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Caspase cleavage of GFAP produces an assembly-compromised proteolytic fragment that promotes filament aggregation.

Chen, M.H. and Hagemann, T.L. and Quinlan, R.A. and Messing, A. and Perng, M.-D. (2013) 'Caspase cleavage of GFAP produces an assembly-compromised proteolytic fragment that promotes filament aggregation.', ASN neuro., 5 (5). AN20130032.

Abstract

IF (intermediate filament) proteins can be cleaved by caspases to generate proapoptotic fragments as shown for desmin. These fragments can also cause filament aggregation. The hypothesis is that disease-causing mutations in IF proteins and their subsequent characteristic histopathological aggregates could involve caspases. GFAP (glial fibrillary acidic protein), a closely related IF protein expressed mainly in astrocytes, is also a putative caspase substrate. Mutations in GFAP cause A×D (Alexander disease). The overexpression of wild-type or mutant GFAP promotes cytoplasmic aggregate formation, with caspase activation and GFAP proteolysis. In this study, we report that GFAP is cleaved specifically by caspase 6 at VELD225 in its L12 linker domain in vitro. Caspase cleavage of GFAP at Asp225 produces two major cleavage products. While the C-GFAP (C-terminal GFAP) is unable to assemble into filaments, the N-GFAP (N-terminal GFAP) forms filamentous structures that are variable in width and prone to aggregation. The effect of N-GFAP is dominant, thus affecting normal filament assembly in a way that promotes filament aggregation. Transient transfection of N-GFAP into a human astrocytoma cell line induces the formation of cytoplasmic aggregates, which also disrupt the endogenous GFAP networks. In addition, we generated a neo-epitope antibody that recognizes caspase-cleaved but not the intact GFAP. Using this antibody, we demonstrate the presence of the caspase-generated GFAP fragment in transfected cells expressing a disease-causing mutant GFAP and in two mouse models of A×D. These findings suggest that caspase-mediated GFAP proteolysis may be a common event in the context of both the GFAP mutation and excess.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1042/AN20130032
Publisher statement:© 2013 The Author(s) This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC-BY) (http://creativecommons.org/licenses/by/3.0/) which permits unrestricted use, distribution and reproduction in any medium, provided the original work is properly cited.
Date accepted:No date available
Date deposited:13 August 2014
Date of first online publication:October 2013
Date first made open access:No date available

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