A novel protein containing Cdc10/SWI6 motifs regulates expression of mRNA encoding catecholamine biosynthesizing enzymes

Dengue Virus Replication Is Associated with Catecholamine Biosynthesis and Metabolism in Hepatocytes

Previously, the association between the catecholamine biosynthetic enzyme L-Dopa decarboxylase (DDC) and Dengue virus (DV) replication was demonstrated in liver cells and was found to be mediated at least by the interaction between DDC and phosphoinositide 3-kinase (PI3K). Here, we show that biogenic amines production and uptake impede DV replication in hepatocytes and monocytes, while the virus reduces catecholamine biosynthesis, metabolism, and transport. To examine how catecholamine biosynthesis/metabolism influences DV, first, we verified the role of DDC by altering DDC expression. DDC silencing enhanced virus replication, but not translation, attenuated the negative effect of DDC substrates on the virus and reduced the infection related cell death. Then, the role of the downstream steps of the catecholamine biosynthesis/metabolism was analyzed by chemical inhibition of the respective enzymes, application of their substrates and/or their products; moreover, reserpine, the inhibitor of the vesicular monoamine transporter 2 (VMAT2), was used to examine the role of uptake/storage of catecholamines on DV. Apart from the role of each enzyme/transporter, these studies revealed that the dopamine uptake, and not the dopamine-signaling, is responsible for the negative effect on DV. Accordingly, all treatments expected to enhance the accumulation of catecholamines in the cell cytosol suppressed DV replication. This was verified by the use of chemical inducers of catecholamine biosynthesis. Last, the cellular redox alterations due to catecholamine oxidation were not related with the inhibition of DV replication. In turn, DV apart from its negative impact on DDC, inhibits tyrosine hydroxylase, dopamine beta-hydroxylase, monoamine oxidase, and VMAT2 expression.

Structural Insights into the Regulation of Actin Capping Protein by Twinfilin C-terminal Tail

Twinfilin is a conserved actin regulator that interacts with actin capping protein (CP) via C terminus residues (TWtail) that exhibits sequence similarity with the CP interaction (CPI) motif of CARMIL. Here we report the crystal structure of TWtail in complex with CP. Our structure showed that although TWtail and CARMIL CPI bind CP to an overlapping surface via their middle regions, they exhibit different CP-binding modes at both termini. Consequently, TWtail and CARMIL CPI restrict the CP in distinct conformations of open and closed forms, respectively. Interestingly, V-1, which targets CP away from the TWtail binding site, also favors the open-form CP. Consistently, TWtail forms a stable ternary complex with CP and V-1, a striking contrast to CARMIL CPI, which rapidly dissociates V-1 from CP. Our results demonstrate that TWtail is a unique CP-binding motif that regulates CP in a manner distinct from CARMIL CPI.

Crystal structure of human V-1 in the apo form

V-1, also known as myotrophin, is a 13 kDa ankyrin-repeat protein that binds and inhibits the heterodimeric actin capping protein (CP), which is a key regulator of cytoskeletal actin dynamics. The crystal structure of V-1 in complex with CP revealed that V-1 recognizes CP via residues spanning several ankyrin repeats. Here, the crystal structure of human V-1 is reported in the absence of the specific ligand at 2.3 Å resolution. In the asymmetric unit, the crystal contains two V-1 monomers that exhibit nearly identical structures (Cα r.m.s.d. of 0.47 Å). The overall structures of the two apo V-1 chains are also highly similar to that of CP-bound V-1 (Cα r.m.s.d.s of <0.50 Å), indicating that CP does not induce a large conformational change in V-1. Detailed structural comparisons using the computational program All Atom Motion Tree revealed that CP binding can be accomplished by minor side-chain rearrangements of several residues. These findings are consistent with the known biological role of V-1, in which it globally inhibits CP in the cytoplasm.

Imidacloprid, a neonicotinoid insecticide, facilitates tyrosine hydroxylase transcription and phenylethanolamine N-methyltransferase mRNA expression to enhance catecholamine synthesis and its nicotine-evoked elevation in PC12D cells

Imidacloprid is a neonicotinoid insecticide acting as an agonist of nicotinic acetylcholine receptors (nAChRs) in the target insects. However, questions about the safety to mammals, including human have emerged. Overactivation of mammalian peripheral catecholaminergic systems leads to onset of tachycardia, hypertension, vomiting, etc., which have been observed in acutely imidacloprid-poisoned patients as well. Physiological activation of the nAChRs is known to drive catecholamine biosynthesis and secretion in mammalian adrenal chromaffin cells. Yet, the impacts of imidacloprid on the catecholaminergic function of the chromaffin cells remain to be evaluated. In this study using PC12D cells, a catecholaminergic cell line derived from the medulla chromaffin-cell tumors of rat adrenal gland, we examined whether imidacloprid itself could impact the catecholamine-synthesizing ability. Imidacloprid alone did facilitate tyrosine hydroxylase (TH) transcription via activation of α3β4 nAChR and the α7 subunit-comprising receptor. The insecticide showed the TH transcription-facilitating ability at the concentrations of 3 and 30 μM, at which acetylcholine is known to produce physiological responses, including catecholamine secretion through the nAChRs in adrenal chromaffin cells. The insecticide-facilitated TH transcription was also dependent on PKA- and RhoA-mediated signaling pathways. The insecticide coincidentally raised levels of TH and phenylethanolamine N-methyltransferase (PNMT) mRNA, and as a consequence, increased catecholamine production, although the efficacy of the neonicotinoid was lesser than that of nicotine, indicating its partial agonist-like action. Intriguingly, in cultured rat adrenal chromaffin cells, imidacloprid did increase levels of TH and PNMT protein. When the chromaffin cells were treated with nicotine in the presence of the insecticide, nicotine-elevated adrenaline production was enhanced due to facilitation of nicotine-increased TH and PNMT protein expression, and simultaneous enhancement of nicotine-elevated adrenaline secretion also took place. These findings thus suggest that imidacloprid may facilitate the physiological functions of adrenal glands in mammals.

