Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.25.1 (proteasome)
 28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Many studies have suggested the ubiquitin-proteasome system played an essential role in the pathogenesis of neurodegenerative disorders. In 1999, we provided evidence that a mutation of the system could directly cause neurodegeneration using the gad mouse. Namely, we identified the gad mutation was caused by an intragenic deletion of a gene encoding ubiquitin C-terminal hydrolase 1(UCH-L1), which is a member of de-ubiquitinating enzyme family. In human, missense mutation of UCH-L1 gene was reported in a German family with Parkinson's disease. As well, the parkin gene product was revealed to be an E3 ubiquitin ligase which recognize a form of alpha-synuclein as a substrate. Thus, the investigation of the ubiquitin-proteasome system should provide a clue for understanding neurodegeneration. We have characterized UCH-L1 and identified candidates of endogenous substrates as well as interacting proteins of UCH-L1. In addition, we found amount of monomeric ubiquitin was decreased in the brain of the gad mouse compared with wild type mice. We have also tried to develop "protein therapy" using UCH-L1 protein with TAT sequence. We observed the protein was delivered to brain after intraperitoneal injection in the wild type mouse. This approach would provide a new therapeutic strategy for neurodegeneration.
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PMID:[The ubiquitin-proteasome system and neurodegeneration]. 1223 99

The alpha-synuclein fibrillation process has been associated with the pathogenesis of several neurodegenerative diseases. Here, we have characterized the cytoplasmic alpha-synuclein aggregates using a fractionation procedure with which different aggregate species can be separated. Overexpression of alpha-synuclein in cells produce two distinct types of aggregates: large juxtanuclear inclusion bodies and small punctate aggregates scattered throughout the cytoplasm. Biochemical fractionation results in an inclusion-enriched fraction and two small aggregate fractions. Electron microscopy and thioflavin S reactivity of the fractions show that the juxtanuclear inclusion bodies are filled with amyloid-like alpha-synuclein fibrils, whereas both the small aggregate fractions contain non-fibrillar spherical aggregates with distinct size distributions. These aggregates appear sequentially, with the smallest population appearing the earliest and the fibrillar inclusions the latest. Based on the structural and kinetic properties, we suggest that the small spherical aggregates are the cellular equivalents of the protofibrils. The proteins that co-exist in the Lewy bodies, such as proteasome subunit, ubiquitin, and hsp70 chaperone, are present in the fibrillar inclusions but absent in the protofibrils, suggesting that these proteins may not be directly involved in the early aggregation stage. As predicted in the aggresome model, disruption of microtubules with nocodazole reduced the number of inclusions and increased the size of the protofibrils. Despite the increased size, the protofibrils remained non-fibrillar, suggesting that the deposition of the protofibrils in the juxtanuclear region is important in fibril formation. This study provides evidence that the cellular fibrillation also involves non-fibrillar intermediate species, and the microtubule-dependent inclusion-forming process is required for the protofibril-to-fibril conversion in cells.
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PMID:Characterization of cytoplasmic alpha-synuclein aggregates. Fibril formation is tightly linked to the inclusion-forming process in cells. 1235 42

Parkinson's disease (PD) is characterized by loss of dopaminergic neurons in the substantia nigra and by the presence of ubiquitinated cytoplasmic inclusions known as Lewy bodies. Alpha-synuclein and Parkin are two of the proteins associated with inherited forms of PD and are found in Lewy bodies. Whereas numerous reports indicate the tendency of alpha-synuclein to aggregate both in vitro and in vivo, no information is available about similar physical properties for Parkin. Here we show that overexpression of Parkin in the presence of proteasome inhibitors leads to the formation of aggresome-like perinuclear inclusions. These eosinophilic inclusions share many characteristics with Lewy bodies, including a core and halo organization, immunoreactivity to ubiquitin, alpha-synuclein, synphilin-1, Parkin, molecular chaperones, and proteasome subunit as well as staining of some with thioflavin S. We propose that the process of Lewy body formation may be akin to that of aggresome-like structures. The tendency of wild-type Parkin to aggregate and form inclusions may have implications for the pathogenesis of sporadic PD.
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PMID:Parkin accumulation in aggresomes due to proteasome impairment. 1236 39

