Purification and molecular cloning of a novel acidic calmodulin binding protein from rat brain

Oligomerization and aggregation of NAP-22 with several metal ions

Metal ions participate in various biochemical processes such as electron transport chain, gene transcription, and enzymatic reactions. Furthermore, the aggregation promoting effect of several metal ions on neuronal proteins such as prion, tau, Aβ peptide, and α-synuclein, has been reported. NAP-22 (also called BASP1 or CAP-23) is a neuron-enriched calmodulin-binding protein and one of the major proteins in the detergent-resistant membrane microdomain fraction of the neuronal cell membrane. Previously, we showed oligomer formation of NAP-22 in the presence of several phospholipids and fatty acids. In this study, we found the aggregation of NAP-22 by FeCl2, FeCl3, and AlCl3 using native-PAGE. Oligomer or aggregate formation of NAP-22 by ZnCl2 or CuSO4 was shown with SDS-PAGE after cross-linking with glutaraldehyde. Morphological analysis with electron microscopy revealed the formation of large aggregates composed of small annular oligomers in the presence of FeCl3, AlCl3, or CuSO4. In case of FeCl2 or ZnCl2, instead of large aggregates, scattered annular and globular oligomers were observed. Interestingly, metal ion induced aggregation of NAP-22 was inhibited by several coenzymes such as NADP+, NADPH, or thiamine pyrophosphate. Since NAP-22 is highly expressed in the presynaptic region of the synapse, this result suggests the participation of metal ions not only on the protein and membrane dynamics at the presynaptic region, but also on the metabolic regulation though the interaction with coenzymes.

BASP1 down-regulates RANKL-induced osteoclastogenesis

The cytokine RANKL (Receptor Activator of NFκB Ligand) is the key driver of differentiation of monocytes/macrophages to form multi-nucleated, bone-resorbing osteoclasts, a process that is accompanied by significant changes in gene expression. We show that exposure to RANKL rapidly down-regulates expression of Brain Acid Soluble Protein 1 (BASP1) in cultured primary mouse bone marrow macrophages (BMMs), and that this reduced expression is causally linked to the osteoclastogenic process in vitro. Knocking down BASP1 expression in BMMs or eliminating its expression in these cells or in RAW 264.7 cells enhanced RANKL-induced osteoclastogenesis, promoted cell-cell fusion, and generated cultures containing larger osteoclasts with increased mineral degrading abilities relative to controls. Expression of exogenous BASP1 in BMMs undergoing osteoclastogenic differentiation produced the opposite effects. Upon exposure to RANKL, primary mouse BMMs in which BASP1 had been knocked down exhibited increased expression of the key osteoclastogenic transcription factor Nfatc1and of its downstream target genes Dc-stamp, Ctsk, Itgb3, and Mmp9 relative to controls. The knock-down cells also exhibited increased sensitivity to the pro-osteoclastogenic effects of RANKL. We conclude that BASP1 is a negative regulator of RANKL-induced osteoclastogenesis, which down-regulates the pro-osteoclastogenic gene expression pattern induced by this cytokine. Decreased expression of BASP1 upon exposure of BMMs to RANKL removes a negative regulator of osteoclastogenesis and promotes this process.

A high-affinity cocaine binding site associated with the brain acid soluble protein 1

Cocaine is a monoamine transport inhibitor. Current models attributing pharmacologic actions of cocaine to inhibiting the activity of the amine transporters alone failed to translate to the clinic. Cocaine inhibition of the dopamine, serotonin, and norepinephrine transporters is relatively weak, suggesting that blockade of the amine transporters alone cannot account for the actions of cocaine, especially at low doses. There is evidence for significantly more potent actions of cocaine, suggesting the existence of a high-affinity receptor(s) for the drug. Identifying and characterizing such receptors will deepen our understanding of cocaine pharmacologic actions and pave the way for therapeutic development. Here we identify a high-affinity cocaine binding site associated with BASP1 that is involved in mediating the drug’s psychotropic actions.

Cocaine exerts its stimulant effect by inhibiting dopamine (DA) reuptake, leading to increased dopamine signaling. This action is thought to reflect the binding of cocaine to the dopamine transporter (DAT) to inhibit its function. However, cocaine is a relatively weak inhibitor of DAT, and many DAT inhibitors do not share cocaine’s behavioral actions. Further, recent reports show more potent actions of the drug, implying the existence of a high-affinity receptor for cocaine. We now report high-affinity binding of cocaine associated with the brain acid soluble protein 1 (BASP1) with a dissociation constant (K_d) of 7 nM. Knocking down BASP1 in the striatum inhibits [³H]cocaine binding to striatal synaptosomes. Depleting BASP1 in the nucleus accumbens but not the dorsal striatum diminishes locomotor stimulation in mice. Our findings imply that BASP1 is a pharmacologically relevant receptor for cocaine.

Truncated YY1 interacts with BASP1 through a 339KLK341 motif in YY1 and suppresses vascular smooth muscle cell growth and intimal hyperplasia after vascular injury

AIMS

In-stent restenosis and late stent thrombosis are complications associated with the use of metallic and drug-coated stents. Strategies that inhibit vascular smooth muscle cell (SMC) proliferation without affecting endothelial cell (EC) growth would be helpful in reducing complications arising from percutaneous interventions. Our group previously showed that the forced expression of the injury-inducible zinc finger (ZNF) transcription factor, yin yang-1 (YY1) comprising 414 residues inhibits neointima formation in carotid arteries of rabbits and rats. YY1 inhibits SMC proliferation without affecting EC growth. Identifying a shorter version of YY1 retaining cell-selective inhibition would make it more amenable for potential use as a gene therapeutic agent.

METHODS AND RESULTS

We dissected YY1 into a range of shorter fragments (YY1A-D, YY1Δ) and found that the first two ZNFs in YY1 (construct YY1B, spanning 52 residues) repressed SMC proliferation. Receptor Binding Domain analysis predicts a three residue (339KLK341) interaction domain. Mutation of 339KLK341 to 339AAA341 in YY1B (called YY1Bm) abrogated YY1B's ability to inhibit SMC but not EC proliferation and migration. Incubation of recombinant GST-YY1B and GST-YY1Bm with SMC lysates followed by precipitation with glutathione-agarose beads and mass spectrometric analysis identified a novel interaction between YY1B and BASP1. Overexpression of BASP1, like YY1, inhibited SMC but not EC proliferation and migration. BASP1 siRNA partially rescued SMC from growth inhibition by YY1B. In the rat carotid balloon injury model, adenoviral overexpression of YY1B, like full-length YY1, reduced neointima formation, whereas YY1Bm had no such effect. CD31 immunostaining suggested YY1B could increase re-endothelialization in a 339KLK341-dependent manner.

CONCLUSIONS

These studies identify a truncated form of YY1 (YY1B) that can interact with BASP1 and inhibits SMC proliferation, migration and intimal hyperplasia after balloon injury of rat carotid arteries as effectively as full length YY1. We demonstrate the therapeutic potential of YY1B in vascular proliferative disease.

