DJ-1 enhances cell survival through the binding of Cezanne, a negative regulator of NF-kappaB

Heightened DJ-1 (Park7) expression is associated with a reduction in chemotherapeutic-induced cell death and poor prognosis in several cancers, whereas the loss of DJ-1 function is found in a subgroup of Parkinson disease associated with neuronal death. This study describes a novel pathway by which DJ-1 modulates cell survival. Mass spectrometry shows that DJ-1 interacts with BBS1, CLCF1, MTREF, and Cezanne/OTUD7B/Za20d1. Among these, Cezanne is a known deubiquitination enzyme that inhibits NF-κB activity. DJ-1/Cezanne interaction is confirmed by co-immunoprecipitation of overexpressed and endogenous proteins, maps to the amino-terminal 70 residues of DJ-1, and leads to the inhibition of the deubiquitinating activity of Cezanne. Microarray profiling of shRNA-transduced cells shows that DJ-1 and Cezanne regulate IL-8 and ICAM-1 expression in opposing directions. Similarly, DJ-1 enhances NF-κB nuclear translocation and cell survival, whereas Cezanne reduces these outcomes. Analysis of mouse Park7(-/-) primary cells confirms the regulation of ICAM-1 by DJ-1 and Cezanne. As NF-κB is important in cellular survival and transformation, IL-8 functions as an angiogenic factor and pro-survival signal, and ICAM-1 has been implicated in tumor progression, invasion, and metastasis; these data provide an additional modality by which DJ-1 controls cell survival and possibly tumor progression via interaction with Cezanne.     

DJ-1 Is a Copper Chaperone Acting on SOD1 Activation

Lack of oxidative stress control is a common and often prime feature observed in many neurodegenerative diseases. Both DJ-1 and SOD1, proteins involved in familial Parkinson disease and amyotrophic lateral sclerosis, respectively, play a protective role against oxidative stress. Impaired activity and modified expression of both proteins have been observed in different neurodegenerative diseases. A potential cooperative action of DJ-1 and SOD1 in the same oxidative stress response pathway may be suggested based on a copper-mediated interaction between the two proteins reported here. To investigate the mechanisms underlying the antioxidative function of DJ-1 in relation to SOD1 activity, we investigated the ability of DJ-1 to bind copper ions. We structurally characterized a novel copper binding site involving Cys-106, and we investigated, using different techniques, the kinetics of DJ-1 binding to copper ions. The copper transfer between the two proteins was also examined using both fluorescence spectroscopy and specific biochemical assays for SOD1 activity. The structural and functional analysis of the novel DJ-1 copper binding site led us to identify a putative role for DJ-1 as a copper chaperone. Alteration of the coordination geometry of the copper ion in DJ-1 may be correlated to the physiological role of the protein, to a potential failure in metal transfer to SOD1, and to successive implications in neurodegenerative etiopathogenesis.     

COPS5 (Jab1) Protein Increases β Site Processing of Amyloid Precursor Protein and Amyloid β Peptide Generation by Stabilizing RanBP9 Protein Levels

Increased processing of amyloid precursor protein (APP) and accumulation of neurotoxic amyloid β peptide (Aβ) in the brain is central to the pathogenesis of Alzheimer''s disease (AD). Therefore, the identification of molecules that regulate Aβ generation is crucial for future therapeutic approaches for AD. We demonstrated previously that RanBP9 regulates Aβ generation in a number of cell lines and primary neuronal cultures by forming tripartite protein complexes with APP, low-density lipoprotein-related protein, and BACE1, consequently leading to increased amyloid plaque burden in the brain. RanBP9 is a scaffold protein that exists and functions in multiprotein complexes. To identify other proteins that may bind RanBP9 and regulate Aβ levels, we used a two-hybrid analysis against a human brain cDNA library and identified COPS5 as a novel RanBP9-interacting protein. This interaction was confirmed by coimmunoprecipitation experiments in both neuronal and non-neuronal cells and mouse brain. Colocalization of COPS5 and RanBP9 in the same subcellular compartments further supported the interaction of both proteins. Furthermore, like RanBP9, COPS5 robustly increased Aβ generation, followed by increased soluble APP-β (sAPP-β) and decreased soluble-APP-α (sAPP-α) levels. Most importantly, down-regulation of COPS5 by siRNAs reduced Aβ generation, implying that endogenous COPS5 regulates Aβ generation. Finally, COPS5 levels were increased significantly in AD brains and APΔE9 transgenic mice, and overexpression of COPS5 strongly increased RanBP9 protein levels by increasing its half-life. Taken together, these results suggest that COPS5 increases Aβ generation by increasing RanBP9 levels. Thus, COPS5 is a novel RanBP9-binding protein that increases APP processing and Aβ generation by stabilizing RanBP9 protein levels.     

