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Biomedical subjects

X Tang

Publications and source records attributed to X Tang.

At least 19 recordsLinked to original sources
PubMed1999

Overexpression of Pto activates defense responses and confers broad resistance.

The tomato disease resistance (R) gene Pto specifies race-specific resistance to the bacterial pathogen Pseudomonas syringae pv tomato carrying the avrPto gene. Pto encodes a serine/threonine protein kinase that is postulated to be activated by a physical interaction with the AvrPto protein. Here, we report that overexpression of Pto in tomato activates defense responses in the absence of the Pto-AvrPto interaction. Leaves of three transgenic tomato lines carrying the cauliflower mosaic virus 35S::Pto transgene exhibited microscopic cell death, salicylic acid accumulation, and increased expression of pathogenesis-related genes. Cell death in these plants was limited to palisade mesophyll cells and required light for induction. Mesophyll cells of 35S::Pto plants showed the accumulation of autofluorescent compounds, callose deposition, and lignification. When inoculated with P. s. tomato without avrPto, all three 35S::Pto lines displayed significant resistance and supported less bacterial growth than did nontransgenic lines. Similarly, the 35S::Pto lines also were more resistant to Xanthomonas campestris pv vesicatoria and Cladosporium fulvum. These results demonstrate that defense responses and general resistance can be activated by the overexpression of an R gene.

Cell Death↗
PubMed1998

Different systems in human brain are involved in presemantic discrimination of pictures as revealed by event-related potentials.

It is uncertain if the several brain areas in response to presemantic picture processing are functionally homogeneous. Subjects were asked to discriminate visual stimulus pairs and event-related potentials (ERPs) were recorded from the scalp. A line-drawing picture (S1) was followed by another stimulus (S2) 600 ms later. S2 was the same as S1 in condition 1, a reversed picture of S1 in condition 2, the corresponding Chinese word in condition 3 and the syllabic alphabet of S1 in condition 4. Amplitudes of ERPs over right posterior scalp with time window from 102-180 ms after the onset of S2 in condition 1 and 2 were significantly larger than condition 3 and 4. The N2 component on the right anterolateral scalp with time window from 182-240 ms was significantly larger in condition 1 than other conditions, whereas the N2 on the left anterolateral scalp with time window from 262-350 ms in condition 2, 3 and 4 was significantly larger than condition 1. It is suggested that pictures and words are processed in different systems at the presemantic stage: repetitive and physically deviant stimuli evoke different responses in different brain regions.

Adult↗
PubMed1998

Analysis of CAG/CTG repeat size in Chinese subjects with schizophrenia and bipolar affective disorder using the repeat expansion detection method.

BACKGROUND: Family studies of schizophrenia and bipolar affective disorder provide evidence for genetic anticipation, which (in common with a number of mendelian disorders), may be caused by triplet repeat expansion. This hypothesis is strengthened by evidence from repeat expansion detection (RED) analysis revealing association between the psychoses and long CAG/CTG trinucleotide repeats. METHODS: We performed RED on Han Chinese subjects with schizophrenia (82), bipolar affective disorder (43), and normal controls (61), using a CTG10 oligonucleotide. RESULTS: Comparison between cases and controls revealed no significant association between long repeats and affected status. We also found no detectable association with age at onset and repeat length in either bipolar affective disorder or schizophrenia. Overall, the size distribution of CAG/CTG repeats in Chinese subjects was not significantly different from those reported previously for Caucasian subjects. CONCLUSIONS: These findings indicate that CAG/CTG repeat expansion is not likely to be a major etiological factor for psychosis in Chinese populations.

Adolescent↗
PubMed1998

Temperature-induced conformational changes in prosomatostatin-II: implications for processing.

