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Neurobiol Dis. 2018 Aug;116:155-165. doi: 10.1016/j.nbd.2018.05.009. Epub 2018 May 22.

Translation of dipeptide repeat proteins from the C9ORF72 expanded repeat is associated with cellular stress.

Author information

1
Department of Neurology, University of Chicago Medical Center, 5841 S. Maryland Ave., Chicago, IL 60637, United States.
2
Laboratory of Mammalian Cell Biology and Development, The Rockefeller University, 1230 York Ave., Box 300, NY, NY, 10021-6399, United States.
3
Department of Neurology, University of Chicago Medical Center, 5841 S. Maryland Ave., Chicago, IL 60637, United States. Electronic address: rroos@neurology.bsd.uchicago.edu.

Abstract

Expansion of a hexanucleotide repeat (HRE), GGGGCC, in the C9ORF72 gene is recognized as the most common cause of familial amyotrophic lateral sclerosis (FALS), frontotemporal dementia (FTD) and ALS-FTD, as well as 5-10% of sporadic ALS. Despite the location of the HRE in the non-coding region (with respect to the main C9ORF72 gene product), dipeptide repeat proteins (DPRs) that are thought to be toxic are translated from the HRE in all three reading frames from both the sense and antisense transcript. Here, we identified a CUG that has a good Kozak consensus sequence as the translation initiation codon. Mutation of this CTG significantly suppressed polyglycine-alanine (GA) translation. GA was translated when the G4C2 construct was placed as the second cistron in a bicistronic construct. CRISPR/Cas9-induced knockout of a non-canonical translation initiation factor, eIF2A, impaired GA translation. Transfection of G4C2 constructs induced an integrated stress response (ISR), while triggering the ISR led to a continuation of translation of GA with a decline in conventional cap-dependent translation. These in vitro observations were confirmed in chick embryo neural cells. The findings suggest that DPRs translated from an HRE in C9ORF72 aggregate and lead to an ISR that then leads to continuing DPR production and aggregation, thereby creating a continuing pathogenic cycle.

KEYWORDS:

C9ORF72; Dipeptide protein repeats (DPRs); Hexanucleotide repeat expansions (HREs); Integrated stress response (ISR); Internal ribosome entry site (IRES); Repeat associated non-AUG (RAN) translation; Unconventional translation; eIF2A

PMID:
29792928
DOI:
10.1016/j.nbd.2018.05.009

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