Effects of maternal separation and methamphetamine exposure on protein expression in the nucleus accumbens shell and core

Early life adversity has been suggested to predispose an individual to later drug abuse. The core and shell sub-regions of the nucleus accumbens are differentially affected by both stressors and methamphetamine. This study aimed to characterize and quantify methamphetamine-induced protein expression in the shell and core of the nucleus accumbens in animals exposed to maternal separation during early development. Isobaric tagging (iTRAQ) which enables simultaneous identification and quantification of peptides with tandem mass spectrometry (MS/MS) was used. We found that maternal separation altered more proteins involved in structure and redox regulation in the shell than in the core of the nucleus accumbens, and that maternal separation and methamphetamine had differential effects on signaling proteins in the shell and core. Compared to maternal separation or methamphetamine alone, the maternal separation/methamphetamine combination altered more proteins involved in energy metabolism, redox regulatory processes and neurotrophic proteins. Methamphetamine treatment of rats subjected to maternal separation caused a reduction of cytoskeletal proteins in the shell and altered cytoskeletal, signaling, energy metabolism and redox proteins in the core. Comparison of maternal separation/methamphetamine to methamphetamine alone resulted in decreased cytoskeletal proteins in both the shell and core and increased neurotrophic proteins in the core. This study confirms that both early life stress and methamphetamine differentially affect the shell and core of the nucleus accumbens and demonstrates that the combination of early life adversity and later methamphetamine use results in more proteins being affected in the nucleus accumbens than either treatment alone.

Two distinct mechanisms for actin capping protein regulation--steric and allosteric inhibition

The actin capping protein (CP) tightly binds to the barbed end of actin filaments, thus playing a key role in actin-based lamellipodial dynamics. V-1 and CARMIL proteins directly bind to CP and inhibit the filament capping activity of CP. V-1 completely inhibits CP from interacting with the barbed end, whereas CARMIL proteins act on the barbed end-bound CP and facilitate its dissociation from the filament (called uncapping activity). Previous studies have revealed the striking functional differences between the two regulators. However, the molecular mechanisms describing how these proteins inhibit CP remains poorly understood. Here we present the crystal structures of CP complexed with V-1 and with peptides derived from the CP-binding motif of CARMIL proteins (CARMIL, CD2AP, and CKIP-1). V-1 directly interacts with the primary actin binding surface of CP, the C-terminal region of the alpha-subunit. Unexpectedly, the structures clearly revealed the conformational flexibility of CP, which can be attributed to a twisting movement between the two domains. CARMIL peptides in an extended conformation interact simultaneously with the two CP domains. In contrast to V-1, the peptides do not directly compete with the barbed end for the binding surface on CP. Biochemical assays revealed that the peptides suppress the interaction between CP and V-1, despite the two inhibitors not competing for the same binding site on CP. Furthermore, a computational analysis using the elastic network model indicates that the interaction of the peptides alters the intrinsic fluctuations of CP. Our results demonstrate that V-1 completely sequesters CP from the barbed end by simple steric hindrance. By contrast, CARMIL proteins allosterically inhibit CP, which appears to be a prerequisite for the uncapping activity. Our data suggest that CARMIL proteins down-regulate CP by affecting its conformational dynamics. This conceptually new mechanism of CP inhibition provides a structural basis for the regulation of the barbed end elongation in cells.

Increased expression of tyrosine hydroxylase and anomalous neurites in catecholaminergic neurons of ATF-2 null mice

ATF-2/CRE-BP1 was originally identified as a cAMP-responsive element (CRE) binding protein abundant in the brain. We previously reported that phosphorylation of ATF-2 increased the expression of tyrosine hydroxylase (TH), which is the rate-limiting enzyme for catecholamine biosynthesis, directly acting on the CRE in the promoter region of the TH gene in PC12D cells (Suzuki et al. [2002] J. Biol. Chem. 277:40768-40774). To examine the role of ATF-2 on transcriptional control of the TH gene in the brain, we investigated the TH expression in ATF-2-/- mice. We found that TH expression was greatly increased in medulla oblongata and locus ceruleus of the ATF-2-deficient embryos. Ectopic expression of TH was observed in the raphe magnus nucleus, where serotonergic neural cell bodies are located. Interestingly, A10 dorsal neurons were lost in the embryos of ATF-2-/- mice. There was no difference in the TH immunoreactivity in the olfactory bulb. The data showed that alteration in TH expression by absence of ATF-2 gradually declined from caudal to rostral part of the brain. We also found anomalous neurite extension in catecholaminergic neurons of ATF-2 null mice, i.e., increased dendritic arborization and shortened axons. These data suggest that ATF-2 plays critical roles for proper expression of the TH gene and for neurite extension of catecholaminergic neurons, possibly through a repressor-like action.

