Microtubule dysfunction by posttranslational nitrotyrosination of alpha-tubulin: a nitric oxide-dependent mechanism of cellular injury

Total and mitochondrial nitrosative stress, decreased brain-derived neurotrophic factor (BDNF) levels and glutamate uptake, and evidence of endoplasmic reticulum stress in the hippocampus of vitamin A-treated rats

Vitamin A supplementation has caused concern among public health researchers due to its ability in decreasing life quality from acute toxicological effects to increasing mortality rates among vitamin supplement users. For example, it was described cognitive decline (i.e. irritability, anxiety, and depression) in patients subjected to long-term vitamin A therapy, as occurs in cancer treatment. However, the mechanism by which vitamin A affects mammalian cognition is not completely understood. Then, we performed the present work to investigate the effects of vitamin A supplementation at clinical doses (1,000-9,000 IU/kg day(-1)) for 28 days on rat hippocampal nitrosative stress levels (both total and mitochondrial), bioenergetics states, brain-derived neurotrophic factor (BDNF), alpha- and beta-synucleins, BiP and dopamine receptor 2 (D2 receptor) contents, and glutamate uptake. We observed mitochondrial impairment regarding respiratory chain function: increased complex I-III, but decreased complex IV enzyme activity. Also, decreased BDNF levels were observed in vitamin A-treated rats. The present data demonstrates, at least in part, that mitochondrial dysfunction and decreased BDNF and D2 receptors levels, as well as decreased glutamate uptake may take an important role in the mechanism behind the previously reported cognitive disturbances associated to vitamin A supplementation.

Site-specific orthogonal labeling of the carboxy terminus of alpha-tubulin

A fluorescent probe has been attached to the carboxy terminus of the alpha-subunit of alpha,beta-tubulin by an enzymatic reaction followed by a chemical reaction. The unnatural amino acid 3-formyltyrosine is attached to the carboxy terminus of alpha-tubulin through the use of the enzyme tubulin tyrosine ligase. The aromatic aldehyde of the unnatural amino acid serves as an orthogonal electrophile that specifically reacts with a fluorophore containing an aromatic hydrazine functional group, which in this case is 7-hydrazino-4-methyl coumarin. Conditions for covalent bond formation between the unnatural amino acid and the fluorophore are mild, allowing fluorescently labeled tubulin to retain its ability to assemble into microtubules. A key feature of the labeling reaction is that it produces a red shift in the fluorophore's absorption and emission maxima, accompanied by an increase in its quantum yield; thus, fluorescently labeled protein can be observed in the presence of unreacted fluorophore. Both the enzymatic and coupling reaction can occur in living cells. The approach presented here should be applicable to a wide variety of in vitro systems.

Clostridium difficile toxin A decreases acetylation of tubulin, leading to microtubule depolymerization through activation of histone deacetylase 6, and this mediates acute inflammation

Clostridium difficile toxin A is known to cause actin disaggregation through the enzymatic inactivation of intracellular Rho proteins. Based on the rapid and severe cell rounding of toxin A-exposed cells, we speculated that toxin A may be involved in post-translational modification of tubulin, leading to microtubule instability. In the current study, we observed that toxin A strongly reduced α-tubulin acetylation in human colonocytes and mouse intestine. Fractionation analysis demonstrated that toxin A-induced α-tubulin deacetylation yielded monomeric tubulin, indicating the presence of microtubule depolymerization. Inhibition of the glucosyltransferase activity against Rho proteins of toxin A by UDP-2',3'-dialdehyde significantly abrogated toxin A-induced α-tubulin deacetylation. In colonocytes treated with trichostatin A (TSA), an inhibitor of the HDAC6 tubulin deacetylase, toxin A-induced α-tubulin deacetylation and loss of tight junction were completely blocked. Administration of TSA also attenuated proinflammatory cytokine production, mucosal damage, and epithelial cell apoptosis in mouse intestine exposed to toxin A. These results suggest that toxin A causes microtubule depolymerization by activation of HDAC6-mediated tubulin deacetylation. Indeed, blockage of HDAC6 by TSA markedly attenuates α-tubulin deacetylation, proinflammatory cytokine production, and mucosal damage in a toxin A-induced mouse enteritis model. Tubulin deacetylation is an important component of the intestinal inflammatory cascade following toxin A-mediated Rho inactivation in vitro and in vivo.

Functional consequences of actin nitration: in vitro and in disease states

To link the phenomena of inflammatory-induced increases in protein nitrotyrosine (NO(2)Tyr) derivatives to protein dysfunction and consequent pathological conditions, the evaluation of discrete NO(2)Tyr modifications on specific proteins must be undertaken. Mass spectrometric (MS) proteomics-based strategies allow for the identification of all individual proteins that are nitrated by separating tissue homogenates using 2D gel electrophoresis, detecting the nitrated proteins using an anti-NO(2)Tyr antibody, and then identifying the peptides generated during an in-gel proteolytic digest using matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) MS. Actin, one of the most abundant proteins in eukaryotic cells, constitutes 5% or more of cell protein and serves with other cytoskeletal proteins as a critical target for nitration-induced functional impairment. Herein, examples of actin nitration detected under physiological conditions in various models of human disease or in clinically derived tissues are given and the impact that this post-translational protein modification can have on cell and organ function is discussed.

Plant cell division is specifically affected by nitrotyrosine

Virtually all eukaryotic alpha-tubulins harbour a C-terminal tyrosine that can be reversibly removed and religated, catalysed by a specific tubulin-tyrosine carboxypeptidase (TTC) and a specific tubulin-tyrosine ligase (TTL), respectively. The biological function of this post-translational modification has remained enigmatic. 3-nitro-L-tyrosine (nitrotyrosine, NO(2)Tyr), can be incorporated into detyrosinated alpha-tubulin instead of tyrosine, producing irreversibly nitrotyrosinated alpha-tubulin. To gain insight into the possible function of detyrosination, the effect of NO(2)Tyr has been assessed in two plant model organisms (rice and tobacco). NO(2)Tyr causes a specific, sensitive, and dose-dependent inhibition of cell division that becomes detectable from 1 h after treatment and which is not observed with non-nitrosylated tyrosine. These effects are most pronounced in cycling tobacco BY-2 cells, where the inhibition of cell division is accompanied by a stimulation of cell length, and a misorientation of cross walls. NO(2)Tyr reduces the abundance of the detyrosinated form of alpha-tubulin whereas the tyrosinated alpha-tubulin is not affected. These findings are discussed with respect to a model where NO(2)Tyr is accepted as substrate by TTL and subsequently blocks TTC activity. The irreversibly tyrosinated alpha-tubulin impairs microtubular functions that are relevant to cell division in general, and cell wall deposition in particular.