Somatostatin (SRIF) is a 14-residue peptide hormone synthesized in the hypothalamus and pancreatic islets. SRIF-14 and an N-terminally extended form, SRIF-28, are generated by the proteolytic processing of an approx. 102-residue precursor prosomatostatin (proSRIF) at a single set of paired basic residues (Arg-Lys) and at a monobasic (Arg) site respectively. Previous work in our laboratory demonstrated that the propeptide of SRIF mediates intracellular sorting; we suggested that this information resides in the prohormone structure. To identify putative sorting domains we have investigated structural features of recombinant anglerfish proSRIF-II purified from Escherichia coli. Two species of proSRIF-II were obtained: a monomeric form and a disulphide-linked dimer. CD analyses revealed that monomeric proSRIF-II lacks appreciable periodic secondary structure; however, on slow heating (2 degrees C/min) and cooling, it assumed a predominantly alpha-helical conformation. When subjected to a second heating-and-cooling cycle, the alpha-helical conformation was maintained. In contrast, the dimeric form of proSRIF-II was predominantly alpha-helical and its helicity did not increase in response to heating and recooling. Our results suggest that proSRIF-II might exist in several different folding intermediate states.

Amino Acid Sequence↗
PubMed1998

Genomic organization and expression of a human gene for Myc-associated zinc finger protein (MAZ).

We have cloned and characterized the genomic structure of the human gene for Myc-associated zinc finger protein (MAZ), which is located on chromosome 16p11.2. This gene is transcribed as an mRNA of 2.7 kilobases (kb) that encodes a 60-kDa MAZ protein. A 40-kb cosmid clone was isolated that includes the promoter, five exons, four introns, and one 3'-untranslated region. All exon-intron junction sequences conform to the GT/AG rule. The promoter region has features typical of a housekeeping gene: a high G + C content (88. 4%); a high frequency of CpG dinucleotides, in particular within the region 0.5 kb upstream of the site of initiation of translation; and the absence of canonical TATA and CAAT boxes. An S1 nuclease protection assay demonstrated the presence of multiple sites for initiation of transcription around a site 174 nucleotides (nt) upstream of the ATG codon and such expression was reflected by the promoter activity of a MAZ promoter/CAT (chloramphenicol acetyltransferase) reporter gene. Cis-acting positive and negative elements controlling basal transcription of the human MAZ gene were found from nucleotides (nt) -383 to -248 and nt -2500 to -948. Moreover, positive and negative autoregulatory elements were also identified in the regions from nt -248 to -189 and from nt -383 to -248 after co-transfection of HeLa cells with plasmids that carried the MAZ promoter/CAT construct and the MAZ-expression vector. Our results indicate that the 5'-end flanking sequences are responsible for the promoter activities of the MAZ gene.

Amino Acid Sequence↗
PubMed1998

A novel integrin-activated pathway forms PKB/Akt-stimulatory phosphatidylinositol 3,4-bisphosphate via phosphatidylinositol 3-phosphate in platelets.

The aggregation of human platelets is an important physiological hemostatic event contingent upon receptor-dependent activation of the surface integrin alphaIIbbeta3 and subsequent binding of fibrinogen. Aggregating platelets form phosphatidylinositol 3, 4-bisphosphate (PtdIns(3,4)P2), which has been reported to stimulate in vitro the activity of the proto-oncogenic protein kinase PKB/Akt, as has phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3). It has been assumed that PtdIns(3,4)P2 is synthesized by either 5-phosphatase-catalyzed hydrolysis of PtdIns(3,4,5)P3 produced by phosphoinositide 3-kinase (PI3K) or phosphorylation by PI3K of PtdIns4P. We investigated the route(s) by which PtdIns(3,4)P2 is formed after directly activating alphaIIbbeta3 with anti-ligand-induced binding site Fab fragment and report that aggregation does not lead to the generation of PtdIns(3,4,5)P3, but to transient formation of PtdIns3P and generation of PtdIns(3,4)P2, the latter primarily by PtdIns3P 4-kinase. Both this novel pathway and the activation of PKB/Akt are inhibited by the PI3K inhibitor, wortmannin, and the calpain inhibitor, calpeptin, constituting the first evidence that PtdIns(3,4)P2 can stimulate PKB/Akt in vivo in the absence of PtdIns(3,4,5)P3. Integrin-activated generation of the second messenger PtdIns(3,4)P2 thus depends upon a route distinct from that known to be utilized initially by growth factors. This pathway is of potential general relevance to the function of integrins.

