Biomedical subjects

W Huang

Publications and source records attributed to W Huang.

At least 163 records · Page 9Linked to original sources

PubMed2001

[The relationship between cell proliferation and apoptosis of vestibular epithelium in the developing guinea pig].

OBJECTIVE: The cell proliferation and apoptosis of vestibular epithelium in normal developing guinea pig were observed to elucidate the relationship and effect between proliferation and apoptosis in developing vestibular epithelium. METHODS: Twenty Guinea pigs with different developing ages were used in our studies. Cell proliferation was detected by proliferation cell nuclear antigen (PCNA) immunocytochemistry while apoptosis was detected by TdT-mediated deoxyuridine triphosphate-biotin nick end labelling (TUNEL) method and transmission electro-microscopy. RESULTS: PCNA staining had been detected in supporting cells but not in hair cells, and the positive cells were gradually decreased with ageing. The differentiated hair cells and supporting cells underwent apoptosis in vestibular sensory epithelium, and TUNEL-positive cells were also markedly decreased with ageing. After birth, TUNEL-positive hair cells were located at the top of ampulla. CONCLUSION: During the development of guinea pig, cell proliferation as well as apoptosis events diminish contemporaneously. The balance between proliferation and apoptosis may regulate the normal number of cells, and is related to guarantee the normal structure and function of inner ear.

Animals↗

PubMed2001

Preservation of the hypothalamic structures in the total resection of craniopharyngioma.

OBJECTIVE: To explore an effective method of surgical management of craniopharyngioma. SUBJECTS AND METHODS: Fifty patients with craniopharyngioma had total and subtotal tumor ectomy. There were 29 males and 21 females, ranging in age from 15 to 56 years (mean 34.1 years). MR imaging showed that the tumors were located in the superior sellar region in 24 cases, in superior sella region and extended into the third ventricular floor in 19 cases, into parasella in 3 cases and down to intrasella in 4 cases. Complete cystic tumors were found in 5 cases, while the partial cystic tumor in 24 cases and complete solid tumors in 21 cases. Pterional approach was used in 48 patients and subfrontal approach in 2 patients. Great attention was paid to the preservation of the perforating arteries from the carotid, posterior and anterior communicating and anterior choroidal arteries to the hypothalamic structures. The clinical outcome was evaluated according to the GOS scale. RESULTS: Of the 50 patients surgically treated, 47 patients obtained total ectomy of the tumor and 3 patients with the secondary surgery had subtotal ectomy of the tumor. The pituitary stalk was preserved in 29 (58%) patients, severed in 14 patients and unidentified in 7 patients. Forty-six patients regained a normal life; one patient needed assist in life. Of the 3 deaths, one patient died of diabetes insipidus, one of inhalation asphyxia, and another one of water and sodium disorders. CONCLUSION: Avoidance of the injury to the neural structures in the third ventricular floor and preservation of the perforating arteries to hypothalamus are the key to achieve good surgical results in treating craniopharyngioma.

Adolescent↗

PubMed2001

[Two-photon fluorescence from recombinant green fluorescent protein].

The photoconversion process of recombinant green fluorescent protein (rGFP) was investigated by two-photon excitation. The results indicated that the rGFP had very strong two-photon excitation fluorescence. The changes of two-photon-induced fluorescence polarization suggest that there is a proton transfer process between two different proton states of rGFP chromophores. The conformation of rGFP chromophores could be changed upon illumination, which partly block the energy transfer processes from amino acid residues to chromophores in rGFP, and result in the decrease of two-photon-induced fluorescence intensity. The fluorescence from amino acid residues in rGFP was also observed by three-photon excitation, which resulted from the blocked amino acid residues in rGFP. These results suggested that it is necessary to optimize rGFP excitation and detection for quantitative fluorescence microscopy.

Energy Transfer↗

PubMed2000

Human immune response to streptococcal inhibitor of complement, a serotype M1 group A Streptococcus extracellular protein involved in epidemics.

