Search PubMed⌕ Search

Biomedical subjects

D Liu

Publications and source records attributed to D Liu.

At least 415 records · Page 23Linked to original sources
PubMed1998

Arachidonic acid and protein synthesis inhibitor act synergistically to suppress insulin-stimulated glucose transport in 3T3-L1 adipocytes.

The effect of arachidonic acid (AA) on insulin-stimulated glucose transport by 3T3-L1 adipocytes was examined in the presence of cycloheximide. We found that AA acted synergistically with cycloheximide to suppress insulin-stimulated glucose transport, although it alone was without effect. Similar phenomena were observed while protein synthesis inhibitors other than cycloheximide were employed. Immunoblot analysis indicated that the increase in plasma membranes of the insulin-regulated glucose transporter (GLUT4) in response to insulin was decreased in cells pretreated with cycloheximide for a prolonged time, while total amount of GLUT4 was not altered. Simultaneous presence of AA with cycloheximide had no further effect on the amount of GLUT4 in either total or plasma membranes. Thus the present study suggests that AA in the presence of a protein synthesis inhibitor seems to decrease the intrinsic activity of GLUT4.

3T3 Cells↗
PubMed1998

Characterization of the germinal and somatic activity of the Arabidopsis transposable element Tag1.

Tag1 is an autonomous transposon of Arabidopsis thaliana. The excision behavior of Tag1 during reproductive and vegetative development was examined using CaMV 35STag1-GUS constructs. Germinal reversion frequencies varied from 0 to 27% and correlated with Tag1 copy number. Southern blot and somatic sector analyses indicated that each revertant was derived from an independent excision event, and approximately 75% of the revertants had new Tag1 insertions. Revertants were obtained with similar frequencies from the male and female parents. In flowers, small somatic sectors were observed in siliques, carpels, petals and sepals while stemlike organs (filaments and pedicels) had larger sectors. No sectors encompassing entire flowers or inflorescences were observed, however, indicating that excision occurs late in flower development and rarely in inflorescence meristems. Late excision was also observed during vegetative development with 99.8% of leaves showing small sectors encompassing no more than 20 cells. Roots and cotyledons, however, showed larger sectors that included entire lateral roots and cotyledons. These results indicate that Tag1 can excise in the embryo and all the organs of the plant with the timing of excision being restricted to late stages of vegetative and reproductive development in the shoot.

Arabidopsis↗
PubMed1998

Characterization of the putative transposase mRNA of Tag1, which is ubiquitously expressed in Arabidopsis and can be induced by Agrobacterium-mediated transformation with dTag1 DNA.

Tag1 is an autonomous transposable element of Arabidopsis thaliana. Tag1 expression was examined in two ecotypes of Arabidopsis (Columbia and No-0) that were transformed with CaMV 35S-Tag1-GUS DNA. These ecotypes contain no endogenous Tag1 elements. A major 2.3-kb and several minor transcripts were detected in all major organs of the plants. The major transcript encoded a putative transposase of 84.2 kD with two nuclear localization signal sequences and a region conserved among transposases of the Ac or hAT family of elements. The abundance of Tag1 transcripts varied among transgenic lines and did not correlate with somatic excision frequency or germinal reversion rates, suggesting that factors other than transcript levels control Tag1 excision activity. In untransformed plants of the Landsberg ecotype, which contain two endogenous Tag1 elements, no Tag1 transcripts were detected. Agrobacterium-mediated transformation of these Landsberg plants with a defective 1.4-kb Tag1 element resulted in the appearance of full-length Tag1 transcripts from the endogenous elements. Transformation with control DNA containing no Tag1 sequences did not activate endogenous Tag1 expression. These results indicate that Agrobacterium-mediated transformation with dTag1 can activate the expression of Tag1.

Agrobacterium tumefaciens↗
PubMed1998

Epicuticular wax accumulation and fatty acid elongation activities are induced during leaf development of leeks

Epicuticular wax production was evaluated along the length of expanding leek (Allium porrum L.) leaves to gain insight into the regulation of wax production. Leaf segments from the bottom to the top were analyzed for (a) wax composition and load; (b) microsomal fatty acid elongase, plastidial fatty acid synthase, and acyl-acyl carrier protein (ACP) thioesterase activities; and (c) tissue and cellular morphological changes. The level of total wax, which was low at the bottom, increased 23-fold along the length of the leaf, whereas accumulation of the hentriacontan-16-one increased more than 1000-fold. The onset of wax accumulation was not linked to cell elongation but, rather, occurred several centimeters above the leaf base. Peak microsomal fatty acid elongation activity preceded the onset of wax accumulation, and the maximum fatty acid synthase activity was coincident with the onset. The C16:0- and C18:0-ACP-hydrolyzing activities changed relatively little along the leaf, whereas C18:1-ACP-hydrolyzing activity increased slightly prior to the peak elongase activity. Electron micrographic analyses revealed that wax crystal formation was asynchronous among cells in the initial stages of wax deposition, and morphological changes in the cuticle and cell wall preceded the appearance of wax crystals. These studies demonstrated that wax production and microsomal fatty acid elongation activities were induced within a defined and identifiable region of the expanding leek leaf and provide the foundation for future molecular studies.

