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W Xu

Publications and source records attributed to W Xu.

At least 325 records · Page 18Linked to original sources
PubMed1998

Quantitative elemental X-ray imaging of frozen-hydrated biological samples.

It is shown that quantitative X-ray imaging of planed, frozen-hydrated, biological bulk samples that have not been etched is possible. X-ray imaging represents a better alternative to static beam (selected area) analysis of fractured frozen-hydrated samples. This procedure avoids the undesirable necessity of etching planed frozen-hydrated samples to provide an interpretable electron image. Qualitative oxygen and carbon X-ray images, which can be acquired in a short time, can be used for distinguishing morphological features and remove the requirement for electron images. In test samples of frozen-hydrated albumin, containing salts, analyses by X-ray images compared well with static beam (selected area) analyses from the same samples. An example of an analysis of frozen-hydrated insect Malpighian tubules is given in which the response to ouabain treatment was analysed. In this example X-ray imaging showed that ouabain resulted in a significant increase in cytoplasmic and luminal Na and a significant decrease in cytoplasmic and luminal K. X-ray imaging also showed that there was a significant increase in cellular water content. The presence of a potassium gradient in soybean root nodules was also demonstrated. The use of standard deviation images for processing low count images increases analytical precision but results in underestimates of the true concentrations.

Animals↗
PubMed1998

Increased expression of TGF-beta receptors by scleroderma fibroblasts: evidence for contribution of autocrine TGF-beta signaling to scleroderma phenotype.

Scleroderma fibroblasts exhibit numerous phenotypic differences when compared with healthy skin fibroblasts. Some of these differences, in particular overexpression of collagen type I and other extracellular matrix proteins, parallel the effect of transforming growth factor-beta (TGF-beta) on dermal fibroblasts, suggesting that the scleroderma fibroblast phenotype may result from activation of autocrine TGF-beta signaling. To test this hypothesis we examined the role of TGF-beta Type I and Type II receptors in regulating collagen type I transcription. We have shown that overexpression of either Type I or Type II receptors significantly (3-4-fold) increases alpha2 (I) collagen promoter activity in transient transfection assays in dermal fibroblasts. Addition of anti-TGF-beta antibody abolished, whereas addition of plasmin enhanced, the stimulatory effect of receptor overexpression on collagen promoter activity, suggesting that this effect depends on autocrine TGF-beta. Moreover, these cotransfection experiments indicated that expression levels of TGF-beta receptors is a limiting factor in the autocrine regulation of collagen type I transcription by TGF-beta. Comparison of the TGF-beta receptor Type I and Type II mRA expression levels in scleroderma and normal fibroblasts have indicated elevated expression (2-fold) of both receptor types in scleroderma cells, which correlated with increased binding of TGF-beta. Significantly, elevated TGF-beta receptor levels correlated with elevated alpha2 (I) collagen mRNA levels. These results suggest that the elevated production of collagen type I by scleroderma fibroblasts results from overexpression of TGF-beta receptors.

Collagen↗
PubMed1998

Molecular genetics of congenital erythropoietic porphyria.

Congenital erythropoietic porphyria (CEP), an autosomal recessive inborn error of heme biosynthesis, results from the markedly deficient activity of the cytosolic enzyme, uroporphyrinogen III synthase (URO-synthase). The accumulation of the nonphysiological and pathogenic porphyrin isomers, uroporphyrin I and coproporphyrin I, leads to the clinical manifestations of CEP. Disease severity in unrelated patients is markedly heterogeneous, ranging from fetal demise or severe transfusion dependency throughout life to milder adult cases with only cutaneous photosensitivity. To date, 18 mutations causing CEP have been described in the URO-synthase gene, including single base substitutions, insertions and deletions, and splicing defects. Most mutations have been identified in one or a few unrelated families with the exception of C73R, L4F, and T228M which occurred in about 33%, 8%, and 7% of the mutant alleles studied, respectively. Prokaryotic expression of the mutant URO-synthase alleles identified those with significant residual activity, thereby permitting genotype/phenotype predictions for severe to milder phenotypes of this clinically heterogeneous disease. As successful bone marrow transplantation in severely affected patients has proven curative, current efforts are underway to develop hematopoietic stem cell gene therapy for CEP.

Humans↗
PubMed1998

Homology model for the ligand-binding domain of the human estrogen receptor.

