Neuronal Ca2+ sensor VILIP-1 leads to the upregulation of functional alpha4beta2 nicotinic acetylcholine receptors in hippocampal neurons

The neuronal Ca2+-sensor protein VILIP-1, known to affect clathrin-dependent receptor trafficking, has been shown to interact with the cytoplasmic loop of the alpha4-subunit of the alpha4beta2 nicotinic acetylcholine receptor (nAChR), which is the most abundant nAChR subtype with high-affinity for nicotine in the brain. The alpha4beta2 nAChR is crucial for nicotine addiction and the beneficial effects of nicotine on cognition. Its dysfunction has been implicated in frontal lobe epilepsy, Alzheimer's disease and schizophrenia. Here we report that overexpression of VILIP-1 enhances ACh responsiveness, whereas siRNA against VILIP-1 reduces alpha4beta2 nAChR currents of hippocampal neurons. The underlying molecular mechanism likely involves enhanced constitutive exocytosis of alpha4beta2 nAChRs mediated by VILIP-1. The two interaction partners co-localize in a Ca2+-dependent manner with syntaxin-6, a Golgi-SNARE protein involved in trans-Golgi membrane trafficking. Thus, we speculate that regulation of VILIP-1-expression might modulate surface expression of ligand-gated ion channels, such as the alpha4beta2 nAChRs, possibly comprising a novel form of physiological up-regulation of ligand-gated ion channels.

Structural determinants of alpha4beta2 nicotinic acetylcholine receptor trafficking

The structural determinants of nicotinic acetylcholine receptor (AChR) trafficking have yet to be fully elucidated. Hydrophobic residues occur within short motifs important for endoplasmic reticulum (ER) export or endocytotic trafficking. Hence, we tested whether highly conserved hydrophobic residues, primarily leucines, in the cytoplasmic domain of the alpha4beta2 AChR subunits were required for cell surface expression of alpha4beta2 AChRs. Mutation of F350, L351, L357, and L358 to alanine in the alpha4 AChR subunit attenuates cell surface expression of mutant alpha4beta2 AChRs. Mutation of F342, L343, L349, and L350 to alanine at homologous positions in the beta2 AChR subunit abolishes cell surface expression of mutant alpha4beta2 AChRs. The hydrophobic nature of the leucine residue is a primary determinant of its function because mutation of L343 to another hydrophobic amino acid, phenylalanine, in the beta2 AChR subunit only poorly inhibits trafficking of mutant alpha4beta2 AChR to the cell surface. All mutant alpha4beta2 AChRs exhibit high-affinity binding for [3H]epibatidine. In both tsA201 cells and differentiated SH-SY5Y neural cells, wild-type alpha4beta2 AChRs colocalize with the Golgi marker giantin, whereas mutant alpha4beta2 AChRs fail to do so. The striking difference between mutant alpha4 versus mutant beta2 AChR subunits on cell surface expression of mutant alpha4beta2 AChRs points to a cooperative or regulatory role for the alpha4 AChR subunit and an obligatory role for the beta2 AChR subunit in ER export. Collectively, our results identify, for the first time, residues within AChR subunits that are essential structural determinants of alpha4beta2 AChR ER export.

Long-term depression: a cellular basis for learning?

Long-term depression (LTD) comprises a persistent activity-dependent reduction in synaptic efficacy which typically occurs following repeated low frequency afferent stimulation. Hippocampal LTD has been a subject of particular interest due to the established role of the hippocampus in certain forms of information storage and retrieval. Recently, it was reported that LTD in the CA1 region may be associated with novelty acquisition in rats. CA1 LTD expression may also be increased in stressful conditions. This suggests a more complex role for this form of plasticity than the oft-cited hypothesis that it simply serves to prevent synapse saturation, by means, for example, of enabling reversal of long-term potentiation (LTP). One possibility is that LTD may be directly involved in the creation of a memory trace. Alternatively, LTD may prime a synapse in readiness for the expression of LTP, thereby contributing indirectly to information storage. There is increasing evidence that LTD is not mechanistically the reverse of LTP. Although some common processes exist, molecular, biochemical, electrophysiological and pharmacological studies all point to several quite distinct induction and maintenance mechanisms for this form of synaptic plasticity. Taken together these findings suggest that hippocampal LTD must be considered in a new light. This review focuses on the interpretation of novel and established information with regard to LTD in the hippocampal CA1 region in terms of its possible role as a cellular basis for learning and memory.

