Biomedical subjects

G Liu

Publications and source records attributed to G Liu.

At least 343 records · Page 19Linked to original sources

PubMed1998

Genistein-mediated attenuation of tamoxifen-induced antagonism from estrogen receptor-regulated genes.

In this study we demonstrate that physiologic concentrations of genistein are sufficient to mediate agonism and to reverse the repressive effects of 4-hydroxytamoxifen on estrogen receptor (ER alpha)-responsive reporter genes. We also show that overexpression of the steroid receptor coactivator (SRC-1) potentiates transactivation by genistein-activated ER alpha and that coexpression of CBP (the cAMP response element binding protein coactivator) synergistically increases this signal. Exogenous expression of a nuclear receptor corepressor (NCoR) was, however, unable to alter genistein-mediated transactivation. In in vitro binding assays, we show that genistein, but not 4-hydroxytamoxifen, induces a direct interaction between radiolabeled ER alpha and a GST-SRC-1 fusion protein. More importantly, coincubation with genistein and 4-hydroxytamoxifen or genistein treatment following preincubation of the ER with 4-hydroxytamoxifen also resulted in a strong physical interaction with SRC-1. These findings imply that genistein-induced shifts in the coregulator status of ER alpha may be involved in transcriptional regulation and suggest that tamoxifen-mediated antagonism at ER-dependent genes is sensitive to attenuation by low levels of genistein.

Drug Synergism↗

PubMed1998

A peptide isolated from a random phage peptide library is a structural mimic to the P1, P4-diadenosine 5'-tetraphosphate binding site on its receptor.

We have previously demonstrated that a monoclonal antibody (mAb TL4), which inhibits P1, P4-diadenosine 5'-tetraphosphate (Ap4A) binding to its receptor, selected a consensus RGS tripeptide from a random phage hexapeptide library. RGS interfered with Ap4A binding to its membrane receptor [Liu, G., Bryant, R. T. & Hilderman, R. H. (1996) Biochemistry 35, 197-201]. However the mechanism by which RGS interfered with Ap4A binding to its receptor was not determined. In this communication, we demonstrate that RGS interacts with Ap4A to prevent [3H]Ap4A binding to the Ap4A membrane receptor. To further characterize the mechanism by which RGS inhibits Ap4A binding to its receptor, we used mAb TL4 to screen a 15-residue random peptide phage library and DNAs from 24 clones were sequenced. 20 clones contain a RGSSS sequence while 17 of these clones contained an identical 15-amino-acid insert (clone A). Gel-filtration studies of previously equilibrated clone A phage and [3H]Ap4A support the idea that [3H]Ap4A interacts specifically with clone A phage while RGS effectively competes for [3H]Ap4A interaction on clone A phage. These data are consistent with RGS mimicking a sequence on the receptor essential for Ap4A binding.

Amino Acid Sequence↗

PubMed1998

The solution structure of parsley [2Fe-2S]ferredoxin.

The [2Fe-2S]ferredoxin I (Fd I) from parsley leaves (Mr = 10,500; 96 amino acids) in the Fe(III)-Fe(III) oxidized form has been studied by 1H-NMR spectroscopy. Sequence-specific 1H-NMR assignments were obtained through two-dimensional classical double-quantum-filtered-COSY, NOESY and TOCSY spectra. NOEs between protons as close as 5.6 A from the paramagnetic Fe(III) atoms were observed at 800 MHz. A total of 3066 NOEs (of which 2533 are meaningful) and 18 distance constraints taken from X-ray crystallography of the Fe2S2 active site were used to obtain the solution structure. From inversion recovery NOESY experiments, 33 longitudinal relaxation rate (Qpara) constraints were used for the structural refinement. The final structure was obtained by a process of restrained energy minimization. Root-mean-square (rmsd) deviation values obtained for the family of 18 structures (with reference to the average structure) are 0.52 +/- 0.10 A and 0.91 +/- 0.12 A for backbone and all heavy atoms respectively. The structure consists of seven-strands of beta-sheets and four short alpha-helices. The quality of the present solution structure is among the best of those reported for [2Fe-2S]ferredoxins. The secondary structure and overall folding are compared with those of Anabaena variabilis Fd and the higher plant Equistum arvense (horse tail) protein determined through X-ray crystallography. The groups believed to be responsible for electron transfer have been analysed.

Amino Acid Sequence↗

PubMed1998

The Kaiser Permanente/USC Patient Consultation Study: change in use and cost of health care services.

