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

Chen, M.H.; Hagemann, T.L.; Quinlan, R.A.; Messing, A.; Perng, M.-D.

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.

Citation

Chen, M., Hagemann, T., Quinlan, R., Messing, A., & Perng, M. (2013). Caspase cleavage of GFAP produces an assembly-compromised proteolytic fragment that promotes filament aggregation. Conversations about pedagogy and teaching underpinned by research enquiry, 5(5), https://doi.org/10.1042/an20130032

• Journal Article Type: Article
• Publication Date: Oct 1, 2013
• Deposit Date: May 1, 2014
• Publicly Available Date: Aug 13, 2014
• Journal: ASN NEURO
• Electronic ISSN: 1759-9091
• Publisher: Portland Press
• Peer Reviewed: Peer Reviewed
• Volume: 5
• Issue: 5
• DOI: https://doi.org/10.1042/an20130032
• Public URL: https://durham-repository.worktribe.com/output/1433610