Publications (93)160.68 Total impact
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Article: Sustained overexpression of Redd1 leads to Akt activation involved in cell survival.
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ABSTRACT: Herein, we show that the constitutive overexpression of Redd1, a negative regulator of mTORC1, induces Akt activation in lung cancer cells. Akt phosphorylation was reduced to basal levels by Rictor siRNA, suggesting the involvement of mTORC2 in this process. Perifosine and PP242, selective inhibitors of Akt and mTORC1/2, respectively, efficiently suppressed the Akt phosphorylation that was induced by the sustained overexpression of Redd1 and increased the sensitivity of the cells to cisplatin. Therefore, the sustained overexpression of Redd1 leads to mTORC1 inhibition and to consequent Akt activation that is involved in cell survival. This finding highlights the importance of Akt activation as a therapeutic target to overcome resistance to chemotherapy.Cancer letters 03/2013; · 4.86 Impact Factor -
Article: Inhibition of S6K1 enhances glucose deprivation-induced cell death via downregulation of anti-apoptotic proteins in MCF-7 breast cancer cells.
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ABSTRACT: Nutrient-limiting conditions are frequently encountered by tumor cells in poorly vascularized microenvironments. These stress conditions may facilitate the selection of tumor cells with an inherent ability to decrease apoptotic potential. Therefore, selective targeting of tumor cells under glucose deprivation conditions may provide an effective alternative strategy for cancer therapy. In the present study, we investigated the effects of S6K1 inhibition on glucose deprivation-induced cell death and the underlying mechanisms in MCF-7 breast cancer cells. PF4708671, a selective inhibitor of S6K1, and knockdown of S6K1 with specific siRNA enhanced cell death induced under glucose deprivation conditions. Moreover, inhibition of S6K1 led to apoptosis in glucose-starved MCF-7 cells via downregulation of the anti-apoptotic proteins, Mcl-1 and survivin. Further experiments revealed that sorafenib, shown to be involved in Mcl-1 and survivin downregulation via mTOR/S6K1 inhibition, significantly promotes cell death under glucose deprivation conditions. These findings collectively suggest that S6K1 plays an important role in tumor cell survival under stress conditions, and thus inhibition of S6K1 may be an effective strategy for sensitizing cells to glucose deprivation.Biochemical and Biophysical Research Communications 01/2013; · 2.48 Impact Factor -
Article: Charge loss mechanism of non-volatile V3Si nano-particles memory device
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ABSTRACT: We studied the charge loss mechanism of a non-volatile memory device with vanadium silicide (V3Si) nano-particles (NPs) embedded in a silicon dioxide dielectric layer. To fabricate the memory device, V3Si NPs with an average size of 4 nm were formed between the tunnel and control oxide layers by a thin film deposition and a post-annealing process at 800 C for 5s. Using the gate structure containing the V3Si NPs, a flash memory structure was fabricated with a channel length and width of 5 lm. This device maintained the memory window at about 1V after 104 s when program/erase voltages of 69V were applied for 1 s. The activation energies of the V3Si NP memory devices with charge loss rates of 10%, 15%, 20%, and 25% were approximately 0.16, 0.24, 0.35, and 0.50 eV, respectively. The charge loss mechanism can be attributed to direct tunneling as a result of the NPs associating with the interface trap in the tunneling oxide, the Pool-Frenkel current, and the oxide defect.Applied Physics Letters 12/2012; 101(23):233510-1. · 3.84 Impact Factor -
Article: Resistive-switching memory effect of hybrid structures with polyimide and SnO2 nanocrystals.
