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Ting Cai

Publications and source records attributed to Ting Cai.

11 recordsLinked to original sources
PubMed2006

Structure and enhanced reactivity rates of the D5h Sc3N@C80 and Lu3N@C80 metallofullerene isomers: the importance of the pyracylene motif.

In this paper we report enhanced reactivity of the D(5h) isomers in comparison with the more common I(h) isomers of Sc(3)N@C(80) and Lu(3)N@C(80) toward Diels-Alder and 1,3-dipolar tritylazomethine ylide cycloaddition reactions. Also, the structure of the D(5h) isomer of Sc(3)N@C(80) has been determined through single-crystal X-ray diffraction on D(5h)-Sc(3)N@C(80).Ni(OEP).2benzene (OEP = octaethylporphyrin). The Sc(3)N portion of D(5h)-Sc(3)N@C(80) is strictly planar, but the plane of these four atoms is tipped out of the noncrystallographic, horizontal mirror plane of the fullerene by 30 degrees . The combination of short bond length and high degree of pyramidization for the central carbon atoms of the pyracylene sites situated along a belt that is perpendicular to the C(5) axis suggests that these are the sites of greatest reactivity in the D(5h) isomer of Sc(3)N@C(80). Consistent with the observation of higher reactivity observed for the D(5h) isomers, cyclic voltammetry and molecular orbital (MO) calculations demonstrate that the D(5h) isomers have slightly smaller energy gaps than those of the I(h) isomers. The first mono- and bis-adducts of D(5h) Sc(3)N@C(80) have been synthesized via 1,3-dipolar cycloaddition of tritylazomethine ylide. The NMR spectrum for the monoadduct 2b is consistent with reaction at the 6,6-ring juncture in the pyracylene unit of the D(5h) Sc(3)N@C(80) cage and is the thermodynamically stable isomer. On the other hand, monoadduct 2a undergoes thermal conversion to other isomeric monoadducts, and three possible structures are proposed.

Computer Simulation↗
PubMed2006

A pirouette on a metallofullerene sphere: interconversion of isomers of N-tritylpyrrolidino I(h) Sc3N@C80.

The pure I(h) isomer of Sc3N@C80 was allowed to react with N-triphenylmethyl-5-oxazolidinone via the corresponding azomethine ylide. The reaction results in the formation of two monoadducts; one (1b) is the kinetic product, and the other (1a) is thermodynamically more stable. Small amounts of the bisadducts were also formed. The structure of the thermodynamic monoadduct 1a was shown conclusively by NMR spectroscopy and X-ray crystallography to result from addition across the 5,6-ring junction. The kinetic product 1b was demonstrated to be the 6,6-ring juncture adduct on the basis of NMR experiments and X-ray crystallography. In refluxing chlorobenzene pure 1b was converted to the more thermodynamically stable 1a isomer. These N-tritylpyrrolidino derivatives are potentially useful precursor compounds for further derivatization for various applications.

Journal Article↗
PubMed2006

Functional characterization of Src-interacting Na/K-ATPase using RNA interference assay.

We have shown that the Na/K-ATPase and Src form a signaling receptor complex. Here we determined how alterations in the amount and properties of the Na/K-ATPase affect basal Src activity and ouabain-induced signal transduction. Several alpha1 subunit knockdown cell lines were generated by transfecting LLC-PK1 cells with a vector expressing alpha1-specific small interference RNA. Although the alpha1 knockdown resulted in significant decreases in Na/K-ATPase activity, it increased the basal Src activity and tyrosine phosphorylation of focal adhesion kinase, a Src effector. Concomitantly it also abolished ouabain-induced activation of Src and ERK1/2. When the knockdown cells were rescued by a rat alpha1, both Na/K-ATPase activity and the basal Src activity were restored. In addition, ouabain was able to stimulate Src and ERK1/2 in the rescued cells at a much higher concentration, consistent with the established differences in ouabain sensitivity between pig and rat alpha1. Finally both fluorescence resonance energy transfer analysis and co-immunoprecipitation assay indicated that the pumping-null rat alpha1 (D371E) mutant could also bind Src. Expression of this mutant restored the basal Src activity and focal adhesion kinase tyrosine phosphorylation. Taken together, the new findings suggest that LLC-PK1 cells contain a pool of Src-interacting Na/K-ATPase that not only regulates Src activity but also serves as a receptor for ouabain to activate protein kinases.

