Biomedical subjects

C Liu

Publications and source records attributed to C Liu.

At least 217 records · Page 12Linked to original sources

PubMed2001

[Spectra of cyanine dye in reversed micelle].

The spectral properties of a cyanine dye were studied in different systems, especially in the reversed micelles, a system for water in oil. Due to the space limitation and electrostatic effect of the water cell in reversed micelles, the optical behavior of the dye in reversed micelles was very different from in water and alcohol. The effect of alcohol content, omega (omega = [water]/[surfactant]) and temperature on absorption and fluorescence spectra in these systems were studied. In reversed micelle the dye showed characteristics of two monomolecular states, the balance between which could be affected by all factors investigated above.

Carbocyanines↗

PubMed2001

[The Raman vibrational characteristics and assignments of three Schiff bases].

The Raman vibrational characteristics of three asymmetric Schiff bases were studied in this paper. By referring to the characteristic Raman spectra of substituent benzene and oxamidoxime compounds, the Raman vibrational modes of three Schiff bases were analyzed and assigned, respectively. The difference of their Raman spectra mainly arises from their different vibrational energy level resulting from the C-OH group to most extents. This result is of importance for further investigating the properties of these three new-type Schiff bases.

Benzene↗

PubMed2001

[Determination of ofloxacin in urine by synchronous-derivative fluorimetry].

The internal hormones in human urine emit strong fluorescence and interfere with the determination of trace ofloxacin. However, the experiments indicate that synchronous-first order derivative fluorimetry can be applied to the determination of trace ofloxacin without interference. The linear range is 0.36-3.6 micrograms.mL-1, detection limit is 0.3 microgram.mL-1, RSD is less than 2.5% and the recovery is within the range of 101%-103%.

Humans↗

PubMed2001

[Targeted killing effect of mucin-1 single chain antibody targeting, lentivirus-mediated suicide gene therapy and ganciclovir in mucin-1+ ovarian epithelial carcinoma cells].

OBJECTIVE: To investigate the targeted killing effect of mucin-1 single chain antibody targeting, lentivirus-mediated suicide gene therapy and ganciclovir(GCV) in mucin-1+ ovarian epithelial carcinoma cells. METHODS: Mucin-1 single chain antibody targeting lentivirus produced by packaging cell line 293T transduced herpes simplex virus thymidine kinase (HSV-tk) gene into the ovarian epithelial cancer cell line SKOV3 (MUC1+). The infection effect was observed through fluorescence microscopy. Polymerase chain reaction (PCR) and reverse transcription-PCR (RT-PCR) were resorted to demonstrate the successful transduction and transcription of the HSV-tk gene. After administration of GCV, changes of those cells were observed through optical microscopy. The cytotoxicity efficacy of HSV-tk/GCV system was evaluated by methyl thiazolyl tetrazolium method. RESULTS: It was observed through fluorescence microscopy that anti-MUC1 directed lentivirus can specificly infect MUC1+ ovarian cancer cells. A fragment of 600 bp was generated through PCR and RT-PCR which indicated successful transduction and transcription of the HSV-tk gene in SKOV3 cells. Changes of cells followed by administration of GCV were observed with optical microscopy. Significant cytotoxicity efficacy of GCV to SKOV3 was observed. CONCLUSIONS: The HSV-tk gene can be targetedly transducted into MUC1+ ovarian cancer cell line under the mediation of anti-MUC1 directed lentivirus, and such HSV-tk/GCV system has targetingly killing effect on MUC1+ cancer cells.

Antibodies, Viral↗

PubMed2000

Erythropoietin stimulates proliferation and interferes with differentiation of myoblasts.

Erythropoietin (Epo) is required for the production of mature red blood cells. The requirement for Epo and its receptor (EpoR) for normal heart development and the response of vascular endothelium and cells of neural origin to Epo provide evidence that the function of Epo as a growth factor or cytokine to protect cells from apoptosis extends beyond the hematopoietic lineage. We now report that the EpoR is expressed on myoblasts and can mediate a biological response of these cells to treatment with Epo. Primary murine satellite cells and myoblast C2C12 cells, both of which express endogenous EpoR, exhibit a proliferative response to Epo and a marked decrease in terminal differentiation to form myotubes. We also observed that Epo stimulation activates Jak2/Stat5 signal transduction and increases cytoplasmic calcium, which is dependent on tyrosine phosphorylation. In erythroid progenitor cells, Epo stimulates induction of transcription factor GATA-1 and EpoR; in C2C12 cells, GATA-3 and EpoR expression are induced. The decrease in differentiation of C2C12 cells is concomitant with an increase in Myf-5 and MyoD expression and inhibition of myogenin induction during differentiation, altering the pattern of expression of the MyoD family of transcription factors during muscle differentiation. These data suggest that, rather than acting in an instructive or specific mode for differentiation, Epo can stimulate proliferation of myoblasts to expand the progenitor population during differentiation and may have a potential role in muscle development or repair.

