• BMB Reports
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• v.51 no.6
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• pp.261-262
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• 2018

Aurora B is an important kinase involved in dynamic cellular events in mitosis. Aurora B activity is controlled by several post-translational modifications (PTMs). Among them, E3 ubiquitin ligase-mediated ubiquitination plays crucial roles in controlling the relocation and degradation of Aurora B. Aurora B, ubiquitinated by different E3 ligases, moves to the exact site for its mitotic function during metaphase-anaphase transition and is then degraded for cell cycle progression at the end of mitosis. However, how the stability of Aurora B is maintained until its degradation has been poorly understood. Recently, we have found that USP35 acts as a deubiquitinating enzyme (DUB) for Aurora B and affects its stability during cell division, thus being involved in the regulation of mitosis. In this review, we discuss the USP35-mediated deubiquitination of Aurora B and the regulation of mitotic progression by USP35.

• The Korean Journal of Mycology
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• v.41 no.1
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• pp.1-8
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• 2013

COP9 signalosome (CSN), which is originally identified as the regulator of the photomorphogenic development in plant, is highly conserved protein complex in diverse eukaryotic organisms. Most eukaryotic CSN complex is composed of 8 subunits, which is structurally and functionally similar to the lid subunit of 26S proteasome and eIF3 translation initiation complex. CSN play important functions in the regulation of cell cycle and checkpoint response by controlling Cullin-Ring E3 ubiquitin ligases (CRL) activities. CSN exhibits an isopeptidase activity which cleaves the neddylated moiety of cullin components. In fission yeast, S-phase cell cycle progression was delayed and the sensitivity to g-ray or UV was increased in CSN1 and CSN2 deletion mutants, indicating that yeast CSN is also involved in the checkpoint regulation. CSN in fungal system more closely resembles that of the higher organisms in the structure and assembly of their components. Functionally, CSN is associated with the regulation of conidiation rhythms in Neurospora crassa and the sexual development in Aspsergillus nidulans. Recent studies also revealed that CSN functions as an essential cell cycle regulator, playing key roles in the regulation of DNA replication and DNA damage response in Aspergillus. Overall, CSN of microorganisms, such as fission yeast and fungi, share functionally common aspects with higher organisms, implying that they can be useful tools to study the role of CSN in the CRL-mediated diverse cellular activities.

• Molecules and Cells
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• v.37 no.5
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• pp.389-398
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• 2014

Siah acts as an E3 ubiquitin ligase that binds proteins destined for degradation. Extensive homology between siah and Drosophila Siah homologue (sina) suggests their important physiological roles during embryonic development. However, detailed functional studies of Siah in vertebrate development have not been carried out. Here we report that Siah2 specifically augments nodal related gene expression in marginal blastomeres at late blastula through early gastrula stages of zebrafish embryos. Siah2 dependent Nodal signaling augmentation is confirmed by cell-based reporter gene assays using 293T cells and 3TP-luciferase reporter plasmid. We also established a molecular hierarchy of Siah as a upstream regulator of FoxH1/Fast1 transcriptional factor in Nodal signaling. Elevated expression of nodal related genes by overexpression of Siah2 was enough to override the inhibitory effects of atv and lft2 on the Nodal signaling. In particular, E3 ubiquitin ligase activity of Siah2 is critical to limit the duration and/or magnitude of Nodal signaling. Additionally, since the embryos injected with Siah morpholinos mimicked the atv overexpression phenotype at least in part, our data support a model in which Siah is involved in mesendoderm patterning via modulating Nodal signaling.

• Animal cells and systems
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• v.16 no.4
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• pp.280-288
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• 2012

