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Biomedical subjects

N Liu

Publications and source records attributed to N Liu.

At least 181 records · Page 10Linked to original sources
PubMed1997

[Comparative molecular field analysis (CoMFA) of allylamine antimycotics].

Active analog approach has been applied to determine the pharmacophoric conformations of the allylamine antimycotics. Comparative molecular field analysis (CoMFA) has been used to establish 3D-QSAR of 48 allylamine antimycotics against six common human pathogenic fungi. Two different alignment rules were compared in the meantime. Five new synthetic compounds have been successfully employed to examine the predictive abilities of the CoMFA models against Trichophyton mentagrophytes and Aspergillus fumigatus.

Allylamine↗
PubMed1997

Angiogenesis correlates with vascular endothelial growth factor expression but not with Ki-ras oncogene activation in non-small cell lung carcinoma.

A total of 195 non-small cell lung carcinoma (NSCLC) specimens were studied for the presence of mutations in their ras family genes, for tumor vascularity, and for their immunostaining pattern with an antibody to vascular endothelial growth factor (VEGF). ras mutation was found in 37 of 104 (34.6%) adenocarcinoma specimens, in 0 of 64 squamous cell carcinomas, and in 2 of 27 (7.4%) large cell undifferentiated carcinomas. All mutations were found on the Ki-ras gene, with 37 (95%) of them on codon 12 and the remaining 2 on codon 13. Thirty (77%) of the mutations were G to T transversions. There was a correlation between increasing tumor vascularity and VEGF immunostaining score, but there was no correlation between either of them with the activation of the ras oncogene. A study of VEGF mRNA expression in 14 NSCLC cell lines also demonstrated a lack of correlation between the constitutive expression levels of VEGF and the presence or absence of ras mutation in these cell lines. The results suggest that VEGF is a major angiogenesis factor in NSCLC but that other factors beside ras mutations may influence tumor vascularity in these tumors. The two parameters may potentially serve as independent prognostic factors in NSCLC.

Alleles↗
PubMed1996

Cell death in the Schwann cell lineage and its regulation by neuregulin.

The development of Schwann cells, the myelin-forming glial cells of the vertebrate peripheral nervous system, involves a neonatal phase of proliferation in which cells migrate along and segregate newly formed axons. Withdrawal from the cell cycle, around postnatal days 2-4 in rodents, initiates terminal differentiation to the myelinating state. During this time, Schwann cell number is subject to stringent regulation such that within the first postnatal week, axons and myelinating Schwann cells attain the one-to-one relationship characteristic of the mature nerve. The mechanisms that underly this developmental control remain largely undefined. In this report, we examine the role of apoptosis in the determination of postnatal Schwann cell number. We find that Schwann cells isolated from postnatal day 3 rat sciatic nerve undergo apoptosis in vitro upon serum withdrawal and that Schwann cell death can be prevented by beta forms of neuregulin (NRG-beta) but not by fibroblast growth factor 2 or platelet-derived growth factors AA and BB. This NRG-beta-mediated Schwann cell survival is apparently transduced through an ErbB2/ErbB3 receptor heterodimer. We also provide evidence that postnatal Schwann cells undergo developmentally regulated apoptosis in vivo. Together with other recent findings, these results suggest that Schwann cell apoptosis may play an important role in peripheral nerve development and that Schwann cell survival may be regulated by access to axonally derived NRG.

Animals↗
PubMed1996

A CHO mutant, UV40, that is sensitive to diverse mutagens and represents a new complementation group of mitomycin C sensitivity.

A new mitomycin C (MMC)-sensitive rodent line, UV40, has been identified in the collection of ultraviolet light- (UV-) sensitive mutants of Chinese hamster ovary (CHO) cells isolated at the previous Facility for Automated Experiments in Cell Biology (FAECB). It was isolated from an UV mutant hunt using mutagenesis of AA8 cells with the DNA intercalating frameshift mutagen ICR170. It is complemented by CHO-UV-1, irsl, irs3, irslSF, MC5, V-C8 and V-H4 with respect to its MMC sensitivity based on cell survival. Despite having approx. 4 X normal UV sensitivity and increased sensitivity to UV inhibition of DNA replication, it has near-normal incision kinetics of UV irradiated DNA, and normal (6-4) photoproducts removal. It also is not hypermutable by UV, and shows near normal levels of UV inhibition of RNA synthesis. UV40 also has approx. 11 x .10 x .5 x and 2 x AA8 sensitivity to MMC, ethyl methanesulfonate (EMS), methyl methanesulfonate (MMS), and X-rays, respectively. Thus, its defect apparently does not involve nucleotide excision repair but rather another process, possibly in replicating past lesions. The spontaneous chromosomal aberration frequency is elevated to 20% in UV40, and the baseline frequency of sister chromatid exchange is also approximately 4-fold increased. The phenotype of UV40 appears to differ from all other rodent mutants that have so far been described.