Analysis of the Legionella longbeachae genome and transcriptome uncovers unique strategies to cause Legionnaires' disease

Legionella pneumophila and L. longbeachae are two species of a large genus of bacteria that are ubiquitous in nature. L. pneumophila is mainly found in natural and artificial water circuits while L. longbeachae is mainly present in soil. Under the appropriate conditions both species are human pathogens, capable of causing a severe form of pneumonia termed Legionnaires' disease. Here we report the sequencing and analysis of four L. longbeachae genomes, one complete genome sequence of L. longbeachae strain NSW150 serogroup (Sg) 1, and three draft genome sequences another belonging to Sg1 and two to Sg2. The genome organization and gene content of the four L. longbeachae genomes are highly conserved, indicating strong pressure for niche adaptation. Analysis and comparison of L. longbeachae strain NSW150 with L. pneumophila revealed common but also unexpected features specific to this pathogen. The interaction with host cells shows distinct features from L. pneumophila, as L. longbeachae possesses a unique repertoire of putative Dot/Icm type IV secretion system substrates, eukaryotic-like and eukaryotic domain proteins, and encodes additional secretion systems. However, analysis of the ability of a dotA mutant of L. longbeachae NSW150 to replicate in the Acanthamoeba castellanii and in a mouse lung infection model showed that the Dot/Icm type IV secretion system is also essential for the virulence of L. longbeachae. In contrast to L. pneumophila, L. longbeachae does not encode flagella, thereby providing a possible explanation for differences in mouse susceptibility to infection between the two pathogens. Furthermore, transcriptome analysis revealed that L. longbeachae has a less pronounced biphasic life cycle as compared to L. pneumophila, and genome analysis and electron microscopy suggested that L. longbeachae is encapsulated. These species-specific differences may account for the different environmental niches and disease epidemiology of these two Legionella species.

Platelets and innate immunity

Although platelets are best known as primary mediators of hemostasis, this function intimately associates them with inflammatory processes, and it has been increasingly recognized that platelets play an active role in both innate and adaptive immunity. For example, platelet adhesive interactions with leukocytes and endothelial cells via P-selectin can lead to several pro-inflammatory events, including leukocyte rolling and activation, production of cytokine cascades, and recruitment of the leukocytes to sites of tissue damage. Superimposed on this, platelets express immunologically-related molecules such as CD40L and Toll-like receptors that have been shown to functionally modulate innate immunity. Furthermore, platelets themselves can interact with microorganisms, and several viruses have been shown to cross-react immunologically with platelet antigens. This review discusses the central role that platelets play in inflammation, linking them with varied pathological conditions, such as atherosclerosis, sepsis, and immune thrombocytopenic purpura, and suggests that platelets also act as primary mediators of our innate defences.

Nitration of profilin effects its interaction with poly (L-proline) and actin

Profilin from bovine spleen was nitrated with peroxynitrite; immunoblotting and spectrophotometric quantitation of nitrotyrosine residues suggested nitration of a single tyrosine residue in profilin with a stoichiometry of 0.6 mol of nitrotyrosine/mole of profilin. A decrease in the nitrotyrosine immunoreactivity of nitroprofilin during digestion with carboxypeptidase Y indicated that nitrotyrosine is located at the C-terminus of profilin. Nitroprofilin interaction with ligands such as phosphatidylinositol 4,5-bisphosphate, actin and poly (l-proline) was analyzed by monitoring the tryptophan fluorescence. Scatchard plot and binding isotherm data obtained revealed no significant difference in affinity of nitroprofilin to phosphatidylinositol 4,5-bisphosphate (K(d) of 4.8 +/- 0.5 muM for profilin, and K(d) of 5.7 +/- 0.6 muM for nitroprofilin), while poly (l-proline) binding studies revealed a twenty-fold increase in the affinity of profilin to poly (l-proline) upon nitration (K(d) of 21.8 +/- 1.7 muM for profilin, and K(d) of 1.1 +/- 0.1 muM for nitroprofilin). Actin polymerization studies involving pyrene-labeled actin indicated that profilin nitration inhibits the actin sequestering property of profilin. The critical actin monomer concentration (C(c)) was 150 and 250 nM in the presence of nitroprofilin and profilin, respectively. Thus, nitric oxide and free radicals produced under different conditions could alter the functions of profilin through nitration, such as its interaction with actin and poly (l-proline).

The brain in acute liver failure. A tortuous path from hyperammonemia to cerebral edema

Acute liver failure (ALF) is a condition with an unfavourable prognosis. Multiorgan failure and circulatory collapse are frequent causes of death, but cerebral edema and intracranial hypertension (ICH) are also common complications with a high risk of fatal outcome. The underlying pathogenesis has been extensively studied and although the development of cerebral edema and ICH is of a complex and multifactorial nature, it is well established that ammonia plays a pivotal role. This review will focus on the effects of hyperammonemia on neurotransmission, mitochondrial function, oxidative stress, inflammation and regulation of cerebral blood flow. Finally, potential therapeutic targets and future perspectives are briefly discussed.

Intragenomic rearrangement in TT viruses: a possible role in the pathogenesis of disease

A role for the ubiquitous Torque teno (TT) viruses in the pathogenesis of disease has not been resolved. In vivo and in vitro intragenomic rearrangement of TT virus genomes has been demonstrated. Replication in cell culture of a subviral molecule (411 bp) occurs through oligomerisation of RNA transcripts. Although the functions of the respective TT viral genes, as well as the newly formed genes in the rearranged subviral molecules, are largely unknown, certain similarities to genes of plant viruses of the family Geminiviridae will be described. A degree of similarity to certain cellular genes poses the question as to a role of molecular mimicry in the pathogenesis of autoimmune disease and diabetes.

Proteomic analysis of protein tyrosine nitration after ischemia reperfusion injury: mitochondria as the major target

Endothelial nitric oxide synthase-derived NO and its derivative, peroxynitrite (ONOO(-)), suppresses oxygen consumption by nitration of mitochondrial proteins after reperfusion. However, very few nitrated proteins are identified to date. In this paper, ischemia/reperfusion (I/R) injury was induced in mouse heart by ligation and release of the left anterior descending coronary artery. Western blotting showed that tyrosine nitration was higher in I/R hearts. Nitrated proteins were identified by capillary-liquid chromatography-nanospray tandem mass spectrometry. A total of 23 proteins were identified as being nitrated after I/R and 10 of them were from mitochondria. The nitrated mitochondrial proteins included 4 subunits from the oxidative phosphorylation system (the 24 and the 30 kDa subunits of complex I, the Rieske ISP of complex III, and the alpha subunit of ATP synthase), five enzymes in the matrix, and voltage-dependent anion channel. In purified complex I treated with ONOO(-), 3-NT was identified locating at the residue of Y247 of the 30 kDa subunit and the residues of Y47, Y53 of the 49 kDa subunit. In conclusion, I/R induced protein nitration and mitochondrial proteins were the major targets. Selective nitration of proteins from the oxidative phosphorylation system at the beginning of reperfusion may contribute to the suppression of oxygen consumption.

Protein tyrosine nitration--an update

Tyrosine nitration is a covalent post-translational protein modification derived from the reaction of proteins with nitrating agents. Tyrosine nitration has been used as a marker of oxidant burden in human diseases. However, it remains unclear whether protein nitration is responsible for alterations in protein function that imparts an increased risk for disease development or unfavorable outcomes. Emerging data implicate tyrosine nitration as a mediator of immune responses suggesting a novel biological function for this protein modification.

A novel immunosuppressive pathway involving peroxynitrite-mediated [corrected] nitration of platelet antigens within antigen-presenting cells

BACKGROUND

Studies have demonstrated that immunity against platelet (PLT) transfusions is dependent on recipient antigen-presenting cells (APCs) and their ability to produce nitric oxide (NO). To further analyze this, we focused on NO's major metabolite peroxynitrite (ONOO(-)) and its ability to affect PLT immunity.

STUDY DESIGN AND METHODS

To address how NO and its major metabolite may mediate PLT immunity, GP91(PHOX) knockout (KO) mice that lack the ability to produce the ONOO(-) were transfused weekly with allogeneic BALB/c PLTs, and donor antibody development was analyzed.

