Neurofibrillary tangles of Alzheimer's disease brains contain 14-3-3 proteins

Proteomic identification of proteins specifically oxidized by intracerebral injection of amyloid beta-peptide (1-42) into rat brain: implications for Alzheimer's disease

Protein oxidation has been shown to result in loss of protein function. There is increasing evidence that protein oxidation plays a role in the pathogenesis of Alzheimer's disease (AD). Amyloid beta-peptide (1-42) [Abeta(1-42)] has been implicated as a mediator of oxidative stress in AD. Additionally, Abeta(1-42) has been shown to induce cholinergic dysfunction when injected into rat brain, a finding consistent with cholinergic deficits documented in AD. In this study, we used proteomic techniques to examine the regional in vivo protein oxidation induced by Abeta(1-42) injected into the nucleus basalis magnocellularis (NBM) of rat brain compared with saline-injected control at 7 days post-injection. In the cortex, we identified glutamine synthetase and tubulin beta chain 15/alpha, while, in the NBM, we identified 14-3-3 zeta and chaperonin 60 (HSP60) as significantly oxidized. Extensive oxidation was detected in the hippocampus where we identified 14-3-3 zeta, beta-synuclein, pyruvate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, and phosphoglycerate mutase 1. The results of this study suggest that a single injection of Abeta(1-42) into NBM can have profound effects elsewhere in the brain. The results further suggest that Abeta(1-42)-induced oxidative stress in rat brain mirrors some of those proteins oxidized in AD brain and leads to oxidized proteins, which when inserted into their respective biochemical pathways yields insight into brain dysfunction that can lead to neurodegeneration in AD.

Gamma-glutamylcysteine ethyl ester protection of proteins from Abeta(1-42)-mediated oxidative stress in neuronal cell culture: a proteomics approach

Protein oxidation mediated by amyloid beta-peptide (1-42) (Abeta[1-42]) has been proposed to play a central role in the pathogenesis of Alzheimer's disease (AD), a neurodegenerative disorder associated with aging and the loss of cognitive function. The specific mechanism by which Abeta(1-42), the primary component of the senile plaque and a pathologic hallmark of AD, contributes to the oxidative damage evident in AD brain is unknown. Moreover, the specific proteins that are vulnerable to oxidative damage induced by Abeta(1-42) are unknown. Identification of such proteins could contribute to our understanding of not only the role of Abeta(1-42) in the pathogenesis of AD, but also provide insight into the mechanisms of neurodegeneration at the protein level in AD. We report the proteomic identification of two proteins found to be oxidized significantly in neuronal cultures treated with Abeta(1-42): 14-3-3zeta and glyceraldehyde-3-phosphate dehydrogenase. We also report that pretreatment of neuronal cultures with gamma-glutamylcysteine ethyl ester, a compound that supplies the limiting substrate for the synthesis of glutathione and results in the upregulation of glutathione in neuronal cultures, protects both proteins against Abeta(1-42)-mediated protein oxidation.

Unchanged survival rates of 14-3-3gamma knockout mice after inoculation with pathological prion protein

The diagnosis of sporadic Creutzfeldt-Jakob disease (CJD) is based on typical clinical findings and is supported by a positive 14-3-3 Western blot of cerebrospinal fluid. However, it is not clear whether 14-3-3 indicates general neuronal damage or is of pathophysiological relevance in CJD. The fact that the 14-3-3 isoform spectrum in cerebrospinal fluid does not correspond to that found in the brain points to a regulated process. To investigate a possible role of 14-3-3 proteins in transmissible spongiform diseases, we generated a 14-3-3gamma-deficient mutant mouse line by using a classical knockout strategy. The anatomy and cage behavior of the mutant mice were normal. Western blot analyses of brain homogenates revealed no changes in the protein expression of other 14-3-3 isoforms (epsilon, beta, zeta, and eta). Proteomic analyses of mouse brains by two-dimensional differential gel electrophoresis showed that several proteins, including growth hormone, 1-Cys peroxiredoxin, CCT-zeta, glucose-6-phosphate isomerase, GRP170 precursor, and alpha-SNAP, were differentially expressed. Mutant and wild-type mice were inoculated either intracerebrally or intraperitoneally with the Rocky Mountain Laboratory strain of scrapie, but no differences were detected in the postinoculation survival rates. These results indicate that 14-3-3gamma is unlikely to play a causal role in CJD and related diseases.

Immunolocalization of 14-3-3 isoforms in brains with Pick body disease

Immunolocalization of 14-3-3 protein isoforms in relation to Pick bodies in Pick body disease (PBD) brains was investigated. Weakly granular immunoreactivity of 14-3-3 proteins was found in neurons in control subjects and in Pick body disease brains. In addition to this granular immunoreactivity, many Pick bodies were immunopositive for 14-3-3 proteins as confirmed with double-immunofluorescence with an anti-PHF tau (AT8) and anti-14-3-3 that recognizes all its isoforms (common). When probed with isoform-specific antibodies, Pick bodies were positive for beta, gamma, epsilon, eta, tau, and zeta isoform and exhibited immunostaining pattern similar to that observed with the anti-14-3-3 proteins (common). In addition, immunoreactivity of sigma isoform, so far considered to be exclusively extraneuronal, was unexpectedly found in Pick bodies, normal hippocampal neurons and brain homogenate from age-matched controls. Although localization of 14-3-3 proteins in Pick bodies suggests their involvement in Pick body formation, their role may be variable dependent on the isoforms differently expressed in different area in the brain.