The effects of phospholipids and fatty acids on the oligomer formation of NAP-22

Recovery of various signal transduction molecules in the detergent-resistant membrane microdomain (DRM) fraction suggests the importance of this region in cellular functions. NAP-22 (also called BASP1 or CAP-23) is a neuron-enriched calmodulin-binding protein and one of the major proteins in the DRM fraction of the neuronal cell membrane. Previous studies showed tight binding activity of NAP-22 to acidic membrane lipids and the self-interaction of NAP-22, i.e., oligomerization. In this study, the effect of various phospholipids, lysophospholipids and fatty acids on the oligomerization of NAP-22 was studied through SDS-PAGE after chemical cross-linking and electron microscopic observation. High molecular mass oligomers were detected by SDS-PAGE after incubation in solutions containing over 20 mM NaCl at pH 6.5-8.5, even in the absence of lipid addition, and the addition of Ca²⁺/calmodulin abolished oligomerization. Higher molecular mass oligomer formation after incubation with acidic phospholipids was detected with gradient SDS-PAGE. Much higher mass oligomers were detected in the presence of polyunsaturated fatty acids. Electron microscopic analysis of the samples after SDS treatment showed tangled rope-like structures. Liposome-bound NAP-22 showed small oval or annular structures after cross-linking and SDS treatment. These oligomers were suggested to make the tangled rope-like structures, for annular structures of the same size were observed in the structure. These results suggest the participation of NAP-22 to liquid-liquid phase separation through oligomerization.

GAP-43 and BASP1 in Axon Regeneration: Implications for the Treatment of Neurodegenerative Diseases

Growth-associated protein-43 (GAP-43) and brain acid-soluble protein 1 (BASP1) regulate actin dynamics and presynaptic vesicle cycling at axon terminals, thereby facilitating axonal growth, regeneration, and plasticity. These functions highly depend on changes in GAP-43 and BASP1 expression levels and post-translational modifications such as phosphorylation. Interestingly, examinations of GAP-43 and BASP1 in neurodegenerative diseases reveal alterations in their expression and phosphorylation profiles. This review provides an overview of the structural properties, regulations, and functions of GAP-43 and BASP1, highlighting their involvement in neural injury response and regeneration. By discussing GAP-43 and BASP1 in the context of neurodegenerative diseases, we also explore the therapeutic potential of modulating their activities to compensate for neuron loss in neurodegenerative diseases.

The brain acid-soluble protein 1 (BASP1) interferes with the oncogenic capacity of MYC and its binding to calmodulin

The MYC protein is a transcription factor with oncogenic potential controlling fundamental cellular processes such as cell proliferation, metabolism, differentiation, and apoptosis. The MYC gene is a major cancer driver, and elevated MYC protein levels are a hallmark of most human cancers. We have previously shown that the brain acid-soluble protein 1 gene (BASP1) is specifically downregulated by the v-myc oncogene and that ectopic BASP1 expression inhibits v-myc-induced cell transformation. The 11-amino acid effector domain of the BASP1 protein interacts with the calcium sensor calmodulin (CaM) and is mainly responsible for this inhibitory function. We also reported recently that CaM interacts with all MYC variant proteins and that ectopic CaM increases the transactivation and transformation potential of the v-Myc protein. Here, we show that the presence of excess BASP1 or of a synthetic BASP1 effector domain peptide leads to displacement of v-Myc from CaM. The protein stability of v-Myc is decreased in cells co-expressing v-Myc and BASP1, which may account for the inhibition of v-Myc. Furthermore, suppression of v-Myc-triggered transcriptional activation and cell transformation is compensated by ectopic CaM, suggesting that BASP1-mediated withdrawal of CaM from v-Myc is a crucial event in the inhibition. In view of the tumor-suppressive role of BASP1 which was recently also reported for human cancer, small compounds or peptides based on the BASP1 effector domain could be used in drug development strategies aimed at tumors with high MYC expression.

A Unique Family of Neuronal Signaling Proteins Implicated in Oncogenesis and Tumor Suppression

The neuronal proteins GAP43 (neuromodulin), MARCKS, and BASP1 are highly expressed in the growth cones of nerve cells where they are involved in signal transmission and cytoskeleton organization. Although their primary structures are unrelated, these signaling proteins share several structural properties like fatty acid modification, and the presence of cationic effector domains. GAP43, MARCKS, and BASP1 bind to cell membrane phospholipids, a process reversibly regulated by protein kinase C-phosphorylation or by binding to the calcium sensor calmodulin (CaM). GAP43, MARCKS, and BASP1 are also expressed in non-neuronal cells, where they may have important functions to manage cytoskeleton architecture, and in case of MARCKS and BASP1 to act as cofactors in transcriptional regulation. During neoplastic cell transformation, the proteins reveal differential expression in normal vs. tumor cells, and display intrinsic tumor promoting or tumor suppressive activities. Whereas GAP43 and MARCKS are oncogenic, tumor suppressive functions have been ascribed to BASP1 and in part to MARCKS depending on the cell type. Like MARCKS, the myristoylated BASP1 protein is localized both in the cytoplasm and in the cell nucleus. Nuclear BASP1 participates in gene regulation converting the Wilms tumor transcription factor WT1 from an oncoprotein into a tumor suppressor. The BASP1 gene is downregulated in many human tumor cell lines particularly in those derived from leukemias, which display elevated levels of WT1 and of the major cancer driver MYC. BASP1 specifically inhibits MYC-induced cell transformation in cultured cells. The tumor suppressive functions of BASP1 and MARCKS could be exploited to expand the spectrum of future innovative therapeutic approaches to inhibit growth and viability of susceptible human tumors.

Interaction of dynamin I with NAP-22, a neuronal protein enriched in the presynaptic region

Neurons have well-developed membrane microdomains called "rafts" that are recovered as a detergent-resistant low-density membrane microdomain fraction (DRM). NAP-22 is one of the major protein components of neuronal DRM and localizes in the presynaptic region. In order to know the role of NAP-22 in the synaptic transmission, NAP-22 binding proteins in the cytosol were searched with an affinity screening with NAP-22 as a bait and several protein bands were detected. Using mass-analysis and western blotting, one of the main band of ∼90 kDa was identified as dynamin I. The GTPase activity of dynamin I was partly inhibited by NAP-22 expressed in bacteria and this inhibition was recovered by the addition of calmodulin, a NAP-22 binding protein. The GTPase activity of dynamin was known to be activated with acidic membrane lipids such as phosphatidylserine and the addition of NAP-22, a phosphatidylserine binding protein, inhibited the activation of the GTPase by this lipid. Since NAP-22 localizes on the presynaptic plasma membrane and on synaptic vesicles, these results suggest the participation of NAP-22 in the membrane cycling through binding to dynamin and acidic membrane lipids at the presynaptic region.

Methylation-associated silencing of BASP1 contributes to leukemogenesis in t(8;21) acute myeloid leukemia

The AML1-ETO fusion protein (A/E), which results from the t(8;21) translocation, is considered to be a leukemia-initiating event. Identifying the mechanisms underlying the oncogenic activity of A/E remains a major challenge. In this study, we identified a specific down-regulation of brain acid-soluble protein 1 (BASP1) in t(8;21) acute myeloid leukemia (AML). A/E recognized AML1-binding sites and recruited DNA methyltransferase 3a (DNMT3a) to the BASP1 promoter sequence, which triggered DNA methylation-mediated silencing of BASP1. Ectopic expression of BASP1 inhibited proliferation and the colony-forming ability of A/E-positive AML cell lines and led to apoptosis and cell cycle arrest. The DNMT inhibitor decitabine up-regulated the expression of BASP1 in A/E-positive AML cell lines. In conclusion, our data suggest that BASP1 silencing via promoter methylation may be involved in A/E-mediated leukemogenesis and that BASP1 targeting may be an actionable therapeutic strategy in t(8;21) AML.