The impacts of three alternative models of pharmacist consultation on the use and cost of health care services were studied. Two studies were conducted concurrently in an HMO over two years. In one, 6000 patients were randomly assigned to one of three consultation models; in the other, the three models were implemented in six geographic regions of California (4600 patients). The models were (1) consultation about new or changed prescriptions as mandated by state law (state model), (2) consultation focused on selected high-risk ambulatory care patients (Kaiser Permanente [KP] model), and (3) a control model. The patients were surveyed three times about their health status and satisfaction, and computerized data on health care use and cost were collected. The effect of the consultation models on the use and cost of health care services was examined across five risk groups that were based on drug-use profiles. An additional 37,750 patients (10% of the patients residing in the areawide study sites) were included in a supplemental analysis of the use and cost of health care services. There was no indication in the random-assignment study that pharmacist consultations affected either drug costs or the cost of office visits. Similar results were found in the areawide study, with the exception that the KP model was associated with lower drug costs than the control model. In the 10% sample, the KP model appeared to be associated with lower office visit costs but higher drug costs. Both models were associated with a lower likelihood of a hospital admission and with lower total health care costs for some high-risk patients compared with the control model. Counseling patients about their medications may be unlikely to reduce medication costs or the cost of office visits but may reduce the likelihood of hospital admissions and the overall costs of health care services; a combination of counseling patients at high risk for drug-related problems and counseling all patients about any new or changed prescription should be considered.

Adult↗

PubMed1998

[Effect of impactor sampling on the ratio of respirable dust concentration to total dust concentration].

The aim of this study was to verify the change of the ratio of Respirable Dust Concentration (RDC) to Total Dust Concentration (TDC) taken by two-stage impactor sampling. The results showed that there was a correlation between the ratio of RDC/TDC and TDC (correlation coefficient was 0.8576, 0.8689, 0.8736 and 0.9674, respectively) under the condition of identical sampling volume, and the ratio increases along with the elevated TDC.

Air Pollutants, Occupational↗

PubMed1998

Molecular structure and biological and pharmacological properties of 3-hydroxy-2-methyl-1-(beta-D-ribofuranosyl or pyranosyl)-4-pyridinone: potential iron overload drugs for oral administration.

Replacing alkyl groups by sugar moieties at N-1 position of 3-hydroxy-2-methyl-4-pyridinone did not affect the geometry of the iron chelating sites but increased the hydrophilic nature. The formation of a polymer cluster through the intermolecular hydrogen bonds was also revealed by X-ray crystal structure analysis for the first time in all known 3-hydroxy-4-pyridinone crystal structures. Iron removal from ferritin by the title compounds was more efficient than with DFO.

Administration, Oral↗

PubMed1998

Accurate and objective preoperative diagnosis of thyroid papillary carcinomas by reverse transcription-PCR detection of oncofetal fibronectin messenger RNA in fine-needle aspiration biopsies.

Recently, the restricted expression of oncofetal fibronectin mRNA was reported in thyroid papillary and anaplastic carcinomas. In this study, by extracting RNA from the leftover cells inside the needles used for fine-needle aspiration biopsy, we establish a new method for gene diagnosis of these carcinomas without further invasiveness to the patient (aspiration biopsy-reverse transcription-PCR, ABRP). RNA was extracted from 177 fine-needle aspiration biopsies of thyroid nodules that were suspicious for malignancy, and then the gene diagnoses made by reverse transciption-PCR detection of oncofetal fibronectin mRNA were compared with cytological diagnoses. Thirty-five (94.6%) of 37 samples that were diagnosed as papillary or anaplastic carcinomas by cytological examination showed a positive result by gene diagnosis, whereas only 4 (3.7%) of 109 samples that were cytologically diagnosed negative for both carcinomas showed a positive result. Among all of the cases, 50 patients underwent surgery, and a histological diagnosis was consequently made. The sensitivity and specificity of this method were 96.9 and 100%, respectively. A combined examination using both genetic and cytological approaches may contribute to a more precise preoperative diagnosis of papillary and anaplastic carcinomas.

Adolescent↗

PubMed1998

Characterization of ATP and P2 agonists binding to the cardiac plasma membrane P1,P4-diadenosine 5'-tetraphosphate receptor.

