Regulation of tyrosine hydroxylase by stress-activated protein kinases

CHIR99021 causes inactivation of Tyrosine Hydroxylase and depletion of dopamine in rat brain striatum

CHIR99021, also known as laduviglusib or CT99021, is a Glycogen-synthase kinase 3β (GSK3β) inhibitor, which has been reported as a promising drug for cardiomyocyte regeneration or treatment of sensorial hearing loss. Since the activation of dopamine (DA) receptors regulates dopamine synthesis and they can signal through the β-arrestin pathway and GSK3β, we decided to check the effect of GSK3β inhibitors (CHIR99021, SB216763 and lithium ion) on the control of DA synthesis. Using ex vivo experiments with minces from rat brain striatum, we observed that CHIR99021, but not SB216763 or lithium, causes complete abrogation of both DA synthesis and accumulation, pointing to off-target effects of CHIR99021. This decrease can be attributed to tyrosine hydroxylase (TH) inhibition since the accumulation of l-DOPA in the presence of a DOPA decarboxylase inhibitor was similarly decreased. On the other hand, CHIR99021 caused a dramatic increase in the DOPAC/DA ratio, an indicator of DA metabolization, and hindered DA incorporation into striatum tissue. Tetrabenazine, an inhibitor of DA vesicular transport, also caused DA depletion and DOPAC/DA ratio increase to the same extent as CHIR99021. In addition, both CHIR99021 or SB216763, but not lithium, decreased TH phosphorylation in Ser19, but not in Ser31 or Ser40. These results demonstrate that CHIR99021 can lead to TH inactivation and DA depletion in brain striatum, opening the possibility of its use in DA-related disorders, and shows effects to be considered in future clinical trials. More work is needed to find the mechanism exerted by CHIR99021 on DA accumulation.

The Effects of Chronic Unpredictable Mild Stress and Semi-Pure Diets on the Brain, Gut and Adrenal Medulla in C57BL6 Mice

Chronic stress is known to perturb serotonergic regulation in the brain, leading to mood, learning and memory impairments and increasing the risk of developing mood disorders. The influence of the gut microbiota on serotonergic regulation in the brain has received increased attention recently, justifying the investigation of the role of diet on the gut and the brain in mood disorders. Here, using a 4-week chronic unpredictable mild stress (CUMS) model in mice, we aimed to investigate the effects of a high-fat high-glycaemic index (HFD) and high-fibre fruit & vegetable "superfood" (SUP) modifications of a semi-pure AIN93M diet on behaviour, serotonin synthesis and metabolism pathway regulation in the brain and the gut, as well as the gut microbiota and the peripheral adrenal medullary system. CUMS induced anxiety-like behaviour, dysregulated the tryptophan and serotonin metabolic pathways in the hippocampus, prefrontal cortex, and colon, and altered the composition of the gut microbiota. CUMS reduced the catecholamine synthetic capacity of the adrenal glands. Differential effects were found in these parameters in the HFD and SUP diet. Thus, dietary modifications may profoundly affect the multiple dynamic systems involved in mood disorders.

Personalized Medicine to Improve Treatment of Dopa-Responsive Dystonia-A Focus on Tyrosine Hydroxylase Deficiency

Dopa-responsive dystonia (DRD) is a rare movement disorder associated with defective dopamine synthesis. This impairment may be due to the fact of a deficiency in GTP cyclohydrolase I (GTPCHI, GCH1 gene), sepiapterin reductase (SR), tyrosine hydroxylase (TH), or 6-pyruvoyl tetrahydrobiopterin synthase (PTPS) enzyme functions. Mutations in GCH1 are most frequent, whereas fewer cases have been reported for individual SR-, PTP synthase-, and TH deficiencies. Although termed DRD, a subset of patients responds poorly to L-DOPA. As this is regularly observed in severe cases of TH deficiency (THD), there is an urgent demand for more adequate or personalized treatment options. TH is a key enzyme that catalyzes the rate-limiting step in catecholamine biosynthesis, and THD patients often present with complex and variable phenotypes, which results in frequent misdiagnosis and lack of appropriate treatment. In this expert opinion review, we focus on THD pathophysiology and ongoing efforts to develop novel therapeutics for this rare disorder. We also describe how different modeling approaches can be used to improve genotype to phenotype predictions and to develop in silico testing of treatment strategies. We further discuss the current status of mathematical modeling of catecholamine synthesis and how such models can be used together with biochemical data to improve treatment of DRD patients.

ADHD symptoms in neurometabolic diseases: Underlying mechanisms and clinical implications

Neurometabolic diseases (NMDs) are typically caused by genetic abnormalities affecting enzyme functions, which in turn interfere with normal development and activity of the nervous system. Although the individual disorders are rare, NMDs are collectively relatively common and often lead to lifelong difficulties and high societal costs. Neuropsychiatric manifestations, including ADHD symptoms, are prominent in many NMDs, also when the primary biochemical defect originates in cells and tissues outside the nervous system. ADHD symptoms have been described in phenylketonuria, tyrosinemias, alkaptonuria, succinic semialdehyde dehydrogenase deficiency, X-linked ichthyosis, maple syrup urine disease, and several mitochondrial disorders, but are probably present in many other NMDs and may pose diagnostic and therapeutic challenges. Here we review current literature linking NMDs with ADHD symptoms. We cite emerging evidence that many NMDs converge on common neurochemical mechanisms that interfere with monoamine neurotransmitter synthesis, transport, metabolism, or receptor functions, mechanisms that are also considered central in ADHD pathophysiology and treatment. Finally, we discuss the therapeutic implications of these findings and propose a path forward to increase our understanding of these relationships.

NT5DC2 affects the phosphorylation of tyrosine hydroxylase regulating its catalytic activity

5'-Nucleotidase domain-containing protein 2 (NT5DC2) has been revealed by genome-wide association studies (GWAS) as a gene implicated in neuropsychiatric disorders related to the abnormality of dopamine (DA) activity in the brain. Based on its amino acid sequence, NT5DC2 is assumed to be a member of the family of haloacid dehalogenase-type phosphatases; although there is no information about its function and structural conformation. We recently reported that NT5DC2 binds to tyrosine hydroxylase (TH) and that the down-regulation of NT5DC2 tended to increase DA synthesis. In this study, we investigated whether NT5DC2 could regulate the catalytic activity of TH, which converts tyrosine to DOPA, because the phosphorylation level of TH, controlled by protein kinases and phosphatases, is well known to regulate its catalytic activity. The down-regulation of NT5DC2 by siRNA increased mainly DOPA synthesis by TH in PC12D cells, although this down-regulation tended to increase the conversion of DOPA to DA by aromatic L-amino acid decarboxylase. The increased DOPA synthesis should be attributed to the catalytic activity of TH controlled by its phosphorylation, because Western blot analysis revealed that the down-regulation of NT5DC2 tended to increase the level of TH phosphorylated at its Ser residues, but not that of the TH protein. Moreover, the induction of kinase activity by forskolin markedly potentiated the phosphorylation of TH at its Ser40 in PC12D cells having down-regulated NT5DC2. Immunocytochemical analysis of PC12D cells demonstrated that NT5DC2, TH protein, and TH phosphorylated at its Ser40 were predominantly localized in the cytoplasm and that the localization of NT5DC2 and TH proteins partially overlapped. Collectively, our results indicate that NT5DC2 could work to inhibit the DOPA synthesis by decreasing the phosphorylation of TH at its Ser40. We propose that NT5DC2 might decrease this phosphorylation of TH by promoting dephosphorylation or by inhibiting kinase activity.