Animals↗

PubMed2000

Non-gridded library: a new approach for BAC (bacterial artificial chromosome) exploitation in hexaploid wheat (Triticum aestivum).

The feasibility of exploiting non-gridded bacterial artificial chromosome (BAC) libraries and some major factors affecting the efficiency of handling such libraries were studied in hexaploid wheat. Even for a bacterial culture containing only 55% recombinants, some 2000 BAC clones with inserts ranging from 45 to 245 kb could be pooled. The pooled BAC clones could be amplified by culturing for up to 6 h without losing any target clones. These results imply that even for hexaploid wheat, which has an extremely large genome, some 250 pools are sufficient for a BAC library that should satisfy many research objectives. This non-gridded strategy would dramatically reduce the cost and make robotic equipment non-essential in exploiting BAC technology. To construct a representative library and to minimise clone competition, thawing and re-freezing ligation mixtures and bacterial cultures should be avoided in BAC library construction and application.

Blotting, Southern↗

PubMed2000

Benefits of glatiramer acetate on disability in relapsing-remitting multiple sclerosis. An analysis by area under disability/time curves. The Copolymer 1 Multiple Sclerosis Study Group.

New immunomodulatory therapies for relapsing-remitting multiple sclerosis (RRMS) have well-documented effects in reducing relapses, but it has been difficult to demonstrate their benefits on disability in relatively short treatment trials. Commonly utilised disability outcome measures are problematic both in usefulness and clinical interpretation when applied to MS subjects with fluctuating and variable disease courses. An alternative technique is to use the summary measure 'area under the disability/time curve' (AUC) to index the total in-trial morbidity experienced by patients. In this study, we applied AUC analyses to the serial Expanded Disability Status Scale (EDSS) scores from the U.S. multicentre, Phase III, two-year core study of glatiramer acetate in 251 RRMS patients. When all available EDSS evaluations were analysed with AUC(CHANGE) ('combined data', including relapse-related assessments), active treatment was significantly superior to placebo (P=0.018). The benefits of glatiramer acetate persisted when transient relapse effects were reduced by using 'scheduled visit data' only (P=0.021). With the more conservative AUC(SUM) measure, significant active treatment effects remained (P=0.029 and 0.046, for both 'combined' and 'scheduled visit' data, respectively). Subgroup calculations performed with baseline disability stratified at EDSS 3.5 also showed benefits of treatment over placebo, but statistical significance was not reached. This analysis of data from a Phase III treatment trial illustrates the AUC summary measure technique and provides further evidence of the efficacy of glatiramer acetate in RRMS.

Disability Evaluation↗

PubMed2000

Prevention of graft-versus-host disease by a novel immunosuppressant, PG490-88, through inhibition of alloreactive T cell expansion.

BACKGROUND: PG490-88 is a water soluble, semisynthetic derivative of a novel compound PG490 (triptolide) purified from the Chinese herb Tripterygium Wilfordii Hook F. METHODS: PG490-88 was administrated into recipient mice in a model (B10.D2-->BALB/c) of lethal graft-versus-host disease (GVHD) to study the effects of PG490-88 on GVHD and on the various steps involved in the pathological course of GVHD. RESULTS: Injection of PG490-88 i.p. at a dose of 0.535 mg/kg/day for the first 3 weeks after transplantation protected all the recipients from developing GVHD up to 100 days after transplantation. PG490-88 inhibited in vivo both CD4+Vbeta3+ and CD8+Vbeta3+ T cell (alloreactive T cells in this model) expansion in the spleen by 64.09 and 34.02%, respectively, at the time when Vbeta3+ cell expansion was in the logarithmic phase (day 3 after transplantation). Intracellular cytokine staining without further in vitro activation demonstrated 47.42% inhibition of IL-2 production among CD4+ spleen cells in PG490-88-treated mice as compared to GVHD control on day 3 after transplantation. In contrast, CD25 (alpha chain of interleukin-2 receptor) expression did not differ. CONCLUSIONS: PG490-88 is highly effective in prevention of murine GVHD. The immunosuppressive effect of PG490-88 is mediated by inhibition of alloreactive T cell expansion through interleukin-2 production.

