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Biomedical subjects

W Feng

Publications and source records attributed to W Feng.

At least 73 records · Page 4Linked to original sources
PubMed1998

Molecular and structural biology of thyroid hormone receptors.

1. Thyroid hormone receptors (TR) are expressed from two separate genes (alpha and beta) and belong to the nuclear receptor superfamily, which also contains receptors for steroids, vitamins and prostaglandins. 2. Unliganded TR are bound to DNA thyroid hormone response elements (TRE) predominantly as homodimers, or as heterodimers with retinoid X-receptors (RXR), and are associated with a complex of proteins containing corepressor proteins. Ligand binding promotes corepressor dissociation and binding of a coactivator. 3. Recent studies from our group have focused on the acquisition and use of X-ray crystallographic structures of ligand-binding domains (LBD) of both the rat (r) TR alpha and the human (h) TR beta bound to several different ligands. We have also developed ligands that bind selectively to the TR beta, which may provide ways to explore the differential functions of TR alpha compared with TR beta isoforms. 4. The LBD is comprised mostly of alpha-helices. The ligand is completely buried in the receptor and forms part of its hydrophobic core. Kinetic studies suggest that the limiting step in formation of high-affinity ligand-receptor complexes is the rate of folding of the receptor around the ligand. Ligands can be fitted tightly in the ligand-binding pocket and small differences in this fitting may explain many structure-activity relationships. Interestingly, analysis of the structures of antagonists suggests that they have chemical groups, 'extensions', that could impair receptor folding around them and, thus, prevent the agonist-induced conformation changes in the receptor. 5. The TR structures allowed us to see that the mutations that occur in the syndrome of generalized resistance to thyroid hormone are located in the vicinity of the ligand-binding pocket. 6. X-ray structure of the TR has also been used to guide construction of mutations in the TR surface that block binding of various proteins important for receptor function. Studies with these TR mutants reveal that the interfaces for homo- and heterodimerization map to similar residues in helix 10 and 11 and also allow the definition of the surface for binding of coactivators, which appears to be general for nuclear receptors. Formation of this surface, which involves packing of helix 12 of the TR into a scaffold formed by helices 3 and 5, appears to be the major change in the receptor structure induced by hormone occupancy.

Animals↗
PubMed1998

Inhibition of airway liquid secretion and its effect on the physical properties of airway mucus.

The combination of both Cl- and HCO3- secretion inhibitors causes an accumulation of mucins within the submucosal gland ducts of acetylcholine (ACh)-treated bronchi [S. K. Inglis, M. R. Corboz, A. E. Taylor, and S. T. Ballard. Am. J. Physiol. 272 (Lung Cell. Mol. Physiol. 16): L372-L377, 1997], suggesting indirectly that these agents block airway gland liquid secretion. The present study tested the hypotheses that ACh-stimulated liquid secretion is driven by Cl- and HCO3- secretion and that inhibition of this process leads to secretion of a dehydrated mucus with altered rheological properties. Excised distal bronchi from pigs were pretreated with either a combination of Cl- and HCO3- secretion inhibitors (bumetanide, acetazolamide, dimethylamiloride, and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid) or the dimethyl sulfoxide vehicle and were then treated with ACh to induce secretion. The rate of mucus liquid secretion was substantially reduced when the airways were pretreated with the anion secretion inhibitors. Mucus liquid from inhibitor-pretreated airways contained almost threefold more nonvolatile solids than the control liquid. Rheological analysis revealed that mucus liquid from inhibitor-pretreated airways expressed a significantly greater log G* (rigidity factor), whereas tangent delta (recoil factor) was significantly reduced. These results suggest that 1) ACh-induced liquid secretion in bronchi is driven by both Cl- and HCO3- secretion and 2) inhibition of ACh-induced liquid secretion results in the secretion of mucus with a reduced water content and altered rheological properties.

Acetylcholine↗
PubMed1998

Improved clearability of cystic fibrosis sputum with dextran treatment in vitro.

