Molecular cloning of cDNA coding for brain-specific 14-3-3 protein, a protein kinase-dependent activator of tyrosine and tryptophan hydroxylases

Role of 14–3–3 Proteins in Eukaryotic Signaling and Development

14-3-3 genes encode a ubiquitous family of highly conserved eukaryotic proteins from fungi to humans and plants with several molecular and cellular functions. Most notably, 14-3-3 proteins bind to phosphoserine/phosphothreonine motifs in a sequence-specific manner. More than 100 14-3-3 binding partners involved in signal transduction, cell cycle regulation, apoptosis, stress responses, and malignant transformation have been identified. The 14-3-3 proteins form homodimers and heterodimers, and there is redundancy of the binding specificity and function of different 14-3-3 proteins because of their highly similar amino acid sequence and tertiary structure. 14-3-3 proteins can regulate target protein function by several mechanisms. Although the molecular and cellular functions of 14-3-3 proteins have been well studied, there have been fewer studies addressing the in vivo role of 14-3-3s. Here we review what is known about 14-3-3 proteins during eukaryotic development.

Proteome analysis of mouse macrophages treated with anthrax lethal toxin

Anthrax toxin produced by Bacillus anthracis is a tripartite toxin comprising of protective antigen (PA), lethal factor (LF) and edema factor (EF). PA is the receptor-binding component, which facilitates the entry of LF or EF into the cytosol. EF is a calmodulin-dependent adenylate cyclase that causes edema whereas LF is a zinc metalloprotease and leads to necrosis of macrophages. It is also important to note that the exact mechanism of LF action is still unclear. With this view in mind, in the present study, we investigated a proteome wide effect of anthrax lethal toxin (LT) on mouse macrophage cells (J774A.1). Proteome analysis of LT-treated and control macrophages revealed 41 differentially expressed protein spots, among which phosphoglycerate kinase I, enolase I, ATP synthase (beta subunit), tubulin beta2, gamma-actin, Hsp70, 14-3-3 zeta protein and tyrosine/tryptophan-3-monooxygenase were found to be down-regulated, while T-complex protein-1, vimentin, ERp29 and GRP78 were found to be up-regulated in the LT-treated macrophages. Analysis of up- and down-regulated proteins revealed that primarily the stress response and energy generation proteins play an important role in the LT-mediated macrophage cell death.

Akt and 14-3-3eta regulate Miz1 to control cell-cycle arrest after DNA damage

The transcription factor Miz1 is required for DNA-damage-induced cell-cycle arrest. We have now identified 14-3-3eta as a gene that inhibits Miz1 function through interaction with its DNA binding domain. Binding of 14-3-3eta to Miz1 depends on phosphorylation by Akt and regulates the recovery of cells from arrest after DNA damage. Miz1 has two functions in response to DNA damage: first, it is required for upregulation of a large group of genes, a function that is regulated by c-Myc, but not by 14-3-3eta; second, Miz1 represses the expression of many genes in response to DNA damage in an Akt- and 14-3-3eta-regulated manner.

Inhibition of Gap Junction Activity through the Release of the C1B Domain of Protein Kinase Cγ (PKCγ) from 14-3-3

We have shown previously that insulin-like growth factor-I or lens epithelium-derived growth factor increases the translocation of protein kinase Cgamma (PKCgamma)to the membrane and the phosphorylation of Cx43 by PKCgamma and causes a subsequent decrease of gap junction activity (Nguyen, T. A., Boyle, D. L., Wagner, L. M., Shinohara, T., and Takemoto, D. J. (2003) Exp. Eye Res. 76, 565-572; Lin, D., Boyle, D. L., and Takemoto, D. J. (2003) Investig. Ophthalmol. Vis. Sci. 44, 1160-1168). Gap junction activity in lens epithelial cells is regulated by PKCgamma-mediated phosphorylation of Cx43. PKCgamma activity is stimulated by growth factor-regulated increases in the synthesis of diacylglycerol but is inhibited by cytosolic docking proteins such as 14-3-3. Here we have identified two sites on the PKCgamma-C1B domain that are responsible for its interaction with 14-3-3epsilon. Two sites, C1B1 (residues 101-112) and C1B5 (residues 141-151), are located within the C1 domain of PKCgamma. C1B1 and/or C1B5 synthetic peptides can directly compete for the binding of 14-3-3epsilon, resulting in the release of endogenous cellular PKCgamma from 14-3-3epsilon, in vivo or in vitro, in activation of PKCgamma enzyme activity, phosphorylation of PKCgamma, in the subsequent translocation of PKCgamma to the membrane, and in inhibition of gap junction activity. Gap junction activity was decreased by at least 5-fold in cells treated with C1B1 or C1B5 peptides when compared with a control. 100 microM of C1B1 or C1B5 peptides also caused a 10- or 4-fold decrease of Cx43 plaque formation compared with control cells. The uptake of these synthetic peptides into cells was verified by using high pressure liquid chromatography and matrix-assisted laser desorption ionization time-of-flight-mass spectrometry. We have demonstrated that the activity and localization of PKCgamma are regulated by its binding to 14-3-3epsilon at the C1B domain of PKCgamma. Synthetic peptides corresponding to these regions of PKCgamma successfully competed for the binding of 14-3-3epsilon to endogenous PKCgamma, resulting in inhibition of gap junction activity. This demonstrates that synthetic peptides can be used to exogenously regulate gap junctions.

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.

Does alpha-synuclein modulate dopaminergic synaptic content and tone at the synapse?

alpha-Synuclein is a key component of the pathological process of neurodegeneration in Parkinson's disease. Although its contributions to normal physiological conditions remain elusive, converging observations suggest that a primary function of this protein in dopaminergic neurons may be the regulation of dopamine content and synaptic tone at the synapse. We review here cumulative evidence that demonstrates the participation of alpha-synuclein in the life cycle of dopamine from its synthesis, storage, release, and reuptake. The regulatory role of alpha-synuclein on dopamine metabolism is assessed by discussing the experimental evidence supporting each of these observations in the healthy physiological maintenance of dopaminergic neurons, as well as showing how disruption of these events can initiate the observed neurotoxicity of alpha-synuclein and the genesis of the degenerative processes associated with Parkinson's disease.