The neuronal calcium sensor protein VILIP-1 is associated with amyloid plaques and extracellular tangles in Alzheimer's disease and promotes cell death and tau phosphorylation in vitro: a link between calcium sensors and Alzheimer's disease?

To investigate whether the observed association of intracellular neuronal calcium sensor (NCS) proteins with amyloid plaques and neurofibrillar tangles in Alzheimer brains is linked to a possible neuroprotective or neurotoxic activity of the protein, we performed cytotoxicity tests in PC12 cells transfected with the calcium sensor protein VILIP-1 (visinin-like protein) and the calcium buffer protein calbindin-D28K. Whereas VILIP-1 expression enhanced the neurotoxic effect of ionomycin already at low ionophore concentrations, calbindin-D28K protected against ionomycin-induced cytotoxicity only at high ionomycin and therefore calcium concentrations. However, in double-transfected cells calbindin-D28K rescued VILIP-1-mediated cytotoxicity at low ionomycin concentrations. Since VILIP-1 was found to be associated with fibrillar tangles in Alzheimer brains, we tested whether VILIP-1 has an influence on tau hyperphosphorylation. VILIP-1 expression enhanced hyperphosphorylation of tau protein compared to nontransfected or calbindin-D28K-transfected cells. These results raise the possibility that the observed reduction in VILIP-1-expressing cells may indicate a selective vulnerability of these neurons and that the calcium sensor protein is involved in the pathophysiology of Alzheimer's disease. The calcium sensor protein may influence tau phosphorylation and have a role in calcium-mediated neurotoxicity opposed to the previously discovered protective effect of calcium buffer proteins.

Intracellular neuronal calcium sensor (NCS) protein VILIP-1 modulates cGMP signalling pathways in transfected neural cells and cerebellar granule neurones

The family of intracellular neuronal calcium-sensors (NCS) belongs to the superfamily of EF-hand proteins. Family members have been shown by in vitro assays to regulate signal cascades in retinal photoreceptor cells. To study the functions of NCS proteins not expressed in photoreceptor cells we examined Visinin-like protein-1 (VILIP-1) effects on signalling pathways in living neural cells. Visinin-like protein-1 expression increased cGMP levels in transfected C6 and PC12 cells. Interestingly, in transfected PC12 cells stimulation was dependent on the subcellular localization of VILIP-1. In cells transfected with membrane-associated wild-type VILIP-1 particulate guanylyl cyclase (GC) was stimulated more strongly than soluble GC. In contrast, deletion of the N-terminal myristoylation site resulted in cytosolic localization of VILIP-1 and enhanced stimulation of soluble GC. To study the molecular mechanisms underlying GC stimulation VILIP-1 was examined to see if it can physically interact with GCs. A direct physical interaction of VILIP-1 with the recombinant catalytic domain of particulate GCs-A, B and with native GCs enriched from rat brain was observed in GST pull-down as well as in surface plasmon resonance interaction studies. Furthermore, following trituration of recombinant VILIP-1 protein into cerebellar granule cells the protein influenced only signalling by GC-B. Together with the observed colocalization of GC-B, but not GC-A, with VILIP-1 in cerebellar granule cells, these results suggest that VILIP-1 may be a physiological regulator of GC-B.

Increased number of nitric oxide synthase immunoreactive Purkinje cells and dentate nucleus neurons in schizophrenia