Biophysical Characterisation of the Small Ankyrin Repeat Protein Myotrophin

The 118 residue protein myotrophin is composed of four ankyrin repeats that stack linearly to form an elongated, predominantly alpha-helical structure. The protein folds via a two-state mechanism at equilibrium. The free energy change of unfolding in water (DeltaG(U-N)(H(2)O)) is 5.8 kcal.mol(-1). The chevron plot reveals that the folding reaction has a broad energy barrier and that it conforms to a two-state mechanism. The rate of folding in water (k(f)(H(2)O)) of 95 s(-1) is several orders of magnitude slower than the value predicted by topological calculations. Proline mutants were used to show that the minor kinetic phases observed for myotrophin arise from heterogeneity of the ground states due to cis-trans isomerisation of prolyl as well as non-prolyl peptide bonds. Myotrophin is the first example of a naturally occurring ankyrin repeat protein that conforms to an apparent two-state mechanism at equilibrium and under kinetic conditions, making it highly suitable for high resolution protein folding studies.

Binding of myotrophin/V-1 to actin-capping protein: implications for how capping protein binds to the filament barbed end

The heterodimeric actin-capping protein (CP) regulates actin assembly and cell motility by binding tightly to the barbed end of the actin filament. Here we demonstrate that myotrophin/V-1 binds directly to CP in a 1:1 molar ratio with a Kd of 10-50 nm. V-1 binding inhibited the ability of CP to cap the barbed ends of actin filaments. The actin-binding COOH-terminal region, the "tentacle," of the CP beta subunit was important for binding V-1, with lesser contributions from the alpha subunit COOH-terminal region and the body of the protein. V-1 appears to be unable to bind to CP that is on the barbed end, based on the observations that V-1 had no activity in an uncapping assay and that the V-1.CP complex had no capping activity. Two loops of V-1, which extend out from the alpha-helical backbone of this ankyrin repeat protein, were necessary for V-1 to bind CP. Parallel computational studies determined a bound conformation of the beta tentacle with V-1 that is consistent with these findings, and they offered insight into experimentally observed differences between the alpha1 and alpha2 isoforms as well as the mutant lacking the alpha tentacle. These results support and extend our "wobble" model for CP binding to the actin filament, in which the two COOH-terminal regions of CP bind independently to the actin filament, and bound CP is able to wobble when attached only via its mobile beta-subunit tentacle. This model is also supported by molecular dynamics simulations of CP reported here. The existence of the wobble state may be important for actin dynamics in cells.

GRK1 and GRK7: unique cellular distribution and widely different activities of opsin phosphorylation in the zebrafish rods and cones

Retinal cone cells exhibit distinctive photoresponse with a more restrained sensitivity to light and a more rapid shutoff kinetics than those of rods. To understand the molecular basis for these characteristics of cone responses, we focused on the opsin deactivation process initiated by G protein-coupled receptor kinase (GRK) 1 and GRK7 in the zebrafish, an animal model suitable for studies on retinal physiology and biochemistry. Screening of the ocular cDNAs identified two homologs for each of GRK1 (1A and 1B) and GRK7 (7-1 and 7-2), and they were classified into three GRK subfamilies, 1 A, 1B and 7 by phylogenetic analysis. In situ hybridization and immunohistochemical studies localized both GRK1B and GRK7-1 in the cone outer segments and GRK1A in the rod outer segments. The opsin/GRKs molar ratio was estimated to be 569 in the rod and 153 in the cone. The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. The reinforced activity of the cone kinase should provide a strengthened shutoff mechanism of the light-signaling in the cone and contribute to the characteristics of the cone responses by reducing signal amplification efficiency.

Mechanism of neurotrophic action of nobiletin in PC12D cells

Nobiletin is a nonpeptide compound with a low molecular weight from a citrus fruit and has the activity to rescue bulbectomy-induced memory impairment. Here we describe that nobiletin itself induces neurite outgrowth in PC12D cells, a rat pheochromocytoma cell line, like NGF, and the molecular mechanism of its neurotrophic action. As cultured in the presence of nobiletin or NGF for 48 h and then assayed using a scanning electron microscope, PC12D cells treated with nobiletin showed morphology with flatter and larger cell bodies than the cells cultured with NGF. Nobiletin-induced neurite outgrowth was inhibited by PD98059 and U0126 but not K252a. Consistently, nobiletin caused a concentration-dependent enhancement of Erk/MAP kinase phosphorylation and a sustained increment of phosphorylation of MEK and Erk/MAP kinase, resulting in a stimulation of CREB phosphorylation and CRE-mediated transcription. This compound also increased intracellular cAMP and CRE-mediated transcription in the presence of forskolin and enhanced PKA activity to stimulate phosphorylation of multiple PKA substrates in PC12D cells. Furthermore, nobiletin preferentially inhibited Ca2+/CaM-dependent phosphodiesterase in vitro. This compound failed to stimulate phosphorylation of Erk5, which is known to be induced by NGF/TrkA signaling. These results suggest that nobiletin induces neurite outgrowth by activating a cAMP/PKA/MEK/Erk/MAP kinase-dependent but not TrkA-dependent signaling pathway coupling with CRE-mediated gene transcription and may thus become a novel type of biochemical probe for elucidation of the molecular mechanism of neuronal differentiation.