Unlocking the code of 14-3-3

One of the most striking 'rags to riches' stories in the protein world is that of 14-3-3, originally identified in 1967 as merely an abundant brain protein. The first clues that 14-3-3 would play an important role in cell biology came almost 25 years later when it was found to interact with various proto-oncogene proteins and signaling proteins. The subsequent identification of 14-3-3 as a phosphoserine/phosphothreonine-binding protein firmly established its importance in cell signaling. 14-3-3 family members are found in all eukaryotes - from plants to mammals - and more than 100 binding partners have been identified to date. The targets of 14-3-3 are found in all subcellular compartments and their functional diversity is overwhelming - they include transcription factors, biosynthetic enzymes, cytoskeletal proteins, signaling molecules, apoptosis factors and tumor suppressors. 14-3-3 binding can alter the localization, stability, phosphorylation state, activity and/or molecular interactions of a target protein. Recent studies now indicate that the serine/threonine protein phosphatases PP1 and PP2A are important regulators of 14-3-3 binding interactions, and demonstrate a role for 14-3-3 in controlling the translocation of certain proteins from the cytoplasmic and endoplasmic reticulum to the plasma membrane. New reports also link 14-3-3 to several neoplastic and neurological disorders, where it might contribute to the pathogenesis and progression of these diseases.

14-3-3 proteins in Lewy body-like hyaline inclusions in patients with sporadic amyotrophic lateral sclerosis

14-3-3 proteins are highly conserved eukaryotic proteins that regulate various types of signal transduction pathways through phosphorylation-dependent protein-protein interactions. 14-3-3 mRNAs have been shown to be up-regulated in the injured rat motor neurons and in the spinal cords of patients with amyotrophic lateral sclerosis (ALS). To investigate the role of 14-3-3 proteins in ALS, we performed immunohistochemical studies on 14-3-3 using autopsied spinal cords from patients with sporadic ALS (sALS) and non-ALS subjects without spinal cord involvement. In the anterior horn of both groups, strong 14-3-3 immunoreactivity was observed in the somata and proximal processes of motor neurons. Many spheroids from all of the sALS cases were also immunopositive for 14-3-3. In addition, Lewy body-like hyaline inclusions (LBHIs), which were present in some sALS cases, were intensely immunostained. Our findings suggest that even in the severely affected anterior horn of patients with sALS, remaining motor neurons may contain abundant 14-3-3 proteins, and that 14-3-3 proteins may be partly associated with the pathogenesis of sALS, in particular with the formation of LBHIs.

14-3-3 proteins and zeta isoform containing neurofibrillary tangles in patients with Alzheimer's disease

Immunolocalization of 14-3-3 proteins in Alzheimer's disease (AD) brains was investigated using isoform-specific antibodies. Weak granular immunoreactivity of 14-3-3 proteins was found in neuronal cytoplasm in control subjects and AD brains. Both intracellular and extracellular neurofibrillary tangles (NFTs), as well as neuropil thread-like structures, were immunopositive for 14-3-3 proteins. This was corroborated by triple-fluorolabeling method visualizing paired helical filament (PHF) tau and 14-3-3 epitopes in relation to fibrillary state detected by thiazin red. Pretangle neurons (positive for PHF-tau without fibrillary structure detected by thiazin red) only contained fine granular immunoreactivity (IR) of 14-3-3, which was similarly found in unaffected neurons. Granular cytoplasmic IR of 14-3-3 proteins in pretangle neurons was not colocalized to granular tau-like IR, which suggests that participation of 14-3-3 proteins in NFT formation was restricted to its later stages. Its zeta isoform was most prominent in these NFTs, suggesting that this isoform is a major component involved in the formation of NFTs. In contrast, IR of epsilon isoform was found in the neuropil of the hippocampus and that of sigma isoform was localized to granule cells of the dentate gyrus in AD brains, as seen in the age-matched controls. Expression of 14-3-3 proteins were found to be highly variable and dependent on their isoforms, regions and cell types. Molecular, as well as topographical, dissection of 14-3-3 proteins will provide us with an improved understanding of this molecule in normal and pathological conditions.

Enhanced expression of 14-3-3 proteins in reactive astrocytes in Creutzfeldt-Jakob disease brains

14-3-3 proteins have been reported to be detected specifically in the cerebrospinal fluid (CSF) from patients with Creutzfeldt-Jakob disease (CJD). To elucidate the role of 14-3-3 proteins in patients with CJD, we performed immunohistochemical studies on 14-3-3 proteins in autopsied brains from five patients with sporadic CJD (sCJD), three patients with Alzheimer's disease (AD), and seven normal control subjects. Formalin-fixed, paraffin-embedded sections from all cases were immunostained with several types of specific anti-14-3-3 antibodies. In the normal control brains, 14-3-3 immunoreactivity was localized mainly in the neuronal somata and processes; in contrast, glial cells showed no or faint immunoreactivity. In the brains from the patients with AD, 14-3-3 immunoreactivity was observed in the surviving neurons as well as some neurofibrillary tangles. In the brains from the patients with sCJD, 14-3-3 immunoreactivity was well preserved in the remaining neurons. Furthermore, the glial cells, especially the reactive astrocytes, were intensely immunostained in the brains affected by sCJD. Our findings suggest that 14-3-3 proteins may be up-regulated in the glial cells, particularly in reactive astrocytes, and that the enhanced expression of 14-3-3 proteins in these glial elements may be associated with the pathogenesis of sCJD.

Examination of stress-related genes in human temporal versus occipital cortex in the course of neurodegeneration: involvement of 14-3-3 zeta in this dynamic process

The progressive invasion of the brain by neurofibrillary tangles characterized by paired helical filaments (PHF) along a precise network is stereotypical and hierarchical from normal aging to severe Alzheimer's disease. We describe here the differential expression of genes in the temporal area with PHF compared with the occipital area non-affected by PHF in cases with cognitive impairment versus the same cortical regions of control human brains without PHF. A stronger overexpression for 14-3-3 zeta gene is demonstrated in the affected temporal cortex of cases with cognitive impairment than in cases with normal mental status. This data obtained directly from human brains confirmed a 14-3-3 zeta implication in the Alzheimer's neuropathology.

14-3-3 Proteins—a focus on cancer and human disease

14-3-3 Proteins are a ubiquitous family of molecules that participate in protein kinase signaling pathways within all eukaryotic cells. Functioning as phosphoserine/phosphothreonine-binding modules, 14-3-3 proteins participate in phosphorylation-dependent protein-protein interactions that control progression through the cell cycle, initiation and maintenance of DNA damage checkpoints, activation of MAP kinases, prevention of apoptosis, and coordination of integrin signaling and cytoskeletal dynamics. In this review, we discuss the regulation of 14-3-3 structure and ligand binding, with a focus on the role of 14-3-3 proteins in human disease, particularly cancer. We discuss the latest data on the role of different 14-3-3 isotypes, the interaction of 14-3-3 proteins with Raf, Cdc25, and various integrin family members, and the likelihood that 14-3-3 proteins could be useful therapeutic targets in the treatment of human disease.

