Soojin Park

Sustained Production of H2O2Activates Pro-matrix Metalloproteinase-2 through Receptor Tyrosine Kinases/Phosphatidylinositol 3-Kinase/NF-κB Pathway

A rate-limiting step of tumor cell metastasis is matrix degradation by active matrix metalloproteinases (MMPs). It is known that reactive oxygen species are involved in tumor metastasis. Sustained production of H2O2 by phenazine methosulfate (PMS) induced activation of pro-MMP-2 through the induction of membrane type 1-MMP (MT1-MMP) expression in HT1080 cells. MMP-2, MMP-9, and tissue inhibitor of metalloproteinase-1 and -2 levels were changed negligibly by PMS. A one time treatment with H2O2 did not induce activation of MMPs. It was also demonstrated that superoxide anions and hydroxyl radicals were not related to PMS action. PMS-induced pro-MMP-2 activation was regulated by the receptor tyrosine kinases, especially the receptors of platelet-derived growth factor and vascular endothelial growth factor, and downstream on the phosphatidylinositol 3-kinase/NF-κB pathway but not Ras, cAMP-dependent protein kinase, protein kinase C, and mitogen-activated protein kinases. PMS did not induce pro-MMP-2 activation in T98G and NIH3T3 cells. This may be related to a low level of MT1-MMP, indicating a threshold level of MT1-MMP is important for pro-MMP-2 activation. Furthermore, PMS increased cell motility and invasion but decreased cell-cell interaction. Cell-matrix interaction was not affected by PMS.

Selenite suppresses hydrogen peroxide-induced cell apoptosis through inhibition of ASK1/JNK and activation of PI3-K/Akt pathways.

The relationship between selenium and signal molecules has not been well elucidated. It was found that physiological concentration of selenite, >3 μM, reduced ASK1 activity and induced PI3‐kinase (PI3‐K)/Akt pathways in HT1080 cells. Duration of these signal molecules by selenite was much longer than that by growth factors and other stresses. The longer duration time of these signal molecules may be important to maintain normal functions against stresses. Selenite increased cell proliferation through up‐regulation of Bcl‐2 expression, mitochondrial membrane potential, adenosine triphosphate (ATP) generation, and glucose uptake mediated by PI3‐K pathway. High concentration of H2O2 increased an apoptotic signal molecule, ASK1, which resulted in Bcl‐2 down‐regulation, membrane potential disruption, decreased ATP and glucose uptake, and activation of caspases. However, an antiapoptotic signal molecule, Akt, was activated also by H2O2, but duration of its activation was much shorter. Selenite blocked apoptosis induced by H2O2, which was related to blocking ASK1 and further stimulating PI3‐kinase/Akt activities. Selenite blocked mitochondrial membrane potential disruption by 400 μM H2O 2. Selenite also blocked caspase‐9 and ‐3 activities and apoptosis induced by 500 μM H2O2, even after mitochondrial membrane potential disruption. These observations demonstrate that selenite increases cell proliferation and maintains cell survival by activating the antiapoptotic signal and blocking the apoptotic signal.

Improved lifetime of highly flexible OLEDs based on multilayered transparent electrodes with enhanced barrier performance

— Flexible organic light-emitting diodes (FOLEDs) showing enhanced barrier properties under repeated mechanical stress are reported. By combining metal-based multilayer transparent electrodes (MTEs) as highly flexible anodes replacing ITO electrodes and sol-gel organic-inorganic hybrimers which function as both planarizing films and barrier layers, the proposed FOLEDs not only exhibit a level of performance comparable to that of ITO-based reference devices but also show a superior mechanical flexibility with “after-bending” lifetime close to that of ITO-based devices.

Damage Detection of Civil Infrastructures with Piezoelectric Oscillator Sensors

Many researches have been reported on the condition monitoring of civil infrastructures by means of piezoelectric sensors. Most of them made use of the impedance change of the piezoelectric device in relation to the creation of internal damages to the structure. The impedance measurement is a well accepted method in the piezoelectric sensor area, and has been proved by many authors to be useful for civil structure diagnosis. However, the impedance measurement normally requires sophisticated equipment and analysis technology. For more general and wide application of the piezoelectric diagnosis tool, a new methodology is desired to overcome the limitations of the impedance measurement. This paper presents the feasibility of a piezoelectric oscillator sensor to detect the damages in civil infrastructures. The oscillator sensor is composed of an electronic feedback oscillator circuit and a piezoelectric thickness mode vibrator to be attached to the structure of interest. Damage to the structure causes a change in the impedance spectrum of the structure, which results in a corresponding change of the resonant frequency of the structure. The oscillator sensors can instantly detect the frequency change in a very simple manner. Feasibility of the piezoelectric oscillator sensor was verified in this work with a sample aluminum plate where artificial cracks of different depth were imposed in sequence. Validity of the measurement was confirmed through comparison of the experimental data with the results of finite element analyses of the plate with cracks. Performance of the oscillator sensor was also compared with that of its conventional counterpart, i.e. impedance measurement, to manifest the superiority of the oscillator sensor.