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L P Liu

Publications and source records attributed to L P Liu.

At least 19 recordsLinked to original sources
PubMed2001

NF-kappaB activation for constitutive expression of VCAM-1 and ICAM-1 on B lymphocytes and plasma cells.

Cytokine stimulation can activate NF-kappaB that triggers inducible expression of E-selectin, VCAM-1 (Vascular Cell Adhesion Molecule-1) and ICAM-1 (Intercellular Cell Adhesion Molecule-1) in endothelial cells. In the previous study, we have shown that B lymphocytes and plasma cells can express E-selectin by constitutive activation of NF-kappaB. Here we show that human B lymphocytes and ARH-77 plasma cells expressed VCAM-1 and ICAM-1 in a cytokine dispensable mechanism. NF-kappaB antagonists could inhibit their expressions in ARH-77 cells. The activities of NF-kappaB for VCAM-1 and ICAM-1 promoters prior to cytokine stimulation were detected in ARH-77 cells using electrophoretic mobility shift assays. Again, NF-kappaB antagonists could abrogate these promoter activities. Taken together, our results demonstrate that NF-kappaB activation is the underlying molecular mechanism for constitutive expression of E-selectin, VCAM-1, and ICAM-1 on human B lymphocytes and plasma cells.

B-Lymphocytes↗
PubMed2001

B lymphocytes and plasma cells express functional E-selectin by constitutive activation of NF-kappaB.

E-selectin (CD62E), a cell adhesion molecule for most leukocytes, is known to be expressed exclusively on the cytokine-stimulated endothelial cells mainly by inductive activation of NF-kappaB. Using immunohistochemistry and in situ hybridization, we showed that B lymphocytes and plasma cells in the spleens and lymph nodes from nude mice (T-lymphocyte-deficient), but not from SCID mice (T- and B-lymphocyte-deficient), expressed E-selectin prior to cytokine stimulation. The expression of E-selectin was also confirmed on human B lymphocytes isolated from peripheral bloods. The mouse J774A.1 monocytes could adhere to the marginal zones of mouse spleens in an E-selectin Ab inhibitable manner, suggesting the functional activity of the expressed E-selectin. In addition, ARH-77 cells, a cell line derived from human plasma cells, were found to express E-selectin mRNA and protein and to have a NF-kappaB activity for an E-selectin promoter. NF-kappaB antagonists, such as TPCK (tosylsulfonyl phenylalanyl chloromethyl ketone), dexamethasone and a IkappaBalpha mutant plasmid could inhibit both the NF-kappaB activity and the expression of E-selectin. Transfection with an E-selectin promoter-driven reporter gene construct further verified the E-selectin promoter activity in ARH-77 cells. Again, TPCK, dexamethasone, and the IkappaBalpha mutant plasmid could neutralize this activity. These findings suggest that B lymphocytes and plasma cells can express E-selectin, which is functional for monocytic leukocytes, by a mechanism of constitutive activation of NF-kappaB.

Animals↗
PubMed2001

Effects of Sheng-Mai injection on the PRPP synthetase activity in BFU-es and CFU-es from bone marrows of mice with benzene-induced aplastic anemia.

160 Kunming mice were divided at random into 3 groups. Group 1: normal control (40 mice). Group 2: aplastic anemia (AA) control (60 mice); benzene inhalation was carried out for 2.5 months and sterilized normal saline was injected i.p. for another 6 weeks. Group 3: treated AA (60 mice); benzene was administered by inhalation in a similar manner, Sheng-Mai Injection (SMI) was administered i.p. for 6 weeks after the AA models were established. SMI is a famous Chinese traditional prescription of Panax ginseng C.A. Meyer (0.1 g/ml), Ophiopogon japonicus (Thunb.) Ker-Gawl (0.312 g/ml) and Fructus Schisandrae (0.158 g/ml). Activities of phosphoribosylpyrophosphate (PRPP) synthetase in BFU-Es and CFU-Es were estimated by ion pair reversed phase HPLC (IPrHPLC). Accompanying the sharp drop in counts of erythroid progenitor cells, the PRPP synthetase activity in CFU-Es of AA mice was reduced significantly (P<0.01), whereas there were no remarkable changes of this enzyme activity in their BFU-Es compared with the control group. Both the counts of erythroid progenitor cells and PRPP synthetase activity in CFU-Es returned nearly to normal levels following treatment with SMI of mice in Group 3 (P<0.01). Our results suggest that the attenuation of PRPP synthetase activity in peripheral erythrocytes of AA patients may originate from the weakening of activity of this enzyme in CFU-Es from their bone marrow. The impairment of PRPP formation would explain ATP depletion and disorders of energy metabolism in AA erythrocytes. SMI can distinctly increase the reduced quantity of erythroid progenitor cells and promote rapid restoration of PRPP synthetase activity in CFU-Es of AA mice.

