Search PubMed⌕ Search

Biomedical subjects

Yu Liu

Publications and source records attributed to Yu Liu.

At least 55 records · Page 3Linked to original sources
PubMed2006

CRM1 mediates nuclear export of HDAC7 independently of HDAC7 phosphorylation and association with 14-3-3s.

CRM1, 14-3-3 proteins, and CaMK play important roles in trafficking of HDAC7, but the interplay between these proteins in this process is not clearly understood. Here, we show that CRM1 is capable of promoting cytoplasmic localization of wild-type and mutant HDAC7 (S178A/S344A/S479A), which is normally found in the nucleus. Using phospho-specific antibodies to HDAC7, we demonstrate that CaMK I promotes phosphorylation of S178, S344, and S479 of HDAC7. We also show that endogenous S178-phosphorylated HDAC7 is localized in both the nucleus and the cytoplasm, whereas S344- and S479-phosphorylated HDAC7 are exclusively localized in the nucleus. An HDAC7 mutant, S178E/S344E/S479E, which lost the ability to bind 14-3-3s, is localized in both the nucleus and the cytoplasm. Furthermore, the nuclear export of S178E/S344E/S479E is inhibited by LMB, but is enhanced by the CRM1. Taken together, these results strongly suggest that CRM1 mediated-nuclear export of HDAC7 is independent of HDAC7 phosphorylation and its association with 14-3-3s.

14-3-3 Proteins↗
PubMed2006

Multiple degradation pathways for misfolded mutants of the yeast plasma membrane ATPase, Pma1.

To understand protein sorting and quality control in the secretory pathway, we have analyzed intracellular trafficking of the yeast plasma membrane ATPase, Pma1. Pma1 is ideal for such studies because it is a very abundant polytopic membrane protein, and its localization and activity at the plasma membrane are essential for cell viability and growth. We have tested whether the cytoplasmic amino- and carboxyl-terminal domains of Pma1 carry sorting information. As the sole copy of Pma1, mutants truncated at either NH2 or COOH termini are targeted at least partially to the plasma membrane and have catalytic activity to sustain cell viability. The mutants are also delivered to degradative pathways. Strikingly, NH2- and COOH-terminal Pma1 mutants are differentially recognized for degradation at distinct cellular locales. COOH-terminal mutants are recognized for destruction by endoplasmic reticulum-associated degradation. By contrast, NH2-terminal mutants escape detection by endoplasmic reticulum-associated degradation entirely, and undergo endocytosis for vacuolar degradation after apparently normal cell surface targeting. Both NH2- and COOH-terminal mutants are conformationally abnormal, as revealed by increased sensitivity to tryptic cleavage, but are able to assemble to form oligomers. We propose that different quality control mechanisms may assess discrete domains of Pma1 rather than a global conformational state.

Catalytic Domain↗
PubMed2006

Molecular recognition thermodynamics of pyridine derivatives by sulfonatocalixarenes at different pH values.

The complex stability constants (Ka) and thermodynamic parameters (DeltaG degrees, DeltaH degrees, and TDeltaS degrees) for 1:1 complexation of water-soluble calix[4]arene, thiacalix[4]arene, and calix[5]arene sulfonates with pyridine and their methylated derivatives have been determined by means of isothermal titration calorimetry at pH 2.0 and 7.2 at 298.15 K, and their binding modes have been investigated by NMR spectroscopy. The results obtained show that sulfonatocalixarenes afford stronger binding ability toward pyridine guests at pH 2.0, attributable to the positive electrostatic interactions and the more extensive desolvation effects, but present higher molecular selectivity at pH 7.2 owing to the strengthened C-H...pi interactions. The pH-responsible binding ability and molecular selectivity are discussed from the viewpoint of electrostatic, pi-stacking, van der Waals interactions and size-fit relationship between host and guest. A close comparison further demonstrates that the C-H...pi interactions and van der Waals interactions play a more important role than pi...pi interactions in the present inclusion complexation.