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ABSTRACT: Hybrid memory devices with polyimide and SnO2 nanocrystals on a flexible polyethersulphone substrate have shown a memristor behavior from current-voltage (I-V) measurements. The resistive-switching effects with a current bistability appeared during cycling voltage sweeping within the range of +/- 4 V. This I-V switching effect might have originated from a resistance fluctuation due to the charge trapping into the SnO2 nanocrystals as well as the oxygen vacancies of the ZnO layer and aluminum oxides that were formed between the polyimide and the interface of the Al gate electrode. In the bipolar resistance-switching behavior, the ratio of the high- and low-resistance state currents was about 3.7 x 10(4) at 1 V.Journal of Nanoscience and Nanotechnology 07/2012; 12(7):5449-52. · 1.56 Impact Factor -
Article: Prognostic Significance of Young Age (
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ABSTRACT: BackgroundYoung age is regarded as an adverse prognostic factor in patients with breast cancer, especially in those with a hormone receptor (HR)-positive tumor. We investigated the prognostic significance of an age of <35years stratified by molecular subtype based on HR and HER2. MethodsTwo large databases of Korean breast cancer patients, which included nationwide registry data, were analyzed. ResultsIn an analysis of 2,474 patients from the single institution, an age of <35years was found to be an independent predictor of recurrence in patients with HR+/HER2− (hazard ratio 1.87; 95% confidence interval [CI]: 1.11–3.14; P=0.018), HR+/HER2+ (hazard ratio 3.09; 95% CI: 1.19–8.03; P=0.020), and HR−/HER2+ (hazard ratio 2.01; 95% CI: 1.03–3.92; P=0.040) subtypes, but not in those with the HR−/HER2− (triple-negative, TN) subtype (hazard ratio 1.08; 95% CI: 0.60–1.95; P=0.802). The results of an analysis of nationwide database data on 31,672 patients also showed that an age of <35years significantly predicted poor cancer-specific survival in patients with HR+/HER2− (hazard ratio 3.40; 95% CI: 2.41–4.82; P<0.001), HR+/HER2+ (hazard ratio 1.96; 95% CI: 1.23–3.12; P=0.005), and HR−/HER2+ (hazard ratio 1.65; 95% CI: 1.07–2.52; P=0.022) subtypes, but again not in those with the TN subtype (hazard ratio 1.21; 95% CI: 0.88–1.67; P=0.240). ConclusionThe prognostic significance of young age was found to depend on molecular subtype. An age of <35years was a poor prognosticator in patients with the HR+/HER2−, HR+/HER2+, and HR−/HER2+ subtypes, but not in those with the TN subtype.World Journal of Surgery 04/2012; 35(6):1244-1253. · 2.36 Impact Factor -
Article: Enhanced of electrical characteristics of nano-crystal floating gate memory with In2O3 nano-particles embedded in polyimide
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ABSTRACT: We fabricated the nano-floating gate memory (NFGM) with In2O3 nano-particles embedded in polyimide gate insulators. Self-assembled In2O3 nano-particles were created by chemical reaction between the polymer precursor and the indium film. The particle size and density of In2O3 nano-particles were about 7nm and 6 × 1011cm−2, respectively. The electrical characterization of the NFGM with In2O3 nano-particles embedded in polyimide layer were measured and the memory window larger than 3.8V was obtained from the fabricated NFGM devices due to the charging effects of In2O3 particles. Subthreshold swing, output current characteristics and retention time of fabricated NFGM devices were considerably improved by the post-annealing process in 3% hydrogen diluted H2/N2 ambient.Journal of Electroceramics 04/2012; 23(2):150-153. · 1.19 Impact Factor -
Article: Resistance switching properties of In2O3 nanocrystals memory device with organic and inorganic hybrid structure
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ABSTRACT: A memory device with In2O3 nanocrystals embedded in a biphenyl-tertracarboxylic dianhydride-phenylen diamine (BPDA-PDA) polyimide layer on a ZnO layer was fabricated, and its electrical properties were evaluated. Then, the transmittance efficiency in the structure of the BPDA-PDA polyimide/In2O3 nanocrystals/ZnO/ITO/double polishing sapphire substrate was measured to be about 80% between 440 to 800nm by ultraviolet-visible transmittance spectroscopy. A bipolar switching current bistability by difference resistance appeared in the sweep voltage rage from −7 to 7V. It was considered that the bipolar behavior of current-voltage may originate from a resistance fluctuation because of the electron charging effect in In2O3 nanocrystals by voltage sweeping, Fowler–Nordheim tunneling, space-charge-limited current, and the migration of O2−ions.Applied Physics A 04/2012; 102(4):933-938. · 1.63 Impact Factor -
