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Biomedical subjects

Q Sun

Publications and source records attributed to Q Sun.

At least 163 records · Page 9Linked to original sources
PubMed1996

Structure-activity relationships of benzimidazoles and related heterocycles as topoisomerase I poisons.

A series of substituted 2-(4-methoxyphenyl)-1H-benzimidazoles were synthesized and evaluated as inhibitors of topoisomerase I. The presence of a 5-formyl-, 5-(aminocarbonyl)-, or 5-nitro group (i.e., substituents capable of acting as hydrogen bond acceptors) correlated with the potential of select derivatives to inhibit topoisomerase I. In contrast to bi- and terbenzimidazoles, the substituted benzimidazoles that were active as topoisomerase I poisons exhibited minimum or no DNA binding affinity. 5-Nitro-2-(4-methoxyphenyl)-1H-benzimidazole exhibited the highest activity and was significantly more active than the 4-nitro positional isomer. The 5- and 6-nitro derivatives of 2-(4-methoxyphenyl) benzoxazole, 2-(4-methoxyphenyl)benzothiazole, and 2-(4-methoxyphenyl)indole were synthesized and their relative activity as topoisomerase I inhibitors determined. None of these heterocyclic analogues were effective in significantly inhibiting cleavable-complex formation in the presence of DNA and topoisomerase I, suggesting a high degree of structural specificity associated with the interaction of these substituted benzimidazoles with the enzyme or the enzyme-DNA complex. In evaluating their cytotoxicity, these new topoisomerase I poisons also exhibited no significant cross-resistance against cell lines that express camptothecin-resistant topoisomerase I.

Antineoplastic Agents, Phytogenic↗
PubMed1996

Alpha-class isozymes of glutathione S-transferase in rat liver cytosol possess glutathione peroxidase activity toward phospholipid hydroperoxide.

Selenium-independent enzymes, found in the liver cytosol of selenium deficient rats, that are capable of reducing dilinoleoyl phosphatidylcholine hydroperoxide in the presence of reduced glutathione [Guan et al., (1995) Biochem. Mol. Biol. Int., 37, 1103-1110] were purified to homogeneity by use of successive chromatography on glutathione affinity and Mono P columns. The molecular weight of the purified protein was estimated by gel filtration to be approximately 50 kDa. Upon isoelectric focusing, the purified preparation showed two protein bands having pI values of 8.6 and 8.8. Both proteins had reactivity against both 1-chloro-2,4-dinitrobenzene and dilinoleoyl phosphatidylcholine hydroperoxide in the presence of reduced glutathione. Each of them consisted of two subunits having molecular weights of 24.3 kDa and 26 kDa, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The large subunit was identified as rat glutathione S-transferase (GST) 2 (Yc subunit) based on the amino-terminal amino acid sequence analysis. The small subunit was considered to be most probably rat GST 1 (Ya subunit). From these results, we conclude that the basic alpha-class isozymes of GST in rat liver cytosol possess glutathione peroxidase activity toward phospholipid hydroperoxide.

Animals↗
PubMed1996

Human interleukin-3 (IL-3) induces disulfide-linked IL-3 receptor alpha- and beta-chain heterodimerization, which is required for receptor activation but not high-affinity binding.

The human interleukin-3 receptor (IL-3R) is a heterodimer that comprises an IL-3 specific alpha chain (IL-3R alpha) and a common beta chain (beta C) that is shared with the receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-5. These receptors belong to the cytokine receptor superfamily, but they are structurally and functionally more related to each other and thus make up a distinct subfamily. Although activation of the normal receptor occurs only in the presence of ligand, the underlying mechanisms are not known. We show here that human IL-3 induces heterodimerization of IL-3R alpha and beta c and that disulfide linkage of these chains is involved in receptor activation but not high-affinity binding. Monoclonal antibodies (MAb) to IL-3R alpha and beta c were developed which immunoprecipitated, in the absence of IL-3, the respective chains from cells labelled with 125I on the cell surface. However, in the presence of IL-3, each MAb immunoprecipitated both IL-3R alpha and beta c. IL-3-induced receptor dimers were disulfide and nondisulfide linked and were dependent on IL-3 interacting with both IL-3R alpha and beta c. In the presence of IL-3 and under nonreducing conditions, MAb to either IL-3R alpha or beta c immunoprecipitated complexes with apparent molecular weights of 215,000 and 245,000 and IL-3R alpha and beta c monomers. Preincubation with iodoacetamide prevented the formation of the two high-molecular-weight complexes without affecting noncovalent dimer formation or high-affinity IL-3 binding. Two-dimensional gel electrophoresis and Western blotting (immunoblotting) demonstrated the presence of both IL-3R alpha and beta c in the disulfide-linked complexes. IL-3 could also be coimmunoprecipitated with anti-IL-3R alpha or anti-beta c MAB, but it was not covalently attached to the receptor. Following IL-3 stimulation, only the disulfide-linked heterodimers exhibited reactivity with antiphosphotyrosine antibodies, with beta c but not IL-3R alpha being the phosphorylated species. A model of IL-3R activation is proposed which may be also applicable to the related GM-CSF and IL-5 receptors.

