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B Liu

Publications and source records attributed to B Liu.

At least 649 records · Page 36Linked to original sources
PubMed1994

Transactivation of the human multidrug resistance (MDR1) gene promoter by p53 mutants.

Multidrug resistance in human cancer is associated with overexpression of the MDR1 gene, which encodes a plasma membrane energy-dependent efflux pump termed P-glycoprotein (or the multidrug transporter), which confers cross-resistance to multiple hydrophobic natural product cytotoxic drugs. We have previously shown in cotransfection experiments that activity of the human MDR1 gene promoter is modulated by Ras and p53, suggesting that expression of the MDR1 gene may be associated with the activation of oncogenes and/or functional loss of tumor suppressor genes during oncogenesis. To further characterize the effects of p53 on the MDR1 promoter, we have shown in the current study that the region of the promoter that is required for transactivation by p53 mutants overlaps with the region that is essential for basal promoter activity. In addition, we also have shown that several different p53 mutants transactivate the MDR1 promoter in several different cell types, including embryo fibroblasts derived from the p53-deficient (p53-l-) mice generated by gene targeting.

Animals↗
PubMed1994

Inhibition of radiation-enhanced expression of integrin and metastatic potential in B16 melanoma cells by a lipoxygenase inhibitor.

Low-dose gamma radiation stimulates expression of phenotypic characteristics in B16 melanoma cells which regulate metastatic potential. A transient increase in the expression of an integrin receptor (alpha IIb beta 3) was observed after exposure of B16 melanoma cells to 0.25 to 2.0 Gy of gamma radiation. This increased receptor expression resulted in enhanced adhesion of tumor cells to fibronectin in vitro and increased experimentally induced metastasis in vivo. In this report, we determined a role for the 12-lipoxygenase metabolite, 12-HETE, in radiation-enhanced metastasis. A significant increase in biosynthesis of 12-HETE in B16 melanoma cells was detected < 5 min after exposure to 0.5 Gy gamma radiation. We then determined that radiation-enhanced expression of alpha IIb beta 3 integrin and adhesion of B16 melanoma cells to fibronectin in vitro and metastasis in vivo were reduced by treatment of the cells with the lipoxygenase inhibitor NDGA prior to irradiation. These findings suggest that low-dose radiation, at levels comparable to those used in fractionated or hyper-fractionated radiotherapy, increases the metastatic potential of surviving tumor cells via a rapid and transient alteration in lipoxygenase metabolism of arachidonic acid and surface expression of an integrin receptor.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1994

Mouse antibody response following repetitive injections of gamma-irradiated human placenta collagen.

Injectable bovine collagen has been used clinically for years. But both the necessity of repeated injections to maintain corrections and the question of adverse allergic reactions developing from the use of a xenogenic collagen have been an area of serious concern. To overcome these adverse effects, we have developed injectable collagen preparations from human placenta. Gamma irradiation was used for sterilization and crosslinking of the collagen. We observed the mouse immune response to gamma-irradiated human placenta soluble and insoluble collagen following multiple injections. After six injections of these materials, no total IgG level increase was found, nor was antibody specifically directed against human collagen found. Mouse antibody levels were also observed following Zyderm II and Zyplast repetitive injections and following repetitive implantations of coated vicryl and chromic gut. No humoral immune response was found in this heterologous type system.

Animals↗
PubMed1994

Biosynthesis of 12(S)-hydroxyeicosatetraenoic acid by B16 amelanotic melanoma cells is a determinant of their metastatic potential.

