Charge separation and transport in conjugated-polymer/semiconductor-nanocrystal composites studied by photoluminescence quenching and photoconductivity.
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Journal Article↗
Biomedical subjects
X Peng
Publications and source records attributed to X Peng.
Analysis of west African hunters for foamy virus infections.
Foamy viruses are a genus of complex retroviruses that infect a wide variety of mammals. However, a clear association with any disease process has yet to be proven for these viruses. A higher human seroprevalence was reported in African populations, perhaps due to exposure to simian foamy viruses (SFV) endemic in primates. However, the earlier serologic surveys were not confirmed by studies employing nucleic acid amplification. Foamy virus infections of humans clearly do occur as rare zoonoses among primate center or laboratory workers exposed to captive primates or their blood. We sought to detect foamy virus infections in a cohort of humans also presumed to be exposed to SFV, i.e., West African hunters. We constructed recombinant vaccinia viruses that expressed human foamy virus (HFV) Gag or Env polyproteins in mammalian cells. The sera from 17 monkey hunters or several controls were tested in radioimmunoprecipitation assays (RIPAs) against the recombinant HFV proteins. Chimpanzee sera or HFV-positive human sera immunoprecipitated gp130, the HFV Env precursor, as well as p74, the HFV Gag polyprotein. None of the hunters' sera recognized both of these recombinant proteins. We then employed a nested polymerase chain reaction (PCR) analysis of the hunters' DNA but also failed to detect foamy virus infections. Therefore, by utilizing a recombinant RIPA and a nested PCR assay, we have not identified foamy virus infections occurring naturally in hunters exposed to wild monkeys in West Africa.
Africa, Western↗
Immortalization of inbred rabbit keratinocytes from a Shope papilloma and tumorigenic transformation of the cells by EJ-ras.
An immortalized cell line of keratinocytes, named SPG1-3, was established from a papilloma induced from cottontail rabbit papillomavirus (CRPV)-infected inbred rabbit skin. The cells have reached 60 passages in culture and are still growing well, but they are not tumorigenic in athymic mice. Although CRPV DNA was present as extrachromosomal episomes in the papilloma from which the cell line was derived from a single colony of keratinocytes, there was no CRPV DNA detectable in the cells. Three sub-cell lines of SPG1-3EJ, SPG1-3EJ1 and SPG1-3EJ2 were then established from the EJ-ras transfected SPG1-3 cells. All of the three sub-lines contained both EJ-ras DNA and a 1.2 kb transcript of EJ-ras, and they are malignantly tumorigenic in athymic mice. These data indicate that CRPV genome and its expression might be essential for the initiation and maintenance of neoplasia, but not for the maintenance of immortalization of the tumor-derived cells. In addition, some oncogenes such as EJ-ras may play an essential role in tumorigenic and malignant conversion of the immortalized cells. These cell lines derived from inbred rabbit skin may provide a useful in vitro system for better understanding of the oncogenic processes of papillomavirus-involved neoplastic progression by transfecting the cells with CRPV genes and serial transplantation to the inbred rabbits for studying host immune responses to the viral oncogenic potential.
Animals↗
Organization of 'nanocrystal molecules' using DNA.
Patterning matter on the nanometre scale is an important objective of current materials chemistry and physics. It is driven by both the need to further miniaturize electronic components and the fact that at the nanometre scale, materials properties are strongly size-dependent and thus can be tuned sensitively. In nanoscale crystals, quantum size effects and the large number of surface atoms influence the, chemical, electronic, magnetic and optical behaviour. 'Top-down' (for example, lithographic) methods for nanoscale manipulation reach only to the upper end of the nanometre regime; but whereas 'bottom-up' wet chemical techniques allow for the preparation of mono-disperse, defect-free crystallites just 1-10 nm in size, ways to control the structure of nanocrystal assemblies are scarce. Here we describe a strategy for the synthesis of 'nanocrystal molecules', in which discrete numbers of gold nanocrystals are organized into spatially defined structures based on Watson-Crick base-pairing interactions. We attach single-stranded DNA oligonucleotides of defined length and sequence to individual nanocrystals, and these assemble into dimers and trimers on addition of a complementary single-stranded DNA template. We anticipate that this approach should allow the construction of more complex two- and three-dimensional assemblies.
Base Sequence↗
Assembly of human neuronal nicotinic receptor alpha5 subunits with alpha3, beta2, and beta4 subunits.