Animals↗

PubMed2000

Human keratocyte migration into collagen gels declines with in vitro ageing.

Although senescence in various cell types has been shown to have detrimental effects on wound repair, the effect of this phenomenon on corneal function with increasing age has yet to be elucidated. This study investigated the effect of in vitro ageing on keratocyte migration into a collagen gel matrix. The keratocyte cell strain EK1. BR was cultured to late passage and a comparison of early passage migration with that of late passage migration was carried out. Early or late passage keratocytes were seeded onto 6 collagen gels (1.75 mg ml(-1)) for each experiment. Gels were incubated at 37 degrees C for 72 h, stained with calcein AM (0.5 mg ml(-1)) and assayed for cell migration using fluorescent microscopy. Changes in the effect of EGF on keratocyte migration with age were assessed by the addition of EGF (20 ng ml(-1)) to 3 of the 6 gels in each experiment. Proliferative lifespan was measured by immunocytochemical detection of Ki67 activity. This study shows for the first time that keratocyte migration, and migration in response to EGF stimulation, significantly declines with increasing age of keratocytes in culture (P<0.001). As keratocyte migration in response to cytokine stimulation is vital for corneal repair, the accumulation of senescent keratocytes with age may impair corneal wound healing.

Cell Line↗

PubMed2000

Alternative splicing of the histamine H(3) receptor mRNA at the third cytoplasmic loop is not detectable in humans.

Histamine regulates neurotransmitter release in the central and peripheral nervous systems through H(3) presynaptic receptors. cDNAs coding for human, guinea pig and rat histamine H(3) receptors have recently been cloned. Cloning of rat and guinea pig H(3) receptors demonstrated the existence of multiple isoforms displaying deletions in the third cytoplasmic loop coding region. We investigated whether a similar splicing pattern might also occur in the human H(3) gene. Using both RT-PCR and RNase protection assays, we detected H(3) receptor mRNA expression in human brain, testes and a cell line expressing recombinant human H(3) receptor (SK-N-MC/H(3)). In all samples tested by both detection methods, only the long mRNA form was detected. We could not find any evidence that humans express other forms equivalent to that seen in the rat or guinea pig. If the alternative splicing seen in rats and guinea pigs presents itself through pharmacological variation, our current findings then have implication for the use of rats or guinea pigs as model system for the development of therapeutic targeting the human H(3) receptor.

Alternative Splicing↗

PubMed2000

Regulation of the yeast transcriptional factor PHO2 activity by phosphorylation.

The induction of yeast Saccharomyces cerevisiae gene PHO5 expression is mediated by transcriptional factors PHO2 and PHO4. PHO4 protein has been reported to be phosphorylated and inactivated by a cyclin-CDK (cyclin-dependent kinase) complex, PHO80-PHO85. We report here that PHO2 can also be phosphorylated. A Ser-230 to Ala mutation in the consensus sequence (SPIK) recognized by cdc2/CDC28-related kinase in PHO2 protein led to complete loss of its ability to activate the transcription of PHO5 gene. Further investigation showed that the Pro-231 to Ser mutation inactivated PHO2 protein as well, whereas the Ser-230 to Asp mutation did not affect PHO2 activity. Since the PHO2 Asp-230 mutant mimics Ser-230-phosphorylated PHO2, we postulate that only phosphorylated PHO2 protein could activate the transcription of PHO5 gene. Two hybrid assays showed that yeast CDC28 could interact with PHO2. CDC28 immunoprecipitate derived from the YPH499 strain grown under low phosphate conditions phosphorylated GST-PHO2 in vitro. A phosphate switch regulates the transcriptional activation activity of PHO2, and mutations of the (SPIK) site affect the transcriptional activation activity of PHO2 and the interaction between PHO2 and PHO4. BIAcore(R) analysis indicated that the negative charge in residue 230 of PHO2 was sufficient to help PHO2 interact with PHO4 in vitro.

Acid Phosphatase↗

PubMed2000

Gating of inward rectifier K+ channels by proton-mediated interactions of N- and C-terminal domains.

