Parkin ubiquitinates the alpha-synuclein-interacting protein, synphilin-1: implications for Lewy-body formation in Parkinson disease

Parkinson's Disease and Cognitive Impairment

Parkinson's disease (PD) is a progressive neurodegenerative disease primarily characterized by the hallmarks of motor symptoms, such as tremor, bradykinesia, rigidity, and postural instability. However, through clinical investigations in patients and experimental findings in animal models of Parkinson's disease for years, it is now well recognized that Parkinson's disease is more than just a motor-deficit disorder. The majority of Parkinson's disease patients suffer from nonmotor disabilities, for instance, cognitive impairment, autonomic dysfunction, sensory dysfunction, and sleep disorder. So far, anti-PD prescriptions and surgical treatments have been mainly focusing on motor dysfunctions, leaving cognitive impairment a marginal clinical field. Within the nonmotor symptoms, cognitive impairment is one of the most common and significant aspects of Parkinson's disease, and cognitive deficits such as dysexecutive syndrome and visuospatial disturbances could seriously affect the quality of life, reduce life expectancy, prolong the duration of hospitalization, and therefore increase burdens of caregiver and medical costs. In this review, we have done a retrospective study of the recent related researches on epidemiology, clinical manifestation and diagnosis, genetics, and potential treatment of cognitive deficits in Parkinson's disease, aiming to provide a summary of cognitive impairment in Parkinson's disease and make it easy for clinicians to tackle this challenging issue in their future practice.

Effects of Intrinsic and Extrinsic Factors on Aggregation of Physiologically Important Intrinsically Disordered Proteins

Misfolding and aggregation of proteins and peptides play an important role in a number of diseases as well as in many physiological processes. Many of the proteins that misfold and aggregate in vivo are intrinsically disordered. Protein aggregation is a complex multistep process, and aggregates can significantly differ in morphology, structure, stability, cytotoxicity, and self-propagation ability. The aggregation process is influenced by both intrinsic (e.g., mutations and expression levels) and extrinsic (e.g., polypeptide chain truncation, macromolecular crowding, posttranslational modifications, as well as interaction with metal ions, other small molecules, lipid membranes, and chaperons) factors. This review examines the effect of a variety of these factors on aggregation of physiologically important intrinsically disordered proteins.

Effect of Schiff base Cu(II) complexes on signaling pathways in HT-29 cells

Schiff base copper (II) complexes are known for their anticancer, antifungal, antiviral and anti‑inflammatory activities. The aim of the current study was to investigate biological effects of Schiff base Cu (II) complexes (0.001‑100 µmol/l)‑[Cu2(sal‑D, L‑glu)2(isoquinoline)2]·2C2H5OH (1), [Cu(sal‑5‑met‑L‑glu)(H2O)].H2O (2), [Cu(ethanol)2(imidazole)4][Cu2(sal‑D, L-glu)2(imidazole)2] (3), [Cu(sal‑D,L‑glu)(2‑methylimidazole)] (4) on the human colon carcinoma cells HT‑29, the mouse noncancerous cell line NIH‑3T3 and the human noncancerous fibroblast cell line VH10. The results suggested that Cu (II) complexes exhibit cytotoxic effects against the HT‑29 cell line, while complexes 3 and 4 were the most effective. Subsequent to 72 h of incubation, apoptosis was observed in the HT‑29 cells induced by Cu (II) complexes 1 (0.1, 1, 10 and 50 µmol/l), 2 (1, 10, 50 and 100 µmol/l), 3 (0.01, 1, 10 and 50 µmol/l) and 4 (0.01, 0.1, 1 and 10 µmol/l). The apoptotic pathways activated by the Cu (II) complexes were identified. The results indicated that complexes 2, 3 and 4 were able to induce the mitochondria‑dependent pathway of apoptosis in HT‑29 cells, while complex 1 was obsered to activate the extrinsic pathway of apoptosis. The levels of the anti‑apoptotic protein Bcl‑2 were reduced and those of the pro‑apoptotic protein Bax increased following treatment with complexes 2, 3 and 4. Complex 1 had no effect on Bax protein expression. Complexes 2 and 3 induced elevation of cytochrome c (cyt c), while complex 4 induced a time‑dependent elevation of cyt c levels. No cyt c was detected in HT‑29 cells exposed to complex 1, suggesting that Cu (II) complexes activated the extrinsic pathway of apoptosis. The results from the current study in addition to previous studies suggest that Schiff base Cu (II) complexes have potential as novel anticancer drugs.

Potential Role of Caffeine in the Treatment of Parkinson's Disease

Parkinson’s disease [PD] is the second most common neurodegenerative disorder after Alzheimer’s disease, affecting 1% of the population over the age of 55. The underlying neuropathology seen in PD is characterised by progressive loss of dopaminergic neurons in the substantia nigra pars compacta with the presence of Lewy bodies. The Lewy bodies are composed of aggregates of α-synuclein. The motor manifestations of PD include a resting tremor, bradykinesia, and muscle rigidity. Currently there is no cure for PD and motor symptoms are treated with a number of drugs including levodopa [L-dopa]. These drugs do not delay progression of the disease and often provide only temporary relief. Their use is often accompanied by severe adverse effects. Emerging evidence from both in vivo and in vitro studies suggests that caffeine may reduce parkinsonian motor symptoms by antagonising the adenosine A_2A receptor, which is predominately expressed in the basal ganglia. It is hypothesised that caffeine may increase the excitatory activity in local areas by inhibiting the astrocytic inflammatory processes but evidence remains inconclusive. In addition, the co-administration of caffeine with currently available PD drugs helps to reduce drug tolerance, suggesting that caffeine may be used as an adjuvant in treating PD. In conclusion, caffeine may have a wide range of therapeutic effects which are yet to be explored, and therefore warrants further investigation in randomized clinical trials.

A genome-wide imaging-based screening to identify genes involved in synphilin-1 inclusion formation in Saccharomyces cerevisiae

Synphilin-1 is a major component of Parkinson's disease (PD) inclusion bodies implicated in PD pathogenesis. However, the machinery controlling synphilin-1 inclusion formation remains unclear. Here, we investigated synphilin-1 inclusion formation using a systematic genome-wide, high-content imaging based screening approach (HCI) in the yeast Saccharomyces cerevisiae. By combining with a secondary screening for mutants showing significant changes on fluorescence signal intensity, we filtered out hits that significantly decreased the expression level of synphilin-1. We found 133 yeast genes that didn't affect synphilin-1 expression but that were required for the formation of synphilin-1 inclusions. Functional enrichment and physical interaction network analysis revealed these genes to encode for functions involved in cytoskeleton organization, histone modification, sister chromatid segregation, glycolipid biosynthetic process, DNA repair and replication. All hits were confirmed by conventional microscopy. Complementation assays were performed with a selected group of mutants, results indicated that the observed phenotypic changes in synphilin-1 inclusion formation were directly caused by the loss of corresponding genes of the deletion mutants. Further growth assays of these mutants showed a significant synthetic sick effect upon synphilin-1 expression, which supports the hypothesis that matured inclusions represent an end stage of several events meant to protect cells against the synphilin-1 cytotoxicity.