Ca2+ channel activating action of maitotoxin in cultured brainstem neurons

The actions of maitotoxin were studied using cultured brainstem cells and adrenal chromaffin cells. Maitotoxin induced a profound increase in the Ca2+ influx into cultured brainstem cells after a brief lag period. The maitotoxin-induced Ca2+ influx was suppressed by various voltage-dependent Ca2+ channel blockers such as Co2+, Mn2+, verapamil and diltiazem. Maitotoxin-catecholamine release in brainstem cells initiated to increase after a lag period of about 1 min and the increase continued even at 4 min after treatment, while in the adrenal chromaffin cells the release started after an about 1-min lag period to attain a maximum within first 2-min and gradually decrease thereafter. These results suggest that maitotoxin acts on Ca2+ channels to increase the Ca2+ influx, accompanied by enhancement of catecholamine release in the brainstem cells with a different temporal profile from that in the adrenal chromaffin cells.

Nobiletin and its related flavonoids with CRE-dependent transcription-stimulating and neuritegenic activities

cAMP response element (CRE) transcription is dysregulated in neurodegenerative disorders in the central nervous system (CNS), including polyglutamine diseases. As the first step to find natural compounds with protective action against neurodegeneration in the CNS, we here examined whether six citrus flavonoids, namely nobiletin, 5-demethylnobiletin, tangeretin, sinensetin, 6-demethoxytangeretin, and 6-demethoxynobiletin, stimulated CRE-dependent transcription and induced neurite outgrowth in PC12D cells. Among the compounds, nobiletin most potently enhanced CRE-dependent transcription and neurite outgrowth by activating ERK/MAP kinase-dependent signalling to increase CREB phosphorylation. The transcription and neurite outgrowth were stimulated by nobiletin in a concentration-dependent manner, with a strong correlation between them. Furthermore, a 11-day oral administration of nobiletin rescued impaired memory in olfactory-bulbectomized mice documented to be accompanied by a cholinergic neurodegeneration. These results suggest that nobiletin with the activity to improve impaired memory may become a potential leading compound for drug development for neurodegenerative disorders exhibiting the dysregulated CRE-dependent transcription.

Intracellular cAMP controls a physical association of V-1 with CapZ in cultured mammalian endocrine cells

V-1, an ankyrin repeat protein with the activity to control tyrosine hydroxylase (TH) gene expression and transmitter release in PC12D cells, associates with CapZ, an actin capping protein, and thereby regulates actin polymerization in vitro. In this study, immunoprecipitation and Western blot analysis showed that V-1 was physically associated with CapZ-beta in PC12D transfectants overexpressing V-1. These proteins were co-localized in the soma of Purkinje cells of rat cerebellum as assayed by immunohistochemistry. Furthermore, in the V-1 transfectants, the amount of CapZ which physically associated with V-1 was steeply reduced at 2h after treatment with forskolin, but was thereafter increased to reach its initial level at 12h after forskolin-treatment. These results suggest that the association of V-1 with CapZ is controlled by a cAMP-dependent signalling pathway probably to play a functional role in the regulatory mechanism of actin dynamics in the endocrine system and the central nervous system.

Nardosinone, the first enhancer of neurite outgrowth-promoting activity of staurosporine and dibutyryl cyclic AMP in PC12D cells

Nardosinone was isolated as an enhancer of nerve growth factor (NGF) from Nardostachys chinensis [Neurosci. Lett. 273 (1999) 53]. Nardosinone (0.1-100 microM) enhanced dibutyryl cyclic AMP (dbcAMP, 0.3 mM)- and staurosporine (10 nM)-induced neurite outgrowth from PC12D cells in a concentration-dependent manner. PD98059 (20 microM), a potent mitogen-activated protein (MAP) kinase kinase inhibitor, partially blocked enhancements of dbcAMP (0.3 mM)- or staurosporine (10 nM)-induced neurite outgrowth by nardosinone. Nardosinone alone had no effect on the phosphorylation of MAP kinase. The dbcAMP-induced increase in phosphorylation of MAP kinase was not affected by nardosinone. Staurosporine almost unaffected the phosphorylation of MAP kinase, and nardosinone potentiated the staurosporine-induced neurite outgrowth without stimulation of the phosphorylation of MAP kinase. Since it is known that MAP kinase signaling is required for neurite outgrowth in PC12D cells, these results suggest that nardosinone enhances staurosporine- or dbcAMP-induced neurite outgrowth from PC12D cells, probably by amplifying both the MAP kinase-dependent and -independent signaling pathways of dbcAMP and staurosporine. It is also suggested that nardosinone enhances a downstream step of MAP kinase in the MAP kinase-dependent signaling pathway. Nardosinone is the first enhancer of the neuritogenic action of dbcAMP and staurosporine and may become a useful pharmacological tool for studying the mechanism of action of not only NGF but also both the neuritogenic substances.