Streptococcal inhibitor of complement (Sic) is a highly polymorphic extracellular protein made by serotype M1 group A Streptococcus strains that contributes to bacterial persistence in the mammalian upper respiratory tract. New variants of the Sic protein arise very rapidly by positive selection in human populations during M1 epidemics. The human antibody response to Sic was analyzed. Of 636 persons living in diverse localities, 43% had anti-Sic serum antibodies, but only 16.4% had anti-M1 protein serum antibody. Anti-Sic antibody was also present in nasal wash specimens in high frequency. Linear B cell epitope mapping showed that serum antibodies recognized epitopes located in structurally variable regions of Sic and the amino terminal hypervariable region of the M1 protein. Phage display analyses confirmed that the polymorphic regions of Sic are primary targets of host antibodies. These results support the hypothesis that selection of Sic variants occurs on mucosal surfaces by a mechanism that involves acquired host antibody.

Adolescent↗

PubMed2000

Immunohistochemical evidence for the Na+/Ca2+ exchanger in squid olfactory neurons.

The olfactory organs from the squid Lolliguncula brevis are composed of a pseudostratified epithelium containing five morphological subtypes of chemosensory neurons and ciliated support cells. Physiological recordings have been made from two of the subtypes and only the type 4 neuron has been studied in detail. Odour-stimulated increases in intracellular calcium and rapid activation of an electrogenic Na+/Ca2+ exchanger current in type 4 neurons suggest that the exchanger proteins are localized very close to the transduction machinery. Electrophysiological studies have shown that olfactory signal transduction takes place in the apical ciliary regions of olfactory neurons. Using polyclonal antiserum against squid Na+/Ca2+ proteins, we observed specific staining in the ciliary region of cells that resemble type 2, 3, 4 and 5 neurons. Staining was also observed in axon bundles, and in muscle tissue. Collectively, these data support the model that Na+/Ca2+ exchanger proteins are localized to transduction machinery in cilia of type 4 neurons and suggest that the other olfactory subtypes also use Ca2+ during chemosensory responses.

Animals↗

PubMed2000

A convenient method for the synthesis of DNA-recognizing polyamides in solution.

A convenient method for the synthesis of polyamides containing N-methylpyrrole (Py) and N-methylimidazole (Im) in solution has been developed. Most of the building blocks have been prepared by a haloform reaction in a simple way that column chromatography can be avoided. By use of the DCC/HOBT coupling reaction, the building blocks prepared have been effectively connected to construct a variety of subchains and polyamides without employing amino protection and deprotection. By use of the present method, an eight-ring polyamide, PyPyPyPygammaPyImImPybetaDp (gamma is gamma-aminobutyric acid, beta is beta-alanine, Dp is N, N-dimethylpropyldiamine), has been synthesized by the coupling of two four-ring subchains in one step.

DNA↗

PubMed2000

Cellular localization of membrane-type serine protease 1 and identification of protease-activated receptor-2 and single-chain urokinase-type plasminogen activator as substrates.

Membrane-type serine protease 1 (MT-SP1) was recently cloned, and we now report its biochemical characterization. MT-SP1 is predicted to be a type II transmembrane protein with an extracellular protease domain. This localization was experimentally verified using immunofluorescent microscopy and a cell-surface biotinylation technique. The substrate specificity of MT-SP1 was determined using a positional scanning-synthetic combinatorial library and substrate phage techniques. The preferred cleavage sequences were found to be (P4-(Arg/Lys)P3-(X)P2-(Ser)P1-(Arg)P1'-(Ala)) and (P4-(X)P3-(Arg/Lys)P2-(Ser)P1(Arg) P1'(Ala)), where X is a non-basic amino acid. Protease-activated receptor 2 (PAR2) and single-chain urokinase-type plasminogen activator are proteins that are localized to the extracellular surface and contain the preferred MT-SP1 cleavage sequence. The ability of MT-SP1 to activate PARs was assessed by exposing PAR-expressing Xenopus oocytes to the soluble MT-SP1 protease domain. The latter triggered calcium signaling in PAR2-expressing oocytes at 10 nm but failed to trigger calcium signaling in oocytes expressing PAR1, PAR3, or PAR4 at 100 nm. Single-chain urokinase-type plasminogen activator was activated using catalytic amounts of MT-SP1 (1 nm), but plasminogen was not cleaved under similar conditions. The membrane localization of MT-SP1 and its affinity for these key extracellular substrates suggests a role of the proteolytic activity in regulatory events.

