A rat cerebellar protein containing the cdc10/SWI6 motif

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.

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.

Molecular characterization, expression patterns and subcellular localization of Myotrophin (MTPN) gene in porcine skeletal muscle

Myotrophin (MTPN) is an effective growth factor in promoting skeletal muscle growth in vitro and vivo and has been purified from porcine skeletal muscle. However, in pigs, the information on MTPN gene is very limited. In this study, we cloned cDNA sequences and analyzed the genomic structure of porcine MTPN gene. The deduced amino acid sequence of porcine MTPN contains two the ankyrin repeat domains. RT-PCR analysis revealed that porcine MTPN gene was widely expressed in many tissues, a high expression level was observed in the spleen, liver and uterus, and transient transfection indicated that porcine MTPN proteins was located in cytoplasms within Pig Kidney Epithelial cells (PK15). Quantitative real-time PCR (qRT-PCR) analyses showed that MTPN expression peaked at embryonic 65 day post conception (dpc). During postnatal muscle development, MTPN expression was down-regulated from the 3 day to the 180 day in Yorkshire pigs. This result suggests that the MTPN gene may be important gene for skeletal muscle growth and provides useful information for further studies on its roles in porcine skeletal muscle.

Anchoring skeletal muscle development and disease: the role of ankyrin repeat domain containing proteins in muscle physiology

The ankyrin repeat is a protein module with high affinity for other ankyrin repeats based on strong Van der Waals forces. The resulting dimerization is unusually resistant to both mechanical forces and alkanization, making this module exceedingly useful for meeting the extraordinary demands of muscle physiology. Many aspects of muscle function are controlled by the superfamily ankyrin repeat domain containing proteins, including structural fixation of the contractile apparatus to the muscle membrane by ankyrins, the archetypical member of the family. Additionally, other ankyrin repeat domain containing proteins critically control the various differentiation steps during muscle development, with Notch and developmental stage-specific expression of the members of the Ankyrin repeat and SOCS box (ASB) containing family of proteins controlling compartment size and guiding the various steps of muscle specification. Also, adaptive responses in fully formed muscle require ankyrin repeat containing proteins, with Myotrophin/V-1 ankyrin repeat containing proteins controlling the induction of hypertrophic responses following excessive mechanical load, and muscle ankyrin repeat proteins (MARPs) acting as protective mechanisms of last resort following extreme demands on muscle tissue. Knowledge on mechanisms governing the ordered expression of the various members of superfamily of ankyrin repeat domain containing proteins may prove exceedingly useful for developing novel rational therapy for cardiac disease and muscle dystrophies.

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.

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.

Large-scale identification of Caenorhabditis elegans proteins by multidimensional liquid chromatography-tandem mass spectrometry

A proteome of a model organism, Caenorhabditis elegans, was analyzed by an integrated liquid chromatography (LC)-based protein identification system, which was constructed by microscale two-dimensional liquid chromatography (2DLC) coupled with electrospray ionization (ESI) tandem mass spectrometry (MS/MS) on a high-resolution hybrid mass spectrometer with an automated data analysis system. Soluble and insoluble protein fractions were prepared from a mixed growth phase culture of the worm C. elegans, digested with trypsin, and fractionated separately on the 2DLC system. The separated peptides were directly analyzed by on-line ESI-MS/MS in a data-dependent mode, and the resultant spectral data were automatically processed to search a genome sequence database, wormpep 66, for protein identification. The total number of proteins of the composite proteome identified in this method was 1,616, including 110 secreted/targeted proteins and 242 transmembrane proteins. The codon adaptation indices of the identified proteins suggested that the system could identify proteins of relatively low abundance, which are difficult to identify by conventional 2D-gel electrophoresis (GE) followed by an offline mass spectrometric analysis such as peptide mass fingerprinting. Among the approximately 5,400 peptides assigned in this study, many peptides with post-translational modifications, such as N-terminal acetylation and phosphorylation, were detected. This expression profile of C. elegans, containing 571 hypothetical gene products, will serve as the basic data of a major proteome set expressed in the worm.

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.

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.

Profiling of Caenorhabditis elegans proteins using two-dimensional gel electrophoresis and matrix assisted laser desorption/ionization-time of flight-mass spectrometry

The nematode Caenorhabditis elegans (C. elegans) is the first animal whose whole 97 Mb genome sequence, encoding ca. 19000 open reading frames (ORF's), has been essentially determined. We tried to establish a 2-DE map of the nematode proteome by means of two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). A soluble protein fraction of mixed stages of the worm, wild-type strain N2, was applied to 2-D PAGE. After Coomassie Brilliant Blue (CBB) staining, 1200 spots were detected and 140 major spots were excised from the gel and subjected to in-gel digestion with Achromobacter protease I (lysyl endopeptidase). Resulting peptides were analyzed by matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) followed by peptide mass fingerprinting for protein identification. With this approach we have obtained a two-dimensional electrophoresis (2-DE) protein map in which 69 spots were localized as landmarks for comparison of expression profiles to elucidate the basis of various biological events.