Article: Scoring system for predicting malignancy in patients diagnosed with atypical ductal hyperplasia at ultrasound-guided core needle biopsy
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ABSTRACT: Background The aim of this study was to determine factors that predict under-evaluation of malignancy in patients diagnosed with atypical ductal hyperplasia (ADH) at ultrasound-guided core needle biopsy (CNB), and to develop a prediction algorithm for scoring the possibility of a diagnosis upgrade to malignancy based on clinical, radiological and pathological factors. Methods The study enrolled patients diagnosed with ADH at ultrasound-guided CNB who subsequently underwent surgical excision of the lesion. Multivariate analysis was used to identify relevant clinical, radiological and pathological factors that may predict malignancy. Results A total of 102 patients with ADH at CNB were identified. Of the 74 patients who underwent subsequent surgical excision, 34 (45.8%) were diagnosed with invasive or insitu malignant foci. Multivariate analysis revealed that age >50years, microcalcification on mammography, size on imaging >15mm and a palpable lesion were independent predictors of malignancy. Focal ADH was a negative predictor. A scoring system was developed based on logistic regression models and beta coefficients for each variable. The area under the ROC curve was 0.903 (95% CI: 0.82–0.94), and the negative predictive value was 100% for a score ≤3.5. Similar findings were observed for a validation dataset of 54 patients at other institutions. Conclusions A scoring system to predict malignancy in patients diagnosed with ADH at CNB was developed based on five factors: age, palpable lesion, microcalcification on mammography, size on imaging and focal ADH. This system was able to identify a subset of patients with lesions likely to be benign, indicating that imaging follow-up rather than surgical excision may be appropriate.Breast Cancer Research and Treatment 04/2012; 112(1):189-195. · 4.43 Impact Factor -
Article: Efficiency enhancement in a-plane InGaN/GaN light emitters with carbon nanotubes.
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ABSTRACT: This study investigates the coupling modes of a-plane InGaN/GaN mutiquantum wells (MQWs) with single-walled carbon nanotubes (SWCNTs). The enhancement of light emissions at resonance photon energies can be explained by the surface plasmon coupling of the MQW-SWCNT hybrid structure. The photoluminescence (PL) enhancement ratios of the indigo (2.90 eV) emission from MQWs with SWCNTs reveal three coupling modes at 2.50 eV, 2.97 eV, and 3.42 eV. In addition, the trend of the PL intensity ratios and efficiencies corresponds to that of the PL enhancement ratios. The PL efficiencies for the green (2.46 eV) and indigo (2.90 eV) emissions of SWCNT-coated MQWs are 32% and 110% better than the corresponding values of uncoated MQWs, respectively. The results show that the MQW-SWCNT hybrid structure has the potential to be applied in high-efficiency light emitters in the visible and ultraviolet range.Journal of Nanoscience and Nanotechnology 04/2012; 12(4):3380-3. · 1.56 Impact Factor -
Article: Formation of Cu or Cu2O nanoparticles embedded in a polyimide film for nanofloating gate memory.
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ABSTRACT: Cu and Cu2O nanoparticles were fabricated in polyimide by curing the stacked polyamic acid/Cu/polyamic acid on Si wafer and post heat treatment. Nanoparticle distribution in polyimide (a monolayer of vertically aligned nanoparticles or the randomly dispersed nanoparticles) can be controlled by changing the reactivity of Cu with PAA and curing atmosphere. About 6-7 nm sized Cu or Cu2O nanoparticles were observed in the polyimide film. The capacitance-voltage curves were measured with Al/particles in polyimide/p-Si(100) specimens at 300 K, and the capacitance hystereses were observed at different sweep voltage ranges, which indicates that Cu2O or Cu nanoparticles can be utilized in next generation flash memories.Journal of Nanoscience and Nanotechnology 12/2011; 11(12):11100-3. · 1.56 Impact Factor -
Article: Thermal stability of metal-silicide nanocrystal nonvolatile memory with barrier engineered tunnel layers.
