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Lee, Geonhee,Jung, Du Won,Lee, Wonki,Nah, Sanghee,Ji, Seulgi,Hwang, Jun Yeon,Lee, Sun Sook,Park, Sungsu,Chae, Soo Sang,Lee, Jeong-O Elsevier 2019 Carbon Vol.141 No.-
<P><B>Abstract</B></P> <P>Reduced graphene oxide (rGO) has potential as a mass-producible and cost-effective substitute for graphene, but displays poor crystal quality due to various types of structural defects. Though many attempts have been reported to improve the quality of rGO, most of them require sophisticated equipment or severe conditions such as toxic chemicals, high temperature, and electron beam or plasma treatment in ultra-high vacuum (UHV) conditions. Here, we report a mild and simple solution-based healing method for obtaining high-quality rGO, with this method involving the use of a simple camera flash light treatment and the nontoxic chemicals <SMALL>L</SMALL>-ascorbic acid and ethanol. Exposing a GO solution containing <SMALL>L</SMALL>-ascorbic acid and ethanol to the flash light irradiation for a short amount of time (<10 min) resulted in the formation of rGO displaying high quality both with respect to its chemical composition and its crystallinity. To elucidate the mechanism of the flash-light-induced healing of rGO, we acquired and analyzed the transient absorption spectrum for the healing reaction by using femtosecond pump-probe spectroscopy; this analysis revealed the photo-catalytic activity of GO by itself to repair chemical and topological defects, and we hence named this process ‘self-catalytic healing’.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lee, Ha-Na,Jin, Hyeon-Ok,Park, Jin-Ah,Kim, Jin-Hee,Kim, Ji-Young,Kim, BoRa,Kim, Wonki,Hong, Sung-Eun,Lee, Yun-Han,Chang, Yoon Hwan,Hong, Seok-Il,Hong, Young Jun,Park, In-Chul,Surh, Young-Joon,Lee, Jin Korean Society for Molecular and Cellular Biology 2015 Molecules and cells Vol.38 No.4
Piperlongumine, a natural alkaloid isolated from the long pepper, selectively increases reactive oxygen species production and apoptotic cell death in cancer cells but not in normal cells. However, the molecular mechanism underlying piperlongumine-induced selective killing of cancer cells remains unclear. In the present study, we observed that human breast cancer MCF-7 cells are sensitive to piperlongumine-induced apoptosis relative to human MCF-10A breast epithelial cells. Interestingly, this opposing effect of piperlongumine appears to be mediated by heme oxygenase-1 (HO-1). Piperlongumine upregulated HO-1 expression through the activation of nuclear factor-erythroid-2-related factor-2 (Nrf2) signaling in both MCF-7 and MCF-10A cells. However, knockdown of HO-1 expression and pharmacological inhibition of its activity abolished the ability of piperlongumine to induce apoptosis in MCF-7 cells, whereas those promoted apoptosis in MCF-10A cells, indicating that HO-1 has anti-tumor functions in cancer cells but cytoprotective functions in normal cells. Moreover, it was found that piperlongumine-induced Nrf2 activation, HO-1 expression and cancer cell apoptosis are not dependent on the generation of reactive oxygen species. Instead, piperlongumine, which bears electrophilic ${\alpha},{\beta}$-unsaturated carbonyl groups, appears to inactivate Kelch-like ECH-associated protein-1 (Keap1) through thiol modification, thereby activating the Nrf2/HO-1 pathway and subsequently upregulating HO-1 expression, which accounts for piperlongumine-induced apoptosis in cancer cells. Taken together, these findings suggest that direct interaction of piperlongumine with Keap1 leads to the upregulation of Nrf2-mediated HO-1 expression, and HO-1 determines the differential response of breast normal cells and cancer cells to piperlongumine.
