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W Zhang

Publications and source records attributed to W Zhang.

At least 757 records · Page 42Linked to original sources
PubMed1998

13C NMR, X-ray, and differential scanning calorimetry investigations of truncated BPTI (aprotinin) analogues.

Truncated BPTI missing residues 1 and 2 is investigated together with variants thereof (Lys-15, Arg-17, and Arg-42 are replaced by other residues in various combinations). A comparison of the X-ray structure of BPTI with that of 3-58BPTI(K15R,R17A,R42S) shows only minor variations for the backbone, but the lack of salt bridge between the terminals and the lack of two N-terminal residues provide a structure open at one end. Comparisons of amide exchange rates show a dramatic increase for the most slowly exchanging NH protons of 3-58BPTI and the analogues thereof, as compared to those of the wild-type despite only small differences in the structures. The amide exchange rates for truncated analogues increase with decreasing TTEP (temperature top endothermic peak) values. On the basis of the known structural changes comparisons to 13C chemical shifts are made. 13C chemical shifts are assigned using the D-isotope and HMBC techniques. Excellent resolution is obtained in these 1D natural abundance spectra. 13C NMR chemical shifts are shown to be able to gauge structural changes. A comparison of 13C chemical shifts of WT BPTI (aprotinin) and 3-58BPTI reveals effects caused by (i) the removal of the salt bridge of the terminii, (ii) the charge of the N-terminus, and (iii) the increased mobility of the side chain of Tyr-23. Small effects are also seen due to a conformational change of the aromatic ring of Phe-4. Ring current shifts at 13C chemical shifts are calculated. The difference in the calculated ring current effects are small comparing the wild-type with 3-58BPTI(K15R,R17A,R42S) provided the structures are relaxed. Protein unfolding as a function of pH and temperature is studied by DSC. Unfolding occurs at lower temperature with N-terminally truncated analogues, and the maximum is shifted toward higher pH.

Amino Acid Substitution↗
PubMed1998

Telomerase activity in prostate cancer, prostatic intraepithelial neoplasia, and benign prostatic epithelium.

Telomerase is a ribonucleoprotein that synthesizes telomeric DNA on chromosomal ends. Telomerase activation has been seen in many immortal cell lines and cancers. Telomerase activity was analyzed in prostate carcinoma; in coexistent prostatic intraepithelial neoplasia (PIN), benign prostatic hyperplasia (BPH), atrophy and normal tissue; and in benign prostate glands. Telomerase activity was detected in 80 of 87 (92%) prostate cancers. Forty-one matched samples (from a total of 32 cases) were available for comparative analysis. The presence of telomerase activity in adjacent PIN, BPH, and normal tissue was correlated with telomerase activity in the malignant epithelium. In these adjacent tissues, telomerase activity was found in 11 of 15 (73%) PINs, 13 of 26 (50%) BPHs, and 1 of 6 (16%) atrophy and 4 of 11 (36%) normal tissues. In contrast to the BPH tissue from cancer-bearing glands, all 16 BPH specimens from patients only diagnosed with BPH were telomerase activity negative. In cancer samples, there was no correlation between telomerase activity and Gleason grade or preoperation prostate-specific antigen level. Our data indicate that telomerase activity is present in most prostate cancers. The high rate of telomerase activity in the benign-appearing areas of these glands may be attributed either to the presence of occult cancer cells or to early molecular alterations of cancer that were histologically inapparent.

Humans↗
PubMed1998

Interaction of presenilins with the filamin family of actin-binding proteins.

Mutations in presenilin genes PS1 and PS2 account for approximately 50% of early-onset familial Alzheimer's disease (FAD). The PS1 and PS2 genes encode highly homologous transmembrane proteins related to the Caenorhabditis elegans sel-12 and spe-4 gene products. A hydrophilic loop region facing the cytoplasmic compartment is likely to be functionally important because at least 14 mutations in FAD patients have been identified in this region. We report here that the loop regions of PS1 and PS2 interact with nonmuscle filamin (actin-binding protein 280, ABP280) and a structurally related protein (filamin homolog 1, Fh1). Overexpression of PS1 appears to modify the distribution of ABP280 and Fh1 proteins in cultured cells. A monoclonal antibody recognizing ABP280 and Fh1 binds to blood vessels, astrocytes, neurofibrillary tangles, neuropil threads, and dystrophic neurites in the AD brain. Detection of ABP280/Fh1 proteins in these structures suggests that these presenilin-interacting proteins may be involved in the development of AD and that interactions between presenilins and ABP280/Fh1 may be functionally significant. The ABP280 gene is located on the human X chromosome, whereas the newly identified Fh1 gene maps to human chromosome 3. These results provide a new basis for understanding the function of presenilin proteins and further implicate cytoskeletal elements in AD pathogenesis.

