Valproic acid inhibits adhesion of vincristine- and cisplatin-resistant neuroblastoma tumour cells to endothelium

Drug resistance to chemotherapy is often associated with increased malignancy in neuroblastoma (NB). In pursuit of alternative treatments for chemoresistant tumour cells, we tested the response of multidrug-resistant SKNSH and of vincristine (VCR)-, doxorubicin (DOX)-, or cisplatin (CDDP)-resistant UKF-NB-2, UKF-NB-3 or UKF-NB-6 NB tumour cell lines to valproic acid (VPA), a differentiation inducer currently in clinical trials. Drug resistance caused elevated NB adhesion (UKF-NB-2(VCR), UKF-NB-2(DOX), UKF-NB-2(CDDP), UKF-NB-3(VCR), UKF-NB-3(CDDP), UKF-NB-6(VCR), UKF-NB-6(CDDP)) to an endothelial cell monolayer, accompanied by downregulation of the adhesion receptor neural cell adhesion molecule (NCAM). Based on the UKF-NB-3 model, N-myc proteins were enhanced in UKF-NB-3(VCR) and UKF-NB-3(CDDP), compared to the drug naïve controls. p73 was diminished, whereas the p73 isoform deltaNp73 was upregulated in UKF-NB-3(VCR) and UKF-NB-3(CDDP). Valproic acid blocked adhesion of UKF-NB-3(VCR) and UKF-NB-3(CDDP), but not of UKF-NB-3(DOX), and induced the upregulation of NCAM surface expression, NCAM protein content and NCAM coding mRNA. Valproic acid diminished N-myc and enhanced p73 protein level, coupled with downregulation of deltaNp73 in UKF-NB-3(VCR) and UKF-NB-3(CDDP). Valproic acid also reverted enhanced adhesion properties of drug-resistant UKF-NB-2, UKF-NB-6 and SKNSH cells, and therefore may provide an alternative approach to the treatment of drug-resistant NB by blocking invasive processes.

Identification of a novel functional specificity signal within the GPI anchor signal sequence of carcinoembryonic antigen

Exchanging the glycophosphatidylinositol (GPI) anchor signal sequence of neural cell adhesion molecule (NCAM) for the signal sequence of carcinoembryonic antigen (CEA) generates a mature protein with NCAM external domains but CEA-like tumorigenic activity. We hypothesized that this resulted from the presence of a functional specificity signal within this sequence and generated CEA/NCAM chimeras to identify this signal. Replacing the residues (GLSAG) 6–10 amino acids downstream of the CEA anchor addition site with the corresponding NCAM residues resulted in GPI-anchored proteins lacking the CEA-like biological functions of integrin modulation and differentiation blockage. Transferring this region from CEA into NCAM in conjunction with the upstream proline (PGLSAG) was sufficient to specify the addition of the CEA anchor. Therefore, this study identifies a novel specificity signal consisting of six amino acids located within the GPI anchor attachment signal, which is necessary and sufficient to specify the addition of a particular functional GPI anchor and, thereby, the ultimate function of the mature protein.

Alteration in serum neural cell adhesion molecule in patients of schizophrenia

INTRODUCTION

The neural cell adhesion molecule (N-CAM) plays important roles in neural migration, synaptogenesis and CNS development. Change of N-CAM fragments in CSF of schizophrenic patients was reported previously, and we aimed to detect difference in circulating N-CAM in the serum of schizophrenic patients and healthy controls.

METHODS

Samples were from 14 chronic schizophrenic patients including 3 drug naïve patients and 11 healthy controls. After removal of albumin and globulin, N-CAM fragments were measured by Western blot technique with monoclonal antibody.

RESULTS

N-CAM immunoreactive bands were detected primarily at 180, 140, 120, 75, 68 and 52 kDa. Samples from patients and controls showed similar patterns of bands, but schizophrenic patients showed increases or decreases at some bands intensity compared to healthy controls. The 68 kDa/73-75 kDa bands intensity ratio was substantially elevated in schizophrenic patients (0.262+/-0.14 in patients, 0.065+/-0.04 in controls) especially, the three drug naïve patients had a higher value of this ratio compared to the medicated patients. One drug naïve patient showed a decrease in this ratio after one month of antipsychotic medication.

