Puromycin-sensitive aminopeptidase protects against aggregation-prone proteins via autophagy

Department of Medical Genetics, Cambridge Institute for Medical Research, University of Cambridge, Cambridge, UK.
Human Molecular Genetics (Impact Factor: 6.39). 12/2010; 19(23):4573-86. DOI: 10.1093/hmg/ddq385
Source: PubMed


A major function of proteasomes and macroautophagy is to eliminate misfolded potentially toxic proteins. Mammalian proteasomes, however, cannot cleave polyglutamine (polyQ) sequences and seem to release polyQ-rich peptides. Puromycin-sensitive aminopeptidase (PSA) is the only cytosolic enzyme able to digest polyQ sequences. We tested whether PSA can protect against accumulation of polyQ fragments. In cultured cells, Drosophila and mouse muscles, PSA inhibition or knockdown increased aggregate content and toxicity of polyQ-expanded huntingtin exon 1. Conversely, PSA overexpression decreased aggregate content and toxicity. PSA inhibition also increased the levels of polyQ-expanded ataxin-3 as well as mutant α-synuclein and superoxide dismutase 1. These protective effects result from an unexpected ability of PSA to enhance macroautophagy. PSA overexpression increased, and PSA knockdown or inhibition reduced microtubule-associated protein 1 light chain 3-II (LC3-II) levels and the amount of protein degradation sensitive to inhibitors of lysosomal function and autophagy. Thus, by promoting autophagic protein clearance, PSA helps protect against accumulation of aggregation-prone proteins and proteotoxicity.

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    • "This hydrolytic activity of ERAPs is essential for generating peptides with appropriate size for binding to major histocompatibility complex type I, which enhances antigen presentation (Kloetzel and Ossendorp, 2004; Saveanu et al., 2009; Van Endert, 2011; Weimershaus et al., 2013). PSA activity of proteasome is the main responsible for the degradation of polyQ, which are highly toxic and associated with neurodegenerative diseases when accumulated (Bhutani et al., 2007; Menzies et al., 2010). Increased PSA activity found in low density microsomal fraction (proteasome-containing fraction) (Brooks et al., 2000) should affect the immune system in obese. "
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    • "Finally, as we have shown that EGb 761 reduces the amount of polyQ aggregates we tested the possible involvement of autophagy in the clearance of polyQ aggregates [42]. Therefore, we analyzed the general autophagosomal flux in HEK293 cells expressing htt_Q103 treated with EGb 761 or vehicle (Figures 4(d) and 4(e)), followed by a challenge with 1 μM lysosome inhibitor bafilomycin A1. "
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    • "As a consequence, polyQ peptides that have a high propensity to aggregate into fibrillar assemblies (Wetzel 2012) are released from the proteasome during the degradation of huntingtin (Holmberg et al. 2004; Venkatraman et al. 2004) and other polyQ proteins. That free polyQ peptides are not readily detected in cells can be due to their immediate capture by DNAJB6-like chaperones and subsequent degradation by peptidases or autophagy (Menzies et al. 2010). If such processing fails, polyQ peptides would, however, become enriched and immediately seed aggregation into both main and side chain hydrogen-bonded fibrillar structures (Berryman et al. 2009; Streets et al. 2013). "
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