Animals↗
PubMed2005

Purification of endohedral trimetallic nitride fullerenes in a single, facile step.

A major hurdle hampering the development of fullerenes, endohedral metallofullerenes, and nanotubes has been the difficulty of obtaining high purity samples. Soots prepared in the usual manner via a Krätschmer-Huffman electric-arc generator consist of mixtures of insoluble carbonaceous materials and soluble fullerenes: C60, C70, C76, C78, C84, etc. When metals are introduced as endohedral species the complexity of the resultant soot is even greater because of the presence of multiple isomers of both the empty fullerenes and the endohedral metallofullerenes. Here, for the first time, we report that lanthanide trimetallic nitride endohedral metallofullerenes, A3N@C80 (A = lanthanide atom, e.g., Er, Gd, Ho, Lu, Sc, Tb, Tm, Y), can be obtained in pure form directly from as-prepared soots in a single facile step by taking advantage of their extraordinary kinetic chemical stability with respect to the other fullerenes in Diels-Alder reactions with a cyclopentadiene-functionalized resin. We show that careful control of conditions (stoichiometry, time, temperature) allows separation of fullerenes with different cage sizes, as well as isomeric species. Furthermore, the Diels-Alder reaction is thermally reversible, and we demonstrated that the bound empty-cage fullerenes and classical endohedral metallofullerenes can be recovered by displacement with maleic anhydride.

Journal Article↗
PubMed2005

Binding of Src to Na+/K+-ATPase forms a functional signaling complex.

We have shown that ouabain activates Src, resulting in subsequent tyrosine phosphorylation of multiple effectors. Here, we tested if the Na+/K+-ATPase and Src can form a functional signaling complex. In LLC-PK1 cells the Na+/K+-ATPase and Src colocalized in the plasma membrane. Fluorescence resonance energy transfer analysis indicated that both proteins were in close proximity, suggesting a direct interaction. GST pulldown assay showed a direct, ouabain-regulated, and multifocal interaction between the 1 subunit of Na+/K+-ATPase and Src. Although the interaction between the Src kinase domain and the third cytosolic domain (CD3) of 1 is regulated by ouabain, the Src SH3SH2 domain binds to the second cytosolic domain constitutively. Functionally, binding of Src to either the Na+/K+-ATPase or GST-CD3 inhibited Src activity. Addition of ouabain, but not vanadate, to the purified Na+/K+-ATPase/Src complex freed the kinase domain and restored the Src activity. Consistently, exposure of intact cells to ouabain apparently increased the distance between the Na+/K+-ATPase and Src. Concomitantly, it also stimulated tyrosine phosphorylation of the proteins that are associated with the Na+/K+-ATPase. These new findings illustrate a novel molecular mechanism of signal transduction involving the interaction of a P-type ATPase and a nonreceptor tyrosine kinase.

Animals↗
PubMed2005

Na/K-ATPase tethers phospholipase C and IP3 receptor into a calcium-regulatory complex.