14-3-3 proteins: a number of functions for a numbered protein

Many signal transduction events are orchestrated by specific interactions of proteins mediated through discrete phosphopeptide-binding motifs. Although several phosphospecific-binding domains are now known, 14-3-3s were the first proteins recognized to specifically bind a discrete phosphoserine or phosphothreonine motif. The 14-3-3 proteins are a family of ubiquitously expressed, exclusively eukaryotic proteins with an astonishingly large number of binding partners. Consequently, 14-3-3s modulate an enormous and diverse group of cellular processes. The effects of 14-3-3 proteins on their targets can be broadly defined using three categories: (i) conformational change; (ii) physical occlusion of sequence-specific or structural protein features; and (iii) scaffolding. This review will describe the current state of knowledge on 14-3-3 proteins, highlighting several important advances, and will attempt to provide a framework by which 14-3-3 functions can be understood.

Keratinocyte-releasable stratifin functions as a potent collagenase-stimulating factor in fibroblasts

Termination of wound healing requires a fine balance between collagen deposition and its hydrolysis. To dissect the underlying control mechanisms for this process, we established a keratinocyte/fibroblast co-culture system and subsequently demonstrated more than a 10-fold increase in collagenase expression in fibroblasts co-cultured with keratinocytes relative to that of control cells. This finding was further confirmed in fibroblasts grown in a keratinocyte/fibroblast collagen-GAG gel. The efficacy of keratinocyte-derived collagenase stimulatory factors on collagenase activity was evaluated, and the results showed that only conditioned medium derived from fibroblasts co-cultured with keratinocytes was able to break down markedly type I collagen to its one-quarter and three-quarter fragments of both alpha (alpha1 and alpha2) and beta (beta1.1 and beta1.2) chains. The results of a dose-response experiment showed that keratinocyte-conditioned medium (KCM) stimulates the expression of collagenase mRNA by dermal fibroblasts in a concentration-dependent fashion. In a similar experiment, the results of a time-response experiment revealed that KCM treatment increases the expression of collagenase mRNA in dermal fibroblasts as early as 6 h and reaches its maximum level within 24-48 h. Considering that this keratinocyte-releasable factor has a potent collagenase stimulatory effect on fibroblasts, which favors the resolution of accumulated type I and type III collagen found in fibrotic tissue, we referred to this protein as a keratinocyte-derived anti-fibrogenic factor (KDAF). In a series of chromatography experiments and a direct trypsin digestion of the proteins and subsequent peptide mapping, a keratinocyte-derived collagenase-stimulating factor turned out to be a releasable form of stratifin, also known as 14-3-3 sigma protein. To validate this finding, stratifin cDNA was cloned into a pGEX-6P-1 expressing vector and more than 50 mg of recombinant stratifin was generated and used to treat fibroblasts with various concentrations for 24 h. The results of northern analysis showed a remarkable dose-response increase in the expression of collagenase mRNA in stratifin-treated fibroblasts relative to that of the control. This finding was consistent with that obtained from collagenase activity assay. In conclusion, we identified a keratinocyte-releasable form of stratifin in KCM that mimics the collagenase stimulatory effect of KCM for dermal fibroblasts. This finding suggests that stratifin is likely to be, at least, one of the KDAFs found in KCM.

Comprehensive proteomic analysis of interphase and mitotic 14-3-3-binding proteins

14-3-3 proteins regulate the cell division cycle and play a pivotal role in blocking cell cycle advancement after activation of the DNA replication and DNA damage checkpoints. Here we describe a global proteomics analysis to identify proteins that bind to 14-3-3s during interphase and mitosis. 14-3-3-binding proteins were purified from extracts of interphase and mitotic HeLa cells using specific peptide elution from 14-3-3 zeta affinity columns. Proteins that specifically bound and eluted from the affinity columns were identified by microcapillary high pressure liquid chromatography tandem mass spectrometry analysis. Several known and novel 14-3-3-interacting proteins were identified in this screen. Identified proteins are involved in cell cycle regulation, signaling, metabolism, protein synthesis, nucleic acid binding, chromatin structure, protein folding, proteolysis, nucleolar function, and nuclear transport as well as several other cellular processes. In some cases 14-3-3 binding was cell cycle-dependent, whereas in other cases the binding was shown to be cell cycle-independent. This study adds to the growing list of human 14-3-3-binding proteins and implicates a role for 14-3-3 proteins in a plethora of essential biological processes.

Parkin and alpha-synuclein: opponent actions in the pathogenesis of Parkinson's disease

Dominant mutations in the gene for alpha-synuclein, a small presynaptic protein, can cause Parkinson's disease. Although there is still substantial debate about the precise mechanisms, alpha-synuclein is toxic to vulnerable neurons, probably as a result of its tendency to aggregate. Opposing this is another gene product that, when mutated, causes a recessive form of parkinsonism, parkin. Parkin has been recently shown to protect cells against alpha-synuclein toxicity. However, the precise details of the mechanism are unclear. This review will discuss the concept that there are multiple neuronal functions that are targeted by mutant alpha-synuclein, and in many cases, there is evidence that parkin can protect cells against damage to the same systems. The authors will also discuss ways in which to test some of these ideas, by using newly identified genes such as DJ-1 that cause similar phenotypes.