DJ-1 is present in a large molecular complex in human brain tissue and interacts with alpha-synuclein

DJ-1 is a ubiquitously expressed protein involved in various cellular processes including cell proliferation, RNA-binding, and oxidative stress. Mutations that result in loss of DJ-1 function lead to early onset parkinsonism in humans, and DJ-1 protein is present in pathological lesions of several tauopathies and synucleinopathies. In order to further investigate the role of DJ-1 in human neurodegenerative disease, we have generated novel polyclonal and monoclonal antibodies to human DJ-1 protein. We have characterized these antibodies and confirmed the pathological co-localization of DJ-1 with other neurodegenerative disease-associated proteins, as well as the decrease in DJ-1 solubility in disease tissue. In addition, we report the presence of DJ-1 in a large molecular complex (> 2000 kDa), and provide evidence for an interaction between endogenous DJ-1 and alpha-synuclein in normal and diseased tissue. These findings provide new avenues towards the study of DJ-1 function and how loss of its activity may lead to parkinsonism. Furthermore, our results provide further evidence for the interplay between neurodegenerative disease-associated proteins.     

PINK1 is activated by mitochondrial membrane potential depolarization and stimulates Parkin E3 ligase activity by phosphorylating Serine 65

Missense mutations in PTEN-induced kinase 1 (PINK1) cause autosomal-recessive inherited Parkinson's disease (PD). We have exploited our recent discovery that recombinant insect PINK1 is catalytically active to test whether PINK1 directly phosphorylates 15 proteins encoded by PD-associated genes as well as proteins reported to bind PINK1. We have discovered that insect PINK1 efficiently phosphorylates only one of these proteins, namely the E3 ligase Parkin. We have mapped the phosphorylation site to a highly conserved residue within the Ubl domain of Parkin at Ser(65). We show that human PINK1 is specifically activated by mitochondrial membrane potential (Δψm) depolarization, enabling it to phosphorylate Parkin at Ser(65). We further show that phosphorylation of Parkin at Ser(65) leads to marked activation of its E3 ligase activity that is prevented by mutation of Ser(65) or inactivation of PINK1. We provide evidence that once activated, PINK1 autophosphorylates at several residues, including Thr(257), which is accompanied by an electrophoretic mobility band-shift. These results provide the first evidence that PINK1 is activated following Δψm depolarization and suggest that PINK1 directly phosphorylates and activates Parkin. Our findings indicate that monitoring phosphorylation of Parkin at Ser(65) and/or PINK1 at Thr(257) represent the first biomarkers for examining activity of the PINK1-Parkin signalling pathway in vivo. Our findings also suggest that small molecule activators of Parkin that mimic the effect of PINK1 phosphorylation may confer therapeutic benefit for PD.     

Rescue of PINK1 Protein Null-specific Mitochondrial Complex IV Deficits by Ginsenoside Re Activation of Nitric Oxide Signaling

PINK1, linked to familial Parkinson''s disease, is known to affect mitochondrial function. Here we identified a novel regulatory role of PINK1 in the maintenance of complex IV activity and characterized a novel mechanism by which NO signaling restored complex IV deficiency in PINK1 null dopaminergic neuronal cells. In PINK1 null cells, levels of specific chaperones, including Hsp60, leucine-rich pentatricopeptide repeat-containing (LRPPRC), and Hsp90, were severely decreased. LRPPRC and Hsp90 were found to act upstream of Hsp60 to regulate complex IV activity. Specifically, knockdown of Hsp60 resulted in a decrease in complex IV activity, whereas antagonistic inhibition of Hsp90 by 17-(allylamino) geldanamycin decreased both Hsp60 and complex IV activity. In contrast, overexpression of the PINK1-interacting factor LRPPRC augmented complex IV activity by up-regulating Hsp60. A similar recovery of complex IV activity was also induced by coexpression of Hsp90 and Hsp60. Drug screening identified ginsenoside Re as a compound capable of reversing the deficit in complex IV activity in PINK1 null cells through specific increases of LRPPRC, Hsp90, and Hsp60 levels. The pharmacological effects of ginsenoside Re could be reversed by treatment of the pan-NOS inhibitor l-NG-Nitroarginine Methyl Ester (l-NAME) and could also be reproduced by low-level NO treatment. These results suggest that PINK1 regulates complex IV activity via interactions with upstream regulators of Hsp60, such as LRPPRC and Hsp90. Furthermore, they demonstrate that treatment with ginsenoside Re enhances functioning of the defective PINK1-Hsp90/LRPPRC-Hsp60-complex IV signaling axis in PINK1 null neurons by restoring NO levels, providing potential for new therapeutics targeting mitochondrial dysfunction in Parkinson''s disease.     