Animals↗
PubMed1996

[Quality control of zhuanggu shenjin capsules].

Studies have been made on the microscopic identification of red jinseng, dog bone, indian bread, yanhusuo and datura flower in Zhuanggu Shenjin Capsules, as well as on the identification of ginsengside and tetrahydropalmatine by TLC and the determination of icariin by dual wavelength TLC-scanning. The content of the latter compound should be no less than 0.380mg/g and the average rate of recovery 97.62% (n = 5).

Berberine Alkaloids↗
PubMed1996

Characterizing the DNA binding modes of a topoisomerase I-poisoning terbenzimidazole: evidence for both intercalative and minor groove binding properties.

We have used a broad range of spectroscopic and viscometric techniques to demonstrate that the complexation of a cytotoxic, topoisomerase I-poisoning terbenzimidazole (5PTB) with the poly(dA).poly(dT) duplex exhibits properties characteristic of both intercalation and minor groove binding. Our results reveal the following features: (i) Optical melting profiles reveal that 5PTB binding enhances the thermal stability of the poly(dA).poly(dT) duplex; (ii) Fluorescence-detected 5PTB binding to the poly(dA).poly(dT) duplex reveals four apparent "site sizes," ranging from 1 to 13 base pairs (bp) per bound drug; (iii) Flow linear dichroism data suggest conformational heterogeneity among the poly(dA).poly(dT)-bound 5PTB molecules, with substantial contributions from drug molecules bound in the minor groove; (iv) Fluorescence resonance energy transfer data reveal properties characteristic of a significant contribution from an intercalative mode of binding; (v) Viscometric, fluorescence quenching, and netropsin competition data are consistent with 5PTB binding to poly(dA).poly(dT) by "mixed" modes, which are operationally defined as single or multiple binding populations that individually and/or collectively express both intercalative and minor groove binding properties. We comment on a potential correlation between drugs that exhibit such "mixed" mode binding motifs and those that express antineoplastic activity through inhibition of topoisomerase I.

Benzimidazoles↗
PubMed1996

Comparative study on the mechanism of formation of pulse manifestations in coronary heart disease and hematopathic patients.

Most patients suffering from coronary heart disease have string--like pulse due mainly to disorder of cardiac function, lowered arterial compliance and increased total peripheral resistance. The common type of pulse in hematopathy patients is rapid, thready, string--like and slippery, due mainly to increased compensatory pumping action of heart, shortening of ejection time of left ventricle, relatively better vessel compliance and blood rheology as well as low total peripheral resistance.

Adolescent↗
PubMed1996

Signal transduction pathways in guinea pig sperm.

Trifluoperazine (TFP), the antagonist of calmodulin (CaM), significantly stimulated the capacitation and acrosome reaction of guinea pig spermatozoa at the concentration of 10-100 mumol/L, independent of the external Ca2+. Forskolin, dbcAMP and caffeine evidently promoted the occurrence of acrosome reaction of spermatozoa at early capacitation stage (5 h) in nonsynchronous system but not in synchronous system. If the spermatozoa were capacitated for 15 h in synchronous system, the above three drugs significantly stimulated acrosome reaction in a Ca(2+)-independent manner. Protein kinase C activators, i.e. phorbol 12-myristate 13-acetate (PMA) and phorbol 12,13-dibutyrate (PDB) did not influence the occurrence of acrosome reaction of spermatozoa at early capacitation stage, but significantly increased the acrosome reaction rate in capacitated spermatozoa in a Ca(2+)-independent manner. In contrast, PKC inhibitor staurosporine significantly inhibited the occurrence of acrosome reaction.