The clinical symptoms of Parkinson's disease

In this review, the clinical features of Parkinson's disease, both motor and non-motor, are described in the context of the progression of the disease. Also briefly discussed are the major treatment strategies and their complications. Parkinson's disease is a slowly progressing neurodegenerative disorder, causing impaired motor function with slow movements, tremor and gait and balance disturbances. A variety of non-motor symptoms are common in Parkinson's disease. They include disturbed autonomic function with orthostatic hypotension, constipation and urinary disturbances, a variety of sleep disorders and a spectrum of neuropsychiatric symptoms. This article describes the different clinical symptoms that may occur and the clinical course of the disease. This article is part of a special issue on Parkinson disease.

Silica-coated magnetic nanoparticles impair proteasome activity and increase the formation of cytoplasmic inclusion bodies in vitro

The potential toxicity of nanoparticles, particularly to neurons, is a major concern. In this study, we assessed the cytotoxicity of silica-coated magnetic nanoparticles containing rhodamine B isothiocyanate dye (MNPs@SiO2(RITC)) in HEK293 cells, SH-SY5Y cells, and rat primary cortical and dopaminergic neurons. In cells treated with 1.0 μg/μl MNPs@SiO2(RITC), the expression of several genes related to the proteasome pathway was altered, and proteasome activity was significantly reduced, compared with control and with 0.1 μg/μl MNPs@SiO2(RITC)-treated cells. Due to the reduction of proteasome activity, formation of cytoplasmic inclusions increased significantly in HEK293 cells over-expressing the α-synuclein interacting protein synphilin-1 as well as in primary cortical and dopaminergic neurons. Primary neurons, particularly dopaminergic neurons, were more vulnerable to MNPs@SiO2(RITC) than SH-SY5Y cells. Cellular polyamines, which are associated with protein aggregation, were significantly altered in SH-SY5Y cells treated with MNPs@SiO2(RITC). These findings highlight the mechanisms of neurotoxicity incurred by nanoparticles.

hVMAT2: A Target of Individualized Medication for Parkinson's Disease

Vesicular monoamine transporter 2 (VMAT2) is responsible for sequestering cytosolically toxic dopamine into intracellular secretory vesicles. Animal genetic studies have suggested that reduced VMAT2 activity contributes to the genetic etiology of Parkinson's disease (PD), but this role has not been established in humans. Based on human genetic association and meta-analysis, we first confirm the human VMAT2 (hVMAT2 or SLC18A2) promoter as a risk factor for PD in both family and unrelated US white people: marker rs363324 at -11.5 kb in the hVMAT2 promoter is reproducibly associated with PD in a cohort of nuclear families (p = 0.04506 in early-onset PD) and 3 unrelated US white people (meta-analysis p = 0.01879). In SH-SY5Y cells, low activity-associated hVMAT2 promoter confers high methylpiperidinopyrazole iodide cytotoxicity, which is likely attributed to functional polymorphisms bound by nuclear proteins. Interestingly, treatments with the dopamine neuron-protecting agent puerarin upregulates the promoter activity in a haplotype- and cell line-dependent manner. These pharmacogenetic findings suggest that hVMAT2 could be a risk factor and imply it as a target of genetic medications for PD.

Molecular Features Underlying Neurodegeneration Identified through In Vitro Modeling of Genetically Diverse Parkinson's Disease Patients

The fact that Parkinson's disease (PD) can arise from numerous genetic mutations suggests a unifying molecular pathology underlying the various genetic backgrounds. To address this hypothesis, we took an integrated approach utilizing in vitro disease modeling and comprehensive transcriptome profiling to advance our understanding of PD progression and the concordant downstream signaling pathways across divergent genetic predispositions. To model PD in vitro, we generated neurons harboring disease-causing mutations from patient-specific, induced pluripotent stem cells (iPSCs). We observed signs of degeneration in midbrain dopaminergic neurons, reflecting the cardinal feature of PD. Gene expression signatures of PD neurons provided molecular insights into disease phenotypes observed in vitro, including oxidative stress vulnerability and altered neuronal activity. Notably, PD neurons show that elevated RBFOX1, a gene previously linked to neurodevelopmental diseases, underlies a pattern of alternative RNA-processing associated with PD-specific phenotypes.

Polyubiquitination of apurinic/apyrimidinic endonuclease 1 by Parkin

Apurinic/apyrimidinic endonuclease 1 (APE1) is an essential protein crucial for repair of oxidized DNA damage not only in genomic DNA but also in mitochondrial DNA. Parkin, a tumor suppressor and Parkinson's disease (PD) associated gene, is an E3 ubiquitin ligase crucial for mitophagy. Although DNA damage is known to induce mitochondrial stress, Parkin's role in regulating DNA repair proteins has not been elucidated. In this study, we examined the possibility of Parkin-dependent ubiquitination of APE1. Ectopically expressed APE1 was degraded by Parkin and PINK1 via polyubiquitination in mouse embryonic fibroblast cells. PD-causing mutations in Parkin and PINK1 abrogated APE1 ubiquitination. Interaction of APE1 with Parkin was observed by co-immunoprecipitation, proximity ligation assay, and co-localization in the cytoplasm. N-terminal deletion of 41 amino acid residues in APE1 significantly reduced the Parkin-dependent APE1 degradation. These results suggested that Parkin directly ubiquitinated N-terminal Lys residues in APE1 in the cytoplasm. Modulation of Parkin and PINK1 activities under mitochondrial or oxidative stress caused moderate but statistically significant decrease of endogenous APE1 in human cell lines including SH-SY5Y, HEK293, and A549 cells. Analyses of glioblastoma tissues showed an inverse relation between the expression levels of APE1 and Parkin. These results suggest that degradation of endogenous APE1 by Parkin occur when cells are stressed to activate Parkin, and imply a role of Parkin in maintaining the quality of APE1, and loss of Parkin may contribute to elevated APE1 levels in glioblastoma. © 2016 Wiley Periodicals, Inc.

