Search PubMed⌕ Search

Biomedical subjects

F Liu

Publications and source records attributed to F Liu.

At least 253 records · Page 14Linked to original sources
PubMed2000

Detection of PACH1, a nuclear factor implicated in the transcriptional regulation of meiotic and early haploid stages of spermatogenesis.

Spermatogenesis occurs in a series of well-defined stages and serves as an excellent model for lineage-specific cell development. Yet, little is known regarding the transcriptional mechanisms responsible for cell- and stage-dependent gene regulation in the male germ line. The rat and mouse proenkephalin genes are expressed from an alternative, spermatogenic cell-specific promoter specifically in meiotically-active pachytene spermatocytes and early post-meiotic spermatids. This promoter thus serves as an excellent model for defining transcriptional regulators involved in germ line-specific gene expression in meiotic cells. Previous transgenic studies identified a proximal, 51 bp 5'-flanking sequence containing two direct repeat elements that are absolutely required for in vivo proenkephalin promoter activity in spermatocytes and spermatids. Here, footprinting analyses were used to further delineate the specific interactions of a spermatogenic cell nuclear factor with the repeat elements within the proximal promoter region. This repeat-binding factor was also shown to be developmentally upregulated specifically in pachytene spermatocytes. Using Southwestern analysis, we have identified a unique nuclear protein enriched in pachytene spermatocytes that specifically recognizes the repeat elements within the proximal 5'-flanking sequence. We propose that this DNA binding factor, termed PACH1, is a key transcriptional regulator of the proenkephalin and potentially other gene promoters, uniquely expressed during meiosis in the male germ line.

Animals↗
PubMed2000

Sex differences in spatial cognition, computational fluency, and arithmetical reasoning.

Alternative explanations for the male advantage in arithmetical reasoning, as measured by the ability to solve complex word problems, include a male advantage in spatial cognition and a male advantage in computational fluency. The current study was designed to test these competing hypotheses. To this end, 113 male and 123 female undergraduates were administered arithmetical computations and arithmetical reasoning tests, along with an IQ test and a test of spatial cognition. There was no sex difference on the IQ test, but males showed significantly higher mean scores on the arithmetical computations, arithmetical reasoning, and spatial cognition measures. A series of structural equation models indicated that individual differences in arithmetical reasoning were related to individual differences in IQ, spatial abilities, and computational fluency. Moreover, the results suggested that the male advantage in arithmetical reasoning is mediated by the male advantages in both computational fluency and spatial cognition.

Adolescent↗
PubMed2000

Effects of L-THP on Ca2+ overload of cultured rat cardiomyocytes during hypoxia and reoxygenation.

The effects of L-tetrahydropalmatine (L-THP) on the cultured rat cardiomyocytes during hypoxia and reoxygenation and the mechanism of L-THP treating reperfusion-arrythmias were studied. The concentration of intracellular free calcium ([Ca2+]i) of single cultured ventricular myocyte was determined by using EPC-9 light-electricity measurement system. It was found that L-THP (100 mumol/L) could reduce the [Ca2+]i augmentation in single cultured ventricular myocyte during hypoxia and reoxygenation. Verapamil (10 mumol/L) had the similar effect. It was concluded that L-THP could inhibit the Ca2+ overload of cultured rat cardiomyocytes during hypoxia and reoxygenation.

Animals↗
PubMed2000

Expression of platelet-derived endothelial cell growth factor and vascular endothelial growth factor in hepatocellular carcinoma and portal vein tumor thrombus.

