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Biomedical subjects

L Wang

Publications and source records attributed to L Wang.

At least 1,279 records · Page 71Linked to original sources
PubMed1998

Molecular consequences of Ds insertion into and excision from the helix-loop-helix domain of the maize R gene.

The R and B proteins of maize are required to activate the transcription of several genes in the anthocyanin biosynthetic pathway. To determine the structural requirements for R function in vivo, we are exploiting its sensitive mutant phenotype to identify transposon (Ds) insertions that disrupt critical domains. Here we report that the ability of the r-m1 allele to activate transcription of at least three structural genes is reduced to only 2% of wild-type activity because of a 396-bp Ds element in helix 2 of the basic helix-loop-helix (bHLH) motif. Residual activity likely results from the synthesis of a mutant protein that contains seven additional amino acids in helix 2. This protein is encoded by a transcript where most of the Ds sequence has been spliced from pre-mRNA. Two phenotypic classes of stable derivative alleles, very pale and extremely pale, condition <1% of wild-type activity as a result of the presence of two- and three-amino-acid insertions, respectively, at the site of Ds excision. Localization of these mutant proteins to the nucleus indicates a requirement for an intact bHLH domain after nuclear import. The fact that deletion of the entire bHLH domain has only a minor effect on R protein activity while these small insertions virtually abolish activity suggests that deletion of the bHLH domain may bypass a requirement for bHLH-mediated protein-protein interactions in the activation of the structural genes in the anthocyanin biosynthetic pathway.

Alleles↗
PubMed1998

Fucosebeta-1-P-Ser is a new type of glycosylation: using antibodies to identify a novel structure in Dictyostelium discoideum and study multiple types of fucosylation during growth and development.

Three antibodies that recognize distinct fucose epitopes were used to study fucosylation during growth and development of Dictyostelium discoideum. mAb83.5 is known to recognize an undefined "fucose epitope" on several proteins with serine-rich domains, while mAb CAB4, and a component of anti-horse-radish peroxidase, specifically recognize Fucalpha1,6GlcNAc and Fucalpha1,3GlcNAc residues respectively in the core of N-linked oligosaccharides. We show that mAb 83.5 defines a new type of O-glycosylation. Serine-containing peptides incubated with GDPbeta[3H]Fuc and microsomes formed two fucosylated products. A neutral product accounting for 30% of the label did not react with the antibody, while the rest of the label was incorporated into a charged product which contained all the mAb83.5 reactive material. beta-Elimination of the labeled peptide or endogenous products produced [3H]Fuc-1-P, indicating phosphodiester linkage to serine. Fucbeta-1-P and GDP-betaFuc at 100 microM blocked mAb83.5 binding to endogenous and peptide products, but their alpha-linked anomers did not. Electrospray ionization mass spectra of the neutral and anionic labeled products showed major peaks of mass units corresponding to O-Fuc-Ser peptide and O-Fuc-phospho-Ser peptide, respectively. The activity of Fuc-phosphotransferase exactly paralleled the accumulation of reactive glycans during growth and development. The expressions of N-glycan core Fucalpha1,6GlcNAc and Fucalpha1,3GlcNAc and their respective fucosyl transferase activities were also synchronous, but their developmental regulation differed from one another. Fucalpha1, 6GlcNAc was expressed maximally during growth but declined during development. In contrast core Fucalpha1,3GlcNAc epitopes were expressed almost exclusively during development. These findings provide direct evidence for a novel type of O-phosphofucosylation, demonstrate the existence of an O-fucosyl transferase, and identify two different types of core fucosylation in the N-glycans of Dictyostelium.

Amino Acid Sequence↗
PubMed1998

Detection of Borrelia burgdorferi from ticks (Acari) in Hebei Province, China.

From May 1992 to August 1993, 1,196 ticks were collected by flagging vegetation and from domestic animals in Chengde, Zhangjiakou, Shijiazhuang, and Handan districts of Hebei Province. Of those ticks collected, 954 were Haemaphysalis japonicum Warburton and H. longicornis Neumann, 205 were Ixodes persulcatus Schulze, and 37 were Dermacentor silvarum Olenev. Four strains of Borrelia burgdorferi were isolated from 135 I. persulcatus collected in Weichang and Zhuolu counties. Three of 574 Haemaphysalis spp. (collected in Laishui, Pingshan, and Xinglong counties) were positive for B. burgdorferi by direct immunofluorescent assay. One of 24 H. japonicum and 1 of 1 I. persulcatus (collected in Zhuolu) were positive for B. burgdorferi by polymerase chain reaction. This is the 1st report of a B. burgdorferi isolation from H. japonicum.

