• 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]

• BMB Reports
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• v.54 no.8
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• pp.413-418
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• 2021

ErbB3-binding protein 1 (EBP1) is a multifunctional protein associated with neural development. Loss of Ebp1 leads to upregulation of the gene silencing unit suppressor of variegation 3-9 homolog 1 (Suv39H1)/DNA (cytosine 5)-methyltransferase (DNMT1). EBP1 directly binds to the promoter region of DNMT1, repressing DNA methylation, and hence, promoting neural development. In the current study, we showed that EBP1 suppresses histone methyltransferase activity of Suv39H1 by promoting ubiquitin-proteasome system (UPS)-dependent degradation of Suv39H1. In addition, we showed that EBP1 directly interacts with Suv39H1, and this interaction is required for recruiting the E3 ligase MDM2 for Suv39H1 degradation. Thus, our findings suggest that EBP1 regulates UPS-dependent degradation of Suv39H1 to govern proper heterochromatin assembly during neural development.

• Molecules and Cells
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• v.41 no.11
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• pp.933-942
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• 2018

Traditionally, small-molecule or antibody-based therapies against human diseases have been designed to inhibit the enzymatic activity or compete for the ligand binding sites of pathological target proteins. Despite its demonstrated effectiveness, such as in cancer treatment, this approach is often limited by recurring drug resistance. More importantly, not all molecular targets are enzymes or receptors with druggable 'hot spots' that can be directly occupied by active site-directed inhibitors. Recently, a promising new paradigm has been created, in which small-molecule chemicals harness the naturally occurring protein quality control machinery of the ubiquitin-proteasome system to specifically eradicate disease-causing proteins in cells. Such 'chemically induced protein degradation' may provide unprecedented opportunities for targeting proteins that are inherently undruggable, such as structural scaffolds and other non-enzymatic molecules, for therapeutic purposes. This review focuses on surveying recent progress in developing E3-guided proteolysis-targeting chimeras (PROTACs) and small-molecule chemical modulators of deubiquitinating enzymes upstream of or on the proteasome.

• BMB Reports
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• v.54 no.12
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• pp.592-600
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• 2021

Parkinson's disease (PD) is one of the most common neurodegenerative diseases in the elderly population and is caused by the loss of dopaminergic neurons. PD has been predominantly attributed to mitochondrial dysfunction. The structural alteration of α-synuclein triggers toxic oligomer formation in the neurons, which greatly contributes to PD. In this article, we discuss the role of several familial PD-related proteins, such as α-synuclein, DJ-1, LRRK2, PINK1, and parkin in mitophagy, which entails a selective degradation of mitochondria via autophagy. Defective changes in mitochondrial dynamics and their biochemical and functional interaction induce the formation of toxic α-synuclein-containing protein aggregates in PD. In addition, these gene products play an essential role in ubiquitin proteasome system (UPS)-mediated proteolysis as well as mitophagy. Interestingly, a few deubiquitinating enzymes (DUBs) additionally modulate these two pathways negatively or positively. Based on these findings, we summarize the close relationship between several DUBs and the precise modulation of mitophagy. For example, the USP8, USP10, and USP15, among many DUBs are reported to specifically regulate the K48- or K63-linked de-ubiquitination reactions of several target proteins associated with the mitophagic process, in turn upregulating the mitophagy and protecting neuronal cells from α-synuclein-derived toxicity. In contrast, USP30 inhibits mitophagy by opposing parkin-mediated ubiquitination of target proteins. Furthermore, the association between these changes and PD pathogenesis will be discussed. Taken together, although the functional roles of several PD-related genes have yet to be fully understood, they are substantially associated with mitochondrial quality control as well as UPS. Therefore, a better understanding of their relationship provides valuable therapeutic clues for appropriate management strategies.

• BMB Reports
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• v.47 no.5
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• pp.292-297
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• 2014

Age-related macular degeneration (AMD) is the leading cause of blindness in the world. Evidence indicates that the suppression of the ubiquitin-proteasome system (UPS) contributes to the accumulation of toxic proteins and inflammation in retinal pigment epithelium (RPE), the functional abnormalities and/or the degeneration of which are believed to be the initiators and major pathologies of AMD. To identify new protein associations with the altered UPS in AMD, we used LC-ESI-MS/MS to perform a proteomic analysis of the aqueous humor (AH) of AMD patients and matched control subjects. Six UPS-related proteins were present in the AH of the patients and control subjects. Four of the proteins, including 26S proteasome non-ATPase regulatory subunit 1 (Rpn2), were increased in patients, according to semi-quantitative proteomic profiling. An LC-MRM assay revealed a significant increase of Rpn2 in 15 AMD patients compared to the control subjects, suggesting that this protein could be a biomarker for AMD.