RESULTS

Compared with controls, GP91(PHOX) KO mice developed significantly (p < 0.0001) higher-titered immunoglobulin G (IgG) donor antibodies by two transfusions, and this immune response could be inhibited by treating the recipient mice with aminoguanidine, a relatively selective inhibitor of inducible nitric oxide synthase. In vitro nitration of PLTs did not alter PLT antibody binding but significantly inhibited the transfused PLT's ability to stimulate IgG immunity in either wild-type or KO mice. The lack of nitrated PLT immunity correlated with an inability of APCs to mediate phagocytosis of nitrated PLTs. The lack of nitrated PLT immunity could only be restored when normal PLTs were mixed with the nitrated PLTs and transfused.

CONCLUSION

The results identify a dual role for NO metabolism within APCs that significantly modulates PLT immunity; nitration of PLT antigens leads to lack of immunity due to an inability of APCs to move PLT antigens intracellularly whereas there exists an NO-dependent pathway that stimulates anti-PLT immunity.

Nitrotyrosine promotes human aortic smooth muscle cell migration through oxidative stress and ERK1/2 activation

Nitrotyrosine is a new biomarker of atherosclerosis and inflammation. The objective of this study was to determine the direct effects of free nitrotyrosine on human aortic smooth muscle cell (AoSMC) migration and molecular mechanisms. By a modified Boyden chamber assay, nitrotyrosine significantly increased AoSMC migration in a concentration-dependent manner. For example, nitrotyrosine at 300 nM increased AoSMC migration up to 152% compared with l-tyrosine-treated control cells (P<0.01). Cell wound healing assay confirmed this effect. Nitrotyrosine significantly increased the expression of some key cell migration-related molecules including PDGF receptor-B, matrix metalloproteinase 2 (MMP2) and integrins alphaV and beta3 at both mRNA and protein levels in AoSMC (P<0.01). In addition, nitrotyrosine increased reactive oxygen species (ROS) production in AoSMC by staining with fluorescent dye DCFHDA. Furthermore, nitrotyrosine induced transient phosphorylation of ERK2 by Bio-Plex luminex immunoassay and western blot analysis. AoSMC were able to uptake nitrotyrosine. Antioxidants including seleno-l-methionine and superoxide dismutase mimetic (MnTBAP) as well as ERK1/2 inhibitor PD98059 effectively blocked the promoting effect of nitrotyrosine on AoSMC migration and the mRNA expression of above cell migration-related molecules. Thus, nitrotyrosine directly increases AoSMC migration in vitro and the expression of migration-related molecules through overproduction of ROS and activation of ERK1/2 pathway. Nitrotyrosine may contribute to cardiovascular pathogenesis.

Oxidative stress-induced disruption of epithelial and endothelial tight junctions

Mounting body of evidence indicates that the disruption of epithelial tight junctions and resulting loss of barrier function play a crucial role in the pathogenesis of a variety of gastrointestinal, hepatic, pulmonary, kidney and ocular diseases. Increased production of inflammatory mediators such as cytokines and reactive oxygen species disrupt the epithelial and endothelial barrier function by destabilizing tight junctions. Oxidative stress induced by various reactive oxygen species such as hydrogen peroxide, nitric oxide, peroxynitrite and hypochlorous acid disrupt the epithelial and endothelial tight junctions in various tissues. The mechanism involved in oxidative stress-induced disruption of tight junction includes protein modification such as thiol oxidation, phosphorylation, nitration and carbonylation. The role of signaling molecules such as protein kinases and protein phosphatases in regulation of tight junctions is discussed in this article. Understanding such mechanisms in oxidative stress-induced disruption of epithelial and endothelial barrier functions is likely to provide insight into the pathogenesis of various inflammatory diseases, and may form a basis for the design of treatment strategies for different diseases.

Activated macrophages inhibit enterocyte gap junctions via the release of nitric oxide

Enterocytes exist in close association with tissue macrophages, whose activation during inflammatory processes leads to the release of nitric oxide (NO). Repair from mucosal injury requires the migration of enterocytes into the mucosal defect, a process that requires connexin43 (Cx43)-mediated gap junction communication between adjacent enterocytes. Enterocyte migration is inhibited during inflammatory conditions including necrotizing enterocolitis, in part, through impaired gap junction communication. We now hypothesize that activated macrophages inhibit gap junctions of adjacent enterocytes and seek to determine whether NO release from macrophages was involved. Using a coculture system of enterocytes and macrophages, we now demonstrate that "activation" of macrophages with lipopolysaccharide and interferon reduces the phosphorylation of Cx43 in adjacent enterocytes, an event known to inhibit gap junction communication. The effects of macrophages on enterocyte gap junctions could be reversed by treatment of macrophages with the inducible nitric oxide synthase (iNOS) inhibitor l-Lysine omega-acetamidine hydrochloride (l-NIL) and by incubation with macrophages from iNOS(-/-) mice, implicating NO in the process. Activated macrophages also caused a NO-dependent redistribution of connexin43 in adjacent enterocytes from the cell surface to an intracellular location, further suggesting NO release may inhibit gap junction function. Treatment of enterocytes with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) markedly inhibited gap junction communication as determined using single cell microinjection of the gap junction tracer Lucifer yellow. Strikingly, activated macrophages inhibited enterocyte migration into a scraped wound, which was reversed by l-NIL pretreatment. These results implicate enterocyte gap junctions as a target of the NO-mediated effects of macrophages during intestinal inflammation, particularly where enterocyte migration is impaired.

Dynamic interplay between nitration and phosphorylation of tubulin cofactor B in the control of microtubule dynamics

Tubulin cofactor B (TCoB) plays an important role in microtubule dynamics by facilitating the dimerization of alpha- and beta-tubulin. Recent evidence suggests that p21-activated kinase 1 (Pak1), a major signaling nodule in eukaryotic cells, phosphorylates TCoB on Ser-65 and Ser-128 and plays an essential role in microtubule regrowth. However, to date, no upstream signaling molecules have been identified to antagonize the functions of TCoB, which might help in maintaining the equilibrium of microtubules. Here, we discovered that TCoB is efficiently nitrated, mainly on Tyr-64 and Tyr-98, and nitrated-TCoB attenuates the synthesis of new microtubules. In addition, we found that nitration of TCoB antagonizes signaling-dependent phosphorylation of TCoB, whereas optimal nitration of TCoB requires the presence of functional Pak1 phosphorylation sites, thus providing a feedback mechanism to regulate phosphorylation-dependent MT regrowth. Together these findings identified TCoB as the third cytoskeleton protein to be nitrated and suggest a previously undescribed mechanism, whereby growth factor signaling may coordinately integrate nitric oxide signaling in the regulation of microtubule dynamics.

Bioenergetic and oxidative effects of free 3-nitrotyrosine in culture: selective vulnerability of dopaminergic neurons and increased sensitivity of non-dopaminergic neurons to dopamine oxidation

Protein bound and free 3-nitrotyrosine (3NT) levels are elevated in neurodegenerative diseases and have been used as evidence for peroxynitrite generation. Intrastriatal injection of free 3NT causes dopaminergic neuron injury and represents a new mouse model of Parkinson's disease (PD). We are investigating the nature of free 3NT neurotoxicity. In primary ventral midbrain cultures, free 3NT damaged dopaminergic neurons, while adjacent non-dopaminergic neurons were unaffected. Combined treatment with free 3NT and subtoxic amounts of dopamine caused extensive death of non-dopaminergic forebrain neurons in culture. Free 3NT alone directly inhibited mitochondrial complex I, decreased ATP, sensitized neurons to mitochondrial depolarization, and increased superoxide production. Subtoxic concentrations of rotenone (instead of free 3NT) caused similar results. Additionally, free 3NT and dopamine combined increased extraneuronal hydrogen peroxide and decreased intraneuronal glutathione levels more than dopamine alone. Oxidative and bioenergetic processes have been proposed to contribute to neurodegeneration in PD. As free 3NT is a compound that is increased in PD, damages dopamine neurons in vivo and in vitro and has detrimental effects on neuronal bioenergetics, it is possible that free 3NT is an endogenous contributing factor to neuronal loss, in addition to being a marker of oxidative and nitrative processes.