Linking F-box protein 7 and parkin to neuronal degeneration in Parkinson's disease (PD)

Mutations of F-box protein 7 (FBXO7) and Parkin, two proteins in ubiquitin-proteasome system (UPS), are both implicated in pathogenesis of dopamine (DA) neuron degeneration in Parkinson's disease (PD). Parkin is a HECT/RING hybrid ligase that physically receives ubiquitin on its catalytic centre and passes ubiquitin onto its substrates, whereas FBXO7 is an adaptor protein in Skp-Cullin-F-box (SCF) SCF(FBXO7) ubiquitin E3 ligase complex to recognize substrates and mediate substrates ubiquitination by SCF(FBXO7) E3 ligase. Here, we discuss the overlapping pathophysiologic mechanisms and clinical features linking Parkin and FBXO7 with autosomal recessive PD. Both proteins play an important role in neuroprotective mitophagy to clear away impaired mitochondria. Parkin can be recruited to impaired mitochondria whereas cellular stress can promote FBXO7 mitochondrial translocation. PD-linked FBXO7 can recruit Parkin into damaged mitochondria and facilitate its aggregation. WT FBXO7, but not PD-linked FBXO7 mutants can rescue DA neuron degeneration in Parkin null Drosophila. A better understanding of the common pathophysiologic mechanisms of these two proteins could unravel specific pathways for targeted therapy in PD.

Parkin Regulation and Neurodegenerative Disorders

Parkin is a unique, multifunctional ubiquitin ligase whose various roles in the cell, particularly in neurons, are widely thought to be protective. The pivotal role that Parkin plays in maintaining neuronal survival is underscored by our current recognition that Parkin dysfunction represents not only a predominant cause of familial parkinsonism but also a formal risk factor for the more common, sporadic form of Parkinson’s disease (PD). Accordingly, keen research on Parkin over the past decade has led to an explosion of knowledge regarding its physiological roles and its relevance to PD. However, our understanding of Parkin is far from being complete. Indeed, surprises emerge from time to time that compel us to constantly update the paradigm of Parkin function. For example, we now know that Parkin’s function is not confined to mere housekeeping protein quality control (QC) roles but also includes mitochondrial homeostasis and stress-related signaling. Furthermore, emerging evidence also suggest a role for Parkin in several other major neurodegenerative diseases including Alzheimer’s disease (AD) and Amyotrophic Lateral Sclerosis (ALS). Yet, it remains truly amazing to note that a single enzyme could serve such multitude of functions and cellular roles. Clearly, its activity has to be tightly regulated. In this review, we shall discuss this and how dysregulated Parkin function may precipitate neuronal demise in various neurodegenerative disorders.

Synphilin-1 attenuates mutant LRRK2-induced neurodegeneration in Parkinson's disease models

Mutations in leucine-rich repeat kinase 2 (LRRK2) cause autosomal-dominant Parkinsonism with pleomorphic pathology including deposits of aggregated protein and neuronal degeneration. The pathogenesis of LRRK2-linked Parkinson's disease (PD) is not fully understood. Here, using co-immunoprecipitation, we found that LRRK2 interacted with synphilin-1 (SP1), a cytoplasmic protein that interacts with α-synuclein and has implications in PD pathogenesis. LRRK2 interacted with the N-terminus of SP1 whereas SP1 predominantly interacted with the C-terminus of LRRK2, including kinase domain. Co-expression of SP1 with LRRK2 increased LRRK2-induced cytoplasmic aggregation in cultured cells. Moreover, SP1 also attenuated mutant LRRK2-induced toxicity and reduced LRRK2 kinase activity in cultured cells. Knockdown of SP1 by siRNA enhanced LRRK2 neuronal toxicity. In vivo Drosophila studies, co-expression of SP1 and mutant G2019S-LRRK2 in double transgenic Drosophila increased survival and improved locomotor activity. Expression of SP1 protects against G2019S-LRRK2-induced dopamine neuron loss and reduced LRRK2 phosphorylation in double transgenic fly brains. Our findings demonstrate that SP1 attenuates mutant LRRK2-induced PD-like phenotypes and plays a neural protective role.

Crosstalk Between Macroautophagy and Chaperone-Mediated Autophagy: Implications for the Treatment of Neurological Diseases

Macroautophagy and chaperone-mediated autophagy (CMA) are two important subtypes of autophagy that play a critical role in cellular quality control under physiological and pathological conditions. Despite the marked differences between these two autophagic pathways, macroautophagy and CMA are intimately connected with each other during the autophagy-lysosomal degradation process, in particular, in the setting of neurological illness. Macroautophagy serves as a backup mechanism to removal of malfunctioning proteins (i.e., aberrant α-synuclein) from the cytoplasm when CMA is compromised, and vice versa. The molecular mechanisms underlying the conversation between macroautophagy and CMA are being clarified. Herein, we survey current overviews concentrating on the complex interactions between macroautophagy and CMA, and present therapeutic potentials through utilization and manipulation of macroautophagy-CMA crosstalk in the treatment of neurological diseases.

Loss of parkin promotes lipid rafts-dependent endocytosis through accumulating caveolin-1: implications for Parkinson's disease

Background

Parkinson’s disease (PD) is characterized by progressive loss of midbrain dopaminergic neurons, resulting in motor dysfunctions. While most PD is sporadic in nature, a significant subset can be linked to either autosomal dominant or recessive mutations. PARK2, encoding the E3 ubiquitin ligase, parkin, is the most frequently mutated gene in autosomal recessive early onset PD. It has recently been reported that PD-associated gene products such as PINK1, α-synuclein, LRRK2, and DJ-1, as well as parkin associate with lipid rafts, suggesting that the dysfunction of these proteins in lipid rafts may be a causal factor of PD. Therefore here, we examined the relationship between lipid rafts-related proteins and parkin.

Results

We identified caveolin-1 (cav-1), which is one of the major constituents of lipid rafts at the plasma membrane, as a substrate of parkin. Loss of parkin function was found to disrupt the ubiquitination and degradation of cav-1, resulting in elevated cav-1 protein level in cells. Moreover, the total cholesterol level and membrane fluidity was altered by parkin deficiency, causing dysregulation of lipid rafts-dependent endocytosis. Further, cell-to-cell transmission of α-synuclein was facilitated by parkin deficiency.

Conclusions

Our results demonstrate that alterations in lipid rafts by the loss of parkin via cav-1 may be a causal factor of PD, and cav-1 may be a novel therapeutic target for PD.

Parkinson's Protein α-Synuclein Binds Efficiently and with a Novel Conformation to Two Natural Membrane Mimics

Binding of human α-Synuclein, a protein associated with Parkinson’s disease, to natural membranes is thought to be crucial in relation to its pathological and physiological function. Here the binding of αS to small unilamellar vesicles mimicking the inner mitochondrial and the neuronal plasma membrane is studied in situ by continuous wave and pulsed electron paramagnetic resonance. Local binding information of αS spin labeled by MTSL at positions 56 and 69 respectively shows that also helix 2 (residues 50–100) binds firmly to both membranes. By double electron-electron resonance (DEER) on the mutant spin labeled at positions 27 and 56 (αS 27/56) a new conformation on the membrane is found with a distance of 3.6 nm/ 3.7 nm between residues 27 and 56. In view of the low negative charge density of these membranes, the strong interaction is surprising, emphasizing that function and pathology of αS could involve synaptic vesicles and mitochondria.

