Search tips
Search criteria

Results 1-9 (9)

Clipboard (0)

Select a Filter Below

Year of Publication
Document Types
author:("Lee, Ji-seen")
1.  Generation of Cancerous Neural Stem Cells Forming Glial Tumor by Oncogenic Stimulation 
Stem cell reviews  2012;8(2):532-545.
Neural stem cells in the brain have been shown to be ‘cells of origin’ of certain brain cancers, most notably astrocytomas and medulloblastoma. In particular, in a mouse model, the targeting of genetic modifications for astrocytoma-relevant tumor suppressors to neural stem cells causes malignant astrocytoma to arise, thereby suggesting that astrocytoma is derived from neural stem cells. However, it remains to be determined whether this important finding is reproducible in humans. Herein, we generated cancerous neural stem cells by introducing a set of oncogenes to human fetal neural stem cells (hfNSCs). Serial genetic modification with v-myc for immortalization and consequent H-Ras for oncogenic stimulation with viral gene delivery proved sufficient to induce the transformation of hfNSCs. The resultant F3.Ras cells evidenced a variety of the hallmarks of brain cancer stem cells and most importantly were tumorigenic, forming brain cancers consisting of both a large number of differentiated and a very few undifferentiated populations of cells in an in vivo mouse model. On the contrary, oligodendrocytes derived from the v-myc expressing parent neural stem cells were not transformed by H-Ras, which suggests that neural stem cells may be more susceptible to cancerous transformation by a combination of oncogenes. We also determined that v-myc expressing fetal neural stem cells were defective in p53 response upon the introduction of H-Ras; this finding suggests that an insufficient p53-dependent tumor suppressive mechanism would be associated with high oncogenic susceptibility to H-Ras introduction.
PMCID: PMC4043123  PMID: 21755312
Human neural stem cells; v-myc; H-Ras; Cancerous stem cells; p53; Glial tumor
2.  SIRT3 Overexpression Attenuates Palmitate-Induced Pancreatic β-Cell Dysfunction 
PLoS ONE  2015;10(4):e0124744.
Abnormally high levels of circulating free fatty acids can lead to pancreatic islet β-cell dysfunction and apoptosis, contributing to β-cell failure in Type 2 diabetes. The NAD+-dependent protein deacetylase Sirtuin-3 (SIRT3) has been implicated in Type 2 diabetes. In this study, we tested whether SIRT3 overexpression affects palmitate-induced β-cell dysfunction in cells of line NIT1, which are derived from mouse pancreatic β-cells. Two different lengths of SIRT3 were overexpressed: full length SIRT3 (SIRT3LF), which was preferentially targeted to mitochondria and partially to the nucleus, and its N-terminal truncated form (SIRT3SF), which was located in the nucleus and cytoplasm. Overexpression of SIRT3LF and SIRT3SF using an adenoviral system alleviated palmitate-induced lipotoxicity such as reduction of cell viability and mitogen-activated protein kinase (MAPK) activation. Chronic exposure to low concentrations of palmitate suppressed glucose-stimulated insulin secretion, but the suppression was effectively reversed by overexpression of SIRT3LF or SIRT3SF. The mRNA levels of the endoplasmic reticulum (ER) stress responsive genes ATF4, GRP94 and FKBP11 were increased by palmitate treatment, but the increases were completely inhibited by SIRT3LF overexpression and less effectively inhibited by SIRT3SF overexpression. This result suggests that overexpression of SIRT3 inhibits induction of ER stress by palmitate. Collectively, we conclude that overexpression of SIRT3 alleviates palmitate-induced β-cell dysfunction.
PMCID: PMC4411148  PMID: 25915406
3.  Tumor necrosis factor-inducible gene 6 promotes liver regeneration in mice with acute liver injury 
Tumor necrosis factor-inducible gene 6 protein (TSG-6), one of the cytokines released by human mesenchymal stem/stromal cells (hMSC), has an anti-inflammatory effect and alleviates several pathological conditions; however, the hepatoprotective potential of TSG-6 remains unclear. We investigated whether TSG-6 promoted liver regeneration in acute liver failure.
The immortalized hMSC (B10) constitutively over-expressing TSG-6 or empty plasmid (NC: Negative Control) were established, and either TSG-6 or NC-conditioned medium (CM) was intraperitoneally injected into mice with acute liver damage caused by CCl4. Mice were sacrificed at 3 days post-CM treatment.