A chromosomal rearrangement commonly observed in certain leukemias selectively inactivates a gene that otherwise thwarts cancerous growth. Between 7 and 12% of acute myeloid leukemia cases exhibit a dramatic alteration in chromosomal structure that results in the production of an abnormal fusion protein. Researchers led by Li Yu at the General Hospital of Shenzen University in China have learned that this protein promotes disease progression by switching off an important tumor suppressor. Yu and colleagues showed that it binds a genomic sequence that regulates the gene encoding a second protein called BASP1, dramatically reducing its production. This gene silencing facilitates tumor growth. Chemicals that reactivated BASP1 production slowed proliferation and initiated ‘self-destruct’ mechanisms in leukemia cells. These findings suggest that BASP1-oriented therapies could offer a fruitful avenue of treatment for some patients.

Calcium-dependent binding of Myc to calmodulin

The bHLH-LZ (basic region/helix-loop-helix/leucine zipper) oncoprotein Myc and the bHLH-LZ protein Max form a binary transcription factor complex controlling fundamental cellular processes. Deregulated Myc expression leads to neoplastic transformation and is a hallmark of most human cancers. The dynamics of Myc transcription factor activity are post-translationally coordinated by defined protein-protein interactions. Here, we present evidence for a second messenger controlled physical interaction between the Ca²⁺ sensor calmodulin (CaM) and all Myc variants (v-Myc, c-Myc, N-Myc, and L-Myc). The predominantly cytoplasmic Myc:CaM interaction is Ca²⁺-dependent, and the binding site maps to the conserved bHLH domain of Myc. Ca²⁺-loaded CaM binds the monomeric and intrinsically disordered Myc protein with high affinity, whereas Myc:Max heterodimers show less, and Max homodimers no affinity for CaM. NMR spectroscopic analyses using alternating mixtures of ¹⁵N-labeled and unlabeled preparations of CaM and a monomeric Myc fragment containing the bHLH-LZ domain corroborate the biochemical results on the Myc:CaM interaction and confirm the interaction site mapping. In electrophoretic mobility shift assays, addition of CaM does not affect high-affinity DNA-binding of Myc:Max heterodimers. However, cell-based reporter analyses and cell transformation assays suggest that increasing CaM levels enhance Myc transcriptional and oncogenic activities. Our results point to a possible involvement of Ca²⁺ sensing CaM in the fine-tuning of Myc function.

Replacing reprogramming factors with antibodies selected from combinatorial antibody libraries

The reprogramming of differentiated cells into induced pluripotent stem cells (iPSCs) is usually achieved by exogenous induction of transcription by factors acting in the nucleus. In contrast, during development, signaling pathways initiated at the membrane induce differentiation. The central idea of this study is to identify antibodies that can catalyze cellular de-differentiation and nuclear reprogramming by acting at the cell surface. We screen a lentiviral library encoding ∼100 million secreted and membrane-bound single-chain antibodies and identify antibodies that can replace either Sox2 and Myc (c-Myc) or Oct4 during reprogramming of mouse embryonic fibroblasts into iPSCs. We show that one Sox2-replacing antibody antagonizes the membrane-associated protein Basp1, thereby de-repressing nuclear factors WT1, Esrrb and Lin28a (Lin28) independent of Sox2. By manipulating this pathway, we identify three methods to generate iPSCs. Our results establish unbiased selection from autocrine combinatorial antibody libraries as a robust method to discover new biologics and uncover membrane-to-nucleus signaling pathways that regulate pluripotency and cell fate.

Tight binding of NAP-22 with acidic membrane lipids

Recovery of various signal transduction molecules in the detergent-resistant membrane microdomain (DRM) fraction suggests the importance of this region in cellular functions. Insolubility of the outer leaflet of DRM to the non-ionic detergent is ascribed to the tight association of cholesterol and sphingolipid. Since, poor localization of sphingolipid is observed in the inner leaflet, the physicochemical background of the insolubility of the inner leaflet is hence still an enigma. NAP-22 (also called BASP1 or CAP-23) is a neuron-enriched calmodulin-binding protein and one of the major proteins in the DRM of the neuronal cell membrane. A previous study showed the presence of several lipids in a NAP-22 fraction after the process of extraction and column chromatography. In this study, the effect of lipid extraction on NAP-22 was studied through native-gel electrophoresis, ultracentrifugation, and electron microscopic observation. The mobility of NAP-22 in native-PAGE was shifted from low to high after delipidation. Delipidated NAP-22 bound phosphatidylserine (PS), phosphatidylinosotol, and ganglioside. Some part of the mixture of PS and NAP-22 was recovered in the insoluble fraction after Triton X-100 treatment and the addition of cholesterol enhanced the amount of NAP-22 in the insoluble fraction.

Ganglioside contained in the neuronal tissue-enriched acidic protein of 22 kDa (NAP-22) fraction prepared from the detergent-resistant membrane microdomain of rat brain inhibits the phosphatase activity of calcineurin

Neurons have well-developed membrane microdomains called "rafts" that are recovered as a detergent-resistant membrane microdomain fraction (DRM). Neuronal tissue-enriched acidic protein of 22 kDa (NAP-22) is one of the major protein components of neuronal DRM. To determine the cellular function of NAP-22, interacting proteins were screened with an immunoprecipitation assay, and calcineurin (CaN) was detected. Further studies with NAP-22 prepared from DRM and CaN expressed in bacteria showed the binding of these proteins and a dose-dependent inhibitory effect of the NAP-22 fraction on the phosphatase activity of CaN. On the other hand, NAP-22 expressed in bacteria showed low binding to CaN and a weak inhibitory effect on phosphatase activity. To solve this discrepancy, identification of a nonprotein component that modulates CaN activity in the DRM-derived NAP-22 fraction was attempted. After lyophilization, a lipid fraction was extracted with chloroform/methanol. The lipid fraction showed an inhibitory effect on CaN without NAP-22, and further fractionation of the extract with thin-layer chromatography showed the presence of several lipid bands having an inhibitory effect on CaN. The mobility of these bands coincided with that of authentic ganglioside (GM1a, GD1a, GD1b, and GT1b), and authentic ganglioside showed an inhibitory effect on CaN. Treatment of lipid with endoglycoceramidase, which degrades ganglioside to glycochain and ceramide, caused a diminution of the inhibitory effect. These results show that DRM-derived NAP-22 binds several lipids, including ganglioside, and that ganglioside inhibits the phosphatase activity of CaN.

