Biomedical subjects

H Tu

Publications and source records attributed to H Tu.

At least 19 recordsLinked to original sources

PubMed2005

Exciton dynamics of GaSe nanoparticle aggregates.

Time-resolved and static spectroscopic results on GaSe nanoparticle aggregates are presented to elucidate the exciton relaxation and diffusion dynamics. These results are obtained in room-temperature TOP/TOPO solutions at various concentrations. The aggregate absorption spectra are interpreted in terms of electrostatic coupling and covalent interactions between particles. The spectra at various concentrations may then be interpreted in terms of aggregate distributions calculated from a simple equilibrium model. These distributions are used to interpret concentration-dependent emission anisotropy kinetics and time-dependent emission spectral shifts. The emission spectra are reconstructed from the static emission spectra and decay kinetics obtained at a range of wavelengths. The results indicate that the aggregate z axis persistence length is about 9 particles. The results also show that the one-dimensional exciton diffusion coefficient is excitation wavelength dependent and has a value of about 2 x 10(-5) cm(2)/s following 406 nm excitation. Although exciton diffusion results in very little energy relaxation, subsequent hopping of trapped electron/hole pairs occurs by a Forster mechanism and strongly red shifts the emission spectrum.

Journal Article↗

PubMed2001

Biological impact of natural COOH-terminal deletions of hepatitis B virus X protein in hepatocellular carcinoma tissues.

The hepatitis B virus (HBV) X protein (HBx) is a transcriptional transactivator that has been implicated in the development of HBV-related hepatocellular carcinoma. Mutations in the HBx open reading frame have been reported, but their general impact on the biological function of HBx remains unknown. To address this issue, we comparatively analyzed the structures and biological functions of HBx sequences isolated from sera and from tumor and nontumor tissues of patients with a HBV-related hepatocellular carcinoma. In addition to the HBx sequences derived from free HBV genomes, HBx from HBV integrants was also obtained from the tumor tissues by use of a HBx-Alu PCR-based approach. Sequence analysis showed that the HBx sequences derived from tumor tissues (6 of 7), particularly those isolated from HBV integrants (4 of 4), contained a deletion in the distal COOH-terminal region. Interestingly, most of the COOH-terminally truncated HBx sequences obtained from tumor tissues, in contrast to the full-length HBx isolated from the sera and nontumor tissues, lost their transcriptional activity and their inhibitory effects on cell proliferation and transformation. Importantly, although full-length HBx suppressed the focus formation induced by the cooperation of ras and myc oncogenes in primary rat embryo fibroblasts, COOH-terminally truncated HBx enhanced the transforming ability of ras and myc. Finally, by analyzing the artificial mutants, we were able to more precisely map the functional domains located at the COOH-terminal of HBx. Taken together, our results suggest a key role for the HBx COOH-terminal end in controlling cell proliferation, viability, and transformation. This study further supports the hypothesis that natural HBx mutants might be selected in tumor tissues and play a role in hepatocarcinogenesis by modifying the biological functions of HBx.

Amino Acid Sequence↗

PubMed2001

High-level production of human type I collagen in the yeast Pichia pastoris.

Four human genes, two of them encoding the proalpha1 and proalpha2 chains of type I procollagen and two of them the two types of subunit of prolyl 4-hydroxylase (4-PH), were integrated into the genome of Pichia pastoris. The proalpha1 and proalpha2 chains expressed formed type I procollagen molecules with the correct 2:1 chain ratio, and the 4-PH subunits formed an active enzyme tetramer that fully hydroxylated the proalpha chains. Chains lacking their N but not C propeptides formed pCcollagen molecules with the 2:1 chain ratio and, surprisingly, the expression levels of pCcollagen were 1.5-3-fold relative to those of procollagen. Both types of molecule could be converted by pepsin treatment to collagen molecules that formed native-type fibrils in vitro. The expression levels obtained for the pCcollagen using only single copies of each of the four genes and a 2 l fermenter ranged up to 0.5 g/l, indicating that it should be possible to optimize this system for high-level production of recombinant human type I collagen for numerous medical applications.