Degradation of Tyrosine Hydroxylase by the Ubiquitin-Proteasome System in the Pathogenesis of Parkinson's Disease and Dopa-Responsive Dystonia

Nigrostriatal dopaminergic systems govern physiological functions related to locomotion, and their dysfunction leads to movement disorders, such as Parkinson’s disease and dopa-responsive dystonia (Segawa disease). Previous studies revealed that expression of the gene encoding nigrostriatal tyrosine hydroxylase (TH), a rate-limiting enzyme of dopamine biosynthesis, is reduced in Parkinson’s disease and dopa-responsive dystonia; however, the mechanism of TH depletion in these disorders remains unclear. In this article, we review the molecular mechanism underlying the neurodegeneration process in dopamine-containing neurons and focus on the novel degradation pathway of TH through the ubiquitin-proteasome system to advance our understanding of the etiology of Parkinson’s disease and dopa-responsive dystonia. We also introduce the relation of α-synuclein propagation with the loss of TH protein in Parkinson’s disease as well as anticipate therapeutic targets and early diagnosis of these diseases.

Subcellular distribution of human tyrosine hydroxylase isoforms 1 and 4 in SH-SY5Y cells

Tyrosine hydroxylase (TH) is the key enzyme that controls the rate of synthesis of the catecholamines. SH-SY5Y cells with stable transfections of either human tyrosine hydroxylase isoform 1 (hTH1) or human tyrosine hydroxylase isoform 4 (hTH4) were used to determined the subcellular distribution of TH protein and phosphorylated TH, under basal conditions and after muscarine stimulation. Muscarine was previously shown to increase the phosphorylation of only serine 19 and serine 40 in hTH1 cells. Under basal conditions, the hTH1 and hTH4 proteins, their serine 19 phosphorylated forms and hTH1 phosphorylated at serine 40 were all similarly distributed; with ~80% in the cytosolic fraction, ~20% in the membrane fraction, and less than 1%, or not detectable, in the nuclear fraction. However, hTH4 phosphorylated at serine 71 had a significantly different distribution with ~65% cytosolic and ~35% membrane associated. Muscarine stimulation led to hTH1 being redistributed from the cytosol and nuclear fractions to the membrane fraction and hTH4 being redistributed from the cytosol to the nuclear fraction. These muscarine stimulated redistributions were not due to TH phosphorylation at serine 19, serine 40, or serine 71 and were most likely due to TH binding to proteins whose phosphorylation was increased by muscarine. This is the first study to show a difference in subcellular distribution between two human TH isoforms under basal and stimulated conditions.

Acrolein-mediated alpha-synuclein pathology involvement in the early post-injury pathogenesis of mild blast-induced Parkinsonian neurodegeneration

Survivors of blast-induced traumatic brain injury (bTBI) have increased susceptibility to Parkinson's disease (PD), characterized by α-synuclein aggregation and the progressive degeneration of nigrostriatal dopaminergic neurons. Using an established bTBI rat model, we evaluated the changes of α-synuclein and tyrosine hydroxylase (TH), known hallmarks of PD, and acrolein, a reactive aldehyde and marker of oxidative stress, with the aim of revealing key pathways leading to PD post-bTBI. Indicated in both animal models of PD and TBI, acrolein is likely a point of pathogenic convergence. Here we show that after a single mild bTBI, acrolein is elevated up to a week, systemically in urine, and in whole brain tissue, specifically the substantia nigra and striatum. Acrolein elevation is accompanied by heightened α-synuclein oligomerization, dopaminergic dysregulation, and acrolein/α-synuclein interaction in the same brain regions. We further show that acrolein can directly modify and oligomerize α-synuclein in vitro. Taken together, our data suggests acrolein likely plays an important role in inducing PD pathology following bTBI by encouraging α-synuclein aggregation. These results are expected to advance our understanding of the long-term post-bTBI pathological changes leading to the development of PD, and suggest intervention targets to curtail such pathology.

The mitochondrial metabolic function of DJ-1 is modulated by 14-3-3β

Mitochondrial metabolic plasticity is a key adaptive mechanism in response to changes in cellular metabolic demand. Changes in mitochondrial metabolic efficiency have been linked to pathophysiological conditions, including cancer, neurodegeneration, and obesity. The ubiquitously expressed DJ-1 (Parkinsonism-associated deglycase) is known as a Parkinson's disease gene and an oncogene. The pleiotropic functions of DJ-1 include reactive oxygen species scavenging, RNA binding, chaperone activity, endocytosis, and modulation of major signaling pathways involved in cell survival and metabolism. Nevertheless, how these functions are linked to the role of DJ-1 in mitochondrial plasticity is not fully understood. In this study, we describe an interaction between DJ-1 and 14-3-3β that regulates the localization of DJ-1, in a hypoxia-dependent manner, either to the cytosol or to mitochondria. This interaction acts as a modulator of mitochondrial metabolic efficiency and a switch between glycolysis and oxidative phosphorylation. Modulation of this novel molecular mechanism of mitochondrial metabolic efficiency is potentially involved in the neuroprotective function of DJ-1 as well as its role in proliferation of cancer cells.-Weinert, M., Millet, A., Jonas, E. A., Alavian, K. N. The mitochondrial metabolic function of DJ-1 is modulated by 14-3-3β.

Short-term sleep deprivation with exposure to nocturnal light alters mitochondrial bioenergetics in Drosophila

Many studies have shown the effects of sleep deprivation in several aspects of health and disease. However, little is known about how mitochondrial bioenergetics function is affected under this condition. To clarify this, we developed a simple model of short-term sleep deprivation, in which fruit-flies were submitted to a nocturnal light condition and then mitochondrial parameters were assessed by high resolution respirometry (HRR). Exposure of flies to constant light was able to alter sleep patterns, causing locomotor deficits, increasing ROS production and lipid peroxidation, affecting mitochondrial activity, antioxidant defense enzymes and caspase activity. HRR analysis showed that sleep deprivation affected mitochondrial bioenergetics capacity, decreasing respiration at oxidative phosphorylation (OXPHOS) and electron transport system (ETS). In addition, the expression of genes involved in the response to oxidative stress and apoptosis were increased. Thus, our results suggest a connection between sleep deprivation and oxidative stress, pointing to mitochondria as a possible target of this relationship.

Phosphorylation of the regulatory domain of human tyrosine hydroxylase 1 monitored using non-uniformly sampled NMR

Human tyrosine hydroxylase 1 (hTH1) activity is regulated by phosphorylation of its regulatory domain (RD-hTH1) and by an interaction with the 14-3-3 protein. The RD-hTH1 is composed of a structured region (66-169) preceded by an intrinsically disordered protein region (IDP, hTH1_65) containing two phosphorylation sites (S19 and S40) which are highly relevant for its increase in activity. The NMR signals of the IDP region in the non-phosphorylated, singly phosphorylated (pS40) and doubly phosphorylated states (pS19_pS40) were assigned by non-uniformly sampled spectra with increased dimensionality (5D). The structural changes induced by phosphorylation were analyzed by means of secondary structure propensities. The phosphorylation kinetics of the S40 and S19 by kinases PKA and PRAK respectively were monitored by non-uniformly sampled time-resolved NMR spectroscopy followed by their quantitative analysis.