Most patients with cystic fibrosis (CF) are infected by Pseudomonas aeruginosa. Dextran exhibits anti-adhesive effects in preventing attachment of P. aeruginosa to epithelial cells (1). The initial purpose of this study was to evaluate the potential of dextran to alter the rheology and ciliary transportability of CF sputum prior to initiation of a clinical trial in patients with CF. Sputum samples were collected from 25 patients with CF not receiving rhDNase therapy for use in in vitro testing. Aliquots of CF sputum were treated with 10% vol. Ringer's or the same volume of Dextran 4000 to give a final concentration of 0.4% (4 mg/ml) or 4% (40 mg/ml) dextran in the sputum. Dog mucus samples were collected from seven healthy, anesthetized dogs from the endotracheal tube cuff. Aliquots of dog mucus were subjected to the same concentrations of dextran as the CF sputum. All treated samples were incubated for 30 min at 37 degrees C, and their rheologic properties (viscoelasticity) were evaluated by magnetic microrheometry. For 17 of the sputum samples, frog palate mucociliary transportability was determined from sputum movement on the ciliated, mucus-depleted frog palate, relative to native frog mucus control. Spinnability (cohesiveness) was evaluated by the filancemeter technique for eight sputum samples. Overall, whether for CF sputum or healthy dog mucus, Dextran 4000 treatment significantly reduced viscoelasticity and increased predicted mucociliary and cough clearability. Direct measurements of sputum mucociliary clearability on frog palate increased significantly with 0.4% dextran and 4% dextran compared with saline control. Sputum spinnability (cohesiveness) decreased significantly with both dextran concentrations, too. The effects on viscoelasticity and spinnability were greater at 4% than at 0.4%. There was a significant positive correlation between spinnability and viscoelasticity, and negative relationships between spinnability and both forms of clearability as predicted from viscoelastic measurements. This study suggests that treatment with Dextran 4000 can reduce the crosslink density and cohesiveness of CF and improve mucociliary and cough clearability. Dextran 4000 is an inexpensive and nontoxic agent that may be of benefit in patients with CF lung disease and perhaps in other respiratory disease where mucus retention is an important feature.

Adolescent↗
PubMed1998

Estrogen receptor activation function 1 works by binding p160 coactivator proteins.

Estrogen receptor-alpha contains two transactivation functions, a weak constitutive activation function (AF-1) and a hormone-dependent activation function (AF-2). AF-2 works by recruiting a large coactivator complex, composed of one or more p160s, CREB-binding protein (CBP)/p300, and P/CAF (p300 and CBP-associated factor), via direct contacts with the p160s. We report here that independent AF-1 activity also requires p160 contacts. Unlike AF-2, which binds signature NR boxes in the center of the p160 molecule, AF-1 binds to sequences near the p160 C terminus. We propose that the ability of AF-1 and AF-2 to interact with separate surfaces of the same coactivator is important for the ability of these transactivation functions to synergize.

Acetyltransferases↗
PubMed1998

[Non-invasive determination of human oxygen metabolism during exercise].

Human muscle oxygenation during exercise was studied with near - infrared spectroscopy (NIRS). Ten athletes performed a 12 min aerobic cycling exercise with increasing workloads. Muscle oxygen content (OC), blood lactate (Bla) and heart rate (HR) were measured continuously throughout the test. The values measured showed a linear correlation (r = -0.962) between Bla and OC during aerobic exercise. The athletes and controls were also selected to compare the variation of OC, Bla and HR under exercise of the same workload. In addition, the muscle oxygen decrease and recovery during sprint were determined and discussed. The results demonstrated that NIRS provides an advantageous method for evaluation of oxygen supply and consumption in working muscles during exercise of varying intensity.

Evaluation Studies as Topic↗
PubMed1998

[The changes of pancreatic function after cardiopulmonary bypass].