Journal Article↗
PubMed2006

Homing and differentiation of mesenchymal stem cells delivered intravenously to ischemic myocardium in vivo: a time-series study.

Mesenchymal stem cells (MSCs) are potential sources of cells for tissue repair. However, little information is available about the time course of homing and differentiation of systemically delivered MSCs after acute myocardial ischemia (MI). In the present study, MSCs were isolated from male rat bone marrow and expanded in vitro. Female rats were divided randomly into three groups. Three hours after coronary ligation, the transplanted group received an infusion of MSCs through the tail vein; at the same time, a coronary-ligated control group was injected with culture medium, and a normal (unligated) group received MSCs. Homing of MSCs to the heart was assessed by expression of the Y chromosome sry gene using fluorescence in situ hybridization (FISH) at 3 days, 1, 4, and 8 weeks after transplantation. Immunofluorescent staining was used to examine markers for cardiomyocytes, endothelial cells, and smooth muscle cells. Hemodynamics in the hearts was also measured to assess cardiac function. At each time point, sry-positive cells were present in the cardiac tissue in transplanted group but not in the hearts of normal and control group animals. The number of sry-positive cells was significantly higher at 1 week compared to 3 days after transplantation. No significant difference was found in the number of sry-positive cells among those of 1, 4, and 8 weeks after transplantation. At 3 days and 1 week after transplantation, the sry-positive cells in the transplanted group lacked troponin, desmin, smooth muscle alpha-actin, and CD31. At the later time points, cardiomyocytes, smooth muscle cells, and endothelial cells bearing sry were identified in the transplanted group. The cardiac function in transplanted group showed higher improvement at 4 and 8 weeks compared to 1 week after transplantation. Our data suggest that intravenously delivered MSCs are capable of homing toward the ischemic myocardium, and the fastigium of homing appeared around 1 week after MI. The differentiation of MSCs to cardiomyocytes, smooth muscle cells, and endothelial cells shows to be time dependent and arises at 1 to 4 weeks after transplantation.

Animals↗
PubMed2006

Organic anion recognition of naphthalenesulfonates by steroid-modified beta-cyclodextrins: enhanced molecular binding ability and molecular selectivity.

Two beta-cyclodextrin (beta-CD) derivatives bearing steroid groups (1 and 2) were synthesized by the condensation of mono(6-aminoethylamino-6-deoxy)-beta-CD with cholic acid and deoxycholic acid, respectively, and their original conformations and binding behavior to the organic anion of naphthalenesulfonate derivatives were investigated by using 1H NMR spectroscopy and spectrofluorometric titration in combination with computational methods. The 2D NMR experiments reveal that the steroid groups attached to the beta-CD rim could be deeply embedded in the beta-CD cavity to form the intramolecular (for 1) or intermolecular (for 2) inclusion complexes in aqueous solution. Upon complexation with naphthalenesulfonate derivatives, modified beta-CDs display two obviously different binding modes, that is, the competitive inclusion mode and the induced-fit inclusion mode, which is consistent with the results of molecular modeling study. The two modes and the strict size/shape fitting relationship between the hosts and guests reasonably explain the different binding behaviors and molecular selectivity of host beta-CDs 1 and 2 toward the naphthalenesulfonate guests. Therefore, the cholic acid- or deoxycholic acid-modified beta-CDs could effectively recognize the size/shape of guest molecules as compared with the parent beta-CD, giving good molecular selectivity up to 24.9 for the disodium 2,6-naphthalenedisulfonate/disodium 1,5-naphthalenedisulfonate pair by the host 1.

Anions↗
PubMed2006

A multifunctional arithmetical processor model integrated inside a single molecule.

