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Articles by T Liu
Total Records ( 10 ) for T Liu
  X Fan , Y Liu , J Jiang , Z Ma , H Wu , T Liu , M Liu , X Li and H. Tang

MicroRNAs (miRNAs) are emerging as a class of small regulated RNAs, and the alterations of miRNAs are implicated in the initiation and progression of human cancers. Our study shows that inhibition of miR-20a in OVCAR3 ovarian cancer cell line could suppress, whereas overexpression of miR-20a could enhance cell long-term proliferation and invasion. We also confirmed amyloid precursor protein (APP) as a direct target gene of miR-20a. Furthermore, suppression of APP expression could also promote ovarian cancer cell proliferation and invasion, which is consistent with the results of miR-20a overexpression. Therefore, we concluded that the regulation of APP is an important mechanism for miR-20a to promote proliferation and invasion in ovarian cancer cells.

  L Ma , D Lai , T Liu , W Cheng and L. Guo

One emerging model for the development of drug-resistant tumors utilizes a pool of self-renewing malignant progenitors known as cancer stem cells (CSCs) or cancer-initiating cells (CICs). The purpose of this study was to propagate such CICs from the ovarian cancer cell line SKOV3. The SKOV3 sphere cells were selected using 40.0 µmol/l cisplatin and 10.0 µmol/l paclitaxel in serum-free culture system supplemented with epidermal growth factor, basic fibroblast growth factor, leukemia inhibitory factor, and insulin or standard serum-containing system. These cells formed non-adherent spheres under drug selection (cisplatin and paclitaxel) and serum-free culture system. The selected sphere cells are more resistant to cisplatin, paclitaxel, adriamycin, and methotrexate. Importantly, the sphere cells have the properties of self-renewal, with high expression of the stem cell genes Nanog, Oct4, sox2, nestin, ABCG2, CD133, and the stem cell factor receptor CD117 (c-kit). Consistently, flow cytometric analysis revealed that the sphere cells have a much higher percentage of CD133+/CD117+-positive cells (71%) than differentiated cells (33%). Moreover, the SKOV3 sphere cells are more tumorigenic. Furthermore, cDNA microarray and subsequent ontological analyses revealed that a large proportion of the classified genes were related to angiogenesis, extracellular matrix, integrin-mediated signaling pathway, cell adhesion, and cell proliferation. The subpopulation isolation from the SKOV3 cell line under this culture system offers a suitable in vitro model for studying ovarian CSCs in terms of their survival, self-renewal, and chemoresistance, and for developing therapeutic drugs that specifically interfere with ovarian CSCs.

  T. C Chu , T Liu , D. T Lee , G. C Lee and A. C. C. Shih

Motivation: Homologous genomic sequences between species usually contain different rearrangement events. Whether some specific patterns existed in the breakpoint regions that caused such events to occur is still unclear. To resolve this question, it is necessary to determine the location of breakpoints at the nucleotide level. The availability of sequences near breakpoints would further facilitate the related studies. We thus need a tool that can identify breakpoints and align the neighboring sequences. Although local alignment tools can detect rearrangement events, they only report a set of discontinuous alignments, where the detailed alignments in the breakpoint regions are usually missing. Global alignment tools are even less appropriate for these tasks since most of them are designed to align the conserved regions between sequences in a consistent order, i.e. they do not consider rearrangement events.

Results: We propose an effective and efficient pairwise sequence alignment algorithm, called GR-Aligner (Genomic Rearrangement Aligner), which can find breakpoints of rearrangement events by integrating the forward and reverse alignments of the breakpoint regions flanked by homologously rearranged sequences. In addition, GR-Aligner also provides an option to view the alignments of sequences extended to the breakpoints. These outputs provide materials for studying possible evolutionary mechanisms and biological functionalities of the rearrangement.

  Y Liao , J Tang , M Ma , Z Wu , M Yang , X Wang , T Liu , X Chen , P. C Fletcher and W. Hao

Ketamine abuse has been shown to have a deleterious impact on brain function. However, the precise mechanisms of ketamine dependence-induced pathological change remain poorly understood. Although there is evidence for white matter changes in drug abuse, the presence of white matter abnormalities in chronic ketamine users has not been studied. White matter volumes were measured using in vivo diffusion tensor magnetic resonance imaging data in 41 ketamine-dependent subjects and 44 drug-free healthy volunteers. White matter changes associated with chronic ketamine use were found in bilateral frontal and left temporoparietal cortices. There was also evidence that frontal white matter fractional anisotropy correlated with the severity of drug use (as measured by estimated total ketamine consumption). We provide direct evidence for dose-dependent abnormalities of white matter in bilateral frontal and left temporoparietal regions following chronic ketamine use. The findings suggest a microstructural basis for the changes in cognition and experience observed with prolonged ketamine use. Moreover, the similarities of these changes to those observed in chronic schizophrenia have implications for the glutamate model of this illness.