A unique central tryptophan hydroxylase isoform

Serotonin (5-hydroxytryptophan, 5-HT) is a neurotransmitter synthesized in the raphe nuclei of the brain stem and involved in the central control of food intake, sleep, and mood. Accordingly, dysfunction of the serotonin system has been implicated in the pathogenesis of psychiatric diseases. At the same time, serotonin is a peripheral hormone produced mainly by enterochromaffin cells in the intestine and stored in platelets, where it is involved in vasoconstriction, haemostasis, and the control of immune responses. Moreover, serotonin is a precursor for melatonin and is therefore synthesized in high amounts in the pineal gland. Tryptophan hydroxylase (TPH) catalyzes the rate limiting step in 5-HT synthesis. Until recently, only one gene encoding TPH was described for vertebrates. By gene targeting, we functionally ablated this gene in mice. To our surprise, the resulting animals, although being deficient for serotonin in the periphery and in the pineal gland, exhibited close to normal levels of 5-HT in the brain stem. This led us to the detection of a second TPH gene in the genome of humans, mice, and rats, called TPH2. This gene is predominantly expressed in the brain stem, while the classical TPH gene, now called TPH1, is expressed in the gut, pineal gland, spleen, and thymus. These findings clarify puzzling data, which have been collected over the last decades about partially purified TPH proteins with different characteristics and justify a new concept of the serotonin system. In fact, there are two serotonin systems in vertebrates, independently regulated and with distinct functions.

Rim, a component of the presynaptic active zone and modulator of exocytosis, binds 14-3-3 through its N terminus

Rim1, a brain-specific Rab3a-binding protein, localizes to the presynaptic cytomatrix and plays an important role in synaptic transmission and synaptic plasticity. Rim2, a homologous protein, is more ubiquitously expressed and is found in neuroendocrine cells as well as in brain. Both Rim1 and Rim2 contain multiple domains, including an N-terminal zinc finger, which in Rim1 strongly enhances secretion in chromaffin and PC12 cells. The yeast two-hybrid technique identified 14-3-3 proteins as ligands of the N-terminal domain. In vitro protein binding experiments confirmed a high-affinity interaction between the N terminus of Rim1 and 14-3-3. The N-terminal domain of Rim2 also bound 14-3-3. The binding domains were localized to a short segment just C-terminal to the zinc finger. 14-3-3 proteins bind to specific phosphoserine residues. Alkaline phosphatase treatment of N-terminal domains of Rim1 and Rim2 almost completely inhibited the binding of 14-3-3. Two serine residues in Rim1 (Ser-241 and Ser-287) and one serine residue in Rim2 (Ser-335) were required for 14-3-3 binding. Incubation with Ca2+/calmodulin-dependent protein kinase II greatly stimulated the interaction of recombinant N-terminal Rim but not the S241/287A mutant with 14-3-3, again indicating the importance of the phosphorylation of these residues for the binding. Rabphilin3, another Rab3a effector, also bound 14-3-3. Serine-to-alanine mutations identified Ser-274 as the likely phosphorylated residue to which 14-3-3 binds. Because the phosphorylation of this residue had been shown to be stimulated upon depolarization in brain slices, the interaction of 14-3-3 with Rabphilin3 may be important in the dynamic function of central nervous system neurons.

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.

The 14-3-3 proteins: gene, gene expression, and function

14-3-3 proteins were discovered by Moore and Perez in the soluble extract of bovine brain. These proteins are highly abundant in the brain. In this review 14-3-3 cDNA cloning, nucleotide sequence of 14-3-3 cDNA, the structure of 14-3-3 gene and 14-3-3 gene expression, in situ hybridization of 14-3-3 mRNA in the brain, the function and regulation of 14-3-3 protein, the binding of 14-3-3 protein to other proteins, the effects of 14-3-3 protein on the binding of a protein to other proteins, and the effect on protein kinase, etc., are concisely described. From the recent rapid development of proteom technology, markedly more target proteins of 14-3-3 protein should be discovered.

Functional regulation of choline acetyltransferase by phosphorylation

Choline acetyltransferase (ChAT) catalyzes synthesis of acetylcholine (ACh) in cholinergic neurons. ACh synthesis is regulated by availability of precursors choline and acetyl coenzyme A or by activity of ChAT; ChAT regulates ACh synthesis under some conditions. Posttranslational phosphorylation is a common mechanism for regulating the function of proteins. Analysis of the primary sequence of 69-kD human ChAT indicates that it has putative phosphorylation consensus sequences for multiple protein kinases. ChAT is phosphorylated on serine-440 and threonine-456 by protein kinase C and CaM kinase II, respectively. These phosphorylation events regulate activity of the enzyme, as well as its binding to plasma membrane and interaction with other cellular proteins. It is relevant to investigate differences in constitutive and inducible patterns of phosphorylation of ChAT under physiological conditions and in response to challenges that cholinergic neurons may be exposed to, and to determine how changes in phosphorylation relate to changes in neurochemical transmission.

Constitutively and autonomously active protein kinase C associated with 14-3-3 zeta in the rodent brain

Persistent activation of protein kinase C (PKC) is required for the expression of synaptic plasticity in the brain. There are several mechanisms proposed that can lead to the prolonged activation of PKC. These include long lasting production of lipid activators (diacylglycerol and fatty acid) through mitogen-activated protein (MAP) kinase pathway, and a modification of PKC by reactive oxygen species. In nerve growth factor (NGF)-differentiated PC12 cells, we found that constitutive and autonomous Ca2+-independent PKC activity is associated with 14-3-3 zeta. Because PKC and 14-3-3 zeta are both involved in synaptic plasticity and learning and memory, we examined whether PKC interacts with 14-3-3 zeta in the brain and whether the PKC/14-3-3 zeta complex has autonomous activity. Here we show that three subclasses of PKC, Ca2+-dependent classical PKC, Ca2+-independent novel PKC, and Ca2+-independent and diacylglycerol-insensitive atypical PKC, all interact with 14-3-3 zeta in the rodent brain. The pool size of 14-3-3 zeta bound form of PKC is small (1-4% of each PKC isoform), but they show constitutive and autonomous activity. Our study indicates that the binding of PKC with 14-3-3 zeta is at least in part independent of phosphorylation of PKC and that the C1 domain of PKC is involved in the binding. As both molecules are enriched in synaptic locus, the constitutive PKC activity and its interaction with 14-3-3 zeta could be a mechanism for the persistent PKC activation in the brain.