PURPOSE: Both platelet-derived endothelial cell growth factor (PD-ECGF) and vascular endothelial growth factor (VEGF) are known to promote the development of new blood vessels, which are fundamental to tumor growth and metastasis. We aimed at evaluating the gene expression of PD-ECGF and VEGF in hepatocellular carcinoma (HCC) and portal vein tumor thrombus (PVTT). PATIENTS AND METHODS: Surgical specimens (28 HCC, 28 nontumorous liver tissues and 18 PVTT) were studied by Northern blot analysis. The levels of PD-ECGF mRNA and VEGF mRNA expression were measured by densitometric scanning of the autoradiographs, and they were normalized to the level of expression of an internal control (glyceraldehydephosphate dehydrogenase) mRNA. RESULTS: The expression rates of PD-ECGF mRNA in PVTT, HCC and nontumorous liver tissues were 77.8% (14/18), 67.9% (19/28) and 35.7% (10/28), being 88.9% (16/18), 75.0% (21/28) and 17.9% (5/28) respectively for VEGF mRNA. The expressions of PD-ECGF mRNA and VEGF mRNA were higher in HCC with PVTT than when PVTT was absent (P < 0.05). The PVTT was more often seen in patients with positive expression of both PD-ECGF mRNA and VEGF mRNA in HCC than in patients who were positive for only one of these factors or negative for both (P < 0.05). CONCLUSION: Both PD-ECGF and VEGF correlated well with the formation of PVTT of HCC.

Adult↗
PubMed2000

Effect of chronic renal failure and growth hormone therapy on the insulin-like growth factors and their binding proteins.

Children with chronic-renal failure (CRF) are often growth retarded, and abnormalities of the growth hormone (GH)/insulin-like growth factor (IGF) axis in CRF may contribute to this poor growth. Despite normal IGF levels in CRF serum, IGF bioactivity is low due to excess IGF-binding proteins (IGFBPs) in the 35-kDa serum fractions. Levels of IGFBP-1, -2, -4 and -6, and a 29-kDa IGFBP-3 fragment, are high in CRF serum, and levels of intact IGFBP- 1 and -2 correlate negatively with height. IGFBP-1 levels may be high due to insulin resistance, suggesting that the FKHR family of transcription factors may play a role in the overexpression of IGFBP-1, and other growth inhibitors, in CRF. GH-treated CRF children show catch-up growth that correlates positively with a rise in each component of the 150-kDa serum ternary complex (IGF-I or -II/IGFBP-3 or -5/acid-labile subunit); IGFBP-1, -2 and -6 levels do not rise, but serum IGF bioactivity does. Thus, GH increases levels of IGFs and ternary complexes in CRF serum. It is likely that increased IGFs contribute to catch-up growth by overcoming the inhibitory effects of excess IGFBPs present in the CRF milieu.

Animals↗
PubMed2000

Antioxidative and free radical scavenging activities of pineal indoles.

The antioxidant action, free radical scavenging activity and pro-oxidant effect of pineal indoles were studied. Serotonin, 5-hydroxytryptophol, 5-methoxytryptophol and 5-methoxytryptamine potently inhibited lipid peroxidation in rat brain, liver and kidney homogenates and hemolysis of rat erythrocytes. 5-Methoxyindole-3-acetic acid and 5-hydroxyindole-3-acetic acid potently suppressed superoxide radical formation. 5-Hydroxytryptophol and 5-hydroxyindole-3-acetic acid inhibited hydroxyl radical generation. Serotonin, 5-hydroxytryptophol and 5-hydroxyindole-3-acetic acid exhibited a pro-oxidant action in the bleomycin-Fe system. This study demonstrated that 5-methoxytryptamine, among the various pineal indoles tested, exhibited the most potent antioxidant action and was devoid of pro-oxidant effect. Serotonin, 5-hydroxytryptophol and 5-methoxytryptophol also had high antioxidative activity. By comparison melatonin had a lower antioxidant potency.

Animals↗
PubMed2000

Dipeptide seryl-histidine and related oligopeptides cleave DNA, protein, and a carboxyl ester.