There is growing interest in the cerebellum as a site of neuropathological changes in schizophrenia. Reports showing that schizophrenics have higher nitric oxide synthase (NOS) activity and MAPKinase levels in the vermis, point to possible aberrations in the cerebellar signal transduction of schizophrenics. It has been speculated that Ca(2+)-dependent extracellular to intracellular signal transduction may be disrupted in the cerebellum of schizophrenics. We decided to test this hypothesis by studying the nitrergic system and markers of the Ca(2+)-triggered signal cascade in the cerebellum of schizophrenics, depressives and controls. The cellular distribution of two calcium sensor proteins (VILIP-1 and VILIP-3) and of neuronal NOS immunoreactivity was studied morphometrically in the flocculonodulus, the inferior vermis and the dentate nucleus of 9 schizophrenics, 7 depressive patients and 9 matched controls. In comparison to controls and depressed patients there were fewer Nissl-stained neurons in the dentate nucleus of schizophrenics. The number of NOS-expressing Purkinje neurons was however strongly increased. In the flocculonodulus and the vermis no differences between the groups were found with regard to the density of Nissl-stained Purkinje cells. The number of NOS-expressing Purkinje neurons was increased in schizophrenics, however. No differences between schizophrenics, depressives and controls were found in the number of VILIP-1 immunoreactive dentate nucleus neurons and VILIP-3 immunoreactive vermal and flocculonodular Purkinje cells. Our data provide further histochemical evidence in favor of structural abnormalities in discrete cerebellar regions of schizophrenics. They confirm and extend earlier reports of increased cerebellar NOS immunoreactivity in schizophrenia and point to possible neurodevelopmental disturbances. Our failure to show an altered expression of two calcium sensor proteins possibly points to a less important role of calcium signaling in cerebellar pathology of the disease.

Ca2+-induced Ca2+ release supports the relay mode of activity in thalamocortical cells

Ca2+ ions play an important role during rhythmic bursting of thalamocortical neurons within sleep. The function of Ca2+ during the tonic relay mode of these neurons during wakefulness is less clear. Here, we report that tonic activity in thalamocortical cells results in an increase in the intracellular Ca2+ concentration and subsequent release of Ca2+ from intracellular stores mediated via ryanodine receptors (RyRs). Blockade of Ca2+ release shifted the regular firing of single action potentials toward the generation of spike clusters. Regular spike firing and intracellular Ca2+ release thus appear to be functionally coupled in a positive feedback manner, thereby supporting the relay mode of thalamocortical cells during wakefulness. Regulatory influences may be coupled to this system via the cyclic ADP ribose pathway.

The neuronal EF-hand calcium-binding protein visinin-like protein-3 is expressed in cerebellar Purkinje cells and shows a calcium-dependent membrane association

Visinin-like protein-3 is a member of the family of intracellular neuronal calcium sensors belonging to the superfamily of EF-hand proteins. Members of this family are involved in the calcium-dependent regulation of signal transduction cascades. To gain insights into the characteristics of visinin-like protein-3, we have generated specific antibodies against visinin-like protein-3 and determined the developmental and tissue distribution of the protein and its exact cellular and subcellular localization. Expression of visinin-like protein-3 protein appeared late in development mainly in the cerebellum. It is strongly expressed in cerebellar Purkinje cells. The protein expression results were further confirmed by in situ hybridization and compared with hippocalcin messenger RNA localization. Native cerebellar visinin-like protein-3 was shown to bind calcium and to associate in a calcium-dependent manner with membrane fractions during subcellular fractionation. Recombinant wild-type visinin-like protein-3 was shown to be N-terminally myristoylated in transfected cells. The membrane association was strongly reduced for the non-myristoylated mutant of visinin-like protein-3 in transfected cells. These results suggest that visinin-like protein-3, which is mainly expressed in Purkinje cells in vivo, shows a calcium-dependent association with cell membranes which is mediated by a calcium-myristoyl switch.

Regional and cellular distribution of neural visinin-like protein immunoreactivities (VILIP-1 and VILIP-3) in human brain

Neural visinin-like proteins (VILIPs) are members of the neuronal subfamily of intracellular EF-hand calcium sensor proteins termed the NCS family, which are thought to play important roles in cellular signal transduction. While numerous studies suggest a wide but uneven distribution of these proteins in rat and chicken brain, their location in, and possible significance for, the human brain, remains to be established. We used specific polyclonal antisera to map the human brain for VILIP-1 and VILIP-3 immunoreactivities. VILIP-1 was detected in cortical pyramidal cells and interneurons, septal, subthalamic and hippocampal neurons (subfields CA1 and CA4 pyramidal cells and especially hilar interneurons) as well as in cerebellar Golgi, basket, granule, stellate and dentate nucleus neurons. Purkinje cells were free of immunoreaction. VILIP-3 was more restricted in its distribution. It was identified in cerebellar Purkinje cells and a subpopulation of granule neurons. Further, neurons belonging to different nuclei of the brain stem and multiple subcortical nerve cells stained for visinin-like protein 3. A weak immunoreaction appeared in cortical and hippocampal neurons. Intracellularly the immunoreactivity appeared in the perikarya, dendrites and some axons. Sometimes, immunostaining was found in the neuropil. Glia did not express visinin-like proteins. Our findings support, from a neuroanatomical viewpoint, the idea that these calcium sensor proteins may be of relevance for neuronal signalling in the human CNS.