Aged↗
PubMed1998

LAT: the ZAP-70 tyrosine kinase substrate that links T cell receptor to cellular activation.

Despite extensive study, several of the major components involved in T cell receptor-mediated signaling remain unidentified. Here we report the cloning of the cDNA for a highly tyrosine-phosphorylated 36-38 kDa protein, previously characterized by its association with Grb2, phospholipase C-gamma1, and the p85 subunit of phosphoinositide 3-kinase. Deduced amino acid sequence identifies a novel integral membrane protein containing multiple potential tyrosine phosphorylation sites. We show that this protein is phosphorylated by ZAP-70/Syk protein tyrosine kinases leading to recruitment of multiple signaling molecules. Its function is demonstrated by inhibition of T cell activation following overexpression of a mutant form lacking critical tyrosine residues. Therefore, we propose to name the molecule LAT-linker for activation of T cells.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Volume-induced chloride transport in HT29 cells studied by X-ray microanalysis.

Ion transport mediated by osmotically induced chloride channels in HT29 cells was investigated by X-ray microanalysis of cell cultures. The cells were cultured on cellulose nitrate filters, and exposed to isotonic, hypotonic, or hypertonic solutions. Then the NaCl-rich medium was removed by rinsing the cells with a washing fluid, the cells were frozen, freeze-dried, and analyzed. As washing solutions, distilled water, ammonium acetate, or mannitol (the latter two at different concentrations) were used. No major effects of the composition of the washing fluid was noted, except for mannitol, which left remnants that caused an apparent decrease in the intracellular elemental concentrations. In response to exposure to hypotonic solution (modified Krebs Ringer's buffer, KRB, with 90 mM NaCl), the cells lost Cl, K, and Na. On the other hand, exposure to hypertonic solution (modified KRB, 290 mM NaCl) caused an increase of the intracellular concentrations of Na and Cl and a decrease in K. In the presence of chloride channel blockers, chloride efflux induced by exposure to hypotonic medium was inhibited. This chloride efflux was also inhibited in the absence of extracellular calcium, indicating that the process is Ca2+ dependent.

Cell Size↗
PubMed1998

Pulsed gradient NMR probes for solid state studies.

Recently introduced studies of the spatial characteristics of spin dynamics in dipolarly coupled solids rely upon NMR probes with strong magnetic field gradients to create spatial magnetization gratings with periods of from 1 micron to 1 nm. The measurements are carried out as scattering experiments where the spatial displacement of spin coherence is recorded as a phase shift or attenuation of the magnetization grating. Recently we have employed these techniques to make a direct measurement of the spin diffusion rate in single crystal CaF2. Here we discuss designs for strong pulsed gradient NMR probes. Three gradient coil sets were designed and constructed, with coil constants of 0.32, 0.67, and 4.15 T/m/A. When driven by a pulsed current source that provides up to 300 A, pulsed gradients of 100, 200, and 600 T/m, respectively, were generated. These designs are fully described, along with practical issues of coil heating and probe stability.

Algorithms↗
PubMed1998

Effects of pHGF on hepatocyte DNA synthesis after partial hepatectomy in rats.

The effects of pHGF on the changes of hepatocyte proliferative cycle and liver regenerative capacity after partial hepatectomized rats were observed by flow cytometry (FCM). The results were as follows: 1) S phase fraction (SPF) in group of normal rats (group A) accounted for 9.89% and increased gradually within 6 h, following a peak at 12th h or 36th h after operation, but in the group of pHGF-treated rats (group B) the peak appeared at 24th h after operation; 2) Proliferation index (PI) of group A was 19.6% before partial hepatectomy, increased to 34.91% within 6 h and reached a peaks at 12th or 36th h after operation, and in group B the peak appeared at 48th h after operation. There were significant differences between two groups in SPF and PI (P < 0.01). The weight of liver began to increase 12 h after operation, and almost reached the preoperative weight 5 days after operation. These findings suggest that pHGF can promote the DNA synthesis and segmentation of hepatocyte.

Animals↗
PubMed1998

Immunohistochemical demonstration of tissue transglutaminase in amyloid plaques.