Nicotinic acetylcholine receptors formed from combinations of alpha3, beta2, beta4, and alpha5 subunits are found in chicken ciliary ganglion neurons and some human neuroblastoma cell lines. We studied the co-expression of various combinations of cloned human alpha3, beta2, beta4, and alpha5 subunits in Xenopus oocytes. Expression on the surface membrane was found only for combinations of alpha3beta2, alpha3beta4, alpha3beta2alpha5, and alpha3beta4alpha5 subunits but not for other combinations of one, two, or three of these subunits. alpha5 subunits assembled inside the oocyte with beta2 but not with alpha3 subunits or other alpha5 subunits. alpha5 subunits coassembled very efficiently with alpha3beta2 or alpha3beta4 combinations. The presence of alpha5 subunits had very little effect on the binding affinities for epibatidine of receptors containing also alpha3 and beta2 or alpha3 and beta4 subunits. The presence of alpha5 subunits increased the rate of desensitization of both receptors containing also alpha3 and beta2 or alpha3 and beta4 subunits. In the case of receptors containing alpha3 and beta4 subunits, the addition of alpha5 subunits had little effect on the responses to acetylcholine or nicotine. However, in the case of receptors containing alpha3 and beta2 subunits, the addition of alpha5 subunits reduced the EC50 for acetylcholine from 28 to 0.5 microM and the EC50 for nicotine from 6.8 to 1.9 microM, while increasing the efficacy of nicotine from 50% on alpha3beta2 receptors to 100% on alpha3beta2alpha5 receptors. Both alpha3beta2 and alpha3beta2alpha5 receptors expressed in oocytes sedimented at the same 11 S value as native alpha3-containing receptors from the human neuroblastoma cell line SH-SY5Y. In the receptors from the neuroblastoma alpha3, beta2, and alpha5 subunits were co-assembled, and 56% of the receptor subtypes containing alpha3 subunits also contained beta2 subunits. The beta2 subunit-containing receptors from SH-SY5Y cells exhibited the high affinity for epibatidine characteristic of receptors formed from alpha3 and beta2 or alpha3, beta2, and alpha5 subunits rather than the low affinity exhibited by receptors formed from alpha3 and beta4 or alpha3, beta4, and alpha5 subunits. Nicotine, like the structurally similar toxin epibatidine, also distinguishes by binding affinity two subtypes of receptors containing alpha3 subunits in SH-SY5Y cells. The affinities of alpha3beta2 receptors expressed in oocytes were similar to the affinities of native alpha3 containing receptors from SH-SY5Y cells for acetylcholine, cytisine, and 1,1-dimethyl-4-phenylpiperazinium.
Acetylcholine↗
Accessory signaling by CD40 for T cell activation: induction of Th1 and Th2 cytokines and synergy with interleukin-12 for interferon-gamma production.
The interaction of CD40 ligand (CD40L) on activated T cells with CD40 on B cells, monocytes and dendritic cells is essential for humoral immunity and for up-regulation of antigen-presenting cell (APC) functions, as a result of signaling through CD40. There are also some indications that after interaction with CD40, CD40L can directly signal T cells. In this study we demonstrate that upon stimulation of human peripheral blood T cells through the T cell receptor (TCR)/CD3 complex, CD40/CD40L interaction strongly enhances the production of Th1 cytokines such as interleukin (IL)-2 and interferon (IFN)-gamma and Th2 cytokines such as IL-4, IL-5 and IL-10 by a direct effect on T cells. Furthermore, CD40/CD40L interaction synergizes with IL-12 in selectively enhancing IFN-gamma production by purified anti-CD3-stimulated T cells. These effects were observed at both the protein and the mRNA level. Both CD4+ and CD8+ T cells were able to produce IFN-gamma in the presence of helper signals from IL-12 and CD40, although CD8+ T cells were less active. Since CD40/CD40L interaction also up-regulates IL-12 production and B7 expression by APC, our results suggest that CD40/CD40L interaction is bidirectional, and promotes activation of both APC and T cells.
Adult↗
Structure and function of neuronal nicotinic acetylcholine receptors.
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Animals↗
Tyrosine phosphorylation of extracellular signal-regulated protein kinase 4 in response to growth factors.