We have modeled the ligand-binding domain (LBD) of the human estrogen receptor protein (hER) by homology to the known crystal structure of the LBD of the alpha isoform of human retinoate-X receptor (hRX). Alignment of hER with members of the nuclear receptor superfamily defined probable secondary structures which we used to constrain backbone torsion angles and hydrogen bonds. From published studies we identified key interactions between hER and estradiol to use to dock the hormone in its ligand-binding pocket. Since the hRX crystal structure corresponds to the unliganded form of the LBD, we adopted the "mousetrap" mechanism proposed by Renaud et al to predict the structure of the E2-bound hER. Refinement by molecular dynamics and energy minimization gave a model which matches well the known facts about the estradiol phamacophore. It also provides a possible explanation for how hER discriminates between estradiol and testosterone.

Amino Acid Sequence↗
PubMed1998

Rickettsia slovaca sp. nov., a member of the spotted fever group rickettsiae.

The name Rickettsia slovaca sp. nov. (type strain is strain B) is proposed for a member of the spotted fever group (SFG) rickettsiae which was isolated from Dermacentor marginatus ticks in Slovakia in 1968, and was recently implicated in human febrile illness. This rickettsia can be phenotypically distinguished from other SFG rickettsiae by microimmunofluorescence serotyping, SDS-PAGE, Western blotting and mAbs. Genotypic differences between R. slovaca and the other SFG representatives can be demonstrated by PCR-RFLP analysis, pulsed-field gel electrophoresis and sequencing of 16S rRNA, gltA and ompA genes.

Animals↗
PubMed1998

Taxonomic relationships among spotted fever group rickettsiae as revealed by antigenic analysis with monoclonal antibodies.

The spotted fever group (SFG) is made up of more than 20 different rickettsial species and strains. Study of the taxonomic relationships among the group has been attempted by phenotypic, genotypic, and phylogenetic analyses. In this study, we determined taxonomic relationships among the SFG rickettsiae by comparative analysis of immunogenic epitopes reactive against a panel of monoclonal antibodies. A total of 98 monoclonal antibodies, which were directed against epitopes on the major immunodominant proteins or on the lipopolysaccharide-like antigens of strains of Rickettsia africae, Rickettsia conorii, Rickettsia massiliae, Rickettsia akari, Rickettsia sibirica, and Rickettsia slovaca, were used in the study. The distribution and expression of the epitopes among 29 SFG rickettsiae and Rickettsia bellii were assessed by determination of reaction titers in a microimmunofluorescence assay. The results were scored as numerical taxonomic data, and cluster analysis was used to construct a dendrogram. The architecture of this dendrogram was consistent with previous taxonomic studies, and the implications of this and other findings are discussed.

Antibodies, Monoclonal↗
PubMed1998

A single amino acid change in the hemagglutinin protein of measles virus determines its ability to bind CD46 and reveals another receptor on marmoset B cells.

This paper provides evidence for a measles virus receptor other than CD46 on transformed marmoset and human B cells. We first showed that most tissues of marmosets are missing the SCR1 domain of CD46, which is essential for the binding of Edmonston measles virus, a laboratory strain that has been propagated in Vero monkey kidney cells. In spite of this deletion, the common marmoset was shown to be susceptible to infections by wild-type isolates of measles virus, although they did not support Edmonston measles virus production. As one would expect from these results, measles virus could not be propagated in owl monkey or marmoset kidney cell lines, but surprisingly, both a wild-type isolate (Montefiore 89) and the Edmonston laboratory strain of measles virus grew efficiently in B95-8 marmoset B cells. In addition, antibodies directed against CD46 had no effect on wild-type infections of marmoset B cells and only partially inhibited the replication of the Edmonston laboratory strain in the same cells. A direct binding assay with insect cells expressing the hemagglutinin (H) proteins of either the Edmonston or Montefiore 89 measles virus strains was used to probe the receptors on these B cells. Insect cells expressing Edmonston H but not the wild-type H bound to rodent cells with CD46 on their surface. On the other hand, both the Montefiore 89 H and Edmonston H proteins adhered to marmoset and human B cells. Most wild-type H proteins have asparagine residues at position 481 and can be converted to a CD46-binding phenotype by replacement of the residue with tyrosine. Similarly, the Edmonston H protein did not bind CD46 when its Tyr481 was converted to asparagine. However, this mutation did not affect the ability of Edmonston H to bind marmoset and human B cells. The preceding results provide evidence, through the use of a direct binding assay, that a second receptor for measles virus is present on primate B cells.

Amino Acid Sequence↗
PubMed1998

Mammalian GCN5 and P/CAF acetyltransferases have homologous amino-terminal domains important for recognition of nucleosomal substrates.

