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Y X Liu

Publications and source records attributed to Y X Liu.

At least 91 records · Page 5Linked to original sources
PubMed1991

Tissue-specific and time-coordinated hormone regulation of plasminogen-activator-inhibitor type I and tissue-type plasminogen activator in the rat ovary during gonadotropin-induced ovulation.

The plasminogen-activator system provides proteolytic activity in many biological processes. The regulation of plasminogen activation may occur at many levels including the synthesis and secretion of plasminogen activators (PA) and the specific inhibition of PA activity by inhibitors. PA-inhibitor type-1 (PAI-1) is an efficient inhibitor of tissue-type PA (tPA) and urokinase-type PA (uPA) that may therefore be instrumental for the control of plasminogen activation. To investigate if coordinated regulation of PA and PA inhibitors take place in vivo in response to physiological signals, we have examined the regulation of PAI-1 and tPA in the ovary during gonadotropin-induced ovulation. We found that PAI-1, as well as tPA activity and mRNA levels, were coordinately regulated by gonadotropins in a time-dependent and cell-specific manner, such that a surge of PA-activity was obtained just prior to ovulation. Both theca-interstitial and granulosa cells synthesized PAI-1, but their maximal PAI-1 expression occurred at different times during the periovulatory period, ensuring inhibition of proteolytic activity in ovarian extra cellular compartments both before and after ovulation. The coordinated regulation of tPA and PAI-1 in the ovary may fine-tune the peak of PA activity which may be important for the regulation of the ovulatory process.

Animals↗
PubMed1991

Expression and characterization of the preS1 peptide of hepatitis B surface antigen in Escherichia coli.

The infectious particles of hepatitis B virus (HBV) contain 3 related surface antigens, i.e., small, medium, and large, all of which are encoded by one large open reading frame with multiple initiation codons. The large surface antigen (L-Ag) contains preS1, preS2, and S regions while both the middle and small surface antigens lack preS1. Several lines of evidence suggested that the preS1 region is involved in the binding of HBV to human hepatocytes as shown by its binding to HepG2 cells and isolated human hepatocyte membranes. To obtain large quantity of preS1 peptide, an expression vector was constructed containing a lac promoter, the 5' half of the beta-galactosidase gene, the Factor Xa tetrapeptide recognition sequence, and the coding region of preS1 plus preS2. This recombinant plasmid constitutively produced high concentration of a fusion protein in inclusion bodies in Escherichia coli. When the fusion protein was treated with Factor Xa, a peptide consisting of the N-terminal 91 amino acids of the preS1 region was released. This preS1 fragment purified by anion exchange chromatography was able to bind specifically to the isolated plasma membranes from human liver. Hence, this recombinant preS1 peptide can be used to identify and isolate hepatocyte receptors for HBV.

Base Sequence↗
PubMed1991

[Changes of ovarian plasminogen activator and inhibitor during gonadotropin-induced ovulation in rhesus monkeys].

Changes of plasminogen activator (PA) and its inhibitor (PAI-1) activity and antigen have been investigated during PMSG/hCG induced ovulation in rhesus monkeys. It has been demonstrated that the ovarian tissue type PA (tPA) activity, which reaches maximum prior to ovulation and declines thereafter, is closely related to follicular rupture; significant increases in urokinase type PA (uPA) only occurs in granulosa cells after ovulation. Since the secretory activity of ovarian PAI-1 reaches its peak level 12-24 h earlier than tPA the rapid decrease in PAI-1 activity in the approach of ovulation is correlated with the elevation of tPA activity. It is, therefore, suggested that a counterbalance of tPA and PAI-1 activity within the ovary may play an important role in the ovulation mechanism, whereas uPA may be involved in the regulation of corpus luteum formation.

Animals↗
PubMed1991

A comparative study on involvement of tPA activity in ovulation induced by hCG and GnRH agonist in hypophysectomized rats.