Overexpression of V-1 prevents nitric oxide-induced cell death: involvement of enhanced tetrahydrobiopterin biosynthesis

Previously we reported that the synthesis of catecholamines, dopamine, and noradrenaline was enhanced by overexpression of V-1 protein, a neuronal protein active in the initial stage of development of the rat cerebellum, in the neuronal cell line PC12D, a model of dopamine cells (Yamakuni et al. [1998] J. Biol. Chem. 273:27051-27054). To investigate the physiological role of this protein, we examined the effect of V-1 overexpression on cell toxicity induced by nitric oxide (NO) used at low concentrations. Two clones of PC12D cells overexpressing V-1, transfectants termed V1-46 and V1-69, were significantly more resistant to NOR3 (an NO donor) but not to etoposide (an inhibitor of topoisomerase II)-induced apoptotic cell death than the control cells (termed C-7 and C-9) that had been transfected with the vector alone. The addition of L-DOPA, dopamine, or noradrenaline to the medium did not abolish NOR3-induced cell death in PC12D cells. Moreover, pretreatment of V1-46 and V1-69 cells with L-alpha-methyl-p-tyrosine (alpha-MPT), an inhibitor of tyrosine hydroxylase, to inhibit catecholamine biosynthesis did not affect the resistance to NO toxicity. These results indicate that the catecholamine levels increased by V-1 overexpression did not produce the protection against NOR3-induced toxicity. We further showed that overexpression of V-1 enhanced the synthesis of (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)). In addition, pretreatment with BH(4) or with sepiapterin, which is converted to BH(4) intracellularly, significantly protected PC12D cells in a dose-dependent manner. The increased BH(4) synthesis by V-1 overexpression was dose dependently inhibited by pretreatment with diaminohydroxypyrimidine (DAHP), an inhibitor of GTP-cyclohydrolase I, which is the rate-limiting enzyme for the biosynthesis of BH(4), concomitantly with the loss of protective effect afforded by V-1 overexpression. Furthermore, the addition of BH(4) or sepiapterin to DAHP-pretreated V146 and V1-69 cells restored cell viability. Taken together, these results indicate that V1 protein plays an important role in protection against cell death induced by NO at low levels by promoting the synthesis of BH(4). Moreover, these findings suggest the up-regulation of V1 expression as a possible therapeutic target for protection against the insult of NO-induced oxidative stress.

V-1, a protein expressed transiently during murine cerebellar development, regulates actin polymerization via interaction with capping protein

V-1 is a 12-kDa protein consisting of three consecutive ANK repeats, which are believed to serve as the surface for protein-protein interactions. It is thought to have a role in neural development for its temporal profile of expression during murine cerebellar development, but its precise role remains unknown. Here we applied the proteomic approach to search for protein targets that interact with V-1. The V-1 cDNA attached with a tandem affinity purification tag was expressed in the cultured 293T cells, and the protein complex formed within the cells were captured and characterized by mass spectrometry. We detected two polypeptides specifically associated with V-1, which were identified as the alpha and beta subunits of the capping protein (CP, alternatively called CapZ or beta-actinin). CP regulates actin polymerization by capping the barbed end of the actin filament. The V-1.CP complex was detected not only in cultured cells transfected with the V-1 cDNA but also endogenously in cells as well as in murine cerebellar extracts. An analysis of the V-1/CP interaction by surface plasmon resonance spectroscopy showed that V-1 formed a stable complex with the CP heterodimer with a dissociation constant of 1.2 x 10(-7) m and a molecular stoichiometry of approximately 1:1. In addition, V-1 inhibited the CP-regulated actin polymerization in vitro in a dose-dependent manner. Thus, our results suggest that V-1 is a novel component that regulates the dynamics of actin polymerization by interacting with CP and thereby participates in a variety of cellular processes such as actin-driven cell movements and motility during neuronal development.

Down-regulation of an ankyrin repeat-containing protein, V-1, during skeletal muscle differentiation and its re-expression in the regenerative process of muscular dystrophy

Using Western blot analysis and immunohistochemical methods, we examined the expression of V-1, a member of the ankyrin repeat-containing protein family, during differentiation and regeneration of skeletal muscle. The expression of V-1 was high in cultured myoblasts and decreased during their differentiation into myotubes, while high expression was maintained when muscle differentiation was inhibited by treatment with basic fibroblast growth factor. Down-regulation of V-1 also occurred during in vivo muscle differentiation from embryonic to postnatal stages, reaching an undetectable level in mature skeletal muscle. In contrast, strong V-1 immunoreactivity was detected again in myoblasts and regenerating muscle fibers with a small diameter, which were observed in Duchenne muscular dystrophy and its animal model, mdx mouse. Thus, it seems that V-1 is a good marker for early stage of muscle regeneration and changes of its expression suggest that V-1 plays a role in prenatal muscle differentiation and postnatal muscle regeneration.