Identification of cofilin and LIM-domain-containing protein kinase 1 as novel interaction partners of 14-3-3 zeta

Proteins of the 14-3-3 family have been implicated in various physiological processes, and are thought to function as adaptors in various signal transduction pathways. In addition, 14-3-3 proteins may contribute to the reorganization of the actin cytoskeleton by interacting with as yet unidentified actin-binding proteins. Here we show that the 14-3-3 zeta isoform interacts with both the actin-depolymerizing factor cofilin and its regulatory kinase, LIM (Lin-11/Isl-1/Mec-3)-domain-containing protein kinase 1 (LIMK1). In both yeast two-hybrid assays and glutathione S-transferase pull-down experiments, these proteins bound efficiently to 14-3-3 zeta. Deletion analysis revealed consensus 14-3-3 binding sites on both cofilin and LIMK1. Furthermore, the C-terminal region of 14-3-3 zeta inhibited the binding of cofilin to actin in co-sedimentation experiments. Upon co-transfection into COS-7 cells, 14-3-3 zeta-specific immunoreactivity was redistributed into characteristic LIMK1-induced actin aggregations. Our data are consistent with 14-3-3-protein-induced changes to the actin cytoskeleton resulting from interactions with cofilin and/or LIMK1.

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.

Stimulation of 14-3-3 protein and its isoform on histamine secretion from permeabilized rat peritoneal mast cells

The effect of the 14-3-3 protein, an adaptor protein of intracellular signal pathways, on histamine release from rat peritoneal mast cells was investigated. The exogenous 14-3-3 protein from bovine brain increased the Ca(2+)-dependent histamine release from permeabilized mast cells, but only slightly affected the non-permeabilized cells. Partial amino acid sequences showed that the bovine brain 14-3-3 protein contained 14-3-3beta, gamma and zeta isoforms, and that these recombinant isoforms were prepared. Among them, 14-3-3zeta was an active species while the 14-3-3beta and gamma were inactive for histamine release from the permeabilized mast cells. Approximately 15% of the histamine release was stimulated by 14-3-3zeta at 2.5 microM, and half-maximal stimulation occurred at 1 microM. Treatment of the mast cells with wortmannin or staurosporine completely inhibited the stimulatory effect on histamine release caused by Ca(2+) or Ca(2+)/14-3-3zeta, and genistein partially inhibited both stimulatory effects. PD 98059, however, had little effect on the histamine release. These results suggest the possibility that 14-3-3zeta is associated with signal transduction for degranulation of the mast cells.

Functional specificity in 14-3-3 isoform interactions through dimer formation and phosphorylation. Chromosome location of mammalian isoforms and variants

14-3-3 is now accepted as a novel type of dimeric protein that can modulate interaction between proteins involved in cell signalling and other functions. Target proteins that interact with 14-3-3 isoforms are involved in regulation of cell cycle, intracellular trafficking/targeting, signal transduction, cytoskeletal structure and transcription. In many cases, these proteins show a distinct preference for a particular isoform(s) of 14-3-3. A specific repertoire of dimer formation may influence which of the 14-3-3 interacting proteins could be brought together. The purpose of this review is to give an overview of mammalian 14-3-3 sequences, structures and post-translational modifications that may explain the known interactions with other proteins and mechanism(s). The regulation of interaction may involve phosphorylation of the interacting protein and in some cases the phosphorylation of 14-3-3 isoforms themselves.

Cerebrospinal fluid brain-derived proteins in the diagnosis of Alzheimer's disease and Creutzfeldt-Jakob disease

The differential diagnosis of dementia can be difficult in the early stages of disease, and with the emergence of new therapeutic agents for Alzheimer's disease (AD) there is an increasing need for reliable and accurate diagnostic tests. The concept of brain-specific proteins was first proposed in the 1960s and, since that time, methods have developed to measure these proteins in the cerebrospinal fluid (CSF). The concentration of individual brain-specific proteins can be altered in disease, and these changes are thought to reflect the underlying pathology. CSF tau protein and amyloid peptide A beta 42 concentrations are altered in AD and have been proposed as early diagnostic tests for this disease. The data from a number of studies suggest that these proteins may be of value, but are less specific than previously thought and further studies with neuropathological confirmation are required before these tests can be introduced into clinical practice. The detection of 14-3-3 in the CSF is an accurate test for sporadic Creutzfeldt-Jakob disease (CJD) and this accuracy has lead the World Health Organization to revise the clinical criteria for probable sporadic CJD to include a positive CSF 14-3-3. However, CSF 14-3-3 is less useful in the diagnosis of variant CJD, where studies are underway investigating the value of other CSF proteins.

The 14-3-3 protein homologues from Saccharomyces cerevisiae, Bmh1p and Bmh2p, have cruciform DNA-binding activity and associate in vivo with ARS307

We have previously shown that, in human cells, cruciform DNA-binding activity is due to 14-3-3 proteins (Todd, A., Cossons, N., Aitken, A., Price, G. B., and Zannis-Hadjopoulos, M. (1998) Biochemistry 37, 14317-14325). Here, wild-type and single- and double-knockout nuclear extracts from the 14-3-3 Saccharomyces cerevisiae homologues Bmh1p and Bmh2p were analyzed for similar cruciform-binding activities in relation to these proteins. The Bmh1p-Bmh2p heterodimer, present in the wild-type strain, bound efficiently to cruciform-containing DNA in a structure-specific manner because cruciform DNA efficiently competed with the formation of the complex, whereas linear DNA did not. In contrast, the band-shift ability of the Bmh1p-Bmh1p and Bmh2p-Bmh2p homodimers present in the bmh2(-) and bmh1(-) single-knockout cells, respectively, was reduced by approximately 93 and 82%, respectively. The 14-3-3 plant homologue GF14 was also able to bind to cruciform DNA, suggesting that cruciform-binding activity is a common feature of the family of 14-3-3 proteins across species. Bmh1p and Bmh2p were found to associate in vivo with the yeast autonomous replication sequence ARS307, as assayed by formaldehyde cross-linking, followed by immunoprecipitation with anti-Bmh1p/Bmh2p antibody and conventional PCR. In agreement with the finding of an association of Bmh1p and Bmh2p with ARS307, another immunoprecipitation experiment using 2D3, an anti-cruciform DNA monoclonal antibody, revealed the presence of cruciform-containing DNA in ARS307.

