• BMB Reports
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• v.50 no.6
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• pp.281-282
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• 2017

Advances in the understanding of the Hippo signaling as a key regulatory pathway of proliferation and apoptosis have provided mechanical insights for controlling organ size and tumorigenicity. Recently, much attention has been directed to the regulation of LATS1/2 (large tumor suppressor) kinases that phosphorylate YAP/TAZ, a transcriptional co-activator in the Hippo pathway, and control the level and nuclear localization of YAP/TAZ. In our recent work, we showed that deubiquitinase YOD1 stabilizes ITCH, and facilitates ITCH-mediated LATS1/2 ubiquitination and degradation, resulting in increased YAP/TAZ level. Furthermore, we found that the YOD1-ITCH-LATS1/2-YAP/TAZ signaling axis is controlled by the differential expression of miR-21 in a cell-density-dependent manner. Using a transgenic mouse model, we showed that the inducible expression of YOD1 enhances the proliferation of hepatocytes and leads to hepatomegaly in a YAP/TAZ-activity-dependent manner. Moreover, a strong correlation was observed between YOD1 and YAP expression in liver cancer patients. Overall, our data suggest that YOD1 is a novel regulator of the Hippo pathway, and thereby a potential therapeutic target for liver cancer.

• BMB Reports
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• v.57 no.5
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• pp.250-255
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• 2024

Due to their stem-like characteristics and immunosuppressive properties, Mesenchymal stem cells (MSCs) offer remarkable potential in regenerative medicine. Much effort has been devoted to enhancing the efficacy of MSC therapy by enhancing MSC migration. In this study, we identified deubiquitinase BRCA1-associated protein 1 (BAP1) as an inhibitor of MSC migration. Using deubiquitinase siRNA library screening based on an in vitro wound healing assay, we found that silencing BAP1 significantly augmented MSC migration. Conversely, BAP1 overexpression reduced the migration and invasion capabilities of MSCs. BAP1 depletion in MSCs upregulates ERK phosphorylation, thereby increasing the expression of the migration factor, osteopontin. Further examination revealed that BAP1 interacts with phosphorylated ERK1/2, deubiquitinating their ubiquitins, and thus attenuating the ERK signaling pathway. Overall, our study highlights the critical role of BAP1 in regulating MSC migration through its deubiquitinase activity, and suggests a novel approach to improve the therapeutic potential of MSCs in regenerative medicine.

• 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.

• BMB Reports
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• v.52 no.2
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• pp.119-126
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• 2019

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) initiates the extrinsic apoptotic pathway through formation of the death-inducing signaling complex (DISC), followed by activation of effector caspases. TRAIL receptors are composed of death receptors (DR4 and DR5), decoy receptors (DcR1 and DcR2), and osteoprotegerin. Among them, only DRs activate apoptotic signaling by TRAIL. Since the levels of DR expressions are higher in cancer cells than in normal cells, TRAIL selectively activates apoptotic signaling pathway in cancer cells. However, multiple mechanisms, including down-regulation of DR expression and pro-apoptotic proteins, and up-regulation of anti-apoptotic proteins, make cancer cells TRAIL-resistant. Therefore, many researchers have investigated strategies to overcome TRAIL resistance. In this review, we focus on protein regulation in relation to extrinsic apoptotic signaling pathways via ubiquitination. The ubiquitin proteasome system (UPS) is an important process in control of protein degradation and stabilization, and regulates proliferation and apoptosis in cancer cells. The level of ubiquitination of proteins is determined by the balance of E3 ubiquitin ligases and deubiquitinases (DUBs), which determine protein stability. Regulation of the UPS may be an attractive target for enhancement of TRAIL-induced apoptosis. Our review provides insight to increasing sensitivity to TRAIL-mediated apoptosis through control of post-translational protein expression.