Tyrosine and tryptophan hydroxylases as therapeutic targets in human disease

INTRODUCTION

The ancient and ubiquitous monoamine signalling molecules serotonin, dopamine, norepinephrine, and epinephrine are involved in multiple physiological functions. The aromatic amino acid hydroxylases tyrosine hydroxylase (TH), tryptophan hydroxylase 1 (TPH1), and tryptophan hydroxylase 2 (TPH2) catalyse the rate-limiting steps in the biosynthesis of these monoamines. Genetic variants of TH, TPH1, and TPH2 genes are associated with neuropsychiatric disorders. The interest in these enzymes as therapeutic targets is increasing as new roles of these monoamines have been discovered, not only in brain function and disease, but also in development, cardiovascular function, energy and bone homeostasis, gastrointestinal motility, hemostasis, and liver function. Areas covered: Physiological roles of TH, TPH1, and TPH2. Enzyme structures, catalytic and regulatory mechanisms, animal models, and associated diseases. Interactions with inhibitors, pharmacological chaperones, and regulatory proteins relevant for drug development. Expert opinion: Established inhibitors of these enzymes mainly target their amino acid substrate binding site, while tetrahydrobiopterin analogues, iron chelators, and allosteric ligands are less studied. New insights into monoamine biology and 3D-structural information and new computational/experimental tools have triggered the development of a new generation of more selective inhibitors and pharmacological chaperones. The enzyme complexes with their regulatory 14-3-3 proteins are also emerging as therapeutic targets.

Anxiolytic and neuroprotective effects of the Traditional Chinese Medicinal formulation Dan-zhi-xiao-yao-san in a rat model of chronic stress

Dan-zhi-xiao-yao-san is a Traditional Chinese Medicinal formulation widely used for the treatment of neuropsychological disorders. The present study examined the anxiolytic and neuroprotective effects of Dan-zhi-xiao-yao-san in a rat model of chronic stress. The results of an elevated plus maze test showed that Dan‑zhi‑xiao‑yao‑san significantly attenuated the levels of anxiety-induced stress as evidenced by increases in the time spent in the open arm region, as well as the percentage of entries into this area. In addition, Dan-zhi-xiao-yao-san alleviated stress‑induced neuronal death, as indicated by histological examination. Furthermore, mechanistic studies suggested that the anxiolytic and neuroprotective effects of Dan-zhi-xiao-yao-san may be mediated via attenuation of chronic stress‑induced upregulation of α‑synuclein and corticosterone, and downregulation of protein phosphatase 2A (PP2A) in the hippocampal region of the brain at the mRNA and protein level. In addition, Dan‑zhi‑xiao‑yao‑san decreased the serum levels of stress‑induced corticosterone in the model animals. In conclusion, the present study demonstrated that Dan‑zhi‑xiao‑yao‑san exerted anxiolytic and neuroprotective effects in a rat model of chronic stress via attenuation of stress‑induced upregulation of α‑synuclein and corticosterone, and downregulation of PP2A in the hippocampus.

Regulation of tyrosine hydroxylase is preserved across different homo- and heterodimeric 14-3-3 proteins

Tyrosine hydroxylase (TH) is regulated by members of the 14-3-3 protein family. However, knowledge about the variation between 14-3-3 proteins in their regulation of TH is still limited. We examined the binding, effects on activation and dephosphorylation kinetics of tyrosine hydroxylase (TH) by abundant midbrain 14-3-3 proteins (β, η, ζ, γ and ε) of different dimer composition. All 14-3-3 homodimers and their respective 14-3-3ε-heterodimers bound with similar high affinity (K_d values of 1.4–3.8 nM) to serine19 phosphorylated human TH (TH-pS19). We similarly observed a consistent activation of bovine (3.3- to 4.4-fold) and human TH-pS19 (1.3–1.6 fold) across all the different 14-3-3 dimer species, with homodimeric 14-3-3γ being the strongest activator. Both hetero- and homodimers of 14-3-3 strongly inhibited dephosphorylation of TH-pS19, and we speculate if this is an important homeostatic mechanism of 14-3-3 target-protein regulation in vivo. We conclude that TH is a robust interaction partner of different 14-3-3 dimer types with moderate variability between the 14-3-3 dimers on their regulation of TH.

The novel RAGE interactor PRAK is associated with autophagy signaling in Alzheimer's disease pathogenesis

BACKGROUND

The receptor for advanced glycation end products (RAGE) has been found to interact with amyloid β (Aβ). Although RAGE does not have any kinase motifs in its cytosolic domain, the interaction between RAGE and Aβ triggers multiple cellular signaling involved in Alzheimer's disease (AD). However, the mechanism of signal transduction by RAGE remains still unknown. Therefore, identifying binding proteins of RAGE may provide novel therapeutic targets for AD.

RESULTS

In this study, we identified p38-regulated/activated protein kinase (PRAK) as a novel RAGE interacting molecule. To investigate the effect of Aβ on PRAK mediated RAGE signaling pathway, we treated SH-SY5Y cells with monomeric form of Aβ. We demonstrated that Aβ significantly increased the phosphorylation of PRAK as well as the interaction between PRAK and RAGE. We showed that knockdown of PRAK rescued mTORC1 inactivation induced by Aβ treatment and decreased the formation of Aβ-induced autophagosome.

CONCLUSIONS

We provide evidence that PRAK plays a critical role in AD pathology as a key interactor of RAGE. Thus, our data suggest that PRAK might be a potential therapeutic target of AD involved in RAGE-mediated cell signaling induced by Aβ.

Epistatic and gene wide effects in YWHA and aromatic amino hydroxylase genes across ADHD and other common neuropsychiatric disorders: Association with YWHAE

Monoamines critically modulate neurophysiological functions affected in several neuropsychiatric disorders. We therefore examined genes encoding key enzymes of catecholamine and serotonin biosynthesis (tyrosine and tryptophan hydroxylases-TH and TPH1/2) as well as their regulatory 14-3-3 proteins (encoded by YWHA-genes). Previous studies have focused mainly on the individual genes, but no analysis spanning this regulatory network has been reported. We explored interactions between these genes in Norwegian patients with adult attention deficit hyperactivity disorder (aADHD), followed by gene-complex association tests in four major neuropsychiatric conditions; childhood ADHD (cADHD), bipolar disorder, schizophrenia, and major depressive disorder. For interaction analyses, we evaluated 55 SNPs across these genes in a sample of 583 aADHD patients and 637 controls. For the gene-complex tests, we utilized the data from large-scale studies of The Psychiatric Genomics Consortium (PGC). The four major neuropsychiatric disorders were examined for association with each of the genes individually as well as in three complexes as follows: (1) TPH1 and YWHA-genes; (2) TH, TPH2 and YWHA-genes; and (3) all genes together. The results show suggestive epistasis between YWHAE and two other 14-3-3-genes - YWHAZ, YWHAQ - in aADHD (nominal P-value of 0.0005 and 0.0008, respectively). In PGC data, association between YWHAE and schizophrenia was noted (P = 1.00E-05), whereas the combination of TPH1 and YWHA-genes revealed signs of association in cADHD, schizophrenia, and bipolar disorder. In conclusion, polymorphisms in the YWHA-genes and their targets may exert a cumulative effect in ADHD and related neuropsychiatric conditions, warranting the need for further investigation of these gene-complexes. © 2015 The Authors. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics Published by Wiley Periodicals, Inc.

