Identification of tyrosine nitration in UCH-L1 and GAPDH

Ubiquitin Carboxyl-Terminal Hydrolase L1 and Its Role in Parkinson's Disease

Ubiquitin carboxyl-terminal hydrolase L1 (UCHL1), also known as Parkinson's disease protein 5, is a highly expressed protein in the brain. It plays an important role in the ubiquitin-proteasome system (UPS), where it acts as a deubiquitinase (DUB) enzyme. Being the smallest member of the UCH family of DUBs, it catalyzes the reaction of ubiquitin precursor processing and the cleavage of ubiquitinated protein remnants, thus maintaining the level of ubiquitin monomers in the brain cells. UCHL1 mutants, containing amino acid substitutions, influence catalytic activity and its aggregability. Some of them protect cells and transgenic mice in toxin-induced Parkinson's disease (PD) models. Studies of putative protein partners of UCHL1 revealed about sixty individual proteins located in all major compartments of the cell: nucleus, cytoplasm, endoplasmic reticulum, plasma membrane, mitochondria, and peroxisomes. These include proteins related to the development of PD, such as alpha-synuclein, amyloid-beta precursor protein, ubiquitin-protein ligase parkin, and heat shock proteins. In the context of the catalytic paradigm, the importance of these interactions is not clear. However, there is increasing understanding that UCHL1 exhibits various effects in a catalytically independent manner through protein-protein interactions. Since this protein represents up to 5% of the soluble protein in the brain, PD-related changes in its structure will have profound effects on the proteomes/interactomes in which it is involved. Growing evidence is accumulating that the role of UCHL1 in PD is obviously determined by a balance of canonic catalytic activity and numerous activity-independent protein-protein interactions, which still need better characterization.

Ubiquitin carboxyl-terminal hydrolase L-1 in brain: Focus on its oxidative/nitrosative modification and role in brains of subjects with Alzheimer disease and mild cognitive impairment

Neurons must remove aggregated, damaged proteins in order to survive. Among the ways of facilitating this protein quality control is the ubiquitin-proteasomal system (UPS). Aggregated, damaged proteins are targeted for destruction by the UPS by acquiring a polymer of ubiquitin residues that serves as a signal for transport to the UPS. However, before this protein degradation can occur, the polyubiquitin chain must be removed, one residue at a time, a reaction facilitated by the enzyme, ubiquitin C-terminal hydrolase (UCH-L1). In Alzheimer disease brain, this normally abundant protein is both of lower levels and oxidatively and nitrosatively modified than in control brain. This causes diminished function of the pleiotropic UCH-L1 enzyme with consequent pathological alterations in AD brain, and the author asserts the oxidative and nitrosative alterations of UCH-L1 are major contributors to mechanisms of neuronal death in this devastating dementing disorder and its earlier stage, mild cognitive impairment (MCI). This review paper outlines these findings in AD and MCI brain.

An investigation of the correlation between the S-glutathionylated GAPDH levels in blood and Alzheimer's disease progression

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by two aggregates, namely, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) of hyperphosphorylated tau protein (tau-p), which are released into the blood in a very small amount and cannot be easily detected. An increasing number of recent studies have suggested that S-glutathionylated glyceraldehyde 3-phosphate dehydrogenase (GAPDH) is highly correlated with Aβ in patients with AD and that S-glutathionylated GAPDH plays a role as a proapoptotic factor in AD. We found that S-glutathionylated GAPDH is abundant in the blood of AD patients, which is unusual because S-glutathionylated GAPDH cannot exist in the blood under normal conditions. The aim of this study was to further explore the correlation between the S-glutathionylated GAPDH levels in blood plasma and AD progression. As controls, we recruited 191 people without AD, which included 111 healthy individuals and 37 patients with depression and insomnia, in the psychosomatic clinic. Moreover, 47 patients with AD (aged 40–89 years) were recruited at the neurology clinic. The blood S-glutathionylated GAPDH levels in the AD patients were significantly (p < 0.001) higher (752.7 ± 301.7 ng/dL) than those in the controls (59.92 ± 122.4 ng/dL), irrespective of gender and age. For AD diagnosis, the criterion blood S-glutathionylated GAPDH level > 251.62 ng/dL exhibited 95.74% sensitivity and 92.67% specificity. In fact, the individuals aged 70–89 years, namely, 37 patients from the psychosomatic clinic and 42 healthy individuals, showed significant blood S-glutathionylated GAPDH levels (230.5 ± 79.3 and 8.05 ± 20.51 ng/dL, respectively). This finding might indicate neurodegenerative AD progression in psychosomatic patients and suggests that the degree of neuronal apoptosis during AD progression might be sensitively evaluated based on the level of S-glutathionylated GAPDH in blood.