CONCLUSIONS

The results suggest elevated membrane turnover and/or abnormalities in the regulation of proteolysis of N-CAM in schizophrenia.

Reduced sialylation status in UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE)-deficient mice

Sialic acids are widely expressed as terminal carbohydrates on glycoconjugates of eukaryotic cells. They are involved in a variety of cellular functions, such as cell adhesion or signal recognition. The key enzyme of sialic acid biosynthesis is the bifunctional UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE), which catalyzes the first two steps of sialic acid biosynthesis in the cytosol. Previously, we have shown that inactivation of the GNE by gene targeting causes early embryonic lethality in mice, whereas heterozygous GNE-deficient mice are vital. In this study we compared the amount of membrane-bound sialic acids of wildtype mice with those of heterozygous GNE-deficient mice. For that we quantified membrane-bound sialic acid concentration in various organs of wildtype- and heterozygous GNE-deficient mice. We found an organ-specific reduction of membrane-bound sialic acids in heterozygous GNE-deficient mice. The overall reduction was 25%. Additionally, we analyzed transferrin and polysialylated neural cell adhesion molecule (NCAM) by one- or two-dimensional gel electrophoresis. Transferrin-expression was unchanged in heterozygous GNE-deficient mice; however the isoelectric point of transferrin was shifted towards basic pH, indicating a reduced sialylation. Furthermore, the expression of polysialic acids on NCAM was reduced in GNE-deficient mice.

Specific inhibition of GPI-anchored protein function by homing and self-association of specific GPI anchors

The functional specificity conferred by glycophosphatidylinositol (GPI) anchors on certain membrane proteins may arise from their occupancy of specific membrane microdomains. We show that membrane proteins with noninteractive external domains attached to the same carcinoembryonic antigen (CEA) GPI anchor, but not to unrelated neural cell adhesion molecule GPI anchors, colocalize on the cell surface, confirming that the GPI anchor mediates association with specific membrane domains and providing a mechanism for specific signaling. This directed targeting was exploited by coexpressing an external domain-defective protein with a functional protein, both with the CEA GPI anchor. The result was a complete loss of signaling capabilities (through integrin–ECM interaction) and cellular effect (differentiation blockage) of the active protein, which involved an alteration of the size of the microdomains occupied by the active protein. This work clarifies how the GPI anchor can determine protein function, while offering a novel method for its modulation.

A Novel α-Helix in the First Fibronectin Type III Repeat of the Neural Cell Adhesion Molecule Is Critical for N-Glycan Polysialylation

Polysialic acid is a developmentally regulated, anti-adhesive glycan that is added to the neural cell adhesion molecule, NCAM. Polysialylated NCAM is critical for brain development and plays roles in synaptic plasticity, axon guidance, and cell migration. The first fibronectin type III repeat of NCAM, FN1, is necessary for the polysialylation of N-glycans on the adjacent immunoglobulin domain. This repeat cannot be replaced by other fibronectin type III repeats. We solved the crystal structure of human NCAM FN1 and found that, in addition to a unique acidic surface patch, it possesses a novel alpha-helix that links strands 4 and 5 of its beta-sandwich structure. Replacement of the alpha-helix did not eliminate polysialyltransferase recognition, but shifted the addition of polysialic acid from the N-glycans modifying the adjacent immunoglobulin domain to O-glycans modifying FN1. Other experiments demonstrated that replacement of residues in the acidic surface patch alter the polysialylation of both N- and O-glycans in the same way, while the alpha-helix is only required for the polysialylation of N-glycans. Our data are consistent with a model in which the FN1 alpha-helix is involved in an Ig5-FN1 interaction that is critical for the correct positioning of Ig5 N-glycans for polysialylation.