A GnRH agonist (5-50 micrograms) is capable of inducing ovulation in PMSG-primed hypophysectomized immature rats, as is the case in hCG-induced ovulation, but 2-4 h earlier than hCG. GnRH-induced ovulation is effectively blocked by the concomitant administration of the GnRH-antagonist which failed to interfere with hCG-induced ovulation, indicating that GnRH and its agonists do not share a receptor with LH/hCG. Like hCG, GnRH is also capable of inducing tissue type (tPA), but not urokinase type (uPA) PA. The plasminogen activator activity in ovarian homogenates and the granulosa and theca-interstitial cells increase in a time-dependent manner, reaching maximum levels just prior to ovulation. Similar to hCG, GnRH also increases tPA activity in cumulus-oocyte complexes in a time-dependent fashion.

Animals↗
PubMed1991

Paradoxical effect of a GnRH agonist on steroidogenesis in cultured monkey granulosa cells.

In this study we demonstrate: (i) The GnRH agonist exerts a direct dose-dependent stimulative effect on the aromatase activity and progesterone production in cultured monkey granulosa cells; (ii) the stimulative effect on steroidogenesis can be completely blocked by concomitant treatment with a GnRH antagonist, suggesting that the actions of GnRH are mediated through stringent stereospecific recognition sites; (iii) in addition to the stimulative effect, the GnRH agonist in the presence of gonadotropins also exerts an inhibitory effect, even though the peptide by itself is more effective in the stimulation of steroidogenesis, and the stimulation of gonadotropin on steroidogenesis could be gradually restored by decreasing the concentration of the GnRH agonist in the culture; and (iv) paradoxical effect can also be observed in the presence of cAMP-inducing agents, suggesting that the inhibitory action of the peptide on gonadotropin-induced steroidogenesis is localized at a step distal to the stringent recognition sites.

Animals↗
PubMed1990

Effects of ethanol and inhibitors on the binding and metabolism of acetaminophen and N-acetyl-p-benzoquinone imine by hepatic microsomes from control and ethanol-treated rats.

Acetaminophen is metabolized by cytochrome P450 to N-acetyl-p-benzoquinone imine (NABQI). This metabolite reacts with critical cellular macromolecules to give toxicity. The administration of 10% ethanol in the drinking water to 100 g male rats for 6 weeks markedly increases the toxicity of acetaminophen. This increase was associated with a 71% increase in microsomal protein binding of acetaminophen [4.8 pmol/min/mg protein in control microsomes versus 8.2 pmol/min/mg protein in ethanol microsomes (P less than 0.01)] and a 131% increase in aniline hydroxylase [0.52 nmol/min/mg protein in control microsomes versus 1.20 nmol/min/mg protein in ethanol microsomes (P less than 0.001)]. On the other hand, cysteine conjugation of acetaminophen showed an increase of only 12% [2.8 nmol/min/mg protein in control microsomes versus 3.1 nmol/min/mg protein in ethanol microsomes (P less than 0.05)]. Ethylmorphine- and benzphetamine N-demethylases did not increase. In microsomes from both control and ethanol animals, imidazole (1 mM) inhibited the two N-demethylases, aniline hydroxylation and acetaminophen binding by 85-95% but inhibited the cysteine conjugation by only 50%. For control and ethanol animals, both 80% CO/20% O2 and SKF-525A (1 mM) totally inhibited cysteine conjugation but only inhibited the other activities by about 36-60%. KCN (1 mM) had no effect on any of the activities except protein binding (60-67% inhibition). Scavengers of reactive oxygen [mannitol (1 mM), dimethyl sulfoxide (1 mM), superoxide dismutase (15 micrograms/mL) and catalase (65 micrograms/mL)] had no effect on any of the reactions. Of all these treatments only CO/O2 decreased the protein binding and cysteine conjugation of NABQI in the presence of either NADP+ or NADPH. The data from the inhibitor studies and the effect of ethanol on acetaminophen and NABQI metabolism would suggest that protein binding and cysteine conjugation are catalyzed by different isozymes of cytochrome P450. Finally, the current results indicate that the increased toxicity of acetaminophen observed with ethanol more closely parallels the increase in protein binding activity rather than cysteine conjugation.

Acetaminophen↗
PubMed1990

Glia maturation factor beta regulates the growth of N18 neuroblastoma cells.

