Proteasome and p62/SQSTM1 are involved in methylmercury toxicity mitigation in mouse embryonic fibroblast cells
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Published on: July 13, 2014
Yasukazu Takanezawa1, Ryosuke Nakamura1, Yuka Ohshiro1
1Department of Public Health, School of Pharmacy, Kitasato University.
Abstract:
Methylmercury (MeHg), an environmental pollutant, disrupts and impairs cellular function. MeHg binds to various cellular proteins, causing dysfunction and misfolding, which are considered underlying causes of MeHg toxicity. The p62 protein, also termed SQSTM1, is a ubiquitin-binding protein that targets ubiquitinated substrates to undergo autophagy and plays a key role in ameliorating MeHg toxicity. p62 also delivers ubiquitinated substrates to proteasomes. However, the role of these degradation systems in mitigating MeHg toxicity remains unknown. Herein, we explored the impact of the proteasome inhibitor MG132 on MeHg toxicity and examined the toxicity of co-treatment with MG132 and MeHg in p62KO mouse embryonic fibroblasts (MEFs) by analyzing cell viability, immunoblotting, mRNA levels, immunofluorescence, and the mercury content. The proteasome inhibitor MG132 enhanced MeHg-induced cytotoxicity while reducing intracellular mercury levels in MEFs. Co-treatment with MG132 and MeHg markedly increased levels of p62 and ubiquitinated proteins. Furthermore, co-treatment with MG132 and MeHg reduced p62KO MEF viability compared to that of wild-type MEFs. Our findings suggest that the proteasome participates in mitigating MeHg cytotoxicity, while p62 may play an important role in transporting MeHg-induced ubiquitinated proteins to the proteasome, as well as in autophagy. Collectively, these results imply that p62, and proteasome, and autophagy are vital for cytoprotection against MeHg toxicity.
Insights
Methylmercury (MeHg) toxicity is reduced by the proteasome and p62 protein, which help clear damaged proteins via autophagy and proteasomal degradation. Impairing these systems increases MeHg
Area of Science:
- Cellular Biology
- Toxicology
- Environmental Health
Background:
- Methylmercury (MeHg) is a neurotoxic environmental pollutant that impairs cellular function by causing protein misfolding and dysfunction.
- The p62 protein (SQSTM1) is crucial for cellular defense, facilitating the degradation of ubiquitinated proteins via autophagy and the proteasome.
- The specific roles of the proteasome and p62 in mitigating MeHg toxicity are not fully understood.
Purpose of the Study:
- To investigate the impact of proteasome inhibition on MeHg toxicity.
- To examine the combined effects of MeHg and proteasome inhibition on cell viability and protein degradation pathways.
- To elucidate the role of p62 in cellular defense against MeHg toxicity.
Main Methods:
- Utilized p62 knockout (p62KO) and wild-type mouse embryonic fibroblasts (MEFs).
- Treated cells with methylmercury (MeHg) and/or the proteasome inhibitor MG132.
- Assessed cell viability, protein levels (p62, ubiquitinated proteins), mRNA expression, immunofluorescence, and intracellular mercury content.
Main Results:
- Proteasome inhibition with MG132 exacerbated MeHg-induced cytotoxicity and decreased intracellular mercury levels.
- Co-treatment with MG132 and MeHg significantly increased levels of p62 and ubiquitinated proteins.
- p62KO MEFs exhibited reduced viability compared to wild-type MEFs when co-treated with MG132 and MeHg.
Conclusions:
- The proteasome plays a protective role against methylmercury toxicity.
- p62 is important for transporting MeHg-induced ubiquitinated proteins to the proteasome and is involved in autophagy.
- p62, proteasomal degradation, and autophagy are essential for cellular protection against MeHg-induced damage.
