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J Liu

Publications and source records attributed to J Liu.

At least 613 records · Page 34Linked to original sources
PubMed2000

Initiation of translation from a downstream in-frame AUG codon on BRCA1 can generate the novel isoform protein DeltaBRCA1(17aa).

Expression of the breast and ovarian cancer gene BRCA1 is regulated at both the transcriptional and post-transcriptional levels. We found that the expression of the BRCA1 protein may also be regulated at the translational level. In addition to an AUG start codon at position 1, BRCA1 mRNA has a second in-frame AUG (+17) that acts as an alternative start codon to generate a novel BRCA1 protein that lacks the first 17 amino acids (DeltaBRCA1(17aa)). We fused cDNAs encoding the second exon of BRCA1 of the wild-type BRCA1 gene (wt-BRCA1) and a mutated BRCA1 gene (mt-BRCA1), in which the first initiation site and its Kozak consensus sequence were abolished, with the nucleophosmin (NPM) reporter gene and used them for in vitro and in vivo translation assays. In both systems, the wt-BRCA1-NPM constructs produced two distinct proteins (18 and 16 kD) begun from the first and second AUGs. The mt-BRCA1-NPM constructs produced only the shorter 16-kD protein lacking the first 17 amino acids of the BRCA1 gene. Next, we analysed the N-terminal protein sequence of purified BRCA1 protein from normal thymocytes and found two different BRCA1 proteins, derived from translation of the first and second in-frame AUGs. Thus, BRCA1 protein expression can be regulated at the translation level in normal cells. Characterization of DeltaBRCA1(17aa) may shed light on the function and regulation of BRCA1 in normal cells as well as the pathogenesis of breast and ovarian cancers. Oncogene (2000).

Amino Acid Sequence↗
PubMed2000

Dimerization of an Inactive Fragment of Huperzine A Produces a Drug with Twice the Potency of the Natural Product This work was supported by the Research Grants Council of Hong Kong (HKUST6156/97M), the Biotechnology Research Institute (HKUST), the Mayo Foundation, and the Istituto Pasteur Fondazione Cenci Bolognetti (E.P.). We thank Prof. X. C. Tang (Shanghai Institute of Materia Medica) for a gift of (-)-1.

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Journal Article↗
PubMed2000

A comparison of fetal and adult porcine islets with regard to Gal alpha (1,3)Gal expression and the role of human immunoglobulins and complement in islet cell cytotoxicity.

BACKGROUND: It is still debated whether fetal or adult porcine islets should be the preferred choice for future clinical islet xenotransplantation. Each type of islet preparation has advantages and disadvantages compared with the other. Here we present a direct comparison between fetal and adult porcine islets with regard to Gal alpha(1,3)Gal expression, immunoglobulin and complement binding, and cytotoxicity after exposure to fresh human serum. METHOD: Islet single cell suspensions were prepared from adult and fetal islets by trypsin digestion. Fluorescein isothiocyanate-conjugated Bandeiraea simplicifolia isolectin B4 (BS-IB4) and affinity-purified chicken anti-Gal alpha(1,3)Gal antibody was used to detect Gal alpha(1,3)Gal expression. Immunoglobulin and complement binding to the islet cells and cytotoxicity for islet cells was compared after incubation with fresh and heat-inactivated human sera and with an immune serum from a diabetic patient who received a fetal porcine islet transplant. Furthermore, two pools of human AB sera were depleted of porcine endothelial cell cytotoxic human anti-Gal alpha(1,3)Gal antibodies by absorption and were used to analyze the effect of Gal alpha(1,3)Gal antibody removal on islet cell cytotoxicity. RESULTS: Fetal islet cells readily bound both BS-IB4 and the chicken anti-Gal alpha(1,3)Gal antibody. None of 10 adult porcine islet preparations were stained by BS-IB4. In comparison, IgY anti-Gal Ab binding was detected in two of eight adult islet isolations, whereas the other six preparations showed marginal/no binding. After incubation of fetal islet cells with fresh human serum, C3c binding was strongly positive and IgM binding variable, with occasional binding of IgG and no detectable binding of IgA. Adult islet cells were also strongly positive for C3c but did not bind detectable amounts of IgM, IgG, or IgA. Immune sera from a patient who had received fetal porcine islets showed the presence of induced antibodies that bound to fetal islet cells and to porcine peripheral blood lymphocytes, whereas binding to adult islet cells was barely detectable. Fresh human sera showed a high and similar level of complement-mediated lytic activity for both adult islet cells (78+/-22%) and fetal islet cells (75+/-16%). Cytotoxicity for fetal islet cells and peripheral blood lymphocytes was significantly reduced when the corresponding sera were depleted of anti-Gal antibodies before use (P=0.002 and P=0.003, respectively). In contrast, no difference in cytotoxicity for adult islet cells was detected when anti-Gal-depleted human sera were used. CONCLUSION: Gal alpha(1,3)Gal expression is occasionally detectable on adult porcine islet cells, but not as readily and at a lower level, compared with fetal islet cells. Thus, as porcine fetal islets mature to adult islets, the expression of the Gal alpha(1,3)Gal epitope gradually diminishes. Consequently, cytotoxic anti-Gal alpha(1,3)Gal antibodies in human serum play an important role in the lysis of fetal but not adult porcine islet cells.