Administration, Inhalation↗
PubMed2001

Analysis of expressions of components in the plasminogen activator system in high- and low-metastatic human lung cancer cells.

PURPOSE: To determine the expressive patterns of the components of the plasminogen activator system in human large-cell lung carcinoma strains and to analyze the effects of the patterns on tumor invasion and metastasis. METHODS: The in vitro and in vivo invasive and metastatic potential of two human large-cell lung carcinoma strains with high (strain 95D) and low (strain 95C) metastatic potential was further confirmed by the Boyden chamber model and nude mice model. After this, the expressions of the components of the plasminogen activator system--including urokinase-type and tissue-type plasminogen activator (uPA and tPA), urokinase receptor (uPAR), and type-1 and type-2 plasminogen activator inhibitor (PAI-1 and PAI-2) in strain 95D and 95C cells--were determined by RT-PCR and immunohistochemical staining. The effects of monoclonal antibodies of uPA, uPAR, and PAI-1 on the invasive potential of strain 95D cell line were also evaluated. RESULTS: Strain 95D cells were found to have a stronger in vitro and in vivo invasive and metastatic potential than strain 95C cells. In the former, the average number of infiltrating cells in the in vitro model in one field of vision (40055) was 73.75 +/- 7.42, while in the latter, it was 56.33 +/- 6.28 (P < 0.001). Lung metastatic loci were observed in all six nude mice inoculated with 95D cells (6/6), but not in any of the nude mice inoculated with 95C cells (0/6). The high-metastatic strain 95D cells expressed higher uPA and uPAR and lower tPA and PAI-2 than the low-metastatic strain 95C cells. The PAI-1 expressions in both 95D and 95C cells were almost the same. Monoclonal antibodies of uPA and uPAR greatly reduced the invasive potential of strain 95D cells in vitro. CONCLUSIONS: These data suggest that the invasive and metastatic potential of human large-cell lung carcinoma cell lines is associated with differential expressions of the components of the plasminogen activator system and that the determination of these components may be used as a marker for judging clinically the possibility of tumor metastasis as well as the prognoses of patients.

Carcinoma, Large Cell↗
PubMed2001

TM Finder: a prediction program for transmembrane protein segments using a combination of hydrophobicity and nonpolar phase helicity scales.

Based on the principle of dual prediction by segment hydrophobicity and nonpolar phase helicity, in concert with imposed threshold values of these two parameters, we developed the automated prediction program TM Finder that can successfully locate most transmembrane (TM) segments in proteins. The program uses the results of experiments on a series of host-guest TM segment mimic peptides of prototypic sequence KK AAAXAAAAAXAAWAAXAAAKKKK-amide (where X = each of the 20 commonly occurring amino acids) through which an HPLC-derived hydropathy scale, a hydrophobicity threshold for spontaneous membrane insertion, and a nonpolar phase helical propensity scale were determined. Using these scales, the optimized prediction algorithm of TM Finder defines TM segments by first searching for competent core segments using the combination of hydrophobicity and helicity scales, and then performs a gap-joining operation, which minimizes prediction bias caused by local hydrophilic residues and/or the choice of window size. In addition, the hydrophobicity threshold requirement enables TM Finder to distinguish reliably between membrane proteins and globular proteins, thereby adding an important dimension to the program. A full web version of the TM Finder program can be accessed at http://www.bioinformatics-canada.org/TM/.

Animals↗
PubMed1999

The portosystemic shunt protects liver against ischemic reperfusion injury.

