[Active anticarcinogenic chemical components in ordinary garlic and selenium-enriched garlic].
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Allyl Compounds↗
Biomedical subjects
X Yang
Publications and source records attributed to X Yang.
Telomerase activity in normal and neoplastic breast.
Telomerase activity is detected in the majority of human tumors and provides a mechanism to escape from proliferative limitations due to telomere loss. Similar to other studies, telomerase activity was detected with a modified telomeric repeat amplification protocol in the majority (76%) of 49 human breast cancer specimens, including most (75%) ductal carcinoma in situ specimens. There were no correlations between telomerase activity and tumor stage or estrogen/progesterone receptor status. In four of seven invasive tumors, telomerase expression seemed to be heterogeneous because not all microdissected regions were telomerase positive. Low levels of telomerase activity were also detected in a minority (17%) of breast specimens from patients without evidence of cancer. These findings suggest that telomerase activation can occur early in breast cancer progression and may be periodically down-regulated during subsequent progression.
Biomarkers, Tumor↗
[Successful replantation of whole scalp avulsion with micro-vascular anastomosis. A case report].
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Adult↗
[Image analysis of tumor cells from common intracranial neoplasms on frozen and paraffined slices].
Image analysis technique was used to measure four parameters [the form factor (FF), area, perimeter and diameter] of nuclei in 76 cases of common intracranial tumors on forzen and paraffined slices. The results showed that the area, perimeter, diameter of nuclei on frozen slices were much larger than those on paraffined slices while the FF showed no significant difference between two kinds of slices (P > 0.05). The parameters of the area, perimeter, and diameter of nuclei on two kinds of slices became larger and the parameters of FF became smaller as the grade of astrocytoma ascended. It is considered that the results of present study will be helpful to the diagnosis of common intracranial tumors on frozen slices.
Astrocytoma↗
Two GTPase isoforms, Ypt31p and Ypt32p, are essential for Golgi function in yeast.
In eukaryotic cells, monomeric GTPases of the Ypt/Rab family function as regulators at defined steps of vesicular transport in exo- and endocytosis. Here we report on the isolation and characterization of two genes (YPT31 and YPT32) of the yeast Saccharomyces cerevisiae which encode members of the Ypt family exhibiting >80% sequence identity. Whereas the disruption of one of the two genes was phenotypically neutral, the disruption of both YPT31 and YPT32 led to lethality. Depletion of wild-type Ypt31p or of a short-lived ubiquitin-Ypt31p in a ypt32 null background led to a massive accumulation of Golgi-like membranes, an inhibition of invertase secretion and defects in vacuolar protein maturation. Similar alterations were observed in a conditional-lethal ypt31-1 mutant at 30 min after shift to the non-permissive temperature. According to subcellular fractionation, a significant part of Ypt31p appeared to be located in Golgi-enriched membrane fractions. In accordance with this, indirect immunofluorescence using affinity-purified anti-Ypt31p antibodies gave a punctate staining similar to that observed with Golgi-located proteins. From the phenotypic alterations observed in ypt31 and ypt32 mutants, it seems likely that the two GTPases are involved in intra-Golgi transport or in the formation of transport vesicles at the most distal Golgi compartment.
Amino Acid Sequence↗
Genetically unstable CXG repeats are structurally dynamic and have a high propensity for folding. An NMR and UV spectroscopic study.