Aging↗
PubMed2000

Alpha(1) adrenergic agonist induction of p21(waf1/cip1) mRNA stability in transfected HepG2 cells correlates with the increased binding of an AU-rich element binding factor.

Stimulation of transfected HepG2 cells (TFG2) with the alpha(1)-adrenergic agonist phenylephrine (PE) significantly activated p21(waf1/cip1) gene expression without affecting p53 gene expression. Northern blotting and reporter assay demonstrated that this induction was due to PE stimulation of p21(waf1/cip1) mRNA stability. To further define the underlying mechanism, we prepared a chloramphenicol acetyltransferase (CAT)-p21(waf1/cip1) 3'-untranslated region (3'-UTR) hybrid construct by inserting the 3'-UTR of p21(waf1/cip1) mRNA just downstream from the CAT coding sequence and transfected it into TFG2 cells. PE treatment enhanced the activity of this construct by 6-fold. Deletion analyses indicated that an AU-rich element (AURE) located between 553 to 625 within the p21(waf1/cip1) 3'-UTR was required for this induction. RNA gel shift assays demonstrated that this AURE bound an RNA-binding protein. This protein has been purified 5000-fold from PE-treated TFG2 cells by heparin-Sepharose and RNA affinity chromatography. SDS-polyacrylamide gel electrophoresis, UV cross-linking, and Northwestern analyses indicated the molecular mass of this protein as 24 and 52 kDa. Finally, PE treatment markedly enhanced this RNA-protein binding by a p42/44 mitogen-activated protein kinase-dependent mechanism. These data suggest that the AURE located between 553 and 625 within the p21(waf1/cip1) mRNA 3'-UTR, which binds an RNA-binding protein, is responsible for PE-induced p21(waf1/cip1) mRNA stability.

3' Untranslated Regions↗
PubMed2000

Receptor-mediated endocytosis in the procyclic form of Trypanosoma brucei.