BACKGROUND: We have previously demonstrated that the metastatic potential of tumor cells can be increased by treatment with exogenous 12(S)hydroxyeicosatetraenoic acid [12(S)-HETE], a lipoxygenase metabolite of arachidonic acid. However, the biosynthesis of the authentic lipid mediator by tumor cells, and especially the correlation of its biosynthesis to tumor cell metastatic capacity have not been characterized. In addition, a role for other mono HETEs in influencing tumor cell metastatic behavior has been suggested, but conclusive evidence is lacking. In this study, we analyzed the biosynthesis of mono HETEs from arachidonic acid in tumor cells of different metastatic ability and correlated biosynthesis to metastatic potential. EXPERIMENTAL DESIGN: The biosynthesis of mono HETEs by low and high metastatic subpopulations of B16 amelanotic melanoma (B16a) cells was analyzed by high performance liquid chromatography (HPLC). The identity of biosynthetic 12-HETE was confirmed by gas chromatography/mass spectrometry (GC/MS) and its stereochemical structure assigned by chiral phase HPLC. The effect of a lipoxygenase inhibitor on the biosynthesis of mono HETEs and its effect on metastatic behavior was examined. RESULTS: HPLC analysis revealed that low (LM180) and high (HM340) metastatic B16a cells exhibited different profiles and efficiencies for conversion of arachidonic acid to mono HETEs. LM180 cells produced equal quantities of 12-HETE and 5-HETE. In contrast, HM340 cells synthesized predominantly 12-HETE and small amounts of 15-, 11- and 5-HETEs. At equal concentrations of substrate, four times more 12-HETE was synthesized by HM340 cells than by LM180 cells. The identity of biosynthetic 12-HETE was confirmed by gas chromatography/mass spectrometry and chiral phase HPLC demonstrated that it was the S enantiomer. The biosynthesis of 12(S)-HETE, but not other HETEs, was significantly inhibited by a lipoxygenase inhibitor, N-benzyl-N-hydroxy-5-phenylpentanamide. N-benzyl-N-hydroxy-5-phenylpentanamide, in a dose-dependent manner, decreased the adhesion of HM340 cells to murine pulmonary microvessel endothelium in vitro and lung colony formation in vivo. Furthermore, re-introduction of 12(S)-HETE, but not other mono HETEs, to HM340 cells pretreated with N-benzyl-N-hydroxy-5-phenylpentanamide, increased their adhesion to endothelium. CONCLUSIONS: Biosynthesis of 12(S)-HETE by tumor cells is a determinant of their metastatic potential and inhibition of 12(S)-HETE biosynthesis in tumor cells may be a crucial target for intervening in metastasis.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1993

Mutations of a mutS homolog in hereditary nonpolyposis colorectal cancer.

Recent studies have shown that a locus responsible for hereditary nonpolyposis colorectal cancer (HNPCC) is on chromosome 2p and that tumors developing in these patients contain alterations in microsatellite sequences (RER+ phenotype). We have used chromosome microdissection to obtain highly polymorphic markers from chromosome 2p16. These and other markers were ordered in a panel of somatic cell hybrids and used to define a 0.8 Mb interval containing the HNPCC locus. Candidate genes were then mapped, and one was found to lie within the 0.8 Mb interval. We identified this candidate by virtue of its homology to mutS mismatch repair genes. cDNA clones were obtained and the sequence used to detect germline mutations, including those producing termination codons, in HNPCC kindreds. Somatic as well as germline mutations of the gene were identified in RER+ tumor cells. This mutS homolog is therefore likely to be responsible for HNPCC.

Amino Acid Sequence↗
PubMed1993

Post-translational processing of proopiomelanocortin (POMC) in mouse pituitary melanotroph tumors induced by a POMC-simian virus 40 large T antigen transgene.

Mice harboring a transgene composed of proopiomelanocortin (POMC) gene promoter sequences (nucleotides -706 to +64) ligated to the simian virus (SV) 40 early gene encoding large T antigen developed large POMC-expressing pituitary tumors. Histologically the tumors arose from the intermediate lobe, contained nuclear SV40 T antigen and POMC peptides, but did not express other pituitary hormones. POMC processing in the pituitary tumors was indistinguishable from normal mouse intermediate lobe melanotrophs and was characterized by high proportions of acetylated and carboxyl-terminal shortened beta-endorphins, and amino-terminal acetylated alpha-melanocyte-stimulating hormone, and virtually no adrenocorticotropic hormone (ACTH)(1-39), beta-lipotropin, or POMC. The tumors contained abundant levels of mRNA for the prohormone convertase PC2 and undetectable levels of PC1. Normal mouse neurointermediate lobe also has a high ratio of PC2/PC1 expression that is distinct from the relative abundance of PC1 in anterior lobe and AtT-20 corticotroph cells. In contrast, extracts from tumors transplanted subcutaneously in nude mice contained predominantly nonacetylated forms of beta-endorphin(1-31) and -(1-27), very little ACTH(1-39), almost no corticotropin-like intermediate peptide or alpha-melanocyte-stimulating hormone, and higher proportions of intact POMC. Surprisingly, despite the less efficient proteolytic cleavage, a transplanted tumor expressed both PC1 and PC2. These studies are the first biochemical documentation of a melanotroph pituitary tumor in a rodent species and provide a new model for the investigation of pituitary oncogenesis and the molecular basis of tissue-specific prohormone post-translational processing.

Adrenocorticotropic Hormone↗
PubMed1993

The DNA replication fork can pass RNA polymerase without displacing the nascent transcript.