白藜芦醇对6-羟基多巴所致SN4741细胞损伤的保护作用和机制研究

目的:探讨白藜芦醇对6-羟基多巴引起的细胞损伤的内在保护机制。方法:以SN4741细胞系为实验对象,分为对照组、6-羟基多巴处理组和白藜芦醇预处理、6-羟基多巴处理组组。MTT法测定细胞活性。Western blot检测细胞内DJ-1表达水平。ROS检测反映细胞的氧化应激水平和线粒体损伤情况。线粒体膜电位检测反映细胞线粒体功能。结果:白藜芦醇可以剂量依赖性方式提高6-OHDA诱导的SN4741细胞的存活率。白藜芦醇预处理显著逆转6-OHDA诱导的SN4741细胞DJ-1水平的下降,降低6-OHDA引起的氧化应激水平和线粒体损伤。结论:白藜芦醇预处理能够保护6-羟基多巴所致的SN4741细胞损伤,可能与提高DJ-1的表达,减轻细胞内的氧化应激水平,改善线粒体功能有关。     

A trio has turned into a quartet: DJ-1 interacts with the IP3R-Grp75-VDAC complex to control ER-mitochondria interaction

The outer mitochondrial membrane protein VDAC interacts with the ER protein IP3R via chaperone Grp75 to form a molecular complex that couples mitochondria to the ER and contributes to functional mitochondria-ER contacts (MERCs), essential for efficient calcium (Ca²⁺) transfer. A new study by Liu et al. identifies the PD protein DJ-1 as a component of the IP3R-Grp75-VDAC complex. DJ-1 ablation impairs mitochondria-ER association and Ca²⁺ crosstalk, and impacts the stability of the trio.     

A myristoylated calcium-binding protein that preferentially interacts with the Alzheimer's disease presenilin 2 protein.

It is well established that mutations in the presenilin 1 and 2 genes cause the majority of early onset Alzheimer's disease (AD). However, our understanding of the cellular functions of the proteins they encode remains rudimentary. Knowledge of proteins with which the presenilins interact should lead to a better understanding of presenilin function in normal and disease states. We report here the identification of a calcium-binding protein, calmyrin, that interacts preferentially with presenilin 2 (PS2). Calmyrin is myristoylated, membrane-associated, and colocalizes with PS2 when the two proteins are overexpressed in HeLa cells. Yeast two-hybrid liquid assays, affinity chromatography, and coimmunoprecipitation experiments confirm binding between PS2 and calmyrin. Functionally, calmyrin and PS2 increase cell death when cotransfected into HeLa cells. These results allude to several provocative possibilities for a dynamic role of calmyrin in signaling, cell death, and AD.     

(ADP-ribose) polymerase 1 and AMP-activated protein kinase mediate progressive dopaminergic neuronal degeneration in a mouse model of Parkinson's disease

Genetic and epidemiologic evidence suggests that cellular energy homeostasis is critically associated with Parkinson''s disease (PD) pathogenesis. Here we demonstrated that genetic deletion of Poly (ADP-ribose) polymerase 1 completely blocked 6-hydroxydopamine-induced dopaminergic neurodegeneration and related PD-like symptoms. Hyperactivation of PARP-1 depleted ATP pools in dopaminergic (DA) neurons, thereby activating AMP-activated protein kinase (AMPK). Further, blockade of AMPK activation by viral infection with dominant-negative AMPK strongly inhibited DA neuronal atrophy with moderate suppression of nuclear translocation of apoptosis-inhibiting factor (AIF), whereas overactivation of AMPK conversely strengthened the 6-OHDA-induced DA neuronal degeneration. Collectively, these results suggest that manipulation of PARP-1 and AMPK signaling is an effective therapeutic approach to prevent PD-related DA neurodegeneration.     