Reperfusion enhances nitrotyrosine formation in rat focal cerebral ischemia

The widespread benefit of thrombolysis has been emphasized, but relatively little is known about reperfusion injury. The purpose of this study is to evaluate the difference in nitrotyrosine formation and infarct volume between permanent and transient focal ischemia in rats. Permanent (n = 14) or transient (n = 12) focal ischemia was induced by permanent or 2-hour occlusion of the middle cerebral artery, respectively, with the permanent ligation of the bilateral common carotid arteries in Sprague-Dawley rats. In both models all animals were killed 24 hours after the start of occlusion. The ratio of nitrotyrosine in the peri-infarct and core-of-infarct regions in transient focal ischemia was significantly higher than in permanent focal ischemia (P < .01). Infarct volume in the cortex, but not caudoputamen or whole brain, was significantly larger in transient ischemia than in permanent ischemia (P < .05), with a significant expansion of brain swelling. These results may reflect the higher production of superoxide and nitric oxide owing to reperfusion, and suggest the need to administer neuroprotective drugs such as anti-oxidants as well as thrombolytic agents in the treatment of acute ischemic cerebral damage.

Tau is Endogenously Nitrated in Mouse Brain: Identification of a Tyrosine Residue Modified In vivo by NO

Nitration of tau protein is normally linked to neurodegeneration but, until now, no comprehensive information is available regarding tau nitration in healthy subjects. It has been previously reported that in differentiated PC12 cells, tau co-immunoprecipitated with alpha-tubulin is nitrated at tyrosine residues and that this post-translation modification doesn't impair the association of tau with the cytoskeleton. The present paper is focused on the identification of tyrosine residues endogenously modified in tau from PC12 cells and reports for the first time that tau is also nitrated in vivo in normal mouse brain and that one tyrosine is endogenously modified.

Tyrosine nitration is a novel post-translational modification occurring on the neural intermediate filament protein peripherin

The biological implication of protein tyrosine nitration in signaling pathways triggered by nitric oxide is recently emerging. Here we report for the first time that nitrotyrosination occurs in the neural intermediate filament protein peripherin. In neuron-like PC12 cells, nitrated peripherin is associated with the cytoskeleton fraction, its level increases during the progression of NGF-induced differentiation and the nitrated protein remains closely associated with stable microtubules. Tyr 17 and Tyr 376 were identified by MALDI-TOF analyses as two specific residues endogenously nitrated. Finally, peripherin nitration is not restricted to PC12 cells but it is also present in vivo in rat brain.

Determination of plasma free 3-nitrotyrosine and tyrosine by reversed-phase liquid chromatography with 4-fluoro-7-nitrobenzofurazan derivatization

Oxidative stress plays an important role in pathogenesis of many diseases. Measurement of 3-nitrotyrosine (NO(2)Tyr), as a potential biomarker for nitric oxide-mediated damage, has recently been the focus of particular attention. We have developed an HPLC method with NBD-F pre-column derivatization followed by C(18) cartridge cleaning. Using this method we achieved limits of detection of 0.5 and 1.1 nm for NO(2)Tyr and tyrosine (Tyr), respectively, close to that achieved by LS-MS/MS. NO(2)Tyr and tyrosine concentrations were linear over the calibration ranges 0.5-100 nm and 1-320 microm, respectively, with correlation coefficients greater than 0.95. To evaluate the utility of this assay in plasma we analysed samples obtained from smokers and non-smoking subjects. Consistent with the presence of elevated oxidative stress, the plasma NO(2)Tyr concentration and NO(2)Tyr:Tyr ratio of smokers were 17.42 +/- 11.6 nm and 0.263 +/- 0.192 nm/microm with 3.8 and 3.9 times higher (both p < 0.05), respectively, than that of non-smoker controls (4.54 +/- 2.75 nm and 0.067 +/- 0.050 nm/microm, respectively). In conclusion, we have developed a novel HPLC assay for NO(2)Tyr without MS detection that is applicable to clinical studies addressing the pathophysiology and importance of oxidative stress.

Detection of Modified Tyrosines as an Inflammation Marker in a Photo-aged Skin Model

Reactive nitrogen species, produced during the process of inflammation induced by various factors including UV radiation, modify amino acids in crucial proteins. It is assumed that skin tissue is more likely to be modified, as it is located at the outer layer of a body that is exposed to UV radiation on a daily basis. To investigate the influence of the modified tyrosine on UV-exposed skin, we detected the nitrotyrosine or halogenated tyrosine and dityrosine in photo-aged model mice. The back skin of mice was exposed to a dose of 10 J cm(-2) day(-1) every day for 15 weeks. Samples exhibiting typical symptoms of photo aging were provided to the immunofluorescence study. The quantification of modified proteins was accomplished through a chemical analytical method known as HPLC-tandem mass spectrometry. Analysis of the irradiated skin samples showed that all modified tyrosine except nitrotyrosine demonstrated statistically significant increases. The molecular weights of major modified proteins, confirmed as 25-50 kDa, were measured using Western blot analysis with an anti-nitrotyrosine antibody. Furthermore, the immunofluorescence study verified that the localization of myeloperoxidase conformed to that of nitrotyrosine. This result suggests that the modified tyrosine was produced during the process of inflammation by UV irradiation. In this study, we used a low dose of UV irradiation to which we are exposed in daily life. Our results suggest that UV exposure in daily life may induce the production of modified tyrosines and skin aging.

Glitazones Induce Astroglioma Cell Death by Releasing Reactive Oxygen Species from Mitochondria: Modulation of Cytotoxicity by Nitric Oxide

The glitazones (or thiazolidinediones) are synthetic compounds used in type-2 diabetes, but they also have broad antiproliferative and anti-inflammatory properties still not well understood. We described previously the apoptotic effects of glitazones on astroglioma cells ( J Biol Chem 279: 8976-8985, 2004 ). At certain concentrations, we found a selective lethality on glioma cells versus astrocytes that was dependent on a rapid production of reactive oxygen species (ROS) and seemed unrelated to the receptor peroxisome proliferator activated receptor-gamma. The present study was aimed at characterizing the oxygen derivatives induced by ciglitazone, rosiglitazone, and pioglitazone in C6 glioma cells and to investigate their intracellular source. We examined the interaction of ROS with nitric oxide (NO) and its consequences for glioma cell survival. Fluorescence microscopy and flow cytometry showed that glitazones induced superoxide anion, peroxynitrite, and hydrogen peroxide, with ciglitazone being the most active. ROS production was completely prevented by uncoupling of the electron transport chain and by removal of glucose as an energy substrate, whereas it was unaffected by inhibition of NADPH-oxidase and xanthine-oxidase. Moreover, glitazones inhibited state 3 respiration in permeabilized cells, and experiments with mitochondrial inhibitors suggested that complex I was the likely target of glitazones. Therefore, these results point to the mitochondrial electron transport chain as the source of glitazone-induced ROS in C6 cells. Glitazones also depolarized mitochondria and reduced mitochondrial pH. NO synthase inhibitors revealed that superoxide anion combines with NO to yield peroxynitrite and that the latter contributes to the cytotoxicity of glitazones in astroglioma cells. Future antitumoral strategies may take advantage of these findings.