In Trypanosomatids, endocytosis and exocytosis occur exclusively at the flagellar pocket, a deep invagination of the plasma membrane where the flagellum extends from the cell. Both bloodstream and procyclic trypanosomes are capable of internalizing macromolecules. However, structures resembling coated vesicles were only identified in bloodstream form and not in procyclic form trypanosomes. Due to the apparent absence of coated vesicles in procyclics, the significance of receptor-mediated endocytosis in procyclic trypanosomes has been considered of minimal importance. We show that the flagellar pocket associated cysteine-rich acidic transmembrane protein (CRAM) may function as an high density lipoprotein receptor in the procyclic form trypanosome. Using anti-CRAM IgG we have characterized the process of CRAM-mediated endocytosis in procyclic form trypanosomes. The wild type procyclic trypanosome binds and internalizes anti-CRAM IgG but not the non-immune IgG in a saturable and time-dependent manner; the binding and uptake of (125)I-labeled anti-CRAM IgG are inhibited by excess unlabeled anti-CRAM IgG. Uptake and degradation of anti-CRAM IgG do not occur at 4 degrees C. At 28 degrees C, the internalized anti-CRAM IgG were efficiently degraded through a process that is inhibited by incubation at 4 degrees C and sensitive to the presence of chloroquine. The uptake and degradation of anti-CRAM IgG does not occur in the CRAM null mutant cell line. These results suggested that the uptake of anti-CRAM IgG in the wild type procyclics occurs via receptor-mediated endocytosis of the CRAM protein. Deletion of the cytoplasmic extension of CRAM drastically reduced the degradation but not the binding of anti-CRAM IgG. This result indicated that potential internalization signals may be present in the cytoplasmic extension of CRAM. This is the first time that the importance of receptor-mediated endocytosis in procyclic form trypanosomes has been demonstrated.

Amino Acid Sequence↗
PubMed2000

Effect of clarithromycin on experimental rhinovirus-16 colds: a randomized, double-blind, controlled trial.

PURPOSE: Macrolide antibiotics are frequently prescribed to patients with symptoms of a common cold. Despite their lack of proven antiviral activity, macrolide antibiotics may have anti-inflammatory actions, such as inhibition of mucus secretion and production of interleukins 6 and 8 by epithelial cells. Because the symptoms of rhinovirus colds are attributed to the inflammatory response to infection, we studied the effects of treatment with clarithromycin on the symptomatic and inflammatory response to nasal inoculation with rhinovirus. SUBJECTS AND METHODS: We performed a prospective, double-blind, controlled trial in 24 healthy subjects who were seronegative for antibodies to rhinovirus-16. Subjects were randomly assigned to receive either clarithromycin (500 mg) or trimethoprim-sulfamethoxazole (800/160 mg, as a control antibiotic) twice a day for 8 days, beginning 24 hours before inoculation with rhinovirus-16. RESULTS: All 12 subjects in each group were infected and developed symptomatic colds. The groups did not differ in the intensity of cold symptoms (median [25th to 75th percentile] score in the clarithromycin group of 25 [5 to 33] versus 21 [11 to 26] in the trimethoprim-sulfamethoxazole group, P = 0.86), weight of nasal secretions (25 g [8 to 56 g] versus 12 g [5 to 28 g], P = 0.27), or decline in nasal peak flow during the 8 days following viral inoculation. In both groups, similar and significant increases from baseline were observed in the numbers of total cells and neutrophils, and in the concentrations of interleukins 6 and 8, in nasal lavage fluid during the cold. The changes that we observed did not differ from those in an untreated historical control group. CONCLUSIONS: We conclude that clarithromycin treatment has little or no effect on the severity of cold symptoms or the intensity of neutrophilic nasal inflammation in experimental rhinovirus-16 colds.

Adult↗
PubMed2000

Apoptosis or senescence-like growth arrest: influence of cell-cycle position, p53, p21 and bax in H2O2 response of normal human fibroblasts.