The neuroligin and neurexin families: from structure to function at the synapse

Proper brain connectivity and neuronal transmission rely on the accurate assembly of neurotransmitter receptors, cell adhesion molecules and several other scaffolding and signaling proteins at synapses. Several new exciting findings point to an important role for the neuroligin family of adhesion molecules in synapse development and function. In this review, we summarize current knowledge of the structure of neuroligins and neurexins, their potential binding partners at the synapse. We also discuss their potential involvement in several aspects of synapse development, including induction, specificity and stabilization. The implication of neuroligins in cognitive disorders such as autism and mental retardation is also discussed.

Structure and function of primitive immunoglobulin superfamily neural cell adhesion molecules: a lesson from studies on planarian

Precise wiring and proper remodeling of the neural network are essential for its normal function. The freshwater planarian is an attractive animal in which to study the formation and maintenance of the neural network due to its high regenerative capability and developmental plasticity. Although a recent study revealed that homologs of netrin and its receptors are required for regeneration and maintenance of the planarian central nervous system (CNS), the roles of cell adhesion in the formation and maintenance of the planarian neural network remain poorly understood. In the present study, we found primitive immunoglobulin superfamily cell adhesion molecules (IgCAMs) in a planarian that are homologous to vertebrate neural IgCAMs. We identified planarian orthologs of NCAM, L1CAM, contactin and DSCAM, and designated them DjCAM, DjLCAM, DjCTCAM and DjDSCAM, respectively. We further confirmed that they function as cell adhesion molecules using cell aggregation assays. DjCAM and DjDSCAM were found to be differentially expressed in the CNS. Functional analyses using RNA interference revealed that DjCAM is partly involved in axon formation, and that DjDSCAM plays crucial roles in neuronal cell migration, axon outgrowth, fasciculation and projection.

NTera2: a model system to study dopaminergic differentiation of human embryonic stem cells

NTera2, a human embryonal carcinoma (EC) stem cell line, shares many characteristics with human embryonic stem cells (hESCs). To determine whether NTera2 can serve as a useful surrogate for hESCs, we compared global gene expression between undifferentiated NTera2, multiple undifferentiated hESC cell lines, and their differentiated derivatives, and we showed that NTera2 cells share multiple markers with hESCs. Similar to hESCs, NTera2 cells differentiated into TH-positive cells that express dopaminergic markers including AADC, DAT, Nurr1, TrkB, TrkC, and GFRA1 when co-cultured with PA6 cells. Flow cytometry analysis showed that tyrosine hydroxylase (TH) and neural cell adhesion molecule (NCAM) expression increased, whereas SSEA4 expression decreased as cells differentiated. Medium conditioned by PA6 cells stimulated differentiation of NTera2 cells to generate TH-positive cells that expressed dopaminergic markers. Flow cytometry selected polysialylated (PSA-NCAM) cells responded to medium conditioned by PA6 cells by differentiating into TH-positive cells and expressed dopaminergic markers. Sorted cells differentiated for 4 weeks in PA6 cell conditioned media included functional neurons that responded to neurotransmitters and exhibited electronic excitability. Therefore, NTera2 cell dopaminergic neuronal differentiation and PSA-NCAM enrichment provides a useful system for the future study of hESCs.

Modulation of the homophilic interaction between the first and second Ig modules of neural cell adhesion molecule by heparin

The second Ig module (IgII) of the neural cell adhesion molecule (NCAM) is known to bind to the first Ig module (IgI) of NCAM (so-called homophilic binding) and to interact with heparan sulfate and chondroitin sulfate glycoconjugates. We here show by NMR that the heparin and chondroitin sulfate-binding sites (HBS and CBS, respectively) in IgII coincide, and that this site overlaps with the homophilic binding site. Using NMR and surface plasmon resonance (SPR) analyses we demonstrate that interaction between IgII and heparin indeed interferes with the homophilic interaction between IgI and IgII. Accordingly, we show that treatment of cerebellar granule neurons (CGNs) with heparin inhibits NCAM-mediated outgrowth. In contrast, treatment with heparinase III or chondroitinase ABC abrogates NCAM-mediated neurite outgrowth in CGNs emphasizing the importance of the presence of heparan/chondroitin sulfates for proper NCAM function. Finally, a peptide encompassing HBS in IgII, termed the heparin-binding peptide (HBP), is shown to promote neurite outgrowth in CGNs. These observations indicate that neuronal differentiation induced by homophilic NCAM interaction is modulated by interactions with heparan/chondroitin sulfates.