Targeted degradation of proteins through ubiquitin-mediated proteolysis is an important control mechanism in various cellular processes. The process of ubiquitin conjugation is achieved by three enzyme complexes, among which the ubiquitin ligase complex (E3) is in charge of substrate specificity. The SCF (SKP1-CUL1-F-box) family portrays the largest and the most characterized member of the E3 ligases. For each SCF complex, the ubiquitination target is recognized by the F-box protein subunit, which interacts with the substrate through a unique C-terminal domain. We have characterized a novel F-box protein CFL-1 that represents a single LRR-type F-box (FBXL) in the Caenorhabditis elegans genome. CFL-1 is highly homologous to FBXL20 and FBXL2 of mammals, which are known to regulate synaptic vesicle release and cell cycle, respectively. A green fluorescence protein (GFP)-reporter gene fused to the cfl-1 promoter showed restricted expression around the amphid and the anus. Modulation of CFL-1 activity by RNAi affected the time interval between defecations. RNAi-treated worms also exhibited reduced tendency to form dauer when exposed to daumone. The potential involvement of CFL-1 in the control of defecation and pheromone response adds to the ever expanding list of cellular processes controlled by ubiquitin-mediated proteolysis in C. elegans. We suggest that CFL-1, as a single LRR-type F-box protein in C. elegans, may portray a prototype gene exerting diverse functions that are allocated among multiple FBXLs in higher organisms.

• Molecules and Cells
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• v.40 no.12
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• pp.897-905
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• 2017

Cellular protein homeostasis is maintained by two major degradation pathways, namely the ubiquitin-proteasome system (UPS) and autophagy. Until recently, the UPS and autophagy were considered to be largely independent systems targeting proteins for degradation in the proteasome and lysosome, respectively. However, the identification of crucial roles of molecular players such as ubiquitin and p62 in both of these pathways as well as the observation that blocking the UPS affects autophagy flux and vice versa has generated interest in studying crosstalk between these pathways. Here, we critically review the current understanding of how the UPS and autophagy execute coordinated protein degradation at the molecular level, and shed light on our recent findings indicating an important role of an autophagy-associated transmembrane protein EI24 as a bridging molecule between the UPS and autophagy that functions by regulating the degradation of several E3 ligases with Really Interesting New Gene (RING)-domains.

• Molecules and Cells
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• v.41 no.5
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• pp.381-389
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• 2018

ARF is a tumor suppressor protein that has a pivotal role in the prevention of cancer development through regulating cell proliferation, senescence, and apoptosis. As a factor that induces senescence, the role of ARF as a tumor suppressor is closely linked to the p53-MDM2 axis, which is a key process that restrains tumor formation. Thus, many cancer cells either lack a functional ARF or p53, which enables them to evade cell oncogenic stress-mediated cycle arrest, senescence, or apoptosis. In particular, the ARF gene is a frequent target of genetic and epigenetic alterations including promoter hyper-methylation or gene deletion. However, as many cancer cells still express ARF, pathways that negatively modulate transcriptional or post-translational regulation of ARF could be potentially important means for cancer cells to induce cellular proliferation. These recent findings of regulators affecting ARF protein stability along with its low levels in numerous human cancers indicate the significance of an ARF post-translational mechanism in cancers. Novel findings of regulators stimulating or suppressing ARF function would provide new therapeutic targets to manage cancer- and senescence-related diseases. In this review, we present the current knowledge on the regulation and alterations of ARF expression in human cancers, and indicate the importance of regulators of ARF as a prognostic marker and in potential therapeutic strategies.

• Molecules and Cells
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• v.43 no.2
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• pp.160-167
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• 2020

Runt-related transcription factor 2 (RUNX2) is a key transcription factor for bone formation and osteoblast differentiation. Various signaling pathways and mechanisms that regulate the expression and transcriptional activity of RUNX2 have been thoroughly investigated since the involvement of RUNX2 was first reported in bone formation. As the regulation of Runx2 expression by extracellular signals has recently been reviewed, this review focuses on the regulation of post-translational RUNX2 activity. Transcriptional activity of RUNX2 is regulated at the post-translational level by various enzymes including kinases, acetyl transferases, deacetylases, ubiquitin E3 ligases, and prolyl isomerases. We describe a sequential and linear causality between post-translational modifications of RUNX2 by these enzymes. RUNX2 is one of the most important osteogenic transcription factors; however, it is not a suitable drug target. Here, we suggest enzymes that directly regulate the stability and/or transcriptional activity of RUNX2 at a post-translational level as effective drug targets for treating bone diseases.