Amino Acids↗

PubMed2001

Deterministic numerical model for treating the three elastic constants in nematic liquid-crystalline polymers.

In this paper, a deterministic model, which considers the three Frank elastic constants, is introduced. It is based on a lattice model and a director is used to represent the orientation of the liquid crystals in each cell. A tensor expression of the so-called "texture field" is deduced so that the nematic symmetry is conserved automatically. In the current model, the evolution of the director field can be viewed as a process towards the state of zero elastic torque. The model forms the basis for an improved understanding of the mesoscale structures and rheological phenomena of nematic liquid-crystalline polymers. It has been tested in its ability to reproduce the Fréedericksz transitions, and simulations of thin liquid crystalline polymer films clearly show the effect of unequal elastic constants on the director microstructure evolution.

Journal Article↗

PubMed2001

Unsaturated fatty acids inhibit transcription of the sterol regulatory element-binding protein-1c (SREBP-1c) gene by antagonizing ligand-dependent activation of the LXR.

Sterol regulatory element-binding protein-1c (SREBP-1c) enhances transcription of genes encoding enzymes of unsaturated fatty acid biosynthesis in liver. SREBP-1c mRNA is known to increase when cells are treated with agonists of liver X receptor (LXR), a nuclear hormone receptor, and to decrease when cells are treated with unsaturated fatty acids, the end products of SREBP-1c action. Here we show that unsaturated fatty acids lower SREBP-1c mRNA levels in part by antagonizing the actions of LXR. In cultured rat hepatoma cells, arachidonic acid and other fatty acids competitively inhibited activation of the endogenous SREBP-1c gene by an LXR ligand. Arachidonate also blocked the activation of a synthetic LXR-dependent promoter in transfected human embryonic kidney-293 cells. In vitro, arachidonate and other unsaturated fatty acids competitively blocked activation of LXR, as reflected by a fluorescence polarization assay that measures ligand-dependent binding of LXR to a peptide derived from a coactivator. These data offer a potential mechanism that partially explains the long-known ability of dietary unsaturated fatty acids to decrease the synthesis and secretion of fatty acids and triglycerides in livers of humans and other animals.

Animals↗

PubMed2001

Type XIII collagen: a novel cell adhesion component present in a range of cell-matrix adhesions and in the intercalated discs between cardiac muscle cells.

Recent analysis of type XIII collagen surprisingly showed that it is anchored to the plasma membranes of cultured cells via a transmembrane segment near its amino terminus. Here we demonstrate that type XIII collagen is concentrated in cultured skin fibroblasts and several other human mesenchymal cell lines in the focal adhesions at the ends of actin stress fibers, co-localizing with the known focal adhesion components talin and vinculin. This co-occurrence was also observed in rapidly forming adhesive structures of spreading and moving fibroblasts and in disrupting focal adhesions following microinjection of the Rho-inhibitor C3 transferase into the cells, suggesting that type XIII collagen is an integral focal adhesion component. Moreover, it appears to have an adhesion-related function since cell-surface expression of type XIII collagen in cells with weak basic adhesiveness resulted in improved cell adhesion on selected culture substrata. In tissues type XIII collagen was found in a range of integrin-mediated adherens junctions including the myotendinous junctions and costameres of skeletal muscle as well as many cell-basement membrane interfaces. Some cell-cell adhesions were found to contain type XIII collagen, most notably the intercalated discs in the heart. Taken together, the results strongly suggest that type XIII collagen has a cell adhesion-associated function in a wide array of cell-matrix junctions.

Animals↗

PubMed2001

Distinct expression of type XIII collagen in neuronal structures and other tissues during mouse development.