Acrosome↗
PubMed1995

Neutrophils activated by granulocyte-macrophage colony-stimulating factor express receptors for interleukin-3 which mediate class II expression.

Freshly isolated peripheral blood neutrophils, unlike monocytes and eosinophils, do not bind interleukin-3 (IL-3) or respond to IL-3). We show that neutrophils cultured for 24 hours in granulocyte-macrophage colony-stimulating factor (GM-CSF) express mRNA for the IL-3 receptor (R) alpha subunit, as shown by RNase protection assays, and IL-3R alpha chain protein, as shown by cytometric analysis using two different specific monoclonal antibodies. This effect was selective for GM-CSF, because granulocyte colony-stimulating factor, tumor necrosis factor-alpha, interferon-gamma, and IL-1 failed to induce the IL-3 receptor. Saturation binding curves with 125I-IL-3 and Scatchard transformation showed the presence of about 100 high-affinity and 4,000 low-affinity receptors. Because neutrophils have been shown to express human leukocyte antigen (HLA)-DR in response to GM-CSF, we examined the possibility that IL-3 could augment HLA-DR expression on GM-CSF-treated cells. We found that neutrophils incubated with 30 ng/mL IL-3 as well as 0.1 ng/mL GM-CSF expressed a mean of 2.1-fold higher levels of HLA-DR than with GM-CSF alone (P < .005), confirming the signaling competence of the newly expressed IL-3R. This increase was seen even at maximal concentrations of GM-CSF and IL-3 can have an additive effect on mature human cells. The augmentation of HLA-DR by IL-3 was specific because it could be inhibited by a blocking anti-IL-3R antibody. Expression of class II molecules by neutrophils under these conditions may have significance for antigen presentation. These results provide further evidence for the role of GM-CSF as an amplification factor in inflammation by inducing neutrophil responsiveness to IL-3 produced by T cells or mast cells.

Cells, Cultured↗
PubMed1995

Ethylene insensitivity conferred by Arabidopsis ERS gene.

ERS (ethylene response sensor), a gene in the Arabidopsis thaliana ethylene hormone-response pathway, was uncovered by cross-hybridization with the Arabidopsis ETR1 gene. The deduced ERS protein has sequence similarity with the amino-terminal domain and putative histidine protein kinase domain of ETR1, but it does not have a receiver domain as found in ETR1. A missense mutation identical to the dominant etr1-4 mutation was introduced into the ERS gene. The altered ERS gene conferred dominant ethylene insensitivity to wild-type Arabidopsis. Double-mutant analysis indicates that ERS acts upstream of the CTR1 protein kinase gene in the ethylene-response pathway.

Amino Acid Sequence↗
PubMed1995

Synthesis and evaluation of terbenzimidazoles as topoisomerase I inhibitors.

The synthesis and pharmacological activity of a series of terbenzimidazoles are described. The ability of these derivatives to induce DNA cleavage in the presence of topoisomerase I was evaluated in vitro. These analogs were also assayed for their cytotoxicity in RPMI 8402 cells and the camptothecin-resistant CPT-K5 cells. In addition the potential for these compounds to serve as substrates for MDR1 was also determined. Several terbenzimidazoles exhibited similar cytotoxicity against variants of human tumor cells that either overexpress MDR1 or are camptothecin-resistant.

Animals↗
PubMed1995

Structure and function of the UvrB protein.

UvrB plays a central role in (A)BC excinuclease. To identify the regions of UvrB which are involved in interacting with UvrA, UvrC, and DNA, deletion mutants, point mutants, and various fusion forms of UvrB were constructed and characterized. We found that the region encompassing amino acid residues 115-250 of UvrB binds to UvrA, while the region encompassing amino acid residues 547-673 binds to both UvrA and UvrC. In addition, the region between these two domains, which contains the helicase motifs II-VI, was found to be involved in binding to DNA. Within this DNA-binding region, two point mutants, E265A and E338A, were found to be unable to bind DNA while two residues, Phe-365 and Phe-496, were identified to interact with DNA. Furthermore, fluorescence quenching studies with mutants F365W and F496W and repair of thymine cyclobutane dimers by photoinduced electron transfer by these mutants suggest that residues Phe-365 and Phe-496 interact with DNA most likely through stacking interactions.