Replication proteins encoded by bacteriophage T4 generate DNA replication forks that can pass a molecule of Escherichia coli RNA polymerase moving in the same direction as the fork in vitro. The RNA polymerase ternary transcription complex remains bound to the DNA and retains a transcription bubble after the fork passes. The by-passed ternary complex can resume faithful RNA synthesis, suggesting that the multisubunit RNA polymerase of E. coli has evolved to retain its transcript after DNA replication, allowing partially completed transcripts to be elongated into full-length RNA molecules.

Bacteriophage T4↗
PubMed1993

Reduced activation of transcriptional factor AP-1 among peripheral blood T cells from elderly humans after PHA stimulation: restorative effect of phorbol diesters.

In the present study, we evaluated if aging influences the activation and characteristics of transcriptional factor AP-1 in human T cells. Using gel mobility shift assays, the activation of AP-1 was quantified in peripheral blood T cells from 11 elderly (mean 74 year) and young (mean 33 year) subjects following stimulation with PHA, PMA, or PHA plus PMA. The results showed that the activation of AP-1 was significantly reduced in PHA-stimulated T cells from the group of elderly subjects when compared to T cells from young subjects (P < 0.05). Even though PHA-stimulated T cells from 8 of the elderly subjects had pronounced impairments in the activation of AP-1, additional signals provided by costimulation with PMA frequently restored AP-1 activation to more normal levels. Other experiments demonstrated that the AP-1 complexes expressed by stimulated T cells of elderly and young subjects exhibited similar properties in gel shift assays with competing unlabeled AP-1 oligonucleotides and with blocking antibodies specific for Fos and Jun. Thus, these data suggest that the activation of AP-1 can be reduced in human T cells during aging and that these reductions may often be related to impairments in signal transduction rather than represent an absolute loss in the ability to express AP-1.

Adult↗
PubMed1993

Gamma-tubulin is associated with a cortical-microtubule-organizing zone in the developing guard cells of Allium cepa L.

A key event in the differentiation of elliptically shaped guard cells such as those in Allium is the formation of a radial array of cortical microtubules (Mts) which, by controlling the orientation of wall microfibrils, plays an important role in cell shaping. Previous experiments strongly indicated that the array is nucleated in a zone adjacent to the new ventral wall soon after cytokinesis. In order to further clarify the function of this zone, we performed dual immunolocalizations on Allium guard cells with anti-beta-tubulin, to detect Mts, and an antibody to gamma-tubulin, a protein known to be present at Mt-organizing centers in other species and recently identified in plants as well. gamma-Tubulin antibody stained the cortical zone adjacent to the ventral wall, while little or no fluorescence was present elsewhere along the radial Mt array or at other sites in the cell. The antibody also stained the mitotic poles and phragmoplast in guard mother cells, as it does in other material. No staining was seen when the primary antibody was omitted. The results are consistent with nucleation of the radial array at a cortical-Mt-organizing zone next to the ventral wall, and set the stage for more in-depth studies on the spatial and temporal control of Mt formation in differentiating cells.

Allium↗
PubMed1993

Retinoic acid increases elastin in neonatal rat lung fibroblast cultures.

The factors that regulate elastin synthesis during pulmonary alveolar septal formation have not been identified. Because maximal alveolar elastin synthesis occurs over a relatively brief period (postnatal days 4-14 in the rat), we hypothesized that changes in the local concentrations of factors that regulate elastin synthesis may precede or accompany this period. Because pulmonary retinoid stores decline just before the fourth postnatal day, we also hypothesized that this decline could be accompanied by the utilization of retinoic acid, one of the most biologically active retinoids, in a regulatory process that increases elastin synthesis. If these hypotheses are correct, then retinoic acid should increase elastin synthesis by pulmonary cells. Therefore, cultures of neonatal rat lung fibroblasts were exposed to retinoic acid, and elastin production was quantitated. Retinoic acid produced a two- to threefold increase in the steady-state level of elastin mRNA, in soluble elastin, and in insoluble elastin. The transcriptional initiation rate of the elastin gene was 1.8-fold higher in nuclei that were isolated from retinoic acid-treated cells than in nuclei that were isolated from control cells. This indicates that the increase in steady-state elastin mRNA results, at least partially, from an increase in elastin transcription. Lung fibroblasts that were isolated from 8-day-old rats, but not cultured, contained retinoic acid. These findings suggest that retinoic acid is a potential regulator of elastin synthesis in developing pulmonary alveoli.

Animals↗
PubMed1993

Effects of temperature and pH on cardiac myofilament Ca2+ sensitivity in rat and ground squirrel.