Journal Article↗
PubMed1998

The wzz (cld) protein in Escherichia coli: amino acid sequence variation determines O-antigen chain length specificity.

The O antigen is a polymer with a repeated unit. The chain length in most Escherichia coli strains has a modal value of 10 to 18 O units, but other strains have higher or lower modal values. wzz (cld/rol) mutants have a random chain length distribution, showing that the modal distribution is determined by the Wzz protein. Cloned wzz genes from E. coli strains with short (7 to 16), intermediate (10 to 18), and long (16 to 25) modal chain lengths were transferred to a model system, and their effects on O111 antigen were studied. The O111 chain length closely resembled that of the parent strains. We present data based on the construction of chimeric wzz genes and site-directed mutagenesis of the wzz gene to show that the modal value of O-antigen chain length of E. coli O1, O2, O7, and O157 strains can be changed by specific amino acid substitutions in wzz. It is concluded that the O-antigen chain length heterogeneity in E. coli strains is the result of amino acid sequence variation of the Wzz protein.

Amino Acid Sequence↗
PubMed1998

Relationships among the O-antigen gene clusters of Salmonella enterica groups B, D1, D2, and D3.

The O antigen is an important cell wall antigen of gram-negative bacteria, and the genes responsible for its biosynthesis are located in a gene cluster. We have cloned and sequenced the DNA segment unique to the O-antigen gene cluster of Salmonella enterica group D3. This segment includes a novel O-antigen polymerase gene (wzyD3). The polymerase gives alpha(1-->6) linkages but has no detectable sequence similarity to that of group D2, which confers the same linkage. We find the remnant of a D3-like wzy gene in the O-antigen gene clusters of groups D1 and B and suggest that this is the original wzy gene of these O-antigen gene clusters.

Antibody Specificity↗
PubMed1998

Poly(A)-driven and poly(A)-assisted termination: two different modes of poly(A)-dependent transcription termination.

We mapped the elements that mediate termination of transcription downstream of the chicken betaH- and betaA-globin gene poly(A) sites. We found no unique element and no segment of 3'-flanking DNA to be significantly more effective than any other. When we replaced the native 3'-flanking DNA with bacterial DNA, it too supported transcription termination. Termination in the bacterial DNA depended on a functional poly(A) signal, which apparently compelled termination to occur in the downstream DNA with little regard for its sequence. We also studied premature termination by poorly processive polymerases close to the promoter. The rate of premature termination varied for different DNA sequences. However, the efficiencies of poly(A)-driven termination and promoter-proximal premature termination varied similarly on different DNAs, suggesting that poly(A)-driven termination functions by returning the transcription complex to a form which resembles a prior state of low processivity. The poly(A)-driven termination described here differs dramatically from the poly(A)-assisted termination previously described for the simian virus 40 (SV40) early transcription unit. In the SV40 early transcription unit, essentially no termination occurs downstream of the poly(A) site unless a special termination element is present. The difference between the betaH-globin and SV40 modes of termination is governed by sequences in the upstream DNA. For maximum efficiency, the betaH-globin poly(A) signal required the assistance of upstream enhancing sequences. Moreover, the SV40 early poly(A) signal also drove termination in betaH-globin style when it was placed in a betaH-globin sequence context. These studies were facilitated by a rapid, improved method of run-on transcription analysis, based on the use of a vector containing two G-free cassettes.

Animals↗
PubMed1998

Activation of protein kinase C triggers its ubiquitination and degradation.

Treatment of cells with tumor-promoting phorbol esters results in the activation but then depletion of phorbol ester-responsive protein kinase C (PKC) isoforms. The ubiquitin-proteasome pathway has been implicated in regulating the levels of many cellular proteins, including those involved in cell cycle control. We report here that in 3Y1 rat fibroblasts, proteasome inhibitors prevent the depletion of PKC isoforms alpha, delta, and epsilon in response to the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Proteasome inhibitors also blocked the tumor-promoting effects of TPA on 3Y1 cells overexpressing c-Src, which results from the depletion of PKC delta. Consistent with the involvement of the ubiquitin-proteasome pathway in the degradation of PKC isoforms, ubiquitinated PKC alpha, delta, and epsilon were detected within 30 min of TPA treatment. Diacylglycerol, the physiological activator of PKC, also stimulated ubiquitination and degradation of PKC, suggesting that ubiquitination is a physiological response to PKC activation. Compounds that inhibit activation of PKC prevented both TPA- and diacylglycerol-induced PKC depletion and ubiquitination. Moreover, a kinase-dead ATP-binding mutant of PKC alpha could not be depleted by TPA treatment. These data are consistent with a suicide model whereby activation of PKC triggers its own degradation via the ubiquitin-proteasome pathway.