Adenosine Triphosphatases↗
PubMed1995

Molecular cloning of SLP-76, a 76-kDa tyrosine phosphoprotein associated with Grb2 in T cells.

The activation of protein tyrosine kinases is a critical event in T cell antigen receptor (TCR)-mediated signaling. One substrate of the TCR-activated protein tyrosine kinase pathway is a 76-kDa protein (pp76) that associates with the adaptor protein Grb2. In this report we describe the purification of pp76 and the molecular cloning of its cDNA, which encodes a novel 533-amino acid protein with a single carboxyl-terminal Src homology 2 (SH2) domain. Although no recognizable motifs related to tyrosine, serine/threonine, or lipid kinase domains are present in the predicted amino acid sequence, it contains several potential motifs recognized by SH2 and SH3 domains. A cDNA encoding the murine homologue of pp76 was also isolated and predicts a protein with 84% amino acid identity to human pp76. Northern analysis demonstrates that pp76 mRNA is expressed solely in peripheral blood leukocytes, thymus, and spleen; and in human T cell, B cell and monocytic cell lines. In vitro translation of pp76 cDNA gives rise to a single product of 76 kDa that associates with a GST/Grb2 fusion protein, demonstrating a direct association between these two molecules. Additionally, a GST fusion protein consisting of the predicted SH2 domain of pp76 precipitates two tyrosine phosphoproteins from Jurkat cell lysates, and antiserum directed against phospholipase C-gamma 1 coprecipitates a tyrosine phosphoprotein with an electrophoretic mobility identical to that of pp76. These results demonstrate that this novel protein, which we term SLP-76 (SH2 domain-containing Leukocyte Protein of 76 kDa), is likely to play an important role in TCR-mediated intracellular signal transduction.

Adaptor Proteins, Signal Transducing↗
PubMed1995

Multiple splicing signals control alternative intron retention of bovine growth hormone pre-mRNA.

A fraction of bovine growth hormone (bGH) pre-mRNA undergoes alternative splicing in which the last intron is retained and transported to the cytoplasm. Our goal was to characterize the cis-acting signals in bGH pre-mRNA that collectively determine the distribution between intron splicing and intron retention. We now demonstrate that the balance between splicing and intron retention in cytoplasmic mRNA is primarily determined by the interaction of three splicing signals and the degree to which these signals deviate from consensus splicing signals. Intron retention requires the presence of both suboptimal 5'- and 3'-splice sites. Mutation of either splice site toward consensus leads to complete splicing of the intron. In the presence of both wild-type, suboptimal splice sites, efficient splicing of this intron is ensured by the presence of a third splicing element, a purine-rich exonic splicing enhancer (ESE). Although strong ESEs can be contained within very small sequences, the bGH ESE activity appears to be composed of multiple sequences spread throughout a 115-nucleotide region of exon 5. Consequently, the final ratio of splicing to intron retention depends on the balance between the relative strengths of each of these three splicing signals, which still allow intron-containing coding sequences to be transported to the cytoplasm.

Alternative Splicing↗
PubMed1995

Identification by differential RT-PCR of a novel paired homeodomain protein specifically expressed in sensory neurons and a subset of their CNS targets.

Sensory neurons are a major derivative of the neural crest for which there have been no definitive molecular markers in mammals. We have developed a method that combines differential hybridization with degenerate RT-PCR to rapidly screen gene families for members exhibiting differential expression among tissues or cell types. We used this approach to search for transcription factor-encoding genes specifically expressed in mammalian sensory neurons. A novel paired homeodomain protein, called DRG11, was identified. DRG11 is expressed in most sensory neurons, including trkA-expressing neurons, but not in glia or sympathetic neurons. Unexpectedly, it is also expressed in the dorsal horn of the spinal cord, a region to which NGF-dependent sensory neurons project. These data suggest that DRG11 is not only a useful marker for sensory neurons, but may also function in the establishment or maintenance of connectivity between some of these neurons and their central nervous system targets.

Animals↗
PubMed1995

Prevention of carcinoma in situ of human papillomavirus type 16-immortalized human endocervical cells by retinoic acid in organotypic raft culture.