Patterns of gene expression in the developing adult sea urchin central nervous system reveal multiple domains and deep-seated neural pentamery

The adult sea urchin central nervous system (CNS) is composed of five radial nerve cords connected to a circular nerve ring. Although much is known about the molecular mechanisms underlying the development and function of the nervous systems of many invertebrate and vertebrate species, virtually nothing is known about these processes in echinoderms. We have isolated a set of clones from a size-selected cDNA library prepared from the nervous system of the sea urchin Heliocidaris erythrogramma for use as probes. A total of 117 expressed sequence clones were used to search the GenBank database. Identified messages include genes that encode signaling proteins, cytoskeletal elements, cell surface proteins and receptors, cell proliferation and differentiation factors, transport and channel proteins, and a RNA DEAD box helicase. Expression was analyzed by RNA gel blot hybridization to document expression through development. Many of the genes have apparently neural limited expression and function, but some have been co-opted into new roles, notably associated with exocytotic events at fertilization. Localization of gene expression by whole-mount in situ hybridization shows that the morphologically simple sea urchin radial CNS exhibits complex organization into localized transcriptional domains. The transcription patterns reflect the morphological pentamery of the echinoderm CNS and provide no indication of an underlying functional bilateral symmetry in the CNS.

Isolation and structure of the mouse 14-3-3 eta chain gene and the distribution of 14-3-3 eta mRNA in the mouse brain

14-3-3 protein is a brain-specific protein discovered by Moore and Perez, but at present is thought to be a multifunctional protein. To clarify the brain-specific function of the protein, we intend constructing a 14-3-3 eta gene knock-out mouse. As the first step of this process, we isolated the mouse 14-3-3 eta chain gene and determined its structure. The mouse gene is about 10 kb long and composed of two exons separated by a long intron. The transcription start site was identified and the polyadenylation signals (AATAAA) were found in exon 2 of the mouse gene. In the 5'-upstream sequence, we found several cis elements including a CRE sequence, a TATA box-like sequence, and a C/EBP element. Furthermore, the distribution of 14-3-3 eta mRNA in the mouse brain was examined by in situ hybridization histochemistry. The highest signals were found in the Purkinje cells of the cerebellum, the pyramidal cells of the hippocampus and the olfactory bulb neurons of the adult mouse. Neuronal expression of 14-3-3 eta in these regions mRNA may generally increase during postnatal brain development. The distribution of protein kinase C gamma in the mouse brain was also examined by immunohistochemistry. From the distribution of 14-3-3 eta mRNA and protein kinase C gamma in the mouse brain, the involvement of these compounds in the induction and maintenance of LTP was discussed.

A role for alpha-synuclein in the regulation of dopamine biosynthesis

The alpha-synuclein gene is implicated in the pathogenesis of Parkinson's disease. Although alpha-synuclein function is uncertain, the protein has homology to the chaperone molecule 14-3-3. In addition, alpha-synuclein can bind to 14-3-3, and both alpha-synuclein and 14-3-3 bind to many of the same proteins. Because 14-3-3 binds to and activates tyrosine hydroxylase, the rate-limiting enzyme in dopamine (DA) biosynthesis, we explored whether alpha-synuclein also bound to tyrosine hydroxylase and influenced its activity. Immunoprecipitation revealed an interaction between alpha-synuclein and tyrosine hydroxylase in brain homogenates and MN9D dopaminergic cells. Colocalization of alpha-synuclein with tyrosine hydroxylase was confirmed by immunoelectron microscopy. To explore the consequences of the interaction, we measured the effect of recombinant alpha-synuclein on tyrosine hydroxylase activity in a cell-free system and observed a dose-dependent inhibition of tyrosine hydroxylase by alpha-synuclein. To measure the impact of alpha-synuclein on tyrosine hydroxylase in dopaminergic cells, we stably transfected MN9D cells with wild-type or A53T mutant alpha-synuclein. Overexpression of wild-type or A53T mutant alpha-synuclein did not significantly alter tyrosine hydroxylase protein levels in our stably transfected cells. However, overexpressing cell lines had significantly reduced tyrosine hydroxylase activity and a corresponding reduction in dopamine synthesis. The reduction in cellular dopamine levels was not caused by increased dopamine catabolism or dopamine efflux. These data suggest that alpha-synuclein plays a role in the regulation of dopamine biosynthesis, acting to reduce the activity of tyrosine hydroxylase. If so, a loss of soluble alpha-synuclein, by reduced expression or aggregation, could increase dopamine synthesis with an accompanying increase in reactive dopamine metabolites.

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.

How do 14-3-3 proteins work?-- Gatekeeper phosphorylation and the molecular anvil hypothesis

14-3-3 proteins were the first signaling molecules to be identified as discrete phosphoserine/threonine binding modules. This family of proteins, which includes seven isotypes in human cells and up to 15 in plants, plays critical roles in cell signaling events that control progress through the cell cycle, transcriptional alterations in response to environmental cues, and programmed cell death. Despite over 30 years of research, distinct roles for most isotypes remain unknown. Though 14-3-3 proteins perform different functions for different ligands, general mechanisms of 14-3-3 action include changes in activity of bound ligands, altered association of bound ligands with other cellular components, and changes in intracellular localization of 14-3-3-bound cargo. We present a speculative model where binding of 14-3-3 to multiple sites on some ligands results in global ligand conformational changes that mediate their biological effects. For these multi-site ligands, one binding site is likely to function as a 'gatekeeper' whose phosphorylation is necessary for 14-3-3 binding but may not always be sufficient for full biological activity. If correct, then 14-3-3 may prove to be a bona fide phosphodependent signaling chaperone.