Prevention of peroxynitrite-induced apoptosis of motor neurons and PC12 cells by tyrosine-containing peptides

Although peroxynitrite stimulates apoptosis in many cell types, whether peroxynitrite acts directly as an oxidant or the induction of apoptosis is because of the radicals derived from peroxynitrite decomposition remains unknown. Before undergoing apoptosis because of trophic factor deprivation, primary motor neuron cultures become immunoreactive for nitrotyrosine. We show here using tyrosine-containing peptides that free radical processes mediated by peroxynitrite decomposition products were required for triggering apoptosis in primary motor neurons and in PC12 cells cultures. The same concentrations of tyrosine-containing peptides required to prevent the nitration and apoptosis of motor neurons induced by trophic factor deprivation and of PC12 cells induced by peroxynitrite also prevented peroxynitrite-mediated nitration of motor neurons, brain homogenates, and PC12 cells. The heat shock protein 90 chaperone was nitrated in both trophic factor-deprived motor neurons and PC12 cells incubated with peroxynitrite. Tyrosine-containing peptides did not affect the induction of PC12 cell death by hydrogen peroxide. Tyrosine-containing peptides should protect by scavenging peroxynitrite-derived radicals and not by direct reactions with peroxynitrite as they neither increase the rate of peroxynitrite decomposition nor decrease the bimolecular peroxynitrite-mediated oxidation of thiols. These results reveal an important role for free radical-mediated nitration of tyrosine residues, in apoptosis induced by endogenously produced and exogenously added peroxynitrite; moreover, tyrosine-containing peptides may offer a novel strategy to neutralize the toxic effects of peroxynitrite.

Photo-activity induced by amyloidogenesis

Accumulation of chemically altered proteins is a noted characteristic of biological aging, and increasing evidence suggests a variety of deleterious cellular developments associated with senescence. Concomitantly, the "aging" of protein deposits associated with numerous neurological disorders may involve covalent modifications of their constituents. However, the link between disease-related protein aggregation and chemical alterations of its molecular constituents has yet to be established. The present study of amyloidogenic alpha-synuclein protein points to a decisive change in the biophysical behavior of growing protein aggregates with progressive photo-activity in the visible range of the electromagnetic spectrum. I hypothesize that the photo-activity induced by filament formation is governed by the same mechanism as seen for the intrinsic chromophore of 4-(p-hydroxybenzylidene)-5-imidazolinone-type in the family of green fluorescent proteins. This type of the covalent alterations is initiated concurrently with amyloid elongation and involves a complex multi-step process of chain cyclization, amino acid dehydration, and aerial oxidation. Given that different stages in filament formation yield distinct optical characteristics, the photo-activity induced by amyloidogenesis may have application in molecular biology by enabling in vivo visualization of protein aggregation and its impact on cellular function.

Current analytical methods for the detection of dityrosine, a biomarker of oxidative stress, in biological samples

Dityrosine is a fluorescent molecule formed as a result of normal posttranslational processing. In many structural proteins, dityrosine confers resistance to proteolysis and physicochemical trauma as a stabilizing crosslink. Dityrosine has also been found in oxidative/nitrative stress under a variety of conditions and biological systems. In this regard, it has been used as an important biomarker for oxidatively modified proteins during UV and gamma-irradiation, aging, and exposure to oxygen free radicals, nitrogen dioxide, peroxynitrite, and lipid hydroperoxides. Renewed interest in dityrosine and other tyrosine oxidation products as clinical indicators of oxidative modification has driven the development of important techniques for the specific analysis and quantification of these molecules. The presence of elevated levels of dityrosine in mammalian tissue and urine samples has been measured by chromatographic separation followed by mass spectrometry GC-MS and HPLC-MS/MS. Increases in dityrosine levels have been associated with pathologies such as eye cataracts, atherosclerosis, acute inflammation, and Alzheimer's disease. The continued development of, and increased accessibility to, improved mass spectrometric instrumentation will expand the capability, feasibility, and sensitivity with which specific biomarkers like dityrosine can be measured.

Posttranslational nitrotyrosination of α-tubulin induces cell cycle arrest and inhibits proliferation of vascular smooth muscle cells

Hyperproliferation of vascular smooth muscle cells is a hallmark of atherosclerosis and related vascular complications. Microtubules are important for many aspects of mammalian cell responses including growth, migration and signaling. alpha-Tubulin, a component of the microtubule cytoskeleton, is unique amongst cellular proteins in that it undergoes a reversible posttranslational modification whereby the C-terminal tyrosine residue is removed (Glu-tubulin) and re-added (Tyr-tubulin). Whereas the reversible detyrosination/tyrosination cycle of alpha-tubulin has been implicated in regulating various aspects of cell biology, the precise function of this posttranslational modification has remained poorly characterized. Herein, we provide evidence suggesting that alpha-tubulin detyrosination is a required event in the proliferation of vascular smooth muscle cells. Proliferation of rat aortic smooth muscle cells in response to serum was temporally associated with the detyrosination of alpha-tubulin, but not acetylation of alpha-tubulin; Glu-tubulin reached maximal levels between 12 and 18h following cell cycle initiation. Inclusion of 3-nitro-l-tyrosine (NO(2)Tyr) in the culture medium resulted in the selective nitrotyrosination of alpha-tubulin, that was paralleled by decreased elaboration of Glu-tubulin, decreased expression of cyclins A and E, decreased association of the microtubule plus-end binding protein EB1, and inhibited cell proliferation. Nitrotyrosination of alpha-tubulin did not induce necrotic or apoptotic death of rat aortic smooth muscle cells, but instead led to cell cycle arrest at the G(1)/S boundary coincident with decreased DNA synthesis. Collectively, these results suggest that the C-terminus of alpha-tubulin and its detyrosination are functionally important as a molecular switch that regulates cell cycle progression in vascular smooth muscle cells.

Tau nitration occurs at tyrosine 29 in the fibrillar lesions of Alzheimer's disease and other tauopathies

The neurodegenerative tauopathies are a clinically diverse group of diseases typified by the pathological self-assembly of the microtubule-associated tau protein. Although tau nitration is believed to influence the pathogenesis of these diseases, the precise residues modified, and the resulting effects on tau function, remain enigmatic. Previously, we demonstrated that nitration at residue Tyr29 markedly inhibits the ability of tau to self-associate and stabilize the microtubule lattice (Reynolds et al., 2005b, 2006). Here, we report the first monoclonal antibody to detect nitration in a protein-specific and site-selective manner. This reagent, termed Tau-nY29, recognizes tau only when nitrated at residue Tyr29. It does not cross-react with wild-type tau, tau mutants singly nitrated at Tyr18, Tyr197, and Tyr394, or other proteins known to be nitrated in neurodegenerative diseases. By Western blot analysis, Tau-nY29 detects soluble tau and paired helical filament tau from severely affected Alzheimer's brain but fails to recognize tau from normal aged brain. This observation suggests that nitration at Tyr29 is a disease-related event that may alter the intrinsic ability of tau to self-polymerize. In Alzheimer's brain, Tau-nY29 labels the fibrillar triad of tau lesions, including neurofibrillary tangles, neuritic plaques, and, to a lesser extent, neuropil threads. Intriguingly, although Tau-nY29 stains both the neuronal and glial tau pathology of Pick disease, it detects only the neuronal pathology in corticobasal degeneration and progressive supranuclear palsy without labeling the predominant glial pathology. Collectively, our findings provide the first direct evidence that site-specific tau nitration is linked to the progression of the neurodegenerative tauopathies.