Animals↗
PubMed1998

Relative fitness of three organophosphate-resistant strains of Culex pipiens pallens (Diptera: Culicidae).

Effects of dipterex, temephos, and chlorpyrifos resistance on the relative fitness of Culex pipiens pallens (L.) were evaluated by examining developmental and reproductive characteristics. Age-specific life tables of Dip-R- (dipterex), Tmo-R- (temephos), and Chl-R- (chlorpyrifos) resistant strains were compared with the susceptible strain to determine relative fitness based on population trend indices (I). The 3 organophosphate-resistant strains possessed reproductive and developmental disadvantages involving fecundity and survival relative compared with the susceptible strain, with relative fitness values of 0.465, 0.520, and 0.501, respectively. These results are discussed in relation to the reversal from resistance to susceptibility in natural populations of mosquitoes.

Animals↗
PubMed1998

Immunohistochemical localization of tissue plasminogen activator in vascular endothelium of stroke-prone regions of the rat brain.

OBJECTIVE: Tissue plasminogen activator (tPA), a major regulator of fibrinolysis, is present in cerebrovascular endothelium. We have suggested that local regulation of tPA synthesis and release in brain microcirculation could be important determinants of the degree of damage after cerebral ischemia. In this study, the normal distribution of tPA antigen was determined in several stroke-prone regions in the rat brain often used to study the pathophysiological consequences of cerebral ischemia. METHODS: Immunohistochemistry and Western blot analysis were performed using an antibody that detects free tPA antigen and tPA complexed to its rapid inhibitor, plasminogen activator inhibitor-1 (PAI-1). Staining for von Willebrand factor, a brain endothelial cell marker, served as a positive control. RESULTS: Relative to von Willebrand factor, 8.6, 13, 11.4, and 20.4% of vessels in the parietal cortex, frontal cortex, striatum, and hippocampus, respectively, were tPA-positive. The majority of tPA-positive vessels (58-75%) were classified as precapillary arterioles and postcapillary venules (7-20 microm), whereas capillaries (4-7 microm) and small arterioles and venules (20-40 microm) accounted for 11 to 22% and 11 to 19%, respectively, of tPA-positive vessels. Western blot analysis of brain microvascular proteins confirmed the presence of free tPA (67 kDa) and a stronger band representing tPA-PAI-1 complexes. CONCLUSION: The tPA-containing cerebrovascular endothelium is distributed mainly in smaller vessels. In addition to the free pool of tPA, a large portion of tPA is complexed to PAI-1 and is therefore functionally inactive. The size of the free tPA cerebrovascular pool may be regulated by PAI-1, which in turn could suppress fibrinolysis in the cerebral microcirculation.

Animals↗
PubMed1998

Dexamethasone stimulates proteasome- and calcium-dependent proteolysis in cultured L6 myotubes.

The effect of dexamethasone on protein degradation and the involvement of different proteolytic pathways were examined in cultured L6 myotubes. Treatment of the cells with dexamethasone resulted in an approximately 20% increase in protein degradation at a hormone concentration of 10(-7) to 10(-6) M. By using various proteolytic blockers, evidence was found that the dexamethasone-induced increase in protein breakdown mainly reflected energy-proteasome-dependent proteolysis and to a lesser extent calcium-dependent protein breakdown. In contrast, the hormone treatment did not increase lysosomal proteolysis. mRNA levels for cathepsin B, ubiquitin, and the proteasome subunit C3 were increased by dexamethasone. The results suggest that glucocorticoids stimulate calcium and energy-proteasome-dependent muscle proteolysis and that changes in mRNA levels for proteolytic enzymes do not necessarily reflect the involvement of different proteolytic pathways.

Adenosine Triphosphate↗
PubMed1998

The vascular pattern of the optic nerve and its potential relevance in glaucoma.

Evidence that vascular factors contribute to the pathogenesis and development of glaucomatous optic neuropathy continues to accumulate. A higher than expected prevalence of systemic vascular disorders in individuals with glaucoma has been documented. New sophisticated in vivo analysis techniques, such as ultrasound color Doppler imaging, suggest that decreased blood flow velocity and increased vascular resistance are present in the vessels serving the optic nerve of human subjects with glaucoma, implying the presence of either organic or functional vascular disorders in these individuals. Recognizing that different analysis techniques have led to conflicting observations, experimental models have been developed to provide an additional tool with which to interpret the effects of compromised optic nerve perfusion.

Animals↗
PubMed1998

Inefficient reinitiation is responsible for upstream open reading frame-mediated translational repression of the maize R gene.

