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Lim, So-Hee,Kwon, Seok-Kyu,Lee, Myung Kyu,Moon, Jeonghee,Jeong, Dae Gwin,Park, Eunha,Kim, Seung Jun,Park, Byung Chul,Lee, Sang Chul,Ryu, Seong-Eon,Yu, Dae-Yeul,Chung, Bong Hyun,Kim, Eunjoon,Myung, Pyu Published for the European Molecular Biology Organ 2009 The EMBO journal Vol.28 No.22
<P>The receptor-type protein tyrosine phosphatases (RPTPs) have been linked to signal transduction, cell adhesion, and neurite extension. PTPRT/RPTPrho is exclusively expressed in the central nervous system and regulates synapse formation by interacting with cell adhesion molecules and Fyn protein tyrosine kinase. Overexpression of PTPRT in cultured neurons increased the number of excitatory and inhibitory synapses by recruiting neuroligins that interact with PTPRT through their ecto-domains. In contrast, knockdown of PTPRT inhibited synapse formation and withered dendrites. Incubation of cultured neurons with recombinant proteins containing the extracellular region of PTPRT reduced the number of synapses by inhibiting the interaction between ecto-domains. Synapse formation by PTPRT was inhibited by phosphorylation of tyrosine 912 within the membrane-proximal catalytic domain of PTPRT by Fyn. This tyrosine phosphorylation reduced phosphatase activity of PTPRT and reinforced homophilic interactions of PTPRT, thereby preventing the heterophilic interaction between PTPRT and neuroligins. These results suggest that brain-specific PTPRT regulates synapse formation through interaction with cell adhesion molecules, and this function and the phosphatase activity are attenuated through tyrosine phosphorylation by the synaptic tyrosine kinase Fyn.</P>
Anti-inflammatory lipid mediator 15d-PGJ2 inhibits translation through inactivation of eIF4A
Kim, Woo Jae,Kim, Joon Hyun,Jang, Sung Key Published for the European Molecular Biology Organ 2007 The EMBO journal Vol.26 No.24
<P>The signaling lipid molecule 15-deoxy-delta 12,14-prostaglandin J2 (15d-PGJ2) has multiple cellular functions, including anti-inflammatory and antineoplastic activities. Here, we report that 15d-PGJ2 blocks translation through inactivation of translational initiation factor eIF4A. Binding of 15d-PGJ2 to eIF4A blocks the interaction between eIF4A and eIF4G that is essential for translation of many mRNAs. Cysteine 264 in eIF4A is the target site of 15d-PGJ2. The antineoplastic activity of 15d-PGJ2 is likely attributed to inhibition of translation. Moreover, inhibition of translation by 15d-PGJ2 results in stress granule (SG) formation, into which TRAF2 is sequestered. The sequestration of TRAF2 contributes to the anti-inflammatory activity of 15d-PGJ2. These findings reveal a novel cross-talk between translation and inflammatory response, and offer new approaches to develop anticancer and anti-inflammatory drugs that target translation factors including eIF4A.</P>
Solution single-vesicle assay reveals PIP2-mediated sequential actions of synaptotagmin-1 on SNAREs.
Kim, Jae-Yeol,Choi, Bong-Kyu,Choi, Mal-Gi,Kim, Sun-Ae,Lai, Ying,Shin, Yeon-Kyun,Lee, Nam Ki Published for the European Molecular Biology Organ 2012 The EMBO journal Vol.31 No.9
<P>Synaptotagmin-1 (Syt1) is a major Ca(2+) sensor for synchronous neurotransmitter release, which requires vesicle fusion mediated by SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors). Syt1 utilizes its diverse interactions with target membrane (t-) SNARE, SNAREpin, and phospholipids, to regulate vesicle fusion. To dissect the functions of Syt1, we apply a single-molecule technique, alternating-laser excitation (ALEX), which is capable of sorting out subpopulations of fusion intermediates and measuring their kinetics in solution. The results show that Syt1 undergoes at least three distinct steps prior to lipid mixing. First, without Ca(2+), Syt1 mediates vesicle docking by directly binding to t-SNARE/phosphatidylinositol 4,5-biphosphate (PIP(2)) complex and increases the docking rate by 10(3) times. Second, synaptobrevin-2 binding to t-SNARE displaces Syt1 from SNAREpin. Third, with Ca(2+), Syt1 rebinds to SNAREpin, which again requires PIP(2). Thus without Ca(2+), Syt1 may bring vesicles to the plasma membrane in proximity via binding to t-SNARE/PIP(2) to help SNAREpin formation and then, upon Ca(2+) influx, it may rebind to SNAREpin, which may trigger synchronous fusion. The results show that ALEX is a powerful method to dissect multiple kinetic steps in the vesicle fusion pathway.</P>
Crystal structures of the structure-selective nuclease Mus81-Eme1 bound to flap DNA substrates.