The yeast transcriptional adapter Gcn5p serves as a histone acetyltransferase, directly linking chromatin modification to transcriptional regulation. Two human homologs of Gcn5p have been reported previously, hsGCN5 and hsP/CAF (p300/CREB binding protein [CBP]-associated factor). While hsGCN5 was predicted to be close to the size of the yeast acetyltransferase, hsP/CAF contained an additional 356 amino-terminal residues of unknown function. Surprisingly, we have found that in mouse, both the GCN5 and the P/CAF genes encode proteins containing this extended amino-terminal domain. Moreover, while a shorter version of GCN5 might be generated upon alternative or incomplete splicing of a longer transcript, mRNAs encoding the longer protein are much more prevalent in both mouse and human cells, and larger proteins are detected by GCN5-specific antisera in both mouse and human cell extracts. Mouse GCN5 (mmGCN5) and mmP/CAF genes are ubiquitously expressed, but maximum expression levels are found in different, complementary sets of tissues. Both mmP/CAF and mmGCN5 interact with CBP/p300. Interestingly, mmGCN5 maps to chromosome 11 and cosegregates with BRCA1, and mmP/CAF maps to a central region of chromosome 17. As expected, recombinant mmGCN5 and mmP/CAF both exhibit histone acetyltransferase activity in vitro with similar substrate specificities. However, in contrast to yeast Gcn5p and the previously reported shorter form of hsGCN5, mmGCN5 readily acetylates nucleosomal substrates as well as free core histones. Thus, the unique amino-terminal domains of mammalian P/CAF and GCN5 may provide additional functions important to recognition of chromatin substrates and the regulation of gene expression.

Acetyltransferases↗
PubMed1998

Expression and rapid purification of an Aedes aegypti salivary allergen by a baculovirus system.

Mosquito salivary proteins cause allergic reactions in humans. Recombinant salivary allergens will facilitate both the diagnosis and immunotherapy of mosquito allergy. The Aed a 1, a 68-kD apyrase in the saliva of Aedes aegypti, has been demonstrated to be an allergen which binds to the IgE of mosquito-allergic subjects. The baculovirus expression vector pBlueBacHis C equipped with an N-terminal histidine tag was used to express the Aed a 1 protein. The cDNA coding for the 3' significant portion of Aed a 1 (Aed a 1 3') (150-562 amino acid residues) was cloned into pBlueBacHis C. The rAed a 1 3' protein expressed by recombinant baculovirus was verified by immunoblot using anti-Aed a 1 and anti-histidine antibodies, respectively. The histidine-tagged fusion protein was purified to apparent homogeneity from infected Sf9 cells by Ni2+ resin affinity chromatography. Both immunoblot and ELISA showed that the purified rAed a 1 3' binds to the IgE and IgG in mosquito allergic sera, indicating that the antigenicity of the rAed a 1 3' is identical to the native Aed a 1 of Aedes aegypti saliva.

Aedes↗
PubMed1998

Pituitary adenomas: the effect of gamma knife radiosurgery on tumor growth and endocrinopathies.

Seventy-three patients have been treated with Gamma Knife radiosurgery (GKR) for pituitary adenomas. 12 had undergone surgery prior to GKR. Three had had previous radiation therapy. The prescription dose administered to the tumor margin ranged from 9 to 35 Gy. 65 patients were followed up for an average of 29 months. A slight expansion of tumor volume occurred in 3 cases. Otherwise, the tumor volume remained unchanged or decreased in the remainder. Endocrine changes were present in all except 3 cases. GKR was followed by a speedy decrease in raised serum hormone levels in the case of both growth hormone (GH)and adrenocortico-tropic hormone (ACTH). In 3 patients there was some visual deterioration associated with a slight increase in tumor volume. In 2 cases, the tumors were removed surgically. Some preliminary conclusions may be drawn. The dose required to correct an endocrinopathy may be higher than that required for control of tumor growth. The recommended prescription dose for endocrine-active adenomas may be more than 30 Gy. While clinical improvement may be noted in patients with raised serum prolactin levels (PRL), normalization of the endocrinopathy may be less readily achieved than in the case of raised GH and ACTH levels. Gamma Knife radiosurgery as a primary treatment of pituitary adenomas can be safe and effective.

Adenoma↗
PubMed1998

Effects of timely antibiotic administration and culture acquisition on the treatment of urinary tract infection.

