Showing papers by "Hongyu Li published in 2008"

Hydrogen peroxide in plants: a versatile molecule of the reactive oxygen species network.

Abstract: Plants often face the challenge of severe environmental conditions, which include various biotic and abiotic stresses that exert adverse effects on plant growth and development. During evolution, plants have evolved complex regulatory mechanisms to adapt to various environmental stressors. One of the consequences of stress is an increase in the cellular concentration of reactive oxygen species (ROS), which are subsequently converted to hydrogen peroxide (H(2)O(2)). Even under normal conditions, higher plants produce ROS during metabolic processes. Excess concentrations of ROS result in oxidative damage to or the apoptotic death of cells. Development of an antioxidant defense system in plants protects them against oxidative stress damage. These ROS and, more particularly, H(2)O(2,) play versatile roles in normal plant physiological processes and in resistance to stresses. Recently, H(2)O(2) has been regarded as a signaling molecule and regulator of the expression of some genes in cells. This review describes various aspects of H(2)O(2) function, generation and scavenging, gene regulation and cross-links with other physiological molecules during plant growth, development and resistance responses.

CpG-free plasmids confer reduced inflammation and sustained pulmonary gene expression.

Abstract: Pulmonary delivery of plasmid DNA (pDNA)/cationic liposome complexes is associated with an acute unmethylated CG dinucleotide (CpG)-mediated inflammatory response and brief duration of transgene expression. We demonstrate that retention of even a single CpG in pDNA is sufficient to elicit an inflammatory response, whereas CpG-free pDNA vectors do not. Using a CpG-free pDNA expression vector, we achieved sustained (>or=56 d) in vivo transgene expression in the absence of lung inflammation.

WNT5A exhibits tumor-suppressive activity through antagonizing the Wnt/β-catenin signaling, and is frequently methylated in colorectal cancer

Abstract: Purpose: Aberrant activation of the Wnt/β-catenin signaling pathway is associated with multiple tumors including colorectal cancer (CRC). WNT5A is a member of the nontransforming Wnt protein family, whose role in tumorigenesis is still ambiguous. We investigated its epigenetic alteration in CRCs. Experimental Design: We examined its expression and methylation in normal colon, CRC cell lines, and tumors. We also evaluated its tumor-suppressive function and its modulation to Wnt signaling in CRC cells. Results: WNT5A is silenced in most CRC cell lines due to promoter methylation, but is expressed in most normal tissues including the colon, and is unmethylated in normal colon epithelial cells. WNT5A expression could be reactivated by pharmacologic or genetic demethylation, indicating that methylation directly mediates its silencing. WNT5A methylation was frequently detected in CRC tumors (14 of 29, 48%), but only occasionally in paired normal colon tissues (2 of 15, 13%; P = 0.025). Ectopic expression of WNT5A , but not its nonfunctional short-isoform with the WNT domain deleted, in silenced CRC cells resulted in substantial inhibition of tumor cell clonogenicity, which is associated with down-regulated intracellular β-catenin protein level and concomitant decrease in β-catenin activity. Conclusions: WNT5A is frequently inactivated in CRC by tumor-specific methylation, and thus, is a potential biomarker. WNT5A could act as a tumor suppressor for CRC by antagonizing the Wnt/β-catenin signaling.

On the origin of ferromagnetism in CeO2 nanocubes

Abstract: Magnetic behaviors of pure CeO2 nanoparticles and nanocubes have been investigated both experimentally and theoretically. It is found that monodisperse CeO2 nanocubes with an average size of 5.3 nm do show ferromagnetic behavior at ambient temperature with a saturation magnetization of about 5.7 memu/g and coercive force of about 69 Oe. First-principles calculations reveal that oxygen vacancies in pure CeO2 cause spin polarization of f electrons for Ce ions surrounding oxygen vacancies, resulting in net magnetic moment for pure CeO2 samples. One oxygen vacancy at surface can induce more magnetic moments than those induced by one oxygen vacancy in bulk. The results obtained here provide evidence that pure CeO2 sample with oxygen vacancies can indeed have magnetic behavior. This study will stimulate more investigations for understanding the origin of ferromagnetic TM-doped CeO2 (TM=3d transition metals) in a particular case and TM-doped semiconductor oxides in general at ambient temperature.

Prolonged treatment of cells with genistein modulates the expression and function of the cystic fibrosis transmembrane conductance regulator.