CCK Response Deficiency in Synphilin-1 Transgenic Mice

Previously, we have identified a novel role for the cytoplasmic protein, synphilin-1(SP1), in the controls of food intake and body weight in both mice and Drosophila. Ubiquitous overexpression of human SP1 in brain neurons in transgenic mice results in hyperphagia expressed as an increase in meal size. However, the mechanisms underlying this action of SP1 remain to be determined. Here we investigate a potential role for altered gut feedback signaling in the effects of SP1 on food intake. We examined responses to peripheral administration of cholecytokinin (CCK), amylin, and the glucagon like peptide-1 (GLP-1) receptor agonist, exendin-4. Intraperitoneal administration of CCK at doses ranging from 1–10 nmol/kg significantly reduced glucose intake in wild type (WT) mice, but failed to affect intake in SP1 transgenic mice. Moreover, there was a significant attenuation of CCK-induced c-Fos expression in the dorsal vagal complex in SP1 transgenic mice. In contrast, WT and SP1 transgenic mice were similarly responsive to both amylin and exendin-4 treatment. These studies demonstrate that SP1 results in a CCK response deficiency that may contribute to the increased meal size and overall hyperphagia in synphillin-1 transgenic mice.

Selective multifaceted E3 ubiquitin ligases barricade extreme defense: Potential therapeutic targets for neurodegeneration and ageing

Efficient and regular performance of Ubiquitin Proteasome System and Autophagy continuously eliminate deleterious accumulation of nonnative protiens. In cellular quality control system, E3 ubiquitin ligases are significant employees for defense mechanism against abnormal toxic proteins. Few findings indicate that lack of functions of E3 ubiquitin ligases can be a causative factor of neurodevelopmental disorders, neurodegeneration, cancer and ageing. However, the detailed molecular pathomechanism implying E3 ubiquitin ligases in cellular functions in multifactorial disease conditions are not well understood. This article systematically represents the unique characteristics, molecular nature, and recent developments in the knowledge of neurobiological functions of few crucial E3 ubiquitin ligases. Here, we review recent literature on the roles of E6-AP, HRD1 and ITCH E3 ubiquitin ligases in the neuro-pathobiological mechanisms, with precise focus on the processes of neurodegeneration, and thereby propose new lines of potential targets for therapeutic interventions.

Parkin Regulates Mitosis and Genomic Stability through Cdc20/Cdh1

Mutations in the E3 ubiquitin ligase Parkin have been linked to familial Parkinson's disease. Parkin has also been implicated in mitosis through mechanisms that are unclear. Here we show that Parkin interacts with anaphase promoting complex/cyclosome (APC/C) coactivators Cdc20 and Cdh1 to mediate the degradation of several key mitotic regulators independent of APC/C. We demonstrate that ordered progression through mitosis is orchestrated by two distinct E3 ligases through the shared use of Cdc20 and Cdh1. Furthermore, Parkin is phosphorylated and activated by polo-like kinase 1 (Plk1) during mitosis. Parkin deficiency results in overexpression of its substrates, mitotic defects, genomic instability, and tumorigenesis. These results suggest that the Parkin-Cdc20/Cdh1 complex is an important regulator of mitosis.

RuvbL1 and RuvbL2 enhance aggresome formation and disaggregate amyloid fibrils

The aggresome is an organelle that recruits aggregated proteins for storage and degradation. We performed an siRNA screen for proteins involved in aggresome formation and identified novel mammalian AAA+ protein disaggregases RuvbL1 and RuvbL2. Depletion of RuvbL1 or RuvbL2 suppressed aggresome formation and caused buildup of multiple cytoplasmic aggregates. Similarly, downregulation of RuvbL orthologs in yeast suppressed the formation of an aggresome-like body and enhanced the aggregate toxicity. In contrast, their overproduction enhanced the resistance to proteotoxic stress independently of chaperone Hsp104. Mammalian RuvbL associated with the aggresome, and the aggresome substrate synphilin-1 interacted directly with the RuvbL1 barrel-like structure near the opening of the central channel. Importantly, polypeptides with unfolded structures and amyloid fibrils stimulated the ATPase activity of RuvbL. Finally, disassembly of protein aggregates was promoted by RuvbL. These data indicate that RuvbL complexes serve as chaperones in protein disaggregation.

Nigral overexpression of alpha-synuclein in the absence of parkin enhances alpha-synuclein phosphorylation but does not modulate dopaminergic neurodegeneration

BACKGROUND

Alpha-synuclein is a key protein in the pathogenesis of Parkinson's disease. Mutations in the parkin gene are the most common cause of early-onset autosomal recessive Parkinson's disease, probably through a loss-of-function mechanism. However, the molecular mechanism by which loss of parkin function leads to the development of the disease and the role of alpha-synuclein in parkin-associated Parkinson's disease is still not elucidated. Conflicting results were reported about the effect of the absence of parkin on alpha-synuclein-mediated neurotoxicity using a transgenic approach. In this study, we investigated the effect of loss of parkin on alpha-synuclein neuropathology and toxicity in adult rodent brain using viral vectors. Therefore, we overexpressed human wild type alpha-synuclein in the substantia nigra of parkin knockout and wild type mice using two different doses of recombinant adeno-associated viral vectors.

RESULTS

No difference was observed in nigral dopaminergic cell loss between the parkin knockout mice and wild type mice up to 16 weeks after viral vector injection. However, the level of alpha-synuclein phosphorylated at serine residue 129 in the substantia nigra was significantly increased in the parkin knockout mice compared to the wild type mice while the total expression level of alpha-synuclein was similar in both groups. The increased alpha-synuclein phosphorylation was confirmed in a parkin knockdown cell line.

CONCLUSIONS

These findings support a functional relationship between parkin and alpha-synuclein phosphorylation in rodent brain.

