Regulation of autophagic proteolysis by the N-recognin SQSTM1/p62 of the N-end rule pathway

Abstract

In macroautophagy/autophagy, cargoes are collected by specific receptors, such as SQSTM1/p62 (sequestosome 1), and delivered to phagophores for lysosomal degradation. To date, little is known about how cells modulate SQSTM1 activity and autophagosome biogenesis in response to accumulating cargoes. In this study, we show that SQSTM1 is an N-recognin whose ZZ domain binds N-terminal arginine (Nt-Arg) and other N-degrons (Nt-Lys, Nt-His, Nt-Trp, Nt-Phe, and Nt-Tyr) of the N-end rule pathway. The substrates of SQSTM1 include the endoplasmic reticulum (ER)-residing chaperone HSPA5/GRP78/BiP. Upon N-end rule interaction with the Nt-Arg of arginylated HSPA5 (R-HSPA5), SQSTM1 undergoes self-polymerization via disulfide bonds of Cys residues including Cys113, facilitating cargo collection. In parallel, Nt-Arg-bound SQSTM1 acts as an inducer of autophagosome biogenesis and autophagic flux. Through this dual regulatory mechanism, SQSTM1 plays a key role in the crosstalk between the ubiquitin (Ub)-proteasome system (UPS) and autophagy. Based on these results, we employed 3D-modeling of SQSTM1 and a virtual chemical library to develop small molecule ligands to the ZZ domain of SQSTM1. These autophagy inducers accelerated the autophagic removal of mutant HTT (huntingtin) aggregates. We suggest that SQSTM1 can be exploited as a novel drug target to modulate autophagic processes in pathophysiological conditions.

p62/SQSTM1 – steering the cell through health and disease

“…These bonds may reinforce PB1-dependent oligomerization to secure autophagic clearance in situations in which cellular homeostasis is compromised by oxidative stress (Carroll et al, 2018). Similarly, SQSTM1 forms disulfide bonds via cysteine 113 after recognition of N-terminally arginylated substrates by its ZZ domain (Cha-Molstad et al, 2018). These substrates of the so called N-end rule pathway are then degraded through autophagy in addition to their canonical proteasomal degradation (Cha-Molstad et al, 2017;Yoo et al, 2018).…”

Inactivation of ribosomal protein S27-like impairs DNA interstrand cross-link repair by destabilization of FANCD2 and FANCI

“…Shown are mean ± SEM from three independent experiments; *p < 0.05, **p < 0.01, ***p < 0.001, ns, no significance. similarity to the regions of p62 overlapping ZZ domain and UBA domain, which are involved in recognition of Nterminally arginylated substrates 36,37 and binding to ubiquitylated cargoes [38][39][40] , respectively, whether and how RPS27L (via its N-terminal portion) modulates the p62-FANCs interaction via direct competition or by the other means need further investigation. Nevertheless, the fact that only RPS27L affects p62-mediated degradation of the FANCD2/FANCI, strongly suggested that the difference in these three amino acids at the N-terminus plays the determinant role.…”

Five enzymes of the Arg/N-degron pathway form a targeting complex: The concept of superchanneling

“…1B) (2,24,(66)(67)(68)). Yet another N-recognin of the human Arg/N-degron pathway is p62, an autophagyregulating protein distinct from E3s (41,69,70). hsUBR1 and hsUBR2 E3s are sequelogous (similar in sequence) (71) (they Fig.…”