OBJECTIVE: To evaluate the changes of endocrine and exocrine pancreatic function in patients who underwent heart valve replacement under cardiopulmonary bypass (CPB) in order to optimally conside clinical management perioperatively. METHOD: Sixteen patients with heart valve disease were selected. Serum glucose, lactate, insulin, C peptide, amylase and lipase were measured. RESULT: Hyperglycemia and hyperlactacemia were noted after CPB and peaked at 19:00 on the operative day. Their changes were correctly correlated. Serum glucose and lactate returned to the baseline level on the third postoperative day. The average level of serum insulin were normal, but higher on the third postoperative day. However, the level of serum C peptide was higher than the baseline. It doubled the baseline level at 19:00 on the operative day. The average level of serum amylase and lipase was normal, except the higher level of serum lipase on the fourth postoperative day. In our group, 12 patients had normal serum amylase level perioperatively, and 4 increased serum amylase level (25%), among them 2 patients accompanied with hyperlipasimia (16%). There were 8 patients with hyperlipasimia (50%). CONCLUSION: The endocrine and exocrine pancreatic functions were influenced by CPB and did produce pathophysiologic changes.

Adult↗
PubMed1998

Mechanisms of thyroid hormone action: insights from X-ray crystallographic and functional studies.

This review summarizes the studies conducted in our laboratory on the mechanisms of thyroid hormone action over the past two decades. We have attempted to place our studies on thyroid hormone receptors (TRs) in perspective with the work conducted by other investigators that established their nuclear localization, DNA-binding properties, DNA response elements, and the role of other proteins involved in TR-mediated regulation of gene transcription. Recently, our crystallographic studies of the TR ligand binding domain (LBD) revealed that the ligand has a structural role in the folding of the receptor's hydrophobic core. The analysis of the structure led to biochemical and genetic studies that have defined the surfaces on the TR LBD required for dimerization and binding of coactivator proteins. Placement of the mutations found in patients with the syndrome of generalized resistance to thyroid hormone on the TR LBD revealed that they were restricted to amino acids in the vicinity of the binding pocket for thyroid hormone. The insights gained from the elucidation of the TR LBD structure will provide the basis for the design of compounds with selective agonistic or antagonistic activities.

Animals↗
PubMed1997

Characterization of the long-lasting activator protein-1 complex induced by kainic acid treatment.

Kainic acid is known to induce seizures, neuronal damage and cell loss in the rat hippocampus. Our laboratory has shown that a single kainic acid injection elicits acute increases of activator protein-1 DNA-binding activity and this activity stays at an elevated level for 2 weeks after kainic acid injection. However, some pathological changes such as mossy fiber sprouting do not occur until 2-3 weeks after the kainic acid injection and the specific transcription factors regulating the long-term events after kainic acid treatment are not clear. To determine the involvement of activator protein-1 transcription factors in the long-term events after kainic acid treatment, gel mobility-shift and Western blot analyses were used. The results showed that two activator protein-1 complexes with different mobilities occur during the acute stage. However, only the faster-migrating complex as well as the 35-37-kDa fos-related antigen and Jun-D proteins were seen during the late stage. These results suggest that different activator protein-1 complexes exist at different stages after convulsions and that they regulate ensembles of different genes.

Animals↗
PubMed1997

Involvement of lysine residues in the gating of the ryanodine receptor/Ca2+-release channel of skeletal muscle sarcoplasmic reticulum.

In this study, the modification of skeletal muscle ryanodine receptor (RyR)/Ca2+-release channel with 7-chloro-4-nitrobenzo-2-oxa-1,3,-diazole (Nbd-Cl) demonstrates that lysyl residues are involved in the channel gating. Nbd-Cl was found to have a dual effect: stimulation and inhibition of ryanodine binding and single channel activities. Nbd-Cl, in a time-dependent manner, first stimulated and subsequently inhibited ryanodine binding to both membrane-bound and purified RyR. Incubation of sacroplasmic reticulum membranes with Nbd-Cl for 5-20 s resulted in enhanced ryanodine-binding activity by 2-4-fold due, to an increased binding affinity by about tenfold, with no effect on the total binding sites (Bmax). However, under prolonged incubation (5-20 min), Nbd-Cl strongly inhibited ryanodine binding by decreasing the Bmax with no effect on the binding affinity. Similar effects of stimulation and inhibition by Nbd-Cl were obtained with single channel activity of RyR reconstituted into planar lipid bilayer. Nbd-Cl initially (within a few seconds) activated the channel to a highly open state, then (within a few minutes) inactivated it to the completely closed state. Nbd-Cl-modified protein, as assayed by ryanodine binding or single channel activities, was stable against thiolysis by dithiothreitol, suggesting Nbd-Cl modification of lysyl residues. Evidence from absorption and fluorescence excitation and emission spectra also demonstrated that lysyl residues in RyR were modified by Nbd-Cl. Spectrophotometric data were used to estimate a ratio of up to 1 mol Nbd bound/mol RyR (tetramer) and up to 4 mol Nbd bound per mol RyR (tetramer) for Nbd-Cl stimulated and inhibited RyR activities, respectively. The results clearly indicate the involvement of two classes of lysyl residues in RyR activity. Modification by Nbd-Cl of the fast-reacting group led to stimulation of ryanodine binding and single channel activities, while modification of the slow-reacting group resulted in inhibition of these activities. Thus, the involvement of lysine residues in the gating of the RyR channel is proposed.