Effect of Second-Hand Tobacco Smoke on the Nitration of Brain Proteins: A Systems Biology and Bioinformatics Approach

Second-hand smoke (SHS) exposure leads to the death of approximately 48,000 nonsmokers per year in the United States alone. SHS exposure has been associated with cardiovascular, respiratory, and neurodegenerative diseases. While cardiac function abnormalities and lung cancer due to SHS have been well characterized, brain injury due to SHS has not undergone a full systematic evaluation. Oxidative stress and nitration have been associated with smoking and SHS exposure. Animal studies suggest that exposure to tobacco smoke increases oxidative stress. Oxidative stress is characterized by an increase in reactive oxygen and nitrogen species (ROS/RNS). Among the oxidative mechanisms affecting protein functionality is the posttranslational modification (PTM)-mediated tyrosine nitration. Protein tyrosine nitration, a covalent posttranslational modification, is commonly used as a marker of cellular oxidative stress associated with the pathogenesis of several neurodegenerative diseases. In our previous published work, the utility of a targeted proteomic approach has been evaluated to identify two brain abundant proteins in an in vivo SHS rat model namely the GAPDH and UCH-L1. In this current study, mass spectrometric-based proteomic and complementary biochemical methods were used to characterize the SHS-induced brain nitroproteome followed by bioinformatics/systems biology approach analysis to characterize protein interaction map. Sprague Dawley rats were exposed to SHS for 5 weeks and then cortical tissues were collected. Nitroprotein enrichment was performed via 3-Nitro tyrosine (3-NT) immunoprecipitation of brain lysates proteins. Protein nitration was validated via Western blotting to confirm the presence of nitroproteins complemented by gel-free neuroproteomic analysis by data-dependent LC-MS/MS. We identified 29 differentially expressed proteins in the 3-NT-enriched samples; seven of these proteins were unique to SHS exposure. Network analysis revealed an association of the proteins to different cellular processes including oxidative stress, ROS generation, and cell death-related pathway. This confirms the association of oxidative stress mechanisms with SHS which may contribute to neuronal injury, an area that has not been well studied in the area smoking.

Peroxynitrite and hydrogen peroxide elicit similar cellular stress responses mediated by the Ccp1 sensor protein

Peroxynitrite [ONOO(H)] is an oxidant associated with deleterious effects in cells. Because it is an inorganic peroxide that reacts rapidly with peroxidases, we speculated that cells may respond to ONOO(H) and H2O2 challenge in a similar manner. We exposed yeast cells to SIN-1, a well-characterized ONOO(H) generator, and observed stimulation of catalase and peroxiredoxin (Prx) activities. Previously, we reported that H2O2 challenge increases these activities in wild-type cells and in cells producing the hyperactive mutant H2O2 sensor Ccp1(W191F) but not in Ccp1-knockout cells (ccp1Δ). We find here that the response of ccp1Δ and ccp1(W191F) cells to SIN-1 mirrors that to H2O2, identifying Ccp1 as a sensor of both peroxides. SIN-1 simultaneously releases (•)NO and O2(•-), which react to form ONOO(H), but exposure of the three strains separately to an (•)NO donor (spermine-NONOate) or an O2(•-) generator (paraquat) mainly depresses catalase or Prx activity, whereas co-challenge with the NONOate and paraquat stimulates these activities. Because Ccp1 appears to sense ONOO(H) in cells, we examined its reaction with ONOO(H) in vitro and found that peroxynitrous acid (ONOOH) rapidly (k2>10(6)M(-1)s(-1)) oxidizes purified Ccp1 to an intermediate with spectral and ferrocytochrome-oxidizing properties indistinguishable from those of its well-characterized compound I formed with H2O2. Importantly, the nitrite released from ONOOH is not oxidized to (•)NO2 by Ccp1(׳)s compound I, unlike peroxidases involved in immune defense. Overall, our results reveal that yeast cells mount a common antioxidant response to ONOO(H) and H2O2, with Ccp1 playing a pivotal role as an inorganic peroxide sensor.