Novelty acquisition is associated with induction of hippocampal long-term depression

Homosynaptic long-term depression (LTD) consists of a persistent nonpathological decrease in synaptic transmission, which is induced by low-frequency stimulation. In vivo, low-frequency stimulation (1 Hz, 900 pulses) induces LTD in Wistar but not Hooded Lister rats. In this study, we investigated the influence of behavioral learning and behavioral state on the expression of LTD in both rat strains. Recordings were taken from freely moving animals that had undergone chronic implantation of a recording electrode in the hippocampal CA1 region and a bipolar stimulating electrode in the ipsilateral Schaffer collateral-commissural pathway. Exposure of the rat strains to stress induced a significant elevation in serum corticosterone levels but did not facilitate LTD expression. However, LFS given during exploration of a novel environment resulted in LTD expression in Hooded Lister, and LTD enhancement in Wistar, rats. Reexposure to the same environment did not result in new expression of LTD. Behavioral comparison between the first and second environmental exposure confirmed that the animals had habituated to the novel environment. These observations strongly implicate an association between novelty acquisition and LTD.

Intracellular neuronal calcium sensor proteins: a family of EF-hand calcium-binding proteins in search of a function

Intracellular neuronal calcium sensors (NCS) constitute a rapidly growing family of calcium-binding proteins which belong to the superfamily of EF-hand proteins. The NCS family includes as subgroups the recoverins and GCAPs (guanylyl cyclase-activating proteins), which are primarily expressed in retinal photoreceptor cells, and the frequenins and VILIPs (visinin-like proteins), which are widely but differentially expressed in the nervous system. In this review the recent developments in elucidating the functional activities of NCS proteins on signal transduction pathways in neurons are surveyed and discussed. We will focus our attention on calcium-dependent membrane association by the so-called calcium-myristoyl switch as a possible mechanism of signal transduction and on the roles of NCS proteins in intraneuronal signaling cascades, which are best studied in the visual and olfactory systems.

Subtype-specific involvement of metabotropic glutamate receptors in two forms of long-term potentiation in the dentate gyrus of freely moving rats

In this study, the role of metabotropic glutamate receptors in N-methyl-D-aspartate receptor-dependent and voltage-gated calcium channel-dependent long-term potentiation in the dentate gyrus of freely moving rats was investigated. Antagonists for group 1 metabotropic glutamate receptors ((S)-4-carboxyphenylglycine), group 1/2 metabotropic glutamate receptors ((RS)-alpha-methyl-4-carboxyphenylglycine) and group 2 metabotropic glutamate receptors ((RS)-alpha-methylserine O-phosphate monophenylester) were used. The N-methyl-D-aspartate receptor antagonist, D(-)-2-amino-5-phosphonopentanoic acid, and the L-type voltage-gated calcium channel antagonist, methoxyverapamil were used to investigate the N-methyl-D-aspartate receptor and voltage-gated calcium channel contribution to the long-term potentiation recorded. Field excitatory postsynaptic potential slope and population spike amplitude were measured. Drugs were applied, prior to tetanus, via a cannula implanted into the lateral cerebral ventricle. 200 Hz tetanization produces a long-term potentiation which is inhibited by application of D(-)-2-amino-5-phosphonopentanoic acid and (RS)-alpha-methyl-4-carboxyphenylglycine. In this study, a dose-dependent inhibition of 200 Hz long-term potentiation expression was obtained with (S)-4-carboxyphenylglycine. Long-term potentiation induced by 400 Hz tetanization was not inhibited by D(-)-2-amino-5-phosphonopentanoic acid, although the amplitude of short-term potentiation was reduced. (RS)-alpha-methyl-4-carboxyphenylglycine and (S)-4-carboxyphenylglycine, both in the presence and absence of D(-)-2-amino-5-phosphonopentanoic acid, inhibited the development of 400 Hz long-term potentiation. (RS)-alpha-methylserine O-phosphate monophenylester had no significant effect on long-term potentiation induced by either 200 or 400 Hz tetanization. Application of methoxyverapamil significantly inhibited 400 Hz long-term potentiation, but had no effect on 200 Hz long-term potentiation. These data suggest that 400 Hz long-term potentiation, induced in the presence of D(-)-2-amino-5-phosphonopentanoic acid, requires activation of L-type calcium channels. Furthermore, these results strongly support a critical role for group 1 metabotropic glutamate receptors in both N-methyl-D-aspartate receptor- and voltage-gated calcium channel-dependent long-term potentiation.

