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Biomedical subjects

H Wang

Publications and source records attributed to H Wang.

At least 667 records · Page 37Linked to original sources
PubMed2000

Negative regulation of growth hormone receptor/JAK2 signaling by signal regulatory protein alpha.

Signal regulatory proteins (SIRPs) are receptor-like transmembrane proteins, the majority of which contain a cytoplasmic proline-rich region and four cytoplasmic tyrosines that, when phosphorylated, bind SH2 domain-containing protein tyrosine phosphatases (SHP). We demonstrated previously that growth hormone (GH) induces tyrosyl phosphorylation of SIRPalpha and association of SIRPalpha with SHP-2. The GH-activated tyrosine kinase JAK2 associates with and tyrosyl-phosphorylates SIRPalpha1. Here we show that JAK2-SIRPalpha1 association does not require phosphotyrosines in SIRPalpha1 or JAK2 or the proline-rich region of SIRPalpha1. However, when the C-terminal 30 amino acids of SIRPalpha1 containing the proline-rich region and tyrosine 495 are deleted, tyrosyl phosphorylation of SIRPalpha1 by JAK2 and association of SHP-2 with SIRPalpha1 are reduced. GH-dependent tyrosyl phosphorylation of JAK2 is reduced when wild-type SIRPalpha1 compared with SIRPalpha1 lacking the four cytoplasmic tyrosines (SIRP 4YF) is expressed in cells, suggesting that SIRPalpha1 negatively regulates GHR/JAK2 signaling. Consistent with reduced JAK2 activity, overexpression of wild-type SIRPalpha1 but not SIRP 4YF reduces GH-induced phosphorylation of ERKs 1 and 2, STAT3, and STAT5B. These results suggest that SIRPalpha1 is a negative regulator of GH signaling and that the ability of SIRPalpha1 mutants to negatively regulate GHR-JAK2 signaling correlates with their ability to bind SHP-2.

3T3 Cells↗
PubMed2000

A new lectin with highly potent antihepatoma and antisarcoma activities from the oyster mushroom Pleurotus ostreatus.

A dimeric lectin, composed of subunits with a molecular weight of 40 and 41 kDa, respectively, and demonstrating similarity in N-terminal sequence to each other and to Aleuria aurantia lectin, was isolated from fresh fruiting bodies of the edible mushroom Pleurotus ostreatus. The lectin was unadsorbed on DEAE-cellulose in 10 mmol/L phosphate buffer (pH 7.5), subsequently adsorbed on CM-cellulose in 10 mmol/L NH(4)OAc (pH 5.4), and came off in the first peak from a Superose 12 column during fast protein liquid chromatography. The lectin was acid-labile, alkali-labile, and heat-labile. Its hemagglutinating activity was sensitive to inhibition by CaCl(2), MgCl(2), MnCL(2) and FeCl(3) and potentiation by AlCl(3). Melibiose, lactose, d-galactose, alpha-methyl-d-galactopyranoside, N-acetylneuraminic acid, raffinose, and inulin were capable of inhibiting its hemagglutinating activity, with melibiose being the most potent. The lectin exerted potent antitumor activity in mice bearing sarcoma S-180 and hepatoma H-22. Survival in these mice was prolonged and body weight increase reduced after lectin treatment.

Amino Acid Sequence↗
PubMed2000

Nicotine is a potent blocker of the cardiac A-type K(+) channels. Effects on cloned Kv4.3 channels and native transient outward current.

BACKGROUND: Nicotine is a main constituent of cigarette smoke and smokeless tobacco, known to increase the risk of sudden cardiac death. This study aimed at establishing ionic mechanisms underlying potential electrophysiological effects of nicotine. METHODS AND RESULTS: Effects of nicotine on Kv4.3 and Kv4.2 channels expressed in Xenopus oocytes were studied at the whole-cell and single-channel levels. The effects of nicotine on the transient outward K(+) current (I:(to)) were studied by use of whole-cell patch-clamp techniques in canine ventricular myocytes. Nicotine potently inhibited Kv4 current. The concentration for half-maximal inhibition (IC(50)) was 40+/-4 nmol/L, and the current was abolished by 100 micromol/L nicotine. The IC(50) for block of native I:(to) was 270+/-43 nmol/L. The steady-state activation properties of Kv4.3 and I:(to) were unaltered by nicotine, whereas positive shifts of the inactivation curves were observed. Of the total inhibition of Kv4.3 and I:(to) by nicotine, 40% was due to tonic block and 60% was attributable to use-dependent block. Activation, inactivation, and reactivation kinetics were not significantly changed by nicotine. Nicotine reduced single-channel conductance, open probability, and open time but increased the closed time of Kv4.3. The effects of nicotine were not altered by antagonists to various neurotransmitter receptors, indicating direct effects on I:(to) channels. CONCLUSIONS: Nicotine is a potent inhibitor of cardiac A-type K(+) channels, with blockade probably due to block of closed and open channels. This action may contribute to the ability of nicotine to affect cardiac electrophysiology and induce arrhythmias.