BACKGROUND: The goal of this study was to characterize the importance of splanchnic viscera in liver ischemic reperfusion injury and to enhance the tolerance of liver to warm ischemia injury with portosystemic shunt. METHODS: The hepatic blood flow of male Sprague Dawley rats was subjected to 45, 60, 120, and 150 min liver warm ischemia with or without portosystemic shunt (splenic-caval shunt). The production of tumor necrosis factor a (TNFa), nuclear factor-kappaB activation, inducible NO synthase (iNOS) expression, and apoptosis were examined. RESULTS: A total of 67% of rats with 45 min liver warm ischemia (n=6) and 100% of rats with 60 min liver warm ischemia (n=6) died within 1 day. However, all rats with 120 min (n=8) liver warm ischemia in splenic-caval shunt group survived for over 1 day, 6/8 for over 3 days, and 5/8 for over 5 days without significant histological changes of the liver. Serum tumor necrosis factor levels in liver warm ischemic rats were increased, This increase was significantly reversed after portosystemic shunt. After challenge with lipopolysaccharide (1 mg/kg, p.v.), naive rats survived for over 5 days (n=4) with the peak value of rat tumor necrosis factor (240 pg/ml) at 90 min. In contrast, all rats died within one day (n=5) with the peak value of rat tumor necrosis factor a (465 pg/ml) at 45 min after administration of lipopolysaccharide in the rats with liver warm ischemia plus splenic-caval shunt. iNOS expression and nuclear factor-kappaB activation were very strongly increased in the hepatocytes after liver warm ischemia with portosystemic shunt, compared with liver ischemia without portosytemic shunt. CONCLUSIONS: We conclude that the splanchnic viscera can contribute to liver ischemic reperfusion injury. Portosystemic shunt enhances the tolerance of liver to warm ischemia through the protective role of iNOS and nuclear factor-kappaB (NF-kappaB).

Animals↗
PubMed1999

Combining hydrophobicity and helicity: a novel approach to membrane protein structure prediction.

In spite of the overwhelming numbers and critical biological functions of membrane proteins, only a few have been characterized by high-resolution structural techniques. From the structures that are known, it is seen that their transmembrane (TM) segments tend to fold most often into alpha-helices. To evaluate systematically the features of these TM segments, we have taken two approaches: (1) using the experimentally-measured residence behavior of specifically designed hydrophobic peptides in RP-HPLC, a scale was derived based directly on the properties of individual amino acids incorporated into membrane-interactive helices: and (2) the relative alpha-helical propensity of each of the 20 amino acids was measured in the organic non-polar environment of n-butanol. By combining the resulting hydrophobicity and helical propensity data, in conjunction with consideration of the 'threshold hydrophobicity' required for spontaneous membrane integration of protein segments, an approach was developed for prediction of TM segments wherein each must fulfill the dual requirements of hydrophobicity and helicity. Evaluated against the available high-resolution structural data on membrane proteins, the present combining method is shown to provide accurate predictions for the locations of TM helices. In contrast, no segment in soluble proteins was predicted as a 'TM helix'.

1-Butanol↗
PubMed1999

Perspective: peptides as mimics of transmembrane segments in proteins.

Peptide-based approaches to protein structure within membranes have proven enormously valuable. When one focusses on the detailed manner through which membrane proteins actually traverse the cell bilayer, a simple observation emerges: helical peptide segments of 20 amino acids each constitute the only tangible connection between the inside and outside of the cell. Thus, a major step towards understanding the key relationships between biological function and membrane protein structure can be taken through characterization, by composition, sequence, chain length, hydrophobicity and conformation, of hydrophobic peptides designed as mimics of transmembrane segments.

Amino Acid Sequence↗
PubMed1999

[The experimental study of repairing bone defects with allogeneic bone matrix gelatin and plaster].

OBJECTIVE: To study the function of the composite of bone matrix gelatin(BMG) and plaster in the repairing process of bone defects. METHODS: Sixteen New Zealand rabbits which were defected in corpus radii were made as implant zone of bone. Sixteen sides of radii were implanted with the composite of BMG and plaster as experimental group. Others were implanted with BMG(8 sides) and bone stored in alcohol(8 sides) as control groups. The repairing process in bone defects were observed by X-ray and histological examination. RESULTS: There was an obvious osteogenesis in experimental group. The defects of radii were almost healed at 12th week after operation. There were osteogenesis in both control groups, but the repairing process was slower than that of the experimental group. CONCLUSION: The composite of BMG and plaster is a good material for bone transplantation.

Animals↗
PubMed1998

Uncoupling hydrophobicity and helicity in transmembrane segments. Alpha-helical propensities of the amino acids in non-polar environments.

Although the chains of amino acids in proteins that span the membrane are demonstrably helical and hydrophobic, little attention has been paid toward addressing the range of helical propensities of individual amino acids in the non-polar environment of membranes. Because it is inappropriate to apply soluble protein-based structure prediction algorithms to membrane proteins, we have used de novo designed peptides (KKAAAXAAAAAXAAWAAXAAAKKKK-amide, where X indicates one of the 20 commonly occurring amino acids) that mimic a protein membrane-spanning domain to determine the alpha-helical proclivity of each residue in the isotropic non-polar environment of n-butanol. Peptide helicities measured by circular dichroism spectroscopy were found to range from theta222 = -17,000 degrees (Pro) to -38,800 degrees (Ile) in n-butanol. The relative helicity of each amino acid is shown to be well correlated with its occurrence frequency in natural transmembrane segments, indicating that the helical propensity of individual residues in concert with their hydrophobicity may be a key determinant of the conformations of protein segments in membranes.