Recent molecular genetics studies have revealed a correlation between spontaneous, progressive expansion of several DNA trinucleotide repeats and certain hereditary neurodegenerative diseases. Triplet repeat (TR) sequences may be present in structured forms that can mediate the processes interrupting normal cellular replication, transcription, or repair activities, eventually leading to gene mutation. Using high resolution NMR spectroscopy and other biophysical methods, we probed the solution structures and properties of single-stranded TR sequences. These studies have led to the discovery of a new duplex motif (e-motif), present in CCG repeats, and to the elucidation of the structure of the (CTG)3 duplex. In this paper we provide a global picture of the solution behavior of the human disease-related CXG (X = A, C, G, or T) and the comparison GXC (X = A, or T) TR sequences. All six triplet repeats form antiparallel duplexes. The mismatched bases in CAG and CGG repeat duplexes are rather flexible and they do not appear to form stable, paired conformations. By comparison, GAC repeat duplexes and their mismatched A residues are well-structured. Most interestingly, the structures of the disease-related CXG repeats exhibit a propensity for folding at chain lengths as short as 12 residues. Furthermore, the energy barrier for the formation of homo-duplexes from the corresponding complementary hetero-duplexes are much lower for the CXG TR sequences than for the GAC or GTC TR sequences. These results provide insights into the conformation and physiochemical properties of TR sequences. Thus, a basis is provided for further studies of the behavior of long TR sequences in an effort to elucidate the molecular mechanisms of in vivo expansion and function of TR sequences.
Base Composition↗
Non-aminergic effects of amphetamine on the NMDA receptor in primary cultured cortical cells.
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Amphetamines↗
Femoral atherosclerosis in middle-aged subjects: association with cardiovascular risk factors and insulin resistance.
The aim of this 8-year follow-up study was to investigate the role of conventional cardiovascular risk factors as predictors for asymptomatic femoral atherosclerosis. The authors also evaluated the association of insulin resistance with atherosclerosis in a cross-sectional setting. Cardiovascular risk factors of 118 subjects were studied at the baseline study in 1983-1985 in Kuopio, Finland. Femoral atherosclerosis, defined as a presence of plaques, was investigated by ultrasonography in the follow-up study in 1992-1993. In the univariate logistic regression analyses, age (p = 0.002), systolic and diastolic blood pressure (p = 0.002 and p = 0.013, respectively), total cholesterol (p = 0.005), low density lipoprotein (LDL) cholesterol (p = 0.005), total triglycerides (p = 0.033), LDL triglycerides (p = 0.033), apolipoprotein B (p = 0.045), and fasting plasma glucose (p = 0.011) had a significant association with the presence of femoral plaques. Plasma insulin levels and insulin sensitivity index, determined in 87 subjects by an intravenous glucose tolerance test and minimal model at the follow-up study, were not associated with femoral plaques. The results demonstrate that atherogenic lipid and lipoprotein pattern and blood pressure are strongly associated with femoral atherosclerosis, whereas insulin sensitivity and hyperinsulinemia seem not to play such a significant role.
Adult↗
Apoptosis of cardiac myocytes during cardiac allograft rejection. Relation to induction of nitric oxide synthase.
BACKGROUND: Apoptosis is a distinct form of programmed cell death characterized by activation of endonucleases that cleave nuclear DNA, condensation and fragmentation of nuclear chromatin, blebbing of intact membranes, and cell shrinkage and fragmentation. The mechanisms responsible are unclear, but nitric oxide (NO) generated by inducible NO synthase (iNOS) has been demonstrated to induce apoptosis in macrophages in vitro. This study investigated whether apoptosis occurs during cardiac allograft rejection and examined the relationship of apoptosis to iNOS expression. METHODS AND RESULTS: Heterotopic abdominal transplantation from Lewis to Wistar-Furth rats was used as a model of cardiac allograft rejection; Lewis-to-Lewis grafts served as controls. Apoptosis was identified by DNA ladders after electrophoresis on agarose gels and by in situ labeling of DNA fragments; cell types were determined by immunohistochemistry. The number of apoptotic cardiac myocytes increased sharply from day 3 (0.31/mm2 ventricular tissue) to day 5 (1.27/mm2) after transplantation. At day 5, allografts showed a significant increase (P < .01) in apoptotic cardiac myocytes, macrophages, and endothelial cells compared with syngeneic grafts. The expression of iNOS mRNA, protein, and enzyme activity paralleled in time and extent the apoptosis of cardiac myocytes. iNOS immunostaining of infiltrating macrophages and cardiac muscle fibers increased significantly in the allografts at days 3 to 5 and was accompanied by immunostaining of both cell types for nitrotyrosine, which is indicative of peroxynitrite formation. CONCLUSIONS: Apoptosis of myocardial cells occurs during cardiac allograft rejection. Apoptosis during rejection parallels the expression of iNOS, which suggests that apoptosis may be triggered by NO and peroxynitrite.