Protein tyrosine nitration in hydrophilic and hydrophobic environments

In this review we address current concepts on the biological occurrence, levels and consequences of protein tyrosine nitration in biological systems. We focused on mechanistic aspects, emphasizing on the free radical mechanisms of protein 3-nitrotyrosine formation and critically analyzed the restrictions for obtaining large tyrosine nitration yields in vivo, mainly due to the presence of strong reducing systems (e.g. glutathione) that can potently inhibit at different levels the nitration process. Evidence is provided to show that the existence of metal-catalyzed processes, the assistance of nitric oxide-dependent nitration steps and the facilitation by hydrophobic environments, provide individually and/or in combination, feasible scenarios for nitration in complex biological milieux. Recent studies using hydrophobic tyrosine analogs and tyrosine-containing peptides have revealed that factors controlling nitration in hydrophobic environments such as biomembranes and lipoproteins can differ to those in aqueous compartments. In particular, exclusion of key soluble reductants from the lipid phase will more easily allow nitration and lipid-derived radicals are suggested as important mediators of the one-electron oxidation of tyrosine to tyrosyl radical in proteins associated to hydrophobic environments. Development and testing of hydrophilic and hydrophobic probes that can compete with endogenous constituents for the nitrating intermediates provide tools to unravel nitration mechanisms in vitro and in vivo; additionally, they could also serve to play cellular and tissue protective functions against the toxic effects of protein tyrosine nitration.

Protein nitration increased by simulated weightlessness and decreased by melatonin and quercetin in PC12 cells

A variety of experiments suggest that space flight is associated with an increase in oxidative stress in organism. To explore the effects of oxidative stress on neuronal cells during microgravity, we used rat pheochromocytoma (PC12) cells as a neuronal cell model, cultured in a clinostat, which could simulate microgravity, to investigate the effects of reactive nitrogen species on protein nitration in PC12 cells during clinorotation. The effects of melatonin and quercetin on protein nitration in PC12 cells were also assayed to evaluate the possible protective role of melatonin or quercetin as an antioxidant. The results of immunological staining showed that after the 3 days' clinorotation the protein expressions of neuronal nitric oxide synthase and inducible nitric oxide synthesis were up-regulated. Our data also reflected that the concentrations of nitric oxide and nitrotyrosine were significantly increased after clinorotation, and they were reduced markedly in cells that were treated with 50 micromol/L melatonin or 0.5 micromol/L quercetin during simulated microgravity, when compared to those of control cells. These results suggest that clinorotation-induced weightlessness increases oxidative stress responses in PC12 cells, and melatonin or quercetin was shown to protect PC12 cells from oxidative damage during simulated weightlessness.

Metabolism of 3-nitrotyrosine induces apoptotic death in dopaminergic cells

Intrastriatal injection of 3-nitrotyrosine, which is a biomarker for nitrating oxidants, provokes dopaminergic neuronal death in rats by unknown mechanisms. Herein, we show that extracellular 3-nitrotyrosine is transported via the l-aromatic amino acid transporter in nondopaminergic NT2 cells, whereas in dopaminergic PC12 cells, it is transported by both the l-aromatic amino acid and the dopamine transporters. In both cell lines, 3-nitrotyrosine is a substrate for tyrosine tubulin ligase, resulting in its incorporation into the C terminus of alpha-tubulin. In NT2 cells, incorporation of 3-nitrotyrosine into alpha-tubulin induces a progressive, reversible reorganization of the microtubule architecture. In PC12 cells, 3-nitrotyrosine decreases intracellular dopamine levels and is metabolized by the concerted action of the aromatic amino acid decarboxylase and monoamine oxidase. Intracellular levels of 133 micromol of 3-nitrotyrosine per mole of tyrosine did not alter NT2 viability but induced PC12 apoptosis. The cell death was reversed by caspases and aromatic amino acid decarboxylase and monoamine oxidase inhibitors. 3-Nitrotyrosine induced loss of tyrosine hydroxylase-positive primary rat neurons, which was also prevented by an aromatic amino acid decarboxylase inhibitor. These findings provide a novel mechanism by which products generated by reactive nitrogen species induce dopaminergic neuron death and thus may contribute to the selective neurodegeneration in Parkinson's disease.

Normal and prostate cancer cells display distinct molecular profiles of alpha-tubulin posttranslational modifications

BACKGROUND

Multiple diverse posttranslational modifications of alpha-tubulin such as detyrosination, further cleavage of the penultimate glutamate residue (Delta2-tubulin), acetylation, and polyglutamylation increase the structural and functional diversity of microtubules.

METHODS

Herein, we characterized the molecular profile of alpha-tubulin posttranslational modifications in normal human prostate epithelial cells (PrEC), immortalized normal prostate epithelial cells (PZ-HPV-7), androgen-dependent prostate cancer cells (LNCaP), transitional androgen-independent prostate cancer cells (LNCaP-cds and CWR22Rv1), and androgen-independent prostate cancer cells (PC3).

RESULTS

Compared to PrEC and PZ-HPV-7 cells, all cancer cells exhibited elevated levels of detyrosinated and polyglutamylated alpha-tubulin, that was paralleled by decreased protein levels of tubulin tyrosine ligase (TTL). In contrast, PrEC and PZ-HPV-7 cells expressed markedly higher levels of Delta2-tubulin. Whereas alpha-tubulin acetylation levels were generally equivalent in all the cell lines, PC3 cells did not display detectable levels of Ac-tubulin.

CONCLUSION

These data may reveal novel biomarkers of prostate cancer and new therapeutic targets.

Subcellular localization of tyrosine-nitrated proteins is dictated by reactive oxygen species generating enzymes and by proximity to nitric oxide synthase

Using high-resolution immuno-electron microscopy the steady-state subcellular distribution of tyrosine-nitrated proteins in different cells and tissues was evaluated. In quiescent eosinophils and neutrophils in the bone marrow intracellular nitrated proteins were mainly restricted to the peroxidase-containing secretory granules. The inducible nitric oxide synthase (iNOS) was expressed in the same granules. Proteins nitrated on tyrosine residues were also abundant in the cytosol of circulating erythrocytes. In the vasculature, nitrated proteins were mainly located in mitochondria and endoplasmic reticulum of the endothelial cells, fibroblasts, and smooth muscle cells. Endogenous nitrated proteins were also found in chondrocytes in cartilage, where it was typically associated with the cytoplasmic interface of the endoplasmic reticulum membrane. Nitrated proteins were also prominent in the peroxisomes of liver hepatocytes and of secretory cells in the lacrimal gland. Challenge of mouse dendritic cells with lipopolysaccharide induced iNOS protein expression in cytosol and peroxisomes and was associated with an increased 3-nitrotyrosine formation in cytosol, mitochondria, and peroxisomes. These data indicate that nitric oxide-dependent protein tyrosine nitration is a physiologically relevant process localized within specific subcellular compartments in close proximity to iNOS and to enzymes capable of peroxidative chemistry and reactive oxygen species production.