Expression of V-1, a novel catecholamine biosynthesis regulatory protein, is enhanced by hypertension in atrial myocytes of Dahl salt-sensitive rats

V-1 positively controls catecholamine synthetic gene transcription to promote catecholamine production in PC12D cells. In this study, immunohistochemical analysis revealed that in Wistar rats, V-1 immunoreactivity was localized not only in sympathetic axons but also in the cytoplasm of cardiomyocytes, and that the immunoreactivity in atrial myocytes was more intense than that in ventricular myocytes. Western blot analysis also showed that V-1 expression level in the atrium was higher than that in the ventricle of Wistar rat hearts. When Dahl salt-sensitive (DS) rats were fed an 8% NaCl diet after the age of 6 weeks, blood pressure was raised 230mm Hg at 18 weeks. V-1 expression was shown to be increased in the atrial myocytes of these DS rats, but not in the sympathetic axons, when assayed by immunohistochemistry. These results suggest that in normotensive rats, V-1 is preferentially expressed in the cytoplasm of cardiomyocytes in the atrium rather than in the ventricle. It is also suggested that V-1 expression is increased by hypertension in DS rat atrium.

Identification of ATF-2 as a transcriptional regulator for the tyrosine hydroxylase gene

Transcriptional regulation of catecholamine-synthesizing genes is important for the determination of neurotransmitters during brain development. We found that three catecholamine-synthesizing genes were transcriptionally up-regulated in cloned PC12D cells overexpressing V-1, a protein that is highly expressed during postnatal brain development (1). To reveal the molecular mechanism to regulate the expression of tyrosine hydroxylase (TH), which is the rate-limiting enzyme for catecholamine biosynthesis, we analyzed the transcription factors responsible for TH induction in the V-1 clonal cells. First, by using reporter constructs, we found that the transcription mediated by cAMP-responsive element (CRE) was selectively enhanced in the V-1 cells, and TH promoter activity was totally dependent on the CRE in the promoter region of the TH gene. Next, immunoblot analyses and a transactivation assay using a GAL4 reporter system revealed that ATF-2, but not cAMP-responsive element-binding protein (CREB), was highly phosphorylated and activated in the V-1 cells, while both CREB and ATF-2 were bound to the TH-CRE. Finally, the enhanced TH promoter activity was competitively attenuated by expression of a plasmid containing the ATF-2 transactivation domain. These data demonstrated that activation of ATF-2 resulted in the increased transcription of the TH gene and suggest that ATF-2 may be deeply involved in the transcriptional regulation of catecholamine-synthesizing genes during neural development.

V-1, a catecholamine biosynthesis regulatory protein, positively controls catecholamine secretion in PC12D cells

Stably transfected PC12D cell lines overexpressing a catecholamine biosynthesis regulatory protein, V-1, were used to examine the functional role of V-1 in catecholamine secretion. High K(+)-induced dopamine secretion in V-1 overexpressing clones was shown to be markedly potentiated compared with control clones carried with a vector alone. As assayed intracellular calcium concentration ([Ca(2+)](i)) using fura-PE3, V-1 overexpression was observed to enhance high K(+)-elicited [Ca(2+)](i) elevation. Electron microscopic analysis revealed an increase in dense-cored vesicle formation by V-1 overexpression. These results suggest that the enhancement of high K(+)-induced dopamine secretion by V-1 overexpression results from the potentiation of high K(+)-induced [Ca(2+)](i) elevation and the increase in the number of dense-cored vesicles.

Neurosecretion competence. A comprehensive gene expression program identified in PC12 cells

The phenotype of neurosecretory cells is characterized by clear vesicles and dense granules, both discharged by regulated exocytosis. However, these organelles are lacking completely in a few neurosecretion-incompetent clones of the pheochromocytoma PC12 line, in which other specific features are maintained (incompetent clones). In view of the heterogeneity of PC12 cells, a differential characterization of the incompetent phenotype based on the comparison of a single incompetent and a single wild-type clone would have been inconclusive. Therefore, we have compared two pairs of PC12 clones, studying in parallel the transcript levels of 4,200 genes and 19,000 express sequence tags (ESTs) by high density oligonucleotide arrays. After accurate data processing for quality control and filtration, a total of 755 transcripts, corresponding to 448 genes and 307 ESTs, was found consistently changed, with 46% up-regulated and 54% down-regulated in incompetent versus wild-type clones. Many but not all neurosecretion genes were profoundly down-regulated in incompetent cells. Expression of endocytosis genes was normal, whereas that of many nuclear and transcription factors, including some previously shown to play key roles in neurogenesis, was profoundly changed. Additional differences appeared in genes involved in signaling and metabolism. Taken together these results demonstrate for the first time that expression of neurosecretory vesicles and granules is part of a complex gene expression program that includes many other features that so far have not been recognized.

