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eNeuro. 2017 Jan 31;4(1). pii: ENEURO.0249-16.2017. doi: 10.1523/ENEURO.0249-16.2017. eCollection 2017 Jan-Feb.

The Proline/Arginine Dipeptide from Hexanucleotide Repeat Expanded C9ORF72 Inhibits the Proteasome.

Author information

1
Department of Chemical and Biomolecular Engineering, School of Engineering and Applied Sciences, University of Pennsylvania, Philadelphia, PA, 19104; Department of Biology, College of Arts and Sciences, University of Pennsylvania, Philadelphia, PA, 19104.
2
Department of Biochemistry, College of Arts and Sciences, University of Pennsylvania , Philadelphia, PA, 19104.
3
Division of Neurology, Department of Pediatrics, Research Institute, Children's Hospital of Philadelphia , Philadelphia, PA, 19104.
4
Department of Biochemistry and Molecular Biology, Seoul National University College of Medicine , Seoul 03080, Republic of Korea.
5
Department of Neurology, University of Michigan , Ann Arbor, MI, 48109.
6
Division of Neurology, Department of Pediatrics, Research Institute, Children's Hospital of Philadelphia, Philadelphia, PA, 19104; Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104.

Abstract

An intronic hexanucleotide repeat expansion (HRE) mutation in the C9ORF72 gene is the most common cause of familial ALS and frontotemporal dementia (FTD) and is found in ∼7% of individuals with apparently sporadic disease. Several different diamino acid peptides can be generated from the HRE by noncanonical translation (repeat-associated non-ATG translation, or RAN translation), and some of these peptides can be toxic. Here, we studied the effects of two arginine containing RAN translation products [proline/arginine repeated 20 times (PR20) and glycine/arginine repeated 20 times (GR20)] in primary rat spinal cord neuron cultures grown on an astrocyte feeder layer. We find that PR20 kills motor neurons with an LD50 of 2 µM, but in contrast to the effects of other ALS-causing mutant proteins (i.e., SOD or TDP43), PR20 does not evoke the biochemical signature of mitochondrial dysfunction, ER stress, or mTORC down-regulation. PR20 does result in a time-dependent build-up of ubiquitylated substrates, and this is associated with a reduction of flux through both autophagic and proteasomal degradation pathways. GR20, however, does not have these effects. The effects of PR20 on the proteasome are likely to be direct because (1) PR20 physically associates with proteasomes in biochemical assays, and (2) PR20 inhibits the degradation of a ubiquitylated test substrate when presented to purified proteasomes. Application of a proteasomal activator (IU1) blocks the toxic effects of PR20 on motor neuron survival. This work suggests that proteasomal activators have therapeutic potential in individuals with C9ORF72 HRE.

KEYWORDS:

ALS; frontotemporal dementia; lysosome-autophagy; motor neuron; proteasome

PMID:
28197542
PMCID:
PMC5282547
DOI:
10.1523/ENEURO.0249-16.2017
[Indexed for MEDLINE]
Free PMC Article

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