The brain of Alzheimer's disease patients contains deposits of the 39-42-amino acid (approximately 4 kDa) amyloid beta-peptide, which is derived from the beta-amyloid precursor protein. These pathological deposits have been shown to consist in part of insoluble 8- and 16-kDa aggregates of the amyloid beta-peptide. This report confirms that the amyloid beta-peptide is a substrate for tissue transglutaminase (TGase) and demonstrates that human brain preparations from Alzheimer's disease patients and control patients form cross-linked dimers from added iodinated amyloid beta-peptide. Immunohistochemical staining for TGase revealed its presence in tissue sections and isolated amyloid plaque cores obtained from brains of patients diagnosed as having Alzheimer's disease. These results provide evidence that the previously described insoluble amyloid deposits in Alzheimer's disease may involve TGase-mediated cross-linked amyloid beta-peptide polymers, and suggest a potential role for TGase in the pathogenesis of this disease.

Aged↗
PubMed1998

Hyper-responsiveness of adrenal sympathetic nerve activity in spontaneously hypertensive rats to ganglionic blockade, mental stress and neuronglucopenia.

Previous investigations indicate that the spontaneously hypertensive rat (SHR) has elevated sympathetic tone at rest. The present study aimed to determine whether SHR has exaggerated sympatho-adrenal activation in response to various sympathetic stimuli. The mean blood pressure (MBP), heart rate (HR) and preganglionic adrenal sympathetic nerve activity (SNA) were recorded from conscious, unrestrained SHR and from its normotensive control, the Wistar-Kyoto rat (WKY) (n=7, respectively).Ganglionic blockade (trimethaphan, 5 mg/kg) reduced MBP identically in both groups of rats. It did not change HR in SHR, but increased HR significantly in WKY (P<0.05). The adrenal SNA increased in both groups, but the magnitude of the increase was more than threefold greater in SHR (P<0.05). Mental stress caused by air-jet induced significantly greater tachycardia (threefold) and sympatho-adrenal activation (tenfold) in SHR than in WKY rats. In SHR the inhibition of glycolysis (2-deoxy-d-glucose, 500 mg/kg) also produced a profound activation of adrenal SNA (sevenfold) and the increased adrenal SNA was not paralleled by an increased HR. We conclude that a variety of sympathetic stimuli, including ganglionic blockade, mental stress and neuronglucopenia, cause exaggerated activation of preganglionic adrenal SNA in SHR compared with WKY, indicating that adrenal SNA in SHR is hyper-responsive.

Adrenal Glands↗
PubMed1998

Chemoattractive effect on the effector cells of the supernatants from melanoma cells transfected with the interleukin-2 (IL-2), IL-4 or IL-6 gene.

By using the Boyden chamber system, the chemoattractive activity of the supernatants from the B16 melanoma cells transfected with the interleukin-2 (IL-2), IL-4 or IL-6 gene was investigated. We found that supernatants from IL-2- or IL-6-gene-transfected B16 melanoma cells showed chemoattractive activity on natural killer (NK) cells, CD4+ T cells and CD8+ T cells, while the supernatants from IL-4-gene-transfected B16 melanoma cells showed chemotactic activity on macrophages but not on NK cells and T cells. Further, the chemoattractive activity of the supernatants from cytokine-gene-transfected B16 cells might be the direct effects of the cytokine that they have been engineered to secrete. These results indicate that reduced tumorigenicity and increased immunogenicity of cytokine-gene-transfected B16 cells may be attributed to the direct recruitment of immune effector cells by the secreted cytokine, which plays an important role in the induction of the local antitumor immunity.

Animals↗
PubMed1998

Localization and surgical treatment of pancreatic insulinomas guided by intraoperative ultrasound.

BACKGROUND: Approximately 20% to 60% of insulinomas cannot be localized preoperatively, and 10% to 20% cannot be found even during surgery. The operative complications associated with the blind surgical explorations are relatively high. METHODS: Between January 1987 and December 1995, intraoperative ultrasound was used to localize insulinomas and guide surgical procedures in 28 patients. RESULTS: Insulinomas were found by intraoperative systematic palpation in 24 patients (85.7%), while intraoperative ultrasound localized the tumors in 27 patients (96.4%). By the combination of these two techniques, all tumors were discovered. The surgical procedures were guided by intraoperative ultrasound. The operative complication rate was 14.3%. CONCLUSION: Intraoperative ultrasound can accurately localize insulinoma, and delineate the spatial relationship between tumor and vital structures, such as pancreatic duct, common bile duct, and critical blood vessels. It can thereby help to increase the successful rate of surgery and avoid unnecessary blind pancreatectomy.