Early-passage human diploid fibroblasts (HDFs) undergo senescence-like growth arrest in response to sublethal concentrations of H(2)O(2) [Chen and Ames (1994) Proc. Natl. Acad. Sci. USA. 95, 4130-4134]. We determine here whether H(2)O(2) can cause apoptosis in HDFs and the molecular changes that differ between apoptosis and senescence-like growth arrest. When exponentially growing early-passage IMR-90 cells were treated for 2 h with 50-200 microM (or 0.25-1 pmol/cell) H(2)O(2), a fraction of cells detached at 16-32 h after the treatment. The cells remaining attached were growth-arrested and developed features of senescence in 1 week. The detached cells showed caspase-3 activation and typical morphological changes associated with apoptosis. Caspase-3 activation was H(2)O(2) dose-dependent and preceded nuclear condensation or plasma membrane leakage. Apoptotic cells were mainly distributed in the S-phase of the cell cycle, while growth-arrested cells exhibited predominantly G1- and G2/M-phase distributions. H(2)O(2) pretreatment induced G1 arrest and prohibited induction of apoptosis by a subsequent H(2)O(2) challenge. The p53 protein showed an average 6.1-fold elevation in apoptotic cells and a 3.5-fold elevation in growth-arrested cells. Reduction of p53 levels with human papillomavirus E6 protein prohibited the activation of caspase-3 and decreased the proportion of apoptotic cells. Growth-arrested cells had elevated p21, while p21 was absent in apoptotic cells. Bcl-2 was elevated in both growth-arrested and apoptotic cells. Finally, although the overall level of bax did not change in growth-arrested or apoptotic cells, the solubility of bax protein increased in apoptotic cells. Our data suggest that in contrast with growth-arrested cells, apoptotic cells show an S-phase cell cycle distribution, a higher degree of p53 elevation, an absence of p21 protein and increased solubility of bax protein.

Apoptosis↗
PubMed2000

Determination of Guan-Fu Base A, a new anti-arrhythmic, in human plasma by gas chromatography and electron-capture detection.

A gas chromatographic-electron capture detection (GC-ECD) method has been developed for determining Guan-Fu Base A (GFA), an experimental anti-arrhythmic, in human plasma. The method was based on one-step liquid-liquid extraction with toluene and chemical derivatization with pentafluoropropionic anhydride followed by GC-ECD. The derivatives of GFA and metoprolol (Met, internal standard) were confirmed by gas chromatography-mass spectrometry (GC-MS) to be dipentafluoropropionyl-GFA and dipentafluoropropionyl-Met. The method was linear over the concentration ranges of 0.1-20.0 and 1.0-30.0 microg/ml with the detection limit of 0.05 microg/ml at S/N=5. The intra- and inter-assay precisions were less than 6 and 10%, and accuracy 99.70+/-3.30 and 97.60+/-5.99%, respectively. The absolute recoveries were 81.88, 77.35, 80.79 and 83.85% for GFA at concentrations of 0.5, 1.0, 5.0 and 14.0 microg/ml and 88.24% for Met at 3.0 microg/ml, respectively.

Adult↗
PubMed2000

Simple and simultaneous analysis of fenfluramine, amphetamine and methamphetamine in whole blood by gas chromatography-mass spectrometry after headspace-solid phase microextraction and derivatization.

A simple and sensitive method for the simultaneous analysis of fenfluramine, amphetamine and methamphetamine in whole blood was developed using a headspace-solid phase microextraction (SPME) and derivatization. A 0.5 g whole blood sample, 5 microl d(5)-methamphetamine (50 micrig/ml) as an internal standard, and 0.5 ml sodium hydroxide (1 M) were placed into a 12 ml vial, and sealed rapidly with a silicone septum and an aluminum cap. Immediately after the vial was heated to 70 degrees C in an aluminium block heater, the needle of the SPME device was inserted through the septum of the vial, and the extraction fiber was exposed in the headspace for 15 min. First, heptafluorobutyric anhydride was injected into the injection port of the GC-MS, and the compounds extracted by the fiber were then desorbed and derivatized simultaneously by exposing the fiber in the injection port. The calibration curves, using an internal standard method, demonstrated good linearity throughout the concentration range from 0.01 to 1.0 microg/g. The detection limits of this method were 5.0 ng/g for fenfluramine and methamphetamine, and 10 ng/g for amphetamine. No interferences were found, and the time for analysis was about 30 min for one sample. This method was applied to a suicide case in which the victim ingested fenfluramine. Fenfluramine was detected in the blood sample collected from the victim at the concentration of 7.7 microg/g.

Adult↗
PubMed2000

Genomic structure and expression of the murine Hmgi(y) gene.

