Ubiquitin-specific protease 14 modulates degradation of cellular prion protein

Abstract

Prion diseases are fatal neurodegenerative disorders characterized by the accumulation of prion protein (PrPC). To date, there is no effective treatment for the disease. The accumulated PrP, termed PrPSc, forms amyloid fibrils and could be infectious. It has been suggested that PrPSc is abnormally folded and resistant to proteolytic degradation, and also inhibits proteasomal functions in infected cells, thereby inducing neuronal death. Recent work indicates that the ubiquitin-proteasome system is involved in quality control of PrPC. To reveal the significance of prion protein ubiqitination, we focused on ubiquitin-specific protease 14 (USP14), a deubiqutinating enzyme that catalyzes trimming of polyubiquitin chains and plays a role in regulation of proteasomal processes. Results from the present study showed that treatment with a selective inhibitor of USP14 reduced PrPC, as well as PrPSc, levels in prion-infected neuronal cells. Overexpression of the dominant negative mutant form of USP14 reduced PrPSc, whereas wildtype USP14 increased PrPSc in prion-infected cells. These results suggest that USP14 prevents degradation of both normal and abnormal PrP. Collectively, a better understanding about the regulation of PrPSc clearance caused by USP14 might contribute greatly to the development of therapeutic strategies for prion diseases.

Meddling with Fate: The Proteasomal Deubiquitinating Enzymes

“…Loss of Ubp6 in yeast destabilizes several model and physiological proteasome substrates in vivo [45], and inhibition of the DUB activity of Usp14 in mammalian cells stimulates the degradation of specific proteasome substrates [41,102–108]. Accordingly, when Usp14 is activated by AKT, the degradation of multiple proteins appears to be suppressed [73].…”

“…Since the original study on IU1, several groups have reported proteins that show accelerated degradation under IU1 treatment, including the Prion protein PrP [102,103], cGAS [108], phosphorylated tyrosine hydroxylase [104], the androgen receptor [105], vimentin [106], aurora kinase [111], CREB-binding protein [75], YFP-tagged CD3δ [107], and the model UPS substrate GFP u [107]. In many of these studies, the on-target nature of the IU1 effect is supported by genetic confirmation [102,105–108].…”

“…In many of these studies, the on-target nature of the IU1 effect is supported by genetic confirmation [102,105–108]. For example, PrP is degraded more rapidly in the presence of IU1 or when Usp14 expression is reduced, and more slowly when Usp14 is overexpressed [102]. Like PrP, cGAS, a key regulator of innate immunity, is an intriguing target [108].…”

USP14 deubiquitinates proteasome-bound substrates that are ubiquitinated at multiple sites

“…USP14 negatively regulates proteasome activity by ubiquitin chain disassembly as well as by a noncatalytic mechanism 1–6 . USP14 inhibitors produce selective effects on the turnover of proteasome substrates 3,8 , suggesting that the rate at which USP14 disassembles proteasome-bound ubiquitin chains may depend on the nature of the substrate. We test this hypothesis in the present work.…”

Targeting the 26S Proteasome To Protect Against Proteotoxic Diseases

“…As a result, deubiquitinated proteins are released from the 26S proteasome undigested [32]. It is possible to accelerate 26S proteasome-mediated proteolysis using small-molecule USP14 inhibitors which have shown utility in cell cultures and primary neurons [33–35]. …”