Amino Acid Sequence↗
PubMed1998

Cystic fibrosis transmembrane conductance regulator: expression and helicity of a double membrane-spanning segment.

The gene responsible for cystic fibrosis encodes a membrane protein--the 1480-residue cystic fibrosis transmembrane conductance regulator (CFTR)--in which membrane-based CF-phenotypic mutants alter pore structure and/or impair ion transport. We report the preparation in milligram quantities and conformational characterization of a polypeptide comprised of CFTR transmembrane (TM) segments 3-4, a putative 'helical hairpin' portion of the CFTR TM1-6 domain. The TM segment 3-4 of CFTR was expressed in E. coli as a fusion protein linked to the C-terminus of His-tagged thioredoxin. Nickel chelate affinity chromatography, followed by release from the carrier by digestion with thrombin protease, gave free CFTR(TM3-4). Monitoring of the folding properties and conformational state(s) of the TM3-4 polypeptide using circular dichroism spectroscopy indicated a partial alpha-helical conformation in aqueous buffer, with up to 30% increase in alpha-helical content observed in membrane-mimetic environments.

Cell Membrane↗
PubMed1998

Guidelines for membrane protein engineering derived from de novo designed model peptides.

Notwithstanding great advances in the engineering and structural analysis of globular proteins, relatively limited success has been achieved with membrane proteins--due largely to their intrinsic high insolubility and the concomitant difficulty in obtaining crystals. Progress with de novo synthesis of model membrane-interactive peptides presents an opportunity to construct simpler peptides with definable structures, and permits one to approach an understanding of the properties of the membrane proteins themselves. In the present article, we review how our laboratory and others have used peptide approaches to assess the detailed interactions of peptides with membranes, and primary folding at membrane surfaces and in membranes. Structural studies of model peptides identified the existence of a "threshold hydrophobicity," which controls spontaneous peptide insertion into membranes. Related studies of the relative helicity of peptides in organic media such as n-butanol indicate that the helical propensity of individual residues--not simply their hydrophobicity--may dictate the conformations of peptides in membranes. The overall experimental results provide fundamental guidelines for membrane protein engineering.

Amino Acid Sequence↗
PubMed1998

Partial purification of embryotrophic factors from human oviductal cells.

Embryotrophic factors from human oviductal cells were partially purified by liquid chromatographic methods. The conditioned medium from human oviductal cell culture was fractionated successively by concanavalin A (Con-A) affinity chromatography, ion-exchange chromatography and gel filtration. The presence of the embryotrophic activity in the eluates was determined by the stimulatory effects on the development of mouse embryos in vitro. The fraction that did not bind to the lectin Con-A possessed no embryotrophic activity. Ion-exchange chromatography separated the glycoproteins that bound to Con-A into five fractions. Three of them significantly enhanced blastulation as well as conceptus formation. Gel filtration further separated these embryotrophic fractions into five fractions. Three of them with molecular weights of 154 +/- 1, 164 +/- 0.2 and 207 +/- 0.3 kDa significantly stimulated blastulation of mouse embryos. The results of this study demonstrated that several embryotrophic factors with different biochemical properties contributed to the embryotrophic effect of the human oviductal cell/mouse embryo co-culture system.

Animals↗
PubMed1998

Differential efficacy of passive immunisation against infection by Lyme disease spirochaetes transmitted by partially fed vector ticks.

The efficacy of passive immunisation against tick-transmitted Lyme disease spirochaetal infection was determined in relation to the duration of previous feeding of infected vector ticks. Thus, mice challenged with spirochaete-infected unfed or partially fed nymphal ticks were passively immunised with monoclonal and polyclonal antibodies against the Lyme disease spirochaete (Borrelia burgdorferi) at various intervals after tick attachment. Spirochaetal infection in challenged mice and engorged ticks was verified by xenodiagnosis and indirect immunofluorescent antibody assay, respectively. Although tick-transmitted spirochaetal infection could be aborted by anti-OspA antibodies and hyperimmune antiserum, nearly all immunised mice challenged with infected ticks that had previous 36-h attachment became infected. More than 72% of the nymphal ticks used in this challenge retained their B. burgdorferi infection after engorgement on mice immunised with anti-spirochaete antibodies, and their subsequent infectivity to mice remained effective. It is concluded that a higher efficiency of transmission by partially fed infected nymphs and a lower efficacy of passive immunisation against infection result from an effect of previous feeding of infected ticks that activates antigenic change and enables the spirochaetes to circumvent OspA-based humoral immunity.

