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Open AccessArticle

C9orf72 Proteins Regulate Autophagy and Undergo Autophagosomal or Proteasomal Degradation in a Cell Type-Dependent Manner

1
A. I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Neulaniementie 2, 70211 Kuopio, Finland
2
Institute of Biomedicine, Yliopistonranta 1E, University of Eastern Finland, 70211 Kuopio, Finland
3
Unit of Clinical Neuroscience, Neurology, University of Oulu, P.O. Box 8000, University of Oulu, 90014 Oulu, Finland
4
MRC Oulu, Oulu University Hospital, P.O. Box 8000, University of Oulu, 90014 Oulu, Finland
*
Author to whom correspondence should be addressed.
Cells 2019, 8(10), 1233; https://doi.org/10.3390/cells8101233
Received: 16 August 2019 / Revised: 8 October 2019 / Accepted: 10 October 2019 / Published: 10 October 2019
(This article belongs to the Special Issue Autophagy in Neurodegenerative Diseases)
Dysfunctional autophagy or ubiquitin-proteasome system (UPS) are suggested to underlie abnormal protein aggregation in neurodegenerative diseases. Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS)-associated C9orf72 is implicated in autophagy, but whether it activates or inhibits autophagy is partially controversial. Here, we utilized knockdown or overexpression of C9orf72 in mouse N2a neuroblastoma cells or cultured neurons to elucidate the potential role of C9orf72 proteins in autophagy and UPS. Induction of autophagy in C9orf72 knockdown N2a cells led to decreased LC3BI to LC3BII conversion, p62 degradation, and formation of LC3-containing autophagosomes, suggesting compromised autophagy. Proteasomal activity was slightly decreased. No changes in autophagy nor proteasomal activity in C9orf72-overexpressing N2a cells were observed. However, in these cells, autophagy induction by serum starvation or rapamycin led to significantly decreased C9orf72 levels. The decreased levels of C9orf72 in serum-starved N2a cells were restored by the proteasomal inhibitor lactacystin, but not by the autophagy inhibitor bafilomycin A1 (BafA1) treatment. These data suggest that C9orf72 undergoes proteasomal degradation in N2a cells during autophagy. Lactacystin significantly elevated C9orf72 levels in N2a cells and neurons, further suggesting UPS-mediated regulation. In rapamycin and BafA1-treated neurons, C9orf72 levels were significantly increased. Altogether, these findings corroborate the previously suggested regulatory role for C9orf72 in autophagy and suggest cell type-dependent regulation of C9orf72 levels via UPS and/or autophagy. View Full-Text
Keywords: amyotrophic lateral sclerosis; autophagy; C9orf72; frontotemporal dementia; proteasomal degradation; ubiquitin-proteasome system amyotrophic lateral sclerosis; autophagy; C9orf72; frontotemporal dementia; proteasomal degradation; ubiquitin-proteasome system
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Leskelä, S.; Huber, N.; Rostalski, H.; Natunen, T.; Remes, A.M.; Takalo, M.; Hiltunen, M.; Haapasalo, A. C9orf72 Proteins Regulate Autophagy and Undergo Autophagosomal or Proteasomal Degradation in a Cell Type-Dependent Manner. Cells 2019, 8, 1233.

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