Extracellular signal-regulated protein kinases (ERKs) are members of the mitogen-activated protein kinase family that are rapidly phosphorylated and activated in response to various extracellular stimuli, including growth factors. Of these, the ERK1 and ERK2 forms are by far the most abundant and the most studied. Much less is known about other ERK forms, including one previously designated ERK4 on the basis of its cross-reactivity with ERK1 and ERK2. We report here that ERK4 in rat PC12 pheochromocytoma cells can be immunoprecipitated by anti-ERK antiserum R2 and have used this re-agent to characterize this species further. We find that ERK4 rapidly becomes tyrosine-phosphorylated in response to nerve growth factor (NGF) and epidermal growth factor (EGF) and, to a lesser degree, in response to insulin and a permeant cyclic AMP analogue. As in the case of ERK1 and ERK2, tyrosine phosphorylation of ERK4 occurs by a ras-dependent pathway in response to NGF and EGF and shows prolonged kinetics for NGF but not EGF treatment. Recognition by multiple antisera directed against various domains of ERK1 supports classification of ERK4 within the ERK family; however, two-dimensional gel analysis clearly distinguishes ERK4 from isoforms of ERK1. These findings thus reveal an additional member of the ERK family that is responsive to growth factors and that could play a distinct role in intracellular signaling.
Animals↗
Immunological evidence for the expression of the Fas antigen in the infant and adult human ovary during follicular regression and atresia.
Immunohistochemical localization of the Fas antigen in the infant and adult human ovary during follicular growth, regression, and atresia was examined by the avidin/biotin immunoperoxidase method with a monoclonal antibody to the Fas antigen. Western blotting was used to confirm the presence of the Fas antigen protein. In primordial and primary follicles within the normal adult ovary, only the oocyte showed moderate immunostaining for the Fas antigen. In secondary and antral follicles, only the oocyte showed weak staining for the Fas antigen, while in preovulatory follicles, neither the oocyte nor the granulosa and theca cells were immunostained for the Fas antigen. In corpora lutea, the Fas antigen staining became apparent in the granulosa lutein cells during the early luteal phase and intensified during the mid luteal phase, while the theca lutein cells became positive for the Fas antigen staining during the mid luteal phase. During the late luteal phase, the staining intensity of the Fas antigen in the regressing corpora lutea further increased. As the regressing corpora lutea were converted into corpora albicans, the staining intensity decreased, and the corpora albicans and stromal cells were negative for the Fas antigen. In atretic primordial and primary follicles, only the degenerating oocyte showed the Fas antigen staining. By contrast, in atretic antral follicles, the Fas antigen staining was profound in the degenerating granulosa cells at the early stage of atresia, and at the mid stage of atresia it was intensified in the cell surface of the scattered granulosa cells and became apparent in the theca cells. At the late stage of atresia the Fas antigen remained only in the hypertrophied theca cells. In the infant ovary, only the oocyte in primordial and primary follicles exhibited intense staining for the Fas antigen. In the postmenopausal ovary, the Fas antigen staining was entirely negative. Western blot analysis revealed the presence of the Fas antigen protein with a molecular mass of 45 kDa in luteal tissues. On the basis of the recent evidence, that the Fas antigen mediates an apoptotic signal in a variety of cells, the abundant expression of the Fas antigen in the regressing corpora lutea and atretic follicles suggests that the Fas antigen participates in luteal regression and follicular atresia through the apoptotic process. Furthermore, notable expression of the Fas antigen in the oocyte of primordial and primary follicles within the infant and adult human ovary followed by the decrease in the Fas antigen expression in the oocyte with the advance of follicular maturation suggests that the Fas antigen expression in the oocyte may play a role in follicular selection.
Adult↗
Comparison of immunocytologic localization of insulin-like growth factor binding protein-4 in normal and polycystic ovary syndrome human ovaries.
The cytologic localization and cellular levels of insulin-like growth factor binding protein-4 (IGFBP-4) in follicular and stromal compartments of normal and polycystic ovary syndrome (PCOS) ovaries during follicular growth and regression were investigated by the avidin/biotin immunoperoxidase method with a polyclonal antibody to human IGFBP-4, and a comparative assessment of IGFBP-4 expression in normal and PCOS ovaries was provided. In normal human ovaries, IGFBP-4 was immunolocalized to the oocyte throughout follicular growth, while the surrounding granulosa and theca cells were negligible for IGFBP-4 immunostaining in primordial, preantral and antral follicles. IGFBP-4 immunostaining became apparent, however, in the lutein cells of corpora lutea and the granulosa and theca cells of atretic follicles. In PCOS ovaries, prominent immunostaining for IGFBP-4 was apparent not only in the oocyte, but also in the surrounding granulosa cells in preantral follicles. In antral follicles from PCOS women without hyperinsulinemia, IGFBP-4 immunostaining was more prominent in the granulosa cells than the theca cells, whereas in antral follicles from PCOS women with hyperinsulinemia IGFBP-4 immunostaining was more prominent in the theca cells than the granulosa cells. Furthermore, in atretic follicles within PCOS ovaries IGFBP-4 immunostaining was prominent in the theca cells, regardless of the association of hyperinsulinemia. These results demonstrate for the first time that there is a great difference in cellular expression of IGFBP-4 between normal and PCOS human ovaries. In light of the high affinity of IGFBP-4 for IGF-1, the abundant expression of IGFBP-4 in granulosa and theca cells of preantral and antral follicles of PCOS ovaries may lead to decreases in the bioavailability of IGF-I in those follicles. The decrease in IGF-I-mediated stimulation of gonadotropin actions on granulosa and theca cells in preantral and antral follicles may impair the induction of aromatase activity, causing an androgenic microenvironment which is characteristic of atretic follicles and PCOS follicles.