Splicing variants of porcine synphilin-1

Parkinson's disease (PD), idiopathic and familial, is characterized by degradation of dopaminergic neurons and the presence of Lewy bodies (LB) in the substantia nigra. LBs contain aggregated proteins of which α-synuclein is the major component. The protein synphilin-1 interacts and colocalizes with α-synuclein in LBs. The aim of this study was to isolate and characterize porcine synphilin-1 and isoforms hereof with the future perspective to use the pig as a model for Parkinson's disease. The porcine SNCAIP cDNA was cloned by reverse transcriptase PCR. The spatial expression of SNCAIP mRNA was investigated by RNAseq. The presented work reports the molecular cloning and characterization of the porcine (Sus scrofa) synphilin-1 cDNA (SNCAIP) and three splice variants hereof. The porcine SNCAIP cDNA codes for a protein (synphilin-1) of 919 amino acids which shows a high similarity to human (90%) and to mouse (84%) synphilin-1. Three shorter transcript variants of the synphilin-1 gene were identified, all lacking one or more exons. SNCAIP transcripts were detected in most examined organs and tissues and the highest expression was found in brain tissues and lung. Conserved splicing variants and a novel splice form of synhilin-1 were found in this study. All synphilin-1 isoforms encoded by the identified transcript variants lack functional domains important for protein degradation.

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The full-length porcine SNCAIP cDNA encoding synphilin-1 was cloned and characterized.

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Three splicing variants of synphilin-1 were identified.

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Both conserved and novel splicing variant were found.

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SNCAIP mRNA was differently expressed in analyzed tissues and organs with highest expression in brain tissue and lung.

Convergence of Parkin, PINK1, and α-Synuclein on Stress-induced Mitochondrial Morphological Remodeling

Mutations in PARKIN (PARK2), an ubiquitin ligase, cause early onset Parkinson disease. Parkin was shown to bind, ubiquitinate, and target depolarized mitochondria for destruction by autophagy. This process, mitophagy, is considered crucial for maintaining mitochondrial integrity and suppressing Parkinsonism. Here, we report that under moderate mitochondrial stress, parkin does not translocate to mitochondria to induce mitophagy; rather, it stimulates mitochondrial connectivity. Mitochondrial stress-induced fusion requires PINK1 (PARK6), mitofusins, and parkin ubiquitin ligase activity. Upon exposure to mitochondrial toxins, parkin binds α-synuclein (PARK1), and in conjunction with the ubiquitin-conjugating enzyme Ubc13, stimulates K63-linked ubiquitination. Importantly, α-synuclein inactivation phenocopies parkin overexpression and suppresses stress-induced mitochondria fission, whereas Ubc13 inactivation abrogates parkin-dependent mitochondrial fusion. The convergence of parkin, PINK1, and α-synuclein on mitochondrial dynamics uncovers a common function of these PARK genes in the mitochondrial stress response and provides a potential physiological basis for the prevalence of α-synuclein pathology in Parkinson disease.

Evaluation of PARKIN gene variants in West Bengal Parkinson's disease patients

Little information is available regarding the molecular pathogenesis of Parkinson's disease (PD) among the Bengalee population in West Bengal, India. This study was undertaken to determine the contribution of Parkin variants in well-defined ethnically identical Bengalee population of India and further to describe the clinical spectrum associated with these mutations. A total of 150 unrelated PD patients and 150 controls were recruited for the study. The entire cohort was screened for mutations in all the 12 exons of the gene along with flanking splice junctions by polymerase chain reaction and DNA sequencing. Eleven nucleotide variants including two novel changes were detected. Cerebrospinal fluid (CSF) parkin protein expression of the novel mutation, Val186Ile (found in heterozygous condition in one patient only) was almost 2.7 folds lower than the controls and other PD patients. Molecular characterization of polymorphisms Ser167Asn and Val380Leu depicted that homozygous Ser167 and Val380 are significantly associated with the disease. We did not find any linkage disequilibrium among the SNPs, the low r(2) for every pair of single-nucleotide polymorphisms (SNPs) indicated that these SNPs cannot be tagged by each other. Another novel intronic change, IVS8+48C>T was present in almost equally in PD patients and controls. Among the ethnically defined Bengalee population of West Bengal, occurrence of Parkin mutation is 4% (6/150) of the PD patient pool supported with decreased folds of expression of CSF PARKIN protein. Parkin polymorphisms, Ser167 and Val380 are risk factors for the progression of the disease, and their frequency is greatly influenced by ethnic origin.

iPS models of Parkin and PINK1

Parkinson disease (PD) is a degenerative disorder of the central nervous system resulting from depletion of dopaminergic neurons and currently remains incurable despite enormous international research efforts. The development of induced pluripotent stem cell (iPSC) technology opened up the unique possibility of studying disease mechanisms in human tissue that was otherwise not accessible, such as the brain. Of particular interest are the monogenetic forms of PD as they closely resemble the more common ‘idiopathic’ PD and, through the mutated protein, provide a clear research target in iPSC-derived neurons. Recessively inherited Parkin and PTEN-induced putative kinase 1 (PINK1) mutations have been investigated in this context and the present review describes the first insights gained from studies in iPSC-derived dopaminergic neurons, which comprise abnormalities in mitochondrial and dopamine homoeostasis, microtubular stability and axonal outgrowth. These new models of PD have a high translational potential that includes the identification of druggable targets, testing of known and novel therapeutic agents in the disease-relevant tissue using well-defined read-outs and potential regenerative approaches.

Mitochondrial alterations by PARKIN in dopaminergic neurons using PARK2 patient-specific and PARK2 knockout isogenic iPSC lines

In this study, we used patient-specific and isogenic PARK2-induced pluripotent stem cells (iPSCs) to show that mutations in PARK2 alter neuronal proliferation. The percentage of TH(+) neurons was decreased in Parkinson's disease (PD) patient-derived neurons carrying various mutations in PARK2 compared with an age-matched control subject. This reduction was accompanied by alterations in mitochondrial:cell volume fraction (mitochondrial volume fraction). The same phenotype was confirmed in isogenic PARK2 null lines. The mitochondrial phenotype was also seen in non-midbrain neurons differentiated from the PARK2 null line, as was the functional phenotype of reduced proliferation in culture. Whole genome expression profiling at various stages of differentiation confirmed the mitochondrial phenotype and identified pathways altered by PARK2 dysfunction that include PD-related genes. Our results are consistent with current model of PARK2 function where damaged mitochondria are targeted for degradation via a PARK2/PINK1-mediated mechanism.

Identification and molecular characterization of Parkin in Clonorchis sinensis

Clonorchis sinensis habitating in the bile duct of mammals causes clonorchiasis endemic in East Asian countries. Parkin is a RING-between-RING protein and has E3-ubiquitin ligase activity catalyzing ubiquitination and degradation of substrate proteins. A cDNA clone of C. sinensis was predicted to encode a polypeptide homologous to parkin (CsParkin) including 5 domains (Ubl, RING0, RING1, IBR, and RING2). The cysteine and histidine residues binding to Zn(2+) were all conserved and participated in formation of tertiary structural RINGs. Conserved residues were also an E2-binding site in RING1 domain and a catalytic cysteine residue in the RING2 domain. Native CsParkin was determined to have an estimated molecular weight of 45.7 kDa from C. sinensis adults by immunoblotting. CsParkin revealed E3-ubiquitin ligase activity and higher expression in metacercariae than in adults. CsParkin was localized in the locomotive and male reproductive organs of C. sinensis adults, and extensively in metacercariae. Parkin has been found to participate in regulating mitochondrial function and energy metabolism in mammalian cells. From these results, it is suggested that CsParkin play roles in energy metabolism of the locomotive organs, and possibly in protein metabolism of the reproductive organs of C. sinensis.