  S Kuljaca , T Liu , T Dwarte , M Kavallaris , M Haber , M. D Norris , J Martin Caballero and G. M. Marshall

The cyclin-dependent kinase inhibitor, p21WAF1, induces cell-cycle arrest and can act as a tumor suppressor. However, increasing evidence indicates that p21WAF1 can also increase resistance to some anticancer therapies and thus promote tumor growth. The mechanisms explaining this paradox have not been explained. We found that conditioned media from MCF-7 breast cancer cells transfected with a p21WAF1-specific small interfering RNA (siRNA) significantly reduced endothelial cell migration, invasion and vascular sprouting. Liquid chromatography/mass spectrometry analysis of the conditioned media revealed that p21WAF1 knockdown significantly reduced secretion of thioredoxin (Trx), a redox protein known to promote tumor angiogenesis. p21WAF1 knockdown decreased Trx enzymatic activity in cancer cells, by effects on the expression levels of intracellular thioredoxin-binding protein 2 (TBP2), known to bind and inactivate Trx. Consistent with these findings, media from cancer cells transfected with TBP2 siRNA promoted endothelial cell invasion and blocked the anti-angiogenic effect of p21WAF1 siRNA. Addition of Trx siRNA blocked the pro-angiogenic effects of TBP2 siRNA. Chromatin immunoprecipitation assays showed p21WAF1 bound TBP2 gene promoter. Taken together, our data suggests that p21WAF1 can induce Trx secretion and angiogenesis in cancer cells, by direct transcriptional repression of the TBP2 promoter.

  M Kohlhaas , T Liu , A Knopp , T Zeller , M. F Ong , M Bohm , B O'Rourke and C. Maack

Background— Oxidative stress is causally linked to the progression of heart failure, and mitochondria are critical sources of reactive oxygen species in failing myocardium. We previously observed that in heart failure, elevated cytosolic Na+ ([Na+]i) reduces mitochondrial Ca2+ ([Ca2+]m) by accelerating Ca2+ efflux via the mitochondrial Na+/Ca2+ exchanger. Because the regeneration of antioxidative enzymes requires NADPH, which is indirectly regenerated by the Krebs cycle, and Krebs cycle dehydrogenases are activated by [Ca2+]m, we speculated that in failing myocytes, elevated [Na+]i promotes oxidative stress.

Methods and Results— We used a patch-clamp–based approach to simultaneously monitor cytosolic and mitochondrial Ca2+ and, alternatively, mitochondrial H2O2 together with NAD(P)H in guinea pig cardiac myocytes. Cells were depolarized in a voltage-clamp mode (3 Hz), and a transition of workload was induced by β-adrenergic stimulation. During this transition, NAD(P)H initially oxidized but recovered when [Ca2+]m increased. The transient oxidation of NAD(P)H was closely associated with an increase in mitochondrial H2O2 formation. This reactive oxygen species formation was potentiated when mitochondrial Ca2+ uptake was blocked (by Ru360) or Ca2+ efflux was accelerated (by elevation of [Na+]i). In failing myocytes, H2O2 formation was increased, which was prevented by reducing mitochondrial Ca2+ efflux via the mitochondrial Na+/Ca2+ exchanger.

Conclusions— Besides matching energy supply and demand, mitochondrial Ca2+ uptake critically regulates mitochondrial reactive oxygen species production. In heart failure, elevated [Na+]i promotes reactive oxygen species formation by reducing mitochondrial Ca2+ uptake. This novel mechanism, by which defects in ion homeostasis induce oxidative stress, represents a potential drug target to reduce reactive oxygen species production in the failing heart.

  T Liu , K Ohashi Ito and D. C. Bergmann
  Tie Liu, Kyoko Ohashi-Ito, and Dominique C. Bergmann

Stomata are adjustable pores in the plant epidermis that regulate gas exchange between the plant and atmosphere; they are present on the aerial portions of most higher plants. Genetic pathways controlling stomatal development and distribution have been described in some detail for one dicot species, Arabidopsis, in which three paralogous bHLH transcription factors, FAMA, MUTE and SPCH, control discrete sequential stages in stomatal development. Orthologs of FAMA, MUTE and SPCH are present in other flowering plants. This observation is of particular interest when considering the grasses, because both the morphology of guard cells and their tissue distributions differ substantially between Arabidopsis and this group. By examining gene expression patterns, insertional mutants and cross-species complementation studies, we find evidence that FAMA function is conserved between monocots and dicots, despite their different stomatal morphologies, whereas the roles of MUTE and two SPCH paralogs are somewhat divergent.