Increasing evidence suggests that proteasomal dysfunction plays a role in the pathogenesis of Lewy body diseases. We have used pharmacological inhibitors of the proteasome to model proteasomal dysfunction in cultured rat cortical neurons. Proteasomal inhibition induced apoptotic death and formation of cytoplasmic ubiquitinated inclusions, which were present only in viable neurons. Actinomycin D, but not a caspase inhibitor, prevented inclusion formation, whereas both agents inhibited cell death. alpha-Synuclein and thioflavin S staining were found within the inclusions. alpha-Synuclein, however, did not appear to be ubiquitinated or aggregated. A dominant-negative mutant of an E2 ubiquitin-conjugating enzyme, cdc34, prevented inclusion formation and attenuated cell death. Our results suggest that in cortical neurons: (a) proteasomal dysfunction plays a role in formation of ubiquitin/alpha-synuclein-positive inclusions, (b) inclusion formation is an active cell process requiring transcription, and (c) ubiquitination of certain proteins is required for inclusion formation and may participate in neuronal death.
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PMID:Proteasomal inhibition-induced inclusion formation and death in cortical neurons require transcription and ubiquitination. 1240 44

Parkinson's disease is characterized by loss of nigral dopaminergic neurons and the presence of cytoplasmic inclusions known as Lewy bodies. alpha-Synuclein and its interacting partner synphilin-1 are among constituent proteins in these aggregates. The presence of ubiquitin and proteasome subunits in these inclusions supports a role for this protein degradation pathway in the processing of proteins involved in this disease. To begin elucidating the kinetics of synphilin-1 in cells, we studied its degradation pathway in HEK293 cells that had been engineered to stably express FLAG-tagged synphilin-1. Pulse-chase experiments revealed that this protein is relatively stable with a half-life of about 16 h. Treatment with proteasome inhibitors resulted in attenuation of degradation and the accumulation of high molecular weight ubiquitinated synphilin-1 in immunoprecipitation/immunoblot experiments. Additionally, proteasome inhibitors stimulated the formation of peri-nuclear inclusions which were immunoreactive for synphilin-1, ubiquitin and alpha-synuclein. Cell viability studies revealed increased susceptibility of synphilin-1 over-expressing cells to proteasomal dysfunction. These observations indicate that synphilin-1 is ubiquitinated and degraded by the proteasome. Accumulation of ubiquitinated synphilin-1 due to impaired clearance results in its aggregation as peri-nuclear inclusions and in poor cell survival.
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PMID:Synphilin-1 degradation by the ubiquitin-proteasome pathway and effects on cell survival. 1242 44

One hypothesis for the etiology of Parkinson's disease (PD) is that subsets of neurons are vulnerable to a failure in proteasome-mediated protein turnover. Here we show that overexpression of mutant alpha-synuclein increases sensitivity to proteasome inhibitors by decreasing proteasome function. Overexpression of parkin decreases sensitivity to proteasome inhibitors in a manner dependent on parkin's ubiquitin-protein E3 ligase activity, and antisense knockdown of parkin increases sensitivity to proteasome inhibitors. Mutant alpha-synuclein also causes selective toxicity to catecholaminergic neurons in primary midbrain cultures, an effect that can be mimicked by the application of proteasome inhibitors. Parkin is capable of rescuing the toxic effects of mutant alpha-synuclein or proteasome inhibition in these cells. Therefore, parkin and alpha-synuclein are linked by common effects on a pathway associated with selective cell death in catecholaminergic neurons.
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PMID:Parkin protects against the toxicity associated with mutant alpha-synuclein: proteasome dysfunction selectively affects catecholaminergic neurons. 1249 18

Parkinson's disease (PD) is characterized pathologically by preferential degeneration of the dopaminergic neurons in the substantia nigra pars compacta (SNc). Nigral cell death is accompanied by the accumulation of a wide range of poorly degraded proteins and the formation of proteinaceous inclusions (Lewy bodies) in dopaminergic neurons. Mutations in the genes encoding alpha-synuclein and two enzymes of the ubiquitin-proteasome system, parkin and ubiquitin C-terminal hydrolase L1, are associated with neurodegeneration in some familial forms of PD. We now show that, in comparison to age-matched controls, alpha-subunits (but not beta-subunits) of 26/20S proteasomes are lost within dopaminergic neurons and 20S proteasomal enzymatic activities are impaired in the SNc in sporadic PD. In addition, while the levels of the PA700 proteasome activator are reduced in the SNc in PD, PA700 expression is increased in other brain regions such as the frontal cortex and striatum. We also found that levels of the PA28 proteasome activator are very low to almost undetectable in the SNc compared to other brain areas in both normal and PD subjects. These findings suggest that failure of the ubiquitin-proteasome system to adequately clear unwanted proteins may underlie vulnerability and degeneration of the SNc in both sporadic and familial PD.
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PMID:Altered proteasomal function in sporadic Parkinson's disease. 1250 66

