NBR1-mediated p62-liquid droplets enhance the Keap1-Nrf2 system

Abstract

10 p62/SQSTM1 is a multivalent protein that has an ability to cause a liquid-liquid phase separation and serves as a receptor protein that participates in cargo isolation during selective autophagy. This protein is also involved in the non-canonical activation of the Keap1-Nrf2 system, a major oxidative stress response pathway. Here we show a role of Neighbor of BRCA1 gene 1 (NBR1), an autophagy receptor structurally similar to 15 p62/SQSTM1, in the p62-liquid droplet formation and the Keap1-Nrf2 pathway. The overexpression of NBR1 blocked selective degradation of p62/SQSTM1 through autophagy and promoted the accumulation and phosphorylation of p62/SQSTM1 in liquid-like bodies, which is required for the activation of Nrf2. NBR1 was induced in response to oxidative stress, and then the p62-mediated Nrf2 activation was up-regulated. 20 Conversely, loss of Nbr1 suppresses not only the formation of p62/SQSTM1-liquid droplets but also p62-dependent Nrf2 activation during oxidative stress. Taken together, our results show that NBR1 mediates p62/SQSTM1-liquid droplet formation to activate the Keap1-Nrf2 pathway.25

p62: Friend or Foe? Evidences for OncoJanus and NeuroJanus Roles

“…Intriguingly, it has been shown that upon ubiquitin binding p62 acquires liquid like properties since it forms droplets that serve as interactive nodes in the context of selective autophagy. The droplet formation is favoured by the interaction through the PB1 domain of p62 with NBR1, as previously mentioned [ 31 ]. Beside p62 regulative phosphorylation within the UBA domain, another important post translational modification is represented by acetylation.…”

“…While the dimeric form of p62 is substantially inactive with respect to autophagy, polymerization of p62 in a filamentous form, which renders the protein functional, is promoted by the interaction of the protein with the autophagic receptor NBR1 (the neighbor of BRCA1 gene). This factor specifically binds to PB1 domain and cooperates with p62 in targeting poly-ubiquitinated proteins to the autophagosome during selective autophagy [ 31 ]. Jacobi at al.…”

Liquid–liquid phase separation in autophagy

“…The p62 condensates show gel-like behaviors, namely slow fusion and low mobility (Sun et al, 2018;Zaffagnini et al, 2018), which suggests that the gel-like state may ensure efficient autophagic degradation of these condensates. Consistent with the notion that higher liquidity is not favorable for degradation, overexpression of NBR1, which promotes p62-mediated phase separation and also dramatically increases the mobility of p62 in the condensates, impairs autophagic degradation of p62 condensates (Sánchez-Martín et al, 2020;Zaffagnini et al, 2018). Aberrant p62-positive aggregates, such as Mallory-Denk bodies, α1 antitrypsin aggregates, Lewy bodies, and huntingtin aggregates, accumulate in a diversity of diseases (Yamamoto and Simonsen, 2011).…”

MOAP‐1‐mediated dissociation of p62/SQSTM1 bodies releases Keap1 and suppresses Nrf2 signaling

“…No difference was noted in the protein levels of TRIM21 (Appendix Fig S4A), which is the E3 ligase that conjugates the K63‐linked ubiquitin chains to p62 (Pan et al , 2016). Recently, K63‐linked poly‐ubiquitin chain and p62‐interacting proteins such as DAXX, NBR1, and TAK1 were shown to facilitate formation of p62 bodies (Sun et al , 2018; Zaffagnini et al , 2018; Kehl et al , 2019; Yang et al , 2019; Sanchez‐Martin et al , 2020). To evaluate whether MOAP‐1 regulates p62 bodies through influencing the interaction of p62 with these proteins, we performed co‐immunoprecipitation (co‐IP) experiments on HepG2 cells stably overexpressing Myc‐MOAP‐1 or Myc‐only control.…”

“…Interestingly, in mice, p62 is required and sufficient to mediate liver tumorigenesis through enhancing the Nrf2 and mTORC1 signaling pathways, separable from its role as an autophagy receptor (Saito et al , 2016; Umemura et al , 2016). p62 activity is known to be regulated by multiple mechanisms that modulate its ability to form aggregates and to recruit Keap1 and ubiquitylated substrates (Matsumoto et al , 2011; Ichimura et al , 2013; Cha‐Molstad et al , 2015; Pan et al , 2016; Lee et al , 2017; Peng et al , 2017; Carroll et al , 2018; Kehl et al , 2019; Xu et al , 2019; Yang et al , 2019; You et al , 2019; Sanchez‐Martin et al , 2020). More recently, p62 was shown to undergo liquid–liquid phase separation and the condensates formed, appearing as “aggregates” or “bodies” visually, are in fact a dynamic structure undergoing fusion constantly (Sun et al , 2018; Zaffagnini et al , 2018; Yang et al , 2019; Sanchez‐Martin et al , 2020).…”