  S Li , T Hu , Y Chen , X Wang , T Liu , G Ma and Z. Su

Carboxylmethylated konjac glucomannan (CKGM) is a carboxylmethylated polymer of mannose and glucose that is derived from the plant Amorphophallus konjac cultivated in East Asia. The CKGM solution had a high volume-expanding efficacy and was evaluated as a plasma substitute in the present study. Ameliorative hemorrhagic shock rabbits were used as the model animals. The in vivo hemodynamic and hemorheologic properties, including blood pressure, blood viscosity, hematocrit, erythrocyte deformation index and erythrocyte aggregation index, were measured in animals treated in the CKGM solution. The in vitro colloid osmotic pressure (COP) of the CKGM solution was measured to estimate its plasma-expanding efficacy. These parameters of the CKGM-treated group were compared with groups exposed to four other treatments: human serum albumin (HSA), hydroxyethyl starch (HES), polygeline and normal saline. The CKGM solution showed an exceptionally higher COP than other therapy solutions. For example, the COP of 1% (weight in volume [w/v]) CKGM solution is comparable to those of 6% (w/v) HES solution and 5% (w/v) HSA solution. Accordingly, the CKGM solution can be transfused in a much lower dosage while maintaining its plasma-expanding efficacy. The CKGM-treated group showed an improved intravascular persistence and good hemodynamic and hemorheological properties. Biopsy analysis suggested no organ dysfunction in the group treated in CKGM solution. Moreover, the high plasma-expanding efficacy and inexpensive availability of the CKGM solution may facilitate its clinical application as a potential plasma substitute.

  J Zhao , T Liu , S. B Jin , N Tomilin , J Castro , O Shupliakov , U Lendahl and M. Nister

Although several proteins involved in mediating mitochondrial division have been reported in mammals, the mechanism of the fission machinery remains to be elucidated. Here, we identified a human nuclear gene (named MTGM) that encodes a novel, small, integral mitochondrial inner-membrane protein and shows high expression in both human brain tumor cell lines and tumor tissues. The gene is evolutionarily highly conserved, and its orthologs are 100% identical at the amino acid level in all analyzed mammalian species. The gene product is characterized by an unusual tetrad of the GxxxG motif in the transmembrane segment. Overexpression of MTGM (mitochondrial targeting GxxxG motif) protein results in mitochondrial fragmentation and release of mitochondrial Smac/Diablo to the cytosol with no effect on apoptosis. MTGM-induced mitochondrial fission can be blocked by a dominant negative Drp1 mutant (Drp1-K38A). Overexpression of MTGM also results in inhibition of cell proliferation, stalling of cells in S phase and...

  T Liu , O. E Guevara , R. R Warburton , N. S Hill , M Gaestel and U. S. Kayyali

Hypoxia triggers responses in endothelial cells that play roles in many conditions including high-altitude pulmonary edema and tumor angiogenesis. Signaling pathways activated by hypoxia modify cytoskeletal and contractile proteins and alter the biomechanical properties of endothelial cells. Intermediate filaments are major components of the cytoskeleton whose contribution to endothelial physiology is not well understood. We have previously shown that hypoxia-activated signaling in endothelial cells alters their contractility and adhesiveness. We have also linked p38-MAP kinase signaling pathway leading to HSP27 phosphorylation and increased actin stress fiber formation to endothelial barrier augmentation. We now show that vimentin, a major intermediate filament protein in endothelial cells, is regulated by hypoxia. Our results indicate that exposure of endothelial cells to hypoxia causes vimentin filament networks to initially redistribute perinuclearly. However, by 1 hour hypoxia these networks reform and appear more continuous across cells than under normoxia. Hypoxia also causes transient changes in vimentin phosphorylation, and activation of PAK1, a kinase that regulates vimentin filament assembly. In addition, exposure to 1 hour hypoxia increases the ratio of insoluble/soluble vimentin. Overexpression of phosphomimicking mutant HSP27 (pmHSP27) causes changes in vimentin distribution that are similar to those observed in hypoxic cells. Knocking-down HSP27 destroys the vimentin filamentous network, and disrupting vimentin filaments with acrylamide increases endothelial permeability. Both hypoxia- and pmHSP27 overexpression-induced changes are reversed by inhibition of phosphatase activity. In conclusion hypoxia causes redistribution of vimentin to a more insoluble and extensive filamentous network that could play a role in endothelial barrier stabilization. Vimentin redistribution appears to be mediated through altering the phosphorylation of the protein and its interaction with HSP27.

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