Maize R genes encode a small family of transcriptional activators of several structural genes in the anthocyanin biosynthetic pathway. The 5' leader region of most R genes contains a 38-codon upstream open reading frame (uORF) that previously was shown to be responsible for the repression of downstream gene expression in a transient transformation assay. In this study, we report that the 5' leader also can repress translation of the downstream luciferase gene both in the rabbit reticulocyte translation system and in transgenic rice plants. The ability to visualize the uORF peptide after in vitro translation permits quantification of both products of dicistronic mRNAs. Similarly, the construction of transgenic rice plants expressing wild-type and mutant constructs permits the quantification and correlation of steady state mRNA levels and reporter gene activities. Using these assays, we demonstrate directly that translation of the uORF is required for repression, that increasing translation of the uORF peptide decreases downstream gene expression, and that repression is unaffected by either subtle or gross changes in the uORF peptide. Rather, we find that ribosomes that translate the uORF reinitiate inefficiently and that the intercistronic sequence downstream of the uORF mediates this effect.

Amino Acid Sequence↗
PubMed1998

Cadaveric liver procurement using aortic perfusion only.

BACKGROUND: To test the effectiveness of a simpler surgical technique for cadaveric liver procurement for liver transplantation, a prospective randomized study was carried out between August 1994 and December 1995, to compare aortic perfusion only (APO) for flush-preservation of the liver with the conventional combined aortic and portal perfusion (APP) technique. METHODS: Forty multiple organ donors were enrolled with 20 in each arm of the trial. Donor parameters (age, bodyweight, liver function tests), surgeons performing the operations, the involvement of other procurement teams and the total ischaemic times were similar in the two groups. The liver recipients had a wide range of native liver pathology but were of similar age, sex and bodyweight in the two groups. RESULTS: The mean procurement operation times for the APO and APP groups were 126.7+/-38.6 and 137.8+/-55.9 min, respectively (P=ns). The perfusion took longer to complete in the APO group (10.2+/-1.7 vs 7.2+/-1.4 min (APP), P < 0.001). The liver temperature fell to its lowest level (12.5+/-3.4 degrees C (APO) vs 11+/-3 degrees C (APP), P=ns) in a similar time (11.9+/-3.8 min (APO) vs 9.3+/-3.4 mins (APP), P=ns). There was no graft primary non-function or graft arterial injury in either group. There was no significant difference between the APO and APP initial graft outcomes. The 3-month patient survival rate was identical in the two groups (95%); 81% of renal grafts from the APO donors functioned well from the time of transplantation as did 76% of those from APP donors. CONCLUSIONS: It is concluded that the APO procurement technique produces equivalent results to those achieved with the APP method. The simplicity of the APO technique makes it the preferred technique.

Adult↗
PubMed1998

Fast Fourier transform analysis of ventricular fibrillation intervals to predict ventricular refractoriness and its spatial dispersion.

A technique of fast Fourier transform analysis has been used to derive mean ventricular fibrillation (VF) intervals, and to confirm that these VF intervals predict ventricular refractory periods. Twenty episodes of VF were induced by a rapid ventricular pacing in 12 sheep. VF activations in a 10-second period were simultaneously acquired from 64 epicardial sites with an electrode sock. The VF electrograms were analyzed by a fast Fourier transform analysis. The dominant peak frequency of the VF spectrum in each epicardial site was converted into milliseconds and served as a mean VF interval. The dominant peak frequency of VF electrograms ranged from 8.1 to 11.5 Hz, and the corresponding mean VF intervals were 87 to 124 ms. In five sheep, the mean VF intervals and the effective refractory periods were determined by the extrastimulus technique obtained from 29 epicardial sites. There was a very good correlation between the two parameters when the effective refractory periods were determined at a basic cycle length of 300 ms (r = 0.89, P < 0.001) and 400 ms (r = 0.87, P < 0.001), respectively. VF was induced twice in eight sheep. The maximum difference in the mean VF intervals between the two VF episodes in the same sheep was 3 ms (P > 0.05). In conclusion, mean VF intervals determined by the fast Fourier transform analysis have a good reproducibility and a good correlation with ventricular refractory periods measured by the classic extrastimulus technique. The mean VF intervals could serve as an index of ventricular refractoriness.

Animals↗
PubMed1998

A patient-specific Monte Carlo dose-calculation method for photon beams.