3-Phosphoinositide-Dependent Protein Kinases↗
PubMed1998

Alignment echo of spin-3/2 9Be nuclei: detection of ultraslow motion

It is demonstrated that the alignment echo of 9Be is quite useful for detecting ultraslow atomic motions in the metallic glass Zr46. 75Ti8.25Cu7.5Ni10Be27.5. The time scale of detectable atomic motion is between T2 = 1.5 ms and T1 of a few seconds. Similar to previous works of 2H NMR, the Jeener-Broekaert sequence is used to create quadrupolar order for spin-32 nuclei upon nonselective excitations. Since the chemical and Knight shift distributions are not negligible for 9Be, the proper choice of the dephasing time between the first and the second pulses is essential for achieving pure quadrupolar order. It is demonstrated experimentally that slow atomic motions contribute significantly to the decay of the alignment echo near the glass transition temperature. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Changes in tropospheric composition and air quality.

Reductions in stratospheric ozone (O3) cause increased penetration of ultraviolet-B (UV-B) radiation to the troposphere, and therefore increases in the chemical activity in the lower atmosphere (the troposphere). Tropospheric ozone levels are sensitive to local concentrations of nitrogen oxides (NOx) and hydrocarbons. Model studies suggest that additional UV-B radiation reduces tropospheric ozone in clean environments (low NOx), and increases tropospheric ozone in polluted areas (high NOx). Assuming other factors remain constant, additional UV-B will increase the rate at which primary pollutants are removed from the troposphere. Increased UV-B is expected to increase the concentration of hydroxyl radicals (OH) and result in faster removal of pollutants such as carbon monoxide (CO), methane (CH4), non-methane hydrocarbons (NMHCs), sulfur and nitrogen oxides, hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs). Concentrations of peroxy radicals (both inorganic and organic) are expected to increase, leading to higher atmospheric levels of hydrogen peroxide (H2O2) and organic peroxides. The effects of UV-B increases on tropospheric O3, OH, methane, CO, and possibly other tropospheric constituents, while not negligible, will be difficult to detect because the concentrations of these species are also influenced by many other variable factors (e.g., emissions). Trifluoroacetic acid (TFA, CF3COOH) is produced in the atmosphere by the degradation of HCFC-123 (CF3CHCl2), HCFC-124 (CF3CHFCl), and HFC-134a (CF3CH2F), which are used as substitutes for ozone-depleting substances. The atmospheric oxidation mechanisms of these replacement compounds are well established. Reported measurements of TFA in rain, rivers, lakes, and oceans show it to be a ubiquitous component of the hydrosphere, present at levels much higher than can be explained by reported sources. The levels of TFA produced by the atmospheric degradation of HFCs and HCFCs emitted up to the year 2020 are estimated to be orders of magnitude below those of concern, and to make only a minor contribution to the current environmental burden of TFA. No significant effects on humans or the environment have been identified from TFA produced by atmospheric degradation of HCFCs and HFCs. Numerous standard short-term studies have shown that TFA has, at most, moderate toxicity.

Air↗
PubMed1998

Biological and genetic differences between lung- and brain-derived isolates of maedi-visna virus.

During the epidemic caused by maedi-visna virus (MVV) of sheep in Iceland, the pulmonary affection, maedi, was the predominant clinical manifestation. In some flocks, however, a central nervous system (CNS) affection, visna, was the main cause of morbidity and mortality. As there is only one breed of sheep in the country, host factors did apparently not play an important role in the different clinical manifestations. To obtain some information on possible viral genetic determinants of neurotropism and neurovirulence we studied both phenotypic and genotypic properties of two maedi-visna virus strains; a strain that was originally isolated from the brain of sheep with encephalitis (visna), and another strain isolated from the lungs of a sheep suffering from pneumonia (maedi). The brain isolate was found to grow faster in sheep choroid plexus cells than the lung isolate, whereas the growth rate in macrophages was similar for the maedi and visna virus strains. Intracerebral inoculation indicated that the visna virus isolate induced more severe brain lesions than the maedi isolate. In addition, a pathogenic molecular clone derived from a visna strain (KV1772kv72/67) was tested for growth in sheep choroid plexus cells and macrophages. The molecularly cloned virus retained the fast growth rate in choroid plexus cells. The nucleotide sequence of the env gene and the U3 of the LTR was determined for the maedi strain and compared to that of the visna strains. There was an 11.7% difference in deduced amino acid sequence in the Env protein and a 6% difference in the LTR. The molecular clone KV1772kv72/67 will be a useful reagent for characterization of viral determinants of cell tropism in vitro and possibly neurovirulence in vivo.