Adenine↗
PubMed1996

Cell cycle-regulated repression of B-myb transcription: cooperation of an E2F site with a contiguous corepressor element.

B-myb belongs to a group of cell cycle genes whose transcription is repressed in G0/early G1 through a binding site for the transcription factor E2F. Here, we show that the B-myb repressor element is specifically recognised by heterodimers consisting of DP-1 and E2F-1, E2F-3 or E2F-4. Surprisingly, E2F-mediated repression is dependent on a contiguous corepressor element that resembles the CHR previously established as a corepressor of the CDE in cell cycle genes derepressed in S/G2, such as cyclin A, cdc2 and cdc25C. A factor binding to the B-myb CHR was identified in fractionated HeLa nuclear extract and found to interact with the minor groove, as previously shown by in vivo footprinting for the cyclin A CHR. The B-myb and cdc25C CHRs are related with respect to protein binding but are functionally clearly distinct. Our results support a model where both E2F- and CDE-mediated repression, acting at different stages in the cell cycle, are dependent on promoter-specific CHR elements.

3T3 Cells↗
PubMed1996

Cell cycle regulation of E2F site occupation in vivo.

DNA-binding E2F complexes have been identified throughout the mammalian cell cycle, including the transcriptionally inactive complexes with pocket proteins, which occur early in the prereplicative G1 phase of the cycle, and the transactivating free E2F, which increases in late G1. Here, a regulatory B-myb promoter site was shown to bind with high affinity to free E2F and to E2F-pocket protein complexes in an indistinguishable way in vitro. In contrast, in vivo footprinting with NIH 3T3 cells demonstrated E2F site occupation specifically in early G1, when the B-myb promoter is inactive. These observations indicate that a novel mechanism governs E2F-DNA interactions during the cell cycle and emphasize the relevance of E2F site-directed transcriptional repression.

3T3 Cells↗
PubMed1996

Transformation of NIH 3T3 cells by HER3 or HER4 receptors requires the presence of HER1 or HER2.

Members of the epidermal growth factor receptor (EGFR) subfamily of receptor protein tyrosine kinases have been implicated in the pathogenesis of various malignancies. The ability of one EGFR subfamily member to influence, or function synergistically with, another is likely to be a general feature of these receptors. To assess the role of receptor heterodimerization, we analyzed the ability of Neu differentiation factor (NDF) to induce cell growth and transformation of NIH 3T3 cells transfected with different combinations of the EGFR subfamily of receptors. NDF induced mitogenesis, but not transformation, of cells expressing either HER3 or HER4 alone. However, NDF-induced cell transformation was observed when either HER1 or HER2 was coexpressed with HER3 or HER4. In analogous receptor phosphorylation experiments, NDF-induced transphosphorylation appears to be correlated with synergistic transformation of NIH 3T3 cells. Interestingly, transphosphorylation between HER1 and HER4 can be stimulated by either EGF or NDF.

3T3 Cells↗
PubMed1996

A new phospholipase C delta 4 is induced at S-phase of the cell cycle and appears in the nucleus.

To discover a new phospholipase C (PLC) related to cell growth, we screened a cDNA library prepared from regenerating rat liver. A novel PLC (PLC delta 4) encoding a polypeptide of 770 amino acids with structural similarity to PLC delta-type isozymes was isolated. PLC delta 4 mRNA is expressed more remarkably in regenerating liver than in normal resting liver. It is also distributed abundantly in tumor cells such as hepatoma and src-transformed cells. Furthermore, its expression can be induced markedly by serum treatment and reaches a maximum at 8 h. Western blot analysis and immunocytochemical staining showed that PLC delta 4 is dominantly present in nucleus. Nuclear PLC delta 4 dramatically increases at the transition from G1- to S-phase, and the high content continues to the end of M-phase. PLC delta 4 almost disappears when cells re-enter the next G1-phase. On the other hand, the contents of PLC beta 1, PLC gamma 1, and PLC delta 1 do not change significantly during the cell cycle. These results suggest that PLC delta 4 is expressed in nucleus in response to mitogenic stimulation and plays important roles in cell growth as one of the early genes expressed during the transition from G1- to S-phase in the cell cycle.

