Biomedical subjects

B Liu

Publications and source records attributed to B Liu.

At least 685 records · Page 38Linked to original sources

PubMed1992

Human cytomegalovirus contains a tegument protein that enhances transcription from promoters with upstream ATF and AP-1 cis-acting elements.

The tegument proteins of human cytomegalovirus are introduced into cells as components of infectious virus. The tegument proteins may affect viral and cellular transcription prior to the synthesis of the immediate-early viral regulatory proteins. The phosphorylated tegument protein of 71 kDa (pp71) is reported to be encoded by the UL82 gene. The UL82 gene products transactivated promoters containing upstream ATF or AP-1 binding sites. In contrast, the phosphorylated tegument protein of 65 kDa (pp65), encoded by the UL83 gene, had no detectable effect on these promoters. Enhancement by UL82 of downstream transcription was directly proportional to the number of upstream ATF sites. Response to UL82 transactivation was abolished by mutation of the ATF site. Mutation in the carboxy-terminal region of UL82 also eliminated transactivation. Even though the major immediate-early promoter of human cytomegalovirus is a strong enhancer-containing promoter, UL82 further enhanced its transcription as much as 20-fold. The mechanism of UL82 enhancement of transcription from viral or cellular promoters is not known, but the enhancement may be mediated by triggering one of the protein kinase signaling pathways, increasing the affinity of ATF or AP-1 for the target sequence, or stabilizing the complex between the eucaryotic transcription factor and the target sequence.

Activating Transcription Factors↗

PubMed1992

Identification of DNA elements cooperatively activating proopiomelanocortin gene expression in the pituitary glands of transgenic mice.

The proopiomelanocortin (POMC) gene is highly expressed in adult mouse pituitary anterior lobe corticotrophs and intermediate lobe melanotrophs. To identify the DNA elements important for this tissue-specific expression, we analyzed a series of POMC reporter genes in transgenic mice. A DNA fragment containing rat POMC 5'-flanking sequences from -323 to -34 recapitulated both basal pituitary cell-specific and hormonally stimulated expression in adult mice when fused to a heterologous thymidine kinase promoter. Developmental onset of the reporter gene expression lagged by 1 day but otherwise closely paralleled the normal ontogeny of murine POMC gene expression, including corticotroph activation at embryonic day 14.5 (E14.5) followed by melanotroph activation at E15.5 to E16.5. AtT20 corticotroph nuclear protein extracts interacted with three specific regions of the functional POMC promoter in DNase I protection assays. The positions of these protected sites were -107 to -160 (site 1), -182 to -218 (site 2), and -249 to -281 (site 3). Individual deletions of these footprinted sites did not alter transgene expression; however, the simultaneous deletion of sites 2 and 3 prevented transgene expression in both corticotrophs and melanotrophs. Electrophoretic mobility shift and Southwestern (DNA-protein) assays demonstrated that multiple AtT20 nuclear proteins bound to these footprinted sites. We conclude that the sequences between -323 and -34 of the rat POMC gene promoter are both necessary and sufficient for correct spatial, temporal, and hormonally regulated expression in the pituitary gland. Our data suggest that the three footprinted sites within the promoter are functionally interchangeable and act in combination with promoter elements between -114 and -34. The inability of any reporter gene construction to dissociate basal and hormonally stimulated expression suggests that these DNA elements are involved in both of these two characteristics of POMC gene expression in vivo.

Animals↗

PubMed1992

Ectopic corticotropin-releasing hormone produced by a transfected cell line chronically activates the pituitary-adrenal axis in transkaryotic rats.