Albumin-induced apoptosis of tubular cells is modulated by BASP1

Albuminuria promotes tubular injury and cell death, and is associated with faster progression of chronic kidney disease (CKD) to end-stage renal disease. However, the molecular mechanisms regulating tubular cell death in response to albuminuria are not fully understood. Brain abundant signal protein 1 (BASP1) was recently shown to mediate glucose-induced apoptosis in tubular cells. We have studied the role of BASP1 in albumin-induced tubular cell death. BASP1 expression was studied in experimental puromycin aminonucleoside-induced nephrotic syndrome in rats and in human nephrotic syndrome. The role of BASP1 in albumin-induced apoptosis was studied in cultured human HK2 proximal tubular epithelial cells. Puromycin aminonucleoside induced proteinuria and increased total kidney BASP1 mRNA and protein expression. Immunohistochemistry localized the increased BASP1 to tubular cells. BASP1 expression colocalized with deoxynucleotidyl-transferase-mediated dUTP nick-end labeling staining for apoptotic cells. Increased tubular BASP1 expression was observed in human proteinuric nephropathy by immunohistochemistry, providing evidence for potential clinical relevance. In cultured tubular cells, albumin induced apoptosis and increased BASP1 mRNA and protein expression at 6–48 h. Confocal microscopy localized the increased BASP1 expression in albumin-treated cells mainly to the perinuclear area. A peripheral location near the cell membrane was more conspicuous in albumin-treated apoptotic cells, where it colocalized with actin. Inhibition of BASP1 expression by a BASP1 siRNA protected from albumin-induced apoptosis. In conclusion, albumin-induced apoptosis in tubular cells is BASP1-dependent. This information may be used to design novel therapeutic approaches to slow CKD progression based on protection of tubular cells from the adverse consequences of albuminuria.

Proteomic identification of the molecular basis of mammalian CNS growth cones

The growth cone, which is a unique structure with high motility that forms at the tips of extending axons and dendrites, is crucial to neuronal network formation. Axonal growth of the mammalian CNS is most likely achieved by the complicated coordination of cytoskeletal rearrangement and vesicular trafficking via many proteins. Before recent advances, no methods to identify numerous proteins existed; however, proteomics revolutionarily resolved such problems. In this review, I summarize the profiles of the mammalian growth cone proteins revealed by proteomics as the molecular basis of the growth cone functions, with molecular mapping. These results should be used as a basis for understanding the mechanisms of the complex mammalian CNS developmental process.

Transcriptional and epigenetic substrates of methamphetamine addiction and withdrawal: evidence from a long-access self-administration model in the rat

Methamphetamine use disorder is a chronic neuropsychiatric disorder characterized by recurrent binge episodes, intervals of abstinence, and relapses to drug use. Humans addicted to methamphetamine experience various degrees of cognitive deficits and other neurological abnormalities that complicate their activities of daily living and their participation in treatment programs. Importantly, models of methamphetamine addiction in rodents have shown that animals will readily learn to give themselves methamphetamine. Rats also accelerate their intake over time. Microarray studies have also shown that methamphetamine taking is associated with major transcriptional changes in the striatum measured within a short or longer time after cessation of drug taking. After a 2-h withdrawal time, there was increased expression of genes that participate in transcription regulation. These included cyclic AMP response element binding (CREB), ETS domain-containing protein (ELK1), and members of the FOS family of transcription factors. Other genes of interest include brain-derived neurotrophic factor (BDNF), tyrosine kinase receptor, type 2 (TrkB), and synaptophysin. Methamphetamine-induced transcription was found to be regulated via phosphorylated CREB-dependent events. After a 30-day withdrawal from methamphetamine self-administration, however, there was mostly decreased expression of transcription factors including junD. There was also downregulation of genes whose protein products are constituents of chromatin-remodeling complexes. Altogether, these genome-wide results show that methamphetamine abuse might be associated with altered regulation of a diversity of gene networks that impact cellular and synaptic functions. These transcriptional changes might serve as triggers for the neuropsychiatric presentations of humans who abuse this drug. Better understanding of the way that gene products interact to cause methamphetamine addiction will help to develop better pharmacological treatment of methamphetamine addicts.

Sequestration of the abrin A chain to the nucleus by BASP1 increases the resistance of cells to abrin toxicity

Abrin, a type II ribosome-inactivating protein, comprises A and B subunits wherein the A subunit harbours toxin activity and the B subunit has a galactose-specific lectin activity. The entry of the protein inside the cell is through the binding of the B chain to cell surface glycoproteins followed by receptor-mediated endocytosis and retrograde transport. A previous study from our laboratory showed that different cell lines exhibited differences of as great as ~200-fold in abrin toxicity, prompting the present study to compare the trafficking of the toxin within cells. Observations made in this regard revealed that the abrin A chain, after being released into the cytosol, is sequestered into the nucleus through interaction with a cellular protein of ~25 kDa, BASP1 (brain acid-soluble protein 1). The nuclear localization of the A chain is seen predominantly in cells that are less sensitive to abrin toxicity and dependent on the levels of BASP1 in cells. The sequestration by BASP1 renders cells increasingly resistant to the inhibition of protein synthesis by abrin and the nucleus act as a sink to overcome cellular stress induced by the toxin.

¹H, ¹³C and ¹⁵N resonance assignments of human BASP1

Brain acid-soluble protein 1 (BASP1, CAP-23, NAP-22) appears to be implicated in diverse cellular processes. An N-terminally myristoylated form of BASP1 has been discovered to participate in the regulation of actin cytoskeleton dynamics in neurons, whereas non-myristoylated nuclear BASP1 acts as co-suppressor of the potent transcription regulator WT1 (Wilms' Tumor suppressor protein 1). Here we report NMR chemical shift assignment of recombinant human BASP1 fused to an N-terminal cleavable His6-tag.

Interaction of NAP-22 with brain glutamic acid decarboxylase (GAD)

NAP-22 (also called BASP1 or CAP-23) is a neuron-enriched protein localized mainly in the synaptic vesicles and the synaptic plasma membrane. Biochemically, it is recovered in the lipid raft fraction. In order to understand the physiological function of the neuronal lipid raft, NAP-22 binding proteins were screened with a pull-down assay. Glutamic acid decarboxylase (GAD) was detected through LC-MS/MS, and Western blotting using a specific antibody confirmed the result. Two isoforms of GAD, GAD65 and GAD67, were expressed in bacteria as GST-fusion forms and the interaction with NAP-22 was confirmed in vitro. Partial co-localization of NAP-22 with GAD65 and GAD67 was also observed in cultured neurons. The binding showed no effect on the enzymatic activity of GAD65 and GAD67. These results hence suggest that NAP-22 could participate in the transport of GAD65 and GAD67 to the presynaptic termini and their retention on the synaptic vesicles as an anchoring protein.

Immunoelectron microscopic study of BASP1 and MARCKS location in the early and late rat spermatids

Immunoelectron microscopy was used to locate the proteins BASP1 and MARCKS in the post-meiotic spermatids of male rat testis. It was shown that in early spermatids, BASP1 and MARCKS accumulate in chromatoid bodies, which are characteristic organelles for these cells. During spermatogenesis, while the spermatid nucleus is still active, the chromatoid body periodically moves to the cell nucleus and absorbs the precursors of definite mRNAs and small RNAs. mRNAs are preserved in the chromatoid body until the corresponding proteins are needed, but their "fresh" mRNA cannot be formed due to the nucleus inactivation. The chromatoid body (0.5-1.5μm in diameter) has a cloud-like fibrous appearance with many fairly round cavities. In the chromatoid body, BASP1 and MARCKS are distributed mainly around the cavities and at periphery. Based on the known functions of BASP1 and MARCKS in neurons, it is conceivable that these proteins participate in non-random movements of the chromatoid body to the nucleus and in Ca(2+)-calmodulin enrichment. In late spermatids, BASP1 and MARCKS are located in the outer dense fiber layer belonging to a metabolically active spermatozoon region, the tail mid-piece. In spermatozoa, as in chromatoid body, BASP1 and MARCKS may bind Ca(2+)-calmodulin and therefore contribute to the activation of calcium-dependent biochemical processes.