Higher expression and the immunosuppressive activity of TSG-6 were observed in CM from TSG-6-hMSC. The obvious histomorphological liver injury and increased level of liver enzymes were shown in CCl4-treated mice with or without NC-CM, whereas those observations were markedly ameliorated in TSG-6-CM-treated mice with CCl4. Ki67-positive hepatocytic cells were accumulated in the liver of the CCl4 + TSG-6 group. RNA analysis showed the decrease in both of inflammation markers, tnfα, il-1β, cxcl1 and cxcl2, and fibrotic markers, tgf-β1, α-sma and collagen α1, in the CCl4 + TSG-6 group, compared to the CCl4 or the CCl4 + NC group. Protein analysis confirmed the lower expression of TGF-β1 and α-SMA in the CCl4 + TSG-6 than the CCl4 or the CCl4 + NC group. Immunostaining for α-SMA also revealed the accumulation of the activated hepatic stellate cells in the livers of mice in the CCl4 and CCl4 + NC groups, but not in the livers of mice from the CCl4 + TSG-6 group. The cultured LX2 cells, human hepatic stellate cell line, in TSG-6-CM showed the reduced expression of fibrotic markers, tgf-β1, vimentin and collagen α1, whereas the addition of the TSG-6 antibody neutralized the inhibitory effect of TSG-6 on the activation of LX2 cells. In addition, cytoplasmic lipid drops, the marker of inactivated hepatic stellate cell, were detected in TSG-6-CM-cultured LX2 cells, only. The suppressed TSG-6 activity by TSG-6 antibody attenuated the restoration process in livers of TSG-6-CM-treated mice with CCl4.
These results demonstrated that TSG-6 contributed to the liver regeneration by suppressing the activation of hepatic stellate cells in CCl4-treated mice, suggesting the therapeutic potential of TSG-6 for acute liver failure.
Electronic supplementary material
The online version of this article (doi:10.1186/s13287-015-0019-z) contains supplementary material, which is available to authorized users.
PMCID: PMC4396561  PMID: 25890163
4.  Retinoid X Receptor α Overexpression Alleviates Mitochondrial Dysfunction-induced Insulin Resistance through Transcriptional Regulation of Insulin Receptor Substrate 1 
Molecules and Cells  2015;38(4):356-361.
Mitochondrial dysfunction is associated with insulin resistance and diabetes. We previously showed that retinoid X receptor α (RXRα) played an important role in transcriptional regulation of oxidative phosphorylation (OXPHOS) genes in cells with mitochondrial dysfunction caused by mitochondrial DNA mutation. In this study, we investigated whether mitochondrial dysfunction induced by incubation with OXPHOS inhibitors affects insulin receptor substrate 1 (IRS1) mRNA and protein levels and whether RXRα activation or overexpression can restore IRS1 expression. Both IRS1 and RXRα protein levels were significantly reduced when C2C12 myotubes were treated with the OXPHOS complex inhibitors, rotenone and antimycin A. The addition of RXRα agonists, 9-cis retinoic acid (9cRA) and LG1506, increased IRS1 transcription and protein levels and restored mitochondrial function, which ultimately improved insulin signaling. RXRα overexpression also increased IRS1 transcription and mitochondrial function. Because RXRα overexpression, knock-down, or activation by LG1506 regulated IRS1 transcription mostly independently of mitochondrial function, it is likely that RXRα directly regulates IRS1 transcription. Consistent with the hypothesis, we showed that RXRα bound to the IRS1 promoter as a heterodimer with peroxisome proliferator-activated receptor δ (PPARδ). These results suggest that RXRα overexpression or activation alleviates insulin resistance by increasing IRS1 expression.
PMCID: PMC4400311  PMID: 25728751
insulin receptor substrate 1; insulin resistance; itochondrial dysfunction; retinoid X receptor α
5.  Identification and Functional Characterization of P159L Mutation in HNF1B in a Family with Maturity-Onset Diabetes of the Young 5 (MODY5) 
Genomics & Informatics  2014;12(4):240-246.