Hypothalamic CRH is the primary positive regulatory factor of the pituitary-adrenal axis. The purpose of our study was to analyze the chronic effects of CRH on the production and secretion of POMC peptides from both the anterior lobe (AL) and neurointermediate lobe (NIL) of the pituitary by mimicking the syndrome of ectopic CRH secretion from neuroendocrine tumors. We first generated stably transfected W2 medullary thyroid carcinoma cell lines with a rat CRH expression vector under the transcriptional control of a cytomegalovirus gene promoter. These cell lines constitutively expressed the foreign gene, accurately processed the encoded prepro-CRH, and secreted biologically active CRH with an estimated potency equivalent to that of synthetic CRH-(1-41)NH2. The cell line designated W2CRH-7 was implanted sc in the syngeneic rat strain WAG/Rij and produced tumors that abundantly secreted CRH into the peripheral circulation. Four weeks postimplantation, W2CRH-7, but not wild-type W2, cells caused significant increases in the AL content of beta-endorphin-like immunoreactivity comparable to that caused by adrenalectomy (ADX). Plasma ACTH and serum beta-endorphin-like immunoreactivity were increased to a greater extent by ADX than by W2CRH-7 cell implantation. The NIL of both male and female rats showed either no change or a tendency to decreased beta-endorphin concentrations with no change in the acetylation or carboxy-shortening profiles judged by cation exchange chromatography in response to the ectopic CRH treatment. Rats of both sexes maintained a profound activation of the pituitary adrenal axis up to 16 weeks postimplantation, with normalized adrenal gland weights 5 times that of controls. The chronic secretion of CRH by W2CRH-7 cells resulted in a complete cessation of body growth in all rats up to the maximum time tested of 16 weeks. The lack of growth was partly ameliorated by concomitant ADX, suggesting an important role for adrenal glucocorticoids in these effects. We conclude that 1) the transplantable W2CRH-7 cell line provides a highly effective and reproducible means of sustained CRH treatment that mimics the syndrome of ectopic CRH expression by neuroendocrine tumors; 2) AL corticotrophs respond to chronic CRH by a sustained production and secretion of POMC peptides, leading to a marked adrenal cortical hyperplasia, with no evidence of biologically significant desensitization; 3) chronic CRH tends to decrease the NIL content of beta-endorphin,with remarkably little effect on posttranslational processing; and 4) the syndrome of chronic ectopic CRH in WAG/Rij rats includes a cessation of body growth at least partly due to products of the adrenal glands.

Adrenalectomy↗

PubMed1992

Pituitary corticotroph hyperplasia in rats implanted with a medullary thyroid carcinoma cell line transfected with a corticotropin-releasing hormone complementary deoxyribonucleic acid expression vector.

CRH stimulates both the synthesis and release of ACTH and other derivatives of POMC by the adenohypophysis. It is uncertain, however, whether it also causes proliferation of corticotrophs. Patients with CRH-producing tumors develop Cushing's syndrome, and some have been reported to have pituitary corticotroph hyperplasia. We now report an animal model that accurately reproduces the human disorder of ectopic production of CRH by a neoplasm. Prolonged CRH secretion by a transplanted medullary thyroid carcinoma cell line stably transfected with a CRH cDNA under transcriptional control of a cytomegalovirus promoter resulted in corticotroph hyperplasia and hypertrophy; the percentage of ACTH-containing cells in animals bearing W2CRH tumors was increased at 9.8 +/- 0.5% (controls, 6.2 +/- 0.3%; W2 implanted tumors, 7.7 +/- 0.4%). Occasional mitotic figures were identified, and the cells were larger, with abundant cytoplasm but generally less intense immunohistochemical staining for ACTH due to relative degranulation compared to controls. Melanotrophs of the intermediate lobe were also increased in number and were larger, with abundant cytoplasm. No corticotroph adenomas were found. Our experiment accurately reproduces the gradually increasing CRH levels in the general circulation produced by a growing tumor, as found in the human ectopic CRH syndrome, and confirms that long term exposure to CRH excess, as produced by a tumor, results in an increased number of corticotrophs in the adenohypophysis.

Adrenocorticotropic Hormone↗

PubMed1992

[Effects of Lycium barbarum L and Drynaria fortunei J Smith on in vitro attachment and growth of human gingival fibroblasts on root surfaces].

In this study, the effects of Lycium barbarum L and Drynarna fortunei J Smith on in vitro attachment and growth of human gingival fibroblasts to root surfaces were investigated. The results revealed that the above herbs at dose of 1.25 mg/ml could improve attachment and growth of fibroblast, on the planed diseased root surfaces to a certain extent. When exposed to Lycium brabrum L cells on the diseased root surfaces increased markedly in number, with more even distribution, better spread, and more exuberant growth. Drynaria fortunei J Smith was not as potent as Lycium brabarum L. The results suggest that the two drugs may improve the formation of new attachment of periodontal tissue.

Cell Adhesion↗

PubMed1992

Construction of a genetically engineered strain producing propionylspiramycin.

