PubMed Health⌕ Search

Biomedical subjects

J Liu

Publications and source records attributed to J Liu.

At least 19 recordsLinked to original sources
PubMed2026

Exploring genomic regions regulating the liver transcriptome and energy homeostasis in pigs.

In pigs, energy homeostasis has an impact on meat quality and health. In a Duroc pig population, 30 quantitative trait locus (QTL) regions associated with fatty acid (FA) composition in adipose tissue, plasma, liver and muscle were previously identified. Mapping of expression quantitative trait locus (eQTL) regions will provide a molecular hypothesis for genotype-phenotype interactions and may allow the identification of shared causal variants, key to increasing our understanding of the genetic regulation of FA composition and energy homeostasis. However, gene expression is impacted by environmental factors, while individual-level allelic imbalance (AI) can be more reliable and can be surveyed via allelic-specific expression (ASE) analysis. Furthermore, treatment of ASE as a quantitative trait allows the identification of allele-specific expression quantitative trait loci (aseQTLs), which are variants whose heterozygosity is linked to the AI of a nearby single-nucleotide polymorphism (SNP), pointing to regulatory elements. In this study, liver was selected as a key metabolic hub with an important role in the regulation of energy homeostasis, and 310 liver RNA sequencing samples were analysed using a combination of (1) eQTL mapping, (2) ASE analysis, and (3) aseQTL mapping methods. A total of 2 188 eQTL regions were identified, mostly cis-eQTL regions (73.17%). ASE analysis reported 1 964 ASE SNPs, associated with 633 genes. Finally, aseQTL mapping reported 64 172 aseQTL, associated with the AI of 31 genes. Colocalisation analysis combined with ASE analysis showed that the expression of FADS1 and FADS2 genes is associated with the polyunsaturated FA composition in several tissues, where microRNA regulation may be present. Finally, in the DGAT2 gene, annotated in a QTL region associated with multiple FAs in adipose tissue, ASE revealed allelic imbalance in the 3' untranslated region (UTR) of this gene. Allelic differential expression can be caused by a 13-bp insertion affecting messenger RNA stability, previously described, exemplifying how allelic imbalance is caused by a post-transcriptional regulatory mechanism undetectable by eQTL mapping. Furthermore, aseQTLs were associated with this gene, linked to a previously identified copy number variant not yet associated with DGAT2 expression. These results demonstrate how ASE analysis and aseQTL mapping can complement eQTL mapping, as they resolved a complex region affected by allelic heterogeneity, a main confounding effect of QTL mapping. In conclusion, the combination of eQTL mapping, ASE analysis and aseQTL mapping allowed the characterisation of the regulation of liver gene expression, improving our understanding of the genetic determinism of energy homeostasis.

Allele-specific expression↗
PubMed1992

Determination of the DNA content of the Reed-Sternberg cell of Hodgkin's disease by image analysis.

The nature of the Reed Sternberg (RS) cell, the malignant cell of Hodgkin's disease (HD), remains unknown. Cytogenetic studies have yielded ambiguous results regarding the chromosomal profile of this cell. In an attempt to further clarify the ploidy status of the RS cell, we analyzed the DNA content of CD30-positive RS cells and RS cell variants in HD lesions from 32 patients using an image analysis system. A diploid and/or near-diploid (DNA index [DI], 1.0 +/- 0.2) and a tetraploid (2.0 +/- 0.2) RS cell population were identified in 9 and in 11 of the 32 cases examined, respectively. An aneuploid RS cell population was identified in 8 of the 32 cases examined. The remaining four cases contained two RS cell subpopulations with different DNA content, each one representing more than 15% of the total RS cell population. There was no significant correlation between the DNA content of the RS cells and the category of HD. Furthermore, analysis of multiple biopsies of an individual patient taken from different lymphoid organs at the same or different time periods showed a constant DNA profile. Our data indicate that RS cells can express variable DNA content and suggests that multiple subpopulations of RS cells with different DNA content may simultaneously coexist within the same HD lesion in some patients. In addition, the RS cell population within each patient appears to express a specific DNA content profile, possibly representing unique clones. These highly individualized profiles potentially may be useful as markers to follow the clinical course of patients with HD.