We have shown that the caveolar Na/K-ATPase transmits ouabain signals via multiple signalplexes. To obtain the information on the composition of such complexes, we separated the Na/K-ATPase from the outer medulla of rat kidney into two different fractions by detergent treatment and density gradient centrifugation. Analysis of the light fraction indicated that both PLC-gamma1 and IP3 receptors (isoforms 2 and 3, IP3R2 and IP3R3) were coenriched with the Na/K-ATPase, caveolin-1 and Src. GST pulldown assays revealed that the central loop of the Na/K-ATPase alpha1 subunit interacts with PLC-gamma1, whereas the N-terminus binds IP3R2 and IP3R3, suggesting that the signaling Na/K-ATPase may tether PLC-gamma1 and IP3 receptors together to form a Ca(2+)-regulatory complex. This notion is supported by the following findings. First, both PLC-gamma1 and IP3R2 coimmunoprecipitated with the Na/K-ATPase and ouabain increased this interaction in a dose- and time-dependent manner in LLC-PK1 cells. Depletion of cholesterol abolished the effects of ouabain on this interaction. Second, ouabain induced phosphorylation of PLC-gamma1 at Tyr(783) and activated PLC-gamma1 in a Src-dependent manner, resulting in increased hydrolysis of PIP2. It also stimulated Src-dependent tyrosine phosphorylation of the IP3R2. Finally, ouabain induced Ca(2+) release from the intracellular stores via the activation of IP3 receptors in LLC-PK1 cells. This effect required the ouabain-induced activation of PLC-gamma1. Inhibition of Src or depletion of cholesterol also abolished the effect of ouabain on intracellular Ca(2+).

Animals↗
PubMed2005

Rotavirus-induced murine biliary atresia is mediated by nuclear factor-kappaB.

BACKGROUND/PURPOSE: Intraperitoneal inoculation of rhesus rotavirus (RRV) was shown to cause atretic-appearing segments of the extrahepatic bile ducts (EHBDs) in a murine model. The factors responsible for the injury of bile ducts, however, remain unknown. In this study, the morphologic status of nuclear factor- kappa B (NF- kappa B) activation in the liver and in the EHBDs from murine model of biliary atresia induced by intraperitoneal injection of rotavirus was investigated. METHODS: Within the first 24 hours of life, the newborn mice were infected through intraperitoneal route with a volume of 50 microL containing different titers of RRV. The pups were killed on days 5, 10, 15, 21, and 28 after inoculation and prepared under a dissecting microscope with photographic documentation. Consecutive sections of specimens were stained with H & E and used for histopathologic studies. The methods of modified Vision immunohistochemical staining was used to detect viral antigen of VP7 and active NF- kappa B. The distribution and intensity of staining were analyzed by image analysis software (GT-2 model, Huakang Co, Chengdu, China). RESULTS: The viral antigen was detected by immunohistochemical staining in specimens from experimental groups on day 5 after infection. The occlusion of the EHBDs could be visualized after intraperitoneal injection of 10(7) plaque-forming unit (pfu) of RRV, whereas the incidence of cholestasis was reduced with an infection dosage of 10(6) pfu or less. Obliteration of the EHBDs did not occur when the injection dosage of RRV was reduced to 10(5) pfu or when inoculation of 10(7) pfu of RRV was combined with pyrolidine dithiocarbamate (PDTC), a chemical inhibitor of active NF- kappa B. The antigen of active NF- kappa B was detected by immunohistochemical staining in the liver and in the EHBDs from pups after inoculation of 10(7), 10(6), and 10(5) pfu RRV. Low or no expression of active NF- kappa B was noted in the specimens obtained from the control group. As the inflammatory reaction in the liver and in the EHBDs gradually subsided on day 28 after inoculation, the expression of active NF- kappa B also decreased. The expression of active NF- kappa B after injection of RRV combined with PDTC was similar to the expression in the control group on days 5 and 10 after infection. CONCLUSIONS: The authors found that occlusion of the EHBDs could be noted in pups after inoculation of 10(7) pfu RRV. Meanwhile, the expression of active NF- kappa B in the liver and in the EHBDs was increased after inoculation of RRV. Simultaneous intraperitoneal injection of PDTC, however, was shown to prevent the obstruction of EHBDs secondary to inoculation of RRV. These results show that the murine biliary atresia induced by RRV is mediated by active NF- kappa B.

Animals↗
PubMed2004

Ouabain assembles signaling cascades through the caveolar Na+/K+-ATPase.

