Loss of C9orf72 Enhances Autophagic Activity via Deregulated mTOR and TFEB Signaling

PLoS Genet. 2016 Nov 22;12(11):e1006443. doi: 10.1371/journal.pgen.1006443. eCollection 2016 Nov.

Abstract

The most common cause of the neurodegenerative diseases amyotrophic lateral sclerosis and frontotemporal dementia is a hexanucleotide repeat expansion in C9orf72. Here we report a study of the C9orf72 protein by examining the consequences of loss of C9orf72 functions. Deletion of one or both alleles of the C9orf72 gene in mice causes age-dependent lethality phenotypes. We demonstrate that C9orf72 regulates nutrient sensing as the loss of C9orf72 decreases phosphorylation of the mTOR substrate S6K1. The transcription factor EB (TFEB), a master regulator of lysosomal and autophagy genes, which is negatively regulated by mTOR, is substantially up-regulated in C9orf72 loss-of-function animal and cellular models. Consistent with reduced mTOR activity and increased TFEB levels, loss of C9orf72 enhances autophagic flux, suggesting that C9orf72 is a negative regulator of autophagy. We identified a protein complex consisting of C9orf72 and SMCR8, both of which are homologous to DENN-like proteins. The depletion of C9orf72 or SMCR8 leads to significant down-regulation of each other's protein level. Loss of SMCR8 alters mTOR signaling and autophagy. These results demonstrate that the C9orf72-SMCR8 protein complex functions in the regulation of metabolism and provide evidence that loss of C9orf72 function may contribute to the pathogenesis of relevant diseases.

MeSH terms

  • Alleles
  • Amyotrophic Lateral Sclerosis / genetics
  • Amyotrophic Lateral Sclerosis / metabolism
  • Amyotrophic Lateral Sclerosis / pathology
  • Animals
  • Autophagy / genetics
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / biosynthesis
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / genetics*
  • C9orf72 Protein
  • Carrier Proteins / genetics*
  • DNA Repeat Expansion / genetics*
  • Frontotemporal Dementia / genetics*
  • Frontotemporal Dementia / metabolism
  • Frontotemporal Dementia / pathology
  • Gene Expression Regulation
  • Guanine Nucleotide Exchange Factors / genetics*
  • Humans
  • Mice
  • Phenotype
  • Ribosomal Protein S6 Kinases, 90-kDa / biosynthesis
  • Signal Transduction / genetics
  • TOR Serine-Threonine Kinases / biosynthesis
  • TOR Serine-Threonine Kinases / genetics*

Substances

  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
  • C9orf72 Protein
  • C9orf72 protein, mouse
  • Carrier Proteins
  • Guanine Nucleotide Exchange Factors
  • SMCR8 protein, mouse
  • Tcfeb protein, mouse
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • Ribosomal Protein S6 Kinases, 90-kDa
  • Rps6ka1 protein, mouse