Adolescent↗
PubMed1992

Conformational analysis of beta-D-fructofuranosyl-(2-->6)-beta-D-glucopyranoside by molecular mechanics (MM2) calculations.

Conformational energies for models of the disaccharide beta-D-fructofuranosyl-(2-->6)-beta-D-glucopyranoside were computed by molecular mechanics using MM2(87). An initial investigation of staggered forms examined the linkage bonds characterized by the torsion angles phi, psi, and omega, and subsequently the fructose hydroxymethyl side groups, characterized by the torsion angles chi-1 and chi-6. Then, in our major search of conformational space, the torsion angles of two linkage bonds, phi and omega, were driven through 360 degrees in 20 degree increments at all staggered side group combinations. From these results, the low-energy forms were minimized without the driver restrictions to generate the global minimum structure found and herein reported. This conformer was then used to map the conformational space of phi and omega by driving only those torsion angles through 360 degrees. Both the 4(3)T (northern) conformer (Cremer-Pople puckering phase angle of phi 2 = 265 degrees) and the 3(4)T, (southern) conformer (phi 2 = 80 degrees) of the fructofuranose ring were tested for comparison, and both were shown to be significant contributors of populated forms. As these two conformers had different minima for a number of important torsion angles, experimental studies may reveal different properties than those expected solely from the preferred northern conformer.

Carbohydrate Conformation↗
PubMed1992

Lipopolysaccharide induces Egr-1 mRNA and protein in murine peritoneal macrophages.

Bacterial LPS has diverse effects on the function of immune cells, in general, and macrophages, in particular. The intracellular molecular events that mediate the effects of LPS are unclear. We undertook a series of studies in thioglycollate-elicited murine peritoneal macrophages to evaluate the effect of LPS on expression of Egr-1, a member of the immediate early response gene family. Egr-1 may function as an intranuclear "third messenger" because it is rapidly induced in a variety of cell types and encodes a 75- to 80-kDa nuclear phosphoprotein that activates transcription of genes containing the DNA consensus sequence GCGGGGGCG. LPS from Salmonella minnesota Re595 induced a maximal increase in Egr-1 mRNA in macrophages after 30 to 60 min of incubation that returned to baseline level by 120 min. LPS increased Egr-1 mRNA at 0.01 to 0.1 ng/ml with a maximal effect at 10 to 100 ng/ml. LPS markedly increased the transcription rate of Egr-1 by 10 min of incubation using nuclear run on analysis. Using a polyclonal anti-Egr-1 antibody, nuclear staining for Egr-1 protein was prominent after 1 to 2 h of incubation with LPS and declined to baseline by 4 h. Inasmuch as protein kinase C (PKC) has been implicated in mediating the effects of LPS, we determined whether PKC was required for LPS to increase Egr-1 mRNA. Two pharmacologic approaches were used to deplete PKC, PMA pretreatment, and H-7. The induction of Egr-1 mRNA by LPS was markedly reduced in PKC-depleted macrophages. These data reveal that LPS induces transcriptional activation of Egr-1 and increases Egr-1 protein in peritoneal macrophages. In addition, these findings support further study of the potential role of Egr-1 in mediating the effects of LPS in peritoneal macrophages.

Animals↗
PubMed1992

Formation of a gated channel by a ligand-specific transport protein in the bacterial outer membrane.

The ferric enterobactin receptor (FepA) is a high-affinity ligand-specific transport protein in the outer membrane of Gram-negative bacteria. Deletion of the cell-surface ligand-binding peptides of FepA generated mutant proteins that were incapable of high-affinity uptake but that instead formed nonspecific, passive channels in the outer membrane. Unlike native FepA, these pores acted independently of the accessory protein TonB, which suggests that FepA is a gated porin and that TonB acts as its gatekeeper by facilitating the entry of ligands into the FepA channel. The sequence homology among TonB-dependent proteins suggests that all ligand-specific outer membrane receptors may function by this gated-porin mechanism.