Improving the processing power of molecules remains the challenge for molecular logic and computation. Here we report a 2-phenylimidazo[4,5-f][1,10]phenanthroline (PIPH)-based three-state molecular switch by controlling its unique emission and absorption spectra in the acid and base condition. On one hand, PIPH can perform simultaneously the functions of an "AND" gate and an "XOR" gate, capable of operating as a half-adder, and the "off-on-off" function as well as comparison function by monitoring its fluorescent spectral changes. On the other hand, the molecule can also implement in parallel the functions of an "XOR" gate and two "INH" gates by monitoring its absorption spectral changes, which constructs two half-subtractors. The cooperative operation of comparator and half-subtractor makes general subtraction operation become possible, which is discussed conceptually in the report.

Journal Article↗
PubMed2006

Secondary assembly of bile salts mediated by beta-cyclodextrin-terbium(III) complex.

A fluorescent cyclodextrin-Tb(III) complex is successfully synthesized and can include bile salts in its hydrophobic cavities. Therefore, it can efficiently induce the secondary assembly of small bile salt primary micelles to large micelle aggregates, and the aggregation process can be easily observed by transmission electron microscopy (TEM) and fluorescence microscopy.

Bile Acids and Salts↗
PubMed2006

Immortalization of normal human cytotrophoblast cells by reconstitution of telomeric reverse transcriptase activity.

Placental trophoblast cells are unique endocrine cells that play vital roles during the processes of embryonic implantation and placentation. However, research into the function of human trophoblast has been largely restrained mainly due to a lack of adequate cell models. A normal placenta-origin cytotrophoblast cell line (NPC) was previously established by our group, but these cells showed replicating senescence after 50 population doublings (PDs). In this study, the human telomerase catalytic subunit gene (htert) was transferred into B6 strain of NPC cells, and strains with reconstituted telomerase activity (B6Tert) were established. It was shown that B6Tert-1 cells produce various biomarkers of normal extravillous cytotrophoblasts during the early weeks of gestation. Meanwhile, the cell invasiveness was inhibited by transforming growth factor beta (TGFbeta). However, their ability to form syncytium was relatively low when stimulated with fetal calf serum (FCS). The cells maintained normal cell growth properties and failed to elicit tumours in nude mice. They proliferated continuously with no signs of senescence until the final count at 210 PDs. The growth rate of B6Tert-1 cells was increased when compared with the parental cells, which results, at least partly, from facilitating release of the G1/S checkpoint during the cell-cycle regulation. This is the first report of immortalizing human normal cytotrophoblast (CTB) cells by activation of telomerase activity. The cells will provide an ideal in vitro model for the study of human extravillous trophoblast (EVT) functions and consequently the mechanisms of embryonic implantation and placentation.

Animals↗
PubMed2006

Synthesis of bridged and metallobridged bis(beta-cyclodextrin)s containing fluorescent oxamidobisbenzoyl linkers and their selective binding towards bile salts.

A series of beta-cyclodextrin (beta-CD) dimers containing fluorescent 2,2'-oxamidobisbenzoyl and 4,4'-oxamidobisbenzoyl linkers--that is, 6,6'-[2,2'-oxamidobis(benzoylamino)]ethyleneamino-6,6'-deoxy-bis(beta-CD) (2), 6,6'-[2,2'-oxamidobis(benzoylamino)]diethylenediamino-6,6'-deoxy-bis(beta-CD) (3), 6,6'-[4,4'-oxamidobis(benzoylamino)]ethyleneamino-6,6'-deoxy-bis(beta-CD) (4), and 6,6'-[4,4'-oxamidobis(benzoylamino)]diethylenediamino-6,6'-deoxy- bis(beta-CD) (5)--were synthesized from the corresponding oxamidobis(benzoic acid)s through treatment with mono[6-aminoethyleneamino-6-deoxy]-beta-CD or mono[6-diethylenetriamino-6-deoxy]-beta-CD. Further treatment of 2-5 with copper perchlorate gave their Cu(II) complexes 6-9 in satisfactory yields. The conformation and binding behavior of 2-9 towards two bile salt guests--sodium cholate (CA) and sodium deoxycholate (DCA)--was comprehensively investigated by circular dichroism, 2D NMR spectroscopy, and fluorescence spectroscopy in Tris-HCl buffer solution (pH 7.2) at 25 degrees C. Thanks to the cooperative host-linker-guest binding mode, the stoichiometric 1:1 complexes formed by bis(beta-CD)s 2-5 with bile salts gave high stability constants (KS values) of up to 10(3)-10(4) M(-1). Significantly, benefiting from the intramolecular 1:2 or 2:4 binding stoichiometry, the resulting complexes of metallobis(beta-CD)s 6-9 with bile salts gave much higher KS values of up to 10(6)-10(7) M(-2). The enhanced binding abilities of bis(beta-CD)s and metallobridged bis(beta-CD)s are discussed from the viewpoints of induced-fit interactions and multiple recognition between host and guest.