Heterogeneous expression and functional relevance of the ubiquitin carboxyl-terminal hydrolase L1 in melanoma

The expression of ubiquitin carboxyl-terminal hydrolase 1 (UCHL1) is deregulated in human cancer cells with tumor inhibiting or promoting functions. Due to less knowledge on the role of UCHL1 in melanoma progression, the expression pattern and function of UCHL1 as well as the deregulated signaling pathways were characterized. A large number of melanoma cell lines, tissue microarrays of melanoma lesions and control tissues were analyzed for UCHL1 expression using PCR, Western blot and/or immunohistochemistry. The analysis revealed that melanocyte cultures, 24 of 331 melanoma lesions, two of 18 short-term cultures and two of 19 melanoma cell lines tested, respectively, heterogeneously expressed UCHL1. The low frequency of UCHL1 expression in melanoma cells was due to gene silencing by promoter DNA hypermethylation. Using different transfection models an enzyme activity-dependent growth promoting function of UCHL1 via the activation of the mitogen-activated protein kinase signaling pathway was found in melanoma cells. Under oxygen stress a dose-dependent effect of UCHL1 was detected, which was mediated by a dynamic modification of the PI3K-Akt signaling. Thus, the aberrant UCHL1 expression in melanoma cells is linked to dynamic changes in growth properties and signal transduction cascades suggesting that UCHL1 provides a novel marker and/or therapeutic target at least for a subset of melanoma patients.

Multiple binding partners

GAPDH interacts with a plethora of diverse cellular proteins. The network of interacting partners, or interactome, is presented for GAPDH with the interacting molecules grouped into specific functional and structural categories. By organizing the binding partners in this way, certain common structural features are beginning to surface, such as acidic dipeptide sequences that are found in several of these binding proteins. Additionally, the consensus sequences for target polynucleotides are being brought to light. The categories, which are presented according to function, offer an opportunity for research into the corresponding structural correlates to these interactions. Recent discoveries of interacting proteins have revealed novel relationships that are generating emerging mechanisms. Proteins that are associated with age-related neurodegenerative diseases appear to be particularly prone to binding GAPDH, suggesting that GAPDH may be playing a role in these diseases. Neurodegenerative diseases that are discussed are the conformational diseases of aging, suggesting that GAPDH may be a global sensor for cellular conformational stress. In addition to GAPDH's oxidoreductase activity, several other enzymatic functions have been discovered, including peroxidase, nitrosylase, mono-ADP-ribosylase and kinase activities.

Target for diverse chemical modifications

The chapter begins with an historical perspective of GAPDH isozymes that is juxtaposed to the fact that there is only one somatic functional gene in humans that is virtually identical among the mammalian species. Over the many years of GAPDH research, dozens of labs have reported the existence of multiple forms of GAPDH, which mostly vary as a function of charge with an occasional report of truncated forms. These observations are in part due to GAPDH being a substrate for many enzymatically-controlled post-translational modifications. While target residues have been identified and predictive algorithms have implicated certain residues, this area of research appears to be in its infancy regarding GAPDH. Equally fascinating, the uniquely susceptible nature of GAPDH to non-enzymatic reactions, that typically are associated with cell stress, such as oxidation and nitration, is also discussed. Two metabolic gases, nitric oxide and hydrogen sulfide, which are enzymatically produced, appear to exert their signaling properties through non-enzymatic reaction with GAPDH. Models of cellular decline are also proposed, including the compelling hypothesis that states cell compromise occurs by the physically blocking the function of chaperonins (i.e. dual-ring multiple-subunit molecular chaperones) by the attachment of misfolded GAPDH.

The good and bad effects of cysteine S-nitrosylation and tyrosine nitration upon insulin exocytosis: a balancing act

As understanding of the mechanisms driving and regulating insulin secretion from pancreatic beta cells grows, there is increasing and compelling evidence that nitric oxide (•NO) and other closely-related reactive nitrogen species (RNS) play important roles in this exocytic process. •NO and associated RNS, in particular peroxynitrite, possess the capability to effect signals across both intracellular and extracellular compartments in rapid fashion, affording extraordinary signaling potential. It is well established that nitric oxide signals through activation of guanylate cyclase-mediated production of cyclic GMP. The intricate intracellular redox environment, however, lends credence to the possibility that •NO and peroxynitrite could interact with a wider variety of biological targets, with two leading mechanisms involving 1) Snitrosylation of cysteine, and 2) nitration of tyrosine residues comprised within a variety of proteins. Efforts aimed at delineating the specific roles of •NO and peroxynitrite in regulated insulin secretion indicate that a highly-complex and nuanced system exists, with evidence that •NO and peroxynitrite can contribute in both positive and negative regulatory ways in beta cells. Furthermore, the ultimate biochemical outcome within beta cells, whether to compensate and recover from a given stress, or not, is likely a summation of contributory signals and redox status. Such seeming regulatory dichotomy provides ample opportunity for these mechanisms to serve both physiological and pathophysiologic roles in onset and progression of diabetes. This review focuses attention upon recent accumulating evidence pointing to roles for nitric oxide induced post-translational modifications in the normal regulation as well as the dysfunction of beta cell insulin exocytosis.