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ABSTRACT: WSi2 nanocrystal nonvolatile memory devices were fabricated with a silicon oxide-nitride-oxide (SiO2: 2 nm/Si3N4:2 nm/SiO2:3 nm) tunnel layer. WSi2 nanocrystals of 2.5 nm diameters and a density of 3.6 x 10(12) cm(-2) were formed using radio frequency magnetron sputtering and annealing processes. The WSi2 nanocrystal nonvolatile memory device exhibited strong thermal stability during writing/erasing operations at temperatures up to 125 degrees C. When the writing/erasing voltages were applied at +10 V/-10 V for 500 ms, the memory window of the initial approximately 2.6 V decreased by approximately 1.1 V at 25 degrees C and 0.4 V at 125 degrees C after 10(4) sec, respectively. These results show that WSi2 nanocrystals with barrier-engineered tunnel layers are possible for application in nonvolatile memory devices.Journal of Nanoscience and Nanotechnology 10/2011; 11(10):9181-4. · 1.56 Impact Factor -
Article: Linearly polarized light emission from InGaN/GaN quantum well structure with high indium composition.
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ABSTRACT: We fabricated yellow (575 nm) emitting a-plane InGaN/GaN light emitting diode (LED). Microstructure and stress relaxation of the InGaN well layer were observed from the images of dark field transmission electron microscopy. The LED chip was operated at 3.7 V, 20 mA, and the polarization-free characteristic in nonpolar InGaN layer was confirmed from a small blue-shift of approximaely 1.7 nm with increase of current density. The high photoluminescence (PL) efficiency of 30.4% showed that this non-polar InGaN layer has a potential of application to green-red long wavelength light emitters. The PL polarization ratio at 290 K was 0.25 and the energy difference between two subbands was estimated to be 40.2 meV. The low values of polarization and energy difference were due to the stress relaxation of InGaN well layer.Journal of Nanoscience and Nanotechnology 10/2011; 11(10):9222-6. · 1.56 Impact Factor -
Article: Nonvolatile-memory characteristics of SiC nanocrystals with variable oxide thickness and crested tunnel barriers.
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ABSTRACT: The electrical characteristics of SiC nanocrystal nonvolatile-memory devices with variable oxide and crested tunnel barriers consisting of a SiO2/Si3N4/SiO2 (ONO) and a Si3N4/SiO2/Si3N4 (NON) layer, respectively, were investigated. The equivalent oxide thickness of the ONO and NON tunnel barriers were about 5.6 nm and 5.2 nm, respectively. When the +/- 13 V bias voltage was applied for 500 ms, the threshold voltage shifts of the SiC-nanocrystal-embedded memory devices with ONO and NON tunnel barriers were about 2.4 V. The operation speeds of the memories with ONO and NON tunnel barriers under the +/- 10 V applied pulse bias were approximately 5 and 20 ms, respectively. The field sensitivity of the ONO tunnel barrier was higher than that of the NON tunnel barrier during electron injection. The tunneling efficiency during the programming/erasing processes could be improved by the engineered tunnel barrier layer. Therefore, the SiC-nanocrystal-embedded memory device with an ONO tunnel barrier can be applied to nonvolatile-memory devices.Journal of Nanoscience and Nanotechnology 07/2011; 11(7):5883-6. · 1.56 Impact Factor -
Article: Capacitance transient analysis of different-sized InAs/GaAs quantum dot structures.
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ABSTRACT: The energy states of InAs/GaAs self-assembled quantum dots (QDs) were analyzed by comparing between two QD systems with different QD sizes. The electrical properties of the QD systems were investigated via capacitance-voltage measurements and capacitance transient spectroscopy (also known as deep-level transient spectroscopy) with selective carrier injection and extraction which can be achieved with very small pulse amplitude under bias variation. For the large QDs, several energy states were found with the use of selective carrier injection and extraction. The thermal-activation energies obtained from the capacitance transient spectra of the large QDs were distributed from 70 to 600 meV. This energy distribution was originated from the quantized states of the individual QDs and the size distribution of the QDs. The spectra of the small QDs showed a well-defined energy state of E(c) - 132 meV. From these results, it was estimated that two to four electrons fill a single QD under the proper measurement bias of 0.2 V pulse.Journal of Nanoscience and Nanotechnology 07/2011; 11(7):6504-9. · 1.56 Impact Factor -
Article: Enhancement of photoluminescence from ZnO film by single wall carbon nanotubes.