The 14-3-3 protein epsilon isoform expressed in reactive astrocytes in demyelinating lesions of multiple sclerosis binds to vimentin and glial fibrillary acidic protein in cultured human astrocytes

The 14-3-3 protein family consists of acidic 30-kd proteins expressed at high levels in neurons of the central nervous system. Seven isoforms form a dimeric complex that acts as a molecular chaperone that interacts with key signaling components. Recent studies indicated that the 14-3-3 protein identified in the cerebrospinal fluid of various neurological diseases including multiple sclerosis (MS) is a marker for extensive brain destruction. However, it remains unknown whether the 14-3-3 protein plays an active role in the pathological process of MS. To investigate the differential expression of seven 14-3-3 isoforms in MS lesions, brain tissues of four progressive cases were immunolabeled with a panel of isoform-specific antibodies. Reactive astrocytes in chronic demyelinating lesions intensely expressed beta, epsilon, zeta, eta, and sigma isoforms, among which the epsilon isoform is a highly specific marker for reactive astrocytes. Furthermore, protein overlay, mass spectrometry, immunoprecipitation, and double-immunolabeling analysis showed that the 14-3-3 protein interacts with both vimentin and glial fibrillary acidic protein in cultured human astrocytes. These results suggest that the 14-3-3 protein plays an organizing role in the intermediate filament network in reactive astrocytes at the site of demyelinating lesions in MS.

Proteomic Characterization of Postmortem Amyloid Plaques Isolated by Laser Capture Microdissection

The presence of amyloid plaques in the brain is one of the pathological hallmarks of Alzheimer's disease (AD). We report here a comprehensive proteomic analysis of senile plaques from postmortem AD brain tissues. Senile plaques labeled with thioflavin-S were procured by laser capture microdissection, and their protein components were analyzed by liquid chromatography coupled with tandem mass spectrometry. We identified a total of 488 proteins co-isolated with the plaques, and we found multiple phosphorylation sites on the neurofilament intermediate chain, implicating the complexity and diversity of cellular processes involved in the plaque formation. More significantly, we identified 26 proteins enriched in the plaques of two AD cases by quantitative comparison with surrounding non-plaque tissues. The localization of several proteins in the plaques was further confirmed by the approach of immunohistochemistry. In addition to previously identified plaque constituents, we discovered novel association of dynein heavy chain with the plaques in human postmortem brain and in a double transgenic AD mouse model, suggesting that neuronal transport may play a role in neuritic degeneration. Overall, our results revealed for the first time the sub-proteome of amyloid plaques that is important for further studies on disease biomarker identification and molecular mechanisms of AD pathogenesis.

Could a loss of alpha-synuclein function put dopaminergic neurons at risk?

The alpha-synuclein gene is implicated in Parkinson's disease, the symptoms of which occur after a marked loss of substantia nigra dopamine neurons. While the function of alpha-synuclein is not entirely elucidated, one function appears to be as a normal regulatory protein that can bind to and inhibit tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Soluble alpha-synuclein levels may be diminished in Parkinson's disease substantia nigra dopamine neurons both by reduced expression and by alpha-synuclein aggregation as Lewy bodies and Lewy neurites form. The loss of functional alpha-synuclein may then result in dysregulation of tyrosine hydroxylase, dopamine transport and dopamine storage, resulting in excess cytosolic dopamine. Because dopamine and its metabolites are reactive molecules capable of generating highly reactive quinones and reactive oxygen species, a failure to package dopamine into vesicles could cause irreversible damage to cellular macromolecules and contribute to resultant neurotoxicity. This review focuses on how a loss of normal alpha-synuclein function may contribute to the dopamine-related loss of substantia nigra neurons during Parkinson's disease pathogenesis.

Zeta 14-3-3 protein favours the formation of human tau fibrillar polymers

Tau protein can aggregate, in an aberrant way, in Alzheimer's disease and other tauopathies. The formation of those aggregates could take place in vitro by the addition of different compounds like polyanions or fatty acids and their derivates. Now, we found that a protein, zeta 14-3-3, facilitates the assembly of tau as well as a tau peptide containing the self-assembly region of tau molecule and a site for PKA phosphorylation. Also, we have found that tau and tau peptide polymerization are reduced, but not abolished upon PKA phosphorylation. The involvement of a scaffolding protein like 14-3-3 in the generation of tau filaments in tauopathies, like AD, is suggested.

Proteome analysis of DNA damage-induced neuronal death using high throughput mass spectrometry

Isotope-coded affinity tag reagents and high throughput mass spectrometry were used to quantitate changes in the expression of 150 proteins in mouse wild-type (p53(+/+)) cortical neurons undergoing DNA damage-induced death. Immunological techniques confirmed several of the changes in protein expression, but microarray analysis indicated that many of these changes were not accompanied by altered mRNA expression. Proteome analysis revealed perturbations in mitochondrial function, free radical production, and neuritogenesis that were not observed in p53-deficient neurons. Changes in Tau, cofilin, and other proteins recapitulated abnormalities observed in neurodegenerative states in vivo. Additionally, DNA damage caused a p53-dependent decrease in expression of members of the protein kinase A (PKA) signaling pathway. PKA inhibition promoted death in the absence of DNA damage, revealing a novel mechanism by which endogenous down-regulation of PKA signaling may contribute to p53-dependent neuronal death. These data demonstrate the power of high throughput mass spectrometry for quantitative analysis of the neuronal proteome.