P1,P4-Diadenosine 5'-tetraphosphate (Ap4A) acts as an extracellular modulator through its interaction with purinoceptors. Our laboratory has demonstrated the presence of an Ap4A receptor in cardiac tissue [1,2]. Due to the rapid hydrolysis of ATP by cardiac membranes the relationship of ATP and Ap4A binding to purinoceptors on cardiac membranes has not been characterized. In this communication we used two approaches to determine the relationship of ATP to the Ap4A receptor. Radioligand binding carried out with [alpha-32P]Ap4A and adenosine 5'-O-¿3-thiotriphosphate¿ ([gamma-35S]ATPgammaS) demonstrates the presence of a single high affinity binding site for Ap4A and the presence of two binding sites for ATPgammaS. The second approach utilized immunoaffinity purified Ap4A receptor that was shown to be free of ATPase and Ap4Aase activities. Non-radiolabeled Ap4A and ATPgammaS effectively inhibited photocrosslinking of [alpha-32P]8-N3Ap4A to the receptor polypeptide while ATP was a much less effective inhibitor. Furthermore, on plasma membranes [alpha-32P]8-N3Ap4A photocrosslinked to only a 50 kDa polypeptide. These data are consistent with Ap4A interacting with a homogeneous population of receptors on cardiac plasma membranes but with ATP having a low affinity for the receptor.

Adenosine Triphosphate↗

PubMed1998

Inhibition of cancer cell growth by all-trans retinoic acid and its analog N-(4-hydroxyphenyl) retinamide: a possible mechanism of action via regulation of retinoid receptors expression.

In order to better understand the mechanisms that underlie the antiproliferative effect of retinoids, we have examined the response of human carcinoma cell lines to all-trans retinoic acid (RA) and N-(4-hydroxyphenyl) retinamide (4HPR) in terms of cell growth, apoptosis and regulation of retinoic acid receptors (RARs) and retinoid X receptors (RXRs) mRNA. GLC82 (lung adenocarcinoma), BGC823 (stomach adenocarcinoma) and EC109 (esophageal squamous carcinoma) cells were treated with 10 microM of RA or 4HPR for various length of time and analyzed. The results show that growth inhibition by RA and 4HPR in GLC82 and BGC823 cells correlates with the induction of RARbeta2 gene, whereas RA resistance in EC109 cells parallels loss of RARbeta2 induction. Exogenous RARbeta2 expression did not restore RA responsiveness in EC109 cells, but potentiated 4HPR-induced growth inhibition, suggesting that 4HPR acts at least in part via the RARbeta receptor. We speculate that the loss of RARbeta2 inducibility in EC109 cells may be due to an unknown repressor.

Adenocarcinoma↗

PubMed1998

Distinct mechanism for antidepressant activity by blockade of central substance P receptors.

The localization of substance P in brain regions that coordinate stress responses and receive convergent monoaminergic innervation suggested that substance P antagonists might have psychotherapeutic properties. Like clinically used antidepressant and anxiolytic drugs, substance P antagonists suppressed isolation-induced vocalizations in guinea pigs. In a placebo-controlled trial in patients with moderate to severe major depression, robust antidepressant effects of the substance P antagonist MK-869 were consistently observed. In preclinical studies, substance P antagonists did not interact with monoamine systems in the manner seen with established antidepressant drugs. These findings suggest that substance P may play an important role in psychiatric disorders.

Adolescent↗

PubMed1998

SB 211475, a metabolite of carvedilol, reduces infarct size after myocardial ischemic and reperfusion injury in rabbits.

The aim of this study was to investigate the effect of SB 211475, a metabolite of carvedilol with weak alpha1-adrenoceptor antagonism and antioxidant effect, on myocardial reperfusion injury and infarct size in anesthetized rabbits. The rabbits were subjected to 60 min of regional myocardial ischemia and 180 min of reperfusion. SB 211475 was administered either as 0.3, 1.0 or 3.0 mg/kg and compared to vehicle and carvedilol (1 mg/kg) treated animals. The lowest dose of SB 211475 (0.3 mg/kg) did not reduce infarct size compared to vehicle, whereas SB 211475 1.0 or 3.0 mg/kg reduced infarct size significantly compared to vehicle (41.2 +/- 2.2% and 40.5 +/- 2.8% vs. 59.1 +/- 3.9%, p < 0.05). Carvedilol reduced infarct size significantly more than SB 211475 1.0 and 3.0 mg/kg (28.8 +/- 3.9% vs. 41.2 +/- 2.2% and 40.5 +/- 2.7%, p < 0.05). Carvedilol and SB 211475 1.0 and 3.0 mg/kg reduced myeloperoxidase activity to the same extent, indicative of reduced inflammation. Rate-pressure product did not differ between doses of SB 211475. In conclusion, SB 211475 in the two highest doses reduced infarct size by protecting from reperfusion injury, possibly by reduced neutrophil accumulation. The superior cardiac protective effect of carvedilol over SB 211475 are most likely due to its adrenergic pharmacology including non-selective beta- and alpha1-adrenoceptor antagonism.

Adrenergic alpha-Antagonists↗

PubMed1998

IFN-gamma inhibits activation-induced expression of E- and P-selectin on endothelial cells.

