Eun Kyung Lee

Activation of Hypoxia-Inducible Factor-1α Is Necessary for Lysophosphatidic Acid–Induced Vascular Endothelial Growth Factor Expression

Purpose: Lysophosphatidic acid (LPA) plays an important role in mediating cell proliferation, survival, and tumor invasion and angiogenesis. This bioactive phospholipid at the concentration in ascitic fluid stimulates the growth of malignant ovarian tumors by increasing the expression of vascular endothelial growth factor (VEGF). In the present study, we investigated whether LPA activates hypoxia inducible factor-1 (HIF-1), a key transcriptional complex in tumor progression and metastasis, thereby increasing the expression of VEGF. Experimental Design: Immunoblotting, reverse transcription-PCR, ELISA, immunofluorescence, and chromatin immunoprecipitation assay were used to examine the expression of VEGF and HIF-1α in various cancer cells. Specific HIF-1α small interfering RNA was transfected to various cancer cells to determine the role of HIF-1α in LPA-induced VEGF expression. Results: LPA induced expressions of VEGF and HIF-1α in OVCAR-3, CAOV-3, PC-3, and SK-Hep1 cells but not in SKOV-3 and Hep-3B cells. In OVCAR-3 and PC-3 cells, the phosphoinositide 3-kinase/Akt/mammalian target of rapamycin/p70S6K and p42/p44 mitogen-activated protein kinase pathways were required for LPA-induced HIF-1α and VEGF expressions, whereas only the phosphoinositide 3-kinase/mammalian target of rapamycin/p70S6K pathway was important in SK-Hep1 cells. Immunofluorescence microscopy assay showed translocation of HIF-1α to nucleus by LPA, and chromatin immunoprecipitation assay revealed the binding of HIF-1α to the promoter of VEGF by LPA. Importantly, we found that small interfering RNA–induced reduction of HIF-1α expression significantly attenuated VEGF expression by LPA. Conclusions: Our results show for the first time that LPA induces VEGF via HIF-1α activation and reveal a critical role of HIF-1α in LPA-induced cancer cell proliferation and angiogenesis.

Histone deacetylase inhibitor apicidin downregulates DNA methyltransferase 1 expression and induces repressive histone modifications via recruitment of corepressor complex to promoter region in human cervix cancer cells.

Dysregulation of DNA methyltransferase (DNMT)1 expression is associated with cellular transformation, and inhibition of DNMT1 exerts antitumorigenic effects. Here, we report that DNMT1 abnormally expressed in HeLa cells is downregulated by a histone deacetylase (HDAC) inhibitor apicidin, which is correlated with induction of repressive histone modifications on the promoter site. Apicidin selectively represses the expression of DNMT1 among DNMTs in HeLa cells, independent of cell cycle arrest at G0/G1. Furthermore, apicidin causes a significant reduction in the recruitment of RNA polymerase II into the promoter. Chromatin immunoprecipitation analysis shows that even though apicidin causes global hyperacetylation of histone H3 and H4, localized deacetylation of histone H3 and H4 occurs at the E2F binding site, which is accompanied by the recruitment of pRB and the replacement of P/CAF with HDAC1 into the sites. In addition, K4-trimethylated H3 on nucleosomes associated with the transcriptional start site is depleted following apicidin treatment, whereas repressive markers, K9- and K27-trimethylation of H3 are enriched on the site. The downregulation of DNMT1 expression seems to require de novo protein synthesis, because the apicidin effect is antagonized by cycloheximide treatment. Moreover, knock down of DNMT1 with siRNA induces the apoptosis of HeLa cells, indicating that downregulation of DNMT1 might be a good strategy for therapeutics of human cervix cancer. Collectively, our findings will provide a mechanistic rationale for the use of HDAC inhibitors in cancer therapeutics.