Picrosides I and II, selective enhancers of the mitogen-activated protein kinase-dependent signaling pathway in the action of neuritogenic substances on PC12D cells

Picrosides I and II caused a concentration-dependent (> 0.1 microM) enhancement of basic fibroblast growth factor (bFGF, 2 ng/ml)-, staurosporine (10 nM)- and dibutyryl cyclic AMP (dbcAMP, 0.3 mM)-induced neurite outgrowth from PC12D cells. PD98059 (20 microM), a potent mitogen-activated protein (MAP) kinase kinase inhibitor, blocked the enhancement of bFGF (2 ng/ml)-, staurosporine (10 nM)- or dbcAMP (0.3 mM)-induced neurite outgrowth by picrosides, suggesting that picrosides activate MAP kinase-dependent signaling pathway. However, PD98059 did not affect the bFGF (2 ng/ml)-, staurosporine (10 nM)- and dbcAMP (0.3 mM)-induced neurite outgrowth in PC12D cells, indicating the existence of two components in neurite outgrowth induced by bFGF, staurosporine and dbcAMP, namely the MAP kinase-independent and the masked MAP kinase-dependent one. Furthermore, picrosides-induced enhancements of the bFGF-action were markedly inhibited by GF109203X (0.1 microM), a protein kinase C inhibitor. The expression of phosphorylated MAP kinase was markedly increased by bFGF (2 ng/ml) and dbcAMP (0.3 mM), whereas that was not enhanced by staurosporine (10 nM). Picrosides had no effect on the phosphorylation of MAP kinase induced by bFGF or dbcAMP and also unaffected it in the presence of staurosporine. These results suggest that picrosides I and II enhance bFGF-, staurosporine- or dbcAMP-induced neurite outgrowth from PC12D cells, probably by amplifying a down-stream step of MAP kinase in the intracellular MAP kinase-dependent signaling pathway. Picrosides I and II may become selective pharmacological tools for studying the MAP kinase-dependent signaling pathway in outgrowth of neurites induced by many kinds of neuritogenic substances including bFGF.

Glucocorticoid inhibits expression of V-1, a catecholamine biosynthesis regulatory protein, in cultured adrenal medullary cells

V-1 acts as a positive and coordinate regulator of gene expression of catecholamine biosynthetic enzymes in PC12D cells. The present study was conducted to investigate the mechanism controlling expression of V-1 in the adrenal gland. Immunohistochemical analysis demonstrated that noradrenergic chromaffin cells more highly expressed V-1 than adrenergic chromaffin cells preferentially expressing the glucocorticoid receptor in rat adrenal glands. Western blotting showed that in cultured bovine adrenal medullary cells, dexamethasone, a synthetic glucocorticoid, inhibited expression of V-1, and that this inhibition was prevented by RU-486, a glucocorticoid receptor antagonist. These results suggest that adrenal expression of V-1 is differentially controlled by glucocorticoids through the specific receptor, and that thereby V-1 regulates catecholamine biosynthesis in a catecholaminergic phenotype-dependent manner.

Myotrophin/V-1, a protein up-regulated in the failing human heart and in postnatal cerebellum, converts NFkappa B p50-p65 heterodimers to p50-p50 and p65-p65 homodimers

Myotrophin/V-1 is a cytosolic protein found at elevated levels in failing human hearts and in postnatal cerebellum. We have previously shown that it disrupts nuclear factor of kappaB (NFkappaB)-DNA complexes in vitro. In this study, we demonstrated that in HeLa cells native myotrophin/V-1 is predominantly present in the cytoplasm and translocates to the nucleus during sustained NFkappaB activation. Three-dimensional alignment studies indicate that myotrophin/V-1 resembles a truncated IkappaBalpha without the signal response domain (SRD) and PEST domains. Co-immunoprecipitation studies reveal that myotrophin/V-1 interacts with NFkappaB proteins in vitro; however, it remains physically associated only with p65 and c-Rel proteins in vivo during NFkappaB activation. In vitro studies indicate that myotrophin/V-1 can promote the formation of p50-p50 homodimers from monomeric p50 proteins and can convert the preformed p50-p65 heterodimers into p50-p50 and p65-p65 homodimers. Furthermore, adenovirus-mediated overexpression of myotrophin/V-1 resulted in elevated levels of both p50-p50 and p65-p65 homodimers exceeding the levels of p50-p65 heterodimers compared with Adbetagal-infected cells, where the levels of p50-p65 heterodimers exceeded the levels of p50-p50 and p65-p65 homodimers. Thus, overexpression of myotrophin/V-1 during NFkappaB activation resulted in a qualitative shift by quantitatively reducing the level of transactivating heterodimers while elevating the levels of repressive p50-p50 homodimers. Correspondingly, overexpression of myotrophin/V-1 resulted in significantly reduced kappaB-luciferase reporter activity. Because myotrophin/V-1 is found at elevated levels during NFkappaB activation in postnatal cerebellum and in failing human hearts, this study cumulatively suggests that myotrophin/V-1 is a regulatory protein for modulating the levels of activated NFkappaB dimers during this period.

Enhanced expression of GTP cyclohydrolase I in V-1-overexpressing PC12D cells

Three of the catecholamine-synthesizing enzymes, i.e., tyrosine hydroxylase (TH), aromatic l-amino acid decarboxylase, and dopamine beta-hydroxylase, were earlier shown to be up-regulated in cloned PC12D cells overexpressing V-1, a cdc10/SWI6 motif-containing protein. GTP cyclohydrolase I (GCH) is the rate-limiting enzyme for the biosynthesis of tetrahydrobiopterin (BH(4)), known as an essential cofactor for TH; and here we found the increased expression of GCH in V-1-overexpressing clones. Both GCH activity and total biopterin content were highly increased in the V-1 clones; whereas the activity of sepiapterin reductase, enzyme in the final step of the BH(4) biosynthesis, was not altered. Biochemical analyses revealed increased levels of GCH protein, mRNA, and transcription in the V-1 clones. Promoter analysis showed increased reporter activity in the construct with 150 bp of the promoter region of the human GCH gene, suggesting the involvement of cAMP-responsive element-mediated transcriptional regulation.