Gwon, Gwang Hyeon,Jo, Aera,Baek, Kyuwon,Jin, Kyeong Sik,Fu, Yaoyao,Lee, Jong-Bong,Kim, Youngchang,Cho, Yunje Published for the European Molecular Biology Organ 2014 The EMBO journal Vol.33 No.9
<P>The Mus81-Eme1 complex is a structure-selective endonuclease with a critical role in the resolution of recombination intermediates during DNA repair after interstrand cross-links, replication fork collapse, or double-strand breaks. To explain the molecular basis of 3' flap substrate recognition and cleavage mechanism by Mus81-Eme1, we determined crystal structures of human Mus81-Eme1 bound to various flap DNA substrates. Mus81-Eme1 undergoes gross substrate-induced conformational changes that reveal two key features: (i) a hydrophobic wedge of Mus81 that separates pre- and post-nick duplex DNA and (ii) a '5' end binding pocket' that hosts the 5' nicked end of post-nick DNA. These features are crucial for comprehensive protein-DNA interaction, sharp bending of the 3' flap DNA substrate, and incision strand placement at the active site. While Mus81-Eme1 unexpectedly shares several common features with members of the 5' flap nuclease family, the combined structural, biochemical, and biophysical analyses explain why Mus81-Eme1 preferentially cleaves 3' flap DNA substrates with 5' nicked ends.</P>
TopBP1 deficiency impairs V(D)J recombination during lymphocyte development.
Kim, Jieun,Lee, Sung Kyu,Jeon, Yoon,Kim, Yehyun,Lee, Changjin,Jeon, Sung Ho,Shim, Jaegal,Kim, In-Hoo,Hong, Seokmann,Kim, Nayoung,Lee, Ho,Seong, Rho Hyun Published for the European Molecular Biology Organ 2014 The EMBO journal Vol.33 No.3
<P>TopBP1 was initially identified as a topoisomerase II-β-binding protein and it plays roles in DNA replication and repair. We found that TopBP1 is expressed at high levels in lymphoid tissues and is essential for early lymphocyte development. Specific abrogation of TopBP1 expression resulted in transitional blocks during early lymphocyte development. These defects were, in major part, due to aberrant V(D)J rearrangements in pro-B cells, double-negative and double-positive thymocytes. We also show that TopBP1 was located at sites of V(D)J rearrangement. In TopBP1-deficient cells, γ-H2AX foci were found to be increased. In addition, greater amount of γ-H2AX product was precipitated from the regions where TopBP1 was localized than from controls, indicating that TopBP1 deficiency results in inefficient DNA double-strand break repair. The developmental defects were rescued by introducing functional TCR αβ transgenes. Our data demonstrate a novel role for TopBP1 as a crucial factor in V(D)J rearrangement during the development of B, T and iNKT cells.</P>
Mitochondrial chaperone HSP ‐60 regulates anti‐bacterial immunity via p38 MAP kinase signaling
Jeong, Dae‐,Eun,Lee, Dongyeop,Hwang, Sun‐,Young,Lee, Yujin,Lee, Jee‐,Eun,Seo, Mihwa,Hwang, Wooseon,Seo, Keunhee,Hwang, Ara B,Artan, Murat,Son, Heehwa G,Jo, Jay‐,Hyun,Baek, Haes Published for the European Molecular Biology Organ 2017 The EMBO journal Vol.36 No.8
<P>Mitochondria play key roles in cellular immunity. How mitochondria contribute to organismal immunity remains poorly understood. Here, we show that HSP-60/HSPD1, a major mitochondrial chaperone, boosts anti-bacterial immunity through the up-regulation of p38 MAP kinase signaling. We first identify 16 evolutionarily conserved mitochondrial components that affect the immunity of Caenorhabditis elegans against pathogenic Pseudomonas aeruginosa (PA14). Among them, the mitochondrial chaperone HSP-60 is necessary and sufficient to increase resistance to PA14. We show that HSP-60 in the intestine and neurons is crucial for the resistance to PA14. We then find that p38 MAP kinase signaling, an evolutionarily conserved anti-bacterial immune pathway, is down-regulated by genetic inhibition of hsp-60, and up-regulated by increased expression of hsp-60. Overexpression of HSPD1, the mammalian ortholog of hsp-60, increases p38 MAP kinase activity in human cells, suggesting an evolutionarily conserved mechanism. Further, cytosol-localized HSP-60 physically binds and stabilizes SEK-1/MAP kinase kinase 3, which in turn up-regulates p38 MAP kinase and increases immunity. Our study suggests that mitochondrial chaperones protect host eukaryotes from pathogenic bacteria by up-regulating cytosolic p38 MAPK signaling.</P>
Differential regulation of p53 and p21 by MKRN1 E3 ligase controls cell cycle arrest and apoptosis.