3T3 Cells↗
PubMed1996

Isolation and structural characterization of recombinant human neu differentiation factor expressed in Escherichia coli.

Recombinant human neu differentiation factor produced in engineered E. coli was isolated and subject to structural characterization. The recombinant molecule can be prepared to apparent purity and is active in stimulating receptor tyrosine autophosphorylation in cultural cells expressing HER2 receptor. The 229 amino-acid polypeptide consists of eight cysteines, of which two cysteines near the N-terminus are disulfide-bonded to form an immunoglobulin-like domain and the remaining six cysteines at the C-terminus cross-link to form an epidermal growth factor-like structure. Detailed chemical characterization of the recombinant molecule by peptide mapping in conjunction with Edman sequencing and mass spectrometry reveals that the bacterially produced recombinant neu differentiation factor preparation is properly folded and contains the correct disulfide structure. The peptide mapping procedure is also useful in identifying abnormal peptides derived from deamidation and oxidation of Asn and Met residues, respectively.

Amino Acid Sequence↗
PubMed1996

NDF induces expression of a novel 46 kD protein in estrogen receptor positive breast cancer cells.

Most human breast tumors start as estrogen-dependent, but during the course of the disease become refractory to hormone therapy. The transition of breast tumors from estrogen dependent to independent behavior may be regulated by autocrine and/or paracrine growth factor(s) that are independent of the estrogen receptor (ER). We have investigated the role(s) of NDF (neu-differentiation factor) in the biology of estrogen positive breast cancer cells by using MCF-7 cells as a model system. Treatment of MCF-7 cells with human recombinant NDF-beta 2 (NDF) inhibited the ER expression by 70% and this was associated with growth stimulation in an estrogen-independent manner. To explore the mechanism(s) of action of NDF in MCF-7 cells, we examined the expression of NDF-inducible gene products. We report here that NDF stimulated the levels of expression of a 46 kD protein (p46) (in addition to few minor proteins) in ER positive breast cancer cells including MCF-7, T-47-D, and ZR-75-R cells but not in ER negative breast cancer cells including MDA-231, SK-BR-3, and MDA-468 cells. This effect of NDF was due to induction in the rate of synthesis of new p46. The observed NDF-mediated induction of p46 expression was specific as there was no such effect by epidermal growth factor or 17-beta-estradiol, and inclusion of actinomycin D partially inhibited the p46 induction elicited by NDF. NDF-inducible stimulation of p46 expression was an early event (2-6 h) which preceded the period of down-regulation of ER expression by NDF. These results support the existence of NDF-responsive specific cellular pathway(s) that may regulate ER, and these interactions could play a role(s) in hormone-independence of ER positive breast cancer cells.

Gene Expression Regulation, Neoplastic↗
PubMed1996

Adult specific expression and induction of cytochrome P450lpr in house flies.

Cytochrome P450lpr is a xenobiotic metabolizing P450 that is found in house flies (Musca domestica). To better understand the regulation of cytochrome P450lpr, the effects of 21 potential monooxygenase inducers were examined for their ability to induce total cytochromes P450 and cytochrome P450lpr levels in adult flies. Six compounds caused induction of total cytochromes P450 per mg protein in adult susceptible (CS) house flies: ethanol (1.6-fold), phenobarbital in food (1.5-fold) or water (1.5-fold), naphthalene (1.3-fold), DDT (1.3-fold), xanthotoxin (1.4-fold), and alpha-pinene (1.2-fold). Six compounds were found to be inducers of cytochrome P450lpr: piperonyl butoxide in food (1.9-fold), phenobarbital in food (1.4-fold) and water (3.4-fold), clofibrate (1.3-fold), xanthotoxin (1.3-fold), methohexital (1.3-fold), and isosafrole (1.3-fold). Comparison of our results with house fly P450 6A1 indicates that there are specific inducers for each of these individual P450s as well as compounds that induce both P450s. Total P450s were inducible by PB in CS house fly larvae, but not in LPR larvae. Immunoblotting revealed no detectable P450lpr in control or PB-treated larvae in either strain. Thus, although total P450s are inducible in the susceptible strain larvae, P450lpr does not appear to be normally present or inducible with PB in larvae of either strain. Northern blots of phenobarbital (in water) treated CS flies indicated that there was a 4.2-fold increase in the P450lpr (i.e., CYP6D1) mRNA levels over the untreated flies. In the multiresistant LPR strain there was no apparent induction of CYP6D1 mRNA by phenobarbital. Following phenobarbital induction, the level of CYP6D1 mRNA in the CS strain was about half of the level in the LPR strain.

