Selective VPS34 Inhibitor Blocks Autophagy and Uncovers a Role for NCOA4 in Ferritin Degradation and Iron Homeostasis in Vivo

Nat Cell Biol. 2014 Nov;16(11):1069-79. doi: 10.1038/ncb3053. Epub 2014 Oct 19.

Abstract

Cells rely on autophagy to clear misfolded proteins and damaged organelles to maintain cellular homeostasis. In this study we use the new autophagy inhibitor PIK-III to screen for autophagy substrates. PIK-III is a selective inhibitor of VPS34 that binds a unique hydrophobic pocket not present in related kinases such as PI(3)Kα. PIK-III acutely inhibits autophagy and de novo lipidation of LC3, and leads to the stabilization of autophagy substrates. By performing ubiquitin-affinity proteomics on PIK-III-treated cells we identified substrates including NCOA4, which accumulates in ATG7-deficient cells and co-localizes with autolysosomes. NCOA4 directly binds ferritin heavy chain-1 (FTH1) to target the iron-binding ferritin complex with a relative molecular mass of 450,000 to autolysosomes following starvation or iron depletion. Interestingly, Ncoa4(-/-) mice exhibit a profound accumulation of iron in splenic macrophages, which are critical for the reutilization of iron from engulfed red blood cells. Taken together, the results of this study provide a new mechanism for selective autophagy of ferritin and reveal a previously unappreciated role for autophagy and NCOA4 in the control of iron homeostasis in vivo.

MeSH terms

  • Animals
  • Autophagy / drug effects
  • Autophagy / physiology*
  • Cells, Cultured
  • Class III Phosphatidylinositol 3-Kinases / antagonists & inhibitors*
  • Ferritins / metabolism*
  • Homeostasis / physiology*
  • Humans
  • Iron / metabolism*
  • Lysosomes / metabolism
  • Mice
  • Nuclear Receptor Coactivators / metabolism*
  • Phagosomes / metabolism
  • Protein Binding

Substances

  • NCOA4 protein, human
  • NcoA4 protein, mouse
  • Nuclear Receptor Coactivators
  • Ferritins
  • Iron
  • Class III Phosphatidylinositol 3-Kinases