A patient-specific, CT-based, Monte Carlo dose-calculation method for photon beams has been developed to correctly account for inhomogeneity in the patient. The method employs the EGS4 system to sample the interaction of radiation in the medium. CT images are used to describe the patient geometry and to determine the density and atomic number in each voxel. The user code (MCPAT) provides the data describing the incident beams, and performs geometry checking and energy scoring in patient CT images. Several variance reduction techniques have been implemented to improve the computation efficiency. The method was verified with measured data and other calculations, both in homogeneous and inhomogeneous media. The method was also applied to a lung treatment, where significant differences in dose distributions, especially in the low-density region, were observed when compared with the results using an equivalent pathlength method. Comparison of the DVHs showed that the Monte Carlo calculated plan predicted an underdose of nearly 20% to the target, while the maximum doses to the cord and the heart were increased by 25% and 33%, respectively. These results suggested that the Monte Carlo method may have an impact on treatment designs, and also that it can be used as a benchmark to assess the accuracy of other dose calculation algorithms. The computation time for the lung case employing five 15-MV wedged beams, with an approximate field size of 13 X 13 cm and the dose grid size of 0.375 cm, was less than 14 h on a 175-MHz computer with a standard deviation of 1.5% in the high-dose region.

Algorithms↗
PubMed1998

Substrate specificity of human recombinant mitochondrial deoxyguanosine kinase with cytostatic and antiviral purine and pyrimidine analogs.

Deoxyguanosine kinase (dGK) is an enzyme responsible for the phosphorylation of purine deoxynucleosides in mitochondria of mammalian cells. Its role in activation of pharmacologically used nucleoside analogs is not well understood, because of the low levels of dGK found in tissue extracts and its inactivation during purification. The cDNA for dGK was recently cloned and expressed in Escherichia coli. Here we present an improved procedure for expression and purification of a highly active form of human recombinant dGK. The enzyme showed a broad substrate specificity toward natural purine and pyrimidine deoxynucleosides as well as toward important nucleoside analogs. The Km and Vmax values for deoxyguanosine, deoxyinosine, deoxyadenosine, and deoxycytidine were 4, 13, 460, 330 microM and 43, 330, 430 and 60 nmol/min/mg of protein, respectively. Antileukemic purine analogs such as arabinosyl guanine, 2-chloro-2'-deoxyadenosine, 2-chloro-2'-arabino-fluoro-2'-deoxyadenosine, and 2-fluoro-arabinosyl-adenine were phosphorylated as efficiently by dGK as the natural nucleoside substrates. This is the first report in which 2-fluoro-arabinosyl-adenine and 2-chloro-2'-arabino-fluoro-2'-deoxyadenosine were shown to be good substrates for dGK. The antiviral analogs dideoxyinosine and arabinosyl adenine also showed significant activity with dGK, as did several pyrimidine analogs (e.g., the cytostatic drugs 5-fluoro-2'-deoxycytidine and difluorodeoxycytidine). The broad specificity of dGK described here may change our understanding of the mechanisms responsible for the efficacy and mitochondrial toxicity of several nucleoside analogs.

Humans↗
PubMed1998

Chronic morphine augments adenylyl cyclase phosphorylation: relevance to altered signaling during tolerance/dependence.

Despite the demonstration that chronic morphine increases phosphorylation of multiple substrate proteins, their identity has, for the most part, remained elusive. Thus far, chronic morphine has not been shown to increase the phosphorylation of any identified effector protein. This is the first demonstration that persistent activation of opioid receptors has profound effects on phosphorylation of adenylyl cyclase (AC). A dramatic increase in phosphorylation of AC (type II family) was observed in ileum longitudinal muscle myenteric plexus preparations obtained from chronic morphine-treated guinea pigs. Analogous results were obtained when AC was immunoprecipitated using two differentially directed AC antibodies. The magnitude of the augmented AC phosphorylation was substantially attenuated by chelerythrine, a protein kinase C-selective inhibitor. These results suggest the potential relevance of increased phosphorylation (protein kinase C-mediated) of AC to opioid tolerant/dependent mechanisms. Because phosphorylation of AC isoforms (type II family) can significantly increase their stimulatory responsiveness to Gsalpha and Gbetagamma, this mechanism could underlie, in part, the predominance of opioid AC stimulatory signaling observed in opioid tolerant/dependent tissue. Moreover, in light of the fact that many G protein-coupled receptors signal through common effector proteins, this effect provides a mechanism for divergent consequences of chronic morphine treatment and could explain the well documented complexity of changes that accompany the opioid tolerant/dependent state.

Adenylyl Cyclases↗
PubMed1998

Possible mechanism by which the carbapenem antibiotic panipenem decreases the concentration of valproic acid in plasma in rats.