Polysialylated neural cell adhesion molecule is necessary for selective targeting of regenerating motor neurons

It is well established that peripheral nerves regenerate after injury. Therefore, incomplete functional recovery usually results from misguided axons rather than a lack of regeneration per se. Despite this knowledge very little is known about the molecular mechanisms regulating axon guidance during regeneration. In the developing neuromuscular system the neural cell adhesion molecule (NCAM) and its polysialic acid (PSA) moiety are essential for proper motor axon guidance. In this study we used a well established model of nerve transection and repair to examine whether NCAM and/or PSA promotes selective regeneration of femoral motor nerves in wild-type and NCAM (-/-) mice. We found that regenerating axons innervating the muscle pathway and, to a lesser extent, cutaneous axons in the sensory pathway reexpress high levels of PSA during the time when the cut axons are crossing the lesion site. Second, we found that motor neurons in wild-type mice preferentially reinnervated muscle pathways, whereas motor neurons in NCAM (-/-) mice reinnervated muscle and cutaneous pathways with equal preference. Preferential regeneration was not observed in wild-type mice when PSA was removed enzymatically from the regenerating nerve, indicating that this form of selective motor axon targeting requires PSA. Finally, transgenic mice were used to show that the number of collateral sprouts, their field of arborization, and the withdrawal of misprojected axons were all attenuated significantly in mice lacking PSA. These results indicate that regenerating motor axons must express polysialylated NCAM, which reduces axon-axon adhesion and enables motor neurons to reinnervate their appropriate muscle targets selectively.

The intracellular concentration of sialic acid regulates the polysialylation of the neural cell adhesion molecule

Sialic acids are expressed as terminal sugars in many glycoconjugates and play an important role during development and regeneration, as they are involved as polysialic acid in a variety of cell-cell interactions mediated by the neural cell adhesion molecule NCAM. The key enzyme for the biosynthesis of sialic acid is the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine-kinase (GNE). Mutations in the binding site of the feedback inhibitor CMP-sialic acid of the GNE leads to sialuria, a disease in which patients produce sialic acid in gram scale. Here, we report on the consequences after expression of a sialuria-mutated GNE. Expression of the sialuria-mutated GNE leads to a dramatic increase of both cellular sialic acid and polysialic acid on NCAM. This could also be achieved by application of the sialic acid precursor N-acetylmannosamine. Our data suggest that biosynthesis of sialic acid regulates and limits the synthesis of polysialic acid.

Single molecule adhesion measurements reveal two homophilic neural cell adhesion molecule bonds with mechanically distinct properties

Neural cell adhesion molecule (NCAM) is a cell surface adhesion glycoprotein that plays an important role in the development and stability of nervous tissue. The homophilic binding mechanism of NCAM is still a subject of debate on account of findings that appear to support different mechanisms. This paper describes single molecule force measurements with both full-length NCAM and NCAM mutants that lack different immunoglobulin (Ig) domains. By systematically applying an external, time-dependent force to the bond, we obtained parameters that describe the energy landscape of NCAM-NCAM bonds. Histograms of the rupture forces between the full-length NCAM extracellular domains revealed two binding events, one rupturing at higher forces than the other. These bond rupture data show that the two bonds have the same dissociation rates. Despite the energetic and kinetic similarities, the bond strengths differ significantly, and are mechanically distinct. Measurements with NCAM domain deletion mutants mapped the weaker bond to the Ig1-2 segment, and the stronger bond to the Ig3 domain. Finally, the quantitative agreement between the fragment adhesion and the strengths of both NCAM bonds shows that the domain deletions considered in this study do not alter the intrinsic strengths of either of the two bonds.

