• Reproductive and Developmental Biology
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• v.38 no.1
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• pp.41-52
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• 2014

Embryonic genome activation (EGA) is a highly complex phenomenon that is controlled at various levels. New studies have ascertained some molecular mechanisms that control EGA in several species; it is apparent that these same mechanisms regulate EGA in all species. Protein phosphorylation, DNA methylation and histone modification regulate transcriptional activities, and mechanisms such as ubiquitination, SUMOylation and microRNAs post-transcriptionally regulate development. Each of these regulations is highly dynamic in the early embryo. A better understanding of these regulatory strategies can provide the possibility to improve the reproductive properties in mammals such as pigs, to develop methods of generating high-quality embryos in vitro, and to find markers for selecting developmentally competent embryos.

• BMB Reports
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• v.48 no.9
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• pp.487-488
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• 2015

The ubiquitin-proteasome system and the autophagy lysosome system are the two major protein degradation machineries in eukaryotic cells. These two systems coordinate the removal of unwanted intracellular materials, but the mechanism by which they achieve this synchronization is largely unknown. The ubiquitination of substrates serves as a universal degradation signal for both systems. Our study revealed that the amino-terminal Arg, a canonical N-degron in the ubiquitin-proteasome system, also acts as a degradation signal in autophagy. We showed that many ER residents, such as BiP, contain evolutionally conserved arginylation permissive pro-N-degrons, and that certain inducers like dsDNA or proteasome inhibitors cause their translocation into the cytoplasm where they bind misfolded proteins and undergo amino-terminal arginylation by arginyl transferase 1 (ATE1). The amino-terminal Arg of BiP binds p62, which triggers p62 oligomerization and enhances p62-LC3 interaction, thereby stimulating autophagic delivery and degradation of misfolded proteins, promoting cell survival. This study reveals a novel ubiquitin-independent mechanism for the selective autophagy pathway, and provides an insight into how these two major protein degradation pathways communicate in cells to dispose the unwanted proteins. [BMB Reports 2015; 48(9): 487-488]

• Molecules and Cells
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• v.27 no.3
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• pp.359-363
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• 2009

Chfr, a checkpoint with FHA and RING finger domains, plays an important role in cell cycle progression and tumor suppression. Chfr possesses the E3 ubiquitin ligase activity and stimulates the formation of polyubiquitin chains by Ub-conjugating enzymes, and induces the proteasome-dependent degradation of a number of cellular proteins, including Plk1 and Aurora A. While Chfr is a nuclear protein that functions within the cell nucleus, how Chfr is localized in the nucleus has not been clearly demonstrated. Here, we show that nuclear localization of Chfr is mediated by nuclear localization signal (NLS) sequences. To reveal the signal sequences responsible for nuclear localization, a short lysine-rich stretch (KKK) at amino acid residues 257-259 was replaced with alanine, which completely abolished nuclear localization. Moreover, we show that nuclear localization of Chfr is essential for its checkpoint function but not for its stability. Thus, our results suggest that NLS-mediated nuclear localization of Chfr leads to its accumulation within the nucleus, which may be important in the regulation of Chfr activation and Chfr-mediated cellular processes, including cell cycle progression and tumor suppression.

• Molecules and Cells
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• v.39 no.8
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• pp.581-586
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• 2016

Post-translational modifications (PTMs) of proteins are essential to increase the functional diversity of the proteome. By adding chemical groups to proteins, or degrading entire proteins by phosphorylation, glycosylation, ubiquitination, neddylation, acetylation, lipidation, and proteolysis, the complexity of the proteome increases, and this then influences most biological processes. Although small RNAs are crucial regulatory elements for gene expression in most eukaryotes, PTMs of small RNA microprocessor and RNA silencing components have not been extensively investigated in plants. To date, several studies have shown that the proteolytic regulation of AGOs is important for host-pathogen interactions. DRB4 is regulated by the ubiquitin-proteasome system, and the degradation of HYL1 is modulated by a de-etiolation repressor, COP1, and an unknown cytoplasmic protease. Here, we discuss current findings on the PTMs of microprocessor and RNA silencing components in plants.

• Biomolecules & Therapeutics
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• v.26 no.1
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• pp.57-68
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• 2018

Nuclear factor E2-related factor 2 (NRF2) plays an important role in redox metabolism and antioxidant defense. Under normal conditions, NRF2 proteins are maintained at very low levels because of their ubiquitination and proteasomal degradation via binding to the kelch-like ECH associated protein 1 (KEAP1)-E3 ubiquitin ligase complex. However, oxidative and/or electrophilic stresses disrupt the KEAP1-NRF2 interaction, which leads to the accumulation and transactivation of NRF2. During recent decades, a growing body of evidence suggests that NRF2 is frequently activated in many types of cancer by multiple mechanisms, including the genetic mutations in the KEAP1-NRF2 pathway. This suggested that NRF2 inhibition is a promising strategy for cancer therapy. Recently, several NRF2 inhibitors have been reported with anti-tumor efficacy. Here, we review the mechanisms whereby NRF2 is dysregulated in cancer and its contribution to the tumor development and radiochemoresistance. In addition, among the NRF2 inhibitors reported so far, we summarize and discuss repurposed NRF2 inhibitors with their potential mechanisms and provide new insights to develop selective NRF2 inhibitors.