E- and P-selectin are cell surface lectins that mediate leukocyte-endothelial cell adhesion and thereby participate in neutrophil recruitment into inflammatory sites. E-selectin can be induced on endothelial cells by various activators, including TNF-alpha, IL-1beta, and PMA. Induction of E-selectin is blocked by pretreatment of endothelial cells with IL-4 or TGF-beta, both of which have antiinflammatory properties in vivo. In addition to its well-known proinflammatory activities, IFN-gamma also has antiinflammatory effects in vivo, one of which is inhibition of neutrophil recruitment. To determine whether IFN-gamma inhibits neutrophil recruitment by inhibiting adhesion molecule expression, the effect of IFN-gamma on activation-induced cell adhesion molecule expression by cultured HUVEC was evaluated. Pretreatment of endothelial cells with IFN-gamma for 24 to 72 h before 6- to 24-h activation with IL-1beta, TNF-alpha, or PMA resulted in significantly reduced levels of cell surface E-selectin, although levels of ICAM-1 and VCAM-1 were the same or increased. The reduction of cell surface E-selectin levels under these conditions was reflected in reduced levels of E-selectin mRNA, indicating an effect at the transcription level or RNA stability. Interestingly, the increase of cell surface P-selectin expression due to IL-4 treatment of HUVEC was also inhibited by IFN-gamma, while constitutive levels of P-selectin were not. These results suggest that the inhibition of neutrophil recruitment by IFN-gamma in vivo may be due, in part, to the ability of IFN-gamma to inhibit E- and P-selectin up-regulation. Furthermore, these findings emphasize the process of leukocyte recruitment as an important step through which IFN-gamma can direct the character of inflammatory reactions.

Cell Adhesion↗

PubMed1998

A peptidoglycan recognition protein in innate immunity conserved from insects to humans.

Innate nonself recognition must rely on common structures of invading microbes. In a differential display screen for up-regulated immune genes in the moth Trichoplusia ni we have found mechanisms for recognition of bacterial cell wall fragments. One bacteria-induced gene encodes a protein that, after expression in the baculovirus system, was shown to be a peptidoglycan recognition protein (PGRP). It binds strongly to Gram-positive bacteria. We have also cloned the corresponding cDNA from mouse and human and shown this gene to be expressed in a variety of organs, notably organs of the immune system-i.e., bone marrow and spleen. In addition, purified recombinant murine PGRP was shown to possess peptidoglycan affinity. From our results and the sequence homology, we conclude that PGRP is a ubiquitous protein involved in innate immunity, conserved from insects to humans.

Amino Acid Sequence↗

PubMed1998

Pyrrolidine-3-carboxylic acids as endothelin antagonists. 3. Discovery of a potent, 2-nonaryl, highly selective ETA antagonist (A-216546).

Previously we have reported the discovery of ABT-627 (1, A-147627, active enantiomer of A-127722), a 2,4-diaryl substituted pyrrolidine-3-carboxylic acid based endothelin receptor-A antagonist. This compound binds to the ETA receptor with an affinity (Ki) of 0. 034 nM and with a 2000-fold selectivity for the ETA receptor versus the ETB receptor. We have expanded our structure-activity studies in this series, in an attempt to further increase the ETA selectivity. When the p-anisyl group of 1 was replaced by an n-pentyl group, the resultant antagonist 3 exhibited substantially increased ETB/ETA activity ratio, but a decreased ETA affinity. Structure-activity studies revealed that substitution and geometry of this alkyl group, and substitution on the benzodioxolyl ring, are important in optimizing this series of highly ETA selective antagonists. In particular, the combination of a (E)-2,2-dimethyl-3-pentenyl group and a 7-methoxy-1,3-benzodioxol-5-yl group provided hydrophobic compound 10b with subnanomolar affinity for human ETA receptor subtype and with an ETB/ETA activity ratio of over 130000. Meanwhile, synthetic efforts en route to olefinic compounds led to the discovery that 2-pyridylethyl (9o) and 2-(2-oxopyrrolidinyl)ethyl (9u) replacement of the p-anisyl group of 1yielded very hydrophilic ETA antagonists with potency and selectivity equal to those of 10b. On the basis of overall superior affinity, high selectivity for the ETA receptor (Ki, 0.46 nM for ETA and 13000 nM for ETB), and good oral bioavailability (48% in rats), A-216546 (10a) was selected as a potential clinical backup for 1.

Administration, Oral↗

PubMed1998

PACS-1 defines a novel gene family of cytosolic sorting proteins required for trans-Golgi network localization.