A Method to Identify p62's UBA Domain Interacting Proteins

The UBA domain is a conserved sequence motif among polyubiquitin binding proteins. For the first time, we demonstrate a systematic, high throughput approach to identification of UBA domain-interacting proteins from a proteome-wide perspective. Using the rabbit reticulocyte lysate in vitro expression cloning system, we have successfully identified eleven proteins that interact with p62’s UBA domain, and the majority of the eleven proteins are associated with neurodegenerative disorders, such as Alzheimer’s disease. Therefore, p62 may play a novel regulatory role through its UBA domain. Our approach provides an easy route to the characterization of UBA domain interacting proteins and its application will unfold the important roles that the UBA domain plays.

Detection of the 14-3-3 protein in the cerebrospinal fluid of Japanese multiple sclerosis patients presenting with severe myelitis

Recent studies showed that the 14-3-3 protein is detectable in the cerebrospinal fluid (CSF) of prion-unrelated neurological diseases, such as meningoencephalitis and myelitis. To investigate the possible association between the amounts of the 14-3-3 protein in the CSF and the clinical severity of multiple sclerosis (MS), its levels were determined by Western blot in the CSF of the patients with relapsing-remitting MS (RRMS) (n=10), secondary progressive MS (SPMS) (n=7), primary progressive MS (PPMS) (n=2), and non-MS inflammatory diseases of the CNS (n=5). The 14-3-3 protein was identified in seven CSF samples, including four patients with SPMS in acute relapse, one with SPMS in remission accompanied by fresh cerebral infarction, one with RRMS in acute relapse, and one with human T-lymphotropic virus type I (HTLV-I)-associated myelopathy. The patients positive for the CSF 14-3-3 protein immunoreactivity showed more severe disability and higher levels of pleocytosis, protein, IgG, beta2-microglobulin, and neuron-specific enolase in the CSF, compared with those negative for its immunoreactivity. Four of these patients exhibited extensive lesions distributed along multiple vertebral segments in the spinal cord on MRI. In contrast, none of the MS patients without an extensive involvement of the spinal cord showed the CSF 14-3-3 protein immunoreactivity. These results suggest that detection of the 14-3-3 protein in the CSF provides a marker for severe inflammation-induced extensive damage of the central nervous system tissues responsible for poor therapeutic responses and irreversible neurological deficits in MS.

Immunoexpression of 14-3-3 proteins in glial cytoplasmic inclusions of multiple system atrophy

Glial cytoplasmic inclusions (GCIs) are the histological hallmark of multiple system atrophy (MSA). In six postmortem brains of patients with MSA, 14-3-3-protein immunoreactivity was identified in GCIs predominately in the white matter tissue of the basal forebrain and cerebellum. Using double immunohistochemistry, co-localization of 14-3-3-protein and alpha-synuclein immunoreactivities in the GCIs was confirmed. The immunolabeling rate of GCIs with 14-3-3 proteins varied regionally from approximately 40% to 90%. Semiquantitative analysis yielded a significant negative correlation between degree of tissue degeneration and density of 14-3-3-protein-immunoreactive GCIs. The 14-3-3 proteins are active cofactors involved in cellular regulation through binding to phosphorylated motifs in target proteins and alpha-synuclein is a known target of 14-3-3. Our study suggests that 14-3-3 proteins are closely associated with alpha-synuclein in GCIs and 14-3-3 proteins may be candidate cofactors of alpha-synuclein in GCI formation.

Interaction of Akt-phosphorylated ataxin-1 with 14-3-3 mediates neurodegeneration in spinocerebellar ataxia type 1

Spinocerebellar ataxia type 1 (SCA1) is one of several neurological disorders caused by a CAG repeat expansion. In SCA1, this expansion produces an abnormally long polyglutamine tract in the protein ataxin-1. Mutant polyglutamine proteins accumulate in neurons, inducing neurodegeneration, but the mechanism underlying this accumulation has been unclear. We have discovered that the 14-3-3 protein, a multifunctional regulatory molecule, mediates the neurotoxicity of ataxin-1 by binding to and stabilizing ataxin-1, thereby slowing its normal degradation. The association of ataxin-1 with 14-3-3 is regulated by Akt phosphorylation, and in a Drosophila model of SCA1, both 14-3-3 and Akt modulate neurodegeneration. Our finding that phosphatidylinositol 3-kinase/Akt signaling and 14-3-3 cooperate to modulate the neurotoxicity of ataxin-1 provides insight into SCA1 pathogenesis and identifies potential targets for therapeutic intervention.

Glycogen synthase kinase 3beta phosphorylates tau at both primed and unprimed sites. Differential impact on microtubule binding

Glycogen synthase kinase 3beta (GSK3beta) phosphorylates substrates, including the microtubule-associated protein tau, at both primed and unprimed epitopes. GSK3beta phosphorylation of tau negatively regulates tau-microtubule interactions; however the differential effects of phosphorylation at primed and unprimed epitopes on tau is unknown. To examine the phosphorylation of tau at primed and unprimed epitopes and how this impacts tau function, the R96A mutant of GSK3beta was used, a mutation that prevents phosphorylation of substrates at primed sites. Both GSK3beta and GSK3beta-R96A phosphorylated tau efficiently in situ. However, expression of GSK3beta-R96A resulted in significantly less phosphorylation of tau at primed sites compared with GSK3beta. Conversely, GSK3beta-R96A phosphorylated unprimed tau sites to a significantly greater extent than GSK3beta. Prephosphorylating tau with cdk5/p25 impaired the ability of GSK3beta-R96A to phosphorylate tau, whereas GSK3beta-R96A phosphorylated recombinant tau to a significantly greater extent than GSK3beta. Moreover, the amount of tau associated with microtubules was reduced by overexpression of GSK3beta but only when tau was phosphorylated at primed sites, as phosphorylation of tau by GSK3beta-R96A did not negatively regulate the association of tau with microtubules. These results demonstrate that GSK3beta-mediated phosphorylation of tau at primed sites plays a more significant role in regulating the interaction of tau with microtubules than phosphorylation at unprimed epitopes.