Benzoates↗
PubMed2006

Pi-conjugated aromatic enynes as a single-emitting component for white electroluminescence.

By use of the organolanthanide catalysts Me2Si(C5Me4)(NAr)Lu(CH2SiMe3)(THF) and (C5Me5)2LaCH(SiMe3)2, carbazole-substituted phenyl enynes (Z)-CPEY and (E)-CPEY were synthesized, respectively, with excellent regio- and stereoselectivity through the catalytic dimerization of the corresponding terminal alkyne. These new pi-conjugated compounds, in particular, the (E)-enyne isomer (E)-CPEY, act as an excellent single-emitting component for white organic light-emitting devices (WOLEDs), as a result of combination of the blue emission from an isolated molecule with the longer-wavelength emissions (green and orange-red) from excimers. The (E)-CPEY-based double-layer device emitted almost pure white light with CIE coordinates of (0.32, 0.33), maximum brightness of 1395 cd m-2, and maximum current efficiency of 2.07 cd A-1. This is perhaps the purest white emission ever reported for a single-emitting-component WOLED. The quality of the white emission remained almost unchanged under varying driving voltages, demonstrating an advantageous potential of single-emitting-component WOLEDs.

Journal Article↗
PubMed2006

Linear polypseudorotaxanes possessing many metal centers constructed from inclusion complexes of alpha-, beta-, and gamma-cyclodextrins with 4,4'-dipyridine.

Three cyclodextrin-based complexes, 1-3, bearing external coordination sites for metal cations were prepared in satisfactory yields (over 50%) by reactions of alpha-, beta-, and gamma-cyclodextrins with 4,4'-dipyridine in aqueous solutions. Subsequently, these inclusion complexes were further assembled to form linear polypseudorotaxanes 4-6 through the coordination linkage of Ni(II) or Cu(II) ions, and their assembly behaviors were comprehensively investigated in both solutions and the solid state by means of 1H NMR, FT-IR, UV-vis spectroscopy, conductivity titration, powder X-ray diffraction patterning, thermogravimetric and differential thermal analysis, scanning electron microscopy, scanning tunneling microscopy, and transmission electron microscopy. The results showed that these polypseudorotaxanes existed as individual linear arrays at a low concentration but tended to form polymeric rodlike fibers at a relatively high concentration. Significantly, the volume of the cyclodextrin cavity used not only determined the inclusion complexation stoichiometry between cyclodextrin and 4,4'-dipyridine but also predominated the morphology of resulting polypseudorotaxanes.

Journal Article↗
PubMed2006

Multi[2]rotaxanes with gold nanoparticles as centers.

[structure: see text] The multi[2]rotaxanes with gold nanoparticles as centers are constructed by introducing chromophoric beta-cyclodextrin-based [2]rotaxanes on the surface of gold nanoparticles, which show good photophysical and electrochemical properties superior to the parent rotaxane.

Journal Article↗
PubMed2006

Recognition-induced supramolecular porous nanosphere formation from cyclodextrin conjugated by cholic acid.