Subcellular and regional location of "brain" proteins BASP1 and MARCKS in kidney and testis

Proteins BASP1 and MARCKS are abundant in axonal endings of neurons. Similarly to brain-specific protein GAP-43, BASP1 and MARCKS are reversibly bound to the plasma membrane. These proteins control both actin polymerization and actin cytoskeleton binding to the membrane. Performing these functions, BASP1 and MARCKS take part in growth cone guidance during development and in neurotransmitter secretion in adults. These activities predetermine the pivotal role of BASP1 and MARCKS in learning and memory. BASP1 and MARCKS were also found in non-nerve tissues, in particular, in the kidney and testis. Evidently, the physiological roles of these proteins differ in different tissues. Correspondingly, their intracellular location and activities may not be similar to those in neurons. In this paper, we analyze subcellular fractions (cytoplasm and nuclei) of rat kidney and testis with the purpose of determining the intracellular location of BASP1 and MARCKS. Western blots demonstrated that in these tissues, as in the brain, both proteins are present in the cytoplasm of the cell. According to our immunohistochemical study, BASP1 and MARCKS are specifically distributed in the tissues studied. In kidney, both proteins are present in cells located in glomeruli. In the testicular tubules, BASP1 is mainly expressed at the late stage of spermatogenesis (in spermatids) and is preserved in mature spermatozoa, while MARCKS appears equally during all stages of spermatogenesis. MARCKS is not found in mature spermatozoa. The results indicate that study of functions of BASP1 and MARCKS in the kidney and in the reproduction system holds much promise.

Oligomeric structure of brain abundant proteins GAP-43 and BASP1

Brain abundant proteins GAP-43 and BASP1 participate in the regulation of actin cytoskeleton dynamics in neuronal axon terminals. The proposed mechanism suggests that the proteins sequester phosphatidylinositol-4,5-diphosphate (PIP(2)) in the inner leaflet of the plasma membrane. We found that model anionic phospholipid membranes in the form of liposomes induce rapid oligomerization of GAP-43 and BASP1 proteins. Multiply charged phosphoinositides produced the most potent effect. Anionic detergent sodium dodecyl sulfate (SDS) at submicellar concentration stimulated formation of similar oligomers in solution. BASP1, but not GAP-43, also formed oligomers at sufficiently high concentration in the absence of lipids and SDS. Electron microscopy study demonstrated that the oligomers have disk-shaped or annular structure of 10-30nm in diameter. BASP1 also formed higher aggregates of linear rod-like structure, with average length of about 100nm. In outward appearance, the oligomers and linear aggregates are reminiscent of oligomers and protofibrils of amyloid proteins. Both the synthetic N-terminal peptide GAP-43(1-40) and the brain-derived fragment GAP-43-3 preserved the ability to oligomerize under the action of acidic phospholipids and SDS. On the contrary, BASP1 fragment truncated by the short N-terminal myristoylated peptide was unable to form oligomers. GAP-43 and BASP1 oligomerization can be regulated by calmodulin, which disrupts the oligomers and displaces the proteins from the membrane. We suggest that in vivo, the role of membrane-bound GAP-43 and BASP1 oligomers consists in accumulation of PIP(2) in functional clusters, which become accessible for other PIP(2)-binding proteins after dissociation of the oligomers.

BASP1 promotes apoptosis in diabetic nephropathy

Apoptosis contributes to the development of diabetic nephropathy (DN), but the mechanisms that lead to diabetes-induced cell death are not fully understood. Here, we combined a functional genomics screen for cDNAs that induce apoptosis in vitro with transcriptional profiling of renal biopsies from patients with DN. Twelve of the 138 full-length cDNAs that induced cell death in human embryonic kidney cells matched upregulated mRNA transcripts in tissue from human DN. Confirmatory screens identified induction of BASP1 in tubular cross sections of human DN tissue. In vitro, apoptosis-inducing conditions such as serum deprivation, high concentrations of glucose, and proinflammatory cytokines increased BASP1 mRNA and protein in human tubular epithelial cells. In normal cells, BASP1 localized to the cytoplasm, but in apoptotic cells, it colocalized with actin in the periphery. Overexpression of BASP1 induced cell death with features of apoptosis; conversely, small interfering RNA (siRNA)-mediated knockdown of BASP1 protected tubular cells from apoptosis. Supporting possible involvement of BASP1 in renal disease other than DN, we also observed significant upregulation of renal BASP1 in spontaneously hypertensive rats and a trend toward increased tubulointerstitial BASP1 mRNA in human hypertensive nephropathy. In summary, a combined functional genomics approach identified BASP1 as a proapoptotic factor in DN and possibly also in hypertensive nephropathy.

N-myristoylated proteins, key components in intracellular signal transduction systems enabling rapid and flexible cell responses

N-myristoylation, one of the co- or post-translational modifications of proteins, has so far been regarded as necessary for anchoring of proteins to membranes. Recently, we have revealed that N(alpha)-myristoylation of several brain proteins unambiguously regulates certain protein-protein interactions that may affect signaling pathways in brain. Comparison of the amino acid sequences of myristoylated proteins including those in other organs suggests that this regulation is involved in signaling pathways not only in brain but also in other organs. Thus, it has been shown that myristoylated proteins in cells regulate the signal transduction between membranes and cytoplasmic fractions. An algorithm we have developed to identify myristoylated proteins in cells predicts the presence of hundreds of myristoylated proteins. Interestingly, a large portion of the myristoylated proteins thought to take part in signal transduction between membranes and cytoplasmic fractions are included in the predicted myristoylated proteins. If the proteins functionally regulated by myristoylation, a posttranslational protein modification, were understood as cross-talk points within the intracellular signal transduction system, known signaling pathways could thus be linked to each other, and a novel map of this intracellular network could be constructed. On the basis of our recent results, this review will highlight the multifunctional aspects of protein N-myristoylation in brain.

Cholesterol-binding toxins and anti-cholesterol antibodies as structural probes for cholesterol localization

Cholesterol is one of the major constituents of mammalian cell membranes. It plays an indispensable role in regulating the structure and function of cell membranes and affects the pathology of various diseases. In recent decades much attention has been paid to the existence of membrane microdomains, generally termed lipid "rafts", and cholesterol, along with sphingolipids, is thought to play a critical role in raft structural organization and function. Cholesterol-binding probes are likely to provide useful tools for analyzing the distribution and dynamics of membrane cholesterol, as a structural element of raft microdomains, and elsewhere within the cell. Among the probes, non-toxic derivatives of perfringolysin O, a cholesterol-binding cytolysin, bind cholesterol in a concentration-dependent fashion with a strict threshold. They selectively recognize cholesterol in cholesterol-enriched membranes, and have been used in many studies to detect microdomains in plasma and intracellular membranes. Anti-cholesterol antibodies that recognize cholesterol in domain structures have been developed in recent years. In this chapter, we describe the characteristics of these cholesterol-binding proteins and their applications to studies on membrane cholesterol localization.