Adult↗
Demographic and social change in Jiangsu and Zhejiang between 1370 and 1900: a study of the genealogy of the Fan family.
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Asia↗
Inhibitory effect of suberogorgin on acetylcholinesterase.
AIM: To study the selection, reversibility, and kinetics of suberogorgin (Sub) on acetylcholinesterase (AChE). METHODS: The human plasma was used as butyrylcholinesterase (BuChE). The activity of ChE was determined with colorimetry. RESULTS: Sub obviously inhibited the AChE in vitro with pl50 4.03, 4.92, 3.82, and 4.67 in RBC membranes (of rat and human) and tissue extracts (of rat brain and earthworm dorsal muscle), respectively. No inhibition on BuChE was observed. The inhibition of Sub on AChE was far lower than that of physostigmine, but was close to that of galanthamine. Sub decreased the AChE activity to the lowest within 3 min after it was incubated with AChE. Centrifugalization washing reactivated the AChE which had been inhibited by Sub. The double-reciprocal plots of different concentrations of Sub on AChE showed parallel lines. CONCLUSION: Sub was a selective, reversible, and contra-competetive inhibitor of AChE at the binding site on the peripheral anion region of AChE.
Acetylcholinesterase↗
Effects of suberogorgin and its derivates on learning and memory in mice.
AIM: To study the relationship between the effects of suberogorgin (Sub) and its derivates on memory and their anti-acetylcholinesterase (AChE) actions. METHODS: The step-down latency (SDL) and the escape latency (EL) of mice were determined at the same time in a passive avoidance task after Sub, N-suberogorgamide-N-N-dicyclohexyl urea (Sub-DU), or N-cyclohexyl suberogorgamide (N-CS) was injected i.p. The AChE activities in brain hemogenates were determined with colorimetry. RESULTS: Sub 1.9, Sub-DU 3.0, or physostigmine (Phys) 0.15 mg.kg-1 obviously lengthened the SDL by 195%, 271%, and 210%, and shortened the EL by 56%, 61%, and 33%, and the two formers inhibited the brain AChE activities by 17% and 19%, respectively in aging (3-4 months) mice. These actions were decreased in a dose-dependent manner when Sub or Sub-DU was increased to 2.9-4.3 or 4.5-6.7 mg.kg-1 respectively. Sub 1.9, Sub-DU 2.0, and Phys 0.15 mg.kg-1 also lengthened the SDL by 187%, 209%, and 152%, and shortened the EL by 52%, 62%, and 57%, respectively in aged (12-14 months) mice. Sub 1.3-1.9, Sub-DU 0.9-2.0, or Phys 0.15 mg.kg-1 reversed the cycloheximide- or scopolamine-induced disruptions of memory retention. No obvious effect of N-CS on the acquisition of memory and the AChE activity in mice was observed. CONCLUSION: The improvements of Sub and Sub-DU on memory were chiefly related to their anti-AChE actions.
Acetylcholinesterase↗
Elimination of glycosylation heterogeneity affecting heparin affinity of recombinant human antithrombin III by expression of a beta-like variant in baculovirus-infected insect cells.