Animals↗
Flk-1, a receptor for vascular endothelial growth factor (VEGF), is expressed by retinal progenitor cells.
Throughout development of the vertebrate retina, progenitor cells are multipotential, producing a variety of distinctive cell types. Little is known of the molecular mechanisms directing the determination of cell fate. We have examined retinal progenitor cells for expression of receptor tyrosine kinases in an attempt to define receptors that could allow a progenitor to respond to its environment. We found that the receptor tyrosine kinase Flk-1, previously shown to be expressed in endothelial cells, is also expressed in neural progenitor cells of the mouse retina. Flk-1 RNA expression in the retinal progenitors commences with the onset of neuronal differentiation and persists throughout retinal neurogenesis. Flk-1 RNA and protein levels in the retina vary temporally during development, as shown by in situ hybridization and Western blot analysis. Patterns of beta-galactosidase expression in mice containing the lacZ gene in place of the Flk-1 gene are consistent with Flk-1 being expressed in retinal progenitors. In addition, we show that the ligand of Flk-1, vascular endothelial growth factor (VEGF), is expressed in the developing retina by differentiated cells and that a chimeric ligand of VEGF fused to alkaline phosphatase binds to proliferating retinal progenitors. Furthermore, the neural retina-derived Flk-1 protein kinase is activated by VEGF in vitro. Thus, the Flk-1 receptor protein kinase is expressed on the surface of neural progenitors in mouse retina and may play a critical role in neurogenesis as well as in vasculogenesis.
Alkaline Phosphatase↗
Structural and functional organization of the DNA polymerase of bacteriophage T7.
The 80-kDa gene 5 protein encoded by bacteriophage T7 shares significant amino acid homology with the large fragment of Escherichia coli DNA polymerase I (Klenow fragment). Like the Klenow fragment, T7 gene 5 protein has both DNA polymerase and 3' to 5' exonuclease activities. However, unlike the Klenow fragment, T7 gene 5 protein binds tightly to E. coli thioredoxin to form a complex that has a high processivity of nucleotide polymerization. In order to identify the domains of gene 5 protein responsible for polymerization, hydrolysis, and binding of thioredoxin, we have analyzed proteolytic fragments of gene 5 protein. Cleavage of the protein within one protease-sensitive region (residue 250-300) yields two molecular weight species of peptides of 32-37 and 43-51 kDa derived from the N-terminal and C-terminal region, respectively. DNA polymerase activity is found within the C-terminal fragments and exonuclease activity within the N-terminal fragments. Thioredoxin stimulates the DNA polymerase activity of the C-terminal fragments. All fragments bind to DNA. In addition to delineating the polymerase and exonuclease domains, the protease-sensitive region appears to interact with E. coli thioredoxin. Thioredoxin protects this region from proteolysis, and alteration of this region reduces the ability of thioredoxin to stimulate polymerase activity.
Amino Acid Sequence↗
Opposing pairs of serine protein kinases and phosphatases transmit signals of environmental stress to activate a bacterial transcription factor.
The general stress response of the bacterium Bacillus subtilis is governed by a signal transduction network that regulates activity of the sigma(B) transcription factor. We show that this network comprises two partner-switching modules, RsbX-RsbS-RsbT and RsbU-RsbV-RsbW, which contribute to regulating sigma(B). Each module consists of a phosphatase (X or U), an antagonist protein (S or V), and a switch protein/kinase (T or W). In the downstream module, the W anti-sigma factor is the primary regulator of sigma(B) activity. If the V antagonist is phosphorylated, the W switch protein binds and inhibits sigma(B). If V is unphosphorylated, it complexes W, freeing sigma(B) to interact with RNA polymerase and promote transcription. The phosphorylation state of V is controlled by opposing kinase (W) and phosphatase (U) activities. The U phosphatase is regulated by the upstream module. The T switch protein directly binds U, stimulating phosphatase activity. The T-U interaction is governed by the phosphorylation state of the S antagonist, controlled by opposing kinase (T) and phosphatase (X) activities. This partner-switching mechanism provides a general regulatory strategy in which linked modules sense and integrate multiple signals by protein-protein interaction.