The E3 ubiquitin ligase parkin is recruited to the 26 S proteasome via the proteasomal ubiquitin receptor Rpn13

Mutations in the Park2 gene, encoding the RING-HECT hybrid E3 ubiquitin ligase parkin, are responsible for a common familial form of Parkinson disease. By mono- and polyubiquitinating target proteins, parkin regulates various cellular processes, including degradation of proteins within the 26 S proteasome, a large multimeric degradation machine. In our attempt to further elucidate the function of parkin, we have identified the proteasomal ubiquitin receptor Rpn13/ADRM1 as a parkin-interacting protein. We show that the N-terminal ubiquitin-like (Ubl) domain of parkin binds directly to the pleckstrin-like receptor for ubiquitin (Pru) domain within Rpn13. Using mutational analysis and NMR, we find that Pru binding involves the hydrophobic patch surrounding Ile-44 in the parkin Ubl, a region that is highly conserved between ubiquitin and Ubl domains. However, compared with ubiquitin, the parkin Ubl exhibits greater than 10-fold higher affinity for the Pru domain. Moreover, knockdown of Rpn13 in cells increases parkin levels and abrogates parkin recruitment to the 26 S proteasome, establishing Rpn13 as the major proteasomal receptor for parkin. In contrast, silencing Rpn13 did not impair parkin recruitment to mitochondria or parkin-mediated mitophagy upon carbonyl cyanide m-chlorophenyl hydrazone-induced mitochondrial depolarization. However, it did delay the clearance of mitochondrial proteins (TIM23, TIM44, and TOM20) and enhance parkin autoubiquitination. Taken together, these findings implicate Rpn13 in linking parkin to the 26 S proteasome and regulating the clearance of mitochondrial proteins during mitophagy.

Role of zinc and copper ions in the pathogenetic mechanisms of Alzheimer's and Parkinson's diseases

Disbalance of zinc (Zn2+) and copper (Cu2+) ions in the central nervous system is involved in the pathogenesis of numerous neurodegenerative disorders such as multisystem atrophy, amyotrophic lateral sclerosis, Creutzfeldt-Jakob disease, Wilson-Konovalov disease, Alzheimer's disease, and Parkinson's disease. Among these, Alzheimer's disease (AD) and Parkinson's disease (PD) are the most frequent age-related neurodegenerative pathologies with disorders in Zn2+ and Cu2+ homeostasis playing a pivotal role in the mechanisms of pathogenesis. In this review we generalized and systematized current literature data concerning this problem. The interactions of Zn2+ and Cu2+ with amyloid precursor protein (APP), β-amyloid (Abeta), tau-protein, metallothioneins, and GSK3β are considered, as well as the role of these interactions in the generation of free radicals in AD and PD. Analysis of the literature suggests that the main factors of AD and PD pathogenesis (oxidative stress, structural disorders and aggregation of proteins, mitochondrial dysfunction, energy deficiency) that initiate a cascade of events resulting finally in the dysfunction of neuronal networks are mediated by the disbalance of Zn2+ and Cu2+.

Synphilin-1 binds ATP and regulates intracellular energy status

Recent studies have suggested that synphilin-1, a cytoplasmic protein, is involved in energy homeostasis. Overexpression of synphilin-1 in neurons results in hyperphagia and obesity in animal models. However, the mechanism by which synphilin-1 alters energy homeostasis is unknown. Here, we used cell models and biochemical approaches to investigate the cellular functions of synphilin-1 that may affect energy balance. Synphilin-1 was pulled down by ATP-agarose beads, and the addition of ATP and ADP reduced this binding, indicating that synphilin-1 bound ADP and ATP. Synphilin-1 also bound GMP, GDP, and GTP but with a lower affinity than it bound ATP. In contrast, synphilin-1 did not bind with CTP. Overexpression of synphilin-1 in HEK293T cells significantly increased cellular ATP levels. Genetic alteration to abolish predicted ATP binding motifs of synphilin-1 or knockdown of synphilin-1 by siRNA reduced cellular ATP levels. Together, these data demonstrate that synphilin-1 binds and regulates the cellular energy molecule, ATP. These findings provide a molecular basis for understanding the actions of synphilin-1 in energy homeostasis.

Arf6 guanine nucleotide exchange factor cytohesin-2 binds to CCDC120 and is transported along neurites to mediate neurite growth

The mechanism of neurite growth is complicated, involving continuous cytoskeletal rearrangement and vesicular trafficking. Cytohesin-2 is a guanine nucleotide exchange factor for Arf6, an Arf family molecular switch protein, controlling cell morphological changes such as neuritogenesis. Here, we show that cytohesin-2 binds to a protein with a previously unknown function, CCDC120, which contains three coiled-coil domains, and is transported along neurites in differentiating N1E-115 cells. Transfection of the small interfering RNA (siRNA) specific for CCDC120 into cells inhibits neurite growth and Arf6 activation. When neurites start to extend, vesicles containing CCDC120 and cytohesin-2 are transported in an anterograde manner rather than a retrograde one. As neurites continue extension, anterograde vesicle transport decreases. CCDC120 knockdown inhibits cytohesin-2 localization into vesicles containing CCDC120 and diffuses cytohesin-2 in cytoplasmic regions, illustrating that CCDC120 determines cytohesin-2 localization in growing neurites. Reintroduction of the wild type CCDC120 construct into cells transfected with CCDC120 siRNA reverses blunted neurite growth and Arf6 activity, whereas the cytohesin-2-binding CC1 region-deficient CCDC120 construct does not. Thus, cytohesin-2 is transported along neurites by vesicles containing CCDC120, and it mediates neurite growth. These results suggest a mechanism by which guanine nucleotide exchange factor for Arf6 is transported to mediate neurite growth.

Alternative splicing generates different parkin protein isoforms: evidences in human, rat, and mouse brain

Parkinson protein 2, E3 ubiquitin protein ligase (PARK2) gene mutations are the most frequent causes of autosomal recessive early onset Parkinson's disease and juvenile Parkinson disease. Parkin deficiency has also been linked to other human pathologies, for example, sporadic Parkinson disease, Alzheimer disease, autism, and cancer. PARK2 primary transcript undergoes an extensive alternative splicing, which enhances transcriptomic diversification. To date several PARK2 splice variants have been identified; however, the expression and distribution of parkin isoforms have not been deeply investigated yet. Here, the currently known PARK2 gene transcripts and relative predicted encoded proteins in human, rat, and mouse are reviewed. By analyzing the literature, we highlight the existing data showing the presence of multiple parkin isoforms in the brain. Their expression emerges from conflicting results regarding the electrophoretic mobility of the protein, but it is also assumed from discrepant observations on the cellular and tissue distribution of parkin. Although the characterization of each predicted isoforms is complex, since they often diverge only for few amino acids, analysis of their expression patterns in the brain might account for the different pathogenetic effects linked to PARK2 gene mutations.