• BMB Reports
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• v.49 no.9
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• pp.459-473
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• 2016

Neurodegenerative diseases (NDs) often involve the formation of abnormal and toxic protein aggregates, which are thought to be the primary factor in ND occurrence and progression. Aged neurons exhibit marked increases in aggregated protein levels, which can lead to increased cell death in specific brain regions. As no specific drugs/therapies for treating the symptoms or/and progression of NDs are available, obtaining a complete understanding of the mechanism underlying the formation of protein aggregates is needed for designing a novel and efficient removal strategy. Intracellular proteolysis generally involves either the lysosomal or ubiquitin-proteasome system. In this review, we focus on the structure and assembly of the proteasome, proteasome-mediated protein degradation, and the multiple dynamic regulatory mechanisms governing proteasome activity. We also discuss the plausibility of the correlation between changes in proteasome activity and the occurrence of NDs.

• Korean Journal of Pharmacognosy
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• v.39 no.1
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• pp.56-59
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• 2008

Ubiquitin-proteasome proteolytic system plays an important role in selective protein degradation and regulates cellular events including apoptosis. Cancer cells have been shown to be more sensitive to the proapoptotic effects of proteasome inhibition than normal cells. Thus, proteasome inhibitor can be potential anticancer agent. Since the MeOH extracts of psoraleae semen and processed psoraleae semen showed potent proteasome inhibition activity, the fractions of the extracts were evaluated on the activity to screen the proteasome inhibitors. The $CHCl_3$ fr. of the processed psoraleae semen showed the most potent activity, of which chemical investigation led to two coumarins, psoralen and isopsoralen. Their structures were determined by spectroscopic methods such as $^1H-NMR$ and EIMS spectra.

• Journal of Microbiology and Biotechnology
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• v.18 no.10
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• pp.1655-1658
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• 2008

Cyanobacteria, blue-green algae, are a rich source of bioactive secondary metabolites with many potential applications. The ubiquitin-proteasome proteolytic system plays an important role in selective protein degradation and regulates cellular events including apoptosis. Cancer cells are more sensitive to the proapoptotic effects of proteasome inhibition than normal cells. Thus, proteasome inhibitors can be potential anticancer agents. Cyanobacteria have been shown to be a rich source of highly effective inhibitors of proteases. A proteasome inhibitor was screened from an extract of the culture of Scytonema hofmanni on the basis of its inhibitory activity, which led to the isolation of nostodione A with an $IC_{50}$ value of 50${\mu}M$. Its structure was determined by spectroscopic methods such as $^{1}H$-NMR and ESI-MS spectral analyses.

• BMB Reports
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• v.44 no.3
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• pp.182-186
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• 2011

Exogenous stimuli such as nerve growth factor (NGF) exert their effects on neurite outgrowth via Trk neurotrophin receptors. TrkA receptors are known to be ubiquitinated via proteasome inhibition in the presence of NGF. However, the effect of proteasome inhibition on neurite outgrowth has not been studied extensively. To clarify these issues, we investigated signaling events in PC12 cells treated with NGF and the proteasome inhibitor MG132. We found that MG132 facilitated NGF-induced neurite outgrowth and potentiated the phosphorylation of the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) and phosphatidylinositol-3-kinase (PI3K)/AKT pathways and TrkA receptors. MG132 stimulated internalization of surface TrkA receptor and stabilized intracellular TrkA receptor, and the $Ub^{K63}$ chain was found to be essential for stability. These results indicate that the ubiquitin-proteasome system potentiated neurite formation by regulating the stability of TrkA receptors.

• Molecules and Cells
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• v.19 no.2
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• pp.228-231
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• 2005

Recent characterization of several genes involved in plant defense responses suggested that ubiquitin-mediated protein degradation has a role in these responses. We isolated two cDNAs (NtUBA1 and NtUBA2) encoding ubiquitin-activating enzyme (E1) from Nicotiana tabacum cv. BY-2. The open reading frames of both encoded 1080 amino acids, corresponding to molecular masses of 120 kDa. The E1s and corresponding transcripts were upregulated by infection with tobacco mosaic virus (TMV) and tomato mosaic virus (ToMV), and to a lesser extent by cucumber mosaic virus (CMV). Furthermore, they were also upregulated by wounding stress, and the plant hormones salicylic acid, jasmonic acid and the ethylene precursor, aminocyclopropane-1-carboxylic acid (ACC). Our findings support the idea that the ubiquitin-proteasome system plays a role in plant disease defenses.