Autophagy-Independent Lysosomal Targeting Regulated by ULK1/2-FIP200 and ATG9

Cell Rep. 2017 Sep 5;20(10):2341-2356. doi: 10.1016/j.celrep.2017.08.034.

Abstract

Iron is vital for many homeostatic processes, and its liberation from ferritin nanocages occurs in the lysosome. Studies indicate that ferritin and its binding partner nuclear receptor coactivator-4 (NCOA4) are targeted to lysosomes by a form of selective autophagy. By using genome-scale functional screening, we identify an alternative lysosomal transport pathway for ferritin that requires FIP200, ATG9A, VPS34, and TAX1BP1 but lacks involvement of the ATG8 lipidation machinery that constitutes classical macroautophagy. TAX1BP1 binds directly to NCOA4 and is required for lysosomal trafficking of ferritin under basal and iron-depleted conditions. Under basal conditions ULK1/2-FIP200 controls ferritin turnover, but its deletion leads to TAX1BP1-dependent activation of TBK1 that regulates redistribution of ATG9A to the Golgi enabling continued trafficking of ferritin. Cells expressing an amyotrophic lateral sclerosis (ALS)-associated TBK1 allele are incapable of degrading ferritin suggesting a molecular mechanism that explains the presence of iron deposits in patient brain biopsies.

Keywords: ALS; ATG9A; NCOA4; TAX1BP1; TBK1; ULK1/2; autophagy; ferritinophagy; pooled CRISPR screen; trafficking.

MeSH terms

  • Autophagy / genetics
  • Autophagy / physiology*
  • Autophagy-Related Protein-1 Homolog / genetics
  • Autophagy-Related Protein-1 Homolog / metabolism*
  • Autophagy-Related Proteins / genetics
  • Autophagy-Related Proteins / metabolism*
  • Cell Line
  • Cell Line, Tumor
  • DNA, Complementary / genetics*
  • Ferritins / genetics
  • Ferritins / metabolism
  • HEK293 Cells
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Lysosomes / metabolism*
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Neoplasm Proteins / genetics
  • Neoplasm Proteins / metabolism
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Protein-Tyrosine Kinases / genetics
  • Protein-Tyrosine Kinases / metabolism*
  • Vesicular Transport Proteins / genetics
  • Vesicular Transport Proteins / metabolism*

Substances

  • Atg9a protein, human
  • Autophagy-Related Proteins
  • DNA, Complementary
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • Neoplasm Proteins
  • RB1CC1 protein, human
  • TAX1BP1 protein, human
  • Vesicular Transport Proteins
  • Ferritins
  • Protein-Tyrosine Kinases
  • Autophagy-Related Protein-1 Homolog
  • Protein-Serine-Threonine Kinases
  • TBK1 protein, human
  • ULK1 protein, human
  • Ulk2 protein, human