Interaction of phosphorylated tyrosine hydroxylase with 14-3-3 proteins: evidence for a phosphoserine 40-dependent association

Tyrosine hydroxylase (TH) has been reported to require binding of 14-3-3 proteins for optimal activation by phosphorylation. We examined the effects of phosphorylation at Ser19, Ser31 and Ser40 of bovine TH and human TH isoforms on their binding to the 14-3-3 proteins BMH1/BMH2, as well as 14-3-3 zeta and a mixture of sheep brain 14-3-3 proteins. Phosphorylation of Ser31 did not result in 14-3-3 binding, however, phosphorylation of TH on Ser40 increased its affinity towards the yeast 14-3-3 isoforms BMH1/BMH2 and sheep brain 14-3-3, but not for 14-3-3 zeta. On phosphorylation of both Ser19 and Ser40, binding to the 14-3-3 zeta isoform also occurred, and the binding affinity to BMH1 and sheep brain 14-3-3 increased. Both phosphoserine-specific antibodies directed against the 10 amino acids surrounding Ser19 or Ser40 of TH, and the phosphorylated peptides themselves, inhibited the association between phosphorylated TH and 14-3-3 proteins. This was also found when heparin was added, or after proteolytic removal of the N-terminal 37 amino acids of Ser40-phosphorylated TH. Binding of BMH1 to phosphorylated TH decreased the rate of dephosphorylation by protein phosphatase 2A, but no significant change in enzymatic activity was observed in the presence of BMH1. These findings further support a role for 14-3-3 proteins in the regulation of catecholamine biosynthesis and demonstrate isoform specificity for both TH and 14-3-3 proteins.

Functional conservation of 14-3-3 isoforms in inhibiting bad-induced apoptosis

14-3-3 proteins are a family of homologous eukaryotic molecules with seven distinct isoforms in mammalian cells. Isoforms of 14-3-3 proteins interact with diverse ligands and are involved in the regulation of mitogenesis, cell cycle progression, and apoptosis. However, whether different 14-3-3 isoforms are responsible for distinct functions remains elusive. Here we report that multiple isoforms of 14-3-3 proteins were capable of binding to several ligands, Bad, Raf-1, and Cbl. In a functional assay of 14-3-3 isoforms, all mammalian 14-3-3 isoforms could inhibit Bad-induced apoptosis. Thus, 14-3-3 function in regulating one of its ligands, Bad, is conserved among mammalian isoforms. We addressed whether 14-3-3 isoforms are differentially expressed in tissues, which may in part determine isoform-specific interactions. In situ hybridization revealed that 14-3-3zeta was present in most tissues tested, but sigma was preferentially expressed in epithelial cells. Thus, isoforms of 14-3-3 can interact and control the function of selected protein ligands, and differential tissue distribution of 14-3-3 isoforms may contribute to their specific interactions and subsequent downstream signaling events.

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.

Increased concentrations of 14-3-3 epsilon, gamma and zeta isoforms in cerebrospinal fluid of AIDS patients with neuronal destruction

BACKGROUND

14-3-3 proteins are major evolutionarily conserved cytosolic proteins that regulate signal transduction, apoptosis and neurotransmitter synthesis. Five homologous 14-3-3 isoforms, beta, gamma, zeta, epsilon and eta, are reported in mammalian neurones. To elucidate the diagnostic value of 14-3-3 in cerebrospinal fluid (CSF), a highly specific antibody against each isoform and studies on the isoform patterns in patients with neuronal destruction are needed.

METHODS

In this study, we raised isoform-specific antibodies against 14-3-3 proteins and established a semiquantitative method of identification of each isoform by Western immunoblotting.

RESULTS

We found that three isoforms, 14-3-3 epsilon, gamma and zeta, appeared in the CSF of HIV patients with AIDS dementia complex or cytomegalovirus encephalitis, but not in AIDS patients without neurological symptoms or the non-HIV patients examined. The isoform patterns in AIDS patients were different from those reported in Creutzfeldt-Jakob disease and herpes simplex encephalitis, suggesting that the isoform patterns may facilitate the differential diagnosis. A high frequency of 14-3-3 in CSF was observed in seriously ill AIDS patients, particularly those with CD4 levels of less than 20 mm(3).

CONCLUSION

These findings suggested that 14-3-3 proteins were released from destroyed neural cells and are useful real-time markers of the rate and amount of neural cell destruction in these patients.

Use of cDNA microarray in the search for molecular markers involved in the onset of Alzheimer's disease dementia

Alzheimer's disease (AD) is the most common form of dementia, affecting as many as 4 million older persons and results from abnormal changes in the brain that most likely begin long before cognitive impairment and other clinical symptoms become apparent. Thus, efforts aimed at identifying methods of early detection and diagnosis for improving AD care might be the most appropriate strategy to initiate promising new treatments and/or prevention. We used cDNA microarray technology to investigate the sequence of changes in gene expression in brain that may take place during the transition from normal cognitive functioning through the early stages of impairment to frank AD. We examined the expression of approximately 7,000 genes in the brains of cases at the early stage of AD dementia using reference sample cases characterized by normal cognitive status. Genes that are differentially regulated in early AD cases were identified and were categorized into gene clusters based on similarities in biological functions. This analysis revealed that selected biological processes, including protein and amino acid metabolism, cytoskeleton integrity, and fatty acid metabolism, are involved in early phases of AD dementia. Most notable is the observation that selected genes involved in neurotransmitter release are differentially regulated in the brains of cases at high risk for dementia. This evidence supports the feasibility and usefulness of cDNA microarray techniques to study sequential changes of distinctive gene-expression patterns in the brain as a function of the progression of AD dementia. The study suggests new means to dissect and classify stages of AD dementia, or neuropathology, at the molecular level.