The amino acids histidine (His) and serine (Ser), or amino acids similar to Ser, function together as key catalytic amino acids in the active sites of such diverse enzymes as the serine- and thiol-proteases, lipases, and esterases. Ser and His are also conserved in the intein-extein junctions of the phylogenetically widespread self-splicing proteins and at the N- and C-termini of the homing endonucleases spliced from them. Here we show that the dipeptide seryl-histidine (Ser-His) and related oligopeptides can themselves cleave DNA, protein, and the ester p-nitrophenyl acetate (p-NPA) over wide ranges of pH and temperature. Denaturing polyacrylamide gel electrophoresis (PAGE) of 5'-end labeled DNA samples incubated with Ser-His reveals a pattern of two bands per nucleotide position, consistent with the generation of both 3'-hydroxyl and 3'-phosphate DNA cleavage fragments, as would be expected of phosphodiester hydrolysis by Ser-His. To the best of our knowledge, Ser-His is the shortest peptide ever reported to show cleavage activity with multiple categories of natural substrates. The amenability of the dipeptide to variation through addition of amino acid residues, either internally or to the C-terminus while retaining its multiple cleavage activities, combined with its reactivity over wide ranges of pH and temperature, demonstrates the evolutionary capacity of the Ser/His dyad and evokes many questions about possible roles it may have played in molecular evolution and its potential role as a core for selection of oligopeptides with enhanced cleavage activities and target specificity.

Amino Acid Sequence↗
PubMed2000

Atomic force microscopy of parallel DNA branched junction arrays.

BACKGROUND: The four arms of the Holliday junction are known to stack in pairs forming two helical domains whose orientations are antiparallel, but twisted positively by about 60 degrees, based on electrophoretic, FRET and AFM measurements. Recent gel retardation studies suggest that a bowtie junction (containing 5',5' and 3',3' linkages in its crossover strands) may adopt a parallel conformation. RESULTS: An AFM study of two-dimensional arrays produced by parallelograms of bowtie junctions shows that the angle between helical domains is in the range of -68+/-2 degrees. We demonstrate by AFM that the domains are parallel by constructing V-shaped structures whose arms are separated by approximately 68 degrees and approximately 112 degrees. CONCLUSIONS: The arms of the bowtie junction are parallel rather than antiparallel. The parallel or antiparallel nature of the junction apparently is determined by the local structure of the junction, but the sign of the angle appears to be a consequence of interarm electrostatic interactions.

DNA↗
PubMed2000

Ribonuclease, cell-free translation-inhibitory and superoxide radical scavenging activities of the iron-binding protein lactoferrin from bovine milk.

The purpose of this study was to characterize the ribonuclease (RNase) and cell-free translation-inhibitory activities of lactoferrin isolated from bovine milk. It was found that bovine lactoferrin exhibited ribonucleolytic activity toward yeast transfer RNA in a dose-dependent manner. The pH optimum for this RNase activity was in the vicinity of 7.5. Lactoferrin exerted RNase activity on poly C with an activity of 2.15 U/mg. No activity was detected toward poly A, poly G, and poly U. The milk protein inhibited cell-free translation in rabbit reticulocyte lysate with an IC50 of 9.6 microM. The protein was devoid of N-glycosidase activity characteristic of ribosome inactivating proteins which also possess RNase and cell-free translation-inhibitory activities. It inhibited superoxide radical formation.

Animals↗
PubMed2000

In vitro selection of novel RNA ligands that bind human cytomegalovirus and block viral infection.

Ribonuclease-resistant RNA molecules that bind to infectious human cytomegalovirus (HCMV) were isolated in vitro from a pool of randomized sequences after 16 cycles of selection and amplification. The two ligands (L13 and L19) characterized exhibited high HCMV-binding affinity in vitro and effectively inhibited viral infection in tissue culture. Their antiviral activity was also specific as they only reacted with two different strains of HCMV but not with the related herpes simplex virus 1 and human cells. These two ligands appeared to function as antivirals by blocking viral entry. Ultraviolet (UV) crosslinking studies suggested that L13 and L19 bind to HCMV essential glycoproteins B and H, respectively. Thus, RNA ligands that bind to different surface antigens of HCMV can be simultaneously isolated by the selection procedure. Our study demonstrates the feasibility of using these RNA ligands as a research tool to identify viral proteins required for infectivity and as an antiviral agent to block viral infection.

Antiviral Agents↗
PubMed2000

Regulation of phospholipase D from human hepatocarcinoma cell line by purine nucleotides and protein kinase A.

