Phosphorylation tunes p62 condensates to drive autophagic degradation of ubiquitinated proteins

Abstract p62/SQSTM1 self-assembles with polyubiquitin into liquid-like condensates (“p62 bodies”) that function as stress-signaling hubs and selective autophagy cargo. We show that TBK1-dependent phosphorylation at Ser403 acts as a threshold-dependent modulator of a condensate’s physical properties and promotes their rapid autophagic clearance. Phosphorylation within p62 bodies drives a transition from large, fluid droplets to compact, gel-like condensates that efficiently capture LC3-positive isolation membranes and accelerate the autophagic removal of ubiquitinated proteins. PP2A holoenzymes containing PPP2R5A/B/E, recruited via a KEAP1 bridge, counteract TBK1 by dephosphorylating Ser403. Homozygous p62S403E/S403E knock-in embryonic stem cells differentiate into post-mitotic neurons enriched in miniaturized, gel-like p62 bodies. Consistently, phosphorylation-mimetic knock-in mice show similar remodeling of p62 condensates in vivo, demonstrating that this phosphorylation-driven mechanism maintains proteostasis across scales. We propose that Ser403 phosphorylation functions as a molecular switch that couples the material state of p62 condensates to their stability and serves as a central control point for p62-mediated protein degradation.