Mitosis-specific Negative Regulation of Epidermal Growth Factor Receptor, Triggered by a Decrease in Ligand Binding and Dimerization, Can Be Overcome by Overexpression of Receptor

The function of epidermal growth factor receptor (EGFR) was found to be negatively regulated in M phase in which it showed less phosphotyrosine content and reduced intrinsic kinase activity accompanied by retarded electrophoretic mobility owing to total hyperphosphorylation. Ligand-induced autophosphorylation and downstream signaling of EGFR were tightly suppressed in M phase due to a decrease in ligand binding affinity and the inability of epidermal growth factor (EGF) to induce receptor dimerization. There was no change in the number of surface-exposed EGF receptors between G0/G1 and M phases of the cell cycle. Hyperphosphorylation (due to serine and/or threonine phosphorylation) correlates with the unresponsiveness of cells to EGF-mediated stimulation of tyrosine phosphorylation in cells that express the normal or basal level of EGFR. This M phase-specific negative regulation was overcome by overexpression of EGFR, which was responsive to ligand throughout the cell cycle and revealed ligand-induced signaling in the M phase. These findings indicate that EGFR does not respond to ligand stimulation in M phase and suggest that a negative regulation of ligand-receptor interactions in M phase may control the normal function of receptor tyrosine kinase and that receptor overexpression will disrupt this cell cycle-dependent regulation of receptor tyrosine kinases.

Reversine Increases the Plasticity of Lineage-committed Cells toward Neuroectodermal Lineage

Functional dedifferentiation of lineage-committed cells toward pluripotency may have a great potential in regenerative medicine. Reversine has been shown to induce dedifferentiation of multiple terminally differentiated mesodermal origin cells, which are capable of being directed to differentiate into other cell types within mesodermal lineages. However, the possibilities of these cells to give rise to other lineages have not been examined. Here we show that large scale gene expression profiling of reversine-treated C2C12 myoblasts identifies a subset of up-regulated genes involved in specification of neuroectodermal as well as mesodermal lineages. Reversine treatment leads to up-regulation of priming genes of neuroectodermal lineages, such as Ngn2, Nts, Irx3, Pax7, Hes1, and Hes6, through active histone modifications in the promoter regions of these genes. Additionally, reversine increases the expression of markers for other cell types of mesodermal lineages, Ogn and apoE, via inducing active histone modifications, while down-regulating the myogenic basic helix-loop-helix factor, MyoD, via repressive histone modifications. Consistent with up-regulation of these genes, reversine-treated C2C12 myoblasts redifferentiate into neural as well as mesodermal lineages, under appropriate stimuli. Taken together, these results indicate that reversine induces a multipotency of C2C12 myoblasts via inducing a specific combination of active histone modifications. Collectively, our findings provide a mechanistic rationale for the application of reversine to dedifferentiation of somatic cells.

Pilomotor seizures in frontal lobe epilepsy: case report

We report a 27-year-old man with pilomotor seizures originating in the right frontal lobe. Subtracted ictal SPECT coregistered with MRI showed multifocal hyperperfused areas in the anterior medial frontal area, mainly involving the cingulate gyrus. Chronic electrocorticography with subdural electrode arrays during the piloerection demonstrated that the pilomotor seizures were originating in the anterior medial frontal region. After resection of the focus, the patient became seizure free.

Decreased expression of glutaredoxin 1 is required for transforming growth factor-β1-mediated epithelial–mesenchymal transition of EpRas mammary epithelial cells

Transforming growth factor-beta (TGF-beta) is a cytokine important in inducing epithelial-mesenchymal transition (EMT), a crucial morphological event in a wide range of physiological and pathological cellular processes. In this study, we demonstrate that TGF-beta1 induces the EMT phenotype through decreasing the expression of the glutaredoxin 1 (Grx1) gene, an anti-oxidant enzyme, in H-Ras transformed EpH4 mammary epithelial cells (EpRas), but not in the parental EpH4 cells. TGF-beta1-induced reduction of Grx1 expression caused an increase of intracellular reactive oxygen species (ROS) in EpRas cells, and pre-treatment of the ROS scavenger N-acetylcysteine (NAC) inhibited TGF-beta1-induced EMT. Grx1-overexpressing EpRas cells showed a reduction in intracellular ROS generation and suppressed the expression of mesenchymal markers upon treatment of TGF-beta1. In addition, MEK/MAP kinase and phosphatidylinositol-3 kinase (PI3K) signaling were found to mediate the decrease in Grx1 expression upon TGF-beta1 treatment, depending on the presence of Ras protein. Thus our findings strongly suggest that TGF-beta1 promotes EMT by increasing intracellular ROS levels via down-regulation of the Grx1 gene in EpRas cells.