Amino Acid Sequence↗
PubMed1992

Stable expression of transdominant Rev protein in human T cells inhibits human immunodeficiency virus replication.

The human immunodeficiency virus (HIV) Rev protein is essential for viral structural protein expression (Gag, Pol, and Env) and, hence, for viral replication. In transient transfection assays, mutant forms of Rev have been identified that inhibit wild-type Rev activity and therefore suppress viral replication. To determine whether such transdominant Rev proteins could provide long-term protection against HIV infection without affecting T cell function, T leukemia cell lines were stably transduced with a retroviral vector encoding a transdominant mutant of the Rev protein, M10. While all the M10-expressing cell lines remained infectable by HIV-1, these same cells failed to support a productive replication cycle when infected with a cloned isolate of HIV-1. In addition, two out of three M10-expressing CEM clones were also resistant to highly productive infection by a heterogeneous HIV-1 pool. Expression of M10 did not affect induction of HIV transcription mediated by the kappa B regulatory element or Tat. Importantly, constitutive expression of Rev M10 did not alter the secretion of interleukin 2 in response to mitogen stimulation of EL-4 and Jurkat cells. The inhibition of HIV infection in cells stably expressing a transdominant Rev protein, in the absence of any deleterious effect on T cell function, suggests that such a strategy could provide a therapeutic effect in the T lymphocytes of acquired immunodeficiency syndrome patients.

Clone Cells↗
PubMed1992

Opposing actions of Fos and Jun on transcription of the phosphoenolpyruvate carboxykinase (GTP) gene. Dominant negative regulation by Fos.

Jun homodimers and Fos/Jun heterodimers bind to the gene for phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) at three sites within the first 350 base pairs of the promoter. These include CRE-1 (-82 to -90), and P3(II) and P4 (-252 to -258 and -268 to -285, respectively). Over-expression of Jun in HepG2 cells resulted in a 10-15-fold increase in the level of transcription of a chimeric PEPCK (-490 to +73)-CAT gene, while expression of Fos decreased transcription and blocked the induction of transcription from the PEPCK promoter by Jun. The action of Fos and Jun on PEPCK gene transcription involved each of the Fos/Jun-binding sites and was modulated by additional transcriptional regulatory elements within the PEPCK promoter. The ability of Fos to inhibit PEPCK transcription was dependent upon P3(I), a region of the promoter which does not bind Fos/Jun heterodimers, but does bind members of the C/EBP family of transcription factors. Stimulation of PEPCK transcription by 8-Br-cAMP or by overexpression of the catalytic subunit of protein kinase A was inhibited by Fos expression. The inhibitory effects of phorbol esters and protein kinase C on PEPCK gene expression may be mediated through the action of Fos and Jun.

Binding Sites↗
PubMed1992

Interleukin-6 signal transducer gp130 mediates oncostatin M signaling.

Oncostatin M (OM) is a multifunctional cytokine that is structurally and functionally related to interleukin 6 (IL-6) and leukemia inhibitory factor (LIF). The specific receptor for OM has been demonstrated (by chemical cross-linking) to be a 150-kDa protein in a number of cell lines. The IL-6 signal transducer, gp130, is also an affinity converter for the LIF receptor. It does not bind to either IL-6 or LIF, but associates with the alpha subunits of the receptors and transduces the signals. We examined the possible involvement of gp130 in OM binding and signaling. We demonstrate that: (a) anti-gp130 monoclonal antibodies (mAbs) block the inhibitory effect of OM on A375 cell growth, (b) the binding and cross-linking of 125I-OM to H2981 cells are completely abolished by anti-gp130 mAbs, (c) the cross-linked OM-receptor complex is immunoprecipitated by anti-gp130 mAbs, and (d) COS-7 cells transfected with the full-length cDNA encoding gp130 exhibit increased OM binding and cross-linking, which are also blocked by anti-gp130 mAbs. Therefore, we conclude that the 150-kDa OM binding protein previously characterized in a variety of cell lines is gp130. OM is the natural ligand for gp130 and gp130 mediates the biological responses of OM.