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ABSTRACT: Optical emissions from ZnO films were enhanced by a formation of hybrid structures with single wall carbon-nanotubes (SWCNTs). The SWCNTs were characterized by the presence of the associated fibers and islands together with many carbon nanotube structures and their average height was about < or = 40 nm from atomic force microscope and scanning electron microscope measurements. The intensities of photoluminescence on ZnO films with SWCNTs were increased up to about 30 and 60% in the region of 3.3 eV (near band edge) and 2.3 eV (deep-level) bands, respectively. It was considered that the enhancement of optical emissions from ZnO might be resulted from the effects of an excitation light scattering by SWCNTs and a surface plasmon resonance between bandgap of ZnO and SWCNTs. The surface plasmon resonance mode in the ultra-violet regions is smaller than the deep-level region relatively. This result showed that the commercial ZnO/carbon nanotubes have a feasibility of application to optoelectronic device.Journal of Nanoscience and Nanotechnology 07/2011; 11(7):6148-51. · 1.56 Impact Factor -
Article: Prognostic significance of young age (<35 years) by subtype based on ER, PR, and HER2 status in breast cancer: a nationwide registry-based study.
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ABSTRACT: Young age is regarded as an adverse prognostic factor in patients with breast cancer, especially in those with a hormone receptor (HR)-positive tumor. We investigated the prognostic significance of an age of <35 years stratified by molecular subtype based on HR and HER2. Two large databases of Korean breast cancer patients, which included nationwide registry data, were analyzed. In an analysis of 2,474 patients from the single institution, an age of <35 years was found to be an independent predictor of recurrence in patients with HR+/HER2- (hazard ratio 1.87; 95% confidence interval [CI]: 1.11-3.14; P=0.018), HR+/HER2+ (hazard ratio 3.09; 95% CI: 1.19-8.03; P=0.020), and HR-/HER2+ (hazard ratio 2.01; 95% CI: 1.03-3.92; P=0.040) subtypes, but not in those with the HR-/HER2- (triple-negative, TN) subtype (hazard ratio 1.08; 95% CI: 0.60-1.95; P=0.802). The results of an analysis of nationwide database data on 31,672 patients also showed that an age of <35 years significantly predicted poor cancer-specific survival in patients with HR+/HER2- (hazard ratio 3.40; 95% CI: 2.41-4.82; P<0.001), HR+/HER2+ (hazard ratio 1.96; 95% CI: 1.23-3.12; P=0.005), and HR-/HER2+ (hazard ratio 1.65; 95% CI: 1.07-2.52; P=0.022) subtypes, but again not in those with the TN subtype (hazard ratio 1.21; 95% CI: 0.88-1.67; P=0.240). The prognostic significance of young age was found to depend on molecular subtype. An age of <35 years was a poor prognosticator in patients with the HR+/HER2-, HR+/HER2+, and HR-/HER2+ subtypes, but not in those with the TN subtype.World Journal of Surgery 04/2011; 35(6):1244-53. · 2.36 Impact Factor -
Article: Redd1 inhibits the invasiveness of non-small cell lung cancer cells.
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ABSTRACT: Redd1 acts as a negative regulator of mTOR in response to various stress conditions, but its specific physiological role is currently unclear. In the present study, we showed that Redd1 inhibits the invasive activity of non-small cell lung cancer (NSCLC) cells. Interestingly, expression of Redd1 was extremely low in H1299 cells displaying high invasiveness, compared with that in H460 cells with lower invasive activity. Overexpression of Redd1 inhibited the invasive activity of H1299 cells, while suppression with specific siRNAs enhanced the invasiveness of H460 cells. Knockdown of the mTOR downstream substrate, S6K, resulted in a decrease in the invasive property of H1299 cells. Our results provide preliminary evidence that Redd1 inhibits the invasive activity of NSCLC cells via suppression of the mTOR downstream pathway.Biochemical and Biophysical Research Communications 03/2011; 407(3):507-11. · 2.48 Impact Factor -
Article: Phosphorylated S6K1 is a possible marker for endocrine therapy resistance in hormone receptor-positive breast cancer.