Involvement of cdc2-mediated phosphorylation in the cell cycle-dependent regulation of p185(neu)

We previously reported cell cycle-dependent negative regulation of p185neu (decreased tyrosine phosphorylation and kinase activity, with electrophoretic mobility retarded by serine/threonine phosphorylation) in M phase and the escape of mutation-activated p185neu* from this regulation. Our present results showed that retardation of electrophoretic mobility occurs independently of the cells transformed status. We found that normal p185neu lost its ability to dimerize in the M phase. We demonstrated a physical association between cdc2 (a serine/threonine kinase, active in M phase) and p185neu. We showed that the carboxy terminal portion of p185neu is phosphorylated in vitro by cdc2. Many phosphopeptides (at least three phosphoserine residues) unique to the M phase were identified, and the in vivo and in vitro phosphopeptide patterns were superimposable. In contrast, mutation-activated p185neu* dimerized in the M phase with no changes in electrophoretic mobility, failed to associate with cdc2 and no unique phosphoserine residues could be identified in the M phase (data not shown), consistent with the escape of p185neu* from cell cycle-dependent regulation. Our results suggest that this escape is an intrinsic property of the mutation-activated p185neu* independent of its ability to transform cells. Our results also suggest the involvement of serine/threonine kinases such as cdc2 in the cell cycle-dependent negative regulation of p185neu.

Decreasing Incidence of Chronic Lung Disease Despite the Gradual Reduction of Postnatal Dexamethasone Use in Very Low Birth Weight Infants

Dexamethasone has been widely used in very low birth weight infants (VLBWI) weighing less than 1,500 g at birth for the prevention or treatment of chronic lung disease (CLD). Recently, however the use of dexamethasone is being reduced, as its association with abnormal neurodevelopmental outcome is known. On the other hand, there have been persistent concerns about the increased risk of CLD according to the reduction of postnatal dexamethasone use. Hence, we did a retrospective cohort study to delineate the change in the incidence of CLD according to the reduction of dexamethasone use in VLBWI. The medical records of 559 VLBWI admitted to neonatal intensive care unit at Samsung Medical Center between November 1994 and December 2002 were reviewed with a focus on the use of postnatal dexamethasone and the incidence of CLD. The use of postnatal dexamethasone has significantly decreased over the study period. Especially, the use of high-dose regimen has markedly decreased. The day when postnatal dexamethasone therapy was begun has also been significantly delayed. The incidence of CLD has significantly decreased over the same period. In conclusion, the incidence of CLD has not increased despite the decreased use of postnatal dexamethasone.

Nuclear factor-κB2 represses Sp1-mediated transcription at the CD99 promoter

Downregulation of the CD99 antigen on the surface of Hodgkin’s lymphoma (HL) cells via EBV LMP1-mediated NF-κB suppression of Sp1 transcriptional activity is known to be associated with the appearance of pathogenic Reed-Sternberg cells. Here, we show that in addition, EBV LMP1 heterologous NF-κB activators such as CD30 and CD40 repress the CD99 promoter, which contains multiple Sp1-binding sites but no NF-κB binding sites. In addition, NF-κB-inducing kinase (NIK) repressed the CD99 promoter while NIK kinase mutants and JNK inhibitory protein failed to do so. Of the NF-κB subunits, NF-κB2 (p52) alone or in combination with other Rel subunits consistently inhibited the CD99, while NF-κB1 (p50) showed a marginal repressive effect. Furthermore, while transfection of LMP1 repressed the CD99 promoter in wild-type or NF-κB1 deficient MEFs, the same repression was not observed in NF-κB2 (p52)-deficient MEFs, indicating that NF-κB2 (p52) is required for LMP1-mediated repression of the CD99 promoter. Consistently, basal activity of the CD99 promoter was significantly higher in IKKα−/− and IKKβ−/− MEFs, but not in IKKΓ−/− MEFs compared to the wild-type control MEFs. Sp1-binding sites were directly used in the repression, because a synthetic Sp1 reporter with 10 Sp1-binding sites from the CD99 promoter was repressed by LMP1 or p52 transfection. These data indicate that LMP1-mediated NF-κB2 exhibits the major inhibitory role in the transcription at the CD99 promoter.