Lee, Eun-Woo,Lee, Min-Sik,Camus, Suzanne,Ghim, Jaewang,Yang, Mi-Ran,Oh, Wonkyung,Ha, Nam-Chul,Lane, David P,Song, Jaewhan Published for the European Molecular Biology Organ 2009 The EMBO journal Vol.28 No.14
<P>Makorin Ring Finger Protein 1 (MKRN1) is a transcriptional co-regulator and an E3 ligase. Here, we show that MKRN1 simultaneously functions as a differentially negative regulator of p53 and p21. In normal conditions, MKRN1 could destabilize both p53 and p21 through ubiquitination and proteasome-dependent degradation. As a result, depletion of MKRN1 induced growth arrest through activation of p53 and p21. Interestingly, MKRN1 used earlier unknown sites, K291 and K292, for p53 ubiquitination and subsequent degradation. Under severe stress conditions, however, MKRN1 primarily induced the efficient degradation of p21. This regulatory process contributed to the acceleration of DNA damage-induced apoptosis by eliminating p21. MKRN1 depletion diminished adriamycin or ultraviolet-induced cell death, whereas ectopic expression of MKRN1 facilitated apoptosis. Furthermore, MKRN1 stable cell lines that constantly produced low levels of p53 and p21 exhibited stabilization of p53, but not p21, with increased cell death on DNA damage. Our results indicate that MKRN1 exhibits dual functions of keeping cells alive by suppressing p53 under normal conditions and stimulating cell death by repressing p21 under stress conditions.</P>
Synaptic removal of diacylglycerol by DGKzeta and PSD-95 regulates dendritic spine maintenance.
Kim, Karam,Yang, Jinhee,Zhong, Xiao-Ping,Kim, Myoung-Hwan,Kim, Yun Sook,Lee, Hyun Woo,Han, Seungnam,Choi, Jeonghoon,Han, Kihoon,Seo, Jinsoo,Prescott, Stephen M,Topham, Matthew K,Bae, Yong Chul,Koretzk Published for the European Molecular Biology Organ 2009 The EMBO journal Vol.28 No.8
<P>Diacylglycerol (DAG) is an important lipid signalling molecule that exerts an effect on various effector proteins including protein kinase C. A main mechanism for DAG removal is to convert it to phosphatidic acid (PA) by DAG kinases (DGKs). However, it is not well understood how DGKs are targeted to specific subcellular sites and tightly regulates DAG levels. The neuronal synapse is a prominent site of DAG production. Here, we show that DGKzeta is targeted to excitatory synapses through its direct interaction with the postsynaptic PDZ scaffold PSD-95. Overexpression of DGKzeta in cultured neurons increases the number of dendritic spines, which receive the majority of excitatory synaptic inputs, in a manner requiring its catalytic activity and PSD-95 binding. Conversely, DGKzeta knockdown reduces spine density. Mice deficient in DGKzeta expression show reduced spine density and excitatory synaptic transmission. Time-lapse imaging indicates that DGKzeta is required for spine maintenance but not formation. We propose that PSD-95 targets DGKzeta to synaptic DAG-producing receptors to tightly couple synaptic DAG production to its conversion to PA for the maintenance of spine density.</P>