Ion channels play an important role in cellular functions, and specific cellular activity can be produced by gating them. One important gating mechanism is produced by intra- or extracellular ligands. Although the ligand-mediated channel gating is an important cellular process, the relationship between ligand binding and channel gating is not well understood. It is possible that ligands are involved in the interactions of different protein domains of the channel leading to opening or closing. To test this hypothesis, we studied the gating of Kir2.3 (HIR) by intracellular protons. Our results showed that hypercapnia or intracellular acidification strongly inhibited these channels. This effect relied on both the N and C termini. The CO(2)/pH sensitivities were abolished or compromised when one of the intracellular termini was replaced. Using purified N- and C-terminal peptides, we found that the N and C termini bound to each other in vitro. Although their binding was weak at pH 7.4, stronger binding was seen at pH 6.6. Two short sequences in the N and C termini were found to be critical for the N/C-terminal interaction. Interestingly, there was no titratable residue in these motifs. To identify the potential protonation sites, we systematically mutated most histidine residues in the intracellular N and C termini. We found that mutations of several histidine residues in the C but not the N terminus had a major effect on channel sensitivities to CO(2) and pH(i). These results suggest that at acidic pH, protons appear to interact with the C-terminal histidine residues and present the C terminus to the N terminus. Consequentially, these two intracellular termini bound to each other through two short motifs and closed the channel. Thus, a novel mechanism for K(+) channel gating is demonstrated, which involves the N- and C-terminal interaction with protons as the mediator.

Amino Acid Motifs↗

PubMed2000

Production and processing of erythropoietin receptor transcripts in brain.

The expression of erythropoietin receptor (EpoR) in brain and neuronal cells, and hypoxia-responsive production of erythropoietin (Epo) in the brain suggests that the function of Epo as a survival or viability factor may extend beyond hematopoietic tissue and erythroid progenitor cells. Epo, produced by astrocytes and neurons, can be induced by hypoxia by severalfold, and in animal models Epo administration is neuroprotective to ischemic challenge. We characterized the human EpoR transcript in brain and neuronal cells to determine its contribution in regulating the Epo response in brain. Screening of a human brain cDNA library and quantitative analysis of EpoR transcripts indicate that the EpoR gene locus is transcriptionally active in brain. In addition to the proximal promoter that is active in hematopoietic cells, a significant proportion of transcripts originates far upstream from the EpoR coding region. Unlike erythroid cells with efficient splicing of EpoR transcripts to its mature form, brain EpoR transcripts are inefficiently or alternately processed with a bias towards the 3' coding region. In human EpoR transgenic mice, anemic stress induces expression of the transgene and endogenous EpoR gene in hematopoietic tissue and brain. In culture of neuronal cells, hypoxia induces EpoR expression and increases sensitivity to Epo. Induction of EpoR expression appears to be a consequence of increased transcription from the upstream region and proximal promoter, and a shift towards increased processing efficiency. These data suggest that in contrast to erythropoiesis where erythroid progenitor cells express high levels of EpoR and are directly responsive to Epo stimulation, the neuroprotective effect of Epo and its receptor may require two molecular events: the induction of Epo production by hypoxia and an increase in EpoR expression in neuronal cells resulting in increased sensitivity to Epo.

Adult↗

PubMed2000

LDL-receptor-related proteins in Wnt signal transduction.

The Wnt family of secreted signalling molecules are essential in embryo development and tumour formation. The Frizzled (Fz) family of serpentine receptors function as Wnt receptors, but how Fz proteins transduce signalling is not understood. In Drosophila, arrow phenocopies the wingless (DWnt-1) phenotype, and encodes a transmembrane protein that is homologous to two members of the mammalian low-density lipoprotein receptor (LDLR)-related protein (LRP) family, LRP5 and LRP6 (refs 12-15). Here we report that LRP6 functions as a co-receptor for Wnt signal transduction. In Xenopus embryos, LRP6 activated Wnt-Fz signalling, and induced Wnt responsive genes, dorsal axis duplication and neural crest formation. An LRP6 mutant lacking the carboxyl intracellular domain blocked signalling by Wnt or Wnt-Fz, but not by Dishevelled or beta-catenin, and inhibited neural crest development. The extracellular domain of LRP6 bound Wnt-1 and associated with Fz in a Wnt-dependent manner. Our results indicate that LRP6 may be a component of the Wnt receptor complex.

Animals↗

PubMed2000

Polarized raman study of single-wall semiconducting carbon nanotubes

Polarized Raman spectra were obtained from a rope of aligned semiconducting single-wall nanotubes (SWNTs) in the vicinity of the D band and the G band. Based on group theory analysis and related theoretical predictions, the G-band profile was deconvolved into four intrinsic SWNT components with the following symmetry assignments: 1549 cm(-1) [E2(E(2g))], 1567 cm(-1) [A(A(1g))+E1(E(1g))], 1590 cm(-1) [A(A(1g))+E1(E(1g))] and 1607 cm(-1) [E2(E(2g))]. The frequency shifts of the tangential G modes from the 2D graphitelike E(2g(2)) frequency are discussed in terms of the nanotube geometry.