Degree of polymerization (DP) of polysialic acid (polySia) on neural cell adhesion molecules (N-CAMS): development and application of a new strategy to accurately determine the DP of polySia chains on N-CAMS

Alpha2,8-linked polysialic acid (polySia) is a structurally unique antiadhesive glycotope that covalently modifies N-linked glycans on neural cell adhesion molecules (N-CAMs). These sugar chains play a key role in modulating cell-cell interactions, principally during embryonic development, neural plasticity, and tumor metastasis. The degree of polymerization (DP) of polySia chains on N-CAM is postulated to be of critical importance in regulating N-CAM function. There are limitations, however, in the conventional methods to accurately determine the DP of polySia on N-CAM, the most serious being partial acid hydrolysis of internal alpha2,8-ketosidic linkages that occur during fluorescent derivatization, a step necessary to enhance chromatographic detection. To circumvent this problem, we have developed a facile method that combines the use of Endo-beta-galactosidase to first release linear polySia chains from N-CAM, with high resolution high pressure liquid chromatography profiling. This strategy avoids acid hydrolysis prior to chromatographic profiling and thus provides an accurate determination of the DP and distribution of polySia on N-CAM. The potential of this new method was evaluated using a nonpolysialylated construct of N-CAM that was polysialylated in vitro using a soluble construct of ST8Sia II or ST8Sia IV. Whereas most of the oligosialic acid/polySia chains consisted of DPs approximately 50-60 or less, a subpopulation of chains with DPs approximately 150 to approximately 180 and extending to DP approximately 400 were detected. The DP of this subpopulation is considerably greater than reported previously for N-CAM. Endo-beta-galactosidase can also release polySia chains from polysialylated membranes expressed in the neuroblastoma cell line, Neuro2A, and native N-CAM from embryonic chick brains.

Two types of detergent-insoluble, glycosphingolipid/cholesterol-rich membrane domains from isolated myelin

Two different types of low-density detergent-insoluble glycosphingolipid-enriched membrane domain (DIG) fractions were isolated from myelin by extraction with Triton X-100 (TX-100) in 50 mM sodium phosphate buffer at room temperature (20 degrees C) (procedure 1), in contrast to a single low-density fraction obtained by extraction with TX-100 in Tris buffer containing 150 mM NaCl and 5 mM EDTA at 4 degrees C (procedure 2). Procedure 1 has been used in the past by others for myelin extraction to preserve the cytoskeleton and/or radial component of oligodendrocytes and myelin, whereas procedure 2 is now more commonly used to isolate myelin DIG fractions. The two DIG fractions obtained by procedure 1 gave opaque bands, B1 and B2, at somewhat lower and higher sucrose density respectively than myelin itself. The single DIG fraction obtained by procedure 2 gave a single opaque band at a similar sucrose density to B1. Both B1 and B2 had characteristics of lipid rafts, i.e. high galactosylceramide and cholesterol content and enrichment in GPI-linked 120-kDa neural cell adhesion molecule (NCAM)120, as found by others for the single low-density DIG fraction obtained by procedure 2. However, B2 had most of the myelin GM1 and more of the sulfatide than B1, and they differed significantly in their protein composition. B2 contained 41% of the actin, 100% of the tubulin, and most of the flotillin-1 and caveolin in myelin, whereas B1 contained more NCAM120 and other proteins than B2. The single low-density DIG fraction obtained by procedure 2 contained only low amounts of actin and tubulin. B1 and B2 also had size-isoform selectivity for some proteins, suggesting specific interactions and different functions of the two membrane domains. We propose that B1 may come from non-caveolar raft domains whereas B2 may derive from caveolin-containing raft domains associated with cytoskeletal proteins. Some kinases present were active on myelin basic protein suggesting that the DIGs may come from signaling domains.

