Defective recognition of LC3B by mutant SQSTM1/p62 implicates impairment of autophagy as a pathogenic mechanism in ALS-FTLD

Goode, Alice and Butler, Kevin and Long, Jed and Cavey, James and Scott, Daniel and Shaw, Barry and Sollenberger, Jill and Gell, Christopher and Johansen, Terje and Oldham, Neil J. and Searle, Mark S. and Layfield, Robert (2016) Defective recognition of LC3B by mutant SQSTM1/p62 implicates impairment of autophagy as a pathogenic mechanism in ALS-FTLD. Autophagy . ISSN 1554-8635 (In Press)

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Abstract

Growing evidence implicates impairment of autophagy as a candidate pathogenic mechanism in the spectrum of neurodegenerative disorders which includes amyotrophic lateral sclerosis and frontotemporal lobar degeneration (ALS-FTLD). SQSTM1, which encodes the autophagy receptor SQSTM1/p62, is genetically associated with ALS-FTLD, although to date autophagy-relevant functional defects in disease-associated variants have not been described. A key protein-protein interaction in autophagy is the recognition of lipid-anchored form of LC3 (LC3-II) within the phagophore membrane by SQSTM1, mediated through its LC3-interacting region (LIR), and notably some ALS-FTLD mutations map to this region. Here we show that although representing a conservative substitution and predicted to be benign, the ALS-associated L341V mutation of SQSTM1 is defective in recognition of LC3B. We place our observations on a firm quantitative footing by showing the L341V-mutant LIR is associated with a ~3-fold reduction in LC3B binding affinity and using protein NMR we rationalize the structural basis for the effect. This functional deficit is realized in motor neuron-like cells, with the L341V mutant EGFP-mCherry-SQSTM1 less readily incorporated into acidic autophagic vesicles than the wild type. Our data supports a model in which the L341V mutation limits the critical step of SQSTM1 recruitment to the phagophore. The oligomeric nature of SQSTM1, which presents multiple LIRs to template growth of the phagophore, potentially gives rise to avidity effects which amplify the relatively modest impact of any single mutation on LC3B binding. Over the lifetime of a neuron, impaired autophagy could expose a vulnerability, which ultimately tips the balance from cell survival towards cell death.

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Item Type: Article
Additional Information: This is an Accepted Manuscript of an article published by Taylor & Francis in Autophagy on [date of publication], available online: http://www.tandfonline.com/[Article DOI].
Keywords: ALS, Atg8/LC3, autophagy, FTLD, LIR, SQSTM1/p62
Schools/Departments: University of Nottingham UK Campus > Faculty of Science > School of Chemistry
University of Nottingham UK Campus > Faculty of Medicine and Health Sciences > School of Life Sciences
Depositing User: Bramwell, Roseanna
Date Deposited: 21 Mar 2016 11:26
Last Modified: 15 Sep 2016 00:27
URI: http://eprints.nottingham.ac.uk/id/eprint/32410

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