Type XIII collagen is a type II transmembrane protein found in adhesive structures of mature tissues. We describe here its expression and spatio-temporal localization during mouse fetal development. Type XIII collagen mRNAs were expressed at a constant rate during development, with an increase of expression towards birth. Strong type XIII collagen expression was detected in the central and peripheral nervous systems of the developing mouse fetus in mid-gestation. Cultured primary neurons also expressed this collagen, and it was found to enhance neurite outgrowth. The results suggest that type XIII collagen is a new member among the proteins involved in nervous system development. Strong expression during early development was also detected in the heart, with localization to cell-cell contacts and accentuation in the intercalated discs perinatally. During late fetal development, type XIII collagen was observed in many tissues, including cartilage, bone, skeletal muscle, lung, intestine and skin. Clear developmental shifts in expression suggest a role in endochondral ossification of bone and the branching morphogenesis in the lung. Notable structures lacking type XIII collagen were the endothelia of most blood vessels and the endocardium. Its initially unique staining pattern began to concentrate in the same adhesive structures where it exists in adult tissues, and started to resemble that of the beta1 integrin subunit and vinculin during late intrauterine development and in the perinatal period.

Animals↗

PubMed2001

The Ras-Byr2RBD complex: structural basis for Ras effector recognition in yeast.

BACKGROUND: The small GTP binding protein Ras has important roles in cellular growth and differentiation. Mutant Ras is permanently active and contributes to cancer development. In its activated form, Ras interacts with effector proteins, frequently initiating a kinase cascade. In the lower eukaryotic Schizosaccharomyces pombe, Byr2 kinase represents a Ras target that in terms of signal-transduction hierarchy can be considered a homolog of mammalian Raf-kinase. The activation mechanism of protein kinases by Ras is not understood, and there is no detailed structural information about Ras binding domains (RBDs) in nonmammalian organisms. RESULTS: The crystal structure of the Ras-Byr2RBD complex at 3 A resolution shows a complex architecture similar to that observed in mammalian homologous systems, with an interprotein beta sheet stabilized by predominantly polar interactions between the interacting components. The C-terminal half of the Ras switch I region contains most of the contact anchors, while on the Byr2 side, a number of residues from topologically distinct regions are involved in complex stabilization. A C-terminal helical segment, which is not present in the known mammalian homologous systems and which is part of the auto-inhibitory region, has an additional binding site outside the switch I region. CONCLUSIONS: The structure of the Ras-Byr2 complex confirms the Ras binding module as a communication element mediating Ras-effector interactions; the Ras-Byr2 complex is also conserved in a lower eukaryotic system like yeast, which is in contrast to other small GTPase families. The extra helical segment might be involved in kinase activation.

Amino Acid Sequence↗

PubMed2001

Determination of sulfur dioxide in vitriol plant wastewater by using a polyNiMe4TAA electrochemically modified Pt microelectrode.

A Pt microelectrode modified with nickel(II) polytetramethyldibenzo[b,i]tetraaza[14]annulene was prepared by electropolymerization of nickel(II) tetramethyldibenzo[b,i]tetraaza[14]annulene monomers and applied to determine sulfur dioxide in vitriol plant wastewater. For determination of SO2 with this electrochemically modified Pt microelectrode, the linear range was from 9.6 x 10(-6) to 2.4 x 10(-4) mol L-1, the sensitivity was 1.8 x 10(-4) A L mol-1, the detection limit was calculated to be 4.8 x 10(-6) mol L-1 (S/N = 3), the response time was less than 20 s and the relative standard deviation was found to be 2.1% on analyzing 4.8 x 10(-5) mol L-1 SO2 solution repeatedly (n = 7). These results demonstrated good accuracy compared with those obtained by the conventional iodimetric method.

Chemical Industry↗

PubMed2001

Type 2 iodothyronin deiodinase transgene expression in the mouse heart causes cardiac-specific thyrotoxicosis.

