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Published on: June 17, 2015
p62/sequestosome 1 attenuates methylmercury-induced endoplasmic reticulum stress in mouse embryonic fibroblasts
Yasukazu Takanezawa1, Ryosuke Nakamura1, Takuro Sugimoto1
1Department of Public Health, School of Pharmacy, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo, 108-8641, Japan.
Abstract:
Methylmercury (MeHg) is a hazardous environmental pollutant that causes serious toxicity in humans and animals, as well as proteotoxic stress. In our previous study, we found that MeHg induces the expression of p62/sequestosome 1 (p62) that selectively targets ubiquitinated proteins for degradation via autophagy, and that p62 might protect cells against MeHg toxicity. To further investigate the role of p62 in MeHg-induced stress responses, we evaluated the role of p62 in MeHg-induced endoplasmic reticulum (ER) stress in p62 knockout (p62KO) mouse embryonic fibroblasts (MEFs). Treatment of wild-type (WT) MEFs were treated with MeHg (1 μM) increased mRNA levels of Chop encoding C/EBP homologous protein, Trib3 encoding Tribbles homolog 3, and Dnajb9 encoding DnaJ heat-shock protein family (Hsp40) member B9 increased, suggesting that ER stress is elicited by MeHg stress. Additionally, p62KO MEFs treated with MeHg showed a higher mRNA expression of Chop and Trib3 relative to that in WT MEFs. Furthermore, knock-in of GFP-p62 to p62KO cells diminished the Chop and Trib3 induction responses to MeHg stress and resulted in a higher cell viability than that of p62KO MEFs. These results suggest that the protective role of p62 against MeHg toxicity is partly mediated by suppressing the ER stress response.
Insights
Methylmercury (MeHg) causes toxicity by inducing proteotoxic and endoplasmic reticulum (ER) stress. The protein p62/sequestosome 1 (p62) protects cells against MeHg by suppressing ER stress responses.
Area of Science:
- Environmental toxicology
- Cellular stress responses
- Molecular biology
Background:
- Methylmercury (MeHg) is a potent environmental neurotoxin causing proteotoxic stress.
- Previous studies indicated that p62/sequestosome 1 (p62) may protect cells against MeHg toxicity.
- The role of p62 in MeHg-induced endoplasmic reticulum (ER) stress remains unclear.
Purpose of the Study:
- To investigate the role of p62 in MeHg-induced ER stress.
- To evaluate the impact of p62 deficiency on cellular responses to MeHg exposure.
- To determine if p62-mediated protection against MeHg toxicity involves the suppression of ER stress.
Main Methods:
- Utilized p62 knockout (p62KO) and wild-type (WT) mouse embryonic fibroblasts (MEFs).
- Exposed MEFs to MeHg and assessed mRNA levels of ER stress markers (Chop, Trib3, Dnajb9).
- Restored p62 expression in p62KO cells (GFP-p62 knock-in) to evaluate rescue effects on MeHg-induced stress and cell viability.
Main Results:
- MeHg treatment increased ER stress markers (Chop, Trib3, Dnajb9) in WT MEFs.
- p62KO MEFs exhibited exacerbated mRNA expression of Chop and Trib3 upon MeHg exposure compared to WT MEFs.
- Restoration of p62 in p62KO cells attenuated MeHg-induced Chop and Trib3 upregulation and improved cell viability.
Conclusions:
- MeHg exposure elicits significant ER stress.
- p62 plays a protective role against MeHg toxicity by suppressing MeHg-induced ER stress.
- p62-mediated cellular defense mechanisms are crucial for mitigating MeHg-induced damage.