OBJECTIVE: To determine the effect of retinoic acid on the development of severe dysplasia or carcinoma in situ from endocervical cells containing human papillomavirus (HPV) type 16. METHODS: Two independent lines of HPV 16-immortalized endocervical cells were reconstructed into two squamous epithelial tissues using the organotypic raft culture system to examine the differentiated phenotype. The effect of retinoic acid on dysplastic morphology of differentiation of the epithelia was examined by light microscopy of stained sections and electron microscopy. The endocervical cell type cytokeratin expression pattern was determined by indirect immunofluorescence using specific monoclonal antibodies. Ribonucleic acid expression of the HPV 16 E7 oncogene was examined by in situ hybridization. RESULTS: Untreated HPV 16-immortalized endocervical cells were reconstructed into squamous dysplastic lesions resembling carcinoma in situ observed in women. Retinoic acid-treated rafts formed epithelia composed of two to three cell layers of columnar-like cells resembling simple epithelium of the endocervix. Electron microscopy and cytokeratin expression patterns confirmed the histology of a differentiated endocervical phenotype after treatment with retinoic acid. Expression of HPV 16 E7 was modestly lower in treated epithelia, preferentially in basal cells. CONCLUSION: Retinoic acid prevents the histology and cytokeratin differentiation markers of carcinoma in situ of HPV 16-immortalized endocervical cells. Because the epithelia closely mimic HPV 16-containing severe dysplasias and native endocervical epithelium in women, this immortalized endocervical cell-raft system may be useful as a model to assess the efficacy of agents such as retinoic acid for preventing progression of these lesions to malignant cervical carcinoma.

Carcinoma in Situ↗
PubMed1995

Alterations in physical state and expression of human papillomavirus type 18 DNA following crisis and establishment of immortalized ectocervical cells.

Integration of episomal human papillomavirus (HPV) DNA in infected cervical lesions during malignant progression is frequently observed, but the importance of integration is poorly understood. We have studied immortalization by HPV-18 of human cervical cells as an in vitro model system. Here, the status and expression of HPV-18 DNA in precrisis ectocervical keratinocytes was compared with that in the same cells after crisis and establishment of immortalization. Southern blots revealed, and two-dimensional gel analysis confirmed, that the precrisis culture contained more than 100 copies/cell of episomal HPV-18 DNA and no detectable integrated viral DNA. In contrast, the postcrisis cells contained a low copy number of only integrated viral genome. The Northern blot patterns of E6-E7 and E2/E4 RNA expression were also different. Analysis of RNA by RT-PCR indicated that neither culture expressed the unspliced HPV-18 E6 oncogene present in tumor cell lines and that the precrisis, but not postcrisis, culture expressed the full-length E2 repressor. The two cultures displayed a similar keratinocyte morphology in vitro and a similar low grade dysplasia in vivo and both were non-tumorigenic. These results suggest that, although insufficient for complete malignant conversion, viral DNA integration during crisis is associated with the establishment of an immortalized phenotype in which HPV-18 DNA is integrated and HPV-18 RNA expression is altered.

Adult↗
PubMed1995

Diabetes induced with low doses of streptozotocin is mediated by V beta 8.2+ T-cells.

T-cells have been shown to cause insulitis and ultimately be responsible for the destruction of beta-cells in animal models of insulin-dependent diabetes mellitus (IDDM). In one murine model, insulitis and hyperglycemia occur after administration of five low doses of streptozotocin (STZ) (multidose STZ-induced diabetes mellitus [MDSM]). Insulitis can first be identified in the islets after the final (fifth) daily dose of STZ is given. We have studied the T-cells that infiltrate the islets of Langerhans during the early stages of diabetes by preparing Southern blots of T-cell receptor (TCR) beta-chain genes amplified by polymerase chain reaction (PCR) from islets from C57BL/KsJ mice given multiple doses of STZ. The relative abundance of TCR gene products in islets was compared with spleen cells stimulated with anti-CD3 monoclonal antibody (mAb). We found that after the fourth dose of STZ, there was a striking increase in the amount of V beta 8.2 TCR gene product (37 +/- 4% of total PCR signal) compared with T-cells in the spleen (9 +/- 2%, P < 0.01), which increased further 2 days after the final dose of STZ (47 +/- 5%, P < 0.001). We studied the heterogeneity of the size of the V beta 8.2 TCR CDR3 region and found primarily products with only two lengths compared with a heterogeneous population in the spleen. Treatment with anti-V beta 8 mAb, but not anti-V beta 9 and anti-V beta 13 mAbs, prevented development of hyperglycemia (P < 0.0001) and insulitis (P < 0.0005) after STZ administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