-kit<low cells have the capacity not only to form CFU-S on day 16 but also to reconstitute the recipients with donor-derived hematolymphoid cells 16 days after transplantation.

Animals↗
PubMed1999

The time course of psychophysical end-stopping.

This study measured the time course of psychophysical end-stopping and compared it with the time course of masking. For a 10' D6 target on an 18' D6 pedestal, two abutting end-zone masks (each 13.5' long) covering the filter end-zones reduce masking. This facilitatory 'end-stopping' effect was measured over a range of exposure durations and stimulus onset asynchronies (SOAs). We found that psychophysical end-stopping has a delayed onset which is around 70-100 ms after stimulus onset, in contrast to masking which is robust immediately after stimulus onset, suggesting intracortical feedback processes in the generation of psychophysical end-stopping. The development course of psychophysical end-stopping is relatively long and lasts for approximately 150-200 ms after stimulus onset, in contrast to that of masking which lasts for approximately 100-150 ms. Our results also showed that end-stopping occurs only when the center mask and the end-zone masks have sufficient temporal overlap, possibly indicating that the feedback process for generating end-stopping is triggered by the activation of the spatial filter center by the center mask. These results are in tune with current knowledge of intracortical feedback modulating activities of receptive fields, and have been incorporated into our model to describe the temporal dynamics within end-stopped spatial filters.

Adult↗
PubMed1999

Tyrosine-PEG-derived poly(ether carbonate)s as new biomaterials. Part I: synthesis and evaluation.

Tyrosine PEG-derived poly(ether carbonate)s were prepared by condensation copolymerization with phosgene. The resulting polymers were random copolymers with weight average molecular weights from 40 000 to 200 000 dalton. Chemical structure and purity were confirmed by NMR and FTIR spectral analysis. General structure property correlations were established. The glass transition temperature decreased with increasing PEG content and increasing pendent chain length. When higher molecular weight PEG blocks were used, the glass transition temperature increased relative to identical polymers having shorter PEG blocks. The tensile modulus increased with decreasing PEG content, decreasing pendent chain length, and when longer PEG blocks were used. Water uptake and the rate of backbone degradation increased with increasing PEG content. Microspheres could be prepared by solvent evaporation techniques from copolymers with low PEG content. Release rate of pNA and FITC-dextran from the microspheres increased with increasing PEG content. While tyrosine-derived polycarbonates were excellent substrates for cell attachment and growth, the presence of only 5 mol% of PEG1000 led to low or no cell attachment in short-term cell culture with both rat lung fibroblasts and osteoblasts. The polymers were non-cytotoxic.

3T3 Cells↗
PubMed1999

Tyrosine-PEG-derived poly(ether carbonate)s as new biomaterials. Part II: study of inverse temperature transitions.

Tyrosine-poly(alkylene oxide)-derived poly(ether carbonate)s represent a new group of degradable biomaterials that exhibit inverse temperature transitions. Poly(DTE co 70%PEG,1000 carbonate) was chosen as an example to study this special phase transition behavior of the polymers. The observed transition temperature varied slightly depending on the technique used, e.g. CD always gave a lower temperature than UV/Vis. CD and UV/Vis studies indicated that the transition temperature was both heating rate and concentration dependent. Thermodynamic parameters of the transition (enthalpy, entropy, and free energy) were determined by DSC. The molecularity of the transition was 2.6, as calculated from UV and DSC data. The transition temperature could be varied from 18 to 58 degrees C by changing the polymer structure. The new poly(ether carbonate)s may be used in medical applications such as injectable drug delivery formulations and bioresorbable barriers for the prevention of surgical adhesions.

Biocompatible Materials↗