14-3-3 protein is a component of Lewy bodies in Parkinson's disease-mutation analysis and association studies of 14-3-3 eta

Mutations in alpha-synuclein have been identified in some rare families with autosomal dominant Parkinson's disease (PD). The synuclein gene family shares physical and functional homology with 14-3-3 proteins and binds to 14-3-3 proteins and to its ligands. We therefore investigated whether 14-3-3 proteins are also involved in the pathogenesis of PD. Here we demonstrate that 14-3-3 proteins are colocalized with Lewy bodies in PD. We investigated the 14-3-3 eta (YWHAH) gene by mutation analysis and association studies as it maps to human chromosome 22q12.1-q13.1, a region which has been recently implicated in PD and carried out immunohistochemical studies of Lewy bodies with two different 14-3-3 eta antibodies. In 358 sporadic and familial PD patients, disease causing mutations were not identified. Furthermore, association studies with intragenic polymorphisms do not provide evidence for an involvement of 14-3-3 eta in the pathogenesis of PD. In accordance with these findings, there was no staining of substantia nigra Lewy bodies with antibodies specific for the 14-3-3 eta subunit.

Accumulation of 14-3-3 proteins in glial cytoplasmic inclusions in multiple system atrophy

Glial cytoplasmic inclusions are the pathological hallmark of multiple system atrophy. However, the molecular mechanisms underlying the formation of glial cytoplasmic inclusions remain unclear. Alpha-synuclein, a major component of glial cytoplasmic inclusions, has the ability to interact with 14-3-3 proteins, which mediate several types of signal transduction pathways. To elucidate the role of these 14-3-3 proteins in patients with multiple system atrophy, we performed immunohistochemical studies on 14-3-3 in brain tissue specimens from 7 control subjects and from 15 patients with multiple system atrophy. In both control and multiple system atrophy cases, 14-3-3 immunoreactivity was observed mainly in the neuronal somata and proximal processes, as well as the nerve fibers. Even in the severely affected regions of patients with multiple system atrophy, 14-3-3 immunoreactivity generally was spared in the surviving neurons, some of which were strongly immunolabeled. In addition, numerous glial cytoplasmic inclusions were intensely immunostained, and neuronal cytoplasmic inclusions and dystrophic neurites were also immunoreactive for 14-3-3. Our results suggest that an aberrant accumulation of 14-3-3 proteins may occur in brains affected by multiple system atrophy, and that 14-3-3 proteins may be associated with the pathogenesis of multiple system atrophy.

Immune response gene expression increases in the aging murine hippocampus

Using GeneChips, basal and lipopolysaccharide (LPS)-induced gene expression was examined in the hippocampus of 3-, 12-, 18- and 24-month-old male C57BL/6 mice to identify genes whose altered expression could influence hippocampal function in advanced age. Gene elements that changed with age were selected with a t-statistic and specific expression patterns were confirmed with real-time quantitative PCR. Basal expression of 128 gene elements clearly changed with age in the hippocampus. Fourteen gene elements showed increased expression with age and these increases were validated after LPS stimulation. Major histocompatibility complex (MHC) TL region and thymic shared antigen (TSA-1) gene expression increased, suggesting T cell activation in the hippocampus with age. Cytokine (interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha) and chemokine (macrophage chemotactic protein-1) expression increased sharply in 24-month-old mice. These findings are in contrast to a decrease in the peripheral immune response, documented by decreased T cell proliferation and decreased ratios of naive to memory T cells. Age-related increases in inflammatory potential in the brain may contribute to neurodegenerative diseases of the aged.

Immunolocalisation of 14-3-3 isoforms in normal and scrapie-infected murine brain

The appearance of 14-3-3 proteins in the cerebrospinal fluid is characteristic of some neurodegenerative conditions which include sporadic Creutzfeldt-Jakob disease. Although 14-3-3 proteins are physiochemically well characterised and are known to be present in neuronal cells little is known of the neuroanatomical localisation of the individual isoforms. Using 14-3-3 isoform specific antibodies we have examined the distribution of the isoforms in normal murine brain and the changes observed during neurodegeneration as a result of ME7 scrapie infection. In normal brain there are two major patterns of immunolabelling. The beta, gamma, eta and zeta isoforms which exhibit a similar distribution pattern showing labelling of neuronal cell bodies often in particular anatomical nuclei. However the individual isoforms exhibit variation revealing subtle differences in location. The tau isoform was found only in the hippocampus and medulla, and the epsilon isoform was found throughout grey matter of the CNS. In the scrapie-infected murine brain, where severe pathological changes occur during the course of the disease, significant differences in the 14-3-3 isoform distribution were observed in the hippocampus and in the thalamus. Importantly, both the 14-3-3 eta isoform and prion protein were seen in the same neurones in both the cerebellar roof nuclei and in the lateral hypothalamic nuclei. Our study of 14-3-3 isoform distribution in adult murine brain clearly demonstrates a heterogeneous pattern of neurolocation for specific 14-3-3 isoforms. The fact that isoform labelling in terminal scrapie CNS is lost in some brain areas, but increases in others, suggests that the processing of these proteins during neurodegeneration may be much more complex than previously recognised.

14-3-3 proteins in Lewy bodies in Parkinson disease and diffuse Lewy body disease brains

Several components of Lewy bodies have been identified, but the precise mechanism responsible for the formation of Lewy bodies remains undetermined. The 14-3-3 protein family is involved in numerous signal transduction pathways and interacts with alpha-synuclein, which is a major constituent of Lewy bodies. To elucidate the role of 14-3-3 proteins in neuro-degenerative disorders associated with Lewy bodies, we performed immunohistochemical studies on 14-3-3 in brains from 5 elderly control subjects and from 10 patients with Parkinson disease (PD) or diffuse Lewy body disease (DLBD). In the normal controls, 14-3-3-like immunoreactivity was mainly observed in the neuronal somata and processes in various cortical and subcortical regions. In the PD and DLBD cases, a similar immunostaining pattern was found and immunoreactivity was generally spared in the surviving neurons from the severely affected regions. In addition, both classical and cortical Lewy bodies were intensely immunolabeled and some dystrophic neurites were also immunoreactive for 14-3-3. Our results suggest that 14-3-3 proteins may be associated with Lewy body formation and may play an important role in the pathogenesis of PD and DLBD.