SIAH-1 interacts with mammalian polyhomeotic homologues HPH2 and affects its stability via the ubiquitin-proteasome pathway

Polycomb Group (PcG) genes encode proteins that form large multimeric and chromatin-associated complexes implicated in the stable repression of developmentally essential genes. HPH2, the Homo sapiens polyhomeotic homologue 2, functions as one of the subunits of PcG complex 1. In our study, SIAH-1, an E3 ligase, could directly associate with HPH2 both in vitro and in vivo. Both the cysteine-rich region of SIAH-1 and the PxVxAxP motif of HPH2 were essential for the interaction. HPH2 was co-localized with SIAH-1 in nuclei. Furthermore, SIAH-1 was able to facilitate the ubiquitination and degradation of HPH2 via ubiquitin-proteasome pathway in vivo. The ubiquitination activity was severely impaired in the SIAH-1 mutant that either lost E3 ligase activity or had weakened binding ability with HPH2, strongly suggesting that SIAH-1 was the direct E3 ligase of HPH2. Thus, our results propose a novel role of SIAH-1 in regulating the expression level of HPH2 through the ubiquitin-proteasome pathway.     

PINK1 protects against cell death induced by mitochondrial depolarization,by phosphorylating Bcl-xL and impairing its pro-apoptotic cleavage

Mutations in the PINK1 gene are a frequent cause of autosomal recessive Parkinson''s disease (PD). PINK1 encodes a mitochondrial kinase with neuroprotective activity, implicated in maintaining mitochondrial homeostasis and function. In concurrence with Parkin, PINK1 regulates mitochondrial trafficking and degradation of damaged mitochondria through mitophagy. Moreover, PINK1 can activate autophagy by interacting with the pro-autophagic protein Beclin-1. Here, we report that, upon mitochondrial depolarization, PINK1 interacts with and phosphorylates Bcl-xL, an anti-apoptotic protein also known to inhibit autophagy through its binding to Beclin-1. PINK1–Bcl-xL interaction does not interfere either with Beclin-1 release from Bcl-xL or the mitophagy pathway; rather it protects against cell death by hindering the pro-apoptotic cleavage of Bcl-xL. Our data provide a functional link between PINK1, Bcl-xL and apoptosis, suggesting a novel mechanism through which PINK1 regulates cell survival. This pathway could be relevant for the pathogenesis of PD as well as other diseases including cancer.     

Loss of Yme1L perturbates mitochondrial dynamics

Yme1L is an AAA protease that is embedded in the mitochondrial inner membrane with its catalytic domain facing the mitochondrial inner-membrane space. However, how Yme1L regulates mammalian mitochondrial function is still obscure. We find that endogenous Yme1L locates at punctate structures of mitochondria, and that loss of Yme1L in mouse embryonic fibroblast (MEF) cells results in mitochondrial fragmentation and leads to significant increased ‘kiss-and-run'' type of mitochondrial fusion; however, Yme1L knockdown (shYme1L (short hairpin-mediated RNA interference of Yme1L)) cells still remain normal mitochondrial fusion although shYme1L mitochondria have a little bit less fusion and fission rates, and the shYme1L-induced fragmentation is due to a little bit more mitochondrial fission than fusion in cells. Furthermore, shYme1L-induced mitochondrial fragmentation is independent on optic atrophy 1 (OPA1) S1 or S2 processing, and shYme1L results in the stabilization of OPA1 long form (L-OPA1); in addition, the exogenous expression of OPA1 or L-OPA1 facilitates the shYme1L-induced mitochondrial fragmentation, thus this fragmentation induced by shYme1L appears to be associated with L-OPA1''s stability. ShYme1L also causes a slight increase of mitochondrial dynamics proteins of 49 kDa and mitochondrial fission factor (Mff), which recruit mitochondrial key fission factor dynamin-related protein 1 (Drp1) into mitochondria in MEF cells, and loss of Drp1 or Mff inhibits the shYme1L-induced mitochondrial fragmentation. In addition, there is interaction between SLP-2 with Yme1L and shYme1L cells retain stress-induced mitochondrial hyperfusion. Taken together, our results clarify how Yme1L regulates mitochondrial morphology.     

