Enhanced liquidity of p62 droplets mediated by Smurf1 links Nrf2 activation and autophagy

Abstract

Background Macro-autophagy/Autophagy is an evolutionarily well-conserved recycling process to maintain the balance through precise spatiotemporal regulation. However, the regulatory mechanisms of biomolecular condensates by the key adaptor protein p62 via liquid-liquid phase separation (LLPS) remain obscure. Results In this study, we showed that E3 ligase Smurf1 enhanced Nrf2 activation and promoted autophagy by increasing p62 phase separation capability. Specifically, the Smurf1/p62 interaction improved the formation and material exchange of liquid droplets compared with p62 single puncta. Additionally, Smurf1 promoted the competitive binding of p62 with Keap1 to increase Nrf2 nuclear translocation in p62 Ser349 phosphorylation-dependent manner. Mechanistically, overexpressed Smurf1 increased the activation of mTORC1 (mechanistic target of rapamycin complex 1), in turn leading to p62 Ser349 phosphorylation. Nrf2 activation increased the mRNA levels of Smurf1, p62, and NBR1, further promoting the droplet liquidity to enhance oxidative stress response. Importantly, we showed that Smurf1 maintained cellular homeostasis by promoting cargo degradation through the p62/LC3 autophagic pathway. Conclusions These findings revealed the complex interconnected role among Smurf1, p62/Nrf2/NBR1, and p62/LC3 axis in determining Nrf2 activation and subsequent clearance of condensates through LLPS mechanism.

Distinct recognition of mutant huntingtin aggregates by autophagy receptor SQSTM1/p62 versus optineurin has differential effects on cell survival

“…Due to this oligomeric property of SQSTM1/p62, it has been suggested that liquid-liquid phase separation (LLPS) may occur when the concentration of SQSTM1/p62 proteins approaches a threshold 29,30 . This phenomenon can lead to the formation of liquid-like condensates known as SQSTM1/p62 bodies which are crucial for autophagic degradation [31][32][33][34] . In fact, we observed the formation of SQSTM1/p62 bodies in HEK293A and STHdhQ7/Q7 cells after the treatment with the autophagy inducer rapamycin (Supplementary Fig.…”