Low level expression of calcium-sensor protein VILIP induces cAMP-dependent differentiation in rat C6 glioma cells

Wild-type visinin-like-protein (VILIP) and a myristoylation-deficient VILIP mutant, when stably expressed at low levels in C6 cells, enhances or reduces the basal cAMP-level, respectively. The morphology of wild-type VILIP-transfected cells resembles that of differentiated astrocytes, whereas the myristoylation mutant shows a phenotype similar to parental cells, but with reduced cell growth. In both parental and myristoylation mutant cells a differentiated phenotype similar to that produced by wild-type VILIP-transfected cells is inducible with 8-bromo-cAMP. The changed morphology parallels an increase in the expression of the astrocytic differentiation marker glial fibrillary acidic protein (GFAP) in wild-type VILIP-transfected and cAMP-differentiated cells, but a decrease of GFAP in myristoylation mutant cells. These results suggest that depending on myristoylation, low level ectopic expression of VILIP affects basal cAMP homeostasis differentially, thereby influencing differentiation of C6 model cells.

The neuronal calcium-sensor protein VILIP modulates cyclic AMP accumulation in stably transfected C6 glioma cells: amino-terminal myristoylation determines functional activity

VILIP (visinin-like protein) is a member of the neuronal subfamily of EF-hand calcium sensor proteins. Members of this family are involved in the calcium-dependent regulation of the desensitization of signal cascades in retinal photoreceptors. To gain insight into the function of VILIP in cell signaling, we have transfected wild-type VILIP and mutant VILIP lacking the myristoylation consensus sequence into C6 glioma cells. Expression of wild-type VILIP did not significantly influence the desensitization of beta-adrenergic receptors, which are coupled to adenylyl cyclase in C6 cells. However, VILIP expression increased the beta-adrenergic receptor-stimulated cyclic AMP (cAMP) level in these cells severalfold. The stimulatory effect was also observed after direct stimulation of the adenylyl cyclase with forskolin, indicating that VILIP acts downstream of receptor and G protein in the beta-adrenergic signaling pathway in C6 cells. In contrast, the nonmyristoylated mutant of VILIP reduced cellular cAMP levels in C6 cells. Myristoylated wild-type VILIP was associated in a calcium-dependent manner with membrane fractions during subcellular fractionation, presumably owing to a calcium-myristoyl switch. In contrast, association of nonmyristoylated mutant VILIP with membranes was strongly reduced. Thus, myristoylation and most likely the calcium-dependent membrane association of VILIP are important prerequisites for the activating effect of wild-type VILIP on cAMP accumulation in C6 cells. These results suggest that VILIP acts as a calcium sensor molecule that modulates cell signaling cascades, possibly by direct or indirect regulation of adenylyl cyclase activity.

Calcium- and myristoyl-dependent subcellular localization of the neuronal calcium-binding protein VILIP in transfected PC12 cells

Wild-type neuronal calcium-binding protein VILIP (visinin-like protein), and a myristoylation mutant of VILIP which lacks the consensus sequence for N-terminal myristoylation, have been stably transfected in PC12 cells. Immunocytochemical studies of VILIP-transfected PC12 cells have revealed the wild-type VILIP is strongly concentrated at the cell membrane, particularly at cell-cell contact sites, but is also distributed throughout the cytosol at moderate levels. In contrast, myristoylation-mutant VILIP shows a more even distribution, with significantly less association at cell-cell contact sites. Western blot analysis of subcellular fractions has shown that wild-type VILIP associates in a calcium-dependent manner with membrane fractions, whereas the myristoylation mutant only weakly associates with this fraction. Therefore, a calcium-myristoyl switch seems to be a major, but not sole determinant for the association of VILIP with membranes in living cells.