Type 2 iodothyronine deiodinase (D(2)) catalyzes intracellular 3, 5, 3' triiodothyronine (T(3)) production from thyroxine (T(4)), and its messenger RNA mRNA is highly expressed in human, but not rodent, myocardium. The goal of this study was to identify the effects of D(2) expression in the mouse myocardium on cardiac function and gene expression. We prepared transgenic (TG) mice in which human D(2) expression was driven by the alpha-MHC promoter. Despite high myocardial D(2) activity, myocardial T(3) was, at most, minimally increased in TG myocardium. Although, plasma T(3) and T(4), growth rate as well as the heart weight was not affected by TG expression, there was a significant increase in heart rate of the isolated perfused hearts, from 284 +/-12 to 350 +/- 7 beats/min. This was accompanied by an increase in pacemaker channel (HCN2) but not alpha-MHC or SERCA II messenger RNA levels. Biochemical studies and (31)P-NMR spectroscopy showed significantly lower levels of phosphocreatine and creatine in TG hearts. These results suggest that even mild chronic myocardial thyrotoxicosis, such as may occur in human hyperthyroidism, can cause tachycardia and associated changes in high energy phosphate compounds independent of an increase in SERCA II and alpha-MHC.

Adenine Nucleotides↗

PubMed2001

[Effect of microgravity simulation with clinostat on different strains in Anabaena oryza].

The Biological responses of Anabana oryza (different strains) to microgravity simulation with clinostat were analyzed. The simulation of growth rate was observed under clinoration all the strains, especially in flight strains (AoR16 and AoSR16-17). Anabana oryza HB23 showed higher activity than flight strains in photosynthesis and respiration. The nitrogen which flight strains with high nitrogrnase activity fixed under culturing in ground was used to accumulate phycobiliprotein in cell and excrete ammonium out of cell after meeting the normal metabolism, however, it was mainly used to simulate growth rate under culturing with clinostat. menwhile, it was different from space flight that microgravity simulation with clinostat was not able to induced the phenotype segregation in Anabana oryzae.

Anabaena↗

PubMed2000

Role of LXRs in control of lipogenesis.

The discovery of oxysterols as the endogenous liver X receptor (LXR) ligands and subsequent gene targeting studies in mice provided strong evidence that LXR plays a central role in cholesterol metabolism. The identification here of a synthetic, nonsteroidal LXR-selective agonist series represented by T0314407 and T0901317 revealed a novel physiological role of LXR. Oral administration of T0901317 to mice and hamsters showed that LXR activated the coordinate expression of major fatty acid biosynthetic genes (lipogenesis) and increased plasma triglyceride and phospholipid levels in both species. Complementary studies in cell culture and animals suggested that the increase in plasma lipids occurs via LXR-mediated induction of the sterol regulatory element-binding protein 1 (SREBP-1) lipogenic program.

Animals↗

PubMed2000

A short sequence in the N-terminal region is required for the trimerization of type XIII collagen and is conserved in other collagenous transmembrane proteins.

The recombinant transmembrane protein type XIII collagen is shown to reside on the plasma membrane of insect cells in a 'type II' orientation. Expressions of deletion constructs showed that sequences important for the association of three alpha1(XIII) chains reside in their N- rather than C-terminal portion. In particular, a deletion of residues 63-83 immediately adjacent to the transmembrane domain abolished the formation of disulfide-bonded trimers. The results imply that nucleation of the type XIII collagen triple helix occurs at the N-terminal region and that triple helix formation proceeds from the N- to the C-terminus, in opposite orientation to that of the fibrillar collagens. Interestingly, a sequence homologous to the deleted residues was found at the same plasma membrane-adjacent location in other collagenous transmembrane proteins, suggesting that it may be a conserved association domain. The type XIII collagen was secreted into insect cell medium in low amounts, but this secretion was markedly enhanced when the cytosolic portion was lacking. The cleavage occurred in the non-collagenous NC1 domain after four arginines and was inhibited by a furin protease inhibitor.