Animals↗
PubMed2000

The interferon- and differentiation-inducible p202a protein inhibits the transcriptional activity of c-Myc by blocking its association with Max.

p202a is a murine protein that is induced during the fusion of myoblasts to myotubes and can also be induced by interferon. Even 2-3-fold overexpression of p202a in cells retards proliferation. p202a was shown to modulate transcription by binding, and inhibiting the activity of several transcription factors including c-Fos, c-Jun, AP-2, E2F1, E2F4, NF-kappaB, MyoD, and myogenin. Here we report that p202a also bound the c-Myc protein in vitro and in vivo; the C-terminal p202a b segment bound the C-terminal basic region helix-loop-helix-leucine zipper (bHLHLZ) region of c-Myc. The transfection of a p202a expression plasmid inhibited the c-Myc-dependent expression of reporter plasmids in transient assays; moreover, overexpression of p202a in stable cell lines decreased the endogenous levels of mRNAs whose expression is driven by c-Myc. These effects of p202a are consistent with our finding that the binding of p202a to c-Myc inhibited the binding of c-Myc to Max in vitro and in vivo. p202a also inhibited the c-Myc-induced anchorage-independent growth and apoptosis of Rat-1 cells. The inhibition of c-Myc-dependent transcription, proliferation, and apoptosis by p202a is in line with the involvement of p202a in differentiation.

Animals↗
PubMed2000

High mobility group 1 protein (HMG-1) stimulates proinflammatory cytokine synthesis in human monocytes.

Lipopolysaccharide (LPS) is lethal to animals because it activates cytokine release, causing septic shock and tissue injury. Early proinflammatory cytokines (e.g., tumor necrosis factor [TNF] and interleukin [IL]-1) released within the first few hours of endotoxemia stimulate mediator cascades that persist for days and can lead to death. High mobility group 1 protein (HMG-1), a ubiquitous DNA-binding protein, was recently identified as a "late" mediator of endotoxin lethality. Anti-HMG-1 antibodies neutralized the delayed increase in serum HMG-1, and protected against endotoxin lethality, even when passive immunization was delayed until after the early cytokine response. Here we examined whether HMG-1 might stimulate cytokine synthesis in human peripheral blood mononuclear cell cultures. Addition of purified recombinant HMG-1 to human monocyte cultures significantly stimulated the release of TNF, IL-1alpha, IL-1beta, IL-1RA, IL-6, IL-8, macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta; but not IL-10 or IL-12. HMG-1 concentrations that activated monocytes were within the pathological range previously observed in endotoxemic animals, and in serum obtained from septic patients. HMG-1 failed to stimulate cytokine release in lymphocytes, indicating that cellular stimulation was specific. Cytokine release after HMG-1 stimulation was delayed and biphasic compared with LPS stimulation. Computer-assisted image analysis demonstrated that peak intensity of HMG-1-induced cellular TNF staining was comparable to that observed after maximal stimulation with LPS. Administration of HMG-1 to Balb/c mice significantly increased serum TNF levels in vivo. Together, these results indicate that, like other cytokine mediators of endotoxin lethality (e.g., TNF and IL-1), extracellular HMG-1 is a regulator of monocyte proinflammatory cytokine synthesis.

Animals↗
PubMed2000

Transperineal brachytherapy in patients with large prostate glands.