Structural biology of NCAM homophilic binding and activation of FGFR

In this review, we analyse the structural basis of the homophilic interactions of the neural cell adhesion molecule (NCAM) and the NCAM-mediated activation of the fibroblast growth factor receptor (FGFR). Recent structural evidence suggests that NCAM molecules form cis-dimers in the cell membrane through a high affinity interaction. These cis-dimers, in turn, mediate low affinity trans-interactions between cells via formation of either one- or two-dimensional 'zippers'. We provide evidence that FGFR is probably activated by NCAM very differently from the way by which it is activated by FGFs, reflecting the different conditions for NCAM-FGFR and FGF-FGFR interactions. The affinity of FGF for FGFR is approximately 10(6) times higher than that of NCAM for FGFR. Moreover, in the brain NCAM is constantly present on the cell surface in a concentration of about 50 microm, whereas FGFs only appear transiently in the extracellular environment and in concentrations in the nanomolar range. We discuss the structural basis for the regulation of NCAM-FGFR interactions by two molecular 'switches', polysialic acid (PSA) and adenosine triphosphate (ATP), which determine whether NCAM acts as a signalling or an adhesion molecule.

NCAM 180 acting via a conserved C-terminal domain and MLCK is essential for effective transmission with repetitive stimulation

NCAM 180 isoform null neuromuscular junctions are unable to effectively mobilize and exocytose synaptic vesicles and thus exhibit periods of total transmission failure during high-frequency repetitive stimulation. We have identified a highly conserved C-terminal (KENESKA) domain on NCAM that is required to maintain effective transmission and demonstrate that it acts via a pathway involving MLCK and probably myosin light chain (MLC) and myosin II. By perfecting a method of introducing peptides into adult NMJs, we tested the hypothesized role of proteins in this pathway by competitive disruption of protein-protein interactions. The effects of KENESKA and other peptides on MLCK and MLC activation and on failures in both wild-type and NCAM 180 null junctions supported this pathway, and serine phosphorylation of KENESKA was critical. We propose that this pathway is required to replenish synaptic vesicles utilized during high levels of exocytosis by facilitating myosin-driven delivery of synaptic vesicles to active zones or their subsequent exocytosis.

Multiple-bond kinetics from single-molecule pulling experiments: evidence for multiple NCAM bonds

The kinetic parameters of single bonds between neural cell adhesion molecules were determined from atomic force microscope measurements of the forced dissociation of the homophilic protein-protein bonds. The analytical approach described provides a systematic procedure for obtaining rupture kinetics for single protein bonds from bond breakage frequency distributions obtained from single-molecule pulling experiments. For these studies, we used the neural cell adhesion molecule (NCAM), which was recently shown to form two independent protein bonds. The analysis of the bond rupture data at different loading rates, using the single-bond full microscopic model, indicates that the breakage frequency distribution is most sensitive to the distance to the transition state and least sensitive to the molecular spring constant. The analysis of bond failure data, however, motivates the use of a double-bond microscopic model that requires an additional kinetic parameter. This double-bond microscopic model assumes two independent NCAM-NCAM bonds, and more accurately describes the breakage frequency distribution, particularly at high loading rates. This finding agrees with recent surface-force measurements, which showed that NCAM forms two spatially distinct bonds between opposed proteins.

Adrenal Chromaffin Cells Exhibit Impaired Granule Trafficking in NCAM Knockout Mice