Inhibition of Myc-induced cell transformation by brain acid-soluble protein 1 (BASP1)

Cell transformation by the Myc oncoprotein involves transcriptional activation or suppression of specific target genes with intrinsic oncogenic or tumor-suppressive potential, respectively. We have identified the BASP1 (CAP-23, NAP-22) gene as a novel target suppressed by Myc. The acidic 25-kDa BASP1 protein was originally isolated as a cortical cytoskeleton-associated protein from rat and chicken brain, but has also been found in other tissues and subcellular locations. BASP1 mRNA and protein expression is specifically suppressed in fibroblasts transformed by the v-myc oncogene, but not in cells transformed by other oncogenic agents. The BASP1 gene encompasses 2 exons separated by a 58-kbp intron and a Myc-responsive regulatory region at the 5' boundary of untranslated exon 1. Bicistronic expression of BASP1 and v-myc from a retroviral vector blocks v-myc-induced cell transformation. Furthermore, ectopic expression of BASP1 renders fibroblasts resistant to subsequent cell transformation by v-myc, and exogenous delivery of the BASP1 gene into v-myc-transformed cells leads to significant attenuation of the transformed phenotype. The inhibition of v-myc-induced cell transformation by BASP1 also prevents the transcriptional activation or repression of known Myc target genes. Mutational analysis showed that the basic N-terminal domain containing a myristoylation site, a calmodulin binding domain, and a putative nuclear localization signal is essential for the inhibitory function of BASP1. Our results suggest that down-regulation of the BASP1 gene is a necessary event in myc-induced oncogenesis and define the BASP1 protein as a potential tumor suppressor.

Dehydration-induced proteome changes in the rat hypothalamo-neurohypophyseal system

The hypothalamo-neurohypophyseal system (HNS) mediates neuroendocrine responses to dehydration through the action of the antidiuretic hormone vasopressin (VP). VP is synthesized as part of a prepropeptide in magnocellular neurons of the hypothalamic supraoptic nucleus (SON) and paraventricular nucleus. This precursor is processed during transport to axon terminals in the posterior pituitary gland, in which biologically active VP is stored until mobilized for secretion by electrical activity evoked by osmotic cues. During release, VP travels through the blood stream to specific receptor targets located in the kidney in which it increases the permeability of the collecting ducts to water, reducing the renal excretion of water, thus promoting water conservation. The HNS undergoes a dramatic function-related plasticity during dehydration. We hypothesize that alterations in steady-state protein levels might be partially responsible for this remodeling. We investigated dehydration-induced changes in the SON and pituitary neurointermediate lobe (NIL) proteomes using two-dimensional fluorescence difference gel electrophoresis. Seventy proteins were altered by dehydration, including 45 in the NIL and 25 in the SON. Using matrix-assisted laser desorption/ionization mass spectrometry, we identified six proteins in the NIL (four down, two up) and nine proteins in the SON (four up, five down) that are regulated as a consequence of chronic dehydration. Results for five of these proteins, namely Hsp1alpha (heat shock protein 1alpha), NAP22 (neuronal axonal membrane protein 22), GRP58 (58 kDa glucose regulated protein), calretinin, and ProSAAS (proprotein convertase subtilisin/kexin type 1 inhibitor), have been confirmed using independent methods such as semiquantitative Western blotting, two-dimensional Western blotting, enzyme-linked immunoassay, and immunohistochemistry. These proteins may have roles in regulating and effecting HNS remodeling.

Perfringolysin O, a cholesterol-binding cytolysin, as a probe for lipid rafts

Gaining an understanding of the structural and functional roles of cholesterol in membrane lipid rafts is a critical issue in studies on cellular signaling and because of the possible involvement of lipid rafts in various diseases. We have focused on the potential of perfringolysin O (theta-toxin), a cholesterol-binding cytolysin produced by Clostridium perfringens, as a probe for studies on membrane cholesterol. We prepared a protease-nicked and biotinylated derivative of perfringolysin O (BCtheta) that binds selectively to cholesterol in cholesterol-rich microdomains of cell membranes without causing membrane lesions. Since the domains fulfill the criteria of lipid rafts, BCtheta can be used to detect cholesterol-rich lipid rafts. This is in marked contrast to filipin, another cholesterol-binding reagent, which binds indiscriminately to cell cholesterol. Using BCtheta, we are now searching for molecules that localize specifically in cholesterol-rich lipid rafts. Recently, we demonstrated that the C-terminal domain of perfringolysin O, domain 4 (D4), possesses the same binding characteristics as BCtheta. BIAcore analysis showed that D4 binds specifically to cholesterol with the same binding affinity as the full-size toxin. Cell-bound D4 is recovered predominantly from detergent-insoluble, low-density membrane fractions where raft markers, such as cholesterol, flotillin and Src family kinases, are enriched, indicating that D4 also binds selectively to lipid rafts. Furthermore, a green fluorescent protein-D4 fusion protein (GFP-D4) was revealed to be useful for real-time monitoring of cholesterol in lipid rafts in the plasma membrane. In addition, the expression of GFP-D4 in the cytoplasm might allow the investigations of intracellular trafficking of lipid rafts. The simultaneous visualization of lipid rafts in plasma membranes and inside cells might help in gaining a total understanding of the dynamic behavior of lipid rafts.

Myelin protein zero is one of the components of the detergent-resistant membrane microdomain fraction prepared from rat pituitary

Pituitary gland is a well-known endocrine tissue. The hypothalamo-neurohypophysial system, containing arginine vasopressin and oxytocin, shows a reversible morphological reorganization of both neurons and glial cells during chronic physiological stimulations. Since many signal transducing and cell adhesion molecules (CAMs) are recovered in membrane microdomain (MD) fractions, MDs are considered as signaling platforms of cells. In order to know the molecular background for these endocrine systems, we characterized MD-components derived from rat pituitary and found specific enrichment of several proteins in the fraction. One of them was identified as myelin protein zero (P0) with mass analysis and this result was further confirmed by a result that a specific antibody to this protein reacted to the authentic P0 protein in the myelin fraction of rat sciatic nerve. P0 is one of type-I transmembrane CAMs and a major structural component of mammalian peripheral nerve myelin. In mammals, expression of P0 has been considered to be restricted to peripheral nervous system. This result however indicates that P0 expresses more widely and its enrichment in the MD-fraction from rat pituitary suggests the participation in cell-cell communications.

Localization of phospholipase Cβ1 on the detergent-resistant membrane microdomain prepared from the synaptic plasma membrane fraction of rat brain

The membrane microdomain (MD), such as detergent-resistant low-density membrane microdomain fraction (DRM), has been paid much attention because many signal-transducing molecules are recovered in this fraction, although precise localization and interactions of these molecules are largely unclear. To identify neuronal MD-localized proteins, monoclonal antibodies (mAbs) against the DRM-components of synaptic plasma membrane fraction (SPM) were produced and the antigens were characterized. One of the antigens reacted with two closely positioned bands of about 140 kDa in SDS-PAGE and the antigen showed age-dependent localization on DRM. The antigen was immunoprecipitated with the mAb after partial solubilization with 0.6 M NaCl from SPM-derived DRM and identified as phospholipase C beta 1 through mass analysis. The identity was further confirmed with Western blotting using a specific polyclonal antibody. The enzyme purified from the DRM was activated by the alpha subunit of trimeric G protein, Gq, expressed in HEK293 cells. The lipid composition of the liposomes affected the enzymatic activity and the addition of NAP-22, a neuronal DRM-localized protein, inhibited the activity. These results suggest that there exists a signal-transducing MD that performs important roles in neuronal functions through PIP(2) signaling and Ca(2+) mobilization.