The regulation of phosphatidylcholine-specific phospholipase D by purine nucleotides and protein kinase A were studied in vitro using an enzyme preparation partially purified from the membranous fraction of 7721 hepatocarcinoma cells. It was found that the enzyme activity was elevated by low concentrations of some purine nucleotides, but the activating effects were decreased when the concentrations of the nucleotides were higher. The optimal concentrations of GTP, GTPgamma[S], GDP and ATP for maximal activation were 0.1 mM, 5 microM, 1 mM and 1 mM respectively. The activation caused by 1 mM ADP was lower. The enzyme was not activated by 1 mM AMP, but significant activation was observed by the addition of 1 mM cAMP. The latter was mediated by protein kinase A, as a specific inhibitor of protein kinase A abolished the activation. There were synergic effects between ATP and GTP, ATP and PIP2, but not between ATP and GTPgamma[S], or PIP2 and GTPgamma[S]. The activating effects of GTP and ATP were abolished by neomycin, a PIP2 scavenger. These results suggest that phospholipase D is regulated by GTP-binding protein and the presence of PIP2 is required for the activation induced by GTP. Protein kinase A may be another protein kinase in addition to protein kinase C and protein tyrosine kinase which regulate the activity of phospholipase D, when the intracellular concentration of cAMP is increased.

Adenine Nucleotides↗
PubMed2000

Inactivation of wild-type BCR/ABL tyrosine kinase in hematopoietic cells by mild hyperthermia.

Temperature-sensitive mutants of BCR/ABL tyrosine kinase have been extensively used to study the mechanisms of cell transformation and signal transduction. However, little is known about the effect of temperature on the activity of wild-type BCR/ABL gene product. In this study, we demonstrate that in vivo tyrosine kinase activity of p210, p190 BCR/ABL and v-abl are temperature-sensitive when expressed in hematopoietic cells and decline when temperature is raised 2 degrees C above normal range. In vitro tyrosine kinase activities of purified recombinant Abl and immunoprecipitated p210 BCR/ABL were also sensitive to increased temperature. Tyrosine phosphorylation of cellular proteins was markedly reduced in BCR/ABL transformed cells after 16 h at 39 degrees C, whereas the expression of BCR/ABL was unchanged. Temperature-induced downregulation of BCR/ABL kinase activity was reversible when cells were shifted back to 37 degrees C. The downregulation of Abl tyrosine kinase activity was not influenced by mutation or deletion of SH2 or SH3 domains or mutation of the GRB2 binding site. No increase in functional activity or expression of protein-tyrosine phosphatases, PTP-1B, SH-PTP1 or SH-PTP2 was detected in cells grown at 39 degrees C. Temperature-induced downregulation in tyrosine kinase activity correlated with decline in phosphotyrosine-associated PI 3-kinase whereas there was no change in growth factor independence of transformed hematopoietic cells. In conclusion, Abl tyrosine kinase has intrinsic sensitivity to temperature and BCR/ABL expressed in hematopoietic cells is downregulated by increasing temperature 2 degrees C. These observations provide a unique opportunity to identify cellular factor(s) which regulate BCR/ABL kinase in vivo and suggests possible novel treatment of CML by a mild hyperthermia.

3T3 Cells↗
PubMed2000

Differential pulse voltammetric indirect determination of aluminium in drinking waters, blood, urine, hair, and medicament samples using L-dopa under alkaline conditions.

The differential pulse voltammetric (DPV) indirect determination of aluminium using L-dopa under alkaline conditions on a glassy carbon working electrode was studied. The proposed method relies on the linear decrease of the DPV anodic peak current of L-dopa with increase in the concentration of aluminium added. Under the optimum experimental conditions (pH 8.5, 0.08 M NH4Cl-NH3.H2O buffer solution, and 4 x 10(-4) M L-dopa), the linear range is 2-18 x 10(-7) M AlIII. The detection limit is 7.6 x 10(-8) M and the relative standard deviation for 8 x 10(-7) M AlIII is 3.5% (n = 8). A number of foreign species were examined as potential interferents. The method was applied to the determination of aluminium in drinking waters, synthetic renal dialysate, sodium chloride injection, sucrafate, hydrothorax, blood, urine and hair samples. The physiological significance is discussed.

Aluminum↗
PubMed2000

Naturally occurring polyphenolic antioxidants modulate IgE-mediated mast cell activation.