In order to promote homogeneity of recombinant antithrombin III interactions with heparin, an asparagine-135 to alanine substitution mutant was expressed in baculovirus-infected insect cells. The N135A variant does not bear an N-linked oligosaccharide on residue 135 and is therefore similar to the beta isoform of plasma antithrombin. Purified bv.hat3.N135A is homogeneous with respect to molecular mass, charge and elution from immobilized heparin. Second-order rate constants for thrombin and factor Xa inhibition determined in the absence and presence of heparin are in good agreement with values established for plasma antithrombin and these enzymes. Based on far- and near-UV CD, bv.hat3.N135A has a high degree of conformational similarity to plasma antithrombin. Near-UV CD, absorption difference and fluorescence spectroscopy studies indicate that it also undergoes an identical or very similar conformational change upon heparin binding. The Kds of bv.hat3.N135A for high-affinity heparin and pentasaccharide were determined and are in good agreement with those of the plasma beta-antithrombin isoform. The demonstrated similarity of bv.hat3.N135A and plasma antithrombin interactions with target proteinases and heparins suggest that it will be a useful base molecule for investigating the structural basis of antithrombin III heparin cofactor activity.
Animals↗
NMR study of the cold, heat, and pressure unfolding of ribonuclease A.
The reversible cold, heat, and pressure unfolding of RNase A and RNase A--inhibitor complex were studied by 1D and 2D 1H NMR spectroscopy. The reversible pressure denaturation experiments in the pressure range from 1 bar to 5 kbar were carried out at pH 2.0 and 10 degrees C. The cold denaturation was carried out at 3 kbar, where the protein solution can be cooled down to -25 degrees C without freezing. Including heat denaturation experiments, the experimental data obtained allowed us to construct the pressure--temperature phase diagram of RNase A. The experimental results suggest the possibility that all three denaturation processes (cold, heat, and pressure) lead to non-cooperative unfolding. The appearance of a new histidine resonance in the cold-denatured and pressure-denatured RNase A spectra, compared to the absence of this resonance in the heat-denatured state, indicates that the pressure-denatured and cold-denatured states may contain partially folded structures that are similar to that of the early folding intermediate found in the temperature-jump experiment reported by Blum et al. [Blum, A. D., et al. (1978) J. Mol. Biol. 118, 305]. A hydrogen-exchange experiment was performed to confirm the presence of partially folded structures in the pressure-denatured state. Stable hydrogen-bonded structures protecting the backbone amide hydrogens from solvent exchange were observed in the pressure-denatured state. These experimental results suggest that the pressure-denatured RNase A displays the characteristics of a the inhibitor 3'-UMP show that the RNase A-inhibitor complex is more stable than RNase without the inhibitor.
Animals↗
Neuronal nicotinic receptor subtypes.
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Animals↗
One and two dimensional 1H-NMR studies of pressure and tetracaine effects on sonicated phospholipid vesicles.
One and two dimensional 1H-NMR experiments have been performed to study the molecular order and dynamics of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) unilamellar vesicles under the influence of high pressure and the local anesthetic, tetracaine (TTC), which can also be considered as a model-charged amphiphile. The TTC molecules have an ordering effect on the headgroups but a disordering effect on the acyl chains, whereas, pressure has an ordering effect on the acyl chains. The results from 2D NOESY experiments on pure DPPC vesicles show that the intensities of NMe3/CH3, NMe3/(CH2)n, and CH3/(CH2)n cross-peaks increase with increasing pressure in the liquid-crystalline phase but decrease with pressure in the gel phase, further suggesting that the appearance of the cross-peaks between the two extremes of the DPPC molecules is due to spin-diffusion. For the DPPC/TTC vesicles, the 2D NOESY experiments confirm that charged TTC molecules are located in the headgroup region of the DPPC bilayers and, in the gel phase, also suggest the formation of an interdigitated gel phase.
1,2-Dipalmitoylphosphatidylcholine↗
Methylation of cottontail rabbit papillomavirus DNA and tissue-specific expression in transgenic rabbits.
Transgenic rabbits carrying multiple copies of CRPV genomic DNA were described previously (Peng et al. (1993) J. Virol. 67, 1698-1701). CRPV DNA was detectable in all tissues of the transgenic rabbits, however, the transcripts of CRPV genes only were found in skin and skin tumors. Tumor development was also restricted to skin. To study the mechanism involving tissue-specific expression of CRPV genes in rabbits, cellular DNAs, isolated from different normal tissues and skin tumors, were digested with the two isoschizomeric restriction endonucleases MspI (methylation resistant) and HpaII (methylation sensitive), respectively, and analyzed by Southern blot. CRPV DNA, especially its upstream regulatory region (URR), was extensively methylated in all normal tissues, but methylation was remarkably reduced in skin tumors. These data suggest that extensive methylation of CRPV genome, especially in the URR, might be a factor in controlling its tissue-specific expression.
5-Methylcytosine↗