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Ubiquitin-specific protease 14 modulates degradation of cellular prion protein.

ABSTRACT: Prion diseases are fatal neurodegenerative disorders characterized by the accumulation of prion protein (PrP(C)). To date, there is no effective treatment for the disease. The accumulated PrP, termed PrP(Sc), forms amyloid fibrils and could be infectious. It has been suggested that PrP(Sc) 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 PrP(C). 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 PrP(C), as well as PrP(Sc), levels in prion-infected neuronal cells. Overexpression of the dominant negative mutant form of USP14 reduced PrP(Sc), whereas wildtype USP14 increased PrP(Sc) 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 PrP(Sc) clearance caused by USP14 might contribute greatly to the development of therapeutic strategies for prion diseases.

SUBMITTER: Homma T

PROVIDER: S-EPMC4462021 | biostudies-literature | 2015 Jun

REPOSITORIES: biostudies-literature

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Ubiquitin-specific protease 14 modulates degradation of cellular prion protein.

Homma Takujiro T Ishibashi Daisuke D Nakagaki Takehiro T Fuse Takayuki T Mori Tsuyoshi T Satoh Katsuya K Atarashi Ryuichiro R Nishida Noriyuki N

Scientific reports 20150610

Prion diseases are fatal neurodegenerative disorders characterized by the accumulation of prion protein (PrP(C)). To date, there is no effective treatment for the disease. The accumulated PrP, termed PrP(Sc), forms amyloid fibrils and could be infectious. It has been suggested that PrP(Sc) 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 sy ...[more]

PMID: 26061634

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Project description:BackgroundUbiquitin-specific protease 14 (USP14) is one of three proteasome-associated deubiquitinating enzymes that remove ubiquitin from proteasomal substrates prior to their degradation. In vitro evidence suggests that inhibiting USP14's catalytic activity alters the turnover of ubiquitinated proteins by the proteasome, although whether protein degradation is accelerated or delayed seems to be cell-type and substrate specific. For example, combined inhibition of USP14 and the proteasomal deubiquitinating enzyme UCH37 halts protein degradation and promotes apoptosis in multiple myeloma cells, whereas USP14 inhibition alone accelerates the degradation of aggregate-prone proteins in immortalized cell lines. These findings have prompted interest in USP14 as a therapeutic target both inside and outside of the nervous system. However, loss of USP14 in the spontaneously occurring ataxia mouse mutant leads to a dramatic neuromuscular phenotype and early perinatal lethality, suggesting that USP14 inhibition may have adverse consequences in the nervous system. We therefore expressed a catalytically inactive USP14 mutant in the mouse nervous system to determine whether USP14's catalytic activity is required for neuromuscular junction (NMJ) structure and function.ResultsMice expressing catalytically inactive USP14 in the nervous system exhibited motor deficits, altered NMJ structure, and synaptic transmission deficits that were similar to what is observed in the USP14-deficient ataxia mice. Acute pharmacological inhibition of USP14 in wild type mice also reduced NMJ synaptic transmission. However, there was no evidence of altered proteasome activity when USP14 was inhibited either genetically or pharmacologically. Instead, these manipulations increased the levels of non-proteasome targeting ubiquitin conjugates. Specifically, we observed enhanced proteasome-independent ubiquitination of mixed lineage kinase 3 (MLK3). Consistent with the direct activation of MLK3 by ubiquitination, we also observed increased activation of its downstrea targets MAP kinase kinase 4 (MKK4) and c-Jun N-terminal kinase (JNK). In vivo inhibition of JNK improved motor function and synapse structure in the USP14 catalytic mutant mice.ConclusionsUSP14's catalytic activity is required for nervous system structure and function and has an ongoing role in NMJ synaptic transmission. By regulating the ubiquitination status of protein kinases, USP14 can coordinate the activity of intracellular signaling pathways that control the development and activity of the NMJ.

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Ubiquitin-specific protease 14 modulates degradation of cellular prion protein.

Publications

Ubiquitin-specific protease 14 modulates degradation of cellular prion protein.

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