Bacillus subtilis↗
Human platelet signaling defect characterized by impaired production of inositol-1,4,5-triphosphate and phosphatidic acid and diminished Pleckstrin phosphorylation: evidence for defective phospholipase C activation.
Signal transduction on platelet activation involves phosphoinositide-specific phospholipase C (PLC)-mediated hydrolysis of phosphatidylinositides and formation of inositol-1,4,5-triphosphate [I(1,4,5)P3], which mediates Ca2+ mobilization, and diacylglycerol (DG), which activates protein kinase C (PKC) to phosphorylate a 47-kD protein (Pleckstrin). We studied these events in two related patients previously reported (Blood 74:664, 1989) to have abnormal aggregation and 14C-serotonin secretion, and impaired intracellular Ca2+ mobilization in response to several agonists. Thrombin-induced I(1,4,5)P3 and phosphatidic acid formation were diminished. Pleckstrin phosphorylation was impaired on activation with thrombin, platelet-activating factor, and ionophore A23187, but was normal with PKC activator 1,2-dioctonyl-sn-glycerol (DiC8). Ca2+ mobilization induced by guanosine triphosphate (GTP) analog guanosine 5'-0-(3 thiotriphosphate) (GTP gamma S) was diminished. Pretreatment with either A23187 or DiC8 did not correct the impaired adenine diphosphate-induced secretion; however, upon stimulation with A23187 plus DiC8, pleckstrin phosphorylation and secretion were normal, indicating that both PKC activation and Ca2+ mobilization are essential for normal secretion. We conclude that these patients have a unique inherited platelet defect in formation of two key intracellular mediators [I(1,4,5)P3 and DG] and in the responses mediated by them due to a defect in postreceptor mechanisms of PLC activation.
Adenosine Diphosphate↗
Decreased expression of phospholipase C-beta 2 isozyme in human platelets with impaired function.
Platelets from a patient with a mild inherited bleeding disorder and abnormal platelet aggregation and secretion show reduced generation of inositol 1,4,5-trisphosphate, mobilization of intracellular Ca2+, and phosphorylation of pleckstrin in response to several G protein mediated agonists, suggesting a possible defect at the level of phospholipase C (PLC) activation (see accompanying report). A procedure was developed that allows quantitation of platelet PLC isozymes. After fractionation of platelet extracts by high-performance liquid chromatography, 7 out of 10 known PLC isoforms were detected by immunoblot analysis. The amount of these isoforms in normal platelets decreased in the order PLC-gamma 2 > PLC-beta 2 > PLC-beta 3 > PLC-beta 1 > PLC-gamma 1 > PLC-delta 1 > PLC-beta 4. Compared with normal platelets, platelets from the patient contained approximately one-third the amount of PLC-beta 2, whereas PLC-beta 4 was increased threefold. These results suggest that the impaired platelet function in the patient in response to multiple G protein mediated agonists is attributable to a deficiency of PLC-beta 2. They document for the first time a specific PLC isozyme deficiency in human platelets and provide an unique opportunity to understand the role of different PLC isozymes in normal platelet function.
Blood Platelets↗
Insights into specificity of cleavage and mechanism of cell entry from the crystal structure of the highly specific Aspergillus ribotoxin, restrictocin.