Adolescent↗
PubMed1998

Detection of complement C1q receptors on human spermatozoa.

Clq, the first component of the classical complement pathway, is known to play roles in promoting phagocytic events, in addition to its role in activation of complement. Although the molecular events in fertilization leading to the entrance of the spermatozoan into the egg are not well understood, ultrastructural observations suggest that the process is quasi-phagocytic in nature. There is increasing evidence that complement components might play roles in fertilization. Previously, we have shown that C1q promoted the agglutination of capacitated human sperm as well as their adhesion to zona-free hamster eggs. In the present experiments, human spermatozoa were solubilized and, following their phase separation in Triton X-114, subject to 1-D polyacrylamide gel electrophoresis and immunoblotting for the presence of C1q receptors. Both gC1q-R and cC1q-R were detected. In addition, the ability of C1q to promote sperm agglutination was shown to be dependent upon capacitation, suggesting the increased expression of C1q receptors during this process.

Agglutination Tests↗
PubMed1998

Tachykinin neuropeptide-evoked intracellular calcium transients in cultured guinea pig myenteric neurons.

Substance P and related tachykinins are present in the mammalian gut and act as neurotransmitters. Microfluorimetric measurement of intracellular calcium ([Ca2+]i) was used to study tachykinin-sensitive myenteric neurons. Substance P (0.001-10 microM) evoked concentration-dependent increases in percentage of neurons responding (6-75%) and delta [Ca2+]i (88 +/- 24 to 212 +/- 16 nM). Neurokinin A (0.001-1 microM) produced similar responses. Removal of extracellular Ca2+ abolished substance P-induced Ca2+ signals, as did the addition of the Ca2+ channel blockers lanthanum chloride (5 mM) and nickel chloride (2.5 mM). Both nifedipine (1-50 microM) and diltiazem (1-50 microM) inhibited substance P-evoked Ca2+ responses in a dose-dependent manner. Substance P and related tachykinins evoke Ca2+ signaling in cultured myenteric neurons by the influx of extracellular Ca2+ through L and N-type plasma membrane Ca2+ channels.

Animals↗
PubMed1998

Effects of inhibitors for intracellular signal transduction systems on the inward current produced by GABA in a snail neuron.

1. An inward current (I[in]) was produced by gamma-aminobutyric acid (GABA) and muscimol, but not by baclofen, in an identifiable giant neuron type, v-LCDN (ventral-left cerebral distinct neuron), of an African giant snail (Achatina fulica Ferussac) under voltage clamp. 2. The pharmacological features of the excitatory GABA receptors in this Achatina neuron type, termed the Achatina muscimol II type GABA receptors, were mainly comparable to those of the mammalian GABA(C) receptors. 3. It was demonstrated in the present study that the following inhibitors for intracellular signal transduction systems showed no significant effect on the I(in) produced by GABA in this Achatina neuron type: H-7 [1-(5-isoquinolinyl sulfonyl)-2-methylpiperazine], an inhibitor of cyclic AMP-dependent protein kinase (PKA), cyclic GMP-dependent protein kinase (PKG) and protein kinase C (PKC); H-8 (N-[2-(methylamino)-ethyl]-5-isoquinolinesulfonamide), a PKA and PKG inhibitor; H-9 [N-(2-aminoethyl)-5-isoquinolinesulfonamide], a PKA inhibitor; staurosporine ((9alpha,10beta,11beta,13alpha)-(+)-2,3,10,11,12 ,13-hexahydro-10-methoxy-9-methyl-11-(methylamino)-9,13-epoxy-1H,9H-d iindolo[1,2,3-gh: 3',2',1'-1m]pyrrolo[3,4-j] [1,7]benzodiazonin-1-one), a PKA and PKC inhibitor; KT5823 ((8R,9S, 11S)-9-methoxy-9-methoxycarbonyl-2N,8-dimethyl-2,3,9,10-tetrahydro-8,11- epoxy-1H,8H,11H-2,7b,11a-triazadibenzo[a,g]cycloocta[c,d,e]- trinden-1-one), a PKG inhibitor; W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide], a calmodulin inhibitor; ML-9 [1-(5-chloronaphthalene-1-sulfonyl-1H-hexahydro-1,4-diazepine hydrochloride], a myosin light-chain kinase inhibitor; genistein [5,7-dihydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one], a tyrosine protein kinase inhibitor; IBMX (3-isobutyl-1-methylxanthine), a cyclic nucleotide phosphodiesterase (PDE) inhibitor; fluphenazine nitrogen-mustard (2-chloroethyl)-4[3-(2-trifluoromethyl-10-phenothiazinyl)-propyl]p iperazine dihydrochloride), a calmodulin-dependent PDE inhibitor; calyculin A, a type 1 protein phosphatase inhibitor; and okadaic acid (9,10-deepithio-9,10-didehydroacanthifolicin), a type 1, 2A and 2B protein phosphatase inhibitor. 4. With these results, it was proposed that the excitatory Achatina muscimol II type GABA receptors in v-LCDN are not metabotropic but ionotropic.