Abstract: Background and purpose: Cystic fibrosis (CF) is caused by dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel. In the search for new CF therapies, small molecules have been identified that rescue the defective channel gating of CF mutants (termed CFTR potentiators). Here, we investigate the long-term effects of genistein, the best-studied CFTR potentiator, on the expression and function of CFTR. Experimental approach: We pre-treated baby hamster kidney (BHK) cells expressing wild-type or F508del-CFTR (the most common CF mutant) with concentrations of genistein that potentiate (30 μM) or inhibit (100 μM) CFTR function for 2 or 24 h at 37 °C before examining CFTR maturation, expression and single-channel activity. Key results: Using the iodide efflux technique, we found that genistein pre-treatment failed to restore function to F508del-CFTR, but altered that of wild-type CFTR. Pre-treatment of cells with genistein for 2 h had little effect on CFTR processing, whereas pre-treatment for 24 h either augmented (30 μM genistein) or impaired (100 μM genistein) CFTR maturation. Using immunocytochemistry, we found that all genistein pre-treatments increased the localization of CFTR protein to the cell surface. However, following the incubation of cells with genistein (100 μM) for 2 h, individual CFTR Cl− channels exhibited characteristics of channel block upon channel activation. Conclusions and implications: Genistein pre-treatment alters the maturation, cell surface expression and single-channel function of CFTR in ways distinct from its acute effects. Thus, CFTR potentiators have the potential to influence CFTR by mechanisms distinct from their effects on channel gating. British Journal of Pharmacology (2008) 153, 1311–1323; doi:10.1038/sj.bjp.0707663; published online 28 January 2008

Signalling pathways for transactivation by dexmedetomidine of epidermal growth factor receptors in astrocytes and its paracrine effect on neurons

Abstract: Background and purpose: Stimulation of astrocytes by the α2-adrenoceptor agonist dexmedetomidine, a neuroprotective drug, transactivates epidermal growth factor (EGF) receptors. The present study investigates signal pathways leading to release of an EGF receptor ligand and those activated during EGF receptor stimulation, and the response of neurons to dexmedetomidine and to astrocyte-conditioned medium. Experimental approach: Phosphorylation of ERK1/2 was determined by western blotting and immunocytochemistry, and phosphorylation of EGF receptors by immunoprecipitation and western blotting. mRNA expression of fos family was measured by RT-PCR. Key results:Pertussis toxin (0.2 μg ml−1) an inhibitor of βγ subunit dissociation from Gαi protein, and GF 109203X (500 nM), a protein kinase C inhibitor, abolished ERK1/2 phosphorylation. PP1 (10 μM), inhibiting Src kinase and GM 6001 (10 μM), an inhibitor of Zn-dependent metalloproteinase, abolished ERK1/2 phosphorylation by dexmedetomidine (50 nM), but not that by EGF (10 ng ml−1), showing Src kinase and metalloproteinase activation during the first stage only; AG 1478 (1 μM), an inhibitor of the EGF receptor tyrosine kinase, abolished ERK1/2 phosphorylation. Dexmedetomidine-induced EGF receptor phosphorylation was prevented by AG 1478, GM 6001, PP1 and GF 109203X and its induction of cfos and fosB by AG 1478 and by U0126 (10 μM), an inhibitor of ERK phosphorylation, indicating downstream effects of ERK1/2 phosphorylation. EGF and conditioned medium from dexmedetomidine-treated astrocytes, but not dexmedetomidine itself, induced ERK phosphorylation in primary cultures of cerebellar neurons. Conclusions and implications: Dexmedetomidine-induced transactivation pathways were delineated. Its paracrine effect on neurons may account for its neuroprotective effects.

Chilling Tolerance of Wheat Seedlings Is Related to an Enhanced Alternative Respiratory Pathway

Abstract: Pretreatment with exogenous hydrogen peroxide (H 2 O 2 ) mitigated the water loss of wheat leaves exposed to 4°C for 24 h. The same treatment also partially reduced the increases of electrolyte leakage and H 2 O 2 production of the chilled plants. These observations suggest that H 2 O 2 pretreatment could effectively induce chilling tolerance. The capacity of the alternative respiratory pathway and the expression of the gene encoding the alternative oxidase (AOX1) were substantially elevated by H 2 O 2 treatment under either normal or chilling conditions. Sali-cylhydroxamic acid (SHAM, an inhibitor of the alternative respiratory pathway) decreased the tolerance of plants to chilling conditions and reversed the chilling tolerance induced by exogenous application of H 2 O 2 These observations indicate that the tolerance of plants to chilling might be related to an enhanced alternative respiratory pathway.