4-Chloro-7-nitrobenzofurazan↗
PubMed1997

Automated analysis of protein NMR assignments using methods from artificial intelligence.

An expert system for determining resonance assignments from NMR spectra of proteins is described. Given the amino acid sequence, a two-dimensional 15N-1H heteronuclear correlation spectrum and seven to eight three-dimensional triple-resonance NMR spectra for seven proteins, AUTOASSIGN obtained an average of 98% of sequence-specific spin-system assignments with an error rate of less than 0.5%. Execution times on a Sparc 10 workstation varied from 16 seconds for smaller proteins with simple spectra to one to nine minutes for medium size proteins exhibiting numerous extra spin systems attributed to conformational isomerization. AUTOASSIGN combines symbolic constraint satisfaction methods with a domain-specific knowledge base to exploit the logical structure of the sequential assignment problem, the specific features of the various NMR experiments, and the expected chemical shift frequencies of different amino acids. The current implementation specializes in the analysis of data derived from the most sensitive of the currently available triple-resonance experiments. Potential extensions of the system for analysis of additional types of protein NMR data are also discussed.

Automation↗
PubMed1997

Borrelia burgdorferi P35 and P37 proteins, expressed in vivo, elicit protective immunity.

p35 and p37 are Borrelia burgdorferi genes encoding 35 and 37 kDa proteins. The gene products were identified by differential screening of a B. burgdorferi expression library with sera from B. burgdorferi infected- and B. burgdorferi-hyperimmunized mice. Northern blot and RT-PCR analyses confirmed that these genes were selectively expressed in vivo. ELISA, using P35 and P37, showed that infected mice (5 of 5, 100%) and patients (31 of 43, 72%) with Lyme borreliosis developed P35 or P37 antibodies. Mice developed peak IgG titers to P35 and P37 within 30 days, followed by decline. Mice given both P35 and P37 antisera were protected from challenge with 10(2) B. burgdorferi, and P35 and P37 antisera also afforded protection when administered 24 hr after spirochete challenge. The use of in vivo-expressed antigens such as P35 and P37 represents a new approach for Lyme disease serodiagnosis and for understanding the role of B. burgdorferi-specific immune responses in host immunity.

Amino Acid Sequence↗
PubMed1997

Mutations in the conserved C-terminal sequence in thyroid hormone receptor dissociate hormone-dependent activation from interference with AP-1 activity.