Tau protein and 14-3-3 protein in the differential diagnosis of Creutzfeldt-Jakob disease

BACKGROUND

Diagnosis of Creutzfeldt-Jakob disease (CJD) is made according to the typical clinical picture and can be supported by a positive 14-3-3 CSF immunoblot. Promising results for the diagnostic sensitivity and specificity of tau-protein measurement in CSF already have been described in a smaller group of patients. Both tests in a larger group of patients with the differential diagnosis of CJD were evaluated.

METHODS

CSF of 297 patients under the differential diagnosis of CJD (109 definite, 55 probable, 39 possible; 85 others, 1 iatrogenic, 8 genetic), 23 nondemented control subjects, and 15 non-CJD patients with positive 14-3-3 immunoblots were analyzed. The 14-3-3 immunoblot bands were semiquantitatively rated as strong, medium, and weak. Tau-protein was analyzed using a commercially available ELISA. In addition, patients were neuropathologically classified according to prion protein type and polymorphism at codon 129.

RESULTS

A diagnostic sensitivity of 94%, a diagnostic specificity of 90%, and a positive predictive value of 92% were achieved for tau-protein at a cut-off of 1,300 pg/mL. These results are comparable with those of the 14-3-3 immunoblot. For patients with type II prion protein and methionine/valine or valine/valine polymorphism at codon 129, tau-protein has a higher diagnostic sensitivity than 14-3-3 protein. Tau-protein levels were significantly higher in patients with higher-rated 14-3-3 immunoblot bands.

CONCLUSION

The differential diagnostic significance of the 14-3-3 immunoblot is similar to that of the tau-protein ELISA. The advantage of the tau-protein ELISA is that it is easy to use in routine laboratories. Patients with a negative 14-3-3 immunoblot already have measurable tau-protein levels. This increases information on 14-3-3-negative patients with CJD and especially on patients with other diseases.

14-3-3 proteins; bringing new definitions to scaffolding

The 14-3-3 proteins are a part of an emerging family of proteins and protein domains that bind to serine/threonine-phosphorylated residues in a context specific manner, analogous to the Src homology 2 (SH2) and phospho-tyrosine binding (PTB) domains. 14-3-3 proteins bind and regulate key proteins involved in various physiological processes such as intracellular signaling (e.g. Raf, MLK, MEKK, PI-3 kinase, IRS-1), cell cycling (e.g. Cdc25, Wee1, CDK2, centrosome), apoptosis (e.g. BAD, ASK-1) and transcription regulation (e.g. FKHRL1, DAF-16, p53, TAZ, TLX-2, histone deacetylase). In contrast to SH2 and PTB domains, which serve mainly to mediate protein-protein interactions, 14-3-3 proteins in many cases alter the function of the target protein, thus allowing them to serve as direct regulators of their targets. This review focuses on the various mechanisms employed by the 14-3-3 proteins in the regulation of their diverse targets, the structural basis for 14-3-3-target protein interaction with emphasis on the role of 14-3-3 dimerization in target protein binding and regulation and provides an insight on 14-3-3 regulation itself.

Accumulation of mutant huntingtin fragments in aggresome-like inclusion bodies as a result of insufficient protein degradation

The huntingtin exon 1 proteins with a polyglutamine repeat in the pathological range (51 or 83 glutamines), but not with a polyglutamine tract in the normal range (20 glutamines), form aggresome-like perinuclear inclusions in human 293 Tet-Off cells. These structures contain aggregated, ubiquitinated huntingtin exon 1 protein with a characteristic fibrillar morphology. Inclusion bodies with truncated huntingtin protein are formed at centrosomes and are surrounded by vimentin filaments. Inhibition of proteasome activity resulted in a twofold increase in the amount of ubiquitinated, SDS-resistant aggregates, indicating that inclusion bodies accumulate when the capacity of the ubiquitin-proteasome system to degrade aggregation-prone huntingtin protein is exhausted. Immunofluorescence and electron microscopy with immunogold labeling revealed that the 20S, 19S, and 11S subunits of the 26S proteasome, the molecular chaperones BiP/GRP78, Hsp70, and Hsp40, as well as the RNA-binding protein TIA-1, the potential chaperone 14-3-3, and alpha-synuclein colocalize with the perinuclear inclusions. In 293 Tet-Off cells, inclusion body formation also resulted in cell toxicity and dramatic ultrastructural changes such as indentations and disruption of the nuclear envelope. Concentration of mitochondria around the inclusions and cytoplasmic vacuolation were also observed. Together these findings support the hypothesis that the ATP-dependent ubiquitin-proteasome system is a potential target for therapeutic interventions in glutamine repeat disorders.

Ubiquitin C-terminal hydrolase-L1 (PGP9.5) expression in human neural cell lines following induction of neuronal differentiation and exposure to cytokines, neurotrophic factors or heat stress

Dysfunction of the ubiquitin-dependent proteolytic pathway contributes to progressive accumulation of ubiquitinated protein inclusions in neurodegenerative disorders, such as Parkinson's disease (PD). Ubiquitin C-terminal hydrolase-L1 (UCH-L1), alternatively designated protein gene product 9.5 (PGP9.5), is a neural deubiquitinating enzyme which is identified as a principal constituent of Lewy bodies. To clarify the regulatory mechanism of UCH-L1 expression in human neural cells, we studied the constitutive, cytokine/neurotrophic factor-regulated, and heat stress-induced expression of UCH-L1 in cultured human neural cell lines by Western blot analysis. The constitutive expression of UCH-L1 was identified in SK-N-SH neuroblastoma cells, IMR-32 neuroblastoma cells, U-373MG astrocytoma cells, and NTera2 teratocarcinoma-derived differentiated neurones (NTera2-N). The levels of UCH-L1 expression were unaltered in these cell lines following treatment with TNF-alpha, IL-1beta, BDNF, GDNF, dibutyryl cyclic AMP, or phorbol 12-myristate 13-acetate, and remained unchanged by exposure to heat stress. In contrast, its levels were elevated substantially in NTera2 teratocarcinoma cells following retinoic acid-induced neuronal differentiation, accompanied with an increased expression of alpha-synuclein and synaptophysin. These results indicate that UCH-L1 is expressed constitutively in human neual cell lines, where it is upregulated following induction of neuronal differentiation, but unaffected by exposure to heat stress, cytokines, or growth/differentiation factors which are supposed to be invloved in the nigral neuronal death and survival in PD.