Our work has demonstrated the cloning of propionyl acylase gene and the expression of S. mycarofaciens mutant in S. lividans TK54. In this paper, we report the transformation of pIJM9 recombinant plasmid containing the propionyl acylase gene into spiramycin producer S. spiramyceticus. The results of colony hybridization and Southern hybridization showed that No. 61 transformant harbored the pIJM9 recombinant plasmid. TLC and bioautography showed that the Rf value of one component of the fermentation products of No. 61 transformant was similar to that of propionylspiramycin. The HPLC retention time of the components of the fermentation products of No. 61 transformant and that of propionylspiramycin were also similar. Mass spectrum analysis showed that there was propionylspiramycin II in the fermentation products of No. 61 transformant. According to these results, No. 61 transformant is shown to be a genetic engineered strain producing propionylspiramycin.

Acyltransferases↗

PubMed1992

[Serum apolipoprotein E levels in 238 healthy adults and 161 hyperlipidemic subjects in Chengdu area].

The serum apoE levels in 238 healthy adults in Chengdu are aware determined by radioimmunodiffusion (RID) assay. The average apoE level was 3.98 +/- 0.98 mg/dl (chi +/- s). The result was basically identical with other reports. There is no difference in sex, and the level has a tendency to increase with age. One hundred and sixty-one hyperlipidemic subjects (including types IIa, IIb, IV and V were compared with the normals. Their serum apoE levels increased by different percentages depending on the type of hyperlipidemia. The percentage of increasing was especially higher in types V and IIb. The content of apoE in serum positively correlated with serum triglyceride (r = 0.65, P < 0.01) and with serum total cholesterol (r = 0.50, P < 0.01).

Adult↗

PubMed1992

[Mutagenesis study of ethylmethane sulfonate with shuttle vector plasmid pZ189].

Shuttle vector plasmid pZ189 was used as a molecular tool and the SupF inserted in the plasmid was worked as a target gene for mutagenesis study. The host cells (E. coli MBM 7070) with pZ189 were treated with ethylmethane sulfonate (EMS) and plated on the selective media containing X-gal (5-bromo-4-chloro-3-indolyl-beta-D-galactoside) and IPTG (isopropyl-beta-D-thiogalactoside). The SupF and the LacZ amber mutant carried by the host cells complemented each other and thus made the colonies blue on the selective media. However the colonies derived from the SupF mutants changed the colour from blue to white. The mutant frequencies in a series of experiments with different concentrations of EMS were estimated. Furthermore, the DNA isolated from 5 SupF mutants was digested with restruiction enzyme Hha I. It suggests that the 214 bp Hha I fragments containing mutant SupF could be distinguished from their wild type counterparts by temperature-gradient gel electrophoresis under optimal conditions.

Electrophoresis, Polyacrylamide Gel↗

PubMed1992

Chemosensitivity of salivary gland and oral cancer cell lines.

Chemosensitivity of salivary gland and oral cancer cell lines to 14 antitumor drugs was tested using a tetrazolium-based colorimetric assay and the relative antitumor activity (RAA) of the drugs was compared. Adriamycin (ADM), methotrexate and fluorouracil (5-FU) showed the most potent RAA against the cell lines while cantharidin did not. The rank orders of other 10 drugs against each cell line differed from each other.

Cantharidin↗

PubMed1992

Antitumor activity of psoralen on mucoepidermoid carcinoma cell line MEC-1.

Psoralen (PSO) was found cytotoxic against in vitro cultured human mucoepidermoid carcinoma cells of MEC-1 cell line. Its IC50 value was 8.6 micrograms/ml, and relative antitumor activity (RAA) 15. PSO suppressed DNA synthesis, damaged microvilli and cell membrane, and induced degeneration of mitochondria. It inhibited the growth of MEC-1 cells transplanted in nude mice by 79.1% which was as strong as pingyanmycin (PYM 81.4%). The body weight loss of PSO treated tumor-bearing mice was 5%, whereas that of PYM treated ones 13.3% (P < 0.01). PSO may be an effective agent for the treatment of human mucoepidermoid carcinoma.

Animals↗

PubMed1992

[Cloning and expression of alpha-hydroxy-gamma-aminobutyl acylase gene of Bacillus circulans NRRL-B3312].

With shot-gun cloning strategy, we used pUB110 plasmid as a vactor to clone DNA fragment of Bacillus circulans NRRL-B3312, which is butirosin producer, into Bacllus subtilis 168. Among the transformants, the results of TLC, bioautography and FAB mass, spectrum analysis for the bioconversion product of No. 733 transformant showed that this transformant could transform kanamycin into amikacin. According to these results, the HABA acylase gene locates on the insert fragment of pUBC733 plasmid harbouring No. 733 transformant. We can confirm that the HABA acylase gene was cloned and expressed in B. subtilis 168. Molecular weight of pUBC733 is 7.3kb. Southern hybridization demonstrated that the 2.8 kb inserted fragment of this plasmid originated from B. circulans NRRL-B3312. The restriction map of pUBC733 plasmid was constructed.