Reactive oxygen species (ROS) are known to modulate activities of a host of kinases, phosphatases and transcription factors. Rutin and chlorogenic acid (CGA) are the major polyphenolic antioxidants present in the small molecular fraction of smokeless tobacco leaf extracts, as ascertained by reverse-phase high-pressure liquid chromatography (HPLC) and mass spectrometry. Levels of intracellular ROS in resting versus antigen-immunoglobulin E (IgE)-challenged murine mast cells were measured at 510 nm by fluorescence-activated cell sorting (FACS) using carboxy-dichlorofluorescein (DCFH-DA). Enhanced ROS production was observed in IgE-sensitized mast cells following antigenic challenge. Rutin and CGA reduced ROS levels in antigen-IgE-activated mast cells. Concomitantly, they also profoundly inhibited histamine release by these activated mast cells. In contrast, rutin and CGA augmented the inducible cytokine messages, i.e. interleukin (IL)-10, IL-13, interferon-gamma (IFN-gamma), IL-6 and tumour necrosis factor-alpha (TNF-alpha) in IgE-sensitized mast cells following antigen challenge. This study indicates that tobacco polyphenolic antioxidants that quench intracellular ROS, differentially affect two effector functions of antigen-IgE-activated mast cells. This model system may be employed to determine the molecular target of polyphenols. The potential role of these polyphenolic antioxidants on IgE-mediated allergy in vivo depends on a balance of their differential effects on mast cell activation.

Animals↗
PubMed2000

Quantitative abductor pollicis brevis strength testing: reliability and normative values.

We conducted this study to establish reliability and normative values for abductor pollicis brevis strength. A portable microprocessor-controlled hand-held device was used for testing. Twelve healthy subjects were used for intrarater and interrater reliability testing. Intraclass correlation coefficients were 0.92 for intrarater testing and 0.89 for interrater reliability. Normative values for abductor pollicis brevis strength are presented by gender and age from the test results of 297 volunteers (121 men and 176 women; age range, 20-59 years) with at least 30 subjects in each subgroup. Abductor pollicis brevis strength was significantly greater in the men than in the women in all age groups. No significant differences were found related to age, side, or dominance. The results suggest that quantitative muscle testing produces consistent values for abductor pollicis brevis strength that remain fairly constant in patients aged 20 to 59 years.

Adult↗
PubMed2000

The TRAPP complex is a nucleotide exchanger for Ypt1 and Ypt31/32.

In yeast, the Ypt1 GTPase is required for ER-to-cis-Golgi and cis-to-medial-Golgi protein transport, while Ypt31/32 are a functional pair of GTPases essential for exit from the trans-Golgi. We have previously identified a Ypt1 guanine nucleotide exchange factor (GEF) activity and characterized it as a large membrane-associated protein complex that localizes to the Golgi and can be extracted from the membrane by salt, but not by detergent. TRAPP is a large protein complex that is required for ER-to-Golgi transport and that has properties similar to those of Ypt1 GEF. Here we show that TRAPP has Ypt1 GEF activity. GST-tagged Bet3p or Bet5p, two of the TRAPP subunits, were expressed in yeast cells and were precipitated by glutathione-agarose (GA) beads. The resulting precipitates can stimulate both GDP release and GTP uptake by Ypt1p. The majority of the Ypt1 GEF activity associated with the GST-Bet3p precipitate has an apparent molecular weight of > 670 kDa, indicating that the GEF activity resides in the TRAPP complex. Surprisingly, TRAPP can also stimulate nucleotide exchange on the Ypt31/32 GTPases, but not on Sec4p, a Ypt-family GTPase required for the last step of the exocytic pathway. Like the previously characterized Ypt1 GEF, the TRAPP Ypt1-GEF activity can be inhibited by the nucleotide-free Ypt1-D124N mutant protein. This mutant protein also inhibits the Ypt32 GEF activity of TRAPP. Coprecipitation and overexpression studies suggest that TRAPP can act as a GEF for Ypt1 and Ypt31/32 in vivo. These data suggest the exciting possibility that a GEF complex common to Ypt1 and Ypt31/32 might coordinate the function of these GTPases in entry into and exit from the Golgi.

Biological Transport↗