We report the role of one member of a novel gene family, PACS-1, in the localization of trans-Golgi network (TGN) membrane proteins. PACS-1 directs the TGN localization of furin by binding to the protease's phosphorylated cytosolic domain. Antisense studies show TGN localization of furin and mannose-6-phosphate receptor, but not TGN46, is strictly dependent on PACS-1. Analyses in vitro and in vivo show PACS-1 has properties of a coat protein and connects furin to components of the clathrin-sorting machinery. Cell-free assays indicate TGN localization of furin is directed by a PACS-1-mediated retrieval step. Together, these findings explain a mechanism by which membrane proteins in mammalian cells are localized to the TGN.

Adaptor Protein Complex alpha Subunits↗

PubMed1998

alpha1-Antitrypsin Portland, a bioengineered serpin highly selective for furin: application as an antipathogenic agent.

The important role of furin in the proteolytic activation of many pathogenic molecules has made this endoprotease a target for the development of potent and selective antiproteolytic agents. Here, we demonstrate the utility of the protein-based inhibitor alpha1-antitrypsin Portland (alpha1-PDX) as an antipathogenic agent that can be used prophylactically to block furin-dependent cell killing by Pseudomonas exotoxin A. Biochemical analysis of the specificity of a bacterially expressed His- and FLAG-tagged alpha1-PDX (alpha1-PDX/hf) revealed the selectivity of the alpha1-PDX/hf reactive site loop for furin (Ki, 600 pM) but not for other proprotein convertase family members or other unrelated endoproteases. Kinetic studies show that alpha1-PDX/hf inhibits furin by a slow tight-binding mechanism characteristic of serpin molecules and functions as a suicide substrate inhibitor. Once bound to furin's active site, alpha1-PDX/hf partitions with equal probability to undergo proteolysis by furin at the C-terminal side of the reactive center -Arg355-Ile-Pro-Arg358- downward arrow or to form a kinetically trapped SDS-stable complex with the enzyme. This partitioning between the complex-forming and proteolytic pathways contributes to the ability of alpha1-PDX/hf to differentially inhibit members of the proprotein convertase family. Finally, we propose a structural model of the alpha1-PDX-reactive site loop that explains the high degree of enzyme selectivity of this serpin and which can be used to generate small molecule furin inhibitors.

ADP Ribose Transferases↗

PubMed1998

Effects of resazurin on bovine oocyte fertilization and embryo development in vitro.

Resazurin is a redox dye (7-hydroxy-3H-phenoxazin-3-one-10-oxide) used for assessing potential fertility of spermatozoa and functional status of eukaryotic cells. In this study, the fertilizing capacity of spermatozoa treated with resazurin and effects of resazurin on bovine embryo development in vitro was examined. Abattoir-derived bovine oocytes were collected and subjected to in vitro maturation (IVM), fertilization (IVF) and culture (IVC). In Experiment 1, bovine oocytes (n = 2767) were fertilized with spermatozoa exposed to resazurin (17.6 micrograms/ml) for 0, 15, 30, 60 min, respectively. There was no significant (P > 0.05) difference in cleavage rates. However, the proportion of embryos that developed into blastocysts, expanded and hatched blastocysts in those groups in which oocytes/embryos were treated with resazurin during IVC or IVM/IVF/IVC was significantly (P < 0.05) less than those exposed to resazurin during IVM only, or during IVF only. We conclude that resazurin did not have significant adverse effects on fertilizing capability of bovine spermatozoa; however, extended treatment of embryos with resazurin may be detrimental to embryonic development.

Animals↗

PubMed1998

[A FISH technique for simultaneous detection of fluorescent R-band and in situ hybridization signals].

OBJECTIVE: To develop a simple method for detecting DNA probes directly on R-banded chromosomes. METHODS: After sixty-seven hours culture, human peripheral blood lymphocytes were synchronized for 5 to 6 hours by adding Hoechst 33258 and BUdR, and then arrested by standard cytogenetic procedures. The slides were mounted with 2 x SSC and exposed with a 20W UV light which was about 10cm above the slides for 20 min at 75 degrees C. The biotinylated probes, such as the cosmid and YAC clones on 5p specific region and pBamX7, were hybridized on to the slides. After washing, the slides were treated with avidin-FITC and amplified with additional layer of biotinylated anti-avidin and avidin-FITC, and counterstained with propidium iodide in an antifade solution. Fluorescent signals and R-bands were observed simultaneously under Olympus BX 60 fluorescence microscope equipped with a WIB filter. RESULTS: The chromosomal location of the greenish-yellow signals could be directly identified on the R-banded chromosome background. CONCLUSION: This method can serve as a rapid and precise system for chromosomal localization of DNA markers.

Chromosome Banding↗