Phosphorylation dependence and stoichiometry of the complex formed by tyrosine hydroxylase and 14-3-3γ

Phosphorylated tyrosine hydroxylase (TH) can form complexes with 14-3-3 proteins, resulting in enzyme activation and stabilization. Although TH was among the first binding partners identified for these ubiquitous regulatory proteins, the binding stoichiometry and the activation mechanism remain unknown. To address this, we performed native mass spectrometry analyses of human TH (nonphosphorylated or phosphorylated on Ser19 (TH-pS19), Ser40 (TH-pS40), or Ser19 and Ser40 (TH-pS19pS40)) alone and together with 14-3-3γ. Tetrameric TH-pS19 (224 kDa) bound 14-3-3γ (58.3 kDa) with high affinity (K_d = 3.2 nM), generating complexes containing either one (282.4 kDa) or two (340.8 kDa) dimers of 14-3-3. Electron microscopy also revealed one major population of an asymmetric complex, consistent with one TH tetramer and one 14-3-3 dimer, and a minor population of a symmetric complex of one TH tetramer with two 14-3-3 dimers. Lower phosphorylation stoichiometries (0.15–0.54 phosphate/monomer) produced moderate changes in binding kinetics, but native MS detected much less of the symmetric TH:14-3-3γ complex. Interestingly, dephosphorylation of [³²P]-TH-pS19 was mono-exponential for low phosphorylation stoichiometries (0.18–0.52), and addition of phosphatase accelerated the dissociation of the TH-pS19:14-3-3γ complex 3- to 4-fold. All together this is consistent with a model in which the pS19 residues in the TH tetramer contribute differently in the association to 14-3-3γ. Complex formation between TH-pS40 and 14-3-3γ was not detected via native MS, and surface plasmon resonance showed that the interaction was very weak. Furthermore, TH-pS19pS40 behaved similarly to TH-pS19 in terms of binding stoichiometry and affinity (K_d = 2.1 nM). However, we found that 14-3-3γ inhibited the phosphorylation rate of TH-pS19 by PKA (3.5-fold) on Ser40. We therefore conclude that Ser40 does not significantly contribute to the binding of 14-3-3γ, and rather has reduced accessibility in the TH:14-3-3γ complex. This adds to our understanding of the fine-tuned physiological regulation of TH, including hierarchical phosphorylation at multiple sites.

Complex molecular regulation of tyrosine hydroxylase

Tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis, is strictly controlled by several interrelated regulatory mechanisms. Enzyme synthesis is controlled by epigenetic factors, transcription factors, and mRNA levels. Enzyme activity is regulated by end-product feedback inhibition. Phosphorylation of the enzyme is catalyzed by several protein kinases and dephosphorylation is mediated by two protein phosphatases that establish a sensitive process for regulating enzyme activity on a minute-to-minute basis. Interactions between tyrosine hydroxylase and other proteins introduce additional layers to the already tightly controlled production of catecholamines. Tyrosine hydroxylase degradation by the ubiquitin-proteasome coupled pathway represents yet another mechanism of regulation. Here, we revisit the myriad mechanisms that regulate tyrosine hydroxylase expression and activity and highlight their physiological importance in the control of catecholamine biosynthesis.

Structure and function of MK5/PRAK: the loner among the mitogen-activated protein kinase-activated protein kinases

Mitogen-activated protein kinase (MAPK) pathways are important signal transduction pathways that control pivotal cellular processes including proliferation, differentiation, survival, apoptosis, gene regulation, and motility. MAPK pathways consist of a relay of consecutive phosphorylation events exerted by MAPK kinase kinases, MAPK kinases, and MAPKs. Conventional MAPKs are characterized by a conserved Thr-X-Tyr motif in the activation loop of the kinase domain, while atypical MAPKs lack this motif and do not seem to be organized into the classical three-tiered kinase cascade. One functional group of conventional and atypical MAPK substrates consists of protein kinases known as MAPK-activated protein kinases. Eleven mammalian MAPK-activated protein kinases have been identified, and they are divided into five subgroups: the ribosomal-S6-kinases RSK1-4, the MAPK-interacting kinases MNK1 and 2, the mitogen- and stress-activated kinases MSK1 and 2, the MAPK-activated protein kinases MK2 and 3, and the MAPK-activated protein kinase MK5 (also referred to as PRAK). MK5/PRAK is the only MAPK-activated protein kinase that is a substrate for both conventional and atypical MAPK, while all other MAPKAPKs are exclusively phosphorylated by conventional MAPKs. This review focuses on the structure, activation, substrates, functions, and possible implications of MK5/PRAK in malignant and nonmalignant diseases.

The solution structure of the regulatory domain of tyrosine hydroxylase

Tyrosine hydroxylase (TyrH) catalyzes the hydroxylation of tyrosine to form 3,4-dihydroxyphenylalanine in the biosynthesis of the catecholamine neurotransmitters. The activity of the enzyme is regulated by phosphorylation of serine residues in a regulatory domain and by binding of catecholamines to the active site. Available structures of TyrH lack the regulatory domain, limiting the understanding of the effect of regulation on structure. We report the use of NMR spectroscopy to analyze the solution structure of the isolated regulatory domain of rat TyrH. The protein is composed of a largely unstructured N-terminal region (residues 1-71) and a well-folded C-terminal portion (residues 72-159). The structure of a truncated version of the regulatory domain containing residues 65-159 has been determined and establishes that it is an ACT domain. The isolated domain is a homodimer in solution, with the structure of each monomer very similar to that of the core of the regulatory domain of phenylalanine hydroxylase. Two TyrH regulatory domain monomers form an ACT domain dimer composed of a sheet of eight strands with four α-helices on one side of the sheet. Backbone dynamic analyses were carried out to characterize the conformational flexibility of TyrH65-159. The results provide molecular details critical for understanding the regulatory mechanism of TyrH.

Neuroprotective function of 14-3-3 proteins in neurodegeneration

14-3-3 proteins are abundantly expressed adaptor proteins that interact with a vast number of binding partners to regulate their cellular localization and function. They regulate substrate function in a number of ways including protection from dephosphorylation, regulation of enzyme activity, formation of ternary complexes and sequestration. The diversity of 14-3-3 interacting partners thus enables 14-3-3 proteins to impact a wide variety of cellular and physiological processes. 14-3-3 proteins are broadly expressed in the brain, and clinical and experimental studies have implicated 14-3-3 proteins in neurodegenerative disease. A recurring theme is that 14-3-3 proteins play important roles in pathogenesis through regulating the subcellular localization of target proteins. Here, we review the evidence that 14-3-3 proteins regulate aspects of neurodegenerative disease with a focus on their protective roles against neurodegeneration.

Locomotor hyperactivity in 14-3-3ζ KO mice is associated with dopamine transporter dysfunction

Dopamine (DA) neurotransmission requires a complex series of enzymatic reactions that are tightly linked to catecholamine exocytosis and receptor interactions on pre- and postsynaptic neurons. Regulation of dopaminergic signalling is primarily achieved through reuptake of extracellular DA by the DA transporter (DAT) on presynaptic neurons. Aberrant regulation of DA signalling, and in particular hyperactivation, has been proposed as a key insult in the presentation of schizophrenia and related neuropsychiatric disorders. We recently identified 14-3-3ζ as an essential component of neurodevelopment and a central risk factor in the schizophrenia protein interaction network. Our analysis of 14-3-3ζ-deficient mice now shows that baseline hyperactivity of knockout (KO) mice is rescued by the antipsychotic drug clozapine. 14-3-3ζ KO mice displayed enhanced locomotor hyperactivity induced by the DA releaser amphetamine. Consistent with 14-3-3ζ having a role in DA signalling, we found increased levels of DA in the striatum of 14-3-3ζ KO mice. Although 14-3-3ζ is proposed to modulate activity of the rate-limiting DA biosynthesis enzyme, tyrosine hydroxylase (TH), we were unable to identify any differences in total TH levels, TH localization or TH activation in 14-3-3ζ KO mice. Rather, our analysis identified significantly reduced levels of DAT in the absence of notable differences in RNA or protein levels of DA receptors D1-D5. Providing insight into the mechanisms by which 14-3-3ζ controls DAT stability, we found a physical association between 14-3-3ζ and DAT by co-immunoprecipitation. Taken together, our results identify a novel role for 14-3-3ζ in DA neurotransmission and provide support to the hyperdopaminergic basis of pathologies associated with schizophrenia and related disorders.