Animals↗
PubMed1996

Genetic analysis of factors controlling high-level expression of cytochrome P450, CYP6D1, cytochrome b5, P450 reductase, and monooxygenase activities in LPR house flies, Musca domestica.

To understand better the biochemical genetics of cytochrome P450 monooxygenase-mediated insecticide resistance, we examined the microsomal monooxygenases in insecticide-susceptible (aabys) and pyrethroid-resistant (LPR) house fly strains, as well as 15 house fly lines derived from crosses of LPR and aabys. In comparison to the aabys strain, LPR had higher levels of total cytochromes P450, cytochrome b5, P450 reductase, CYP6D1, and three P450 monooxygenase activities: 7-ethoxycoumarin O-deethylase (ECOD), methoxyresorufin O-demethylase (MROD), and aromatic hydrocarbon hydroxylase (AHH). The elevated levels of cytochrome b5 were linked to factors on autosomes 1 and 2. This is similar to previous reports on monooxygenase-mediated resistance and is consistent with the idea that elevated cytochrome b5 levels are involved in monooxygenase-mediated resistance in the LPR strain. Linkage of the elevated P450 reductase is different from that of monooxygenase-mediated resistance. Strains having high levels of CYP6D1 (i.e., like LPR) had high levels of P450 reductase, while strains having intermediate levels of CYP6D1 also had high levels of reductase. Therefore, there is no clear evidence that the elevated P450 reductase in the LPR strain is required for the increased monooxygenase activity. Overexpression of total cytochromes P450, CYP6D1 (mRNA and protein), and CYP6D1-mediated monooxygenase activities (MROD and AHH) in LPR microsomes was linked to a combination of factors on autosomes 1 and 2. This demonstrates that increased expression of CYP6D1 in the LPR strain is both cis regulated by a factor(s) on autosome 1 and trans regulated by a factor(s) on autosome 2. The correlation between the overexpression of CYP6D1 mRNA and protein suggests that CYP6D1 expression is regulated transcriptionally. Monooxygenase-mediated resistance in LPR is controlled by factors on autosomes 1 and 2, which supports previous claims that CYP6D1 is responsible for monooxygenase-mediated resistance in the LPR strain.

Animals↗
PubMed1996

The Ca2+/calmodulin-dependent protein kinase II-associated protein complex isolated from chicken retina.

Retinal cytosolic Ca2+/calmodulin-dependent protein kinase II (CaM KII) was isolated from hatched 6-wk chicken retinae by ultracentrifugation and affinity chromatography using calmodulin (CaM) and anti-CaM KII-alpha columns. Samples from different fractions were examined with SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining or immunoblotting. Comparisons were made between the final antibody affinity eluates from retina and forebrain. Silver-stained gels showed that multiple proteins were present in the antibody affinity eluates from retina, including major proteins of 178, 56, and 45 kDa and several minor proteins. Immunoblots revealed that CaM KII-alpha was present in eluates from the retina and forebrain. CaM KII-beta was present in the antibody eluate from forebrain but not retina. The latter subunit was present in the crude homogenates of the retina. Regarding the antibody eluate from retina, the possibility that the major 56 kDa protein was tubulin was ruled out, but protein tau (tau) and synapsin I were present. The presence of multiple proteins in the antibody affinity eluate indicates that these proteins were coisolated in a CaM KII-alpha-associated protein complex. The finding that protein tau and synapsin I are associated with retinal CaM KII provides further insight into the mechanisms underlying the function of the kinase in this tissue. The lack of cytosolic CaM KII-beta subunit in the antibody affinity eluate from retina is indicative of a brain region-specificity in subunit composition of the kinase.

Animals↗
PubMed1996

Toxic levels of selenium in enzymes and selenium uptake in tissues of a marine fish.

Acute toxicity of selenium as selenite in Zosterisessor ophiocephalus by ip injection was studied. The 50% lethal dose and 50% lethal time were measured to be 0.29 ppm and 96 h, respectively. Se concentrations in liver, gill, skin and muscle, and Cyt. P450 level, Se-GPx, and Total GPx enzyme activities in liver were also assessed at different doses and times after injection. Starting at 0.3 ppm injected dose, enzyme activities and Se concentration in tissues, but not in muscle, showed significant differences from the control group. A threshold behavior was inferred. Normal conditions of enzyme activities and Se concentration in tissues were restored about 1 wk after injection. Biological elimination half-lives were about 2 d for liver and gill, and 5 d for skin.

Animals↗
PubMed1996

Comparison between radionuclide ejection fraction and fractional area changes derived from transesophageal echocardiography using automated border detection.