Lee, Yeon-Hwa,Song, Na-Young,Suh, Jinyoung,Kim, Do-Hee,Kim, Wonki,Ann, Jihyae,Lee, Jeewoo,Baek, Jeong-Heum,Na, Hye-Kyung,Surh, Young-Joon Elsevier 2018 Cancer letters Vol.431 No.-
<P><B>Abstract</B></P> <P>SIRT1, an NAD<SUP>+</SUP>-dependent histone/protein deacetylase, has diverse physiological actions. Recent studies have demonstrated that SIRT1 is overexpressed in colorectal cancer, suggesting its oncogenic potential. However, the molecular mechanisms by which overexpressed SIRT1 induces the progression of colorectal cancer and its inhibition remain largely unknown. Curcumin (diferuloymethane), a major component of the spice turmeric derived from the plant <I>Curcuma longa</I> L., has been reported to exert chemopreventive and anti-carcinogenic effects on colon carcinogenesis. In the present study, we found that curcumin reduced the expression of SIRT1 protein without influencing its mRNA expression in human colon cancer cells, suggesting posttranslational regulation of SIRT1 by this phytochemical. Notably, ubiquitination and subsequent proteasomal degradation of SIRT1 were induced by curcumin treatment. Results of nano-LC-ESI-MS/MS revealed the direct binding of curcumin to cysteine 67 of SIRT1. In line with this result, the protein stability and clonogenicity of a mutant SIRT1 in which cysteine 67 was substituted by alanine were unaffected by curcumin. Taken together, these observations suggest that curcumin facilitates the proteasomal degradation of oncogenic SIRT1 through covalent modification of SIRT1 at the cysteine 67 residue.</P> <P><B>Highlights</B></P> <P> <UL> <LI> SIRT1 is overexpressed in colorectal cancer tissues compared with normal colon tissues. </LI> <LI> SIRT1 knockdown attenuates viability and migration of human colon cancer cells. </LI> <LI> Silencing of SIRT1 suppressed the growth of HCT-116 derived tumor xenografts. </LI> <LI> Curcumin inhibits migration and growth of HCT-116 cells. </LI> <LI> Curcumin covalently modifies SIRT1 on the cysteine 67 residue, thereby stimulating its proteasomal degradation. </LI> </UL> </P>
Increase of Available Phosphorus by Fly-Ash Application in Paddy Soils
Lee, Chang Hoon,Lee, Hyup,Lee, Yong Bok,Chang, Hong Hee,Ali, Muhamad Aslam,Min, Wonki,Kim, Suk,Kim, Pil Joo M.Dekker 2007 Communications in soil science and plant analysis Vol.38 No.11-12
<P> Fly ash from the coal-burning industry may be a potential inorganic soil amendment to increase rice productivity and to restore the soil nutrient balance in paddy soil. In this study, fly ash was applied at rates of 0, 40, 80, and 120 Mg ha-1 in two paddy soils (silt loam in Yehari and loamy sand in Daegok). During rice cultivation, available phosphorus (P) increased significantly with fly ash application, as there was high content of P (786 mg kg-1) in the applied fly ash. In addition, high content of silicon (Si) and high pH of fly ash contributed to increased available-P content by ion competition between phosphate and silicate and by neutralization of soil acidity, respectively. With fly-ash application, water-soluble P (W-P) content increased significantly together with increasing aluminum-bound P (Al-P) and calcium-bound P (Ca-P) fractions. By contrast, iron-bound P (Fe-P) decreased significantly because of reduction of iron under the flooded paddy soil during rice cultivation. The present experiment indicated that addition of fly ash had a positive benefit on increasing the P availability.</P>
Cluster Analysis of the Challenges of Teaching Korean to Immigrant Learners
Wonki Lee,Hojung Kim 서울대학교 언어교육원 2021 語學硏究 Vol.57 No.2
This study examined challenges Korean language teachers face in classroom teaching contexts, based on typologies derived from a cluster analysis. A total of 181 teachers teaching adult immigrants were surveyed on their challenges using a 24-item survey across the following five dimensions: (1) teaching contents and teaching methods, (2) curriculum design and resource development, (3) language ability assessment, (4) learner counseling, and (5) cultural education. The cluster analysis suggested a three-cluster pattern based on the degree of challenge. Results indicate that the clusters differed significantly in the degree and order of perceived challenges. In addition, when socio-demographic data were considered, results revealed contrasts in the motivation for pursuing professional development, teaching experiences, teaching region, and professional development experience. This study thus provides insight into the multifaceted challenges Korean language teachers face and holds important implications for future professional development.