Animals↗
PubMed1998

Direct comparison of infrared and ultraviolet wavelength matrix-assisted laser desorption/ionization mass spectrometry of proteins.

In an effort to gain an understanding of the processes governing matrix-assisted laser desorption/ionization (MALDI), we made a direct comparison of ultraviolet (UV)- and infrared (IR)-MALDI linear time-of-flight mass spectra of proteins obtained from the same samples and matrices (on the same sample surface), using two different lasers, each having short duration (< 10-ns) pulses, i.e., a tunable wavelength Nd:yttrium aluminum garnet (YAG) pumped optical parametric oscillator laser operating at 2.94 microns and a Nd:YAG laser operating at 355 nm. We observed that (1) the IR-MALDI and UV-MALDI spectra of a given protein from the same matrix were strikingly similar; (2) protein ions produced by IR-MALDI experienced less fragmentation than those produced by UV-MALDI; and (3) photochemical adducts produced during UV-MALDI were absent in IR-MALDI. These results lead us to speculate on the mechanisms for the ionization process in UV- and IR-MALDI. Because photons with a wavelength of approximately 3 microns are unlikely to effect electronic excitation of the matrix at the irradiance used for MALDI we propose that ionization in IR-MALDI occurs as a natural consequence of the solid-to-gas phase transition induced by the IR irradiation, and involves proton transfer reactions in the intermediate phase between solid and gas. The strikingly similar UV- and IR-MALDI mass spectra leads us to the additional proposal that ionization in UV-MALDI may also be a natural consequence of the phase transition and that electronic excitation may not play a primary role in the ionization process.

Animals↗
PubMed1998

Exploring infrared wavelength matrix-assisted laser desorption/ionization of proteins with delayed-extraction time-of-flight mass spectrometry.

We report a study of the application of delayed extraction (DE) to infrared-wavelength matrix-assisted time-of-flight mass spectrometry (IR-MALDI-TOF-MS) of proteins. The shapes of the spectral peaks obtained with DE-IR-MALDI-MS are compared with those obtained from the same samples and matrix using continuous extraction (CE) IR-MALDI-MS. Application of DE results in significant improvements in the peak resolution, revealing spectral features (in proteins with molecular masses < 12 kDa) that were not resolved in the corresponding CE-IR-Maldi mass spectra. Particularly significant is a series of peaks on the high mass side of the protonated protein peaks that arise through replacement of protons by adventitious sodium ions in the sample. We deduced that these sodium replacement species are a significant contributor to the broad tails (and resulting peak asymmetries) that are a feature of the DE-IR-MALDI mass spectra of proteins with molecular masses > or = 17 kDa. The peak width reduction observed in IR-MALDI by DE suggests that, as in UV-MALDI, the initial velocity distribution for ions produced in the MALDI process contributes to the peak broadness in the CE mass spectra. In a systematic comparison between DE UV-MALDI and DE IR-MALDI, we determined that photochemical matrix adduction is present in UV-MALDI but absent in IR-MALDI. In addition, we find that protein ions produced by IR irradiation are less internally excited (i.e., cooler), exhibiting less fragmentation, more Na+ replacement and/or unspecified noncovalent adduction, and more heme adduction with apomyoglobin. Thus, IR-MALDI appears to be a softer means for producing gas-phase protein ions than is UV-MALDI. It will be of considerable practical interest to determine whether large protein ions produced by IR-MALDI are sufficiently cool to survive transport through reflecting TOF mass spectrometers (without loss of small neutral species such as H2O, NH3, and CO2) and the extended time periods required for detection by quadrupole ion trap and Fourier transform ion cyclotron resonance mass analyzers.

Infrared Rays↗