• Journal of Life Science
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• v.33 no.6
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• pp.523-529
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• 2023

Ubiquitination is a post-translational modification that is involved in the quality control of proteins and responsible for modulating a variety of cellular physiological processes. Protein ubiquitination and deubiquitination are reversible processes that regulate the stability of target substrates. The ubiquitin proteasome system (UPS) helps regulate tumor-promoting processes, such as DNA repair, cell cycle, apoptosis, metastasis, and angiogenesis. The UPS comprises a combination of ubiquitin, ubiquitin-activating enzymes (E1), ubiquitin-conjugating enzymes (E2), and ubiquitin-ligase enzymes (E3), which complete the degradation of target proteins. Ubiquitin-conjugating enzymes (UBE2s) play an inter-mediate role in the UPS process by moving activated ubiquitin to target proteins through E3 ligases. UBE2s consist of 40 members and are classified according to conserved catalytic ubiquitin-conjugating (UBC) domain-flanking extensions in humans. Since UBE2s have specificity to substrates like E3 ligase, the significance of UBE2 has been accentuated in tumorigenesis. The dysregulation of multiple E2 enzymes and their critical roles in modulating oncogenic signaling pathways have been reported in several types of cancer. The elevation of UBE2 expression is correlated with a worse prognosis in cancer patients. In this review, we summarize the basic functions and regulatory mechanisms of UBE2s and suggest the possibility of their use as therapeutic targets for cancer.

• Journal of Life Science
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• v.26 no.3
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• pp.364-375
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• 2016

Post-translational modification is an efficient process to rapidly transduce external stimulus into cellular response. Ubiquitination is a typical post-translational modification which is a highly conserved process in eukaryotes. UPS (Ubiquitin/Proteasome System) mediated by the ubiquitination is to target diverse cellular proteins for degradation. Among E3 ubiquitin ligases that function as the key determinant for substrate recognition, CRL (cullin–RING E3 ubiquitin ligase) is the largest family and forms the complex composed of cullin, RBX1, adaptor and substrate receptor. Although CRL1, also known as SCF complex, has been widely researched for its biological role, the functional studies of CRL4 have been relatively elusive. In Arabidopsis, there are 119 substrate receptors named DCAF (DDB1 CUL4 Associated Factor) proteins for CRL4 and a fraction of DCAF proteins have been identified for their potential functions so far. In this paper, current understanding on structure and biological roles of plant CRL4 complexes in a diverse of cellular events is reviewed, especially focusing on CRL4 substrate receptors. Moreover, the regulatory mechanism of CRL4’s activity is also introduced. These studies will be helpful to further understand the signal transduction pathways in which such CRL4 complexes are involved and give a clue to establish the action network of entire CRL4 complexes in plants.

• IMMUNE NETWORK
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• v.9 no.6
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• pp.248-254
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• 2009

[ $TGF-{\beta}1$ ]is well known to induce Ig germ-line ${\alpha}$ ($GL{\alpha}$) transcription and subsequent IgA isotype class switching recombination (CSR). Homeodomain protein TG-interacting factor (TGIF) and E3-ubiquitin ligases TGIF interacting ubiquitin ligase 1 (Tiul1) are implicated in the negative regulation of $TGF-{\beta}$ signaling. In the present study, we investigated the roles of Tiul1 and TGIF in $TGF{\beta}1$-induced IgA CSR. We found that over-expression of Tiul1 decreased $TGF{\beta}1$-induced $GL{\alpha}$ promoter activity and strengthened the inhibitory effect of Smad7 on the promoter activity. Likewise, overexpression of TGIF also diminished $GL{\alpha}$ promoter activity and further strengthened the inhibitory effect of Tiul1, suggesting that Tiul1 and TGIF can down-regulate $TGF{\beta}1$-induced $GL{\alpha}$ expression. In parallel, overexpression of Tiul1 decreased the expression of endogenous IgA CSR-predicitive transcripts ($GLT_{\alpha},\;PST_{\alpha},\;and\;CT_{\alpha}$) and $TGF{\beta}1$-induced IgA secretion, but not $GLT_{\gamma3}$ and IgG3 secretion. Here, over-expressed TGIF further strengthened the inhibitory effect of Tiul1. These results suggest that Tiul1 and TGIF act as negatively regulators in $TGF{\beta}1$-induced IgA isotype expression.