Dataset Information

Ubiquitin-specific protease 14 regulates c-Jun N-terminal kinase signaling at the neuromuscular junction.

ABSTRACT:

Background

Ubiquitin-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.

Results

Mice 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.

Conclusions

USP14'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.

SUBMITTER: Vaden JH

PROVIDER: S-EPMC4417291 | biostudies-literature | 2015 Jan

REPOSITORIES: biostudies-literature

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Publications

Ubiquitin-specific protease 14 regulates c-Jun N-terminal kinase signaling at the neuromuscular junction.

Vaden Jada H JH Bhattacharyya Bula J BJ Chen Ping-Chung PC Watson Jennifer A JA Marshall Andrea G AG Phillips Scott E SE Wilson Julie A JA King Gwendalyn D GD Miller Richard J RJ Wilson Scott M SM

Molecular neurodegeneration 20150110

<h4>Background</h4>Ubiquitin-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 proteas ...[more]

PMID: 25575639

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Project description:Terminal Schwann cells are non-myelinating glial cells localized to the neuromuscular junction. They play an important role in regulating many aspects of neuromuscular junction form and function, in health and during disease. However, almost all previous studies of mammalian terminal Schwann cells have used rodent models. Despite a growing awareness of differences in the cellular and molecular anatomy of rodent and human neuromuscular junctions, it remains unclear as to whether these differences also extend to the terminal Schwann cells. Here, we have adapted immunohistochemical protocols to facilitate visualization and comparative morphometric analyses of terminal Schwann cells at the human and mouse neuromuscular junction. We labelled terminal Schwann cells in the peroneus brevis muscle in six adult mice and five humans with antibodies against S100 protein. All human neuromuscular junctions were associated with at least one terminal Schwann cell, consistent with findings from other species, with an average of ∼1.7 terminal Schwann cells per neuromuscular junction in both humans and mice. In contrast, human terminal Schwann cells were significantly smaller than those of mice (P ≤ 0.01), in keeping with differences in overall synaptic size. Human terminal Schwann cell cytoplasm extended significantly beyond the synaptic boundaries of the neuromuscular junction, whereas terminal Schwann cells in mice were largely restricted to the synapse. Moreover, there was a significant difference in the location of terminal Schwann cell nuclei (P ≤ 0.01), with human terminal Schwann cells having their nuclear compartment located beyond the perimeter of the synapse more than the mouse. Taken together, these findings demonstrate that terminal Schwann cells at the human neuromuscular junction have notable differences in their morphology and synaptic relationships compared to mice. These fundamental differences need to be considered when translating the findings of both neuromuscular junction biology and pathology from rodents to humans.

Dataset Information

Ubiquitin-specific protease 14 regulates c-Jun N-terminal kinase signaling at the neuromuscular junction.

Background

Results

Conclusions

Publications

Ubiquitin-specific protease 14 regulates c-Jun N-terminal kinase signaling at the neuromuscular junction.

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