The purpose of this study is to help clarify the use of prostate size as a selection factor for prostate brachytherapy. From 1997 to 1998, 33 patients with a TRUS-based prostate volume greater than 50 cc were treated at the University of Washington by I-125 (144 Gy) or Pd-103 (115 Gy) implantation for prostatic carcinoma. These 33 patients comprised 7% of the total implants performed. Each patient underwent a preimplant TRUS study in the lithotomy position, taking serial axial images of the prostate at 0.5 cm intervals from the base of the gland to the apex. The contours on the preimplant TRUS images were used to calculate the prostate volumes reported here. Only one patient received supplemental external beam irradiation prior to implantation. Twelve patients were treated with neoadjuvant androgen ablation prior to implantation. The prostate volumes quoted here are those taken after hormonal downsizing. Postimplant axial CT images were digitized to calculate the CT-based target coverage. Preimplant urinary obstructive symptoms were quantified by the criteria of the American Urologic Association. Each patient was contacted at the time of this article preparation to update postimplant morbidity information. In all cases, at least 80% of the postimplant volume was covered, despite a median implant-related volume increase of 15%. Five of the 33 patients' postimplant CT scans showed some degree of incomplete target coverage of the anterior/lateral prostate margin. There was no clear association between inadequate anterior/lateral coverage and the degree of interference. Twelve of the 33 patients developed acute postimplant urinary retention, all occurring within 24 hr of implantation. Within this group of 33 patients with a large prostate volume, there was no relationship between the likelihood of acute or chronic urinary retention and preimplant prostate size or obstructive symptoms. Patients who developed postimplant retention lasting more than one week were generally managed by intermittent self-catheterization. By one month, 85% of patients were catheter-free. Based on the data reported here, we are more inclined to accept patients with a large prostate for implantation without insisting on preimplant size reduction. Int. J. Cancer (Radiat. Oncol. Invest.) 90, 199-205 (2000).

Brachytherapy↗
PubMed2000

Transforming growth factor-beta 1 inhibits cytokine-mediated induction of human metalloelastase in macrophages.

Matrix metalloproteinases (MMP) have been identified in vulnerable areas of atherosclerotic plaques and may contribute to plaque instability through extracellular matrix degradation. Human metalloelastase (MMP-12) is a macrophage-specific MMP with broad substrate specificity and is capable of degrading proteins found in the extracellular matrix of atheromas. Despite its potential importance, little is known about the regulation of MMP-12 expression in the context of atherosclerosis. In this study, we report that in human peripheral blood-derived macrophages, MMP-12 mRNA was markedly up-regulated by several pro-atherosclerotic cytokines and growth factors including interleukin-1beta, tumor necrosis factor-alpha, macrophage colony-stimulating factor, vascular endothelial growth factor, and platelet-derived growth factor-BB. In contrast, the pleiotropic anti-inflammatory growth factor transforming growth factor-beta1 (TGF-beta1) inhibited cytokine-mediated induction of MMP-12 mRNA, protein, and enzymatic activity. Analyses of MMP-12 promoter through transient transfections and electrophoretic mobility shift assays indicated that both its induction by cytokines and its inhibition by TGF-beta1 depended on signaling through an AP-1 site at -81 base pairs. Moreover, the inhibitory effect of TGF-beta1 on MMP-12 was dependent on Smad3. Taken together, MMP-12 is induced by several factors implicated in atherosclerosis. The inhibition of MMP-12 expression by TGF-beta1 suggests that TGF-beta1, acting via Smad3, may promote plaque stability.

Animals↗
PubMed2000

Molecular targets of a human HNF1 alpha mutation responsible for pancreatic beta-cell dysfunction.

The reverse tetracycline-dependent transactivator system was employed in insulinoma INS-1 cells to achieve controlled inducible expression of hepatocyte nuclear factor-1 alpha (HNF1 alpha)-P291fsinsC, the most common mutation associated with subtype 3 of maturity-onset diabetes of the young (MODY3). Nuclear localized HNF1 alpha-P291fsinsC protein exerts its dominant-negative effects by competing with endogenous HNF1 alpha for the cognate DNA-binding site. HNF1 alpha controls multiple genes implicated in pancreatic beta-cell function and notably in metabolism- secretion coupling. In addition to reduced expression of the genes encoding insulin, glucose transporter-2, L-pyruvate kinase, aldolase B and 3-hydroxy-3-methylglutaryl coenzyme A reductase, induction of HNF1 alpha-P291fsinsC also significantly inhibits expression of mitochondrial 2-oxoglutarate dehydrogenase (OGDH) E1 subunit mRNA and protein. OGDH enzyme activity and [(14)C]pyruvate oxidation were also reduced. In contrast, the mRNA and protein levels of mitochondrial uncoupling protein-2 were dramatically increased by HNF1 alpha-P291fsinsC induction. As predicted from this altered gene expression profile, HNF1 alpha-P291fsinsC also inhibits insulin secretory responses to glucose and leucine, correlated with impaired nutrient-evoked mitochondrial ATP production and mitochondrial membrane hyperpolarization. These unprecedented results suggest the molecular mechanism of HNF1 alpha-P291fsinsC causing beta-cell dysfunction.

Adenosine Triphosphate↗
PubMed2000

5-Alkyltryptamine derivatives as highly selective and potent 5-HT1D receptor agonists.