Animals↗
PubMed1992

Platelet-derived growth factor activation of gastric mucosal calcium channels.

Gastric mucosal calcium channel complex was isolated from the solubilized epithelial cell membranes by affinity chromatography on wheat germ agglutinin. The complex following labeling with [3H]PN200-100 was reconstituted into phospholipid vesicles which exhibited active 45Ca2+ uptake. The channels responded in a dose dependent manner to dihydropyridine calcium antagonist, PN200-110, which at 0.5 microM exerted maximal inhibitory affect of 66% on 45Ca2+ uptake, while a 52% enhancement in 45Ca2+ uptake occurred with a specific calcium channel activator, BAY K8644. On platelet-derived growth factor (PDGF) binding in the presence of ATP, channels showed an increase in protein tyrosine phosphorylation of 55 and 170kDa subunits of calcium channel. Such phosphorylated channels following reconstitution into vesicles displayed a 78% greater 45Ca2+ uptake. The results point towards the importance of PDGF in the regulation of gastric mucosal calcium homeostasis.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1992

Conformational analysis of levanbiose by molecular mechanics.

A relaxed conformational energy map for levanbiose, O-beta-D-fructofuranosyl-(2----6)-beta-D-fructofuranoside, was computed with the molecular mechanics program MM2(87). All torsion angles of the three linkage bonds were driven by 30 degrees increments while two primary alcohol groups were held at three staggered forms. The steric energy of all other parameters was optimized. The side groups were retained at the same relative positions on the two rings in this first part of the study so our results are directly applicable to the study of polymeric levan with identical repeating units. The low-energy dimers did not lead to viable polymers. The interresidue linkage torsion angles defined by C-6-O-2'-C-2'-C-1' (phi) and O-5-C-5-C-6-O-2' (omega) have minima at +60 degrees and -60 degrees, respectively, with accessible minima at other staggered forms. As observed in inulobiose, the preferred torsion angle at central linkage bond defined by C-5-C-6-O-2'-C-2' (psi) was antiperiplanar. An analysis of all conformations of staggered side groups showed that the C-1 and C-1' groups had little effect but the C-6' group showed a preference for chi-6'(O-5'-C-5'-C-6'-O-6') = -60 degrees. The fructofuranose rings were started at the low-energy 4(3)T conformation (angle of pseudorotation, phi 2 = 265 degrees) that was retained except when the linkage conformations created severe inter-residue conflict.

Carbohydrate Conformation↗
PubMed1992

Experimental evaluation of the separation efficiency in capillary electrophoresis using open tubular and gel-filled columns.

The band dispersion phenomena in capillary zone electrophoresis (CZE) using untreated and surface-treated open tubular and gel-filled capillaries were experimentally evaluated, with emphasis on small capillary diameters (10-100 microns). Laser-induced fluorescence detection was used for high-sensitivity detection of the isoindoles originated from model amino acids. The plots of plate height vs electric field strength were generated for different column radii and compared with a theoretical model for CZE. In addition to the diffusion-controlled band dispersion in the relatively low electric field range, adsorptive interactions between a solute and the capillary wall may play a certain role in band-broadening. The sorption-desorption kinetics become important with increasing electric field strength. Thermal effects appear to contribute little to band-broadening in relatively small capillaries (less than 50-microns i.d.) within normal operating voltages (less than 30 kV), but could become significant in capillaries with larger bores (greater than 75-microns i.d.). With gel-filled capillaries of small diameters (less than 50-microns i.d.), diffusion processes can be minimized. In addition, thermal effects do not appear critical in such columns at reasonable voltages.

Animals↗
PubMed1992

Efficiency and accuracy of polymerase-chain-reaction assay for cystic fibrosis allele delta F508 in single cell.

