A selective ER-phagy exerts procollagen quality control via a Calnexin-FAM134B complex

EMBO J. 2019 Jan 15;38(2):e99847. doi: 10.15252/embj.201899847. Epub 2018 Dec 17.

Abstract

Autophagy is a cytosolic quality control process that recognizes substrates through receptor-mediated mechanisms. Procollagens, the most abundant gene products in Metazoa, are synthesized in the endoplasmic reticulum (ER), and a fraction that fails to attain the native structure is cleared by autophagy. However, how autophagy selectively recognizes misfolded procollagens in the ER lumen is still unknown. We performed siRNA interference, CRISPR-Cas9 or knockout-mediated gene deletion of candidate autophagy and ER proteins in collagen producing cells. We found that the ER-resident lectin chaperone Calnexin (CANX) and the ER-phagy receptor FAM134B are required for autophagy-mediated quality control of endogenous procollagens. Mechanistically, CANX acts as co-receptor that recognizes ER luminal misfolded procollagens and interacts with the ER-phagy receptor FAM134B. In turn, FAM134B binds the autophagosome membrane-associated protein LC3 and delivers a portion of ER containing both CANX and procollagen to the lysosome for degradation. Thus, a crosstalk between the ER quality control machinery and the autophagy pathway selectively disposes of proteasome-resistant misfolded clients from the ER.

Keywords: Calnexin; FAM134B; autophagy; collagen; endoplasmic reticulum.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Autophagy
  • Calnexin / genetics
  • Calnexin / metabolism*
  • Cell Line
  • Endoplasmic Reticulum / metabolism*
  • Gene Knockdown Techniques
  • HeLa Cells
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Mice
  • Microtubule-Associated Proteins / metabolism
  • Oryzias
  • Procollagen / metabolism*
  • Protein Folding

Substances

  • CANX protein, human
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • Microtubule-Associated Proteins
  • Procollagen
  • RETREG1 protein, human
  • light chain 3, human
  • Calnexin