Acyltransferases↗

PubMed1992

[Apolipoprotein C III binding sites (receptor) on non-parenchymal cells from rat liver].

Binding sites of apolipoprotein (apo) C III on non-parenchymal cells (NPC) isolated from rat liver were found. Apo C III was purified from delipided human plasma very low density lipoproteins. 125I-labeled-apo C III was prepared by chloramine-T method. Non-parenchymal cells were isolated from rat liver by collagenase method. Freshly isolated rat liver NPC bound 125I-labeled apo C III in a saturable way with Kd 0.1-0.55 mumol/L and Bmax 18.1-42.0 ng/ml cell protein. There were about 1.0-4.5 x 10(5) specific binding sites of apo C III on each NPC. Unlabeled apo C III, but not apo AI and B100, could inhibit these binding activities. The results demonstrate the presence of saturable and specific apo C III receptors (binding sites) on rat liver NPC, but their nature and biologic properties remain to be investigated.

Animals↗

PubMed1992

[Composition and distribution of lipid and apolipoprotein in plasma lipoproteins of endogenous hypertriglyceridemia].

Lipids and apolipoproteins in plasma VLDL, IDL, LDL, HDL2 and HDL3 isolated by one-step density gradient ultracentrifugation from 7 subjects with endogenous hypertriglyceridemia (HTG) and 4 normalipemics were determined. HTG VLDL was enriched with cholesterol, and its triglyceride (TG), phospholipid (PL) and apo CII, CIII contents (mg/100 mg protein) were significantly higher than those in normal VLDL. ApoE content in HTG VLDL was prone to increasing, and apoB100 content had no apparent difference from that in normal VLDL. Compared with normal HDL2 and HDL3, the contents of total cholesterol (TC), apoAI, CII, and CIII in HTG HDL2, and apoCII, CIII in HTG HDL3 decreased. HTG HDL2 and HDL3 were rich in TG. By analysis of distribution of these lipids and apolipoproteins in various plasma lipoproteins, it was found that the abnormal composition of VLDL and HDL in HTG seemed to be a result of transport of TC, PL, and apoCII, CIII from HDL to VLDL. There was a significantly positive correlation between TC and apoAI, CII, CIII in HDL respectively, which indicated that apoCII and CIII were also associated with the alteration of HDL cholesterol. It is suggested that the elevated plasma VLDL-TG concentration in endogenous hypertriglyceridemia may induce abnormal redistribution of lipid and apolipoprotein among apoCII plasma lipoproteins, and and CIII may play an important role in these changes.

Apolipoprotein C-II↗

PubMed1992

[Atmosphere pollution by sulfur dioxide during processing of zirantong].

This paper reports the colorimetric determination of total SO2 in Zirantong by the method of rosaniline hydrochlorid. Samper of processed Zirantong from the pharmacy have been analyzed and the quality specifications established. Optimum conditions for processing have been chosen and a procedure has been proposed for the recovery of the poisonous matter SO2 which is then transformed into a beneficial material.

Air Pollution↗

PubMed1991

Crystal structure of a MAT alpha 2 homeodomain-operator complex suggests a general model for homeodomain-DNA interactions.

The MAT alpha 2 homeodomain regulates the expression of cell type-specific genes in yeast. We have determined the 2.7 A resolution crystal structure of the alpha 2 homeodomain bound to a biologically relevant DNA sequence. The DNA in this complex is contacted primarily by the third of three alpha-helices, with additional contacts coming from an N-terminal arm. Comparison of the yeast alpha 2 and the Drosophila engrailed homeodomain-DNA complexes shows that the protein fold is highly conserved, despite a 3-residue insertion in alpha 2 and only 27% sequence identity between the two homeodomains. Moreover, the orientation of the recognition helix on the DNA is also conserved. This docking arrangement is maintained by side chain contacts with the DNA--primarily the sugar-phosphate backbone--that are identical in alpha 2 and engrailed. Since these residues are conserved among all homeodomains, we propose that the contacts with the DNA are also conserved and suggest a general model for homeodomain-DNA interactions.