There is evidence indicating that the carbapenem antibiotic panipenem decreases plasma concentrations of valproic acid (VPA) in epileptic patients during VPA therapy. The mechanism for panipenem-induced changes in the pharmacokinetics of VPA was investigated in rats with and without bile duct cannulation. The effect of panipenem on the pharmacokinetics of diclofenac, which undergoes extensive enterohepatic recirculation, was also examined. VPA (50 mg/kg of body weight) or diclofenac (10 mg/kg of body weight) was administered intravenously under the steady-state plasma panipenem concentration of 4 microgram/ml, which had been achieved by a constant infusion rate. Panipenem decreased the plasma VPA concentrations in rats without bile duct cannulation but did not change the volume of the initial space and protein binding of VPA. However, panipenem had no effect on the plasma VPA concentrations and the biliary excretion of VPA in rats with bile duct cannulation. The secondary increase in plasma diclofenac concentration observed in the absence of panipenem was diminished in the presence of panipenem. These findings suggest that panipenem decreases plasma VPA concentrations by suppressing its enterohepatic recirculation, probably due to a panipenem-induced decrease in the numbers of enteric bacteria.

Animals↗
PubMed1998

Granulocyte colony-stimulating factor enhances endotoxin-induced decrease in biliary excretion of the antibiotic cefoperazone in rats.

We have recently reported that endotoxin (lipopolysaccharide [LPS]) derived from Klebsiella pneumoniae dramatically decreased the biliary excretion of the beta-lactam antibiotic cefoperazone (CPZ), which is primarily excreted into the bile via the anion transport system, in rats. The present study was designed to investigate the effect of human recombinant granulocyte colony-stimulating factor (G-CSF), which is reported to be beneficial in experimental models of inflammation, on the pharmacokinetics and biliary excretion of CPZ in rats. CPZ (20 mg/kg of body weight) was administered intravenously 2 h after the intravenous injection of LPS (250 microgram/kg). G-CSF was injected subcutaneously at 12 microgram/kg for 3 days and was administered intravenously at a final dose of 50 microgram/kg 1 h before LPS injection. Peripheral blood cell numbers were also measured. LPS dramatically decreased the systemic and biliary clearances of CPZ and the bile flow rate. Pretreatment with G-CSF enhanced these decreases induced by LPS. The total leukocyte numbers were increased in rats pretreated with G-CSF compared to the numbers in the controls, while the total leukocyte numbers were decreased (about 3,000 cells/microliter) by treatment with LPS. Pretreatment with G-CSF produces a deleterious effect against the LPS-induced decrease in biliary secretion of CPZ, and leukocytes play an important role in that mechanism.

Animals↗
PubMed1998

Organization of Escherichia coli O157 O antigen gene cluster and identification of its specific genes.

The O157:H7 clone of Escherichia coli, which causes major, often prolonged outbreaks of gastroenteritis with hemolytic-uremic syndrome (HUS) such as those in Japan, Scotland, and the United States recently, is thought to be resident normally in cattle or other domestic animals. This clone is of major significance for public health and the food industry. We have developed a fast method for sequencing a given O antigen gene cluster and applied it to O157. The O157 O antigen gene cluster is 14 kb in length, comprising 12 genes and a remnant H-repeat unit. Based on sequence similarity, we have identified all the necessary O antigen genes, including five sugar biosynthetic pathway genes, four transferase genes, the O unit flippase gene, and the O antigen polymerase gene. By PCR testing against all 166 E. coli O serogroups and a range of gram-negative bacterial strains, including some that cross-react serologically with E. coli O157 antisera, we have found that certain O antigen genes are highly specific to O157 E. coli. This work provides the basis for a sensitive test for rapid detection of O157 E. coli. This is important both for decisions on patient care, since early treatment may reduce the risk of life-threatening complications, and for detection of sources of contamination. The method for fast sequencing of O antigen gene clusters plus an ability to predict which genes will be O antigen specific will enable PCR tests to be developed as needed for other clones of E. coli or, once flanking genes are identified, clones of any gram-negative bacterium.

Base Sequence↗
PubMed1998

FtsI and FtsW are localized to the septum in Escherichia coli.

The localization of FtsI (PBP3), a penicillin-binding protein specifically required for cell division in Escherichia coli, was investigated by immunofluorescence microscopy and found to localize to the septum. The localization of FtsI was not observed in ftsZ or ftsA mutants, indicating that it was dependent on the prior localization of these proteins. Addition of furazlocillin, a specific inhibitor of FtsI, prevented localization of FtsI even though FtsZ and FtsA localization occurred. Interestingly, the localization of FtsN was also prevented by furazlocillin. FtsZ displayed limited localization in furazlocillin-treated cells, whereas it was efficiently localized in FtsI-depleted cells. FtsW, another essential cell division protein, was also localized to the septum.

Azlocillin↗