Increase in lipid content in potato tubers modified by 14-3-3 gene overexpression

Recently, transgenic potato plants were created with overexpression of the 14-3-3 protein derived from Cucurbita pepo. Detailed analysis of those plants suggested that the function of the isolated 14-3-3 isoform is in the control of carbohydrate and lipid metabolism in the plants. 14-3-3 protein overexpression gave rise to an increase in soluble sugar and catecholamine contents in both leaves and tubers. It is proposed that 14-3-3 protein affects carbohydrate metabolism in potato plants via regulation of catecholamine synthesis. Furthermore, genetically modified potato tubers with 14-3-3 protein overexpression showed changes in lipid content and composition. The transgenic potato tubers contained 69% more total fat compared to the wild-type plant. Separation of tuber lipids into polar and nonpolar fractions revealed that the transgenic potato tubers contained almost 3 times more nonpolar lipids than the control. Analysis of fatty acid composition, conducted by the means of gas chromatography, showed that linoleic acid was the main fatty acid present in the tubers of both modified and control potato plants. In the nonpolar fraction of the fat of the transgenic tubers the unsaturated fatty acids exhibited a higher participation in the sum of all fatty acids.

Application of cDNA microarrays to examine gene expression differences in schizophrenia

Using cDNA microarrays we have investigated gene expression patterns in brain regions of patients with schizophrenia. A cDNA neuroarray, comprised of genes related to brain function, was used to screen pools of samples from the cerebellum and prefrontal cortex from a matched set of subjects, and middle temporal gyrus, from a separate subject cohort. Samples of cerebellum and prefrontal cortex from neuroleptic naive patients were also included. Genes that passed a 3% reproducibility criterion for differential expression in independent experiments included 21 genes for drug-treated patients and 5 genes for drug-naive patients. Of these 26 genes, 10 genes were increased and 16 were decreased. Many of the differentially expressed genes were related to synaptic signaling and proteolytic functions. A smaller number of these genes were also differentially expressed in the middle temporal gyrus. The five genes that were differentially expressed in two brain regions from separate cohorts are: tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein, eta polypeptide; sialyltransferase; proteasome subunit, alpha type 1; ubiquitin carboxyl-terminal esterase L1; and solute carrier family 10, member 1. Identification of patterns of changes in gene expression may lead to a better understanding of the pathophysiology of schizophrenia disorders.

A 14-3-3 protein homologue is expressed in feline enteroepithelial-stages of Toxoplasma gondii

Fourteen cDNA clones encoding epitopes of proteins of Toxoplasma gondii feline enteroepithelial-stages parasites were isolated and expressed in Escherichia coli in an effort to determine the antigenecity of the parasites. Sequence analysis showed that four of the cDNA clones had a 930-bp open-reading frame encoding a product showing similarity to the 14-3-3 protein mRNA sequence.(1) Southern hybridization of DIG-labeled positive clone with T. gondii genomic DNA cleaved with EcoRI, BamHI and HindIII resulted in one or two bands in each case. In an immunofluorescence assay, polyclonal and monoclonal antibodies raised against the expressed protein showed strong reactivity with feline enteroepithelial-stages parasites and sporozoites. In a complementation assay in which a plasmid carrying the protein-coding region of the isolated cDNA was introduced into a Saccharomyces cerevisiae mutant, strain DS9-22, the expressed protein showed complementation of the function of the 14-3-3 protein in yeast transformants. These findings suggest that T. gondii parasites produce a protein showing partial homology with members of the 14-3-3 protein family and this protein is expressed in feline enteroepithelial-stages parasites.

A 14-3-3 mRNA is up-regulated in amyotrophic lateral sclerosis spinal cord

We have recently isolated a 2.2-kb cDNA clone (1C5) from a human spinal cord cDNA library with partial identity to the 14-3-3 protein mRNA encoding the theta protein (YWHAQ). 14-3-3 protein transcripts are highly expressed in large projection neurones of the hippocampus, cerebellum, and spinal cord and have been found to be significantly up-regulated in rat motor neurones following hypoglossal nerve axotomy. In this study we investigated whether the 1C5 transcript (YWHAQ) isolated from spinal cord was involved in amyotrophic lateral sclerosis (ALS). We found a significant up-regulation of 1C5 (YWHAQ) in lumbar spinal cord from patients with sporadic ALS compared with controls, with the highest levels of expression being found in individuals with predominant lower motor neurone involvement. A 6-bp tandem repeat in the 5'-untranslated region of the gene was found to be polymorphic, but no significant association with disease was found following genomic analysis of this region. The localisation of 1C5 (YWHAQ) to chromosome 2 was determined and coincides with that reported for clone HS1 (EMBL accession no. X57347). These results show the marked up-regulation of the 14-3-3 isoform (YWHAQ) in ALS spinal cord and indicate the involvement of a potential 14-3-3-mediated survival pathway in the pathogenesis of ALS.

14-3-3 protein family members have a regulatory role in retinoic acid-mediated induction of cytokeratins in F9 cells

We have found that the expression of five 14-3-3 protein isoforms is induced during the retinoic acid (RA)-mediated differentiation of mouse embryonal carcinoma F9 cells. The induced expression of the 14-3-3 proteins is presumed to have a role in enhancing the mitogen-activated protein kinase (MAPK) activity during RA-mediated F9 cell differentiation, because using genetically engineered budding yeast we showed that these isoforms enhanced the signaling in the MAPK cascade mainly through the interaction with Raf-1. Then we assessed the role of increased MAPK activity in F9 cell differentiation by interfering with signaling in the MAPK cascade in F9 cells. The exogenous expression of dominant-negative MEK1 efficiently abrogated RA-mediated induction of the cytokeratins EndoA and EndoC in the F9 cells. These results suggest that the 14-3-3 proteins play a role in the efficient induction of the cytokeratins during F9 cell differentiation through their signal enhancing activity in the MAPK cascade.