Peroxynitrite-modified collagen-II induces p38/ERK and NF-kappaB-dependent synthesis of prostaglandin E2 and nitric oxide in chondrogenically differentiated mesenchymal progenitor cells

OBJECTIVE

Peroxynitrite (ONOO(-)) is formed in the inflamed and degenerating human joint. Peroxynitrite-modified collagen-II (PMC-II) was recently discovered in the serum of patients with osteoarthritis (OA) and rheumatoid arthritis (RA). Therefore we investigated the cellular effects of PMC-II on human mesenchymal progenitor cells (MPCs) as a model of cartilage and cartilage repair cells in the inflamed and degenerating joint.

DESIGN

MPCs were isolated from the trabecular bone of patients undergoing reconstructive surgery and were differentiated into a chondrogenic lineage. Cells were exposed to PMC-II and levels of the proinflammatory mediators nitric oxide (*NO) and prostaglandin E(2) (PGE(2)) measured. Levels of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), phosphorylated mitogen activated protein kinases (MAPKs) and nuclear factor kappa B (NF-kappaB) activation were measured by enzyme linked immunosorbent assay (ELISA) together with specific MAPK and NF-kappaB inhibitors.

RESULTS

PMC-II induced ()NO and PGE(2) synthesis through upregulation of iNOS and COX-2 proteins. PMC-II also lead to the phosphorylation of MAPKs, extracellularly regulated kinase 1/2 (ERK1/2) and p38 [but not c-Jun NH(2)-terminal kinase (JNK1/2)] and the activation of proinflammatory transcription factor NF-kappaB. Inhibitors of p38, ERK1/2 and NF-kappaB prevented PMC-II induced ()NO and PGE(2) synthesis, iNOS and COX-2 protein expression and NF-kappaB activation.

CONCLUSION

iNOS, COX-2, NF-kappaB and MAPK are known to be activated in the joints of patients with OA and RA. PMC-II induced iNOS and COX-2 synthesis through p38, ERK1/2 and NF-kappaB dependent pathways suggesting a previously unidentified pathway for the synthesis of the proinflammatory mediators, ()NO and PGE(2), further suggesting that inhibitors of these pathways may be therapeutic in the inflamed and degenerating human joint.

Misincorporation of free m-tyrosine into cellular proteins: a potential cytotoxic mechanism for oxidized amino acids

In vitro studies demonstrate that the hydroxyl radical converts L-phenylalanine into m-tyrosine, an unnatural isomer of L-tyrosine. Quantification of m-tyrosine has been widely used as an index of oxidative damage in tissue proteins. However, the possibility that m-tyrosine might be generated oxidatively from free L-phenylalanine that could subsequently be incorporated into proteins as an L-tyrosine analogue has received little attention. In the present study, we demonstrate that free m-tyrosine is toxic to cultured CHO (Chinese-hamster ovary) cells. We readily detected radiolabelled material in proteins isolated from CHO cells that had been incubated with m-[14C]tyrosine, suggesting that the oxygenated amino acid was taken up and incorporated into cellular proteins. m-Tyrosine was detected by co-elution with authentic material on HPLC and by tandem mass spectrometric analysis in acid hydrolysates of proteins isolated from CHO cells exposed to m-tyrosine, indicating that free m-tyrosine was incorporated intact rather than being metabolized to other products that were subsequently incorporated into proteins. Incorporation of m-tyrosine into cellular proteins was sensitive to inhibition by cycloheximide, suggesting that protein synthesis was involved. Protein synthesis using a cell-free transcription/translation system showed that m-tyrosine was incorporated into proteins in vitro by a mechanism that may involve L-phenylalanine-tRNA synthetase. Collectively, these observations indicate that m-tyrosine is toxic to cells by a pathway that may involve incorporation of the oxidized amino acid into proteins. Thus misincorporation of free oxidized amino acids during protein synthesis may represent an alternative mechanism for oxidative stress and tissue injury during aging and disease.

Nitric oxide impairs mitochondrial movement in cortical neurons during hypoxia

Cortical nitric oxide (NO) production increases during hypoxia/ischemia in the immature brain and is associated with both neurotoxicity and mitochondrial dysfunction. Mitochondrial redistribution within the cell is critical to normal neuronal function, however, the effects of hypoxia on mitochondrial dynamics are not known. This study tested the hypothesis that hypoxia impairs mitochondrial movement via NO-mediated pathways. Fluorescently labeled mitochondria were studied using time-lapse digital video microscopy in cultured cortical neurons exposed either to hypoxia/re-oxygenation or to diethyleneamine/nitric oxide adduct, DETA-NO (100-500 microm). Two NO synthase inhibitors, were used to determine NO specificity. Mitochondrial mean velocity, the percentage of movement (i.e. the time spent moving) and mitochondrial morphology were analyzed. Exposure to hypoxia reduced mitochondrial movement to 10.4 +/- 1.3% at 0 h and 7.4 +/- 1.7% at 1 h of re-oxygenation, versus 25.6 +/- 1.4% in controls (p < 0.05). Mean mitochondrial velocity (microm s(-1)) decreased from 0.374 +/- 0.01 in controls to 0.146 +/- 0.01 at 0 h and 0.177 +/- 0.02 at 1 h of re-oxygenation (p < 0.001). Exposure to DETA-NO resulted in a significant decrease in mean mitochondrial velocity at all tested time points. Treatment with NG-nitro-L-arginine methyl ester (L-NAME) prevented the hypoxia-induced decrease in mitochondrial movement at 0 h (30.1 +/- 1.6%) and at 1 h (26.1 +/- 9%) of re-oxygenation. Exposure to either hypoxia/re-oxygenation or NO also resulted in the rapid decrease in mitochondrial size. Both hypoxia and NO exposure result in impaired mitochondrial movement and morphology in cultured cortical neurons. As the effect of hypoxia on mitochondrial movement and morphology can be partially prevented by a nitric oxide synthase (NOS) inhibitor, these data suggest that an NO-mediated pathway is at least partially involved.

Cabergoline scavenges peroxynitrite enhanced by l-DOPA therapy in patients with Parkinson's disease

Long-term or high-dose L-DOPA therapy in patients with Parkinson's disease (PD) may accelerate degeneration of dopaminergic neurons, possibly by increasing oxidative stress. To investigate the effects of cabergoline on peroxynitrite-mediated oxidative damage caused by L-DOPA, the concentration of 3-nitrotyrosine in cerebrospinal fluid (CSF) of 18 PD patients was compared with that in 20 normal controls. The concentration of 3-nitrotyrosine in patients following L-DOPA therapy was significantly higher than in untreated PD patients and controls. On the other hand, the concentration in PD patients after cabergoline therapy was significantly lower than in PD patients after L-DOPA therapy alone. These data suggest that cabergoline scavenges peroxynitrite induced by L-DOPA in patients with PD.

Reactive nitrogen species in the respiratory tract

Endogenous Nitric Oxide (NO) plays a key role in the physiological regulation of airway functions. In response to various stimuli activated inflammatory cells (e.g., eosinophils and neutrophils) generate oxidants ("oxidative stress") which in conjunction with exaggerated enzymatic release of NO and augmented NO metabolites produce the formation of strong oxidizing reactive nitrogen species, such as peroxynitrite, in various airway diseases including asthma, chronic obstructive pulmonary diseases (COPD), cystic fibrosis and acute respiratory distress syndrome (ARDS). Reactive nitrogen species provoke amplification of inflammatory processes in the airways and lung parenchyma causing DNA damage, inhibition of mitochondrial respiration, protein dysfunction and cell damage ("nitrosative stress"). These effects alter respiratory homeostasis (such as bronchomotor tone and pulmonary surfactant activity) and the long-term persistence of "nitrosative stress" may contribute to the progressive deterioration of pulmonary functions leading to respiratory failure. Recent studies showing that protein nitration can be dynamic and reversible ("denitration mechanisms") open new horizons in the treatment of chronic respiratory diseases affected by the deleterious actions of "nitrosative stress".