Glia maturation factor beta (GMF-beta) is a 17-kDa growth regulating protein isolated from the brain. The effect of bovine GMF-beta on neurons was tested on the neuroblastoma line N18 and the pheochromocytoma line PC12. GMF-beta inhibited the proliferation of N18 cells and promoted their neurite outgrowth, with an increase in neurofilament protein, but had no effect on PC12 cells. This was in contrast to nerve growth factor (NGF) which regulated PC12 but not N18. Acidic fibroblast growth factor (FGF), on the other hand, had a weak effect on PC12 but none on N18. Antisera against GMF-beta and NGF neutralized the biological activity of the corresponding growth factors but showed no cross-neutralization. Fluorescence visualization revealed the binding of GMF-beta to N18 cells but not to PC12 cells; the opposite was true with NGF.

Adrenal Gland Neoplasms↗
PubMed1990

Interaction of leukotriene C4 and Chinese hamster lung fibroblasts (V79A03 cells). 1. Characterization of binding.

A novel, specific, and potent biological action of leukotriene C4 (LTC4) was demonstrated in the Chinese hamster lung fibroblast cell line V79A03 (V79 cells), namely the confirment of protection against subsequent gamma-irradiation. Consequently, studies were conducted to determine whether LTC4-conferred radioprotection could be attributed to a receptor-mediated phenomenon. Specific binding sites for leukotriene C4 (LTC4) were identified and characterized using intact V79 cells incubated at 4 degrees C in the presence of serine-borate, during which time conversion of LTC4 to LTD4 or LTE4 was undetectable. Binding was maximal in a broad region between pH 6.2 and 8.8. Ca2+, Mg2+, and Na+ were not required for binding, and binding was not altered by GTP, ATP, or cAMP, by leukotrienes B4, D4, or E4, or by the leukotriene end point antagonists LY 171883, FPL 55712, or Revlon 5901-5. Scatchard analyses and kinetic experiments indicated the presence of high-affinity [Kd = 2.5 +/- 0.63 nM, approximately 9.9 x 10(5) sites/cell] and low-affinity [Kd = 350 +/- 211 nM, approximately 2.7 x 10(6) sites/cell] binding sites. The observed binding characteristics of LTC4 to V79 cells are consistent with a receptor-mediated phenomenon. In a companion communication which follows this report, we report the subcellular distribution of LTC4 binding to V79 cells and demonstrate that this binding is unlikely to be attributed principally to interaction with glutathione-S-transferase.

Animals↗
PubMed1990

Interaction of leukotriene C4 and Chinese hamster lung fibroblasts (V79A03 cells). 2. Subcellular distribution of binding and unlikely role of glutathione-S-transferase.

It was reported previously that radiation-induced cytotoxicity in V79A03 (V79) cells was attenuated by pretreatment of cells with leukotriene C4 (LTC4), leading us to determine that V79 cells possessed specific binding sites, with characteristics of receptors, for LTC4 (see the preceding, companion communication). Additional studies were conducted to determine the subcellular distribution and the chemical nature of the LTC4 binding site in V79 cells. Trypsin treatment of cells before LTC4 binding assays resulted in a 74% reduction in high-affinity binding. In tests to examine the subcellular location of LTC4 binding, plasma membrane and nuclear fractions were obtained from V79 cells. In contrast to Scatchard analyses of LTC4 binding to intact cells which were curvilinear, Scatchard analyses of nuclear and plasma membrane fractions were linear, indicative of the presence in these cellular substituents of low and high-affinity binding, respectively. To examine the nature of the high-affinity LTC4 binding sites, intact V79 cells were photolyzed with [3H]-LTC4 rendered photoactive by preincubation with N-hydroxysuccinimidyl-4-azidobenzoate. The cell-bound radioactivity migrated during sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with an apparent molecular weight of approximately 40 kdal. Five different commercial preparations of glutathione-S-transferase (GST), which has been implicated as a source of LTC4 "specific binding" in other cells, migrated in the same SDS-PAGE system with an apparent molecular weight of 20-24 kdal. Furthermore, preincubations of V79 cells with three antisera generated against GST had minimal effects upon subsequent LTC4 binding to intact cells. These data, taken together with the data from the preceding companion communication, suggest that the radioprotective effect of LTC4 upon V79 cells may be attributable to a receptor-mediated phenomenon which appears distinct from leukotriene binding to GST.