• Molecules and Cells
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• v.44 no.2
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• pp.101-115
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• 2021

The INO80 chromatin remodeling complex has roles in many essential cellular processes, including DNA replication. However, the mechanisms that regulate INO80 in these processes remain largely unknown. We previously reported that the stability of Ino80, the catalytic ATPase subunit of INO80, is regulated by the ubiquitin proteasome system and that BRCA1-associated protein-1 (BAP1), a nuclear deubiquitinase with tumor suppressor activity, stabilizes Ino80 via deubiquitination and promotes replication fork progression. However, the E3 ubiquitin ligase that targets Ino80 for proteasomal degradation was unknown. Here, we identified the C-terminus of Hsp70-interacting protein (CHIP), the E3 ubiquitin ligase that functions in cooperation with Hsp70, as an Ino80-interacting protein. CHIP polyubiquitinates Ino80 in a manner dependent on Hsp70. Contrary to our expectation that CHIP degrades Ino80, CHIP instead stabilizes Ino80 by extending its half-life. The data suggest that CHIP stabilizes Ino80 by inhibiting degradative ubiquitination. We also show that CHIP works together with BAP1 to enhance the stabilization of Ino80, leading to its chromatin binding. Interestingly, both depletion and overexpression of CHIP compromise replication fork progression with little effect on fork stalling, as similarly observed for BAP1 and Ino80, indicating that an optimal cellular level of Ino80 is important for replication fork speed but not for replication stress suppression. This work therefore idenitifes CHIP as an E3 ubiquitin ligase that stabilizes Ino80 via nondegradative ubiquitination and suggests that CHIP and BAP1 act in concert to regulate Ino80 ubiquitination to fine-tune its stability for efficient DNA replication.

• Molecules and Cells
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• v.46 no.8
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• pp.476-485
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• 2023

Gastric cancer stem-like cells (GCSCs) possess stem cell properties, such as self-renewal and tumorigenicity, which are known to induce high chemoresistance and metastasis. These characteristics of GCSCs are further enhanced by autophagy, worsening the prognosis of patients. Currently, the mechanisms involved in the induction of stemness in GCSCs during autophagy remain unclear. In this study, we compared the cellular responses of GCSCs with those of gastric cancer intestinal cells (GCICs) whose stemness is not induced by autophagy. In response to glucose starvation, the levels of β-catenin and stemness-related genes were upregulated in GCSCs, while the levels of β-catenin declined in GCICs. The pattern of deubiquitinase ubiquitin C-terminal hydrolase-L3 (UCH-L3) expression in GCSCs and GCICs was similar to that of β-catenin expression depending on glucose deprivation. We also observed that inhibition of UCH-L3 activity reduced β-catenin protein levels. The interaction between UCH-L3 and β-catenin proteins was confirmed, and it reduced the ubiquitination of β-catenin. Our results suggest that UCH-L3 induces the stabilization of β-catenin, which is required to promote stemness during autophagy activation. Also, UCH-L3 expression was regulated by c-Fos, and the levels of c-Fos increased in response to autophagy activation. In summary, our findings suggest that the inhibition of UCH-L3 during nutrient deprivation could suppress stress resistance of GCSCs and increase the survival rates of gastric cancer patients.

• Journal of Life Science
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• v.30 no.5
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• pp.483-490
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• 2020

The ubiquitin system uses ligases and deubiquitinases (DUBs) to regulate ubiquitin position on protein substrates and is involved in many biological processes which determine stability, activity, and interaction of the target substrate. DUBs are classified in six groups according to catalytic domain, namely ubiquitin-specific proteases (USPs); ubiquitin C-terminal hydrolases (UCHs); ovarian tumor proteases (OTUs); Machado Joseph Disease proteases (MJDs); motif interacting with Ub (MIU)-containing novel DUB family (MINDY); and Jab1/MPN/MOV34 metalloenzymes (JAMMs). Otubain 1 (OTUB1) is a DUB in the OTU family which possesses both canonical and non-canonical activity and can regulate multiple cellular signaling pathways. In this review, we describe the function of OTUB1 through regulation of its canonical and non-canonical activities in multiple specifically cancer-associated pathways. The canonical activity of OTUB1 inhibits protein ubiquitination by cleaving Lys48 linkages while its non-canonical activity prevents ubiquitin transfer onto target proteins through binding to E2-conjugating enzymes, resulting in the induction of protein deubiquitination. OTUB1 can therefore canonically and non-canonically promote tumor cell proliferation, invasion, and drug resistance through regulating FOXM1, ERα, KRAS, p53, and mTORC1. Moreover, clinical research has demonstrated that OTUB1 overexpresses with high metastasis in many tumor types including breast, ovarian, esophageal squamous, and glioma. Therefore, OTUB1 has been suggested as a diagnosis marker and potential therapeutic target for oncotherapy.