Tyrosine hydroxylase: regulation by feedback inhibition and phosphorylation

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of the catecholamines dopamine, noradrenaline, and adrenaline. In response to short-term stimuli, TH activity is regulated by feedback inhibition by the catecholamines and relief of that inhibition by phosphorylation. This chapter examines the current understanding of these regulatory mechanisms and the roles that they play in different catecholaminergic cells. This chapter also examines hierarchical phosphorylation in TH and how it provides a mechanism for the differential regulation of the major human TH isoforms.

The Protective Effect of Minocycline in a Paraquat-Induced Parkinson's Disease Model in Drosophila is Modified in Altered Genetic Backgrounds

Epidemiological studies link the herbicide paraquat to increased incidence of Parkinson's disease (PD). We previously reported that Drosophila exposed to paraquat recapitulate PD symptoms, including region-specific degeneration of dopaminergic neurons. Minocycline, a tetracycline derivative, exerts ameliorative effects in neurodegenerative disease models, including Drosophila. We investigated whether our environmental toxin-based PD model could contribute to an understanding of cellular and genetic mechanisms of minocycline action and whether we could assess potential interference with these drug effects in altered genetic backgrounds. Cofeeding of minocycline with paraquat prolonged survival, rescued mobility defects, blocked generation of reactive oxygen species, and extended dopaminergic neuron survival, as has been reported previously for a genetic model of PD in Drosophila. We then extended this study to identify potential interactions of minocycline with genes regulating dopamine homeostasis that might modify protection against paraquat and found that deficits in GTP cyclohydrolase adversely affect minocycline rescue. We further performed genetic studies to identify signaling pathways that are necessary for minocycline protection against paraquat toxicity and found that mutations in the Drosophila genes that encode c-Jun N-terminal kinase (JNK) and Akt/Protein kinase B block minocycline rescue.

Synthesis and evaluation of hexahydropyrrolo[3,4-d]isoxazole-4,6-diones as anti-stress agents

A series of 2,3-diphenyl-5-(naphthalen-1-yl)-4H-2,3,3a,5,6,6a-hexahydropyrrolo[3,4-d]isoxazole-4,6-dione derivatives were synthesized via 1,3-dipolar cycloaddition of azomethine N-oxides with N-(α-naphthyl)maleimide. The pyrrolo-isoxazole derivatives were assigned cis- and trans- configurations (3-A and 3-B) with respect to proton C(3)-H on azomethinic carbon on the basis of their (1)H NMR. The reaction proceeds through cis- endo addition rule indicating the predominance of cis isomer. The cis- and trans- isomers of a prototype compound 3ai.e., compound 3a-A and compound 3a-B were evaluated for anti-stress activity in immobilization-induced acute stress. Compound 3a-A (5 and 10 mg/kg) and compound 3a-B (10 mg/kg) attenuated immobilization stress-induced behavioral alterations in Swiss albino mice suggesting that pyrrolo-isoxazole may serve as lead molecule for the development of anti-stress agents.

The 14-3-3 proteins in regulation of cellular metabolism

Thirty years ago, it was discovered that 14-3-3 proteins could activate enzymes involved in amino acid metabolism. In the following decades, 14-3-3s have been shown to be involved in many different signaling pathways that modulate cellular and whole body energy and nutrient homeostasis. Large scale screening for cellular binding partners of 14-3-3 has identified numerous proteins that participate in regulation of metabolic pathways, although only a minority of these targets have yet been subject to detailed studies. Because of the wide distribution of potential 14-3-3 targets and the resurging interest in metabolic pathway control in diseases like cancer, diabetes, obesity and cardiovascular disease, we review the role of 14-3-3 proteins in the regulation of core and specialized cellular metabolic functions. We cite illustrative examples of 14-3-3 action through their direct modulation of individual enzymes and through regulation of master switches in cellular pathways, such as insulin signaling, mTOR- and AMP dependent kinase signaling pathways, as well as regulation of autophagy. We further illustrate the quantitative impact of 14-3-3 association on signal response at the target protein level and we discuss implications of recent findings showing 14-3-3 protein membrane binding of target proteins.

Physiological roles of mitogen-activated-protein-kinase-activated p38-regulated/activated protein kinase

Mitogen-activated protein kinases (MAPKs) are a family of proteins that constitute signaling pathways involved in processes that control gene expression, cell division, cell survival, apoptosis, metabolism, differentiation and motility. The MAPK pathways can be divided into conventional and atypical MAPK pathways. The first group converts a signal into a cellular response through a relay of three consecutive phosphorylation events exerted by MAPK kinase kinases, MAPK kinase, and MAPK. Atypical MAPK pathways are not organized into this three-tiered cascade. MAPK that belongs to both conventional and atypical MAPK pathways can phosphorylate both non-protein kinase substrates and other protein kinases. The latter are referred to as MAPK-activated protein kinases. This review focuses on one such MAPK-activated protein kinase, MAPK-activated protein kinase 5 (MK5) or p38-regulated/activated protein kinase (PRAK). This protein is highly conserved throughout the animal kingdom and seems to be the target of both conventional and atypical MAPK pathways. Recent findings on the regulation of the activity and subcellular localization, bona fide interaction partners and physiological roles of MK5/PRAK are discussed.

Physiological roles of mitogen-activated-protein-kinase-activated p38-regulated/activated protein kinase

Mitogen-activated protein kinases (MAPKs) are a family of proteins that constitute signaling pathways involved in processes that control gene expression, cell division, cell survival, apoptosis, metabolism, differentiation and motility. The MAPK pathways can be divided into conventional and atypical MAPK pathways. The first group converts a signal into a cellular response through a relay of three consecutive phosphorylation events exerted by MAPK kinase kinases, MAPK kinase, and MAPK. Atypical MAPK pathways are not organized into this three-tiered cascade. MAPK that belongs to both conventional and atypical MAPK pathways can phosphorylate both non-protein kinase substrates and other protein kinases. The latter are referred to as MAPK-activated protein kinases. This review focuses on one such MAPK-activated protein kinase, MAPK-activated protein kinase 5 (MK5) or p38-regulated/activated protein kinase (PRAK). This protein is highly conserved throughout the animal kingdom and seems to be the target of both conventional and atypical MAPK pathways. Recent findings on the regulation of the activity and subcellular localization, bona fide interaction partners and physiological roles of MK5/PRAK are discussed.

A miniaturized technique for assessing protein thermodynamics and function using fast determination of quantitative cysteine reactivity

Protein thermodynamic stability is a fundamental physical characteristic that determines biological function. Furthermore, alteration of thermodynamic stability by macromolecular interactions or biochemical modifications is a powerful tool for assessing the relationship between protein structure, stability, and biological function. High-throughput approaches for quantifying protein stability are beginning to emerge that enable thermodynamic measurements on small amounts of material, in short periods of time, and using readily accessible instrumentation. Here we present such a method, fast quantitative cysteine reactivity, which exploits the linkage between protein stability, sidechain protection by protein structure, and structural dynamics to characterize the thermodynamic and kinetic properties of proteins. In this approach, the reaction of a protected cysteine and thiol-reactive fluorogenic indicator is monitored over a gradient of temperatures after a short incubation time. These labeling data can be used to determine the midpoint of thermal unfolding, measure the temperature dependence of protein stability, quantify ligand-binding affinity, and, under certain conditions, estimate folding rate constants. Here, we demonstrate the fQCR method by characterizing these thermodynamic and kinetic properties for variants of Staphylococcal nuclease and E. coli ribose-binding protein engineered to contain single, protected cysteines. These straightforward, information-rich experiments are likely to find applications in protein engineering and functional genomics.

