C9orf72 Binds SMCR8, Localizes to Lysosomes, and Regulates mTORC1 Signaling

Mol Biol Cell. 2016 Oct 15;27(20):3040-3051. doi: 10.1091/mbc.E16-01-0003. Epub 2016 Aug 24.

Abstract

Hexanucleotide expansion in an intron of the C9orf72 gene causes amyotrophic lateral sclerosis and frontotemporal dementia. However, beyond bioinformatics predictions that suggested structural similarity to folliculin, the Birt-Hogg-Dubé syndrome tumor suppressor, little is known about the normal functions of the C9orf72 protein. To address this problem, we used genome-editing strategies to investigate C9orf72 interactions, subcellular localization, and knockout (KO) phenotypes. We found that C9orf72 robustly interacts with SMCR8 (a protein of previously unknown function). We also observed that C9orf72 localizes to lysosomes and that such localization is negatively regulated by amino acid availability. Analysis of C9orf72 KO, SMCR8 KO, and double-KO cell lines revealed phenotypes that are consistent with a function for C9orf72 at lysosomes. These include abnormally swollen lysosomes in the absence of C9orf72 and impaired responses of mTORC1 signaling to changes in amino acid availability (a lysosome-dependent process) after depletion of either C9orf72 or SMCR8. Collectively these results identify strong physical and functional interactions between C9orf72 and SMCR8 and support a lysosomal site of action for this protein complex.

Publication types

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

MeSH terms

  • Biophysical Phenomena
  • C9orf72 Protein
  • Carrier Proteins / metabolism
  • HEK293 Cells
  • HeLa Cells
  • Humans
  • Lysosomes / metabolism
  • Mechanistic Target of Rapamycin Complex 1
  • Multiprotein Complexes / metabolism
  • Mutation
  • Phenotype
  • Proteins / metabolism*
  • Proteins / physiology*
  • TOR Serine-Threonine Kinases / metabolism

Substances

  • C9orf72 Protein
  • C9orf72 protein, human
  • Carrier Proteins
  • Multiprotein Complexes
  • Proteins
  • SMCR8 protein, mouse
  • TOR Serine-Threonine Kinases
  • Mechanistic Target of Rapamycin Complex 1