BACKGROUND: Restriction, a highly specific ribotoxin made by the fungus Aspergillus restrictus, cleaves a single phosphodiester bond in the 28S RNA of eukaryotic ribosomes, inhibiting protein synthesis. The sequence around this cleavage site is a binding site for elongation factors, and is conserved in all cytoplasmic ribosomes. The catalytic mechanism of restrictocin and the reasons for its high substrate specificity are unknown. No structure has been determined for any other member of the Aspergillus ribotoxin family. RESULTS: The crystal structure of restrictocin was determined at 2.1 A resolution by single isomorphous replacement and anomalous scattering techniques, and refined to 1.7 A resolution using synchrotron Laue data. The structural core of the protein, in which a three-turn alpha helix is packed against a five-stranded antiparallel beta sheet, can be well aligned with that of ribonuclease T1. Large positively charged peripheral loops near the active site construct a platform with a concave surface for RNA binding. CONCLUSIONS: Restriction appears to combine the catalytic components of T1 ribonucleases with the base recognition components of Sa ribonucleases. Modeling studies using an NMR structure of an RNA substrate analog suggest that the tertiary structure of the substrate RNA is important in protein-RNA recognition, fitting closely into the concavity of the presumed binding site. We speculate that the large 39-residue loop L3, which has similarities to loops found in lectin sugar-binding domains, may be responsible for restrictocin's ability to cross cell membranes.
Allergens↗
Cloning and characterization of the promoter for murine 84-kDa heat-shock protein.
The 90-kDa heat-shock (HS) proteins (HSP90) are members of the HSP family. Their synthesis is inducible by HS and a variety of stress signals. HSP90 is also abundant under normal physiological conditions and its synthesis can be regulated during growth and differentiation. Therefore, HSP90 is speculated to have important biological functions, in addition to its role in mediating stress responses. However, the mechanism(s) regulating hsp90 gene expression in nonstressed cells is poorly understood. As a prerequisite towards understanding the basis for hsp90 regulation, we have cloned and characterized the 5' flanking region of murine hsp84, one of two genes which code for HSP90 proteins. Full basal promoter activity of hsp84 was found to be associated with a 627-bp region immediately upstream from the transcription start point (tsp). Sequence analysis revealed several putative regulatory elements, including a HS element (HSE), an AP1-binding site (AP1), a cyclic AMP response element (CRE), and four stimulatory protein-1-binding sites (SP1). HS inducibility required the HSE which was bound by HS transcription factor-1(HSF-1) present in extracts prepared from cells exposed to HS. The HSE was not required for basal (non-HS) expression, but, interestingly, two protein-HSE complexes, devoid of HSF-1 and HSF-2, were formed under these conditions. The potential significance of these findings to the expression of hsp84 under normal physiological conditions is discussed.
3T3 Cells↗
Perpendicular-electric-field dependence of exciton binding energy studied by continuous-wave photoluminescence.
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Journal Article↗
Genetically determined differences in IL-10 and IFN-gamma responses correlate with clearance of Chlamydia trachomatis mouse pneumonitis infection.
Cytokine patterns elicited by infection are critical in the regulation of the adaptive immune response and in the resolution of infection. Using a murine model of pneumonia induced by intranasal inoculation with the Chlamydia trachomatis mouse pneumonitis (MoPn) biovar, we found that the patterns of immune responses and cytokine production by spleen cells were correlated with quantitative growth of MoPn in the lungs of C57BL/6 and BALB/c mice. Specifically, BALB/c (H-2d) mice had a significantly higher mortality rate and a slower clearance of the organism from the lungs than did C57BL/6 mice (H-2b). BALB/c mice exhibited higher IL-10 production, higher IgG1 Ab responses, and less IFN-gamma production than C57BL/6 mice, which showed higher IFN-gamma production, stronger delayed-type hypersensitivity (DTH) responses, and significantly less IL-10 production. In vivo neutralization of IL-10 in BALB/c mice with an anti-IL-10 mAB during MoPn infection significantly increased the DTH response and enhanced clearance of MoPn. These findings support the hypothesis that excessive IL-10 production in BALB/c mice inhibits Th1-like responses, including IFN-gamma expression and the DTH response following chlamydial infection and consequently delay infection resolution.
Animals↗