A short C-terminal sequence that is deleted in the v-ErbA oncoprotein and conserved in members of the nuclear receptor superfamily is required for normal biological function of its normal cellular counterpart, the thyroid hormone receptor alpha (T3R alpha). We carried out an extensive mutational analysis of this region based on the crystal structure of the hormone-bound ligand binding domain of T3R alpha. Mutagenesis of Leu398 or Glu401, which are surface exposed according to the crystal structure, completely blocks or significantly impairs T3-dependent transcriptional activation but does not affect or only partially diminishes interference with AP-1 activity. These are the first mutations that clearly dissociate these activities for T3R alpha. Substitution of Leu400, which is also surface exposed, does not affect interference with AP-1 activity and only partially diminishes T3-dependent transactivation. None of the mutations affect ligand-independent transactivation, consistent with previous findings that this activity is mediated by the N-terminal domain of T3R alpha. The loss of ligand-dependent transactivation for some mutants can largely be reversed in the presence of GRIP1, which acts as a strong ligand-dependent coactivator for wild-type T3R alpha. There is excellent correlation between T3-dependent in vitro association of GRIP1 with T3R alpha mutants and their ability to support T3-dependent transcriptional activation. Therefore, GRIP1, previously found to interact with the glucocorticoid, estrogen, and androgen receptors, may also have a role in T3R alpha-mediated ligand-dependent transcriptional activation. When fused to a heterologous DNA binding domain, that of the yeast transactivator GAL4, the conserved C terminus of T3R alpha functions as a strong ligand-independent activator in both mammalian and yeast cells. However, point mutations within this region have drastically different effects on these activities compared to their effect on the full-length T3R alpha. We conclude that the C-terminal conserved region contains a recognition surface for GRIP1 or a similar coactivator that facilitates its interaction with the basal transcriptional apparatus. While important for ligand-dependent transactivation, this interaction surface is not directly involved in transrepression of AP-1 activity.

Amino Acid Sequence↗
PubMed1997

Trophic effects by epidermal growth factor on duodenal mucosa and exocrine pancreas in rats.

Epidermal growth factor (EGF) is a potent growth factor with possible implications on the regulation of pancreatic secretion and duodenal absorption but also on pancreatic tumor growth. In the present study the growth effect on duodenal mucosa and pancreas by a 14-day continuous infusion of three different doses of EGF (4, 30 and 60 micrograms EGF/kg/24 h) was studied in rats. The EGF content in duodenal mucosa and pancreatic tissue was significantly increased by 30 and 60 micrograms/kg/24 h of EGF while plasma levels were only marginally increased. Neither duodenal mucosal nor pancreatic weights were changed but DNA content in both tissues was increased with the higher EGF doses. Long-term EGF infusion has moderate trophic effect on duodenal mucosa and the pancreas. There is a high tissue uptake of EGF, specially in duodenal mucosa. The hyperplasia seems to be related to tissue levels of EGF but not to plasma levels.

Animals↗
PubMed1997

[Antitumor activity of Hypsizigus marmoreus. II. Preventive effect against lung metastasis of Lewis lung carcinoma].

Antitumor activity of Hypsizigus marmoreus, an edible mushroom, was investigated by in vivo bioassay. The aqueous extract, hereinafter referred to as YH, was tested against syngeneic tumor, Lewis lung carcinoma. YH was found to give a significant increase in life span when assayed using a solid tumor, Lewis lung carcinoma, by intraperitoneal administration, but not as much by oral administration. It was also found that YH have an inhibitory activity of spontaneous tumor metastasis in mice bearing Lewis lung carcinoma by intraperitoneal administration. YH significantly decreased the number of metastasized nodules. It was suggested by Winn test that antitumor and antimetasatic activities shown by YH was effective in increasing activity on immunological by competent cells.

Animals↗
PubMed1997

[Detection of bcl-2/JH fusion gene in patients with B cell non-Hodgkin's lymphoma by polymerase chain reaction and its clinical implication].

OBJECTIVE: To investigate the frequency and clinical implication of bcl-2/JH gene rearrangement in B cell non-Hodgkin's lymphomas(B-NHLs). METHODS: Major breakpoint region (MBR) and minor cluster region(mcr) of bcl-2 rearrangement were amplified by polymerase chain reaction in fresh tumor tissue, bone marrow and peripheral blood samples from 23 cases of B-NHL. RESULTS: Translocation breakpoint was revealed in 10 fresh tumor tissue (71.4% of follicular NHL, 31.3% of diffuse NHL), 8 bone marrow and 7 peripheral blood specimens. The MBR was involved in most of the cases, while the mcr only in one. In addition, of 18 patients with normal bone marrow morphology, 4 were PCR positive, including 2 in early stage ( I and II). Untreated patients with bcl-2 gene rearrangement obtained lower complete remission rate than those without the rearrangement. CONCLUSION: Detection of bcl-2/JH fusion gene was helpful in diagnosing and staging lymphomas, selecting treatment protocols, and monitoring minimal residual diseases.

Adolescent↗