Amino Acid Sequence↗

PubMed2000

DARPP-32 and CREB are present in type 2 iodothyronine deiodinase-producing tanycytes: implications for the regulation of type 2 deiodinase activity.

Type 2 iodothyronine deiodinase, an enzyme involved in the conversion of thyroxin to the biologically active 3,5, 3'-triiodothyronine, is highly concentrated in a group of specialized ependymal cells, tanycytes, lining the wall and floor of the third ventricle. As this distribution is highly reminiscent of the distribution of cells containing the phosphatase inhibitor, DARPP-32, we raised the possibility that these two proteins may coexist in tanycytes and that DARPP-32 may modulate type 2 deiodinase activity by regulating the phosphorylation state of the cAMP regulatory factor, CREB. To address this question, double-labeling histochemical studies were performed for type 2 deiodinase mRNA and DARPP-32 immunoreactivity (IR), or DARPP-32- and CREB-IR in the same tissue sections. Type 2 deiodinase mRNA was found in the cell bodies of all DARPP-32-immunolabeled tanycytes. Both type 2 deiodinase mRNA and DARPP-32-IR also extended into tanycyte processes that ramified in the arcuate nucleus and median eminence, in close association with blood vessels and portal capillaries. In contrast, type 2 deiodinase mRNA was not present in the same cells that contained DARPP-32-IR in the pituitary gland. All tanycytes containing DARPP-32-IR also contained CREB-IR in their nucleus. Since type 2 deiodinase activity can be induced by substances that increase cAMP, we hypothesize that DARPP-32 may regulate the activity of type 2 deiodinase by prolonging the activation of CREB. Selectivity for the colocalization of these factors to tanycytes but not the pituitary gland, may explain the heterogeneous response of type 2 deiodinase activity in these two loci in response to specific stimuli such as fasting.

Animals↗

PubMed2000

Distinct recognition of collagen subtypes by alpha(1)beta(1) and alpha(2)beta(1) integrins. Alpha(1)beta(1) mediates cell adhesion to type XIII collagen.

Two integrin-type collagen receptors, alpha(1)beta(1) and alpha(2)beta(1), are structurally very similar. However, cells can concomitantly express the both receptors and they might have independent functions. Here, Chinese hamster ovary (CHO) cells, which lack endogenous collagen receptors, were transfected with either alpha(1) or alpha(2) integrin cDNA. Cells were allowed to adhere to various collagen types and their integrin function was tested by observing the progression of cell spreading. The cells expressing alpha(1)beta(1) integrin could spread on collagen types I, III, IV, and V but not on type II, while alpha(2)beta(1) integrin could mediate cell spreading on collagen types I-V. Type XIII is a transmembrane collagen and its interaction with the integrins has not been previously studied. CHO-alpha1beta1 cells could spread on human recombinant type XIII collagen, unlike CHO-alpha2beta1 cells. Integrins alpha(1)beta(1) and alpha(2)beta(1) recognize collagens with the specific alphaI domains. The alpha(1)I and alpha(2)I domains were produced as recombinant proteins, labeled with europium and used in a sensitive solid-phase binding assay based on time-resolved fluorescence. alpha(1)I domain, unlike the alpha(2)I domain, could attach to type XIII collagen. The results indicate, that alpha(1)beta(1) and alpha(2)beta(1) have different ligand binding specificity. Distinct recognition of different collagen subtypes by the alphaI domains can partially explain the differences seen in cell spreading. However, despite the fact that CHO-alpha1beta1 cells could not spread on type II collagen alpha(1)I domain could bind to this collagen type. Thus, the cell spreading on collagens may also be regulated by factors other than the integrins.

Animals↗

PubMed2000

Collagen XVII is destabilized by a glycine substitution mutation in the cell adhesion domain Col15.