Animals↗
PubMed1998

Senile degeneration and cognitive impairment in chronic schizophrenia.

OBJECTIVE: This study was an investigation of the role of Alzheimer-type senile degenerative abnormalities in the cognitive impairment of chronic schizophrenia. METHOD: The study group comprised 145 deceased elderly institutionalized psychiatric patients: 66 with schizophrenia, 26 with mood disorders, 36 with dementia, and 17 with other psychiatric diagnoses. The comparison group included 16 deceased elderly individuals without neurologic or psychiatric disease. Psychiatric diagnoses and cognitive status were established by standardized review of medical records. Neuritic senile plaques and neurofibrillary tangles were identified immunohistochemically and counted, by investigators blind to clinical information, in standardized regions of each brain. RESULTS: Of the subjects with schizophrenia, 68% had definite cognitive impairment, but only 8% satisfied neuropathological criteria for Alzheimer's disease. Among the schizophrenia subjects without Alzheimer's disease, definite cognitive impairment was associated with higher levels of plaques and tangles. The schizophrenia subjects without definite cognitive impairment had fewer plaques and tangles than the unimpaired nonpsychiatric subjects. CONCLUSIONS: Most cases of cognitive impairment in schizophrenia could not be attributed to Alzheimer's disease. An association of mild Alzheimer-type pathology with definite cognitive impairment was unique to schizophrenia. Enhanced sensitivity to the effects of aging on the brain may be a manifestation of diminished cognitive reserve in schizophrenia.

Aged↗
PubMed1998

Prolonged air leak following radical upper lobectomy: an analysis of incidence and possible risk factors.

STUDY OBJECTIVES: To examine the incidence and clinical significance of prolonged air leak (PAL) in patients undergoing radical upper lobectomy and to determine potential risk factors for PAL in this group of patients. DESIGN: Retrospective review of a prospective database. SETTING: Experience of one thoracic surgeon at a tertiary care cancer center. PATIENTS: One hundred consecutive patients undergoing right upper lobectomy and mediastinal lymph node dissection for non-small cell lung cancer over an 11-year period. MEASUREMENTS: PAL was defined as an air leak lasting >7 days. Preoperative, intraoperative, and postoperative clinical data were collected and analyzed to determine the factors associated with PAL. RESULTS: PAL was the most prevalent postoperative complication, comprising 25.5% of all complications seen, and lasting an average of 12.1+/-5.3 days. In 21 of the 26 patients with PAL, this complication was the only morbidity identified. There was no statistically significant difference in patient age, gender, preoperative FEV1 and diffusion of carbon monoxide, exposure to neoadjuvant chemotherapy, status of pulmonary fissures, or pathologic stage between the PAL group vs the remaining 74 patients without this complication. A significantly greater proportion of patients with PAL had FEV1/FVC ratio < or =50% (6/26 vs 5/74; p=0.02). Patients with PAL had significantly longer median length of hospital stay (11 vs 7 days; p=0.0001). Moreover, PAL was the single most common reason for an extended length of hospitalization (21/58, 36% of all causes). CONCLUSION: PAL is an alarmingly common postoperative complication and is the most frequent cause of an extended length of hospital stay in patients undergoing radical upper lobectomy. Severe obstructive pulmonary disease predisposes patients to the development of this complication.

Adult↗
PubMed1998

Studies on chemical constituents and immunological function activity of hairy root of Astragalus membranaceus.

Using a large-scale culture technique, the hairy roots of Astragalus membranaceus were produced with a yield reaching 10 g/L. The results from RP-HPLC detection showed that the contents of crude saponin and astragaloside i.v. in the hairy roots were 5.81% and 0.14%, respectively. Six isoflavonoid compounds were also determined. Polysaccharide analysis showed that the total polysaccharide content in the hairy roots was 22.97%; of this content, acidic 8.29% and soluble 14.88%. In comparison with the dry roots, the hairy roots contained higher crude saponin and soluble polysaccharide contents, similar astragaloside i.v. content and lower contents of 6 isoflavonoids, total and acidic polysaccharides, showing that the quality of both types of roots was similar. Regaining the immunity function of rats with low immunity after feeding the aqueous extract of the hairy roots produced by large-scale culture showed that its capacity was similar to the dry roots of A. membranaceus in increasing the immunity function. The results in this paper give evidence that the hairy roots may be a new source of A. membranaceus.

Animals↗
PubMed1998

[Analysis of 24-hour dynamic electrocardiogram in 394 elderly population].