A series of 5-alkyltryptamines (6) and the corresponding conformationally constrained analogues (8) have been synthesized. The structure activity relationships (SAR) at the 5-position of the indole skeleton and the ethylamine side chain have been studied. Functional activities were assessed using isolated rabbit saphenous vein. Potent, selective ligands were found (6e, Ki 2.5 nM, 5-HT1B/5-HT1D 125-fold) that have potential for treating acute migraine.

Animals↗
PubMed2000

Primary structure, genomic organization, and functional and electrogenic characteristics of human system N 1, a Na+- and H+-coupled glutamine transporter.

We have cloned the human Na(+)- and H(+)-coupled amino acid transport system N (hSN1) from HepG2 liver cells and investigated its functional characteristics. Human SN1 protein consists of 504 amino acids and shows high homology to rat SN1 and rat brain glutamine transporter (GlnT). When expressed in mammalian cells, the transport function of human SN1 could be demonstrated with glutamine as the substrate in the presence of LiCl (instead of NaCl) and cysteine. The transport activity was saturable, pH-sensitive, and specific for glutamine, histidine, asparagine, and alanine. Analysis of Li(+) activation kinetics showed a Li(+):glutamine stoichiometry of 2:1. When expressed in Xenopus laevis oocytes, the transport of glutamine or asparagine via human SN1 was associated with inward currents under voltage-clamped conditions. The transport function, monitored as glutamine- or asparagine-induced currents, was saturable, Na(+)-dependent, Li(+)-tolerant, and pH-sensitive. The transport cycle was associated with the involvement of more than one Na(+) ion. Uptake of asparagine was directly demonstrable in these oocytes by using radiolabeled substrate, and this uptake was inhibited by membrane depolarization. In addition, simultaneous measurement of asparagine influx and charge influx in the same oocyte yielded an asparagine:charge ratio of 1. These data suggest that SN1 mediates the influx of two Na(+) and one amino acid substrate per transport cycle coupled to the efflux of one H(+), rendering the transport process electrogenic.

Amino Acid Transport Systems, Neutral↗
PubMed2000

Human brain sub-systems for discrimination of visual shapes.

To investigate whether stereo and plane visual shapes are processed in the same brain system, participants were instructed to discriminate whether two visual stimuli presented in sequence were identical and event-related potential (ERP) was recorded from their scalp. The first (S1) and the second stimuli (S2) were the same stereo shapes in condition 1, but were different in condition 3. They were the same plane shapes in condition 2, but different in condition 4. A negative component (N270) was recorded in condition 3 and 4, which showed the maximal amplitude in the right posterior scalp in condition 3 and in the anterior scalp in condition 4. A different cognition mechanism is involved in the processing of non-matched stereo and plane visual shapes.

Adult↗
PubMed2000

Changes of reliability and efficiency of micronucleus bioassay in Vicia faba after exposure to metal contamination for several generations.

Mitotic root micronucleus (MCN) frequency in Vicia faba as a bioassay, is primarily based on the extent of the sentinel Vicia response in terms of cytogenetic damage quantitatively or qualitatively to indicate the presence of mutagenic contaminants. This paper describes an investigation designed to assess changes in MCN frequencies of Vicia faba from three generation plants obtained, respectively from a reference site (RS) and a metal-contaminated experimental field (EF) in the bioassay of mutagenic Cd(2+) and NaN(3). The background value, dose-response to Cd(2+) and to NaN(3) in three generation (F(1), F(2) and F(3)) plants of the EF and the initial (F(0)) plants were determined in terms of MCN frequencies. With more generations of growing Vicia plants in the EF, a higher background value of MCN frequency, a lower slope value in the regression equation, a smaller ratio of MCN frequency between the control and treatment in the same generation and larger perturbation values were observed. This denotes that the decreased reliability and efficiency are represented in Vicia plants from the EF if the plants are used as sentinels in the bioassay of mutagenic Cd(2+) and NaN(3). It was concluded that the Vicia MCN bioassay should be used as an endpoint biomarker acceptable in biomonitoring environmental mutagens when the sentinel plants were collected from clean areas. Because no place is absolutely without pollutants, it is suggested that several seed stock centers should be established for providing sentinel Vicia if Vicia MCN bioassay is used as a biomarker to identify the global environmental status.

Journal Article↗
PubMed2000

Primary structure, functional characteristics and tissue expression pattern of human ATA2, a subtype of amino acid transport system A.

