Proteotoxic stress induces phosphorylation of p62/SQSTM1 by ULK1 to regulate selective autophagic clearance of protein aggregates

PLoS Genet. 2015 Feb 27;11(2):e1004987. doi: 10.1371/journal.pgen.1004987. eCollection 2015.

Abstract

Disruption of proteostasis, or protein homeostasis, is often associated with aberrant accumulation of misfolded proteins or protein aggregates. Autophagy offers protection to cells by removing toxic protein aggregates and injured organelles in response to proteotoxic stress. However, the exact mechanism whereby autophagy recognizes and degrades misfolded or aggregated proteins has yet to be elucidated. Mounting evidence demonstrates the selectivity of autophagy, which is mediated through autophagy receptor proteins (e.g. p62/SQSTM1) linking autophagy cargos and autophagosomes. Here we report that proteotoxic stress imposed by the proteasome inhibition or expression of polyglutamine expanded huntingtin (polyQ-Htt) induces p62 phosphorylation at its ubiquitin-association (UBA) domain that regulates its binding to ubiquitinated proteins. We find that autophagy-related kinase ULK1 phosphorylates p62 at a novel phosphorylation site S409 in UBA domain. Interestingly, phosphorylation of p62 by ULK1 does not occur upon nutrient starvation, in spite of its role in canonical autophagy signaling. ULK1 also phosphorylates S405, while S409 phosphorylation critically regulates S405 phosphorylation. We find that S409 phosphorylation destabilizes the UBA dimer interface, and increases binding affinity of p62 to ubiquitin. Furthermore, lack of S409 phosphorylation causes accumulation of p62, aberrant localization of autophagy proteins and inhibition of the clearance of ubiquitinated proteins or polyQ-Htt. Therefore, our data provide mechanistic insights into the regulation of selective autophagy by ULK1 and p62 upon proteotoxic stress. Our study suggests a potential novel drug target in developing autophagy-based therapeutics for the treatment of proteinopathies including Huntington's disease.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism*
  • Autophagy / genetics
  • Autophagy-Related Protein-1 Homolog
  • Humans
  • Huntingtin Protein
  • Huntington Disease / genetics*
  • Huntington Disease / metabolism
  • Huntington Disease / pathology
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Nerve Tissue Proteins / biosynthesis*
  • Nerve Tissue Proteins / metabolism
  • Peptides / metabolism
  • Phagosomes / genetics
  • Phagosomes / pathology
  • Phosphorylation
  • Protein Aggregates / genetics*
  • Protein Binding
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Sequestosome-1 Protein
  • Ubiquitin / metabolism
  • Ubiquitinated Proteins / metabolism

Substances

  • Adaptor Proteins, Signal Transducing
  • HTT protein, human
  • Huntingtin Protein
  • Intracellular Signaling Peptides and Proteins
  • Nerve Tissue Proteins
  • Peptides
  • Protein Aggregates
  • SQSTM1 protein, human
  • Sequestosome-1 Protein
  • Ubiquitin
  • Ubiquitinated Proteins
  • polyglutamine
  • Autophagy-Related Protein-1 Homolog
  • Protein-Serine-Threonine Kinases
  • ULK1 protein, human