Biochemical and morphologic evidence of the interaction of oligodendrocyte membrane rafts with actin filaments

Cytoskeletal structures under the cell membrane carry out pivotal roles in the maintenance and remodeling of the cell structures. Reforming of the cytoskeletal networks after partial extraction of membrane components could be a good clue to identify molecular components pertaining the interaction of cytoskeleton with membrane. A detergent extract from 3-week-old rat brain membrane fraction was found to make an actin-based gel upon incubation at 25 degrees C. Some protein components of the gelation products were recovered in a Triton-insoluble low-density microdomain fraction (raft) after depolymerization of actin filaments. Some of these proteins were identified as 2',3'-cyclic nucleotide-3'-phosphodiesterase (CNPase), proteolipid protein (PLP), and myelin oligodendrocyte glycoprotein (MOG) through electrospray time-of-flight (ESI-TOF) analysis and Western blotting. Because these proteins are well-known marker proteins of oligodendrocytes, localization of these proteins and cholesterol, a raft-localized lipid, with actin filaments was studied using cultured oligodendrocytes. Clear colocalization of these proteins and cholesterol with actin filaments was observed after Triton treatment at 4 degrees C before fixation. These results indicate that raft microdomains participate in the formation of cell shape through interaction with microfilaments in oligodendrocytes.

Fibroblast growth factor 2 negatively regulates the induction of neuronal progenitors from neural stem cells

Fibroblast growth factor 2 (FGF2) exhibits pleiotropic functions during embryogenesis. In neural development, both pro- and antineurogenic activities of FGF2 have been described in the differentiation of neuronal progenitors into postmitotic neurons. We used cultured neural stem cells (NSCs) derived from rat embryonic day 14.5 cortex to determine the FGF2 effect on the induction of early neuronal progenitors. Our data showed that the presence of FGF2 during serum-induced differentiation of NSCs reduced the number of Tuj1(+) neurons. A bromodeoxyuridine (BrdU)/Tuj1 double-labeling assay and expression analyses of the pro- and antineurogenic basic helix-loop-helix (bHLH) factors showed that FGF2 blocked the generation of early neuronal progenitors, but not the cell-cycle exit of dividing neurons. This negative regulation of neuronal induction by FGF2 was associated with the persistent expression of an antineurogenic bHLH, hairy and enhancer of split (HES)-1. A gene-profiling study demonstrated that the developmental programs underlying neuronal differentiation were altered as a whole and identified several developmentally regulated, neural-enriched genes. This work shows that FGF2 exerts an antineurogenic effect during the developmental window when neuronal progenitors are first induced from NSCs. It also provides a novel experimental system that can be used to prospectively identify genes expressed at different stages of neuronal differentiation.

Nerve Ending “Signal” Proteins GAP‐43, MARCKS, and BASP1

Mechanisms of growth cone pathfinding in the course of neuronal net formation as well as mechanisms of learning and memory have been under intense investigation for the past 20 years, but many aspects of these phenomena remain unresolved and even mysterious. "Signal" proteins accumulated mainly in the axon endings (growth cones and the presynaptic area of synapses) participate in the main brain processes. These proteins are similar in several essential structural and functional properties. The most prominent similarities are N-terminal fatty acylation and the presence of an "effector domain" (ED) that dynamically binds to the plasma membrane, to calmodulin, and to actin fibrils. Reversible phosphorylation of ED by protein kinase C modulates these interactions. However, together with similarities, there are significant differences among the proteins, such as different conditions (Ca2+ contents) for calmodulin binding and different modes of interaction with the actin cytoskeleton. In light of these facts, we consider GAP-43, MARCKS, and BASP1 both separately and in conjunction. Special attention is devoted to a discussion of apparent inconsistencies in results and opinions of different authors concerning specific questions about the structure of proteins and their interactions.

Localization of the Cl(-)-ATPase activity on NAP-22 enriched membrane microdomain (raft) of rat brain

Much attention has been paid to the membrane microdomain enriched in cholesterol and sphingolipids called raft. In the central nervous system, however, the physiological role of this domain is not so evident at present, partly because of the complexity of the protein components in the raft fraction. In this study we surveyed ATPase activities in the raft fraction obtained from the synaptic plasma membrane of rat brain and found the enrichment of an ethacrynic acid-sensitive ATPase (Cl(-)-pump) activity. Immunoprecipitation experiments using antibodies to raft-localized proteins showed the co-precipitation of the ATPase activity with NAP-22, a major raft-localized protein. This result suggests the participation of the raft in the regulation of ion transport in addition to the presence of heterogeneity of raft domains in neurons.

Motor, sensory and autonomic nerve terminals containing NAP-22 immunoreactivity in the rat muscle

Neuron-enriched acidic protein having a molecular mass of 22 kDa, NAP-22, is a Ca(2+)-dependent calmodulin-binding protein and is phosphorylated with protein kinase C (PKC). This protein is localized to the biological membrane via myristoylation and found in the membrane fraction of the brain and in the synaptic vesicle fraction. Recent studies showed that NAP-22 is localized in the membrane raft domain in a cholesterol-dependent manner and suggest a role for NAP-22 in maturation and/or maintenance of nerve terminals by controlling cholesterol-dependent membrane dynamics. The present study revealed the immunohistochemical distribution of NAP-22 in the peripheral nerves in rat muscles. In all examined muscles, nerve terminals in the motor endplates showed NAP-22 immunoreactivity associated with the membranes of synaptic vesicles and nerve terminals. In the muscle spindles, annulospiral endings, which made spirals around the intrafusal muscles, showed intense NAP-22 immunoreactivity. Autonomic nerve fibers around the intramuscular blood vessels also showed the immunoreactivity for NAP-22. NAP-22 immunoreactivity in these peripheral nerves was observed from birth to adulthood (100 days after birth). Though growth-associated protein-43 (GAP-43) immunoreactivity in these nerves was observed from birth, this immunoreactivity decreased from 20 days after birth. These findings suggest that NAP-22 is distributed and regulates functions in the motor, sensory and autonomic nerve terminals in the peripheral nervous system.

The use of suppression subtractive hybridization for the study of SDF-1α induced gene-expression in human endothelial cells

Stromal cell-derived factor-1 (SDF-1), the only ligand of the CXCR4 receptor, is mainly known as a chemotactic factor for hematopoietic progenitor cells. However, studies of knock-out mice have shown malformation of different organ-systems suggesting that SDF-1 may have a role in angiogenesis and cardiac and cerebral development. However, the underlying mechanisms of its action are largely unknown. Therefore, we performed suppression subtractive hybridization (SSH) in order to identify genes that are differentially expressed after stimulation of human arterial endothelial cells (HUAEC) with SDF-1. Using SSH we found ten genes, with varied functions, whose mRNA expression is induced by SDF-1alpha in HUAEC. We show that SSH is a reliable method for identifying differentially expressed genes and that SDF-1alpha may have more functions than previously reported.

Natural N-terminal fragments of brain abundant myristoylated protein BASP1

BASP1 (also known as CAP-23 and NAP-22) is a novel myristoylated calmodulin-binding protein, abundant in nerve terminals. It is considered as a signal protein participating in neurite outgrowth and synaptic plasticity. BASP1 is also present in significant amounts in kidney, testis, and lymphoid tissues. In this study, we show that BASP1 is accompanied by at least six BASP1 immunologically related proteins (BIRPs), which are present in all animal species studied (rat, bovine, human, chicken). BIRPs have lower molecular masses than that of BASP1. Similarly to BASP1, they are myristoylated. Peptide mapping and partial sequencing have shown that BIRPs represent a set of BASP1 N-terminal fragments devoid of C-terminal parts of different length. In a definite species, the same set of BASP1 fragments is present in both brain and other tissues. The sum amount of the fragments is about 50% of the BASP1 amount in a tissue. Obligatory accompanying of BASP1 by a set of specific fragments indicates that these fragments are of physiological significance.