Protein profiling of rat cerebella during development

Protein profiles of developing rat cerebella were analyzed by means of two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS). The analysis of adult rat cerebellum gave rise to a protein map comprising approximately 3000 spots detectable by silver staining following high resolution 2-DE with a pH range of 3-10 and a mass range of 8-100 kDa. To obtain landmarks for comparison of developmental profiles of cerebellar proteins, 100 spots were subjected to peptide mass fingerprinting using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and 67 spots were assigned on the map. Analysis of profiles of the developing cerebella revealed significant changes in the expression of proteins during development. In most cases the expression levels of proteins increased as the cerebellum matured, while the expression of 42 spots appeared specific or remarkably abundant in the immature cerebellum. Peptide mass fingerprinting of these spots allowed us to identify 29 proteins, which include, in addition to proteins of unknown function, many proteins known to have roles in the development of the central nervous system. These results suggest that the proteomic approach is valuable for mass identification of proteins involved in cerebellar morphogenesis.

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

Catecholaminergic (dopaminergic, noradrenergic, and adrenergic) transmitter phenotypes require the cooperative actions of four biosynthetic enzymes: tyrosine hydroxylase, aromatic L-amino acid decarboxylase, dopamine beta-hydroxylase, and phenylethanolamine N-methyltransferase. Mechanisms that control expression of these enzymes in a transmitter phenotype-specific manner, however, are poorly understood. Here, we provide evidence that overexpression of a novel cdc10/SWI6 motif-containing protein, V-1, elicits the coordinate up-regulation of tyrosine hydroxylase, aromatic L-amino acid decarboxylase, and dopamine beta-hydroxylase mRNAs in the neuronal cell line PC12D, and as a result, catecholamine levels are increased. Furthermore, V-1 is strongly expressed in the cytoplasm of rat chromaffin cells of adrenal medulla. Thus, V-1 may act as a cytoplasmic protein/protein adapter and be involved in control of the catecholaminergic phenotype expression via an intracellular pathway signaling to the nucleus.

Tissue-specific regulation by vitamin D3 of a novel protein containing ankyrin-like repeats

Vitamin D3 is the precursor of the steroid hormone 1,25-dihydroxyvitamin D3 which is involved in the regulation of calcium metabolism, growth and differentiation. We used differential display of mRNA populations from kidney and intestine of vitamin D3-deficient and -replete chicks to determine the steady-state abundance of approximately 5000 mRNAs. One of these sequences, whose differential expression in kidney and down-regulation by vitamin D3 was confirmed by Northern analysis, was used to screen a cDNA library from vitamin D3-deficient chick kidney in order to obtain a full length cDNA. Subcloning and sequencing revealed that this cDNA encodes a novel protein containing ankyrin-like repeats and a C-terminal Fe-S binding region signature. The encoded protein consists of 617 amino acids and contains two sets of four ankyrin-like repeats separated by 146 amino acids. This motif consists of approximately 33 amino acids containing a highly conserved central hydrophobic alpha helix and is abundant in a wide variety of proteins, particularly those participating in the protein-protein or protein-membrane interactions involved in signal transduction, regulation of the cell cycle and control of transcription. Outside of the ankyrin-like domains, no homologies with other proteins in existing data bases were found. Our results have revealed a novel protein containing ankyrin-like repeats tissue-specifically down-regulated by vitamin D3 in the kidney.

Murine central neurons express a novel member of the cdc10/SWI6 motif-containing protein superfamily

V-1 protein is a novel member of the cdc10/SWI6 motif-containing protein superfamily several members of which have been demonstrated to play crucial roles in the regulation of intracellular signaling. In the present study we examined the distribution of V-1 mRNA in the murine central nervous system (CNS). Northern analysis revealed the expression of V-1 mRNA in various regions of the brain with the following rank order: hippocampus, cerebellum > cerebral cortex, olfactory bulb, medulla oblongata, pons > thalamus. In situ hybridization also showed that V-1 mRNA is widely distributed in various regions of the brain, with parallel expression levels to those revealed by Northern analysis. Immunohistochemical analysis revealed that the V-1 protein exists in various types of neurons, mainly in cell bodies but also in dendrites, axons and possibly in synaptic areas. These expression patterns of the V-1 gene in the murine CNS suggest that the V-1 protein performs some common function in different classes of neurons. We found no significant difference in the expression level of V-1 mRNA in cerebellar granule cells between the control and mutant mice of Purkinje cell degeneration (pcd). In comparison with our previous data obtained in another mutant, staggerer, we discussed the effects of target deprivation on the expression of V-1 mRNA in cerebellar granule cells.