Amino Acid Sequence↗
PubMed1998

Clinicopathological factors predicting retroperitoneal lymph node metastasis and survival in endometrial cancer.

BACKGROUND: By clarifying the significance of clinicopathological factors for retroperitoneal lymph node metastasis and survival of patients with endometrial cancer, we suggest ideas for optimal treatment of this disease. METHODS: A retrospective study was conducted in 310 women with endometrial cancer who underwent surgery with retroperitoneal lymphadenectomy. To evaluate retroperitoneal lymph node metastasis, age-adjusted and multivariable analyses were carried out for six clinicopathological factors including pathological grade, myometrial invasion, cervical invasion, peritoneal cytology, lymphatic permeation and vascular invasion. To evaluate survival, besides the above factors, a positive rate of metastasis of dissected retroperitoneal lymph nodes was included. RESULTS: In 40 patients (13%) with nodal metastasis, the average positive rate of metastasis of dissected retroperitoneal lymph nodes was 22%. For retroperitoneal lymph node metastasis, the odds ratio of deep myometrial invasion, cervical invasion and severe lymphatic permeation were 5.97, 2.72 and 12.01, respectively. For survival, the hazard ratios of the positive rates of metastasis of dissected retroperitoneal lymph nodes (both 25% and < 25%), positive peritoneal cytology and poor pathological grade were 7.10, 3.24, 3.82 and 3.27, respectively, and 5-year survival rates for them were 0, 50, 72 and 77%, respectively. CONCLUSIONS: For retroperitoneal lymph node metastasis, lymphatic permeation, deep myometrial invasion and cervical invasion were the independent prognostic factors. For survival, retroperitoneal lymph metastasis, poor pathological grades and positive peritoneal cytology were the independent prognostic factors. The positive rate of metastasis of dissected retroperitoneal lymph metastasis plays an important role in predicting survival of endometrial cancer. Lymph node biopsy is insufficient in treatment of this disease.

Adenocarcinoma↗
PubMed1998

Immunoreactive endothelin-1 and its receptors in human adrenal tissues.

To elucidate the pathophysiologic significance of endothelin-1 (ET-1) in adrenal and the mechanism for reduced responsiveness to exogenous ET-1 in aldosterone-producing adenoma (APA), we have investigated ET-1 receptors by radioligand binding assay (RBA) in human normal adrenal (NA), APA, idiopathic hyperaldosteronism (IHA), and pheochromocytoma (PHEO), immunoreactive (ir-) ET-1 content in NA, APA and PHEO by radioimmunoassay (RIA), and immunohistochemical staining of ET-1 with the peroxidase-anti-peroxidase (PAP) method in NA, APA, and PHEO. A single class of high-affinity binding sites for ET-1 was found in human NA and tumor tissues. Dissociation constant (Kd) values of ET-1 receptors were similar in NA, APA, and IHA, but maximal binding capacity (Bmax) of ET-1 receptors was lower in APA than in NA and IHA. Both Kd and Bmax in PHEO were higher than those in NA, APA, and IHA. Ir-ET-1 content in tumors of APA and PHEO were higher than in NA. Immunohistochemical staining was more intense in the tumor cells of APA and PHEO than in NA. These results suggest that the reduced response to exogenous ET-1 in APA could be related to downregulation of ET-1 receptors in the tumor. Increased ET-1 content and receptors may lead to hypersecretion of catecholamine in PHEO. ET-1 produced in normal and tumor adrenal tissues may regulate aldosterone and catecholamine secretion from adrenals in a paracrine/autocrine fashion.