The purpose of this study was to assess the timeliness of initial antibiotic administration and culture acquisition for Medicare patients discharged with a principal diagnosis of urinary tract infection. The main outcome measurement was reduced length of stay. Data were collected retrospectively from 24,389 randomly selected discharged Medicare patients from September 1, 1994, to August 31, 1995. Only 61% of the cases as urinary tract infection had adequate criteria to confirm the diagnosis. Of these cases, antibiotics were administered within 4 hr after presentation in 40.9% patients. Urine cultures within 24 hr of presentation were noted more frequently (94%)than blood cultures (66%). Urine cultures obtained before antibiotic administration were noted more frequently (82%) than were blood cultures (58%). Timely antibiotic administration and the acquisition of urine cultures in the first 24 hr of hospitalization were independently associated with shorter length of stay.

Aged↗
PubMed1998

Vinculin knockout results in heart and brain defects during embryonic development.

The vinculin gene codes for a cytoskeletal protein, found in focal adhesion plaques and in cell-cell adherens junctions. Vinculin was inactivated by homologous recombination using a targeting vector in embryonic stem (ES) cells. The heterozygous ES cells were introduced into mice by established procedures to produce heterozygous animals that were normal and fertile. No homozygous vinculin-/- embryos were born and analyses during the gestational period showed that the vinculin null embryos were small and abnormal from day E8 but some survived until E10. The most prominent defect was lack of midline fusion of the rostral neural tube, producing a cranial bilobular appearance and attenuation of cranial and spinal nerve development. Heart development was curtailed at E9.5, with severely reduced and akinetic myocardial and endocardial structures. Mutant embryos were 30-40% smaller, somites and limbs were retarded and ectodermal tissues were sparse and fragile. Fibroblasts (MEF) isolated from mutant embryos were shown to have reduced adhesion to fibronectin, vitronectin, laminin and collagen compared to wild-type levels. In addition, migration rates over these substrata were two-fold higher and the level of focal adhesion kinase (FAK) activity was three-fold higher. We conclude that vinculin is necessary for normal embryonic development, probably because of its role in the regulation of cell adhesion and locomotion, cell behaviors essential for normal embryonic morphogenesis, although specific roles in neural and cardiac development cannot be ruled out.

Animals↗
PubMed1998

Rescue of the mutant phenotype by reexpression of full-length vinculin in null F9 cells; effects on cell locomotion by domain deleted vinculin.

Vinculin plays a role in signaling between integrins and the actin cytoskeleton. We reported earlier that F9-derived cells lacking vinculin are less spread, less adhesive, and move two times faster than wild-type F9 cells. Expression of intact vinculin in null cells restored all wild-type characteristics. In contrast, expression of the head (90 kDa) fragment exaggerated mutant characteristics, especially locomotion, which was double that of vinculin null cells. Expression of the tail domain also had a marked effect on locomotion in the opposite direction, reducing it to very low levels. The expression of the head plus tail domains together (no covalent attachment) effected a partial rescue towards wild-type phenotype, thus indicating that reexpressed polypeptides may be in their correct location and are interacting normally. Therefore, we conclude that: (1) the head domain is part of the locomotory force of the cell, modulated by the tail, and driven by the integrin/matrix connection; (2) intact vinculin is required for normal regulation of cell behavior, suggesting that vinculin head-tail interactions control cell adhesion, spreading, lamellipodia formation and locomotion.

Cell Line↗
PubMed1998

Vinculin and cell-cell adhesion.

Vinculin, a 117-kDa protein, is a constituent of adhesion plaques and adherence junctions in non-muscle cells. We investigated the role of vinculin on the physical strength of cell-cell adhesion by conducting disaggregation assays on aggregates of parental wild-type F9 mouse embryonal carcinoma cells (clone BIM), two vinculin-depleted F9 cell lines, gamma 227 and gamma 229, and a reconstituted gamma 229 cell line (R3) that re-express vinculin. Immunoblotting demonstrated that the four cell lines used in the study had similar expressions of the cell-cell adhesion molecule E-cadherin and associated membrane proteins alpha- and beta-catenin. Double immunofluorescence analysis showed that, in contrast to the vinculin-null cell lines. BIM and R3 cells expressed abundant vinculin at the cell margins in adhesion plaques and in cell-cell margins that also contained actin. Laminar flow assays showed that both the vinculin-positive and vinculin-negative cell aggregates that were formed in culture in the course of 24 to 48 hours largely remained intact despite the imposition of shear flow at high shear rates. Since laminar flow imposed on cell aggregates act to separate cells from each other, our data indicate that F9 cells that were adherent to a substrate formed strong cell-cell adhesion bonds independent of vinculin expression. On the other hand, aggregates of vinculin-depleted gamma 229 and gamma 227 cells that were formed in suspension during a two-hour static incubation at 37 degrees C were desegregated more easily with the imposition of shear flow than the BIM and R3 cell aggregates formed under identical conditions. Loss of vinculin was associated with a reduction in cell-cell adhesion strength only among those cells lacking contact to a substrate. Overall, the results indicate that vinculin is not needed for forming strong cell-cell adhesion bonds between neighboring carcinoma cells which are adherent to the basal lamina.