• 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.

• Molecules and Cells
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• v.39 no.12
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• pp.909-914
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• 2016

Epithelial-mesenchymal transition (EMT) is a critical step in the acquisition of the migratory and invasive capabilities associated with metastatic competence. Cysteine-rich protein 61 (CCN1/Cyr61) has been implicated as an important mediator in the proliferation and metastasis of breast cancer. Hence, Cyr61 and associated pathways are attractive targets for therapeutic interventions directed against the EMT. In the present study, we report that baicalein significantly inhibits the expression of Cyr61 and migration and invasion of MDA-MB231 human breast cancer cells. Exposure to baicalein led to increased E-cadherin expression, possibly due to the ubiquitination of Snail and Slug, which was mediated by the Cyr61/Akt/glycogen synthase kinase $3{\beta}$ ($GSK3{\beta}$) pathway. Further analysis revealed that baicalein inhibited the expression of lysyl oxidase like-2 (LOXL-2), which is a functional collaborator of Snail and Slug, and subsequently attenuated the direct interaction between LOXL-2 and Snail or Slug, thereby enhancing $GSK3{\beta}$-dependent Snail and Slug degradation. Our findings provide new insights into the antimetastatic mechanism of baicalein and may contribute to its beneficial use in breast cancer therapies.

• Animal cells and systems
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• v.4 no.2
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• pp.165-171
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• 2000

Ubiquitinated proteins in lysosomes were characterized by using two monoclonal antibodies (mAbs): LYS8-1, a mAb to lysosomal proteins, and NYA124, a mAb to ubiquitin. LYS8-1 stained lysosome-like vesicles in immunofluorescence microscopy of Amoeba proteus and Acanthamoeba castellanii. In immunoblotting, LYS8-1's antigens (LYS proteins) were detected as 68-kDa and 77-kDa proteins in A. proteus, and as 30-kDa and 39-kDa proteins in A. castellanii. In immunoprecipitation of A. castellanii, at least four distinct LYS proteins, LVS35p, LyS39p, LyS42p, and LYS46p, were detected and accumulated upon inhibition of lysosome functions but not upon that of 26S proteasome functions. They were all found to be ubiquitinated, and were recovered in the lysosome fractions in subcellular fractionation experiments. In chemical fractionation analyses, LYS35p and LYS39p were demonstrated to be peripherally associated with lysosome membrane, while LYS42p and LYS46p tightly bound to the membrane. These results suggest that the LYS proteins become associated to lysosomal membrane upon ubiquitination.

• Molecules and Cells
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• v.24 no.2
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• pp.194-199
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• 2007

GCN4 is a typical eukaryotic transcriptional activator that is implicated in the expression of many genes involved in amino acids and purine biosyntheses under stress conditions. It is degraded by 26S proteasomes following ubiquitination. However, the immediate receptor for ubiquitinated Gcn4p has not yet been identified. We investigated whether ubiquitinated Gcn4p binds directly to Rpn10p as the ubiquitinated substrate receptor of the 26S proteasome. We found that the level of Gcn4p increased in cells deleted for Rpn10p but not in cells deleted for RAD23 and DSK2, the other ubiquitinated substrate receptors and, unlike Rpn10p, neither of these proteins recognized ubiquitinated Gcn4p. These results suggest that Rpn10p is the receptor that binds the polyubiquitin chain during ubiquitin-dependent proteolysis of Gcn4p.

• BMB Reports
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• v.53 no.1
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• pp.56-63
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• 2020

The ubiquitin-proteasome system (UPS) and autophagy are two major degradative pathways of proteins in eukaryotic cells. As about 30% of newly synthesized proteins are known to be misfolded under normal cell conditions, the precise and timely operation of the UPS and autophagy to remove them as well as their tightly controlled regulation, is so important for proper cell function and survival. In the UPS, target proteins are labeled by small proteins called ubiquitin, which are then transported to the proteasome complex for degradation. Alternatively, many greatly damaged proteins are believed to be delivered to the lysosome for autophagic degradation. Although these autophagy and UPS pathways have not been considered to be directly related, many recent studies proposed their close link and dynamic interconversion. In this review, we'll focus on the several regulatory molecules that function in both UPS and autophagy and their crosstalk. Among the proposed multiple modulators, we will take a closer look at the so-called main connector of UPS-autophagy regulation, p62. Last, the functional role of p62 in the mitophagy and its implication for the pathogenesis of Parkinson's disease, one of the major neurodegenerative diseases, will be briefly reviewed.