Adrenal Gland Neoplasms↗
PubMed1998

Update on Pneumocystis carinii f. sp. hominis typing based on nucleotide sequence variations in internal transcribed spacer regions of rRNA genes.

Pneumocystis carinii f. sp. hominis isolates from 207 clinical specimens from nine countries were typed based on nucleotide sequence variations in the internal transcribed spacer regions I and II (ITS1 and ITS2, respectively) of rRNA genes. The number of ITS1 nucleotides has been revised from the previously reported 157 bp to 161 bp. Likewise, the number of ITS2 nucleotides has been changed from 177 to 192 bp. The number of ITS1 sequence types has increased from 2 to 15, and that of ITS2 has increased from 3 to 14. The 15 ITS1 sequence types are designated types A through O, and the 14 ITS2 types are named types a through n. A total of 59 types of P. carinii f. sp. hominis were found in this study.

Base Sequence↗
PubMed1998

Determination of copy number of rRNA genes in Pneumocystis carinii f. sp. hominis.

Differential PCR was performed to determine the copy number of rRNA genes in Pneumocystis carinii f. sp. hominis. Two different reference genes, thymidylate synthase (TS) and beta-tubulin (BTU) genes, were used. Primers for the internal transcribed spacer (ITS) region of nuclear rRNA genes and either the TS or BTU gene were mixed together to perform PCR on seven different bronchoalveolar lavage specimens from patients with P. carinii pneumonia. The radioactivity derived from the incorporated radioactive nucleotides of each PCR product band was then used to calculate the copy number of the ITS relative to that of the TS or BTU gene. The copy number ratio between the ITS and the TS gene was determined to be 0.8, and that between the ITS and the BTU gene was also 0.8. These results suggest that the ITS has the same copy number as the TS or BTU gene. Since the copy number of the TS or BTU gene is presumed to be 1, the results also suggest that P. carinii f. sp. hominis has only one copy of the ITS and thus one copy of the nuclear rRNA genes. Therefore, two types of ITS sequences derived from a specimen would indicate that the patient is infected by two types of P. carinii f. sp. hominis.

Bronchoalveolar Lavage Fluid↗
PubMed1997

Outside-in signaling in the chondrocyte. Nitric oxide disrupts fibronectin-induced assembly of a subplasmalemmal actin/rho A/focal adhesion kinase signaling complex.

Elevated levels of fibronectin (Fn) in articular cartilage have been linked to the progression of both rheumatoid and osteoarthritis. In this study, we examined intracellular events which follow ligation of Fn to its receptor, the integrin alpha5beta1. In addition, we examined the regulatory influence of nitric oxide on these events, since this free radical has been implicated in cartilage degradation. Exposure of chondrocytes to Fn-coated beads resulted in the circumferential clustering of the alpha5beta1 integrin receptor, which was accompanied by the subplasmalemmal assembly of a focal activation complex comprised of F-actin, the tyrosine kinase, focal adhesion kinase (FAK), the ras related G protein rho A, as well as tyrosine-phosphorylated proteins. Treatment with exogenous nitric oxide (NO) or catabolic cytokines which induce nitric oxide synthase blocked the assembly of F-actin, FAK, rho A and tyrosine-phosphorylated proteins while not affecting the total number of beads bound per cell nor the clustering of alpha5beta1 integrin. Use of a cGMP antagonist (Rp-8-Br cGMPS) or cGMP agonist (Sp-cGMPS) either abolished or mimicked the NO effect, respectively. Adherence of chondrocytes to fibronectin enhanced proteoglycan synthesis by twofold (vs. albumin). In addition, basic fibroblast growth factor (FGF) and insulin growth factor (IGF-1) induced proteoglycan synthesis in chondrocytes adherent to Fn but not albumin suggesting a costimulatory signal transduced by alpha5betal and the FGF receptor. Both constitutive and FGF stimulated proteoglycan synthesis were completely inhibited by nitric oxide. These data indicate that the ligation of alpha5beta1 in the chondrocyte induced the intracellular assembly of an activation complex comprised of the cytoplasmic tail of alpha5beta1 integrin, actin, and the signaling molecules rho A and FAK. We show that NO inhibits the assembly of the intracellular activation complex and the synthesis of proteoglycans, but has no effect on the extracellular aggregation of alpha5beta1 integrin. These observations provide a basis by which nitric oxide can interfere with chondrocyte functions by affecting chondrocyte-matrix interactions.