Tyrosine hydroxylase and regulation of dopamine synthesis

Tyrosine hydroxylase is the rate-limiting enzyme of catecholamine biosynthesis; it uses tetrahydrobiopterin and molecular oxygen to convert tyrosine to DOPA. Its amino terminal 150 amino acids comprise a domain whose structure is involved in regulating the enzyme's activity. Modes of regulation include phosphorylation by multiple kinases at four different serine residues, and dephosphorylation by two phosphatases. The enzyme is inhibited in feedback fashion by the catecholamine neurotransmitters. Dopamine binds to TyrH competitively with tetrahydrobiopterin, and interacts with the R domain. TyrH activity is modulated by protein-protein interactions with enzymes in the same pathway or the tetrahydrobiopterin pathway, structural proteins considered to be chaperones that mediate the neuron's oxidative state, and the protein that transfers dopamine into secretory vesicles. TyrH is modified in the presence of NO, resulting in nitration of tyrosine residues and the glutathionylation of cysteine residues.

Serine 129 phosphorylation reduces the ability of alpha-synuclein to regulate tyrosine hydroxylase and protein phosphatase 2A in vitro and in vivo

Alpha-synuclein (a-Syn), a protein implicated in Parkinson disease, contributes significantly to dopamine metabolism. a-Syn binding inhibits the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine synthesis. Phosphorylation of TH stimulates its activity, an effect that is reversed by protein phosphatase 2A (PP2A). In cells, a-Syn overexpression activates PP2A. Here we demonstrate that a-Syn significantly inhibited TH activity in vitro and in vivo and that phosphorylation of a-Syn serine 129 (Ser-129) modulated this effect. In MN9D cells, a-Syn overexpression reduced TH serine 19 phosphorylation (Ser(P)-19). In dopaminergic tissues from mice overexpressing human a-Syn in catecholamine neurons only, TH-Ser-19 and TH-Ser-40 phosphorylation and activity were also reduced, whereas PP2A was more active. Cerebellum, which lacks excess a-Syn, had PP2A activity identical to controls. Conversely, a-Syn knock-out mice had elevated TH-Ser-19 phosphorylation and activity and less active PP2A in dopaminergic tissues. Using an a-Syn Ser-129 dephosphorylation mimic, with serine mutated to alanine, TH was more inhibited, whereas PP2A was more active in vitro and in vivo. Phosphorylation of a-Syn Ser-129 by Polo-like-kinase 2 in vitro reduced the ability of a-Syn to inhibit TH or activate PP2A, identifying a novel regulatory role for Ser-129 on a-Syn. These findings extend our understanding of normal a-Syn biology and have implications for the dopamine dysfunction of Parkinson disease.

Progesterone decreases tyrosine hydroxylase phosphorylation state and increases protein phosphatase 2A activity in the stalk-median eminence on proestrous afternoon

The progesterone (P(4)) rise on proestrous afternoon is associated with dephosphorylation of tyrosine hydroxylase (TH) and reduced TH activity in the stalk-median eminence (SME), which contributes to the proestrous prolactin surge in rats. In the present study, we investigated the time course for P(4) effect on TH activity and phosphorylation state, as well as cAMP levels and protein phosphatase 2A (PP2A) activity and quantity, in the SME on proestrous morning and afternoon. P(4) (7.5 mg/kg, s.c.) treatment on proestrous afternoon decreased TH activity and TH phosphorylation state at Ser-31 and Ser-40 within 1 h, whereas morning administration of P(4) had no 1 h effect on TH. PP2A activity in the SME was enhanced after P(4) treatment for 1 h on proestrous afternoon without a change in PP2A catalytic subunit quantity, whereas P(4) treatment had no effect on PP2A activity or quantity on proestrous morning. cAMP levels in the SME were unchanged with 1 h P(4) treatment. At 5 h after P(4) treatment, TH activity and phosphorylation state declined coincident with an increase in plasma prolactin in both P(4)-treated morning and afternoon groups. PP2A activity in the SME was unchanged in 5 h P(4)-treated rat. Our data suggest that P(4) action on tuberoinfundibular dopaminergic (TIDA) neurons involves at least two components. A more rapid (1 h) P(4) effect engaged only on proestrous afternoon likely involves the activation of PP2A. The longer P(4) action on TIDA neurons is evident on both the morning and afternoon of proestrus and may involve a common, as yet unidentified, mechanism.

Differential regulation of human tyrosine hydroxylase isoforms 1 and 2 in situ: Isoform 2 is not phosphorylated at Ser35

The major human tyrosine hydroxylase isoforms (hTH1 and 2) differ in their ability to be phosphorylated in vitro. hTH1 is phosphorylated at Ser31 by extracellular signal-regulated kinase (ERK). This kinase is not capable of phosphorylating hTH2 at Ser35 (the residue that corresponds to Ser31 in hTH1). We have stably transfected SH-SY5Y cells with hTH1 or hTH2 to determine if hTH2 can be phosphorylated at Ser35 in situ. Forskolin increased the phosphorylation of Ser40 in hTH1 and Ser44 in hTH2. Muscarine increased the phosphorylation of both Ser19 and Ser40/44 in both hTH1 and hTH2. EGF increased the phosphorylation of Ser31 in hTH1. Phosphorylation of Ser35 in hTH2 was not detected under any of the conditions tested. Inhibition of ERK by UO126 decreased the phosphorylation of Ser31 and this lead to a 50% decrease in the basal level of phosphorylation of Ser40 in hTH1. The basal level of Ser44 phosphorylation in hTH2 was not altered by treatment with UO126. Therefore, phosphorylation of Ser31 contributes to the phosphorylation of Ser40 in hTH1 in situ; however, this effect is absent in hTH2. This represents a major difference between the two human TH isoforms, and has implications for the regulation of catecholamine synthesis in vivo.

Three-way interaction between 14-3-3 proteins, the N-terminal region of tyrosine hydroxylase, and negatively charged membranes

Tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of catecholamines, is activated by phosphorylation-dependent binding to 14-3-3 proteins. The N-terminal domain of TH is also involved in interaction with lipid membranes. We investigated the binding of the N-terminal domain to its different partners, both in the unphosphorylated (TH-(1-43)) and Ser(19)-phosphorylated (THp-(1-43)) states by surface plasmon resonance. THp-(1-43) showed high affinity for 14-3-3 proteins (K(d) approximately 0.5 microM for 14-3-3gamma and -zeta and 7 microM for 14-3-3eta). The domains also bind to negatively charged membranes with intermediate affinity (concentration at half-maximal binding S(0.5) = 25-58 microM (TH-(1-43)) and S(0.5) = 135-475 microM (THp-(1-43)), depending on phospholipid composition) and concomitant formation of helical structure. 14-3-3gamma showed a preferential binding to membranes, compared with 14-3-3zeta, both in chromaffin granules and with liposomes at neutral pH. The affinity of 14-3-3gamma for negatively charged membranes (S(0.5) = 1-9 microM) is much higher than the affinity of TH for the same membranes, compatible with the formation of a ternary complex between Ser(19)-phosphorylated TH, 14-3-3gamma, and membranes. Our results shed light on interaction mechanisms that might be relevant for the modulation of the distribution of TH in the cytoplasm and membrane fractions and regulation of L-DOPA and dopamine synthesis.