We report here on the primary structure and functional characteristics of the protein responsible for the system A amino acid transport activity that is known to be expressed in most human tissues. This transporter, designated ATA2 for amino acid transporter A2, was cloned from the human hepatoma cell line HepG2. Human ATA2 (hATA2) consists of 506 amino acids and exhibits a high degree of homology to rat ATA2. hATA2-specific mRNA is ubiquitously expressed in human tissues. When expressed in mammalian cells, hATA2 mediates Na+-dependent transport of alpha-(methylamino)isobutyric acid, a specific model substrate for system A. The transporter is specific for neutral amino acids. It is pH-sensitive and Li+-intolerant. The Na+:amino acid stoichiometry is 1:1.

Amino Acid Sequence↗
PubMed2000

Bgs2p, a 1,3-beta-glucan synthase subunit, is essential for maturation of ascospore wall in Schizosaccharomyces pombe.

Previously we have reported that Drc1p/Cps1p, a 1,3-beta-glucan synthase subunit, is essential for division septum assembly in Schizosaccharomyces pombe. In this report, we present evidence that S. pombe Bgs2p, a 1,3-beta-glucan synthase that shows 56% identity to Drc1p/Cps1p, is essential for maturation of ascospore wall in S. pombe, but is not required for vegetative growth. Diploid cells homozygous for the bgs2-null mutation, as well as homothallic bgs2-null mutant haploids undergo meiosis normally. However, a 1, 3-beta-glucan containing spore wall is not assembled in these cells. The spores resulting from meiosis of a bgs2-null mutant lyse upon release from the ascus and are therefore inviable. Using a green fluorescent protein-tagged Bgs2p, we demonstrate that Bgs2p is localized at the periphery of the ascospores during meiosis and sporulation. However, Bgs2p is not detected in vegetative cells. We conclude that Bgs2p is required for 1,3-beta-glucan synthesis during ascospore wall maturation.

Cell Division↗
PubMed2000

A biomimetic total synthesis of (-)-spirotryprostatin B and related studies.

The prenylated natural products spirotryprostatin A and B derived from the Trp-Pro diketopiperazine also feature an oxidative rearrangement of the indole to form a spirooxindole. Synthetically, formation of the oxindole ring was stereoselectively accomplished by reaction of the appropriate indole precursor with N-bromosuccinimide. For optimum results, the oxidation should be carried out prior to diketopiperazine cyclization. In this manner, we have synthesized the tetrahydro- and dihydro- analogues of spirotryprostatin B in four steps from L-tryptophan methyl ester. The dihydro derivative was then converted to spirotryprostatin B by unsaturation of the pyrrolidine ring to a pyrroline, thus unambiguously confirming the structure of the natural product.

Alkaloids↗
PubMed2000

The gamma-aminobutyric acid type A receptor (GABAAR)-associated protein GABARAP interacts with gephyrin but is not involved in receptor anchoring at the synapse.

gamma-Aminobutyric acid type A receptors (GABA(A)Rs) are ligand-gated chloride channels that exist in numerous distinct subunit combinations. At postsynaptic membrane specializations, different GABA(A)R isoforms colocalize with the tubulin-binding protein gephyrin. However, direct interactions of GABA(A)R subunits with gephyrin have not been reported. Recently, the GABA(A)R-associated protein GABARAP was found to bind to the gamma2 subunit of GABA(A)Rs. Here we show that GABARAP interacts with gephyrin in both biochemical assays and transfected cells. Confocal analysis of neurons derived from wild-type and gephyrin-knockout mice revealed that GABARAP is highly enriched in intracellular compartments, but not at gephyrin-positive postsynaptic membrane specializations. Our data indicate that GABARAP-gephyrin interactions are not important for postsynaptic GABA(A)R anchoring but may be implicated in receptor sorting and/or targeting mechanisms. Consistent with this idea, a close homolog of GABARAP, p16, has been found to function as a late-acting intra-Golgi transport factor.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Cloning and functional expression of ATA1, a subtype of amino acid transporter A, from human placenta.

This report describes the primary structure and functional characteristics of human ATA1, a subtype of the amino acid transport system A. The human ATA1 cDNA was isolated from a placental cDNA library. The cDNA codes for a protein of 487 amino acids with 11 putative transmembrane domains. The transporter mRNA ( approximately 9.0 kb) is expressed most prominently in the placenta and heart, but detectable level of expression is evident in other tissues including the brain. When expressed heterologously in mammalian cells, the cloned transporter mediates Na(+)-coupled transport of the system A-specific model substrate alpha-(methylamino)isobutyric acid. The transport process is saturable with a Michaelis-Menten constant of 0. 89 +/- 0.12 mM. The Na(+):amino acid stoichiometry is 1:1 as deduced from the Na(+)-activation kinetics. The transporter is specific for small short-chain neutral amino acids. The gene for the transporter is located on human chromosome 12.

Amino Acid Sequence↗