The E3 ligase Smurf1 regulates Wolfram syndrome protein stability at the endoplasmic reticulum

The HECT-type ubiquitin ligase (E3) Smad ubiquitination regulatory factor 1 (Smurf1) targets various substrates, including Smad1/5, RhoA, Prickle 1, MEKK2, and JunB for degradation and thereby regulates adult bone formation and embryonic development. Here, we identify the endoplasmic reticulum (ER)-localized Wolfram syndrome protein (WFS1) as a specific degradation substrate of Smurf1. Mutations in the WFS1 gene cause Wolfram syndrome, an autosomal recessive disorder characterized by diabetes mellitus and optic atrophy. WFS1 negatively regulates the ER stress response, and WFS1 deficiency in mice increases ER stress and triggers apoptosis. We show that Smurf1 interacts with WFS1 at the ER and promotes the ubiquitination and proteasomal degradation of WFS1. A C-terminal luminal region in WFS1, including residues 667-700, is involved in this degradation. Wild-type WFS1 as well as a subset of WFS1 mutants that include this degron region are susceptible to Smurf1-mediated degradation. By contrast, pathophysiological deletion mutants of WFS1 lacking the degron, such as W648X, Y660X, and Q667X, are resistant to degradation by Smurf1. Depletion of Smurf1 by RNA interference results in increased WFS1 and decreased ATF6α levels. Furthermore, we show that ER stress induces Smurf1 degradation and WFS1 up-regulation. These findings reveal for the first time that Smurf1 targets an ER-localized protein for degradation and that Smurf1 is regulated by ER stress.     

DJ-1 mediates the resistance of cancer cells to dihydroartemisinin through reactive oxygen species removal

Dihydroartemisinin (DHA), one of the main metabolites of artemisinin and its derivatives, presents anti-cancer potential in vitro and in vivo. To explore the mechanisms of resistance toward DHA, a DHA-resistant cell line, HeLa/DHA, was established with a resistance factor of 7.26 in vitro. Upon DHA treatment, apoptotic cells were significantly elicited in parental HeLa cells but minimally induced in HeLa/DHA cells. HeLa/DHA cells also displayed much less sensitivity to DHA-induced tumor suppression in cancer xenograft models than HeLa cells. Intriguingly, DHA-resistant cells did not display a multidrug-resistant phenotype. Based on a proteomic study employing LC–ESI–MS/MS together with pathway analysis, DJ-1 (PARK7) was found to be highly expressed in HeLa/DHA cells. Western blot and immunofluorescence assays confirmed the higher expression of DJ-1 in HeLa/DHA cells than in parental cells in both cell line and xenograft models. DJ-1 is translocated to the mitochondria of HeLa/DHA cells and oxidized, providing DJ-1 with stronger cytoprotection activity. Further study revealed that DJ-1 knockdown in HeLa/DHA cells abolished the observed resistance, whereas overexpression of DJ-1 endowed the parental HeLa cells with resistance toward DHA. Reactive oxygen species (ROS) were also significantly induced by either DHA or hydrogen peroxide in HeLa cells but not in resistant HeLa/DHA cells. When the cells were pretreated with N-acetyl-l-cysteine, the effect of DJ-1 knockdown on sensitizing HeLa/DHA cells to DHA was significantly attenuated. In summary, our study suggests that overexpression and mitochondrial translocation of DJ-1 provides HeLa/DHA cells with resistance to DHA-induced ROS and apoptosis.     

Parkin ubiquitinates Drp1 for proteasome-dependent degradation: implication of dysregulated mitochondrial dynamics in Parkinson disease

Mutations in Parkin, an E3 ubiquitin ligase that regulates protein turnover, represent one of the major causes of familial Parkinson disease, a neurodegenerative disorder characterized by the loss of dopaminergic neurons and impaired mitochondrial functions. The underlying mechanism by which pathogenic Parkin mutations induce mitochondrial abnormality is not fully understood. Here, we demonstrate that Parkin interacts with and subsequently ubiquitinates dynamin-related protein 1 (Drp1), for promoting its proteasome-dependent degradation. Pathogenic mutation or knockdown of Parkin inhibits the ubiquitination and degradation of Drp1, leading to an increased level of Drp1 for mitochondrial fragmentation. These results identify Drp1 as a novel substrate of Parkin and suggest a potential mechanism linking abnormal Parkin expression to mitochondrial dysfunction in the pathogenesis of Parkinson disease.