The cell cycle Cdc25A tyrosine phosphatase is activated in degenerating postmitotic neurons in Alzheimer's disease

The Cdc25 phosphatases play key roles in cell-cycle progression by activating cyclin-dependent kinases. The latter are absent from neurons that are terminally differentiated in adult brain. However, accumulation of mitotic phosphoepitopes, and re-expression and activation of the M phase regulator, Cdc2/cyclin B, have been described in neurons undergoing degeneration in Alzheimer's disease (AD). To explain this atypical mitotic activation in neurons we investigated the Cdc2-activating Cdc25A phosphatase in human brain. The structural hallmarks of AD neurodegeneration, neurofibrillary tangles and neuritic plaques, were prominently immunolabeled with Cdc25A antibodies. In addition numerous neurons without visible structural alterations were also intensely stained, whereas control brain was very weakly positive. After immunoprecipitation from control and AD tissue, we found that the tyrosine dephosphorylating activity of Cdc25A against exogenous Cdc2 substrate was elevated in AD. Accordingly, Cdc25A from AD tissue displayed increased immunoreactivity with the mitotic phosphoepitope-specific antibody, MPM-2, and co-localized with MPM-2 immunoreactivity in AD neurons. These data suggest that Cdc25A participates in mitotic activation during neurodegeneration. The involvement of Cdc25A in cellular transformation, modulation of the DNA damage checkpoint, and linkage of mitogenic signaling to cell cycle machinery, also implicates one of these cell-cycle pathways in AD pathogenesis.

14-3-3 proteins: structure, function, and regulation

The 14-3-3 proteins are a family of conserved regulatory molecules expressed in all eukaryotic cells. A striking feature of the 14-3-3 proteins is their ability to bind a multitude of functionally diverse signaling proteins, including kinases, phosphatases, and transmembrane receptors. This plethora of interacting proteins allows 14-3-3 to play important roles in a wide range of vital regulatory processes, such as mitogenic signal transduction, apoptotic cell death, and cell cycle control. In this review, we examine the structural basis for 14-3-3-ligand interactions, proposed functions of 14-3-3 in various signaling pathways, and emerging views of mechanisms that regulate 14-3-3 actions.

14-3-3zeta is an effector of tau protein phosphorylation

Neurofibrillary tangles associated with Alzheimer's disease are composed mainly of paired helical filaments that are formed by the aggregation of abnormally phosphorylated microtubule-associated protein tau. 14-3-3, a highly conserved protein family that exists as seven isoforms and regulates diverse cellular processes is present in neurofibrillary tangles (Layfield, R., Fergusson, J., Aitken, A., Lowe, J., Landon, M., Mayer, R. J. (1996) Neurosci. Lett. 209, 57-60). The role of 14-3-3 in Alzheimer's disease pathogenesis is not known. In this study, we found that the 14-3-3zeta isoform is associated with tau in brain extract and profoundly stimulates cAMP-dependent protein kinase catalyzed in vitro phosphorylation on Ser(262)/Ser(356) located within the microtubule-binding region of tau. 14-3-3zeta binds to both phosphorylated and nonphosphorylated tau, and the binding site is located within the microtubule-binding region of tau. From brain extract, 14-3-3zeta co-purifies with microtubules, and tubulin blocks 14-3-3zeta-tau binding. Among four 14-3-3 isoforms tested, beta and zeta but not gamma and epsilon associate with tau. Our data suggest that 14-3-3zeta is a tau protein effector and may be involved in the abnormal tau phosphorylation occurring during Alzheimer's disease ontogeny.

Increased levels of 14-3-3 gamma and epsilon proteins in brain of patients with Alzheimer's disease and Down syndrome

The 14-3-3 family consists of homo- and heterodimeric proteins representing a novel type of "adaptor proteins" modulating the interaction between components of signal transduction pathways. 14-3-3 isoforms interact with phosphoserine motifs on many proteins as kinases, phosphatases, apoptosis related proteins etc. Performing protein mapping by 2D electrophoresis in human brain we identified two isoforms, 14-3-3 gamma and epsilon and decided to determine these two multifunctional proteins in several brain regions of aged patients with Alzheimer's disease (AD) and Down Syndrome (DS) with AD neuropathology in comparison with control brains. 14-3-3 gamma and 14-3-3 epsilon proteins were increased in several brain regions of AD and DS patients. These changes may contribute to the complex pathomechanisms of AD and AD in DS, evolving inevitably from the fourth decade of life. Deranged 14-3-3 isoforms gamma and epsilon may reflect impaired signaling and/or apoptosis in the brain as several kinases (protein kinase C, Ras, mitogen-activated kinase MEK) involved in signaling and apoptotic factors as bcl-2-related proteins BAD and BAG-1 are binding to 14-3-3 motifs.

Aberrant expression of nNOS in pyramidal neurons in Alzheimer's disease is highly co-localized with p21ras and p16INK4a

Aberrancies of growth and proliferation-regulating mechanisms might be critically involved in the processes of neurodegeneration in Alzheimer's disease (AD). Expression of p21ras and further downstream signalling elements involved in regulation of proliferation and differentiation as, for example, MEK, ERK1/2, cyclins, cyclin-dependent kinases and their inhibitors such as those of the p16INK4a family, are elevated early during the course of neurodegeneration. Activation of p21ras can also directly be triggered by nitric oxide (NO), synthesized in the brain by various isoforms of nitric oxide synthase (NOS) that might be differentially involved into the pathomechanism of AD. To study the potential link of NO and critical regulators of cellular proliferation and differentiation in the process of neurofibrillary degeneration, we analyzed the expression pattern of NOS-isoforms, p21ras and p16INK4a compared to neurofibrillary degeneration in AD. Additionally to its expression in a subtype of cortical interneurons that contain the nNOS-isoform also in normal brain, nNOS was detected in pyramidal neurons containing neurofibrillary tangles or were even unaffected by neurofibrillary degeneration. Expression of nNOS in these neurons was highly co-localized with p21ras and p16INK4a. Because endogenous NO can activate p21ras in the same cell which in turn leads to cellular activation and stimulation of NOS expression [H.M. Lander, J.S. Ogiste, S.F.A. Pearce, R. Levi, A. Novogrodsky, Nitric oxide-stimulated guanine nucleotide exchange on p21 ras, J. Biol. Chem. 270 (1995) 7017-7020], the high level of co-expression of NOS and p21ras in neurons vulnerable to neurofibrillary degeneration early in the course of AD thus provides the basis for an autocrine feedback mechanism that might exacerbate the progression of neurodegeneration in a self-propagating manner.