Alternative Respiratory Pathway under Drought is Partially Mediated by Hydrogen Peroxide and Contributes to Antioxidant Protection in Wheat Leaves

Abstract: Water stress significantly enhanced the capacity of alternative respiratory pathway and induced AOX1 transcript in wheat (Triticum aestivum L.) leaves. The water-stressed seedlings pretreated with 1 mM salicylhydroxamic acid (SHAM) had higher level of production of reactive oxygen species (ROS) than the seedlings either subjected to drought or SHAM treatment alone did. This observation suggests that cyanide-resistant respiration could play a role in antioxidant protection under the condition of drought. Exogenous application of hydrogen peroxide effectively increased the capacity of alternative respiratory pathway and induced AOX1 transcription. Pretreatment with ROS scavengers, such as 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron) and dimethylthiourea (DMTU), arrested the increase of ROS and partly inhibited the induction of both cyanide-resistant respiration and AOX1 transcript under water stress. These results suggest that the enhancement of cyanide-resistant respiration under drought might be partially mediated by hydrogen peroxide.

Mesosome formation is accompanied by hydrogen peroxide accumulation in bacteria during the rifampicin effect.

Abstract: Ultrastructural alteration and hydrogen peroxide localization were examined in Xanthomonas campestris pv. phaseoli during rifampicin effect using transmission electron microscopy. Bacterial cells were treated with rifampicin and then were examined by electron microscopy to observe the changes of ultrastructure or hydrogen peroxide accumulation in living cells that took place before lysis. Intriguingly, rifampicin treatment led to presence of an additional location of hydrogen peroxide accumulation within the cells. There was an association between the frequency and size of the additional location of hydrogen peroxide accumulation and the concentration of rifampicin. Furthermore, an additional ultrastructure, mesosomes, was also present in cells during rifampicin effect. The frequency and size of mesosome increased with the increasing concentration of rifampicin. Result of multiple linear regression showed that the size of mesosome plays as a key factor in the quantity of excess hydrogen peroxide accumulation in cells during rifampicin effect. Linear correlation was confirmed between quantity of excess hydrogen peroxide accumulation and the size of mesosome in cells during rifampicin effect. This finding intensely indicated that mesosomes are just the additional location of hydrogen peroxide accumulation in cells under cellular injury caused by rifampicin treatment. The mesosome formation is always accompanied by excess hydrogen peroxide accumulation in X. campestris pv. phaseoli during rifampicin effect.

Impact of packaging design on reliability of large die Cu/low-κ (BD) interconnect

Abstract: This paper presents the study on the effect of low k stacked layer, chip pad design structures, and shift pad design TM of a large die size Cu/low kappa (BDtrade) chip for improving assembly and reliability performance on organic buildup substrate FCBGA (FlipChip ball grid array). Bump shear characterization has been performed on the integrity of different stacked layer and pad structure, supported by bump shear modeling analysis. Initial reliability testing was performed on assembled package to identify the best choice of design and finally implemented on the reliability test vehicle for verification. In addition, a potential chip crack problem due to excessive warpage in FCBGA with large die assembly is examined and a simple failure criterion is proposed.

Kernel-based spectral color image segmentation.

Abstract: In this work, we propose a new algorithm for spectral color image segmentation based on the use of a kernel matrix. A cost function for spectral kernel clustering is introduced to measure the correlation between clusters. An efficient multiscale method is presented for accelerating spectral color image segmentation. The multiscale strategy uses the lattice geometry of images to construct an image pyramid whose hierarchy provides a framework for rapidly estimating eigenvectors of normalized kernel matrices. To prevent the boundaries from deteriorating, the image size on the top level of the pyramid is generally required to be around 75×75, where the eigenvectors of normalized kernel matrices would be approximately solved by the Nystrom method. Within this hierarchical structure, the coarse solution is increasingly propagated to finer levels and is refined using subspace iteration. In addition, to make full use of the abundant color information contained in spectral color images, we propose using spectrum extension to incorporate the geometric features of spectra into similarity measures. Experimental results have shown that the proposed method can perform significantly well in spectral color image segmentation as well as speed up the approximation of the eigenvectors of normalized kernel matrices.

