Showing papers by "Sung Hee Baek published in 2017"

RORα controls hepatic lipid homeostasis via negative regulation of PPARγ transcriptional network

Abstract: The retinoic acid receptor-related orphan receptor-α (RORα) is an important regulator of various biological processes, including cerebellum development, circadian rhythm and cancer. Here, we show that hepatic RORα controls lipid homeostasis by negatively regulating transcriptional activity of peroxisome proliferators-activated receptor-γ (PPARγ) that mediates hepatic lipid metabolism. Liver-specific Rorα-deficient mice develop hepatic steatosis, obesity and insulin resistance when challenged with a high-fat diet (HFD). Global transcriptome analysis reveals that liver-specific deletion of Rorα leads to the dysregulation of PPARγ signaling and increases hepatic glucose and lipid metabolism. RORα specifically binds and recruits histone deacetylase 3 (HDAC3) to PPARγ target promoters for the transcriptional repression of PPARγ. PPARγ antagonism restores metabolic homeostasis in HFD-fed liver-specific Rorα deficient mice. Our data indicate that RORα has a pivotal role in the regulation of hepatic lipid homeostasis. Therapeutic strategies designed to modulate RORα activity may be beneficial for the treatment of metabolic disorders. Hepatic steatosis development may result from dysregulation of lipid metabolism, which is finely tuned by several transcription factors including the PPAR family. Here Kim et al. show that the nuclear receptor RORα inhibits PPARγ-mediated transcriptional activity by interacting with HDAC3 and competing for the promoters of lipogenic genes.

Sumoylation and Its Contribution to Cancer

Abstract: Post-translational modifications play an important role in regulating protein activity by altering their functions. Sumoylation is a highly dynamic process which is tightly regulated by a fine balance between conjugating and deconjugating enzyme activities. It affects intracellular localization and their interaction with their binding partners, thereby changing gene expression. Consequently, these changes in turn affect signaling mechanisms that regulate many cellular functions, such as cell growth, proliferation, apoptosis, DNA repair, and cell survival. It is becoming apparent that deregulation in the SUMO pathway contributes to oncogenic transformation by affecting sumoylation/desumoylation of many oncoproteins and tumor suppressors. Loss of balance between sumoylation and desumoylation has been reported in a number of studies in a variety of disease types including cancer. This chapter summarizes the mechanisms and functions of the deregulated SUMO pathway affecting oncogenes and tumor suppressor genes.

PKCα-mediated phosphorylation of LSD1 is required for presynaptic plasticity and hippocampal learning and memory.

Abstract: Lysine-specific demethylase 1 (LSD1) is a histone demethylase that participates in transcriptional repression or activation. Recent studies reported that LSD1 is involved in learning and memory. Although LSD1 phosphorylation by PKCα was implicated in circadian rhythmicity, the importance of LSD1 phosphorylation in learning and memory is unknown. In this study, we examined the roles of LSD1 in synaptic plasticity and memory using Lsd1 SA/SA knock-in (KI) mice, in which a PKCα phosphorylation site is mutated. Interestingly, short-term and long-term contextual fear memory as well as spatial memory were impaired in Lsd1 KI mice. In addition, short-term synaptic plasticity, such as paired pulse ratio and post-tetanic potentiation was impaired, whereas long-term synaptic plasticity, including long-term potentiation and long-term depression, was normal. Moreover, the frequency of miniature excitatory postsynaptic current was significantly increased, suggesting presynaptic dysfunction in Lsd1 KI mice. Consistent with this, RNA-seq analysis using the hippocampus of Lsd1 KI mice showed significant alterations in the expressions of presynaptic function-related genes. Intriguingly, LSD1n-SA mutant showed diminished binding to histone deacetylase 1 (HDAC1) compared to LSD1n-WT in SH-SY5Y cells. These results suggest that LSD1 is involved in the regulation of presynaptic gene expression and subsequently regulates the hippocampus-dependent memory in phosphorylation-dependent manner.

RORα2 requires LSD1 to enhance tumor progression in breast cancer.