Isoform pattern of 14-3-3 proteins in the cerebrospinal fluid of patients with Creutzfeldt-Jakob disease

Two-dimensional polyacrylamide gel electrophoresis of CSF has been used in the diagnosis of Creutzfeldt-Jakob disease (CJD). One of the two diagnostic protein spots was identified as isoform(s) of the 14-3-3 family of abundant brain proteins. This has led to the development of one-dimensional 14-3-3 sodium dodecyl sulfate polyacrylamide gel electrophoresis immunoblot, which is currently used to support the diagnosis of CJD. In the present study employing western blot analysis, we have identified the panel of 14-3-3 isoforms that appear in the CSF of 10 patients with CJD compared with 10 patients with other dementias. The results clearly show that the 14-3-3 isoforms beta, gamma, epsilon, and eta are present in the CSF of patients with CJD and can be used to differentiate other dementias. 14-3-3eta also gave a baseline signal in all patients with other dementias, including six patients with Alzheimer's disease. The presence of 14-3-3eta in the CSF of a patient with herpes simplex encephalitis was particularly noteworthy. This study has determined that isoform-specific 14-3-3 antibodies against beta, gamma, and epsilon should be considered for the neurochemical differentiation of CJD from other neurodegenerative diseases.

alpha-Synuclein shares physical and functional homology with 14-3-3 proteins

alpha-Synuclein has been implicated in the pathophysiology of many neurodegenerative diseases, including Parkinson's disease (PD) and Alzheimer's disease. Mutations in alpha-synuclein cause some cases of familial PD (Polymeropoulos et al., 1997; Kruger et al., 1998). In addition, many neurodegenerative diseases show accumulation of alpha-synuclein in dystrophic neurites and in Lewy bodies (Spillantini et al., 1998). Here, we show that alpha-synuclein shares physical and functional homology with 14-3-3 proteins, which are a family of ubiquitous cytoplasmic chaperones. Regions of alpha-synuclein and 14-3-3 proteins share over 40% homology. In addition, alpha-synuclein binds to 14-3-3 proteins, as well as some proteins known to associate with 14-3-3, including protein kinase C, BAD, and extracellular regulated kinase, but not Raf-1. We also show that overexpression of alpha-synuclein inhibits protein kinase C activity. The association of alpha-synuclein with BAD and inhibition of protein kinase C suggests that increased expression of alpha-synuclein could be harmful. Consistent with this hypothesis, we observed that overexpression of wild-type alpha-synuclein is toxic, and overexpression of alpha-synuclein containing the A53T or A30P mutations exhibits even greater toxicity. The activity and binding profile of alpha-synuclein suggests that it might act as a protein chaperone and that accumulation of alpha-synuclein could contribute to cell death in neurodegenerative diseases.

Ischemic rat brains contain immunoreactivity of 14-3-3 proteins

14-3-3 proteins and tissue damage association were determined. The localization of 14-3-3 proteins in section of cortex from ischemia produced rats was examined by immunohistochemistry. Ischemia was produced in rats by unilaterally clamping the carotid artery for 6 hrs at the distal side. Following recovery for 6 hrs, the animals were sacrificed. The intensity of neuronal necrosis stained with antibody raised against 14-3-3 protein was markedly more in the cortex than the other parts of the brain, since there was occlusion of the artery which feeds this region. 14-3-3 antibody was confined to neuronal cell body. Since 14-3-3 proteins are central to mitogen-activated protein (MAP) kinase signaling, this pathway is in part responsible for the hyperphosphorylation of neurofilaments or cytoskeletal proteins of neuron, which may possibly lead to neuronal inclusions.

14-3-3 proteins in neuronal development and function

The 14-3-3 proteins are small, cytosolic, evolutionarily conserved proteins expressed abundantly in the nervous system. Although they were discovered more than 30 yr ago, their function in the nervous system has remained enigmatic. Several recent studies have helped to clarify their biological function. Crystallographic investigations have revealed that 14-3-3 proteins exist as dimers and that they contain a specific region for binding to other proteins. The interacting proteins, in turn, contain a 14-3-3 binding motif; proteins that interact with 14-3-3 dimers include PKC and Raf, protein kinases with critical roles in neuronal signaling. These proteins are capable of activating Raf in vitro, and this role has been verified by in vivo studies in Drosophila. Most interestingly, mutations in the Drosophila 14-3-3 genes disrupt neuronal differentiation, synaptic plasticity, and behavioral plasticity, establishing a role for these proteins in the development and function of the nervous system.

Structure and sites of phosphorylation of 14-3-3 protein: role in coordinating signal transduction pathways

The 14-3-3 family are homo- and heterodimeric proteins whose biological role has been unclear for some time, although they are now gaining acceptance as a novel type of 'adaptor' protein that modulates interactions between components of signal transduction pathways, rather than by direct activation or inhibition. It is becoming apparent that phosphorylation of the binding partner and possibly also the 14-3-3 proteins may regulate these interactions. 14-3-3 isoforms interact with a novel phosphoserine (Sp) motif on many proteins, RSX1,2SpXP. The two isoforms that interact with Raf-1 are phosphorylated in vivo on Ser185 in a consensus sequence motif for proline-directed kinases. The crystal structure of 14-3-3 indicates that this phosphorylation could regulate interaction of 14-3-3 with its target proteins. We have now identified a number of additional phosphorylation sites on distinct mammalian and yeast isoforms.