Chemically skinned papillary muscles from active and hibernating ground squirrels were used to determine whether the enhanced cardiac contractility observed in hibernation is due to a change in myofilament Ca2+ sensitivity. A similar preparation from rats was used to reflect the changes in a nonhibernator. When examined at pH 7.00 in all three groups and under physiological pH with varying temperatures in the ground squirrels, the calcium concentration at which muscle tension is at 50% maximum (pCa2+50) decreased significantly (P < 0.05) with decreasing temperature (25, 15, and 5 degrees C). When hibernating and active ground squirrels were compared, no significant difference in pCa2+50 was observed at 25 degrees C; however, the values at 15 and 5 degrees C were significantly higher (P < 0.05) in the hibernating squirrels. The results indicate that cardiac myofilament Ca2+ sensitivity decreases significantly at low temperature in both active and hibernating ground squirrels; however, the higher Ca2+ sensitivity in the hibernating squirrels at 15 and 5 degrees C could partially contribute to the enhanced cardiac contractility typically seen during hibernation.

Actin Cytoskeleton↗
PubMed1993

Rat and mouse proopiomelanocortin gene sequences target tissue-specific expression to the pituitary gland but not to the hypothalamus of transgenic mice.

The proopiomelanocortin (POMC) gene is expressed predominantly in corticotrophs of the pituitary anterior lobe, melanotrophs of the intermediate lobe and neurons of the arcuate nucleus of the hypothalamus. The different ontogeny of POMC mRNA as well as the complicated hormonal regulation of POMC gene expression in the three different cell types suggests a concerted interaction between several cis-acting elements in the POMC gene and transcription factors located in each of the three cell types. To investigate cell-specific elements in the POMC gene we tested two different constructs in transgenic mice. The construct -4000rPOMCLacZ, carrying 4 kb of the rat POMC promoter fused to the Escherichia coli beta-galactosidase gene, showed appropriate expression in melanotrophs in 50% of the mice analyzed. beta-Galactosidase activity was less evident in corticotrophs under basal environmental conditions. In brain, 7 out of 15 independently derived transgenic founders had ectopic expression of the transgene in different areas; however, none of the animals analyzed expressed beta-galactosidase in neurons of the arcuate nucleus. The construct HAL*, a 'tagged' 10.2-kb mouse genomic fragment, was more efficiently targeted to the pituitary. Using in situ hybridization, we detected uniform expression of HAL* in melanotrophs in 100% of the 6 pedigrees analyzed and transgenic mRNA levels paralleled those of the endogenous POMC mRNA. In corticotrophs, basal expression was low but after adrenalectomy HAL* mRNA levels were comparable to those of POMC. None of the 6 pedigrees had appropriate expression of HAL* in the brain; however, 2 lines had ectopic expression in the dentate gyrus of the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Regulation of parathyroid hormone-related peptide production in vitro by the rat hypercalcemic Leydig cell tumor H-500.

The transplantable rat Leydig cell tumor H-500 is known to cause hypercalcemia in vivo by the release of abundant PTH-related peptide (PTHRP) and to closely reproduce the human syndrome of malignancy-associated hypercalcemia. In the rat only a single messenger RNA species of 1.4 kilobases is expressed which encodes a peptide of 141 amino acid as the sole molecular form. We have examined in cultured rat Leydig tumor cells H-500, the capacity of multiple factors to regulate PTHRP messenger RNA expression and secretion. Both fetal bovine serum and epidermal growth factor stimulated PTHRP gene expression and secretion into conditioned culture medium. Dexamethasone and 1,25-dihydroxyvitamin D3 produced inhibition of PTHRP gene expression and secretion. Furthermore, in these testicular cells, after 12 h or more of incubation, testosterone produced a dose-dependent (10(-9)-10(-7) M) inhibition of PTHRP production. No significant difference in this inhibitory response was seen between testosterone and its 5 alpha-reduced metabolite dihydrotestosterone whereas 17 beta-estradiol, progesterone, LH, FSH, and PRL were ineffective. An androgen receptor antagonist Win 49596 blocked the androgen-mediated inhibition of PTHRP gene expression and secretion, but not that due to dexamethasone. Epidermal growth factor caused an increase, whereas androgen caused a decrease in PTHRP gene transcription. These studies demonstrated that growth factors, dexamethasone, and 1,25-dihydroxyvitamin D3 are broadly active regulatory agents of PTHRP production which cross species and tissue barriers. Testosterone may be a more selective modulator which can regulate PTHRP in tissues such as Leydig cell neoplasms which express the androgen receptor.