Antigens expressed in feline enteroepithelial-stages parasites of Toxoplasma gondii

In an investigation aimed to identify Toxoplasma gondii antigens expressed in feline enteroepithelial-stages parasites, a cDNA library was constructed and fourteen positive clones were isolated by immunoscreening using sera from cats immunized with feline enteroepithelial-stages parasites. By DNA sequence homology analysis, these fourteen isolated clones were classified into four groups: hypoxanthine-guanine phosphoribosyl transferase (HGPRT) cDNA, heat shock protein 70 (HSP70) cDNA, 14-3-3 protein homologue cDNA, and cDNA encoding an unknown product. In an indirect immunofluorescence antibody test, sera from mice immunized with the recombinant protein encoded by the cDNA for HGPRT, HSP70, 14-3-3 protein, or the unknown product each showed a relatively high level of immunoreactivity with feline enteroepithelial-stages parasites.

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.

Cloning of Schistosoma japonicum 14-3-3 epsilon (Sj14-3-3 epsilon), a new member of the 14-3-3 family of proteins from schistosomes

A new member of the 14-3-3 protein family from Schistosoma japonicum has been identified. Phylogenetic analysis showed that this member belongs to the epsilon subfamily of the 14-3-3 proteins, and it is therefore named Sj14-3-3 epsilon. Consistent with the findings for the previously reported S. japonicum 14-3-3 protein (Sj14-3-3), Southern analysis suggested the presence of more than one gene, and/or introns or allelic polymorphism in this epsilon isoform. By RT-PCR, Sj14-3-3 epsilon was shown to be stage-specifically transcribed, being abundant in adults, present in sporocysts but absent in cercariae. Furthermore, mRNA of the epsilon isoform seemed to be much less abundant in the sporocyst stage, compared with Sj14-3-3. This suggests varying requirements of the different 14-3-3 isoforms at different stages of the life cycle.

Tetrahydropterin-dependent amino acid hydroxylases

Phenylalanine hydroxylase, tyrosine hydroxylase, and tryptophan hydroxylase constitute a small family of monooxygenases that utilize tetrahydropterins as substrates. When from eukaryotic sources, these enzymes are composed of a homologous catalytic domain to which are attached discrete N-terminal regulatory domains and short C-terminal tetramerization domains, whereas the bacterial enzymes lack the N-terminal and C-terminal domains. Each enzyme contains a single ferrous iron atom bound to two histidines and a glutamate. Recent mechanistic studies have begun to provide insights into the mechanisms of oxygen activation and hydroxylation. Although the hydroxylating intermediate in these enzymes has not been identified, the iron is likely to be involved. Reversible phosphorylation of serine residues in the regulatory domains affects the activities of all three enzymes. In addition, phenylalanine hydroxylase is allosterically regulated by its substrates, phenylalanine and tetrahydrobiopterin.

14-3-3 proteins and growth control

The 14-3-3 proteins constitute a family that is highly conserved in a wide range of organisms, including higher eukaryotes, invertebrates and plants. Variants of 14-3-3 proteins assembled in homo- and heterodimers were found to interact with diverse cellular proteins. Until recently, the biological role of 14-3-3 members was still poorly understood. However, the results of an increasing number of studies on their structure and function are converging to define 14-3-3 proteins as a novel type of adaptor that modulates interactions between components involved in signal transduction pathway and in cell cycle control.

Association study between genetic polymorphisms in the 14-3-3 eta chain and dopamine D4 receptor genes and alcoholism

BACKGROUND

The dopaminergic system may be involved in the development of alcoholism. As part of our ongoing studies on the association between alcoholism and dopaminergic genes, we report herein a mutation analysis of the 14-3-3 eta chain gene (YWHAH) and an association study between alcoholism and the YWHAH and dopamine D4 receptor gene (DRD4) polymorphisms.

METHODS

Nucleotide mutations were investigated using single-strand conformation polymorphism methods. Associations were analyzed using a case-control design involving 185 Japanese alcoholics and 286 Japanese controls.

RESULTS

Five polymorphisms, -147G>A, -134(GCCTGCA)2-4, IVS1+31(G)7-8, IVS1+73-74ins(G), and 753A>G, were detected on the YWHAH, and three of them were novel. No significant associations were found between alcoholism and these polymorphisms or two additional polymorphisms on DRD4 exon III and DRD4 -521C/T.

CONCLUSIONS

YWHAH and DRD4 do not appear to play a major role in the development of alcoholism.

Uncoupling proteins 2 and 3 interact with members of the 14.3.3 family

Uncoupling proteins (UCPs) are members of the superfamily of the mitochondrial anion carrier proteins (MATP). Localized in the inner membrane of the organelle, they are postulated to be regulators of mitochondrial uncoupling. UCP2 and 3 may play an important role in the regulation of thermogenesis and, thus, on the resting metabolic rate in humans. To identify interacting proteins that may be involved in the regulation of the activity of UCPs, the yeast two-hybrid system was applied. Segments of hUCP2 containing the hydrophilic loops facing the intermembrane space, or combinations of these, were used to screen an adipocyte activation domain (AD) fusion library. The 14.3.3 protein isoforms theta, beta, zeta were identified as possible interacting partners of hUCP2. Screening of a human skeletal muscle AD fusion library, on the other hand, yielded several clones all of them encoding the gamma isoform of the 14.3.3 family. Mapping experiments further revealed that all these 14.3.3 proteins interact specifically with the C-terminal intermembrane space domain of both hUCP2 and hUCP3 whereas no interactions could be detected with the C-terminal part of hUCP1. Direct interaction between UCP3 and 14.3.3 theta could be demonstrated after in vitro translation by coimmunoprecipitation. When coexpressed in a heterologous yeast system, 14.3.3 proteins potentiated the inhibitory effect of UCP3 overexpression on cell growth. These findings suggest that 14.3.3 proteins could be involved in the targeting of UCPs to the mitochondria.