Collagen XVII is a hemidesmosomal transmembrane molecule important for epithelial adhesion in the skin. It exists in two forms, as a full-length protein and as a soluble ectodomain that is shed from the keratinocyte surface by furin-mediated proteolysis. To obtain information on the conformation and the functions of this unusual collagen, its largest collagenous domain, Col15, was expressed in a eukaryotic episomal expression system and purified by DEAE and fast protein liquid- Mono S chromatography. The protein was triple-helical (T(m) of 26.5 degrees C) when produced in cultures containing ascorbic acid. When the vitamin supply was limited, the 4-hydroxyproline content was reduced from 74 to 9%, which, in turn, resulted in a drastic reduction of the stability of the triple helix. The glycine substitution mutation G627V associated with junctional epidermolysis bullosa, a human blistering skin disease, also had a striking effect on thermal stability of rCol15 causing partial unfolding already at 4 degrees C. Col15 promoted cell adhesion of epithelial and fibroblastic cell lines with a beta1 integrin-mediated mechanism. In concert with this, in acquired autoimmune blistering skin diseases, circulating IgG and IgA autoantibodies were found to target rCol15r.

Amino Acid Substitution↗

PubMed2000

Dietary phosphorus regulates intestinal transport and plasma concentrations of phosphate in rainbow trout.

Intestinal inorganic phosphate transport and its regulation have not been studied in fish. In this study, we initially characterized the mechanisms of intestinal inorganic phosphate transport in rainbow trout (Oncorhynchus mykiss) then determined the effects of dietary phosphorus concentrations on intestinal inorganic phosphate uptake, plasma inorganic phosphate, and intestinal luminal inorganic phosphate concentrations. In 11-g trout, the saturable mechanism of brushborder inorganic phosphate uptake had a Kt= 1.2 mmol l(-1) and a Vmax = 0.22 nmol mg(-1) min(-1), while the diffusive component had a Kd = 0.012 min(-1). Similar kinetic constants were obtained from 51-g trout, suggesting that development or size had little effect on transport. Tracer inorganic phosphate (1.18 mmol l(-1)) uptake was almost completely inhibited (>95%) by 20 mmol l(-1) unlabeled inorganic phosphate. Inorganic phosphate uptake (0.2 mmol l(-1)) was strongly inhibited (approximately 75% inhibition) by phosphonoformic acid, a competitive inhibitor of mammalian inorganic phosphate transport, as well as by the absence of Na+ (approximately 90% inhibition). Northern blot and reverse transcription-polymerase chain reaction indicated that the intestinal inorganic phosphate transporter in trout is not related to the cloned Na+ inorganic phosphate-II transporter of winter flounder. Intestinal luminal and plasma inorganic phosphate concentrations each increased with dietary P concentrations. Intestinal inorganic phosphate, but not proline, absorption rates decreased with dietary phosphorus concentrations. As in mammals and birds, a Na-dependent inorganic phosphate carrier that is tightly regulated by diet is present in trout small intestine.

Animal Nutritional Physiological Phenomena↗

PubMed2000

FXR, a bile acid receptor and biological sensor.

Bile acid synthesis is a major pathway for cholesterol disposal and thus represents a potential therapeutic target pathway for the treatment of hypercholesterolemia. Recently, the nuclear farnesoid X receptor (FXR) was identified as a bile acid receptor and biological sensor for the regulation of bile acid biosynthesis. FXR was shown to regulate cholesterol metabolism in two ways: (1) chenodeoxycholic acid (CDCA), a primary bile acid, binds directly to and activates FXR, which then mediates the feedback suppression by bile acids of cholesterol 7 alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in bile acid biosynthesis from cholesterol; and (2) FXR participates in the activation of intestinal bile acid binding protein (IBABP), which is involved in the enterohepatic circulation of bile acids. Thus FXR constitutes a potential therapeutic target that can be modulated to enhance the removal of cholesterol from the body.

Animals↗