Actins↗
PubMed1997

The Pto kinase conferring resistance to tomato bacterial speck disease interacts with proteins that bind a cis-element of pathogenesis-related genes.

In tomato, the Pto kinase confers resistance to bacterial speck disease by recognizing the expression of a corresponding avirulence gene, avrPto, in the pathogen Pseudomonas syringae pv. tomato. Using the yeast two-hybrid system, we have identified three genes, Pti4, Pti5 and Pti6, that encode proteins that physically interact with the Pto kinase. Pti4/5/6 each encode a protein with characteristics that are typical of transcription factors and are similar to the tobacco ethylene-responsive element-binding proteins (EREBPs). Using a gel mobility-shift assay, we demonstrate that, similarly to EREBPs, Pti4/5/6 specifically recognize and bind to a DNA sequence that is present in the promoter region of a large number of genes encoding 'pathogenesis-related' (PR) proteins. Expression of several PR genes and a tobacco EREBP gene is specifically enhanced upon Pto-avrPto recognition in tobacco. These observations establish a direct connection between a disease resistance gene and the specific activation of plant defense genes.

Amino Acid Sequence↗
PubMed1997

Purification and characterization of Gbetagamma-responsive phosphoinositide 3-kinases from pig platelet cytosol.

A G-protein betagamma subunit (Gbetagamma)-responsive phosphoinositide 3-kinase (PI 3-kinase) was purified approximately 5000-fold from pig platelet cytosol. The enzyme was purified by polyethylene glycol precipitation of the cytosol followed by column chromatography on Q-Sepharose fast flow, gel filtration, heparin-Sepharose, and hydroxyapatite. The major Gbetagamma-responsive PI 3-kinase is distinct from p85 containing PI 3-kinase as the activities can be distinguished chromatographically and immunologically and is related to p110gamma as it cross-reacts with anti-p110gamma-specific antibodies. The p110gamma-related PI 3-kinase cannot be activated by G-protein alphai/o subunits, and it has an apparent native molecular mass of 210 kDa. The p110gamma-related PI 3-kinase phosphorylates phosphatidylinositol (PtdIns), phosphatidylinositol 4-phosphate (PtdIns4P), and phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2). The apparent Km values for ATP were found to be 25 microM with PtdIns, 44 microM with PtdIns4P, and 37 microM with PtdIns(4,5)P2 as the substrate. Gbetagamma subunits did not alter the Km of the enzyme for ATP; however, Vmax increased 2-fold with PtdIns as substrate, 3.5-fold with PtdIns4P, and 10-fold with PtdIns(4,5)P2. Under basal conditions the apparent Km values for lipid substrates were 64, 10, and 15 microM for PtdIns, PtdIns4P, and PtdIns(4,5)P2, respectively. In the presence of Gbetagamma subunits the dependence of PI 3-kinase activity on the concentrations of lipid substrates became complex with the highest level of stimulation occurring at high substrate concentration, suggesting that the binding of Gbetagamma and lipid substrate (particularly PtdIns(4,5)P2) may be mutually cooperative. Wortmannin and LY294002 inhibit the Gbetagamma-responsive PI 3-kinase activity with IC50 values of 10 nM and 2 microM, respectively. Unlike the p85 containing PI 3-kinase in platelets, the p110gamma-related PI 3-kinase is not associated with a PtdIns(3,4,5)P3 specific 5-phosphatase. The p85-associated PI 3-kinase was not activated by Gbetagamma alone but could be synergistically activated by Gbetagamma and phosphotyrosyl platelet-derived growth factor receptor peptides. This may represent a form of coincidence detection through which the effects of tyrosine kinase and G-protein-linked receptors might be coordinated.

Androstadienes↗