BACKGROUND: Left ventricular fractional area changes (FAC) can be derived from transesophageal echocardiography using an automated border detection system. However, FAC has not yet been compared to left ventricular ejection fraction (EF) evaluated by a reference technique. The aim of this study was to correlate transesophageal echocardiography automated FAC to EF derived from radionuclide angiography to obtain a quantifying method of global left ventricular systolic function at the bedside. METHODS: Ten critically ill patients, whose lungs were mechanically ventilated, were included in this prospective study. Patients were scheduled for radionuclide EF evaluation when at least 75% of the endocardium was clearly visualized on transesophageal echocardiography. Patients with esophageal pathology or cardiac dysrhythmia were excluded. Ejection fraction derived from radionuclide angiography was measured using technetium 99m. Echocardiographic data were obtained using an ultrasound system with automated border capabilities. Simultaneous measurements of left ventricular EF and FAC were obtained for each patient, both before and after starting a dobutamine intravenous infusion to modify left ventricular contractility. RESULTS: Mean values for radionuclide EF and transesophageal echocardiography FAC were, respectively: 55% +/- 19% (range 19-89%) and 46% +/- 18% (range 17-80%). Left ventricular EF and FAC were significantly correlated (r = 0.85, SEE = 9.6%). Variations of EF and FAC, induced by dobutamine, were also correlated (r = 0.70, SEE = 4.9%). CONCLUSIONS: Fractional area changes determined by transesophageal echocardiography using automated border detection correlate well with radionuclide EF and may be used at the bedside to quantify left ventricular function in selected intensive care unit patients.

Echocardiography, Transesophageal↗
PubMed1996

Statistical analysis of real-time, environmental radon monitoring results at the Fernald Environmental Management Project.

A comprehensive real-time, environmental radon monitoring program is being conducted at the Fernald Environmental Management Project, where a large quantity of radium-bearing residues have been stored in two covered earth-bermed silos. Statistical analyses of radon measurement results were conducted to determine what impact, if any, radon emitted by the radium bearing materials contained in the silos has on the ambient radon concentration at the Fernald Environmental Management Project site. The distribution that best describes the outdoor radon monitoring data was determined before statistical analyses were conducted. Random effects associated with the selection of radon monitoring locations were accommodated by using nested and nested factorial classification models. The Fernald Environmental Management Project site was divided into four general areas according to their characteristics and functions: 1) the silo area, where the radium-bearing waste is stored; 2) the production/administration area; 3) the perimeter area, or fence-line, of the Fernald Environmental Management Project site; and 4) a background area, located approximately 13 km from the Fernald Environmental Management Project site, representing the naturally-occurring radon concentration. A total of 15 continuous, hourly readout radon monitors were installed in these 4 areas to measure the outdoor radon concentration. Measurement results from each individual monitor were found to be log-normally distributed. A series of contrast tests, which take random effects into account, were performed to compare the radon concentration between different areas of the site. These comparisons demonstrate that the radon concentrations in the production/administration area and the perimeter area are statistically equal to the natural background, whereas the silo area is significantly higher than background. The study also showed that the radon concentration in the silo area was significantly reduced after a sealant barrier was applied to the contents of the silos.

Environmental Monitoring↗
PubMed1996

Na-K-ATPase in lacrimal gland acinar cell endosomal system: correcting a case of mistaken identity.

Na-K-ATPase is associated with a variety of membrane populations in lacrimal acinar cells. Acinus-like structures formed by rabbit acinar cells in primary culture were incubated with horseradish peroxidase (HRP) to label basolateral and endosomal membranes and then analyzed by electron microscopy cytochemistry with the 3-3'-diaminobenzidine reaction or by fractionation and measurement of marker catalytic activities or immunoreactivities. HRP adsorbed to basolateral membranes at 4 degrees C. Fractionation showed it associated with low-density membranes enriched in acid phosphatase and TGN38 but containing only minor amounts of Na-K-ATPase. Cells internalized HRP to cytoplasmic vesicles, Golgi structures, and lysosomes at 37 degrees C. The major endosomal compartment revealed by fractionation coincided with major peaks of Na-K-ATPase and Rab6 and secondary peaks of galactosyltransferase and gamma-adaptin. Carbachol (10 microM) increased lysosomal and Golgi labeling. Thus most of the Na-K-ATPase is located in the basolateral membrane-oriented endosomal system, concentrated in a compartment possibly related to the trans-Golgi network. Constitutive and stimulation-accelerated traffic to and from this compartment may serve several exocrine cell functions.

Animals↗