Abstract: Retinoic acid-related orphan receptor α (RORα) regulates diverse physiological processes, including inflammatory responses, lipid metabolism, circadian rhythm, and cancer biology. RORα has four different isoforms which have distinct N-terminal domains but share identical DNA binding domain and ligand binding domain in human. However, lack of specific antibody against each RORα isoform makes biochemical studies on each RORα isoform remain unclear. Here, we generate RORα2-specific antibody and characterize the role of RORα2 in promoting tumor progression in breast cancer. RORα2 requires lysine specific demethylase 1 (LSD1/KDM1A) as a coactivator for transcriptional activation of RORα2 target genes, exemplified by CTNND1. Intriguingly, RORα2 and LSD1 protein levels are dramatically elevated in human breast cancer specimens compared to normal counterparts. Taken together, our studies indicate that LSD1-mediated RORα2 transcriptional activity is important to promote tumor cell migration in human breast cancer as well as breast cancer cell lines. Therefore, our data establish that suppression of LSD1-mediated RORα2 transcriptional activity may be potent therapeutic strategy to attenuate tumor cell migration in human breast cancer.

Abstract 917: CD82/KAI1 maintains the dormancy of long-term hematopoietic stem cells through interaction with DARC-expressing macrophages

Abstract: Hematopoiesis is regulated by crosstalk between long-term repopulating hematopoietic stem cells (LT-HSCs) and supporting niche cells in the bone marrow (BM). Here, we examine the role of CD82/KAI1 (CD82 hereafter) in niche-mediated LT-HSC maintenance. We found that CD82 is expressed predominantly on LT-HSCs and rarely on other hematopoietic stem-progenitor cells (HSPCs). In Cd82 -/- mice, LT-HSCs were selectively lost as they exited from quiescence and differentiated. Mechanistically, CD82-based TGF-b1/Smad3 signaling leads to induction of CDK inhibitors and cell-cycle inhibition. The CD82 binding partner DARC/CD234 is expressed on macrophages and stabilizes CD82 on LT-HSCs, promoting their quiescence. When DARC + BM macrophages were ablated, the level of surface CD82 on LT-HSCs decreased, leading to cell-cycle entry, proliferation, and differentiation. A similar interaction appears to be relevant for human HSPCs. Thus, CD82 is a functional surface marker of LT-HSCs that maintains quiescence through interaction with DARC-expressing macrophages in the BM stem cell niche. Finally, we hope that further development of our study will allow us to improve leukemia treatment by awakening not only “good” stem cells to keep beneficial stem cell functions, but also “bad” stem cells (e.g. cancer stem cells) in order to increase the sensitivity to treatment and avoid relapse. Citation Format: Jae-Il Choi, Jin Hur, Hwan Lee, Pniel Nham, Cheong-Whan Chae, Young-Eun Choi, Taewan Kim, Ga-Young Lee, Sung Hee Baek, Hyo-Soo Kim. CD82/KAI1 maintains the dormancy of long-term hematopoietic stem cells through interaction with DARC-expressing macrophages [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 917. doi:10.1158/1538-7445.AM2017-917

Method for screening angiogenesis inhibitor targeting methylation of hif-1α

Abstract: Disclosed in the present application is a method for screening an angiogenesis inhibitor targeting the interaction of HIF1-α protein with SET7/9 methyltransferase or LSD1 demethylase A substance screened by the method according to the present application can be usefully developed into therapeutic agents, such as an anticancer drug, etc, for retinopathy or various diseases requiring the inhibition of angiogenesis

Shedding light on the DARC knight as a guardian of hematopoietic stem cell quiescence

Abstract: In-depth understanding of the crosstalk between hematopoietic stem cells (HSCs) and their niche, and identification of ‘functional’ surface markers of HSCs are vital in the advancement of therapies for hematological disorders (e.g., ex vivo expansion or transplantation of HSCs). MacNamara (1) and Perez-Fernandez et al . (2) respectively provided constructive comments on our results and made very interesting suggestions regarding clinical application of the CD82/DARC axis. In this Correspondence, we aim to add to the discussion (1,2) on our recent article (3).