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

Nitric oxide synthase/COX cross-talk: nitric oxide activates COX-1 but inhibits COX-2-derived prostaglandin production.

It is recognized that there is molecular cross-talk between the inflammatory mediators NO and PGs that may regulate tissue homeostasis and contribute to pathophysiological processes. However, the literature is divided with respect to whether NO activates or inhibits PG production. In this study, we sought to determine whether conflicting observations could be accounted for by divergent effects of NO on the two cyclooxygenase (COX) isoforms. Exposure of resting macrophages to NO (30 microM) enhanced PGE2 release by 4. 5-fold. This enhancement was inhibited by indomethacin but not by the COX-2 selective inhibitor NS398. To separate the activation of phospholipase A2 and COX, we performed experiments using fibroblasts derived from COX-1-deficient or COX-2-deficient mice. These cells exhibit increased basal PG production, which is due to a constitutively stimulated cytosolic phospholipase A2 and enhanced basal expression of the remaining COX isozyme. The exposure of COX- 2-deficient cells to exogenous NO (10 microM) resulted in a 2.4-fold increase of PGE2 release above controls. Further studies indicated that NO stimulated PGE2 release in COX-2-deficient cells, without altering COX-1 mRNA or protein expression. In contrast, NO inhibited COX-2-derived PGE2 production in both LPS-stimulated macrophages and COX-1 knockout cells. This inhibition was associated with both decreased expression and nitration of COX-2. Thus, these studies demonstrate divergent effects of NO on the COX isoforms. The regulation of PGE production by NO is therefore complex and will depend on the local environment in which these pleiotropic mediators are produced.

Animals↗

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

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↗

PubMed2000

Expression and differential polarization of the reduced-folate transporter-1 and the folate receptor alpha in mammalian retinal pigment epithelium.

The differential polarized distribution of the reduced- folate transporter (RFT-1) and folate receptor alpha (FRalpha), the two proteins involved in the transport of folate, has been characterized in normal mouse retinal pigment epithelium (RPE) and in cultured human RPE cells. RPE cells mediate the vectorial transfer of nutrients from choroidal blood to neural retina. Whereas FRalpha is known to be present in many cell types of the neural retina, in situ hybridization analysis in the present study demonstrated that RFT-1 is present only in RPE. Laser-scanning confocal microscopy using antibodies specific for RFT-1 demonstrated an apical distribution of this protein in cultured human and intact mouse RPE, which contrasts with the basolateral distribution of FRalpha in these cells. The expression of RFT-1 in the RPE cell apical membrane was confirmed by functional studies with purified apical membrane vesicles from bovine RPE. These studies, done with N(5)-methyltetrahydrofolate (the predominant folate derivative in blood) and folate as substrates, have shown that RFT-1 functions in a Na(+)- and C1(-)-independent manner. The transporter is specific for folate and its analogs. A transmembrane H(+) gradient influences the transport function of this protein markedly; the transport mechanism is likely to be either folate/H(+) co-transport or folate/OH(-) exchange. Based on the differential polarization of FRalpha and RFT-1 in RPE, we suggest that these two proteins work in a concerted manner to bring about the vectorial transfer of folate across the RPE cell layer from the choroidal blood to the neural retina. This constitutes the first report of the differential polarization of the two folate transport proteins in any polarized epithelium.