Androgen Receptor Antagonists↗
PubMed1993

A gamma-tubulin-related protein associated with the microtubule arrays of higher plants in a cell cycle-dependent manner.

An antibody specific for a conserved gamma-tubulin peptide identifies a plant polypeptide of 58 kDa. gamma-Tubulin antibody affinity purified from this polypeptide recognizes the centrosome in mammalian cells. Using immunofluorescence microscopy, we determined the distribution of this gamma-tubulin-related polypeptide during the complex changes in microtubule arrays that occur throughout the plant cell cycle. We report a punctate association of gamma-tubulin-related polypeptide with the cortical microtubule array and the preprophase band. As cells enter prophase, gamma-tubulin-related polypeptide accumulates around the nucleus and forms a polar cap from which early spindle microtubules radiate. During metaphase and anaphase, gamma-tubulin-related polypeptide preferentially associates with kinetochore fibers and eventually accumulates at the poles. In telophase, localization occurs over the phragmoplast. gamma-Tubulin-related polypeptide appears to be excluded from the plus ends of microtubules at the metaphase plate and cell plate. Its distribution during the cell cycle may be significant in light of differences in the behavior and organization of plant microtubules. The identification of gamma-tubulin-related polypeptide could help characterize microtubule organizing centers in these organisms.

Amino Acid Sequence↗
PubMed1993

Effect of reduced aprotinin dosage on blood loss and use of blood products in patients undergoing cardiopulmonary bypass.

High-dose aprotinin reduces bleeding after cardiac surgery, but has also evoked concern with regard to potential side effects and hospital costs. To evaluate the effects of reduced-dose aprotinin on blood loss and need for blood transfusion, 40 patients undergoing myocardial revascularization were studied (double-blind, placebo-controlled). Postoperative bleeding was reduced by 40% and erythrocyte infusion by 85% in the group given 3 x 10(6) KIU aprotinin (1 x 10(6) as a loading dose before cardiopulmonary bypass, 1 x 10(6) in the priming volume and 2.5 x 10(5)/hour intraoperatively) Aprotinin concentrations during the operation were monitored and maintained above the required level. There were no adverse effects of the drug. Hospital expenditure on blood products was reduced by 51% when aprotinin was used. Our study suggests that aprotinin in reduced dosage diminishes bleeding and requirements for blood products, and that it should be given before, during and after cardiopulmonary bypass.

Aged↗
PubMed1993

The influence of heparin-coated and uncoated extracorporeal circuits on blood rheology during cardiac surgery.

The effect of heparin-coated perfusion circuits on blood trauma during clinical cardiopulmonary bypass (CPB) was studied in order to find out if traumatic changes in the blood could be minimized. Twenty-four patients undergoing coronary artery bypass surgery were randomized prospectively to CPB with heparin-coated circuits (HCC) or non-coated circuits (NCC). The trauma to blood was assessed by measuring damage to blood cells by estimating red and white cell rheology changes. These were measured as red cell filtration rate (RFR) and white cell filtration rate (WFR) using standard microfiltration methods. Furthermore, changes in plasma hemoglobin (P-Hb), whole blood and plasma viscosity were simultaneously assessed. The RFR was significantly reduced in both groups during CPB by 10% in the HCC and 32% in the NCC groups (p less than 0.01). When comparing the HCC and NCC groups, a significant difference was first seen after 30 minutes of bypass (p less than 0.05) and increased at the end of CPB (p less than 0.01). Similar results were seen regarding WFR (15% and 36%, p less than 0.01). After 30 minutes of bypass, a significant difference was seen between HCC and NCC groups (p less than 0.05). Furthermore, a significant increase in P-Hb levels were seen during CPB in both patient groups. At the end of CPB, there was a significant difference in P-Hb levels (HCC 305+/-90 mg/L; NCC 455+/-78 mg/L, p less than 0.01) when comparing the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

[Measurement of the concentrations of PGF2 alpha and PG12 in the cochlear lateral wall of guinea pigs following intravenous injection of ethacrynic acid].

The concentrations of prostaglandin F2 alpha(PGF2 alpha) and prostacyclin (PGI2) in the cochlear lateral wall of guinea pigs following intravenous injection of ethacrynic acid (EA) were measured with radioimmunoassay. After injection of EA (60mg/kg) 30, 60, 120 minutes, the concentrations of PGF2 alpha and PGI2 in the cochlear lateral wall of three experimental groups were not significantly different from control ones respectively. The results suggested that there was no remarkable relationship between PGF2 alpha PGI2 and the changes of the microcirculation of cochlear lateral wall caused by EA.

6-Ketoprostaglandin F1 alpha↗