Cardiac myotrophin exhibits rel/NF-kappa B interacting activity in vitro

Myotrophin is a soluble-12 kilodalton protein isolated from hypertrophied spontaneously hypertensive rat and dilated cardiomyopathic human hearts. We have recently cloned the gene coding for myotrophin and expressed it in Escherichia coli. In the present study, the expression of myotrophin gene was analyzed, and at least seven transcripts have been detected in rat heart and in other tissues. We have further analyzed the primary structure of myotrophin protein and identified significant new structural and functional domains. Our analysis revealed that one of the ankyrin repeats of myotrophin is highly homologous specifically to those of myotrophin is highly homologous specifically to those of I kappa B alpha/rel ankyrin repeats. In addition, putative consensus phosphorylation sites for protein kinase C and casein kinase II, which were observed in I kappa B alpha proteins, were identified in myotrophin. To verify the significance of these homologies, kappa B gel shift assays were performed with Jurkat T cell nuclear extract proteins and the recombinant myotrophin. Results of these assays indicate that the recombinant myotrophin has the ability to interact with NF-kappa B/rel proteins as revealed by the formation of ternary protein-DNA complexes. While myotrophin-specific antibodies inhibited the formation of these complexes, rel-specific p50 and p65 antibodies supershifted these complexes. Thus, these results clearly indicate that the myotrophin protein to be a unique rel/NF-kappa B interacting protein.

Isolation of cDNA clones encoding the mouse protein V-1

The amino acid (aa) sequence of rat V-1, a developmentally regulated brain protein, was used to isolate clones encoding mouse V-1, a protein of 118 aa, from an embryoid body cDNA library. The aa sequences of rat and mouse V-1 are identical. V-1 shares several properties (including a 23 of 24 aa match of a tryptic peptide) with myotrophin, a protein that induces cardiac myocyte hypertrophy. Attempts to show that V-1 produced in Escherichia coli could induce the cardiac myocyte hypertrophy ascribed to myotrophin were unsuccessful.

A nuclear factor containing the leucine-rich repeats expressed in murine cerebellar neurons

A nuclear protein, termed leucine-rich acidic nuclear protein (LANP), has been isolated from among rat cerebellar proteins whose expression was transiently increased during an early stage of postnatal development. The amino acid sequence, deduced from its cDNA, showed that LANP contains 247 amino acids consisting of two distinct structural domains: the N-terminal domain characterized by "leucine-rich repeat," which is found in many eukaryotic proteins and which potentially functions in mediating protein-protein interactions, and the C-terminal domain characterized by a cluster of acidic amino acids with a putative nuclear localization signal. Immunohistochemical study using an antibody against LANP revealed that the protein is localized mainly in nuclei of Purkinje cells. In the rat cerebellum on postnatal day 7, LANP mRNA was expressed moderately in the external granule and Purkinje cells and weakly in the internal granule cells. The expression in these cells, especially in Purkinje cells, increased in the second postnatal week and thereafter decreased to an adult level. The structural characteristics, localization, and the stage- and cell type-specific expression suggest a potential role of LANP in a signal transduction pathway that directs differentiation of cerebellar neurons.

The Drosophila ankyrin repeat protein cactus has a predominantly alpha-helical secondary structure

The cactus protein is the Drosophila homologue of the mammalian I kappa B family of cytoplasmic anchor proteins. We have expressed in E. coli and purified a cactus fusion protein, CACT-Bgl. CACT-Bgl protein contains the six ankyrin repeat sequences which are necessary for specific binding to the Drosophila rel family transcription factor dorsal. We show that the purified CACT-Bgl protein can bind specifically to dorsal and, using circular dichroism spectroscopy, that the protein adopts a largely alpha-helical secondary structure. A further analysis of the ankyrin repeat domains of cactus, using an improved secondary structure prediction program indicates that the N-terminal of the repeat will form into a loop structure and the C-terminal section into an interrupted, amphipathic alpha-helix. On the basis of these findings we propose that the ankyrin repeats of cactus fold together into helical bundles interconnected by diverged loops.

Hundreds of ankyrin-like repeats in functionally diverse proteins: mobile modules that cross phyla horizontally?

Based on pattern searches and systematic database screening, almost 650 different ankyrin-like (ANK) repeats from nearly all phyla have been identified; more than 150 of them are reported here for the first time. Their presence in functionally diverse proteins such as enzymes, toxins, and transcription factors strongly suggests domain shuffling, but their occurrence in prokaryotes and yeast excludes exon shuffling. The spreading mechanism remains unknown, but in at least three cases horizontal gene transfer appears to be involved. ANK repeats occur in at least four consecutive copies. The terminal repeats are more variable in sequence. One feature of the internal repeats is a predicted central hydrophobic alpha-helix, which is likely to interact with other repeats. The functions of the ankyrin-like repeats are compatible with a role in protein-protein interactions.