Journal Article↗

PubMed2000

The interferon- and differentiation-inducible p202a protein inhibits the transcriptional activity of c-Myc by blocking its association with Max.

p202a is a murine protein that is induced during the fusion of myoblasts to myotubes and can also be induced by interferon. Even 2-3-fold overexpression of p202a in cells retards proliferation. p202a was shown to modulate transcription by binding, and inhibiting the activity of several transcription factors including c-Fos, c-Jun, AP-2, E2F1, E2F4, NF-kappaB, MyoD, and myogenin. Here we report that p202a also bound the c-Myc protein in vitro and in vivo; the C-terminal p202a b segment bound the C-terminal basic region helix-loop-helix-leucine zipper (bHLHLZ) region of c-Myc. The transfection of a p202a expression plasmid inhibited the c-Myc-dependent expression of reporter plasmids in transient assays; moreover, overexpression of p202a in stable cell lines decreased the endogenous levels of mRNAs whose expression is driven by c-Myc. These effects of p202a are consistent with our finding that the binding of p202a to c-Myc inhibited the binding of c-Myc to Max in vitro and in vivo. p202a also inhibited the c-Myc-induced anchorage-independent growth and apoptosis of Rat-1 cells. The inhibition of c-Myc-dependent transcription, proliferation, and apoptosis by p202a is in line with the involvement of p202a in differentiation.

Animals↗

PubMed2000

Viscoelastic properties of linseed oil-based medium chain length poly(hydroxyalkanoate) films: effects of epoxidation and curing.

Medium-chain-length poly(hydroxyalkanoate) (mcl-PHA) polymers derived from linseed oil (PHA-L) have a relatively small molar mass and contain a high concentration of unsaturated side-chains. As such, these polymers are amorphous and take on the consistency of a viscous liquid at room temperature. In order to increase the application potential of this material, the side-chain olefinic groups of PHA-L were converted to epoxy derivatives (PHA-LE) using m-chloroperoxybenzoic acid (m-CPBA). Epoxidation resulted in a 37% conversion of olefinic to epoxy groups. The epoxy groups enhanced the PHA-LE film susceptibility to crosslinking upon exposure to air. PHA-LE films began to crosslink and stiffen in less than 25 days, whereas PHA-L films began to crosslink between days 50 and 75. The PHA-LE films showed an increase in tensile strength (TS, from 4.8 to 20.7 MPa) and Young's modulus (YM, from 12.9 to 510.6 MPa) between 25 and 100 days. In contrast, PHA-L had a TS of 25.0 MPa and YM of 767.8 MPa after 100 days. Epoxidation helped induce crosslink formation; however, aging for 100 days ultimately resulted in crosslinked films from both PHA-L and PHA-LE with higher strength and durability than the original materials.

Biomechanical Phenomena↗

PubMed2000

Mammalian peptidoglycan recognition protein binds peptidoglycan with high affinity, is expressed in neutrophils, and inhibits bacterial growth.

Peptidoglycan recognition protein (PGRP) is conserved from insects to mammals. In insects, PGRP recognizes bacterial cell wall peptidoglycan (PGN) and activates prophenoloxidase cascade, a part of the insect antimicrobial defense system. Because mammals do not have the prophenoloxidase cascade, its function in mammals is unknown. However, it was suggested that an identical protein (Tag7) was a tumor necrosis factor-like cytokine. Therefore, the aim of this study was to identify the function of PGRP in mammals. Mouse PGRP bound to PGN with fast kinetics and nanomolar affinity (K(d) = 13 nm). The binding was specific for polymeric PGN or Gram-positive bacteria with unmodified PGN, and PGRP did not bind to other cell wall components or Gram-negative bacteria. PGRP mRNA and protein were expressed in neutrophils and bone marrow cells, but not in spleen cells, mononuclear cells, T or B lymphocytes, NK cells, thymocytes, monocytes, and macrophages. PGRP was not a PGN-lytic or a bacteriolytic enzyme, but it inhibited the growth of Gram-positive but not Gram-negative bacteria. PGRP inhibited phagocytosis of Gram-positive bacteria by macrophages, induction of oxidative burst by Gram-positive bacteria in neutrophils, and induction of cytokine production by PGN in macrophages. PGRP had no tumor necrosis factor-like cytotoxicity for mammalian cells, and it was not chemotactic on its own or in combination with PGN. Therefore, mammalian PGRP binds to PGN and Gram-positive bacteria with nanomolar affinity, is expressed in neutrophils, and inhibits growth of bacteria.

Adult↗