Based on the observation that the Na(+)/K(+)-ATPase alpha subunit contains two conserved caveolin-binding motifs, we hypothesized that clustering of the Na(+)/K(+)-ATPase and its partners in caveolae facilitates ouabain-activated signal transduction. Glutathione S-transferase pull-down assay showed that the Na(+)/K(+)-ATPase bound to the N terminus of caveolin-1. Significantly, ouabain regulated the interaction in a time- and dose-dependent manner and stimulated tyrosine phosphorylation of caveolin-1 in LLC-PK1 cells. When added to the isolated membrane fractions, ouabain increased tyrosine phosphorylation of proteins from the isolated caveolae but not other membrane fractions. Consistently, ouabain induced the formation of a Na(+)/K(+)-ATPase-Src-caveolin complex in the isolated caveolae preparations as it did in live cells. Finally, depletion of either cholesterol by methyl beta-cyclodextrin or caveolin-1 by siRNA significantly reduced the caveolar Na(+)/K(+)-ATPase and Src. Concomitantly, cholesterol depletion abolished ouabain-induced recruitment of Src to the Na(+)/K(+)-ATPase signaling complex. Like depletion of caveolin-1, it also blocked the effect of ouabain on ERKs, which was restored after cholesterol repletion. Clearly, the caveolar Na(+)/K(+)-ATPase represents the signaling pool of the pump that interacts with Src and transmits the ouabain signals.

Amino Acid Sequence↗
PubMed2003

Na+-K+--ATPase-mediated signal transduction: from protein interaction to cellular function.

The Na+-K+--ATPase, or Na+ pump, is a member of the P-type ATPase superfamily. In addition to pumping ions, Na+-K+--ATPase is engaged in assembly of multiple protein complexes that transmit signals to different intracellular compartments. The signaling function of the enzyme appears to have been acquired through the evolutionary incorporation of many specific binding motifs that interact with proteins and ligands. In some cell types the signaling Na+ --ATPase and its protein partners are compartmentalized in coated pits (i.e., caveolae) the plasma membrane. Binding of ouabain to the signaling Na+-K+--ATPase activates the cytoplasmic tyrosine kinase Src, resulting in the formation of an active "binary receptor" that phosphorylates and assembles other proteins into different signaling modules. This in turn activates multiple protein kinase cascades including mitogen-activated protein kinases and protein kinase C isozymes in a cell-specific manner. It also increases mitochondrial production of reactive oxygen species (ROS)and regulates intracellular calcium concentration. Crosstalk among the activated pathways eventually results in changes in the expression of a number of genes. Although ouabain stimulates hypertrophic growth in cardiac myocytes and proliferation in smooth muscle cells, it also induces apoptosis in many malignant cells. Finally, the signaling function of the enzyme is also pivotal to ouabain-induced nongenomic effects on cardiac myocytes.

Amino Acid Motifs↗
PubMed2002

Cytomegalovirus glycoprotein B sequence variation in Chinese liver transplant recipients.

OBJECTIVE: To investigate human cytomegalovirus infection and genetic variations in glycoprotein B (gB) in liver transplant recipients in south-east China. METHODS: EDTA-blood samples were obtained from 21 liver transplant recipients. The semi-nested PCR was used to amplify a region of high sequence variability in the gB gene of human cytomegalovirus (HCMV) followed by direct sequence analysis. RESULTS: Out of the 21 liver transplant recipients, 5 were proved HCMV positive 62 to 180 days after transplantation. The nucleotide and encoded amino acid sequences were compared with published sequences of AD169 and Towne laboratory strains. Within the region sequenced, 2 out of 5 strains possessed a peptide configuration similar to that of strain AD169, while another 2 strains displayed a peptide configuration similar to that of strain Towne. One strain had amino acid substitution, which was different from those of both AD169 and Towne in the cleavage site. CONCLUSION: Our results provide molecular epidemiological data for HCMV strains circulating among transplant recipients in south-east China.

Adult↗