Oxidative status of DJ-1-dependent activation of dopamine synthesis through interaction of tyrosine hydroxylase and 4-dihydroxy-L-phenylalanine (L-DOPA) decarboxylase with DJ-1

Parkinson disease (PD) is caused by loss of dopamine, which is synthesized from tyrosine by two enzymes, tyrosine hydroxylase (TH) and 4-dihydroxy-L-phenylalanine decarboxylase (DDC). DJ-1 is a causative gene for the familial form of PD, but little is known about the roles of DJ-1 in dopamine synthesis. In this study, we found that DJ-1 directly bound to TH and DDC and positively regulated their activities in human dopaminergic cells. Mutants of DJ-1 found in PD patients, including heterozygous mutants, lost their activity and worked as dominant-negative forms toward wild-type DJ-1. When cells were treated with H(2)O(2), 6-hydroxydopamine, or 1-methyl-4-phenylpyridinium, changes in activities of TH and DDC accompanied by oxidation of cysteine 106 of DJ-1 occurred. It was found that DJ-1 possessing Cys-106 with SH and SOH forms was active and that DJ-1 possessing Cys-106 with SO(2)H and SO(3)H forms was inactive in terms of stimulation of TH and DDC activities. These findings indicate an essential role of DJ-1 in dopamine synthesis and contribution of DJ-1 to the sporadic form of PD.

Identification by hydrogen/deuterium exchange of structural changes in tyrosine hydroxylase associated with regulation

The activity of tyrosine hydroxylase is regulated by reversible phosphorylation of serine residues in an N-terminal regulatory domain and catecholamine inhibition at the active site. Catecholamines such as dopamine bind very tightly to the resting enzyme; phosphorylation of Ser40 decreases the affinity for catecholamines by 3 orders of magnitude. The effects of dopamine binding and phosphorylation of Ser40 on the kinetics of deuterium incorporation into peptide bonds were examined by mass spectrometry. When dopamine is bound, three peptic peptides show significantly slower deuterium incorporation, 35-41 and 42-71 in the regulatory domain and 295-299 in the catalytic domain. In the phosphorylated enzyme, peptide 295-299 shows more rapid incorporation of deuterium, while 35-41 and 42-71 can not be detected. These results are consistent with tyrosine hydroxylase existing in two different conformations. In the closed conformation, the regulatory domain lies across the active site loop containing residues 295-298; this is stabilized when dopamine is bound in the active site. In the open conformation, the regulatory domain has moved out of the active site, allowing substrate access; this conformation is favored by phosphorylation of Ser40.

14-3-3zeta contributes to tyrosine hydroxylase activity in MN9D cells: localization of dopamine regulatory proteins to mitochondria

The 14-3-3 proteins stimulate the activation of tyrosine hydroxylase (TH), the rate-limiting catecholamine biosynthetic enzyme. To explore if particular endogenous 14-3-3 isoforms specifically affected TH activity and dopamine synthesis, we utilized rodent nigrostriatal tissues and midbrain-derived MN9D dopaminergic cells. Extracts from ventral midbrain and MN9D cells contained similar pools of 14-3-3 mRNAs, with 14-3-3zeta being relatively abundant in both. Protein levels of 14-3-3zeta were also abundant. [(32)P]Orthophosphate labeling of MN9D cells, followed by co-immunoprecipitation with pan-TH and pan-14-3-3 antibodies brought down similar amounts of phosphorylated TH in each, confirming that 14-3-3-bound phosphorylated TH in our cells. Co-immunoprecipitation of striatal tissues with a pan-TH antibody precipitated 14-3-3zeta but not another potential TH regulatory isoform, 14-3-3eta. In whole cell extracts from MN9D cells after 14-3-3 small interfering RNA treatments, we found that 14-3-3zeta knockdown significantly reduced TH activity and dopamine synthesis whereas knockdown of 14-3-3eta had no effect. 14-3-3zeta was found co-localized on mitochondria with TH, and its knockdown by small interfering RNA reduced TH phosphorylation and TH activity in the mitochondrial pool. Together the data support a role for 14-3-3zeta as an endogenous activator of TH in midbrain dopaminergic neurons and furthermore, identify mitochondria as a potential novel site for dopamine synthesis, with implications for Parkinson disease.

Glial cell line-derived neurotrophic factor reverses ethanol-mediated increases in tyrosine hydroxylase immunoreactivity via altering the activity of heat shock protein 90

We previously found that glial cell line-derived neurotrophic factor (GDNF) in the midbrain ventral tegmental area (VTA) negatively regulates alcohol drinking (He, D. Y., McGough, N. N., Ravindranathan, A., Jeanblanc, J., Logrip, M. L., Phamluong, K., Janak, P. H., and Ron, D. (2005) J. Neurosci. 25, 619-628). Several studies suggest a role for GDNF in the regulation of tyrosine hydroxylase (TH) levels in the midbrain (Georgievska, B., Kirik, D., and Bjorklund, A. (2004) J. Neurosci. 24, 6437-6445). Up-regulation of TH levels has been reported as a hallmark of biochemical adaptations to in vivo chronic exposure to drugs of abuse, including ethanol (Ortiz, J., Fitzgerald, L. W., Charlton, M., Lane, S., Trevisan, L., Guitart, X., Shoemaker, W., Duman, R. S., and Nestler, E. J. (1995) Synapse 21, 289-298). We hypothesized that GDNF plays an important role in regulating prolonged ethanol-mediated increases in TH protein levels. Using the SH-SY5Y dopaminergic-like cell line, we found that the increase in TH levels in the presence of ethanol required the activation of the cAMP/PKA pathway and was reversed by GDNF. Ethanol treatment did not alter the mRNA level or protein translation of TH, but enhanced the stability of the protein that was decreased by GDNF. Interestingly, we observed that ethanol treatment resulted in an increase in TH association with the chaperone heat shock protein (HSP90) that was mediated by the cAMP/PKA pathway and inhibited by GDNF. Taken together, these data suggest that prolonged ethanol exposure leads to increased association of TH and HSP90 via the cAMP/PKA pathway, resulting in the stabilization and subsequent accumulation of TH. GDNF reverses this ethanol-mediated adaptation by inhibiting the interaction of TH with HSP90.

Phosphorylation state of tyrosine hydroxylase in the stalk-median eminence is decreased by progesterone in cycling female rats

Progesterone has the capacity to suppress hypothalamic dopaminergic neuronal activity on proestrous afternoon and prolong or amplify the preovulatory prolactin surge in rats. In the present study, we examined enzyme activity and phosphorylation state of tyrosine hydroxylase (TH) in the stalk-median eminence of cycling female rats on proestrus and estrus and related these to circulating progesterone levels. Phospho-TH levels were evaluated by Western blot analysis. TH activity was determined from the rate of 3,4-dihydroxyphenylalanine (DOPA) accumulation. Phospho-TH levels at Ser-19, Ser-31, and Ser-40 were similar at 1100, 1300, and 1500 h on proestrus but declined at 1700, 1900, and 2200 h, coincident with rising serum progesterone levels. Similarly, DOPA accumulation was 30-50% lower at 1700, 1900, and 2200 h as compared with 1100-1500 h on proestrus. Ser-31 and Ser-40 phosphorylation states were increased by 1100 h on estrus to a level similar to 1100 h on proestrus, whereas DOPA accumulation was 30% greater on estrous as compared with proestrous morning. There were no significant differences among the several time points on proestrus and estrus with regard to TH protein or beta-tubulin levels. Exogenous progesterone administration (7.5 mg/kg, sc) before the preovulatory progesterone surge decreased TH activity and phospho-TH at Ser-19, Ser-31, and Ser-40, accompanied by premature increased serum prolactin. Our study suggests that decreased TH phosphorylation at Ser-19, Ser-31, and Ser-40 contributes to the decline in TH activity in the stalk-median eminence on proestrous afternoon and that progesterone may cause this initial cytoplasmic response of TH dephosphorylation.