Mammalian HMGI proteins belong to the high mobility group (HMG) of small non-histone nuclear proteins, and function as architectural factors to mediate structural changes in DNA. The HMGI family consists of three members: HMGI, HMGY and HMGI-C. As pseudogenes have complicated the genomic analysis of murine Hmgi(y), a mouse lambda FIX II genomic library was screened with an intron-specific probe to identify and characterize the authentic Hmgi(y) gene. The murine Hmgi(y) gene is 7.2kb long and contains four protein coding exons and two additional exons encoding part of the 5' untranslated region. Sequencing confirms that an alternative splicing site within exon 3 results in the two protein isoforms: Hmgi and Hmgy. Primer extension experiments revealed that at least three transcription start sites exist in the 5' end of the gene. It has been well established that the expression of both Hmgi-c and Hmgi(y) is readily detectable throughout embryogenesis. Unlike Hmgi-c, whose expression is restricted to embryogenesis, a Northern hybridization analysis showed low-level expression of Hmgi(y) in adult mouse tissues. Similarly, when tissues from newborn animals were examined, Hmgi(y) expression was readily detected at a level of intensity intermediate between that found in embryos and adults. Understanding the gene structure and expression pattern will provide important insights into the in-vivo function of Hmgi(y).

Amino Acid Sequence↗
PubMed2000

Dual role of glutathione in selenite-induced oxidative stress and apoptosis in human hepatoma cells.

It is well known that glutathione, the major intracellular antioxidant, is closely involved in the metabolism and bioactivity of selenium. In the present study, glutathione was demonstrated to play a dual role on selenite (Se)-induced oxidative stress and apoptosis in human hepatoma HepG(2) cells. The experiment was carried out in two different modes to modulate intracellular reduced glutathione (GSH) content. In Mode A (pretreatment), cells were pretreated with N-acetylcysteine (NAC), buthionine sulfoximine (BSO), or GSH prior to Se exposure. In Mode B (simultaneous treatment), cells were treated with Se and NAC, BSO, or GSH simultaneously. It was found that Se-induced oxidative stress and apoptosis are closely related to the intracellular level of GSH. Both the increase and depletion of GSH content significantly enhanced Se-induced oxidative stress and apoptosis in HepG(2) cells. Results from this study clearly demonstrated that GSH has a dual role in the effects of Se on cancer cells: (i) GSH acts as a pro-oxidant, facilitating Se-induced oxidative stress, and (ii) GSH acts as an antioxidant, protecting against Se-induced oxidative stress and apoptosis. Understanding such a unique association between GSH and Se may help to explain the controversy in the literature over the complex relationship between selenium and glutathione, and ultimately the capability of selenium to prevent cancer.

Acetylcysteine↗
PubMed2000

Fundamental cryobiology of rat immature and mature oocytes: hydraulic conductivity in the presence of Me(2)SO, Me(2)SO permeability, and their activation energies.

The hydraulic conductivity in the presence of dimethyl sulfoxide Me(2)SO (L(p)(Me(2)SO)), Me(2)SO (P(Me(2)SO)) permeability and reflection coefficient (sigma) of immature (germinal vesicle; GV) and mature (metaphase II; MII) rat oocytes were determined at various temperatures. A temperature controlled micropipette perfusion technique was used to conduct experiments at five different temperatures (30, 20, 10, 4, and -3 degrees C). Kedem and Katchalsky membrane transport theory was used to describe the cell volume kinetics. The cell volumetric changes of oocytes were calculated from the measurement of two oocyte diameters, assuming a spherical shape. The activation energies (E(a)) of L(p)(Me(2)SO) and P(Me(2)SO) were calculated using the Arrhenius equation. Activation energies of L(p)(Me(2)SO) for GV and MII oocytes were 34.30 Kcal/mol and 16.29 Kcal/mol, respectively; while the corresponding E(a)s of P(Me(2)SO) were 19.87 Kcal/mol and 21.85 Kcal/mol, respectively. These permeability parameters were then used to calculate cell water loss in rat oocytes during cooling at subzero temperatures. Based on these values, the predicted optimal cooling rate required to maintain extra- and intracellular water in near equilibrium for rat GV stage oocytes was found to be between 0.05 degrees C/min and 0. 025; while for rat MII oocytes, the corresponding cooling rate was 1 degrees C/min. These data suggest that standard cooling rates used for mouse oocytes (e.g., 0.5-1 degrees C/min) can also be employed to cryopreserve rat MII oocytes. However, the corresponding cooling rate required to avoid damage must be significantly slower for the GV stage rat oocyte. J. Exp. Zool. 286:523-533, 2000.