The accumulation of aggregated alpha-synuclein is thought to contribute to the pathophysiology of Parkinson's disease, but the mechanism of toxicity is poorly understood. Recent studies suggest that aggregated proteins cause toxicity by inhibiting the ubiquitin-dependent proteasomal system. In the present study, we explore how alpha-synuclein interacts with the proteasome. The proteasome exists as a 26 S and a 20 S species. The 26 S proteasome is composed of the 19 S cap and the 20 S core. Aggregated alpha-synuclein strongly inhibited the function of the 26 S proteasome. The IC(50) of aggregated alpha-synuclein for ubiquitin-independent 26 S proteasomal activity was 1 nm. Aggregated alpha-synuclein also inhibited 26 S ubiquitin-dependent proteasomal activity at a dose of 500 nm. In contrast, the IC(50) of aggregated alpha-synuclein for 20 S proteasomal activity was > 1 microm. This suggests that aggregated alpha-synuclein selectively interacts with the 19 S cap. Monomeric alpha-synuclein also inhibited proteasomal activity but with lower affinity and less potency. Recombinant monomeric alpha-synuclein inhibited the activity of the 20 S proteasomal core with an IC(50) > 10 microm, exhibited no inhibition of 26 S ubiquitin-dependent proteasomal activity at doses up to 5 microm, and exhibited only partial inhibition (50%) of the 26 S ubiquitin-independent proteasomal activity at doses up to 10 mm. Binding studies demonstrate that both aggregated and monomeric alpha-synuclein selectively bind to the proteasomal protein S6', a subunit of the 19 S cap. These studies suggest that proteasomal inhibition by aggregated alpha-synuclein could be mediated by interaction with S6'.
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PMID:Aggregated and monomeric alpha-synuclein bind to the S6' proteasomal protein and inhibit proteasomal function. 1255 28

Ubiquitinated inclusions and selective neuronal cell death are considered the pathological hallmarks of Parkinson's disease and other neurodegenerative diseases. Recent genetic, pathological and biochemical evidence suggests that dysfunction of ubiquitin-dependent protein degradation by the proteasome might be a contributing, if not initiating factor in the pathogenesis of these diseases. In neuronal cell culture models inhibition of the proteasome leads to cell death and formation of fibrillar ubiquitin and alpha-synuclein-positive inclusions, thus modeling some aspects of Lewy body diseases. The processes of inclusion formation and neuronal cell death share some common mechanisms, but can also be dissociated at a certain level.
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PMID:Ubiquitinated inclusions and neuronal cell death. 1264 2

The etiopathogenesis of Parkinson's disease (PD) has been elusive. Recently, several lines of evidence have converged to suggest that defects in the ubiquitin-proteasome system and proteolytic stress underlie nigral pathology in both familial and sporadic forms of the illness. In support of this concept, mutations in alpha-synuclein that cause the protein to misfold and resist proteasomal degradation cause familial PD. Similarly, mutations in two enzymes involved in the normal function of the ubiquitin-proteasome system, parkin and ubiquitin C-terminal hydrolase L1, are also associated with hereditary PD. Furthermore, structural and function defects in 26/20S proteasomes with accumulation and aggregation of potentially cytotoxic abnormal proteins have been identified in the substantia nigra pars compacta of patients with sporadic PD. Thus, a defect in protein handling appears to be a common factor in sporadic and the various familial forms of PD. This hypothesis may also account for the vulnerability of the substantia nigra pars compacta in PD, why the disorder is age related, and the nature of the Lewy body. It has also facilitated the development of experimental models that recapitulate the behavioral and pathological features of PD, and hopefully will lead to the development of novel neuroprotective therapies for the disorder.
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PMID:Proteolytic stress: a unifying concept for the etiopathogenesis of Parkinson's disease. 1266


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