Mutation in HNF1B, the hepatocyte nuclear factor-1β (HNF-1β) gene, results in maturity-onset diabetes of the young (MODY) 5, which is characterized by gradual impairment of insulin secretion. However, the functional role of HNF-1β in insulin secretion and glucose metabolism is not fully understood. We identified a family with early-onset diabetes that fulfilled the criteria of MODY. Sanger sequencing revealed that a heterozygous P159L (CCT to CTT in codon 159 in the DNA-binding domain) mutation in HNF1B was segregated according to the affected status. To investigate the functional consequences of this HNF1B mutation, we generated a P159L HNF1B construct. The wild-type and mutant HNF1B constructs were transfected into COS-7 cells in the presence of the promoter sequence of human glucose transporter type 2 (GLUT2). The luciferase reporter assay revealed that P159L HNF1B had decreased transcriptional activity compared to wild-type (p < 0.05). Electrophoretic mobility shift assay showed reduced DNA binding activity of P159L HNF1B. In the MIN6 pancreatic β-cell line, overexpression of the P159L mutant was significantly associated with decreased mRNA levels of GLUT2 compared to wild-type (p < 0.05). However, INS expression was not different between the wild-type and mutant HNF1B constructs. These findings suggests that the impaired insulin secretion in this family with the P159L HNF1B mutation may be related to altered GLUT2 expression in β-cells rather than decreased insulin gene expression. In conclusion, we have identified a Korean family with an HNF1B mutation and characterized its effect on the pathogenesis of diabetes.
PMCID: PMC4330261  PMID: 25705165
glucose transporter type 2; hepatocyte nuclear factor-1β; point mutation; type 2 diabetes mellitus
6.  Loss of E-cadherin activates EGFR-MEK/ERK signaling, which promotes invasion via the ZEB1/MMP2 axis in non-small cell lung cancer 
Oncotarget  2013;4(12):2512-2522.
Loss of E-cadherin, a hallmark of epithelial-mesenchymal transition (EMT), can significantly affect metastatic dissemination. However, the molecular mechanism of EMT-associated metastatic dissemination by loss of E-cadherin still remains unclear in non-small cell lung cancers (NSCLCs). In the present study, we show that the knockdown of E-cadherin was sufficient to convert A549 NSCLC cells into mesenchymal type with the concurrent up-regulation of typical EMT inducers such as ZEB1 and TWIST1. Interestingly, the EMT-induced cells by E-cadherin depletion facilitate invasion in a matrix metalloproteinase-2 (MMP2)-dependent manner with aberrant activation of EGFR signaling. We demonstrated that the elevated invasiveness was a result of the activated EGFR-MEK/ERK signaling, which in turn leads to ZEB1 dependent MMP2 induction. These results suggest that the EGFR-MEK/ERK/ZEB1/MMP2 axis is responsible for promoted invasion in EMT-induced NSCLCs. Consistently, ERK activation and loss of E-cadherin were both observed in the disseminating cancer cells at the invasive tumor fronts in NSCLC cancer tissues. Thereby, these data suggest that the EGFR-MEK/ERK signaling would be a promising molecular target to control aberrant MMP2 expression and consequent invasion in the EMT-induced NSCLCs
PMCID: PMC3926845  PMID: 24318272
E-Cadherin; EGFR-MEK/ERK signaling; ZEB1; MMP2; Invasion
7.  Fine Mapping of Xq28: Both MECP2 and IRAK1 Contribute to Risk for Systemic Lupus Erythematosus in Multiple Ancestral Groups 
Annals of the rheumatic diseases  2012;72(3):437-444.
The Xq28 region containing IRAK1 and MECP2 has been identified as a risk locus for systemic lupus erythematosus (SLE) in previous genetic association studies. However, due to the strong linkage disequilibrium between IRAK1 and MECP2, it remains unclear which gene is affected by the underlying causal variant(s) conferring risk of SLE.
We fine-mapped ≥136 SNPs in a ~227kb region on Xq28, containing IRAK1, MECP2 and 7 adjacent genes (L1CAM, AVPR2, ARHGAP4, NAA10, RENBP, HCFC1 and TMEM187), for association with SLE in 15,783 case-control subjects derived from 4 different ancestral groups.