Influence of ammoniating temperature on Co-catalyzed GaN nanowires

Abstract: GaN nanowires (NWS) were synthesized at different temperatures by ammoniating Ga2O3/Co films deposited on Si (111) substrate. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscope (HRTEM), Fourier transformed infrared spectra (FTIR) and photoluminence (PL) spectra were used to characterize the influences of the ammoniating temperature on the morphology, crystallinity and optical properties of GaN NWS. Our results indicate that the samples are all of wurtzite structure and also show that the GaN NWS ammoniated at 950 °C have the best morphology and crystallinity with a single-crystalline structure, and at this temperature the PL spectrum with the strongest ultraviolet (UV) peak is observed.

High performance embedded RF passive device process integration

Abstract: We report the process evaluation and integration for the embedded RF passive device in this paper. Two sets of test vehicle were designed and fabricated for the evaluation of RF passive devices embedded in USG (undoped silicate glass) and BCB (Benzocylcobutene) dielectric. We encountered resistor uniformity issue and BCB capacitor limitation during the process set up. After process issue solving and final platform setting, resistor, capacitor, inductor and bandpass filter were integrated and the high performance functions were demonstrated.

Integration of RF MEMS and CMOS IC on a Printed Circuit Board for a Compact RF System Application Based on Wafer Transfer

Abstract: In this paper, a novel platform technology for integrating radio-frequency microelectromechanical systems (RF-MEMS) and CMOS on a printed circuit board (PCB) is demonstrated. An RF-MEMS switch is constructed on top of a CMOS IC wafer. The stacked structure is subsequently transferred onto a PCB substrate (i.e., FR-4) by thermal compressive bonding, mechanical grinding, and wet removal of bulk silicon. The measurement of the fabricated RF-MEMS switch on the FR-4 substrate shows promising results. It has an insertion loss of 0.25 dB at 20 GHz and an isolation of 25 dB at 20 GHz. At the same time, the performance of CMOS is not degraded during the integration process; the drain current in the p-MOS transistor remained unchanged, whereas that in the n-MOS transistor showed a slight improvement after transfer. This technology is very useful for compact RF system on PCB material with low power consumption and high performance for wearable, wireless, and implantable device applications.

Recurrence spectra and dynamical simulation of Rydberg hydrogen atom near a metal surface

Abstract: By using the closed-orbit theory including the effect of Coulomb scattering together with an electrical image potential approach, the recurrence spectra and the dynamical behaviours of the Rydberg hydrogen atom near a metal surface are presented. Theoretical analysis and numerical simulation reveal that the impacts of the image potential contributing to the recurrence spectrum are qualitatively analogous to that of the parallel electrical and magnetic fields on the Rydberg atom. The recurrence spectra are computed for a few selected scaled energies and the results demonstrate that the scaled energy dominates the dynamical properties of system. With the increase of the scaled energy e from small to large, the whole trend of spectral structure is from simple to complex,and then simple.

Integration of RF-MEMS, passives and CMOS-IC on silicon substrate by low temperature wafer to wafer bonding technique

Abstract: In this paper, a novel platform technology for system level integration of RF-MEMS, RF passives and CMOS-IC on silicon substrate is reported. The RF passives and RF MEMS devices are fabricated on a low resistivity silicon wafer using Cu damascene process. After bonding the wafer to a CMOS wafer with recesses using benzocyclobutene (BCB) as intermediate layer and subsequently removal of bulk silicon, the RF passive components and RF MEMS devices are fully transferred onto CMOS wafer with silicon recesses underneath. The RF performance of RF-passive devices is improved significantly, e.g. the Q-factor of an inductor is improved by 174% and the resonant frequency is increased by 30%; the maximum available gain of a transformer is improved by 28%. RF-MEMS switch is sealed at wafer level and CMOS devices showed preserved device performance. This technology demonstrates the feasibility of building high performance, compact RF system on silicon substrate.

Flexible High Performance Capacitor on Soft Elastic Material

Abstract: Flexible capacitors have been realized on soft elastic material with the demonstration of good electrical and reliability performance. metal-insulator-metal (MIM) capacitors (~2 pF to ~16 pF) were pre-fabricated by 0.18 ?m Cu-backend technology on Si-substrate and later transferred onto the soft elastic material (polydimethylsiloxane PDMS) by the wafer-transfer technology. After transfer process development, our results show MIM capacitor can be reliably realized over elastic substrate PDMS. The changing of capacitance is below 0.3 pF for all the capacitors (from 2 pF to 16 pF). The flexible capacitors are still functional when bending radius reach 5.3 cm. At the same time, the changes of capacitance are below 3% at different bending radius.