Diagnosis of genetic disorders in the embryo before implantation, though possible by removal of one or two blastomeres at the eight-cell stage, is still experimental because the procedures of gene analysis of DNA from a single cell are not yet reliable enough for clinical application. We have evaluated the efficiency and accuracy of polymerase-chain-reaction (PCR) amplification of a single-copy gene, wild-type or cystic fibrosis delta F508 allele, on single sperm cells from a donor known to be a heterozygous carrier of the delta F508 mutation. DNA from single spermatozoa was decontaminated by restriction-enzyme treatment, then the region around the delta F508 site was amplified by nested PCR. The distribution of the wild-type and mutant alleles (59 [55%] and 48 [45%, respectively]) in the 107 single spermatozoa did not differ from that expected (50% each). 1 sample did not provide an amplified signal. To check that the two alleles would be amplified with equal efficiency when they were both present within a cell, we did PCR for 51 two-sperm samples. Again the distribution did not deviate from that expected (17 [33%] both wild-type; 21 [41%] one wild-type, one delta F508; 13 [26%] both delta F508 vs 25%; 50%; 25% expected). None of the 74 blanks in these experiments was contaminated. We conclude that our delta F508 single-cell assay is efficient and accurate and can be used for analysis of blastomere DNA to diagnose cystic fibrosis before embryo implantation.

Alleles↗
PubMed1992

Inhibition of T cell signaling by immunophilin-ligand complexes correlates with loss of calcineurin phosphatase activity.

Calcineurin, a Ca2+, calmodulin-dependent protein phosphatase, was recently found to bind with high affinity to two different immunosuppressant binding proteins (immunophilins) with absolute dependence on the presence of the immunosuppressants FK506 or cyclosporin A (CsA) [Liu et al. (1991) Cell 66, 807-815]. The binding affinities of the immunophilin-drug complexes toward calcineurin and the stoichiometry of the resultant multimeric complexes have now been determined, and structural elements of FK506, CsA, and calcineurin that are critical for mediating their interactions have been identified. Analogues of FK506 (FK520, FK523, 15-O-demethyl-FK520) and CsA (MeBm2t1-CsA and MeAla6-CsA) whose affinities for their cognate immunophilins do not correlate with their immunosuppressive activities have been prepared and evaluated in biochemical and cellular assays. We demonstrate a strong correlation between the ability of these analogues, when bound to their immunophilins, to inhibit the phosphatase activity of calcineurin and their ability to inhibit transcriptional activation by NF-AT, a T cell specific transcription factor that regulates IL-2 gene synthesis in human T cells. In addition, FKBP-FK506 and CyP-CsA do not inhibit members of the PP1, PP2A, and PP2C classes of serine/threonine phosphatases. These data suggest that calcineurin is the relevant cellular target of these immunosuppressive agents and is involved in Ca(2+)-dependent signal transduction pathways in, among others, T cells and mast cells.

Amino Acid Sequence↗
PubMed1992

Stepped surfaces of sapphire (alpha-Al2O3) with low Miller indices.

Oxygen-annealed surfaces of sapphire with low Miller indices ((0001), [1010], [1120], [1011]) have been studied in both transmission electron microscopy (TEM) and reflection electron microscopy (REM) configurations. The significance of REM diffraction conditions for the determination of the nature of the step heights is discussed. The relationship between the TEM and REM images is explained. The structural features are those that might be expected from considerations of the atom arrangement in the low Miller index planes. The structural features on the surfaces varied with respect to annealing temperature and surface condition. Thermally stable structures that might appear from consideration of the equilibrium-annealing temperature are proposed.

Aluminum Oxide↗
PubMed1992

Characterization of the annealed (0001) surface of sapphire (alpha-Al2O3) and interaction with silver by reflection electron microscopy and scanning reflection electron microscopy.