Animals↗
PubMed2000

[Effects of electromagnetic radiation from handsets of cellular telephone on neurobehavioral function].

In order to study the effects of electromagnetic radiation from handsets of cellular telephone on neurobehavioral function, 81 staff with handsets of cellular telephone and 63 staff without handsets of cellular telephone from corporations were selected as the subjects. The subjects were investigated by questionnaire on their general health, lifestyle habit, suppress of spirit, handset using of cellular telephone, environmental exposure, morbidity, and the neurobehavioral core test battery(NCTB). The data was analyzed by chi-square, stepwise regression analysis and covariance statistics. The results showed that the average reaction time in user's group was longer than that in control group (P < 0.01). The time of using handset was negatively associated with corrected reaction number (P < 0.01). The fast reaction time and the slowest reaction time were positively associated with the length of handset using (P < 0.01, P < 0.05). The results suggested that the handset using could cause adverse health effects in neurobehavioral function.

Behavior↗
PubMed2000

The Arabidopsis thaliana SOS2 gene encodes a protein kinase that is required for salt tolerance.

In Arabidopsis thaliana, the Salt Overly Sensitive 2 (SOS2) gene is required for intracellular Na(+) and K(+) homeostasis. Mutations in SOS2 cause Na(+) and K(+) imbalance and render plants more sensitive toward growth inhibition by high Na(+) and low K(+) environments. We isolated the SOS2 gene through positional cloning. SOS2 is predicted to encode a serine/threonine type protein kinase with an N-terminal catalytic domain similar to that of the yeast SNF1 kinase. Sequence analyses of sos2 mutant alleles reveal that both the N-terminal catalytic domain and the C-terminal regulatory domain of SOS2 are functionally essential. The steady-state level of SOS2 transcript is up-regulated by salt stress in the root. Autophosphorylation assays show that SOS2 is an active protein kinase. In the recessive sos2-5 allele, a conserved glycine residue in the kinase catalytic domain is changed to glutamate. This mutation abolishes SOS2 autophosphorylation, indicating that SOS2 protein kinase activity is required for salt tolerance.

Adaptation, Physiological↗
PubMed2000

Bis(7)-tacrine, a novel acetylcholinesterase inhibitor, reverses AF64A-induced deficits in navigational memory in rats.

The novel dimer bis(7)-tacrine (1,7-N-Heptylene-bis-9,9'-amino-1,2,3, 4-tetrahydroacridine), which exhibits higher potency, selectivity and oral activity on acetylcholinesterase inhibition in vivo than tacrine, was evaluated for its ability to reverse AF64A-induced spatial memory impairment in rats using the Morris water maze. The intracerebroventricular injection of AF64A (3 nmol/side) resulted in a substantial increase in the escape latency to find the platform (F(1,7)=30.2, P<0.01). The observed impairment of spatial memory was paralleled by a 47% decrease in choline acetyltransferase activity in the hippocampus. Oral administration of bis(7)-tacrine (0.22-0.89 micromol/kg) dose-dependently reversed the AF64A-induced latency delay to the level of the saline control group (F(4,28)=7.45, P<0. 05). The present study provides additional evidence of bis(7)-tacrine as an ideal candidate for the palliative treatment of Alzheimer's disease.

Animals↗