Animals↗

PubMed2000

Novel photoluminescent polymers containing oligothiophene and m-phenylene-1,3,4-oxadiazole moieties: synthesis and spectroscopic and electrochemical studies

Three conjugated polymers containing oligothiophene units (from one to three thiophene rings) and aromatic 1,3,4-oxadiazole moieties have been successfully synthesized. The polymer structures were characterized and confirmed by (1)H and (13)C NMR, FT-IR, and elemental analysis. Thermogravimetric analysis demonstrated that the polymers are highly thermal stable. Tunable absorption (from 342 to 428 nm) and fluorescence (from 411 to 558 nm) properties of polymers were observed. The electrochemical investigation indicated that the LUMO and HOMO energy levels of the new polymers could be adjusted. It was also revealed by the electrochemical analysis that the polymers have good charge injection properties for both p-type and n-type charge carriers, as well as good color tunable luminescence and film-forming properties, which makes them potentially useful for fabricating efficient light-emitting devices.

Journal Article↗

PubMed2000

Structure-function analysis of protease-activated receptor 4 tethered ligand peptides. Determinants of specificity and utility in assays of receptor function.

Thrombin activates protease-activated receptors (PARs) by specific cleavage of their amino-terminal exodomains to unmask a tethered ligand that binds intramolecularly to the body of the receptor to effect transmembrane signaling. Peptides that mimic such ligands are valuable as agonists for probing PAR function, but the tethered ligand peptide for PAR4, GYPGKF, lacks potency and is of limited utility. In a structure-activity analysis of PAR4 peptides, AYPGKF was approximately 10-fold more potent than GYPGKF and, unlike GYPGKF, elicited PAR4-mediated responses comparable in magnitude to those elicited by thrombin. AYPGKF was relatively specific for PAR4 in part due to the tyrosine at position 2; substitution of phenylalanine or p-fluorophenylalanine at this position produced peptides that activated both PAR1 and PAR4. Because human platelets express both PAR1 and PAR4, it might be desirable to inhibit both receptors. Identifying a single agonist for both receptors raises the possibility that a single antagonist for both receptors might be developed. The AYPGKF peptide is a useful new tool for probing PAR4 function. For example, AYPGKF activated and desensitized PAR4 in platelets and, like thrombin, triggered phosphoinositide hydrolysis but not inhibition of adenylyl cyclase in PAR4-expressing cells. The latter shows that, unlike PAR1, PAR4 couples to G(q) and not G(i).

Adenylate Cyclase Toxin↗

PubMed2000

Use of the arabinose p(bad) promoter for tightly regulated display of proteins on bacteriophage.

Phage display is a widely used method to optimize the binding characteristics of protein-ligand interactions. In addition, it has been used to clone genes from genomic and cDNA libraries based on their ligand-binding characteristics. One difficulty often encountered when expressing heterologous proteins by phage display is the toxicity of the protein on the Escherichia coli host. Previous studies have shown that heterologous protein expression can be tightly controlled using plasmids with the P(BAD) promoter of the arabinose operon of E. coli, and the araC gene, which is both a positive and negative regulator of the promoter. We constructed a set of phage display vectors that utilize the P(BAD) promoter to control the expression of proteins on the surface of the M13 bacteriophage. These vectors exhibit tightly controlled expression of proteins on the surface of the phage. In addition, the amount of protein displayed on the phage is modulated by the amount of arabinose present in the growth medium during phage propagation. This may be useful for altering the stringency of binding enrichment during phage display.

Antibodies, Monoclonal↗

PubMed2000

p50(cdc37) is a nonexclusive Hsp90 cohort which participates intimately in Hsp90-mediated folding of immature kinase molecules.