Activation and stabilization of human tryptophan hydroxylase 2 by phosphorylation and 14-3-3 binding

TPH (tryptophan hydroxylase) catalyses the rate-limiting step in the synthesis of serotonin, and exists in two isoforms: TPH1, mainly found in peripheral tissues and the pineal body, and TPH2, a neuronal form. In the present study human TPH2 was expressed in Escherichia coli and in HEK (human embryonic kidney)-293 cells and phosphorylated using several different mammalian protein kinases. TPH2 was rapidly phosphorylated to a stoichiometry of 2 mol of phosphate/mol of subunit by PKA (protein kinase A), but only to a stoichiometry of 0.2 by Ca(2+)/calmodulin dependent protein kinase II. Both kinases phosphorylated Ser(19), but PKA also phosphorylated Ser(104), as determined by MS, phosphospecific antibodies and site-directed mutagenesis of several possible phosphorylation sites, i.e. Ser(19), Ser(99), Ser(104) and Ser(306). On average, purified TPH2 WT (wild-type) was activated by 30% after PKA phosphorylation and studies of the mutant enzymes showed that enzyme activation was mainly due to phosphorylation at Ser(19). This site was phosphorylated to a stoichiometry of up to 50% in HEK-293 cells expressing TPH2, and the enzyme activity and phosphorylation stoichiometry was further increased upon treatment with forskolin. Purified PKA-phosphorylated TPH2 bound to the 14-3-3 proteins gamma, epsilon and BMH1 with high affinity, causing a further increase in enzyme stability and activity. This indicates that 14-3-3 proteins could play a role in consolidating and strengthening the effects of phosphorylation on TPH2 and that they may be important for the regulation of serotonin function in the nervous system.

Relations between the mitogen-activated protein kinase and the cAMP-dependent protein kinase pathways: comradeship and hostility

Inter- and intracellular communications and responses to environmental changes are pivotal for the orchestrated and harmonious operation of multi-cellular organisms. These well-tuned functions in living organisms are mediated by the action of signal transduction pathways, which are responsible for receiving a signal, transmitting and amplifying it, and eliciting the appropriate cellular responses. Mammalian cells posses numerous signal transduction pathways that, rather than acting in solitude, interconnect with each other, a phenomenon referred to as cross-talk. This allows cells to regulate the distribution, duration, intensity and specificity of the response. The cAMP/cAMP-dependent protein kinase (PKA) pathway and the mitogen-activated protein kinase (MAPK) cascades modulate common processes in the cell and multiple levels of cross-talk between these signalling pathways have been described. The first- and best-characterized interconnections are the PKA-dependent inhibition of the MAPKs ERK1/2 mediated by RAF-1, and PKA-induced activation of ERK1/2 interceded through B-RAF. Recently, novel interactions between components of these pathways and new mechanisms for cross-talk have been elucidated. This review discusses both known and novel interactions between compounds of the cAMP/PKA and MAPKs signalling pathways in mammalian cells.

Alpha-synuclein aggregation alters tyrosine hydroxylase phosphorylation and immunoreactivity: lessons from viral transduction of knockout mice

Tyrosine hydroxylase (TH), the rate limiting enzyme in catecholamine synthesis, is frequently used as a marker of dopaminergic neuronal loss in animal models of Parkinson's disease (PD). We have been exploring the normal function of the PD-related protein alpha-synuclein (alpha-Syn) with regard to dopamine synthesis. TH is activated by the phosphorylation of key seryl residues in the TH regulatory domain. Using in vitro models, our laboratory discovered that alpha-Syn inhibits TH by acting to reduce TH phosphorylation, which then reduces dopamine synthesis [X.-M. Peng, R. Tehranian, P. Dietrich, L. Stefanis, R.G. Perez, Alpha-synuclein activation of protein phosphatase 2A reduces tyrosine hydroxylase phosphorylation in dopaminergic cells, J. Cell. Sci. 118 (2005) 3523-3530; R.G. Perez, J.C. Waymire, E. Lin, J.J. Liu, F. Guo, M.J. Zigmond, A role for alpha-synuclein in the regulation of dopamine biosynthesis, J. Neurosci. 22 (2002) 3090-3099]. We recently began exploring the impact of alpha-Syn on TH in vivo, by transducing dopaminergic neurons in alpha-Syn knockout mouse (ASKO) olfactory bulb using wild type human alpha-Syn lentivirus. At 3.5-21 days after viral delivery, alpha-Syn expression was transduced primarily in periglomerular dopaminergic neurons. Cells with modest levels of alpha-Syn consistently co-labeled for Total-TH. However, cells bearing aggregated alpha-Syn, as revealed by proteinase K or Thioflavin-S treatment had significantly reduced Total-TH immunoreactivity, but high phosphoserine-TH labeling. On immunoblots, we noted that Total-TH immunoreactivity was equivalent in all conditions, although tissues with alpha-Syn aggregates again had higher phosphoserine-TH levels. This suggests that aggregated alpha-Syn is no longer able to inhibit TH. Although the reason(s) underlying reduced Total-TH immunoreactivity on tissue sections await(s) confirmation, the dopaminergic phenotype was easily verified using phosphorylation-state-specific TH antibodies. These findings have implications not only for normal alpha-Syn function in TH regulation, but also for measuring cell loss that is associated with synucleinopathy.

The 14-3-3 protein affects the conformation of the regulatory domain of human tyrosine hydroxylase

Tyrosine hydroxylase (TH) catalyzes the first step in the biosynthesis of catecholamines. Regulation of TH enzyme activity is controlled through the posttranslational modification of its regulatory domain. The regulatory domain of TH can be phosphorylated at four serines (8, 19, 31, and 40) by a variety of protein kinases. Phosphorylation of Ser19 does not by itself increase TH activity but induces its binding to the 14-3-3 protein. That leads to the enhancement of TH activity with a still not fully understood mechanism. The main goal of this work was to investigate whether the 14-3-3 protein binding affects the conformation of the regulatory domain of human TH isoform 1 (TH1R). Site-directed mutagenesis was used to generate five single-tryptophan mutants of TH1R with the Trp residue located at five different positions within the domain (positions 14, 34, 73, 103, and 131). Time-resolved tryptophan fluorescence measurements revealed that phosphorylation of Ser19 and Ser40 does not itself induce any significant structural changes in regions surrounding inserted tryptophans. On the other hand, the interaction between the 14-3-3 protein and phosphorylated TH1R decreases the solvent exposure of tryptophan residues at positions 14 and 34 and induces distinct structural change in the vicinity of Trp73. The 14-3-3 protein binding also reduces the sensitivity of phosphorylated TH1R to proteolysis by protecting its N-terminal part (first 33 residues). Circular dichroism measurements showed that TH1R is an unstructured protein with a low content of secondary structure and that neither phosphorylation nor the 14-3-3 protein binding changes its secondary structure.

Transgenic mice expressing constitutive active MAPKAPK5 display gender-dependent differences in exploration and activity

Background

The mitogen-activated protein kinases, MAPKs for short, constitute cascades of signalling pathways involved in the regulation of several cellular processes that include cell proliferation, differentiation and motility. They also intervene in neurological processes like fear conditioning and memory. Since little remains known about the MAPK-Activated Protein Kinase, MAPKAPK5, we constructed the first MAPKAPK knockin mouse model, using a constitutive active variant of MAPKAPK5 and analyzed the resulting mice for changes in anxiety-related behaviour.

Methods

We performed primary SHIRPA observations during background breeding into the C57BL/6 background and assessed the behaviour of the background-bred animals on the elevated plus maze and in the light-dark test. Our results were analyzed using Chi-square tests and homo- and heteroscedatic T-tests.

Results

Female transgenic mice displayed increased amounts of head dips and open arm time on the maze, compared to littermate controls. In addition, they also explored further into the open arm on the elevated plus maze and were less active in the closed arm compared to littermate controls. Male transgenic mice displayed no differences in anxiety, but their locomotor activity increased compared to non-transgenic littermates.

Conclusion

Our results revealed anxiety-related traits and locomotor differences between transgenic mice expressing constitutive active MAPKAPK5 and control littermates.