A supramolecular porous nanosphere is constructed from amphiphilic cholic acid-modified cyclodextrin triggered by guest sodium 1-naphthylamino-4-sulfonate and is comprehensively characterized by nuclear magnetic resonance (NMR), light scattering, transmission electron microscopy, and gas adsorption experiments. The results obtained show that the porous nanosphere with the radius of 25-35 nm has moderate nitrogen adsorption ability. Further NMR, circular dichroism, and the fluorimetric titrations on the self-assembling behavior in aqueous solution reveal that the substituting group of the guest molecule and pH values are the key to induce the formation of the porous nanosphere.

Journal Article↗
PubMed2006

Colloidal phase transition driven by alternating electric field.

The transverse two-dimensional assembly of colloidal particles near an electrode surface subjected to ac polarization is studied by varying the frequency and field strength in the absence and presence of an added electrolyte. The variation of the translational and bond-orientational correlation functions with frequency suggests the existence of a hexatic phase in which the particles retain the remnants of the crystalline long-range orientational order, but has a liquidlike translational order. The electrohydrodynamic (EHD) flow is analyzed in the light of the existing theoretical models. The equilibrium distribution of particles is considered to be the resultant of the two opposing forces--Stoke's force due to EHD flow and the screened Coulomb interaction between the colloidal particles. Several features of the experimental results are discussed, such as the role played by the EHD flow in the particle aggregation, the dependence of the equilibrium interparticle separation on ionic strength, zeta potential, and particle size.

Journal Article↗
PubMed2006

Cirp protects against tumor necrosis factor-alpha-induced apoptosis via activation of extracellular signal-regulated kinase.

Mild hypothermia shows protective effects on patients with brain damage and cardiac arrest. To elucidate the molecular mechanisms underlying these effects, we analyzed the effects of low culture temperature (32 degrees C) and cold-inducible RNA-binding protein (Cirp) expression on apoptosis in vitro. In BALB/3T3 cells treated with tumor necrosis factor (TNF)-alpha and cycloheximide, the down-shift in temperature from 37 degrees C to 32 degrees C increased the expression of Cirp and suppressed the apoptosis. Activation of caspase-8 was suppressed, and the level of phosphorylated extracellular signal-regulated kinase (ERK) was increased. Transduction of Cirp into the Cirp-deficient mouse fibroblasts increased the level of phosphorylated ERK and suppressed the TNF-alpha-induced apoptosis both at 37 degrees C and 32 degrees C. The ERK-specific inhibitor PD98059 decreased the cytoprotective effect of Cirp as well as that of low culture temperature. These data suggest that mild hypothermia protects cells from TNF-alpha-induced apoptosis, at least partly, via induction of Cirp, and that Cirp protects cells by activating the ERK pathway.

Animals↗
PubMed2006

Highly acidic mesostructured aluminosilicates assembled from surfactant-mediated zeolite hydrolysis products.

The surfactant-mediated hydrolysis of ZSM-5 zeolite affords five-membered ring subunits that can be readily incorporated into the framework walls of a hexagonal mesostructured aluminosilicate, denoted MSU-Z. The five-membered ring subunits, which are identifiable by infrared spectroscopy, impart unprecedented acidity to the mesostructure, as judged by cumene cracking activity at 300 degrees C. Most notably, MSU-Z aluminosilicate made through the base hydrolysis of ZSM-5 in the presence of cetyltrimethylammonium ions exhibits a cumene conversion of 73%, which is 6.7-fold higher than the conversion provided by a conventional MCM-41. This approach to stabilizing zeolitic subunits through surfactant-mediated hydrolysis of zeolites appears to be general. The hydrolysis of USY zeolite under analogous hydrolytic conditions also affords zeolitic fragments that boost the acidity of the mesostructure in comparison to equivalent compositions prepared from conventional aluminosilicate precursors.

Letter↗