Animals↗
PubMed1990

Cell-surface expression of glia maturation factor beta in astrocytes.

Glia maturation factor beta (GMF-beta) is a 17-kDa acidic protein isolated from the brain. When added to cultured cells, GMF-beta promotes the phenotypic expression of glia and neurons and inhibits the proliferation of their respective tumors. Although astrocytes produce GMF-beta and store it inside the cells, they do not secrete the protein into the cultured medium. This poses a question as to how GMF-beta mediates intercellular communication. This paper provides an answer by demonstrating the presence of GMF-beta on the surface of astrocytes, using gold-labeled antibody enhanced with silver. It appears that cell-surface GMF-beta acts on the target cells at close range when cells are in direct contact. In contrast to astrocytes, we failed to detect GMF-beta on the surface of C6 glioma cells, although these cells, like astrocytes, possess endogenous intracellular GMF-beta and are also responsive to GMF-beta added to the medium. The lack of cell-surface expression of GMF-beta in C6 cells may reflect a breakdown in intercellular communication in these malignant cells.

Animals↗
PubMed1990

Characterization of pp85, a target of oncogenes and growth factor receptors.

An 85,000-molecular-weight polypeptide (85K polypeptide) has previously been identified as a common substrate for tyrosine phosphorylation upon polyomavirus middle T transformation or upon platelet-derived growth factor stimulation of 3T3 cells. In each case, pp85 has an associated phosphatidylinositol kinase activity. The tissue distribution of pp85 was determined by middle T blotting experiments; the highest levels were found in brain, lung, and spleen tissues. High-resolution examination of 85K by isoelectric focusing demonstrated that there are at least 10 different forms. These were resolved into two families, 85K and 86K; the ratio of the two families changed in different cells. Similar forms were found for pp85 associated with pp60v-src. Individual species within each family differed by phosphorylation. Analysis of pp85 and pp86 by immunoprecipitation with anti-phosphotyrosine antibody showed increasing phosphorylation in response to middle T or pp60v-src transformation. The association of middle T with pp85 and pp60c-src was examined in pulse-chase experiments. Association of middle T with pp60c-src was slow and was accompanied by progressive modification of middle T. pp85 formed a dissociable complex with middle T within 2.5 min.

1-Phosphatidylinositol 4-Kinase↗
PubMed1990

[Heat and ozone resistance of Bacillus spores isolated from laboratory animals].

Heat resistance of free-spores of 78 Bacillus strains isolated from laboratory animals was examined. Spores of 41 out of 78 strains survived for 320 minutes at 70 degrees C, 27 for 160 min, at 100 degrees C, only one for 20 min. at 110 degrees C by autoclaving, and none for 5 min. at 120 degrees C. D-values at 100 degrees C of 9 strains determined were between 5.03 and 30.06 min. Spores of 9 strains from stock cultures were exposed to ozone gas at various conditions. Ozone resistance of spores was closely dependent upon relative humidity. D-values of the spores tested by treatment with 200 ppm ozone at 60% RH were over 200 min., especially over 1,000 min. in 4 strains, indicating that exposure to ozone at a moderate humidity for 6 hours could not sterilize Bacillus spores. At 90% RH, however, treatment with 200 ppm ozone for 6 hr. might be effective for a routine sterilization in laboratory animal facilities.

Animals↗
PubMed1990

Regulation of steroidogenesis of infant and adult rhesus monkey granulosa cells in vitro.

The present studies have demonstrated that infant monkey granulosa cells, like the adult ones, have the potential of responding markedly in vitro to human FSH, cyclic-AMP and forskolin, resulting in the increase of progesterone and estrogen production. Exogenous hCG was also capable of increasing FSH-stimulated progesterone biosynthesis in both infant and adult granulosa cells, but did not stimulate the infant granulosa cells to secrete estrogen. Addition of a synthetic estrogen, diethylstilbestrol, to the culture of monkey granulosa cells enhanced the FSH-stimulated progesterone and estrogen production. The steroidogenesis of monkey granulosa cells was also dramatically stimulated by a gonadotropin-releasing hormone agonist. Monkey granulosa cells, unlike the other animal cells, secrete measurable amount of estrogen in the absence of androgen substrate. The findings reported here are significant in regard to understanding of the mechanism of hormonal regulation of primate ovarian function.