Plasma-Enabled Carbon Nanostructures for Early Diagnosis of Neurodegenerative Diseases

Carbon nanostructures (CNs) are amongst the most promising biorecognition nanomaterials due to their unprecedented optical, electrical and structural properties. As such, CNs may be harnessed to tackle the detrimental public health and socio-economic adversities associated with neurodegenerative diseases (NDs). In particular, CNs may be tailored for a specific determination of biomarkers indicative of NDs. However, the realization of such a biosensor represents a significant technological challenge in the uniform fabrication of CNs with outstanding qualities in order to facilitate a highly-sensitive detection of biomarkers suspended in complex biological environments. Notably, the versatility of plasma-based techniques for the synthesis and surface modification of CNs may be embraced to optimize the biorecognition performance and capabilities. This review surveys the recent advances in CN-based biosensors, and highlights the benefits of plasma-processing techniques to enable, enhance, and tailor the performance and optimize the fabrication of CNs, towards the construction of biosensors with unparalleled performance for the early diagnosis of NDs, via a plethora of energy-efficient, environmentally-benign, and inexpensive approaches.

Synphilin-1A is a phosphoprotein phosphatase 1-interacting protein and affects PPP1 sorting to subcellular compartments

Lewy bodies (LBs) are synphilin-1 (Sph1)-containing aggregates and histological hallmarks of Parkinson's disease. Therefore, understanding processes which modulate the aggregation of Sph1, or its isoform Sph1A, will contribute to our understanding of LBs formation. Protein phosphorylation promotes aggregation, but protein phosphatases with activity towards Sph1 have not been described. The present study documents the identification of a novel Sph1A/phosphoprotein phosphatase 1 (PPP1) complex and unravels its regulatory effect on Sph1A aggregation. Using yeast co-transformation and overlay blot assay, the interaction between Sph1A and PPP1 was mapped to the Sph1A RVTF motif. Then, Sph1A overexpression in human embryonic kidney 293 cells demonstrated that Sph1A specifically targets endogenous PPP1 isoforms to inclusion bodies and that Sph1A/PPP1 complex disruption enhances inclusion bodies formation. Finally, as Sph1A interacted with PPP1CC2, a PPP1 sperm-specific isoform, Sph1 and Sph1A expression was addressed in male germ cells by qRT-PCR, revealing high expression levels in round spermatids. Together, these observations established Sph1A as a novel PPP1-interacting protein able to affect PPP1 sorting to subcellular compartments and Sph1A/PPP1 complex as a negative modulator of LBs formation. Contrarily, in physiological conditions, Sph1 isoforms are pointed as putative participants in vesicle dynamics with implications in neurotransmission and spermiogenesis.

Behavioral characterization of the hyperphagia synphilin-1 overexpressing mice

Synphilin-1 is a cytoplasmic protein that has been shown to be involved in the control of energy balance. Previously, we reported on the generation of a human synphilin-1 transgenic mouse model (SP1), in which overexpression of human synphilin-1 resulted in hyperphagia and obesity. Here, behavioral measures in SP1 mice were compared with those of their age-matched controls (NTg) at two time points: when there was not yet a group body weight difference ("pre-obese") and when SP1 mice were heavier ("obese"). At both time points, meal pattern analyses revealed that SP1 mice displayed higher daily chow intake than non-transgenic control mice. Furthermore, there was an increase in meal size in SP1 mice compared with NTg control mice at the obese stage. In contrast, there was no meal number change between SP1 and NTg control mice. In a brief-access taste procedure, both "pre-obese" and "obese" SP1 mice displayed concentration-dependent licking across a sucrose concentration range similar to their NTg controls. However, at the pre-obese stage, SP1 mice initiated significantly more trials to sucrose across the testing sessions and licked more vigorously at the highest concentration presented, than the NTg counterparts. These group differences in responsiveness to sucrose were no longer apparent in obese SP1 mice. These results suggest that at the pre-obese stage, the increased trials to sucrose in the SP1 mice reflects increased appetitive behavior to sucrose that may be indicative of the behavioral changes that may contribute to hyperphagia and development of obesity in SP1 mice. These studies provide new insight into synphilin-1 contributions to energy homeostasis.

RBR E3 ubiquitin ligases: new structures, new insights, new questions

The RBR (RING-BetweenRING-RING) or TRIAD [two RING fingers and a DRIL (double RING finger linked)] E3 ubiquitin ligases comprise a group of 12 complex multidomain enzymes. This unique family of E3 ligases includes parkin, whose dysfunction is linked to the pathogenesis of early-onset Parkinson's disease, and HOIP (HOIL-1-interacting protein) and HOIL-1 (haem-oxidized IRP2 ubiquitin ligase 1), members of the LUBAC (linear ubiquitin chain assembly complex). The RBR E3 ligases share common features with both the larger RING and HECT (homologous with E6-associated protein C-terminus) E3 ligase families, directly catalysing ubiquitin transfer from an intrinsic catalytic cysteine housed in the C-terminal domain, as well as recruiting thioester-bound E2 enzymes via a RING domain. Recent three-dimensional structures and biochemical findings of the RBRs have revealed novel protein domain folds not previously envisioned and some surprising modes of regulation that have raised many questions. This has required renaming two of the domains in the RBR E3 ligases to more accurately reflect their structures and functions: the C-terminal Rcat (required-for-catalysis) domain, essential for catalytic activity, and a central BRcat (benign-catalytic) domain that adopts the same fold as the Rcat, but lacks a catalytic cysteine residue and ubiquitination activity. The present review discusses how three-dimensional structures of RBR (RING1-BRcat-Rcat) E3 ligases have provided new insights into our understanding of the biochemical mechanisms of these important enzymes in ubiquitin biology.