Two steroidal saponins from Camassia cusickii induce L1210 cell death through the apoptotic mechanism

Two steroidal saponins, tigogenin hexasaccharide-1 (TGHS-1, (25R)-5α-spirostan-3β-yl 4-O-[2-O-[3-O- (α-L-rhamnopyranosyl)-β-D-glucopyranosyl]-3-O-[4-O-(α-L-rhamnopyranosyl)-β-D-glucopyranosyl]-β-D-glucopyranosyl]- β-D-galactopyranoside) and tigogenin hexasaccharide-2 (TGHS-2, (25R)-5α-spirostan-3β-yl 4-O-[2-O-[3-O- (β-D-glucopyranosyl)-β-D-glucopyranosyl]-3-O-[4-O-(α-L-rhamnopyranosyl)-β-D-glucopyranosyl]-β-D-glucopyranosyl]- β-D-galactopyranoside), were isolated from the fresh bulbs of Camassia cusickii. In murine leukemic L1210 cells, both compounds showed cytotoxicity with an EC50 value of 0.06 µM. The morphological observation revealed that TGHS-1 and TGHS-2 induced shrinkage in cell soma and chromatin condensation, suggesting apoptotic cell death. The cell death was confirmed to be apoptosis by Annexin V binding to phosphatidylserine in the cell membrane and excluding propidium iodide. A typical apoptotic DNA ladder and the cleavage of caspase-3 were observed after treatment with TGHS-1 and TGHS-2. In the presence of both the compounds, cells with sub-G1 DNA content were detected by flow cytometric analysis, indicating that TGHS-1 and TGHS-2 (each EC50 value of 0.1 µM) are the most powerful apoptotic saponins known. These results suggest that TGHS-1 and TGHS-2 induce apoptotic cell death through caspase-3 activation.Key words: steroidal saponin, tigogenin hexasaccharide, apoptosis, DNA fragmentation, murine leukemic L1210 cells.

Potentiation of nerve growth factor-action by picrosides I and II, natural iridoids, in PC12D cells

Natural iridoid, picroside I (beta-D-glucopyranoside, 1a,1b,2,5a,6, 6a-hexahydro-6-hydroxy-1a-(hydroxymethyl)oxireno[4,5]cyclopenta[1, 2-c]pyran-2-yl, 6-(3-phenyl-2-propenoate)) or II (beta-D-glucopyranoside, 1a,1b,2,5a,6, 6a-hexahydro-6-[(4-hydroxy-3-methoxybenzoyl)oxy]-1a-(hydroxymethyl )ox ireno[4,5]cyclopenta[1,2-c]pyran-2-yl) alone did not exhibit neuritogenic activity, but caused a concentration-dependent (>0.1 microM) enhancement of nerve growth factor (NGF, 2 ng/ml)-induced neurite outgrowth from PC12D cells. The picroside-induced enhancing action of NGF was abolished by GF109203X (2-[1-(3-dimethylaminopropyl)-indol-3-yl]-3-(indol-3-yl)maleimide) (0.1 microM), a protein kinase C inhibitor. Furthermore, PD98059 (2-(2'-amino-3'-methoxyphenyl)-oxanaphthalen-4-one) (20 microM), a potent mitogen-activated protein (MAP) kinase kinase inhibitor, completely blocked the picroside-induced enhancement of neurite outgrowth in the presence of NGF (2 ng/ml), suggesting that picrosides activate the MAP kinase-dependent signaling pathway. Interestingly, no increase in the expression of phosphorylated MAP kinase was observed in picroside-treated (60 microM) PC12D cells in the presence of NGF (2 ng/ml). These results suggest that picroside I or II enhances NGF-induced neurite outgrowth from PC12D cells, probably by amplifying a down-stream step of MAP kinase in the NGF receptor-mediated intracellular MAP kinase-dependent signaling pathway.

Neurosecretory cells without neurosecretion: evidence of an independently regulated trait of the cell phenotype

Neurosecretion competence is a fundamental property that enables differentiated neurones and professional neurosecretory cells to store neurotransmitters and hormones in specialized organelles, the synaptic-like vesicles and dense granules, and to release them by regulated exocytosis. In our laboratory, the study of rat phaeochromocytoma (PC12) clones that fail to express the above organelles or any other components involved in neurosecretion, whilst maintaining most of the general markers of the parental population, has served to demonstrate that this trait is controlled independently from the rest of the phenotype. The present review focuses on recent advances in elucidating the molecular mechanisms governing neurosecretion competence. Moreover, the opportunities that such neurosecretion-defective PC12 clones offer for the investigation of new aspects of regulated exocytosis and the localization of its components are summarized.