Multiple SNPs showed strong association with SLE in European Americans, Asians and Hispanics at P<5×10−8 with consistent association in subjects with African ancestry. Of these, 6 SNPs located in the TMEM187-IRAK1-MECP2 region captured the underlying causal variant(s) residing in a common risk haplotype shared by all 4 ancestral groups. Among them, rs1059702 best explained the Xq28 association signals in conditional testings and exhibited the strongest P value in trans-ancestral meta-analysis (Pmeta=1.3×10−27, OR=1.43), and thus was considered to be the most-likely causal variant. The risk allele of rs1059702 results in the amino acid substitution S196F in IRAK1 and had previously been shown to increase NF-κB activity in vitro. We also found that the homozygous risk genotype of rs1059702 was associated with lower mRNA levels of MECP2, but not IRAK1, in SLE patients (P=0.0012) and healthy controls (P=0.0064).
These data suggest contributions of both IRAK1 and MECP2 to SLE susceptibility.
PMCID: PMC3567234  PMID: 22904263
Systemic Lupus Erythematosus; Gene Polymorphism; Xq28; IRAK1; MECP2
8.  Association of PPP2CA polymorphisms with SLE susceptibility in multiple ethnic groups 
Arthritis and rheumatism  2011;63(9):2755-2763.
T cells from patients with SLE express increased amounts of PP2Ac which contribute to decreased production of IL-2. Because IL-2 is important in the regulation of several aspects of the immune response, it has been proposed that PP2Ac contributes to the expression of SLE. This study was designed to determine whether genetic variants of PPP2AC are linked to the expression of SLE and specific clinical manifestations and account for the increased expression of PP2Ac.
We conducted a trans-ethnic study consisting of 8,695 SLE cases and 7,308 controls from four different ancestries. Eighteen single-nucleotide polymorphisms (SNPs) across the PPP2CA were genotyped using an Illumina custom array. PPP2CA expression in SLE and control T cells was analyzed by real-time PCR.
A 32-kb haplotype comprised of multiple SNPs of PPP2CA showed significant association with SLE in Hispanic Americans (HA), European Americans (EA) and Asians but not in African-Americans (AA). Conditional analyses revealed that SNP rs7704116 in intron 1 showed consistently strong association with SLE across Asian, EA and HA populations (pmeta=3.8×10−7, OR=1.3[1.14–1.31]). In EA, the largest ethnic dataset, the risk A allele of rs7704116 was associated with the presence of renal disease, anti-dsDNA and anti-RNP antibodies. PPP2CA expression was approximately 2-fold higher in SLE patients carrying the rs7704116 AG genotype than those carrying GG genotype (p = 0.008).
Our data provide the first evidence for an association between PPP2CA polymorphisms and elevated PP2Ac transcript levels in T cells, which implicates a new molecular pathway for SLE susceptibility in EA, HA and Asians.
PMCID: PMC3163110  PMID: 21590681
9.  Wip1 directly dephosphorylates gamma-H2AX and attenuates the DNA damage response 
Cancer research  2010;70(10):4112-4122.
The integrity of DNA is constantly challenged throughout the life of a cell by both endogenous and exogenous stresses. A well-organized rapid damage response and proficient DNA repair, therefore, becomes critically important for maintaining genomic stability and cell survival. When DNA is damaged, the DNA damage response (DDR) can be initiated by alterations in chromosomal structure and histone modifications, such as the phosphorylation of the histone H2AX (the phosphorylated form is referred to as γ-H2AX). γ-H2AX plays a crucial role in recruiting DDR factors to damage sites for accurate DNA repair. Upon repair completion,γ-H2AX must then be reverted to H2AX by dephosphorylation for attenuation of the DDR. Here, we report that Wip1 phosphatase, which is often over-expressed in a variety of tumors, effectively dephosphorylates γ-H2AX in vitro and in vivo. Ectopic expression of Wip1 significantly reduces the level of γ-H2AX after ionizing as well as ultraviolet radiation. Forced premature dephosphorylation of γ-H2AX by Wip1 disrupts recruitment of important DNA repair factors to damaged sites, and delays DNA damage repair. Additionally, deletion of Wip1 enhances γ-H2AX levels in cells undergoing constitutive oncogenic stress. Taken together our studies demonstrate that Wip1 is an important mammalian phosphatase for γ-H2AX and demonstrates an additional mechanism for Wip1 in the tumor surveillance network.
PMCID: PMC2904079  PMID: 20460517
Wip1; PPM1D; H2AX; gamma-H2AX; ionizing radiation; ultraviolet radiation; DNA damage; DNA repair

Results 1-9 (9)