Long-term overexpression of human wild-type and T240R mutant Parkin in rat substantia nigra induces progressive dopaminergic neurodegeneration

Mutations in the parkin gene are the most common cause of early-onset autosomal recessive Parkinson disease (PD). The pathogenic mechanisms of how parkin mutations lead to the development of PD are not fully understood. Studies of cell cultures and of Drosophila have suggested a dominant negative effect for the clinical parkin mutant T240R. Conversely, the neuroprotective capacity of parkin has been widely reported; this suggests that the parkin protein may have a potential therapeutic role in PD. Here, we aimed to develop a novel genetic rodent model of PD by overexpression of T240R-parkin and human wild-type parkin as a control in the dopaminergic neurons of adult rats using adeno-associated viral vectors (rAAV2/8). Surprisingly, we found that overexpression not only of T240R-parkin but also of human wild-type parkin induced progressive and dose-dependent dopaminergic cell death in rats, starting from 8 weeks after injection. This degeneration was specific for parkin because similar overexpressionof enhanced green fluorescent protein did not lead to nigral degeneration. Our results warrant caution to the development of therapeutic strategies for PD based on overexpression of parkin or enhancing parkin activity because this might be deleterious for dopaminergic neurons in the long-term.

Mutations in PRKN and SNCA Genes Important for the Progress of Parkinson's Disease

Although Parkinson’s disease (PD) was first described almost 200 years ago, it remains an incurable disease with a cause that is not fully understood. Nowadays it is known that disturbances in the structure of pathological proteins in PD can be caused by more than environmental and genetic factors. Despite numerous debates and controversies in the literature about the role of mutations in the SNCA and PRKN genes in the pathogenesis of PD, it is evident that these genes play a key role in maintaining dopamine (DA) neuronal homeostasis and that the dysfunction of this homeostasis is relevant to both familial (FPD) and sporadic (SPD) PD with different onset. In recent years, the importance of alphasynuclein (ASN) in the process of neurodegeneration and neuroprotective function of the Parkin is becoming better understood. Moreover, there have been an increasing number of recent reports indicating the importance of the interaction between these proteins and their encoding genes. Among others interactions, it is suggested that even heterozygous substitution in the PRKN gene in the presence of the variants +2/+2 or +2/+3 of NACP-Rep1 in the SNCA promoter, may increase the risk of PD manifestation, which is probably due to ineffective elimination of over-expressed ASN by the mutated Parkin protein. Finally, it seems that genetic testing may be an important part of diagnostics in patients with PD and may improve the prognostic process in the course of PD. However, only full knowledge of the mechanism of the interaction between the genes associated with the pathogenesis of PD is likely to help explain the currently unknown pathways of selective damage to dopaminergic neurons in the course of PD.

Genetic screens in Caenorhabditis elegans models for neurodegenerative diseases

Caenorhabditis elegans comprises unique features that make it an attractive model organism in diverse fields of biology. Genetic screens are powerful to identify genes and C. elegans can be customized to forward or reverse genetic screens and to establish gene function. These genetic screens can be applied to "humanized" models of C. elegans for neurodegenerative diseases, enabling for example the identification of genes involved in protein aggregation, one of the hallmarks of these diseases. In this review, we will describe the genetic screens employed in C. elegans and how these can be used to understand molecular processes involved in neurodegenerative and other human diseases. This article is part of a Special Issue entitled: From Genome to Function.

Proteasome failure promotes positioning of lysosomes around the aggresome via local block of microtubule-dependent transport

Ubiquitinated proteins aggregate upon proteasome failure, and the aggregates are transported to the aggresome. In aggresomes, protein aggregates are actively degraded by the autophagy-lysosome pathway, but why targeting the aggresome promotes degradation of aggregated species is currently unknown. Here we report that the important factor in this process is clustering of lysosomes around the aggresome via a novel mechanism. Proteasome inhibition causes formation of a zone around the centrosome where microtubular transport of lysosomes is suppressed, resulting in their entrapment and accumulation. Microtubule-dependent transport of other organelles, including autophagosomes, mitochondria, and endosomes, is also blocked in this entrapment zone (E-zone), while movement of organelles at the cell periphery remains unaffected. Following the whole-genome small interfering RNA (siRNA) screen for proteins involved in aggresome formation, we defined the pathway that regulates formation of the E-zone, including the Stk11 protein kinase, the Usp9x deubiquitinating enzyme, and their substrate kinase MARK4. Therefore, upon proteasome failure, targeting of aggregated proteins of the aggresome is coordinated with lysosome positioning around this body to facilitate degradation of the abnormal species.

Isolated RING2 domain of parkin is sufficient for E2-dependent E3 ligase activity

The E3 ubiquitin ligase activity of the parkin protein is implicated in playing a protective role against neurodegenerative disorders including Parkinson's, Huntington's, and Alzheimer's diseases. Parkin has four zinc-containing domains: RING0, RING1, IBR (in-between ring), and RING2. Mutational analysis of full-length parkin suggests that the C-terminal RING2 domain contains the catalytic core. Here, a catalytically competent recombinant RING2 containing an N-terminal GB1 solubility peptide is described. In cell-free in vitro ubiqitination reactions, the RING2 construct catalyzes the transfer of ubiquitin from the E2 enzyme UbcH7 to the attached GB1 tag. This intramolecular autoubiquitination reaction indicates that (a) ubiquitination by RING2 can occur in the absence of other parkin domains and (b) UbcH7 can interact directly with RING2 to transfer its bound ubiquitin. Mass spectrometry identified sites of mono- and diubiquitin attachment to two surface-exposed lysine residues (Lys24 and Lys39) on the GB1 peptide. The sites of diubiquitination involved Lys11 and Lys48 linkages, which have been identified as general signals for proteasome degradation. Cleaving the linker between the GB1 tag and RING2 resulted in loss of ubiquitination activity, indicating that the substrate must be tethered to RING2 for proper presentation to the active site. Atomic absorption spectrometry and selective mutation of zinc ligands indicated that only one of the two zinc binding sites on RING2, the N-terminal site, needs to be occupied by zinc for expression of ubiquitination activity. This is consistent with the hypothesis that the second, C-terminal, zinc binding site on RING2 has a regulatory rather than a catalytic function.

Oxidative stress mechanisms underlying Parkinson's disease-associated neurodegeneration in C. elegans

Oxidative stress is thought to play a significant role in the development and progression of neurodegenerative diseases. Although it is currently considered a hallmark of such processes, the interweaving of a multitude of signaling cascades hinders complete understanding of the direct role of oxidative stress in neurodegeneration. In addition to its extensive use as an aging model, some researchers have turned to the invertebrate model Caenorhabditis elegans (C. elegans) in order to further investigate molecular mediators that either exacerbate or protect against reactive oxygen species (ROS)-mediated neurodegeneration. Due to their fully characterized genome and short life cycle, rapid generation of C. elegans genetic models can be useful to study upstream markers of oxidative stress within interconnected signaling pathways. This report will focus on the roles of C. elegans homologs for the oxidative stress-associated transcription factor Nrf2, as well as the autosomal recessive, early-onset Parkinson’s disease (PD)-associated proteins Parkin, DJ-1, and PINK1, in neurodegenerative processes.