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ABSTRACT: Cross-talk between the estrogen receptor and the mammalian target of rapamycin (mTOR) pathway is one of the mechanisms of endocrine therapy resistance, and the phosphorylated S6 kinase 1(p-S6K1) is known to be a marker of the mTOR pathway activation. The authors assessed the prognostic significance of p-S6K1 according to the hormone receptor (HR) status. The expression of p-S6K1 was evaluated in 304 breast cancer tissues, and the association between its expression and patient outcomes was investigated. Among 197 cases with the HR (+) tumor, 70 (35.5%) were positive for p-S6K1. Most of the patients (97.5%) with the HR (+) tumor received adjuvant endocrine therapy. The expression of p-S6K1 was found to be an independent worse prognosticator affecting overall survival (OS) and breast cancer-specific survival (BCSS) in the HR (+) group (hazard ratio, 2.62; 95% confidence interval [CI], 1.19-5.76; P = 0.017 and hazard ratio, 3.25; 95% CI, 1.20-8.82; P = 0.020, respectively). In the HR (-) group, however, the p-S6K1 expression was not associated with patients' survival. The expression of p-S6K1 is a worse prognostic factor in patients with HR (+) tumors. These results suggest that the p-S6K1 expression might be a marker for endocrine therapy resistance in patients with HR (+) tumors.Breast Cancer Research and Treatment 02/2011; 126(1):93-9. · 4.43 Impact Factor -
Article: Nonvolatile memory characteristics of WSi2 nanocrystals embedded in SiO2 dielectrics.
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ABSTRACT: A nano-floating gate capacitor with WSi2 nanocrystals embedded in SiO2 dielectrics was fabricated. The WSi2 nanocrystals were created from ultrathin WSi2 film during rapid thermal annealing process and their average size and density were about 2.5 nm and 3.59 x 10(12) cm(-2), respectively. The flat-band voltage shift due to the carrier charging effect of WSi2 nanocrystals were measured up to 5.9 V when the gate voltage sweep in the range of +/- 9 V. The memory window was decreased from 3.7 V to 1.9 V after 1 h and remained about 3.7 V after 10(5) programming/erasing cycles. These results show that there is a possibility for the WSi2 nanocrystals to be applied to nonvolatile memory devices.Journal of Nanoscience and Nanotechnology 01/2011; 11(1):441-4. · 1.56 Impact Factor -
Article: In2O3 nanocrystal memory with the barrier engineered tunnel layer.
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ABSTRACT: In2O3 nanocrystal memories with barrier-engineered tunnel layers were fabricated on a p-type Si substrate. The structure and thickness of the barrier-engineered tunnel layers were SiO2/Si3N4/SiO2 (ONO) and 2/2/3 nm, respectively. The equivalent oxide thickness of the ONO tunnel layers was 5.64 nm. The average size and density of the In2O3 nanocrystals after the reaction between BPDA-PDA polyimide and the In thin film were about 8 nm and 4 x 10(11) cm(-2), respectively. The electrons were charged from the channel of the memory device to the quantum well of the In2O3 nanocrystal through the ONO tunnel layer via Fowler-Nordheim tunneling. The memory window was about 1.4 V when the program and erase conditions of the In2O3 nanocrystal memory device were 12 V for 1 s and -15 V for 200 ms.Journal of Nanoscience and Nanotechnology 01/2011; 11(1):437-40. · 1.56 Impact Factor
Top co-authors
Top Journals
Institutions
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2011–2012
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National Cancer Center Korea
Seoul, Seoul, South Korea
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2008–2011
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Seoul National University Hospital
Seoul, Seoul, South Korea
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2002–2011
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Hanyang University
- Division of Materials Science and Engineering (MSE)
Ansan, Gyeonggi, South Korea
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1990–2007
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Korea Institute of Science and Technology
Seoul, Seoul, South Korea
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2001
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Korea University
- Department of Materials Science and Engineering
Seoul, Seoul, South Korea
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2000
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Silla University
Pusan, Busan, South Korea
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1997
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Inha University
- Department of Electrical Engineering
Seoul, Seoul, South Korea
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