Androgens↗
PubMed1989

Fractionation of immunoglobulins by liquid-liquid partition chromatography in aqueous two-phase systems.

In this paper we show that although immunoglobulins are easily precipitated in solutions containing polyethylene glycol (PEG), especially at pH's where the conformation of the proteins should be close to native, human and rabbit IgG can be solubilized in aqueous dextran/PEG two-phase systems containing glycine and sodium chloride at pH 7.0 and that human IgA and IgM can be solubilized in such systems if the pH is increased to 9.0. Liquid-liquid partition chromatography (LLPC) on Li-ParGel was used to separate immunoglobulins into subfractions. Human IgG, IgM, and IgA all gave three peaks in the system used. These results indicate the possibility of separating different classes of immunoglobulins with this method. Specific IgG antibodies isolated from a rabbit antiserum against human serum proteins gave only two peaks in the LLPC system while the total IgG population gave three, as did human IgG. Thus, partitioning of immunoglobulins seems to be related to antibody activity.

Animals↗
PubMed1989

Overproduction of yeast viruslike particles by strains deficient in a mitochondrial nuclease.

Saccharomyces cerevisiae strains are often host to several types of cytoplasmic double-stranded RNA (dsRNA) genomes, some of which are encapsidated by the L-A dsRNA product, an 86,000-dalton coat protein. Here we present the finding that nuclear recessive mutations in the NUC1 gene, which encodes the major nonspecific nuclease of yeast mitochondria, resulted in at least a 10-fold increase in amounts of the L-A dsRNA and its encoded coat protein. The effect of nuc1 mutations on L-A abundance was completely suppressed in strains that also hosted the killer-toxin-encoding M dsRNA. Both NUC1 and nuc1 strains containing the L-A genome exhibited an increase in coat protein abundance and a concomitant increase in L-A dsRNA when the cells were grown on a nonfermentable carbon source rather than on glucose, an effect independent of the increase in coat protein due to nuc1 mutations or to the absence of M. The increase in L-A expression in nuc1 strains was similar to that observed in strains with mutations in the nuclear gene encoding the most abundant outer mitochondrial membrane protein, porin. nuc1 mutations did not affect the level of porin in the mitochondrial outer membrane. Since the effect of mutations in nuc1 was to alter the copy number of the L-A coat protein genome rather than to change the level of the M toxin genome (as do mak and ski mutations), these mutations define a new class of nuclear genes affecting yeast dsRNA abundance.

Amino Acid Sequence↗
PubMed1989

[Plasminogen activator activity in mouse ovaries during periovulatory period].

Immature mice were injected subcutaneously with 5 IU PMSG for 2 days to stimulate follicle development, which was followed by administration of 5 IU hCG to induce ovulation. The ovaries were removed at various periovulatory stages for preparing ovarian homogenates, granulosa cells and cumulus-oocyte complexes. The activity of plasminogen activator in the samples, separated by SDS-PAGE, were determined by fibrin-overlay technique. The results show that 15% of the gonadotropin-treated animals were ovulated 8h after hCG administration, about 6-8h earlier than that occurred in rat. Moreover, both tPA, and uPA activity were stimulated following PMSG treatment in ovarian homogenates and granulosa cells. Subsequent hCG injection further increased the two types of PA activity in a time-dependent manner, reaching maximum 4-8h after hCG treatment, and declined following ovulation. Greater uPA activity (70%) in the cultured mouse granulosa cells was found. It is, therefore, suggested that both tPA and uPA may be involved in the regulation of ovulation in mouse. The cumulus-oocyte complexes contained mainly tPA, which activity showed a time-dependent increase and reached a maximum between 12-24h after hCG treatment. Since cumulus-oocyte complexes collected from oviducts post ovulation still retain a considerable amount of tPA, the enzyme in the complexes may also play a role in the process of cumulus dispersion, oocyte transportation and implantation.

Animals↗