Base Sequence↗

PubMed1991

Temperature effects on the Na and Ca currents in rat and hedgehog ventricular muscle.

Cardiac transmembrane potentials and Na and Ca currents were recorded at different temperatures in rat and hedgehog ventricular muscle. At 35 degrees C in both species resting potential was about -80 mV and upstroke velocity (Vmax) of the action potential above 100 V/s. The shape of the action potential in hedgehog ventricular cells at 35 degrees C was similar to that in the rat showing a fast repolarization phase. When temperature was decreased, the membrane resting potential depolarized and action potential amplitude and Vmax declined. In rat ventricular cells at 10 degrees C, the resting potential was about -40 to -50 mV and Vmax was reduced to about 5 V/s. In hedgehog ventricular cells, however, the transmembrane potentials and Vmax were better maintained at low temperature. Phase 3 of the action potential was markedly prolonged below 20 degrees C in hedgehog but not in rat ventricular cells. When temperature was decreased to 10 degrees C the availability curve of the Na current shifted toward more negative potentials and ICa.peak declined in rat ventricular cells. In hedgehog cardiac preparations, the Na current was less influenced by the cooling and ICa.peak did not change very much at low temperatures. A transient inward current usually considered to induce cardiac arrhythmias could be recorded in rat ventricular cells below 20 degrees C but not in hedgehog preparations. These features of hedgehog cardiac membranes may contribute to the cold tolerance and the resistance to ventricular fibrillation during the hypothermia in mammalian hibernators.

Action Potentials↗

PubMed1991

Colchicine-induced increases in immunoreactive neuropeptide levels in hypothalamus: use as an index of biosynthesis.

The colchicine-induced accumulation of vasopressin (AVP) and oxytocin (OXT) has recently been applied to estimate the synthesis and turnover rates for these neuropeptides in whole rat hypothalamus. In the present studies, this pharmacologic procedure has been examined as a potential method for estimating hypothalamic somatostatin (SRIF) synthesis rate, and evaluated further for its utility in estimating nonapeptide synthesis in individual hypothalamic nuclei. Adult male rats received a single injection of colchicine (8 micrograms) into the third ventricle under pentobarbital anesthesia. Twenty-four hr later, immunoreactive (IR) levels of AVP and OXT increased considerably, as previously noted. Hypothalamic IR-SRIF levels, however, were unaffected. The absolute increases in IR-AVP and IR-OXT were greatest in the supraoptic nucleus (SON), with smaller increments in the para/periventricular hypothalamus (PVH) and the median eminence (ME). IR-SRIF levels showed no changes in the PVH or the ME. As a test, the method was applied to the detection of changes in AVP synthesis in diabetic rats. The colchicine procedure reported increases in AVP synthesis in both the SON and PVH in diabetic animals, a result compatible with that obtained previously for whole hypothalamus using radiolabeled procedures. Together, the results indicate that the colchicine procedure is useful in detecting changes in the syntheses of some (AVP and OXT) but not all (SRIF) neuropeptides, and that when applicable, the method is sufficiently sensitive to detect changes in small hypothalamic regions. The method may prove useful in estimating changes in peptide synthesis analogous to that used for serotonin and dopamine; e.g., 5-hydroxytryptophan and dopa accumulation following inhibition of aromatic L-amino acid decarboxylase.

Animals↗

PubMed1991

Effect of low temperature on the cytosolic free Ca2+ in rat ventricular myocytes.

The effect of low temperature on the cytosolic free Ca2+ [( Ca2+]i) has been investigated in isolated ventricular myocytes from adult rats using the fluorescent probe Indo-1. The distribution of Indo-1 between the mitochondrial and cytoplasmic compartments was first determined in the isolated myocytes using the digitonin and Triton X-100 treatments. By subtracting the mitochondrial [Ca2+]i from the total [Ca2+]i measured with Indo-1, the average cytosolic [Ca2+]i was found to increase significantly (P less than 0.05) from 139 nM to 255 and 297 nM when the temperature was decreased from 37 degrees C to 15 degrees and 5 degrees C, respectively. A marked increase in cytosolic [Ca2+]i to a new steady state level was observed when the membrane of myocytes was depolarized by 60 mM KCI; the average magnitude of increase being 110, 243 and 186 nM, at 37 degrees, 15 degrees and 5 degrees C respectively. Our results support the hypothesis that the cardiac arrhythmia typically observed in the hypothermic rat is due to an increased cytosolic [Ca2+]i with decreasing body temperature.

Animals↗