Annealed (0001) surfaces of single-crystal sapphire (alpha-Al2O3) rod have been studied in the electron microscope using reflection electron microscopy (REM), scanning reflection electron microscopy (SREM), and reflection high energy electron diffraction (RHEED). Annealed surfaces of (0001) sapphire are vicinal and characterized by close-packed (0001)-oriented terraces separated by faceted multiple-height steps, with edges parallel to energetically preferred low-index directions (less than 1010 greater than and less than 1120 greater than). These structural features are not seen on cleaved surfaces or polished surfaces treated at temperatures less than 1,250 degrees C. Oxygen-annealing produces clean surfaces which prove useful for investigating the interaction of deposited metals with the (0001) sapphire. Both REM and SREM (with microdiffraction spots) techniques have been used to observe fine structure of flat Ag islands on the scale of 1-100 nm on the (0001)-oriented terraces as well as aggregations at the steps. A preliminary result on interaction with Cu is also included.

Aluminum Oxide↗
PubMed1992

Adenovirus E1A represses the cyclic AMP-induced transcription of the gene for phosphoenolpyruvate carboxykinase (GTP) in hepatoma cells.

Adenovirus infection of hepatoma cells inhibited transcription of the phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) (PEPCK) gene and virtually eliminated transcription of a chimeric gene which contained the PEPCK promoter linked to the structural gene for chloramphenicol acetyltransferase (CAT). This effect is due to the viral protein E1A, since adenovirus containing a deletion in the E1A gene did not repress transcription from the PEPCK promoter. Both the 243R and 283R products of the E1A gene were effective. The conserved region 1 (CR-1) domain of E1A was required for this effect. Treatment of hepatoma cells with 8-bromo-cAMP or transfection with plasmids coding for the catalytic subunit of protein kinase A, CAAT/enhancer binding protein alpha (C/EBP), or Jun, all potent inducers of PEPCK gene transcription, did not relieve the inhibition caused by E1A. This inhibition does not appear to be mediated by major enhancer elements and in the PEPCK gene since transcription from the PEPCK promoter containing block mutations in binding domains for C/EBP and cAMP regulatory element binding protein (CREB) was also inhibited by E1A. Transcription of chimeric genes containing two copies each of the major cAMP response domains (CRE-1 and P-3) linked to a neutral promoter and fused to the CAT structural gene was stimulated by the catalytic subunit of protein kinase A, but this effect was totally inhibited by E1A. The strong repressive effect of E1A on PEPCK gene transcription seems to involve an interruption of an obligatory interaction between factors which bind to the cAMP response element in the PEPCK promoter and the TATA box.

Adenoviridae↗
PubMed1992

Usefulness of exercise-induced ST-segment depression in the inferior leads during exercise testing as a marker for coronary artery disease.

Multiple lead systems are shown to have a higher sensitivity than that of single leads for detecting coronary artery disease (CAD) during exercise testing, but the value of ST-segment depression isolated to the inferior leads is questionable. To ascertain the diagnostic accuracy of inferior limb lead II compared with that of precordial lead V5, a retrospective analysis of 173 men was performed (108 in a training population and 65 in a validation cohort). All patients had a standard exercise test and underwent diagnostic coronary angiography within 15 days of the exercise test (range 1 to 65). Sixty-three patients had greater than or equal to 1 coronary stenoses greater than or equal to 70%, or left main lesion greater than or equal to 50%, whereas 45 patients in the training population did not. Exclusion criteria were female sex, left ventricular hypertrophy, left bundle branch block or resting ST-segment depression on the baseline electrocardiogram, previous myocardial infarction or revascularization procedures, and any significant valvular or congenital heart disease. Lead V5 had a better combination of sensitivity (65%) and specificity (84%) (chi-square = 24.11; p less than 0.001) than that of lead II (sensitivity 71%, specificity 44%) (chi-square = 2.25; p = 0.13) at a single cut point, and this improved specificity was substantial (95% confidence interval for observed difference 22 to 58%). Receiver-operating characteristic curve analysis also revealed that lead V5 (area = 0.759) was markedly superior to lead II (area = 0.582) over multiple cut points (z = 3.032; 2p = 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