Myeloperoxidase and its contributory role in inflammatory vascular disease

Myeloperoxidase (MPO), a heme protein abundantly expressed in polymorphonuclear neutrophils (PMN), has long been viewed to function primarily as a bactericidal enzyme centrally linked to innate host defense. Recent observations now extend this perspective and suggest that MPO is profoundly involved in the regulation of cellular homeostasis and may play a central role in initiation and propagation of acute and chronic vascular inflammatory disease. For example, low levels of MPO-derived hypochlorous acid (HOCl) interfere with intracellular signaling events, MPO-dependent oxidation of lipoproteins modulates their affinity to macrophages and the vessel wall, MPO-mediated depletion of endothelial-derived nitric oxide (NO) impairs endothelium-dependent vasodilatation, and nitrotyrosine (NO(2)Tyr) formation by MPO sequestered into the vessel wall may affect matrix protein structure and function. Future studies are needed to further elucidate the significance of MPO in the development of acute and chronic vascular disease and to evaluate MPO as a potential target for treatment.

Detection of hypothetical proteins in human fetal perireticular nucleus

There is a legion of hypothetical proteins (HP) in prokaryotic and eukaryotic proteomes and the aim of this study was to describe HP in the perireticular nucleus (PN), a key structure in human brain development. Tissue from four PNs was homogenized and extracted proteins were run on two-dimensional gel electrophoresis followed by in-gel digestion and mass spectrometrical identification of proteins. Several databases were used for obtaining bioinformatic information and searching for functional and structural domains. Five spots represented HP: KIAA0423 protein (Q9Y4F4), hypothetical protein KIAA0153 (Q14166), hypothetical protein DKFZp564A2416 (Q9NTW4), hypothetical protein DKFZp564H1122 (Q9H0W9), and hypothetical protein DKFZp564D1378 (Q9H0R4). These structures were predicted to serve in cell cycle, DNA-condensation, neurogenesis, or apoptosis. The existence of formerly HP proteins in the PN of human fetal brain is shown, thus extending knowledge of the brain proteome and proposing the method used as a suitable analytical tool for searching HP.

Back on track – On the role of the microtubule for kinesin motility and cellular function

The evolution of cytoskeletal filaments (actin- and intermediate-filaments, and the microtubules) and their associated motor- and non-motor-proteins has enabled the eukaryotic cell to achieve complex organizational and structural tasks. This ability to control cellular transport processes and structures allowed for the development of such complex cellular organelles like cilia or flagella in single-cell organisms and made possible the development and differentiation of multi-cellular organisms with highly specialized, polarized cells. Also, the faithful segregation of large amounts of genetic information during cell division relies crucially on the reorganization and control of the cytoskeleton, making the cytoskeleton a key prerequisite for the development of highly complex genomes. Therefore, it is not surprising that the eukaryotic cell continuously invests considerable resources in the establishment, maintenance, modification and rearrangement of the cytoskeletal filaments and the regulation of its interaction with accessory proteins. Here we review the literature on the interaction between microtubules and motor-proteins of the kinesin-family. Our particular interest is the role of the microtubule in the regulation of kinesin motility and cellular function. After an introduction of the kinesin-microtubule interaction we focus on two interrelated aspects: (1) the active allosteric participation of the microtubule during the interaction with kinesins in general and (2) the possible regulatory role of post-translational modifications of the microtubule in the kinesin-microtubule interaction.

Tubulin nitration in human gliomas

Immunohistochemical and biochemical investigations showed that significant protein nitration occurs in human gliomas, especially in grade IV glioblastomas at the level of astrocytes and oligodendrocytes and neurones. Enhanced alpha-tubulin immunoreactivity was co-present in the same elements in the glioblastomas. Proteomic methodologies were employed to identify a nitrated protein band at 55 kDa as alpha-tubulin. Peptide mass fingerprinting procedures demonstrated that tubulin is nitrated at Tyr224 in grade IV tumour samples but is unmodified in grade I samples and in non-cancerous brain tissue. These results provide the first characterisation of endogenously nitrated tubulin from human tumour samples.

The testis-specific apoptosis related gene TTL.6 underwent adaptive evolution in the lineage leading to humans

The TTL.6 gene is a member of the tubulin-tyrosine ligase (TTL) family involved in apoptosis and preferentially expressed in the testis. We sequenced the coding region and part of the introns of TTL.6 in world wide human populations and five representative nonhuman primate species covering great apes, lesser ape and Old World monkey. The sequence substitution patterns of TTL.6 in primates demonstrated a sharp difference in evolutionary rates among different primate lineages. Our results indicated an accelerated evolution of TTL.6 in the human lineage, which was caused by Darwinian positive selection. Further analysis on sequence variations in human populations demonstrated an excess of derived common alleles, which was likely caused by genetic hitchhiking, an implication of recent positive selection on TTL.6 in human populations.

Protein oxidation injury occurs during pediatric cardiopulmonary bypass

OBJECTIVE

Proteins are the major effectors of biological structure and function. Oxidation-induced changes to protein structure can critically impair protein function, with important pathologic consequences. This study was undertaken to examine whether oxidation-induced changes to protein structure occur during pediatric cardiopulmonary bypass and to examine the association with postoperative outcome.

METHODS

Elevation of the 3,4-dihydroxyphenylalanine content of a protein relative to its native tyrosine content indicates structural damage due to oxidation. Protein 3,4-dihydroxyphenylalanine/native tyrosine ratios were measured before surgery and up to 6 hours after institution of cardiopulmonary bypass in 24 children undergoing repair of congenital heart disease, who were prospectively selected to form a cyanotic and comparable acyanotic control group. Results were correlated with perioperative variables and postoperative outcomes.

RESULTS

Elevation of protein 3,4-dihydroxyphenylalanine/tyrosine ratios above baseline (0.48 mmol/mol [SD, 0.11 mmol/mol] vs 0.36 mmol/mol [SD, 0.13 mmol/mol]; P = .001) occurred within 30 minutes of initiating cardiopulmonary bypass in cyanotic but not in acyanotic children and correlated inversely with preoperative arterial oxygen saturation (R = -0.52; P = .03). Protein 3,4-dihydroxyphenylalanine/tyrosine ratios were also increased above baseline at 120 minutes (0.44 mmol/mol [SD, 0.12 mmol/mol]; P = .007) and 180 minutes (0.40 mmol/mol [SD, 0.14 mmol/mol]; P = .01) after the institution of cardiopulmonary bypass in children who underwent prolonged procedures. Elevation of 3,4-dihydroxyphenylalanine/tyrosine during prolonged procedures was associated with postoperative arrhythmias and the need for increased inotropic support (P = .001).

CONCLUSIONS

Oxidative injury to proteins occurs during pediatric cardiopulmonary bypass. Cyanotic children are most at risk, particularly those undergoing prolonged procedures, in whom elevation of the protein 3,4-dihydroxyphenylalanine/tyrosine ratio is associated with increased postoperative morbidity.