To analyse the incidences of arrhythmiases, myocardial ischemia and the minimal heart rate detected by 24-hour dynamic electrocardiogram, three hundred and ninety-four elderly cases of 24-hour dynamic electrocardiogram were studied. The results were shown as follows: 1. the incidence rates of isolated superventricular ectopic beat 97.2%, and paired were 96.2%; nonparaxysmal superventricular tachycardia (SVT) was 55.6%, and paraxysmal SVT was 18.8% respectively. The incidence rates of isolated ventricular ectopic beat and paired were 85.3%, 16.2%, while nonparaxysmal ventricular tachycardia (VT) was 5.6%, paraxysmal VT was 1.8% respectively; 2. 6 cases of minimal heart rate less than 30 beats per minute without subjective symptoms was found while minimal beart rate did not decline with increase of age; 3. 81 (93.1%) of 87 cases (22.1%) who showed myocardial ischemia were completely asymptomatic. It is assumed that the occurances of superventricular and ventricular ectopic beats were of no clinic significance. However, it is important to pay more attention to those whose minimal heart rate is less than 30 beats per minute or who has had episodes of myocardial ischemia.

Aged↗
PubMed1998

[Clinical analysis of PIH with abnormal liver function in 66 patients].

Sixty-six patients of severe pregnancy induced-hypertension(PIH) with abnormal liver function were studied. The results showed that the incidence of abnormal liver function in severe PIH was 20.62%, which was significantly higher than that in moderate PIH and closely related to the course of the disease. The incidence of abnormal liver function in patients who were sick longer than 1 month was much higher than those with short course (P < 0.05). The liver function abnormality in PIH mainly showed the elevation of SGPT activity, increase of serum bilirubin was rarely seen. Besides these, the incidences of the fetal distress and postpartum hemorrhage in patients with abnormal liver function were significantly higher as compared with those having normal liver function (P < 0.05).

Adult↗
PubMed1998

[Cloning and expression of subunit genes of pertussis toxin and its immunological evaluation].

OBJECTIVE: To clone the gene encoding pertussis toxin (PT) from Bordetella Pertussis CS strain and five genes encoding subunits of PT, to investigate the possibility of expressing the genes encoding for mature methionyl subunits of PT in insect cell and to evaluate the immunological characteristics of recombinant subunits. METHODS: The genes encoding for PT and its subunits were cloned by PCR and confirmed by restriction enzyme digestion and Southern blot. Using recombinant baculovirus technology, the recombinant subunits were expressed in Sf9 insect cells and analyzed by immunofluorescence assay. The immunological properties of recombinant subunits were analyzed by ELISA. RESULTS: The genes encoding for PT and its subunits were cloned and expressed in Sf9 cells. The level of specific antibodies against nature PT induced by five recombinant subunits polymerized was higher than that unpolymerized and polymerized by four recombinant subunits (without S1) in mice. The results indicate that PT subunits had weak ability to induce specific antibodies against PT, and also anti-nature PT sera had poor recognition to PT subunits. CONCLUSION: The ability of PT to induce specific antibody is conformation dependent of intact PT, and antibody induction domains are located dominantly in S1 subunit of intact PT.

Animals↗
PubMed1998

[Quantitative evaluation of nasalance after vertical hemilaryngectomy].

It was important and requisite how to quantitatively evaluate nasalance after vertical hemilaryngectomy in patients with carcinoma of the larynx. The lately invented instrument nasometer, which can evaluate objectively vocal function, were used to determine separately in 30 healthy adults and 30 patient's with laryngeal carcinoma treated primarily by vertical hemilaryngectomy from 1984 to 1994. The results showed that the determined nasalance, have significant difference among surgical groups and normal group (P < 0.001 and P < 0.05). We also found that the determined values of nasalance have significant difference between postoperative two years and postoperative ten years groups (P < 0.01). It proved that the longer postoperative time, the better the patient's vocal function.

Adult↗
PubMed1998

[CT scanning of the cervical lymph node metastases: compared with histologic sections].

With the development of new imaging modality, MRI and CT scanning has become the most useful adjunct to physical examination for the preoperative evaluation of cervical lymph node metastases of squamous cell carcinoma of the head and neck(SCHN). The study was designed to compare CT scans of metastatic lymph node with corresponding histologic sections on 26 dissections in total and discussed the criteria for assessment of nodal metastases with histologic sections. With pathologic findings as the standard, sensitivity, specificity and accuracy of CT in the detection of nodal disease is 93.8%, 90.0% and 92.3%. Regarding extracapsular nodal spread, CT scanning results in the accuracy of 72.7%. The accuracy of CT detecting central nodal necrosis was 88.9%. This study indicated that CT is accurate in detecting cervical lymph node metastases from head and neck squamous cell carcinoma.

Aged↗