Actins↗
PubMed1998

[Application of biomarkers in homologous clone identification of enterotoxigenic Escherichia coli].

OBJECTIVE: To study the application of multiple molecular biotechniques and multi-biomarkers in homologous clone identification of enterotoxigenic Escherichia coli (ETEC). METHODS: On the basis of detection and typing for toxigenic genes, plasmid analysis combined with multilocus enzyme electrophoresis (MEE) was used for the first time in the comprehensive research on ETEC homologous clone. RESULTS: Two hundred and six strains of ETEC could be classified into 93 plasmid types with plasmid profiling, and 140 strains with unique genotype. Those 206 strains of ETEC could be classified into 148 electrophoresis-types by MEE further, and altogether 190 strains with unique genotype, by combination of three methods. CONCLUSION: Multiple molecular biotechniques and multi-biomarkers can provide much more and more reliable information in homologous clone identification.

Diarrhea↗
PubMed1998

The pathogenetic role of endogenous angiotensin II in stress ulcer in obstructive jaundice rats.

OBJECTIVE: To investigate the pathogenetic role of endogenous angiotensin II (Ang II) in the mechanism of stress ulcer in obstructive jaundice rats and to detect the effect of angiotensin converting enzyme inhibitor (ACEI) on stress ulcer in obstructive jaundice rats. METHODS: After common bile duct ligation (CBDL) in Wistar rats, the content of plasma and gastric mucosal Ang II, gastric mucosal blood flow (GMBF) and gastric mucosal damage were measured, and the relationship among them was analyzed. RESULTS: The plasma Ang II contents increased much more significantly at 1, 3, 7 and 14 days following CBDL than those in non-CBDL rats (P < 0.05, < 0.01, < 0.01 and < 0.01, respectively). Within 120 minutes following cold-restraint stress, plasma and gastric mucosal Ang II contents were elevated, GMBF decreased, and ulcer index and gastric mucosal damage increased more significantly than those in non-cold-restraint stress rats (P < 0.05, < 0.05, < 0.01, < 0.01 and < 0.05, respectively). Administration of an ACEI, enalaprili, to CBDL rats (5 mg.kg-1.day-1, orally for two days) before stress reduced both the plasma and gastric mucosal Ang II levels, inhibited the decrease of GMBF and decreased ulcer index and gastric mucosal damage (P < 0.001, < 0.01, < 0.01, < 0.01 and < 0.05, respectively). CONCLUSION: The endogenous Ang II plays a significant pathogenetic role in the development of stress ulcer in obstructive jaundice rats, and ACEI may prevent stress ulcer.

Angiotensin II↗
PubMed1998

[An analysis of bacterial resistance to antimicrobial agents in a burn centre].

OBJECTIVE: To investigate bacterial resistance to antimicrobial agents in the background of extensive employment of third-generation cephalosporins in the treatment of burn infection. METHODS: Bacterial susceptibility testing was carried out using Kirby-Bauer method. RESULTS: Out of 259 Gram negative bacilli isolates, 31% of these strains were all resistant to cefotaxime, ceftriaxone, cefoperazone and ceftazidime. In vitro test, susceptibility of 52% third-generation cephlosporins resistant strains were restored by cefoperazone/sulbactum. 23.8% of P. aeruginosa were resistant to imipenem, 51.2% to ciprofloxacin. 28.6% of A. anitratum were resistant to imipenem, 21.4% to ciprofloxacin. 9.9% of enterobacteriaceae were resistant to imipenem, 20.4% to ciprofloxacin. 26.9% of MRSA were resistant to imipenem, 73% to ciprofloxacin. No norvancomycin resistance was detected. 2.7% of E. faecalis were resistant to norvancomycin. CONCLUSION: It is likely that the observed resistance to third-generation cephalosporins may be partially due to chromosome-mediated type-1 beta- lactamase.

Burns↗