Neural cell adhesion molecule (NCAM) plays several critical roles in neuron path-finding and intercellular communication during development. In the clinical setting, serum NCAM levels are altered in both schizophrenic and autistic patients. NCAM knockout mice have been shown to exhibit deficits in neuronal functions including impaired hippocampal long term potentiation and motor coordination. Recent studies in NCAM null mice have indicated that synaptic vesicle trafficking and active zone targeting are impaired, resulting in periodic synaptic transmission failure under repetitive physiological stimulation. In this study, we tested whether NCAM plays a role in vesicle trafficking that is limited to the neuromuscular junction or whether it may also play a more general role in transmitter release from other cell systems. We tested catecholamine release from neuroendocrine chromaffin cells in the mouse adrenal tissue slice preparation. We utilize electrophysiological and electrochemical measures to assay granule recruitment and targeting in wild-type and NCAM −/− mice. Our data show that NCAM −/− mice exhibit deficits in normal granule trafficking between the readily releasable pool and the highly release-competent immediately releasable pool. This defect results in a decreased rate of granule fusion and thus catecholamine release under physiological stimulation. Our data indicate that NCAM plays a basic role in the transmitter release mechanism in neuroendocrine cells through mediation of granule recruitment and is not limited to the neuromuscular junction and central synapse active zones.

Binding of Madindoline A to the Extracellular Domain of gp130†

Elevated levels of IL-6 and IL-11 are associated with multiple myeloma, rheumatoid arthritis, hypercalcemia, cancer cachexia, and Castleman's disease. Madindoline A (MadA), isolated from Streptomyces nitrosporeus K93-0711, specifically inhibits the growth of IL-6- and IL-11-dependent cell lines, most likely by interfering with the homodimerization of gp130. This raises the possibility that MadA can be used as a model compound for the development of novel chemotherapeutic agents. In this report, we demonstrate that the binding of MadA to gp130 is specific and noncovalent, and displays a relatively low affinity. Furthermore, we show that the tricyclic 3a-hydroxytetrahydrofuro[2,3-b]indole (HFI) moiety of MadA alone is not sufficient for binding. Matrix-bound MadA precipitates a protein composed of the extracellular domain of gp130 fused to the Fc region of the immunoglobulin heavy chain. Binding is inhibited in a dose-dependent manner by preincubation with free MadA. The K(D) for binding of MadA to gp130 is 288 microM, as determined by surface plasmon resonance (SPR)-based biosensor analysis. The HFI portion of MadA does not bind to gp130 in either affinity precipitation or SPR analyses. Finally, MadA, but not the HFI portion, inhibits IL-6-dependent Stat3 tyrosine phosphorylation in HepG2 cells.

Fluorometric cell-ELISA for quantifying rabies infection and heparin inhibition

The purpose of the present study was to implement a fluorometric method for detecting and quantifying viral antigens in human meduloblastoma cells infected by two types of fixed rabies virus (CVS-MB and CVS-BHK) and a street virus using a cell-enzyme linked immunosorbent assay (cell-ELISA) technique; alkaline phosphatase was used as the antibody-marker enzyme and 4-methyl-umbelliferyl-phosphate as the fluorogenic substrate. The system was used for detecting up to 1:10,000 viral inoculums, followed by evaluating the effect of heparin on infection. Infected cultures were reliably differentiated from their respective negative controls in both assays allowing data to be analysed statistically. As reported in another study, heparin produces strong inhibition when the CVS-BHK viral strain is used for infection; it has thus been suggested that it binds to the neural cell adhesion molecule and could be blocked by using this drug. This fluorometric method is less time-consuming, has increased reproducibility and useful for quantitation of collected data and can therefore be considered as a useful tool for research.

Molecular cloning and analysis of the mouse gicerin gene

Gicerin is a cell adhesion molecule, which has five immunoglobulin-like loop structures in an extracellular domain followed by a single transmembrane domain and a short cytoplasmic tail. We have reported that gicerin participates in neurite extension and structural organization of the nervous system, and its expression in the nervous system is high during the development and dramatically decreased after birth. To elucidate the mechanism how the expression of gicerin is regulated, we performed a genomic cloning of a mouse gicerin. A fragment of 16 kbp genomic clone contained 8 kbp gicerin gene composed of 16 exons with 6 kbp upstream region. Genomic cloning revealed that two isoforms of gicerin were generated by an alternative splicing of exon 15 results in cytoplasmic domains composed of either 63 or 21 amino acids. As for an expressional regulation of gicerin, we found that the mRNA content of gicerin in PC12 cells was regulated by cAMP. Quantitative-PCR analysis revealed that forskolin induced four-fold increase of gicerin mRNA. To characterize the involvement of its promoter region, we examined the promoter activity in PC12 cells by a luciferase-reporter assay. We found that a CRE site located at 60 bp upstream of gicerin gene was responsible for the increase of its mRNA induced by forskolin.

