• Biomedical Science Letters
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• v.27 no.3
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• pp.182-186
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• 2021

Parkinson disease (PD) is becoming one of the most neurodegenerative disorder worldwide. The deposited aggregates have been connected in the pathophysiology of PD, which are degraded either by ubiquitin-proteasomal system (UPS) or autophagy-lysosomal pathway (ALP). Leucin-rich repeat kinase 2 (LRRK2), one of the neurodegenerative proteins of PD is also stringently controlled by both UPS and ALP degradation as well. However, the polyubiquitination pattern of LRRK2 aggregates is largely unknown. Here, we found that K63-linked polyubiquitinations of G2019S mutant, most familial variant for PD, is highly enhanced compared to those of wild type LRRK2 (WT). In addition, in the presence of overexpressed p62/SQSTM-1, ubiquitination of LRRK2 WT or D1994A was reduced, whereas G2019S mutant was not diminished significantly. Therefore, we propose that degradation of G2019S via UPS is more involved with K63-linked ubiquitination than K48-linked ubiquitination, and overexpressed p62/SQSTM-1 does not enhance degradative effect on G2019S variant.

• Journal of Cancer Prevention
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• v.23 no.4
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• pp.153-161
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• 2018

Imbalance of protein homeostasis (proteostasis) is known to cause cellular malfunction, cell death, and diseases. Elaborate regulation of protein synthesis and degradation is one of the important processes in maintaining normal cellular functions. Protein degradation pathways in eukaryotes are largely divided into proteasome-mediated degradation and lysosome-mediated degradation. Proteasome is a multisubunit complex that selectively degrades 80% to 90% of cellular proteins. Proteasome-mediated degradation can be divided into 26S proteasome (20S proteasome + 19S regulatory particle) and free 20S proteasome degradation. In 1980, it was discovered that during ubiquitination process, wherein ubiquitin binds to a substrate protein in an ATP-dependent manner, ubiquitin acts as a degrading signal to degrade the substrate protein via proteasome. Conversely, 20S proteasome degrades the substrate protein without using ATP or ubiquitin because it recognizes the oxidized and structurally modified hydrophobic patch of the substrate protein. To date, most studies have focused on protein degradation via 26S proteasome. This review describes the 26S/20S proteasomal pathway of protein degradation and discusses the potential of proteasome as therapeutic targets for cancer treatment as well as against diseases caused by abnormalities in the proteolytic system.

• 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.

• Journal of Life Science
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• v.28 no.9
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• pp.1007-1015
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• 2018

The E6-associated protein (E6AP) is known to induce the ubiquitination and proteasomal degradation of HCV core protein and thereby directly impair capsid assembly, resulting in a decline in HCV replication. To counteract this anti-viral host defense system, HCV core protein has evolved a strategy to inhibit E6AP expression via DNA methylation. In the present study, we further explored the mechanism by which HCV core protein inhibits E6AP expression. HCV core protein upregulated both the protein levels and enzyme activities of DNA methyltransferase 1 (DNMT1), DNMT3a, and DNMT3b to inhibit E6AP expression via promoter hypermethylation in HepG2 cells but not in Hep3B cells, which do not express p53. Interestingly, p53 overexpression alone in Hep3B cells was sufficient to activate DNMTs in the absence of HCV core protein and thereby inhibit E6AP expression via promoter hypermethylation. In addition, upregulation of p53 was absolutely required for the HCV core protein to inhibit E6AP expression via promoter hypermethylation, as evidenced by both p53 knockdown and ectopic expression experiments. Accordingly, levels of the ubiquitinated forms of HCV core protein were lower in HepG2 cells than in Hep3B cells. Based on these observations, we conclude that HCV core protein evades ubiquitin-dependent proteasomal degradation in a p53-dependent manner.

• Korean Journal of Agricultural Science
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• v.48 no.4
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• pp.935-944
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• 2021

It has been suggested that bisphenol A (BPA), a known endocrine disruptor, interferes with the endocrine system, causing reproductive dysfunction. Recently, BPA has been found in waste water due to incomplete sewage purification, possibly threatening health through its ingestion via tap water. In this study, young male mice (6 - 7 weeks old) were administered water containing BPA (50 mg·kg^-1) for four weeks, while control mice consumed water without BPA. Serum, epididymal spermatozoa and testicular sections were assessed after sacrificing the mice on day 28. No significant differences were obtained between the groups in the body, testis and seminal vesicle weights. However, the epididymal sperm motility and count levels were significantly reduced in BPA-fed mice. Significantly higher hepatotoxicity levels were also observed in mice ingesting BPA as compared to the control mice. The level of serum testosterone was reduced, and testicular sections revealed incomplete and irregular spermatogenesis in BPA-ingested mice. The sperm proteasomal-proteolytic activity level has been implicated in sperm function and is measured in motile spermatozoa using fluorometric substrates. High ubiquitin C-terminal hydrolase activity levels were observed in the control mice without BPA. During a mating trial, a low pregnancy rate (71.4%) was observed in females mated with males who had consumed BPA (100% in the control mice). Overall, BPA adversely affected spermatogenesis and quality, as indicated by decreased sperm motility, concentration and serum testosterone levels, resulting in reduced fertility competence.

• Food Science of Animal Resources
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• v.44 no.1
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• pp.132-145
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• 2024

Sarcopenia, the age-related muscle atrophy, is a serious concern as it is associated with frailty, reduced physical functions, and increased mortality risk. Protein supplementation is essential for preserving muscle mass, and horse meat can be an excellent source of proteins. Since sarcopenia occurs under conditions of oxidative stress, this study aimed to investigate the potential anti-muscle atrophy effect of horse meat hydrolysate using C2C12 cells. A horse meat hydrolysate less than 3 kDa (A4<3kDa) significantly increased the viability of C2C12 myoblasts against H₂O₂-induced cytotoxicity. Exposure of C2C12 myoblasts to lipopolysaccharide led to an elevation of cellular reactive oxygen species levels and mRNA expression of proinflammatory cytokines, including tumor necrosis factor-α and interleukin 6, and these effects were attenuated by A4<3kDa treatment. Additionally, A4<3kDa activated protein synthesis-related proteins through the protein kinase B/mechanistic target of rapamycin pathway, while decreasing the expression of activity and degradation-related proteins, such as Forkhead box O3, muscle RING finger protein-1, and Atrogin-1 in dexamethasone-treated C2C12 myotubes. Therefore, the natural material A4<3kDa has the potential of protecting against muscle atrophy, while further in vivo study is needed.