Molecular characterization of the detergent-insoluble cholesterol-rich membrane microdomain (raft) of the central nervous system

Many fundamental neurological issues such as neuronal polarity, the formation and remodeling of synapses, synaptic transmission, and the pathogenesis of the neuronal cell death are closely related to the membrane dynamics. The elucidation of functional roles of a detergent-insoluble cholesterol-rich domain (raft) could therefore provide good clues to the molecular understanding of these important phenomena, for the participation of the raft in the fundamental cell functions, such as signal transduction and selective transport of lipids and proteins, has been elucidated in nonneural cells. Interestingly, the brain is rich in raft and the brain-derived raft differs in its lipid and protein components from other tissue-derived rafts. Since many excellent reviews are written on the membrane lipid dynamics of this microdomain, signal transduction, and neuronal glycolipids, we review on the characterization of the raft proteins recovered in the detergent-insoluble low-density fraction from rat brain. Special focus is addressed on the biochemical characterization of a neuronal enriched protein, NAP-22, for the lipid organizing activity of this protein has become increasingly clear.

Localization of cyclic nucleotide phosphodiesterase 2 in the brain-derived Triton-insoluble low-density fraction (raft)

The cyclic nucleotides perform a variety of roles in the formation and remodeling of the neuronal interaction. The membrane microdomain called "raft" has been paid much attention, for this domain contains many signal-transducing molecules including trimeric G proteins and cytoskeletal proteins. The raft domain is recovered in a low-density fraction after the treatment of the membrane with a non-ionic detergent such as Triton X-100. The enrichment of cholesterol and sphingolipids is ascribed to be responsible for the detergent insolubility. In this study we focused on the cyclic nucleotide signaling process in rafts prepared from the cerebral cortex of 10-day-old rat and the synaptic plasma membrane fraction and found the presence of a high cAMP and cGMP phosphodiesterase (PDE) activity. The activity was effectively inhibited with erythro-9-(2-hydroxy-3-nonyl)adenine, a PDE2-specific inhibitor but not with other inhibitors such as vinpocetine, quazione, or zaprinast. Further western blotting analysis confirmed the localization of PDE2 in the raft fraction. The presence of adenylyl cyclase V/VI and PKA in the raft fraction was also shown with Western blotting. These results suggest the participation of the raft in the cyclic nucleotide signaling cascade in neurons.

The arrangement of cholesterol in membranes and binding of NAP-22

Cholesterol forms crystals when the mol fraction of sterol in a membrane bilayer exceeds a certain value. The solubility limit of cholesterol is very dependent on the nature of the phospholipid with which it is mixed. NMR methods have proven useful in quantifying the amount of cholesterol monohydrate crystals present in mixtures with phospholipids. A protein, NAP-22, present in high abundance in the synaptic cell membrane and synaptic vesicle, promotes the formation of cholesterol crystallites in lipid mixtures in which cholesterol would be completely dissolved in the membrane in the absence of protein. This finding, along with effects of the protein on the phase transitions of mixtures of phosphatidylcholine (PC) and cholesterol indicate that NAP-22 facilitates the formation of cholesterol-rich domains. This protein will bind only to membranes of PC that contain either cholesterol or phosphatidylethanolamine (PE). The process requires the presence of a myristoyl group on the N-terminus of NAP-22. The phenomenon also does not occur with a 19 amino acid myristoylated peptide corresponding to the amino terminal segment of NAP-22. The basis of the selectivity of NAP-22 for interacting with membranes of specific composition is suggested to be due to the accessibility of the myristoyl group.

Lipid binding activity of a neuron-specific protein NAP-22 studied in vivo and in vitro

There exists a microdomain called "raft" in the cell membrane. The enrichment of cholesterol and sphingolipids in its outer leaflet is well recognized. In contrast, little is known of the lipid composition of the inner leaflet of raft, where many acylated signal-transducing molecules, such as trimeric G proteins and protein tyrosine kinases, associate. NAP-22 is a neuronal protein localized on the inner leaflet of raft domain. This protein was found to bind cholesterol in the liposome. In this study, we further analyze the lipid binding activity of NAP-22 using eukaryotic and bacterial expression systems. In addition to cholesterol, NAP-22 showed a phosphatidylethanolamine (PE)- and polyphosphoinositide-dependent membrane binding in the liposome assay. The N-terminal myristoylation was essential for the liposome binding. The C-terminal deletion up to D61 showed little effect on the binding. The lipid binding region was hence judged to be in the N-terminal 60-amino-acid sequence. NAP-22 was then expressed in COS7 cells, and the intracellular localization was studied. Biochemical analysis showed the localization of NAP-22 in a Triton-insoluble low-density fraction. Cell staining analysis showed colocalization patterns of NAP-22 with PE and cholesterol in the membrane.

A new millenium for spinal cord regeneration: growth-associated genes

INTRODUCTION

Neurons surviving spinal cord injury undergo extensive reorganization that may result in the formation of functional synaptic contacts. Many neurons, however, fail to activate the necessary mechanisms for successful regeneration. In this review, we discuss the implications of growth cone genes that we have correlated with successful spinal cord axonal regeneration.

METHOD

Factors that inhibit regeneration, and activation of genes that promote it are discussed.

RESULTS/DISCUSSION

The early progress n understanding mechanisms that seem to promote or inhibit regeneration in the central nervous system may have significant clinical utility in the future.

Expression of high levels of tubulin and microtubule-associated protein 2d in the neurohypophysial astrocytes of adult rat

The hypothalamo-neurohypophysial system, containing arginine vasopressin and oxytocin, is well known to show reversible morphological reorganization for both neurons and glial cells during chronic physiological stimulation. To determine the molecular background for these morphological changes, we investigated the expression of tubulin and microtubule-associated protein (MAP) 2d in the neurohypophysial astrocytes, pituicytes of adult rats by using reverse transcription-polymerase chain reaction, western blot, and immunohistochemistry. The mRNA of MAP2d was expressed at higher levels than that of MAP2c in the neurohypophysis, cerebral cortex, and cerebellum. In contrast, predominant expression of mRNA of MAP2c was detected in the olfactory bulb. Western blot analysis showed the presence of MAP2d in the neurohypophysis, however the amount was below the detection level in the cerebral cortex and cerebellum. A double labeling study using a confocal laser scanning microscope showed intense tubulin immunoreactivity in the glial fibrillary acidic protein (GFAP)-positive pituicytes of the intact neurohypophysis. Almost no tubulin immunoreactivity was observed in the astrocytes of the intact cerebral cortex, cerebellum, and supraoptic nucleus, in contrast to strong tubulin immunoreactivity in neuronal dendrites and somata. Interestingly, intense tubulin immunoreactivity was also observed in the GFAP-positive reactive astrocytes in the immediate vicinity of the artificial lesion of the cerebral cortex. Electron microscopic observation further demonstrated the presence of a lot of microtubules in the pituicytes of intact rats.The present results demonstrate that pituicytes in the adult rat neurohypophysis expresses high levels of tubulin and MAP2d compared with normal brain astrocytes, and suggest that the ability of astrocytic morphological alteration may be at least partly ascribed to this high expression of microtubule proteins.