Novel Cytosolic Binding Partners of the Neural Cell Adhesion Molecule: Mapping the Binding Domains of PLCγ, LANP, TOAD-64, Syndapin, PP1, and PP2A

The neural cell adhesion molecule (NCAM) is implicated in important functions during development and maintenance of the nervous system. Two of the three major isoforms, NCAM 140 and NCAM 180, are transmembrane glycoproteins with large cytoplasmic domains of different length. The purpose of this study was to identify novel intracellular binding partners of NCAM 140 and NCAM 180. We expressed both cytoplasmic domains, as well as cytoplasmic fragments of NCAM, as fusion proteins in Escherichia coli and used them for ligand affinity chromatography or glutathione S-transferase (GST) pull-down assays. By peptide mass fingerprinting Western blot analysis, or both, we identified PLCgamma, LANP, syndapin, PP1, and PP2A as binding partners for both NCAM 140 and NCAM 180, whereas TOAD-64 was identified as a NCAM 180-specific interacting protein. Furthermore, we were able to show that binding of these novel binding proteins, as well as the previously described interaction partners ROK alpha (rho A binding kinase alpha) and alpha- and beta-tubulin, bind to specific cytosolic sequences of NCAM. For this purpose, we performed GST pull-down experiments using cytosolic fragments of NCAM as GST-fusion proteins and cytosolic- or cytoskeleton-enriched protein fractions of rat brain.

Triple Effect of Mimetic Peptides Interfering with Neural Cell Adhesion Molecule Homophilic Cis Interactions

The neural cell adhesion molecule (NCAM) is pivotal in neural development, regeneration, and learning. Here we characterize two peptides, termed P1-B and P2, derived from the homophilic binding sites in the first two N-terminal immunoglobulin (Ig) modules of NCAM, with regard to their effects on neurite extension and adhesion. To evaluate how interference of these mimetic peptides with NCAM homophilic interactions in cis influences NCAM binding in trans, we employed a coculture system in which PC12-E2 cells were grown on monolayers of fibroblasts with or without NCAM expression and the rate of neurite outgrowth subsequently was analyzed. P2, but not P1-B, induced neurite outgrowth in the absence of NCAM binding in trans. When PC12-E2 cells were grown on monolayers of NCAM-expressing fibroblasts, the effect of both P1-B and P2 on neurite outgrowth was dependent on peptide concentrations. P1-B and P2 acted as conventional antagonists, agonists, and reverse agonists of NCAM at low, intermediate, and high peptide concentrations, respectively. The demonstrated in vitro triple pharmacological effect of mimetic peptides interfering with the NCAM homophilic cis binding will be valuable for the understanding of the actions of these mimetics in vivo.

Simulation of proliferation of neural stem cells on a surface with emphasis on spatial constraints on cell division

We present Monte Carlo lattice simulations of proliferation of cells on a surface in the situation when the cell-cell adhesion is relatively strong and the cells may form islands and/or flattened hemispheres. The model parameters were chosen to mimic proliferation of adult rat neural stem cells (or, more specifically, adult hippocampal progenitor cells) deposited on polyornithine and laminin coated polystyrene. The results obtained show that the spatial constraints on cell division may result in slowdown of the exponential growth. Depending on the rules used for cell division, this effect may be either nearly negligible or appreciable. In the latter case, the scale of the deviations from the exponential growth is comparable with that observed in our experiments. In the simulations, the slowdown of the growth starts however somewhat earlier and occurs in a less abrupt manner. This seems to indicate that the spatial constraints on division of cells are not the main factor behind the experimentally observed termination of the growth.