Animals↗
PubMed1998

Effect of procainamide on ultrastructure of blood platelet in rabbits.

AIM: To study the effect of procainamide (PA) on the ultrastructure of blood platelets. METHODS: Arachidonic acid was added to PA-treated platelet-rich plasma to induce platelet aggregation. The 50-nm sections were examined with a transmission electron microscope. RESULTS: PA 8.5-136 mumol.L-1 markedly inhibited changes of pseudopods, alpha-granules, dense granules, glycogens, open canalicular system, and dense tubular system. CONCLUSION: PA markedly inhibited the changes of ultrastructure of blood platelet and releasing response.

Animals↗
PubMed1997

Anionic phospholipids modulate peptide insertion into membranes.

While the insertion of a hydrophobic peptide or membrane protein segment into the bilayer can be spontaneous and driven mainly by the hydrophobic effect, anionic lipids, which comprise ca. 20% of biological membranes, provide a source of electrostatic attractions for binding of proteins/peptides into membranes. To unravel the interplay of hydrophobicity and electrostatics in the binding of peptides into membranes, we designed peptides de novo which possess the typical sequence Lys-Lys-Ala-Ala-Ala-X-Ala-Ala-Ala-Ala-Ala-X-Ala-Ala-Trp-Ala-Ala-X-Ala-Al a-Ala-Lys-Lys-Lys-Lys-amide, where X residues correspond to "guest" residues which encompass a range of hydrophobicity (Leu, Ile, Gly, and Ser). Circular dichroism spectra demonstrated that peptides were partially (40-90%) random in aqueous buffer but were promoted to form 100% alpha-helical structures by anionic lipid micelles. In neutral lipid micelles, only the relatively hydrophobic peptides (X = L and I) spontaneously adopted the alpha-helical conformation, but when 25% of negatively charged lipids were mixed in to mimic the content of anionic lipids in biomembranes, the less hydrophobic (X = S and G) peptides then formed alpha-helical conformations. Consistent with these findings, fluorescence quenching by the aqueous-phase quencher iodide indicated that in anionic (dimyristoylphosphatidylglycerol) vesicles, the peptide Trp residue was buried in the lipid vesicle hydrophobic core, while in neutral (dimyristoylphosphatidylcholine) vesicles, only hydrophobic (X = L and I) peptides were shielded from the aqueous solution. Trp emission spectra of peptides in the presence of phospholipids doxyl-labeled at the 5-, 7-, 10-, 12-, and 16-fatty acid positions implied not only a transbilayer orientation for inserted peptides but also that mixed peptide populations (transbilayer + surface-associated) may arise. Overall results suggest that for hydrophobic peptides with segmental threshold hydrophobicity below that which promotes spontaneous membrane insertion, primary electrostatic attractions provided by anionic phospholipids become essential for peptide binding and insertion to membranes.

Amino Acid Sequence↗
PubMed1997

Human babesiosis in Taiwan: asymptomatic infection with a Babesia microti-like organism in a Taiwanese woman.

An asymptomatic Babesia infection was confirmed by laboratory diagnoses. The intraerythrocytic protozoan (designed TW1) isolated from a 51-year-old Taiwanese woman appeared to be morphologically consistent with small-form piroplasm, and measurements indicated that it had a body size of 1.5 to 2.5 microm in diameter. The typical features of ring, binary, and tetrad forms were observed in Giemsa-stained thin blood smears. A persistent and low-grade parasitemia was established after hamster inoculation. Indirect immunofluorescent-antibody reactivities indicate that this strain (TW1) of Babesia was serologically related to, but not identical to, the Babesia species (B. microti) that infects rodents. Antibody titers in the patient's sera combined with the clinical symptoms suggested that the present case was a chronic and subclinical babesial infection. A neighborhood human serologic survey indicated that the infection may have been acquired accidentally from an infected rodent and localized within the same family. Indeed, rodents from areas around the neighborhood were trapped, and a high prevalence (83%) of babesial infection was observed. The possible vector responsible for the transmission remains to be identified.

Animals↗