Boogi Chang

Sookmyung Women's University, Sŏul, Seoul, South Korea

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Publications (4)15 Total impact

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    ABSTRACT: Ascorbate is an important natural antioxidant that can selectively kill cancer cells at pharmacological concentrations. Despite its benefit, it is quite difficult to predict the antitumor effects of ascorbate, because the relative cytotoxicity of ascorbate differs between cancer cell lines. Therefore, it is essential to examine the basis for this fundamental disagreement. Because p53 is activated by DNA-damaging stress and then regulates various cellular conditions, we hypothesized that p53 can sensitize cancer cells to ascorbate. Using isogenic cancer cells, we observed that the presence of p53 can affect ascorbate cytotoxicity, and also reactivation of p53 can make cancer cells sensitive to ascorbate. p53-dependent enhancement of ascorbate cytotoxicity is caused by increased reactive oxygen species generation via a differentially regulated p53 transcriptional network. We also found that transcriptionally activated p53 was derived from MDM2 ubiquitination by ascorbate and subsequently its signaling network renders cancer cells more susceptible to oxidative stress. Similar to the p53 effect on in vitro ascorbate cytotoxicity, inhibition of tumor growth is also stronger in p53-expressing tumors than in p53-deficient ones in vivo. This is the first observation that ascorbate cytotoxicity is positively related to p53 expression, activating its transcriptional network to worsen intracellular oxidative stress and consequently enhancing its cytotoxicity. Based on our study, reactivation of p53 may help to achieve more consistent cytotoxic effects of ascorbate in cancer therapies.
    Free Radical Biology and Medicine 08/2012; 53(8):1607-15. · 5.27 Impact Factor
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    ABSTRACT: Aberrant activation of the Wnt/β-catenin signaling pathway is common in human cervical cancers. However, the mechanisms of Wnt activation in cervical cancer remain largely unknown. In the present study, we demonstrate that Klotho, a Wnt antagonist, is downregulated in invasive human cervical tumors and in a cell line we analyzed. Our data demonstrated that in vivo Klotho expression was not observed in invasive cervical carcinoma. In vitro restoration of Klotho expression in SiHa cells resulted in a decreased cell motility and invasiveness through upregulation of E-cadherin, downregulation of N-cadherin and reduced expression of MMP7 and -9. Ectopic expression of Klotho also reduced the expression of the epithelial-to-mesenchymal transition (EMT) transcription factors Slug and Twist. Furthermore, Klotho causes a significant inhibition of the Wnt/β-catenin pathway in cervical cancer cells, as supported by the expression of Wnt/β-catenin transcriptional target genes such as c-Myc and cyclin D1. Consequently, our findings demonstrate for the first time that Klotho regulates tumor invasion through the EMT process and provide novel mechanistic insights into the role of Klotho in cervical cancer progression and contribute to treatment for metastatic cervical cancer patients.
    Oncology Reports 06/2012; 28(3):1022-8. · 2.30 Impact Factor
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    ABSTRACT: The homo sapiens LIM homeobox domain LHX6 gene, hLHX6, is a putative transcription regulator with homeo-domain. Multiple cytosine guanine dinucleotides (CpG island) are found in the genomic sequences between exon 4a and exon 5 of the gene encoding hLHX6s (alternative short iso-form of hLHX6 gene). This specific CpG island, hLHX6-HMR, is found frequently hypermethylated in 7 cervical cancer cell lines as shown in MSP, BSP, and COBRA assays. Methylation densities were also investigated with human tissue samples with a distinctive degree of malignant transformation. Our data showed that the hLHX6-HMR was rarely or partly methylated in the normal and CIN I cells, respectively. In contrast, it was frequently hypermethylated in CIN II, CIN III, and invasive carcinoma cells. In summary, this methylation study led to two conclusions. First, hLHX6-HMR hypermethylation is exclusively associated with cervical carcinogenesis. Second, the epigenetic change in hLHX6-HMR seems to start at CIN I, relatively early stage of cervical cancer development. Therefore, hLHX6-HMR can be used as an effective and sensitive methylation biomarker for early diagnosis of cervical cancer.
    Oncology Reports 06/2010; 23(6):1675-82. · 2.30 Impact Factor
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    ABSTRACT: Klotho was originally characterized as an anti-aging gene that predisposed Klotho-deficient mice to a premature aging-like syndrome. Recently, KLOTHO was reported to function as a secreted Wnt antagonist and as a tumor suppressor. Epigenetic gene silencing of secreted Wnt antagonists is considered a common event in a wide range of human malignancies. Abnormal activation of the canonical Wnt pathway due to epigenetic deregulation of Wnt antagonists is thought to play a crucial role in cervical tumorigenesis. In this study, we examined epigenetic silencing of KLOTHO in human cervical carcinoma. Loss of KLOTHO mRNA was observed in several cervical cancer cell lines and in invasive carcinoma samples, but not during the early, preinvasive phase of primary cervical tumorigenesis. KLOTHO mRNA was restored after treatment with either the DNA demethylating agent 2'-deoxy-5-azacytidine or histone deacetylase inhibitor trichostatin A. Methylation-specific PCR and bisulfite genomic sequencing analysis of the promoter region of KLOTHO revealed CpG hypermethylation in non-KLOTHO-expressing cervical cancer cell lines and in 41% (9/22) of invasive carcinoma cases. Histone deacetylation was also found to be the major epigenetic silencing mechanism for KLOTHO in the SiHa cell line. Ectopic expression of the secreted form of KLOTHO restored anti-Wnt signaling and anti-clonogenic activity in the CaSki cell line including decreased active beta-catenin levels, suppression of T-cell factor/beta-catenin target genes, such as c-MYC and CCND1, and inhibition of colony growth. Epigenetic silencing of KLOTHO may occur during the late phase of cervical tumorigenesis, and consequent functional loss of KLOTHO as the secreted Wnt antagonist may contribute to aberrant activation of the canonical Wnt pathway in cervical carcinoma.
    Molecular Cancer 01/2010; 9:109. · 5.13 Impact Factor