Hsp90 and p50(cdc37) provide a poorly understood biochemical function essential to certain protein kinases, and recent models describe p50(cdc37) as an exclusive hsp90 cohort which links hsp90 machinery to client kinases. We describe here the recovery of p50(cdc37) in immunoadsorptions directed against the hsp90 cohorts FKBP52, cyp40, p60HOP, hsp70, and p23. Additionally, monoclonal antibodies against FKBP52 coadsorb maturation intermediates of the hsp90-dependent kinases p56(lck) and HRI, and the presence of these maturation intermediates significantly increases the representation of p50(cdc37) and hsp90 on FKPB52 machinery. Although the native heterocomplex between hsp90 and p50(cdc37) is salt-labile, their dynamic interactions with kinase substrates produce kinase-chaperone heterocomplexes which are highly salt-resistant. The hsp90 inhibitor geldanamycin does not directly disrupt the native association of hsp90 with p50(cdc37) per se, but does result in the formation of salt-labile hsp90-kinase heterocomplexes which lack the p50(cdc37) cohort. We conclude that p50(cdc37) does not simply serve as a passive structural bridge between hsp90 and its kinase substrates; instead, p50(cdc37) is a nonexclusive hsp90 cohort which responds to hsp90's nucleotide-regulated conformational switching during the generation of high-affinity interactions within the hsp90-kinase-p50(cdc37) heterocomplex.

Cell Cycle Proteins↗

PubMed2000

Cloning of an amino acid transporter with functional characteristics and tissue expression pattern identical to that of system A.

We report here on the cloning and functional characterization of the protein responsible for the system A amino acid transport activity that is known to be expressed in most mammalian tissues. This transporter, designated ATA2 for amino acid transporter A2, was cloned from rat skeletal muscle. It is distinct from the neuron-specific glutamine transporter (GlnT/ATA1). Rat ATA2 consists of 504 amino acids and bears significant homology to GlnT/ATA1 and system N (SN1). ATA2-specific mRNA is ubiquitously expressed in rat tissues. When expressed in mammalian cells, ATA2 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. When expressed in Xenopus laevis oocytes, transport of neutral amino acids via ATA2 is associated with inward currents. The substrate-induced current is Na(+)-dependent and pH-sensitive. The amino acid transport system A is particularly known for its adaptive and hormonal regulation, and therefore the successful cloning of the protein responsible for this transport activity represents a significant step toward understanding the function and expression of this transporter in various physiological and pathological states.

Amino Acid Sequence↗

PubMed2000

Structural and functional characteristics and tissue distribution pattern of rat OCTN1, an organic cation transporter, cloned from placenta.

This report describes the structure, function, and tissue distribution pattern of rat OCTN1 (novel organic cation transporter 1). The rat OCTN1 cDNA was isolated from a rat placental cDNA library. The cDNA is 2258 bp long and codes for a protein of 553 amino acids. Its amino acid sequence bears high homology to human OCTN1 (85% identity) and rat OCTN2 (74% identity). When expressed heterologously in mammalian cells, rat OCTN1 mediates Na(+)-independent and pH-dependent transport of the prototypical organic cation tetraethylammonium. The transporter interacts with a variety of structurally diverse organic cations such as desipramine, dimethylamiloride, cimetidine, procainamide, and verapamil. Carnitine, a zwitterion, interacts with rat OCTN1 with a very low affinity. However, the transport of carnitine via rat OCTN1 is not evident in the presence or absence of Na(+). We conclude that rat OCTN1 is a multispecific organic cation transporter. OCTN1-specific mRNA transcripts are present in a wide variety of tissues in the rat, principally in the liver, intestine, kidney, brain, heart and placenta. In situ hybridization shows the distribution pattern of the transcripts in the brain (cerebellum, hippocampus and cortex), kidney (cortex and medulla with relatively more abundance in the cortical-medullary junction), heart (myocardium and valves) and placenta (labyrinthine zone).

Amino Acid Sequence↗