The calcium-binding protein VILIP in olfactory neurons: regulation of second messenger signaling

Visinin-like-protein (VILIP), a member of the neuronal subfamily of EF-hand calcium-sensor proteins is shown to be expressed in olfactory sensory cells of the rat nasal epithelium. Its prominent localization in cilia and dendritic knobs-the chemosensory compartments of olfactory neurons-suggests that the calcium-binding protein could be involved in olfactory signal transduction. Consistent with this assumption, it was found that recombinant VILIP attenuates in a calcium-dependent manner odorant-induced cAMP formation in olfactory cilia preparations. Kinetic data indicate that VILIP does not interfere with odorant-induced receptor desensitization. Since VILIP inhibits the forskolin-induced formation of cAMP, it is conceivable that VILIP may directly affect the olfactory adenylyl cyclase. Thus, VILIP may play a role in adaptation of olfactory neurons.

The neuronal EF-hand Ca(2+)-binding protein VILIP: interaction with cell membrane and actin-based cytoskeleton

VILIP is a member of the visinin/recoverin family of neuronal EF-hand Ca(2+)-binding proteins. Cell fractionation revealed cytoplasmic, membrane- and cytoskeleton-associated pools of VILIP. The association with the cytoskeletal protein fraction is Ca(2+)-dependent and may be mediated by direct interaction with actin. This is concluded from the observations that (i) Ca(2+)-loaded recombinant VILIP binds actin in an overlay assay; (ii) in the presence of Ca(2+), beta-actin co-immunoprecipitates with native VILIP from brain extracts, and (iii) actin and VILIP are co-localized in PC12 cells stably transfected with VILIP cDNA. The interaction of VILIP with the cortical cytoskeleton through actin may facilitate a Ca(2+)-dependent recruitment of VILIP to the cell membrane.

Control of neuronal morphology in vitro: interplay between adhesive substrate forces and molecular instruction

Among the factors which influence neuronal morphology, the degree of substrate adhesivity has been suggested to play an important role in the growth and guidance of neurites. The present study was undertaken to investigate apparently contradictory results relating substrate adhesivity to the extent of neurite outgrowth. By using substrates coated with different concentrations of polyornithine to vary adhesivity, we could show that intermediate levels of neuron-to-substrate adhesive strength favored neurite outgrowth more than substrates of high or low adhesivity. However, when neurons were plated on substrates derived from the extracellular matrix, the strength of neuron-to-substrate adhesion was important for the growth of dendrite-like minor neurites, but not for the extension of axon-like major neurites, which grew independently of adhesive forces. On substrates of the cell adhesion molecule L1, growth of both major and minor neurites was adhesion-independent. Finally, in the presence of tenascin added to the culture medium, neurite growth was inhibited irrespective of the adhesivity of the substrate and the presence of substrate-bound extracellular matrix molecules or L1. These observations suggest that intermediate forces of adhesivity favor neurite growth in general, but that purely adhesive forces can be dominated by specific molecular instructions which differentially affect growth of major and minor neurites in positive and negative ways.

Functional involvement of sciatic nerve-derived versican- and decorin-like molecules and other chondroitin sulphate proteoglycans in ECM-mediated cell adhesion and neurite outgrowth

We have previously described two proteoglycans from human sciatic nerve which are immunochemically related to the chondroitin sulphate proteoglycans versican and decorin. The chondroitin sulphate of the versican-like molecule and the core protein of the decorin-like molecule have been found previously to be up-regulated after lesioning the adult mouse sciatic nerve. To investigate if the versican- and decorin-like molecules are involved in cell-extracellular matrix interactions, we studied the effect of both molecules on cell adhesion. The versican- and decorin-like molecules, substrate-coated in a mixture with fibronectin, but not with laminin or collagen types I or IV, inhibited the adhesion of several cell lines, neonatal dorsal root ganglion neurons and Schwann cells. The inhibitory activity was concentration-dependent and mediated by the chondroitin sulphate. Furthermore, when different proteoglycans were incubated with fibronectin, only the versican- and decorin-like molecules and the chondroitin sulphate proteoglycan aggrecan, but not the heparan sulphate proteoglycan perlecan, were able to inhibit fibronectin-mediated cell adhesion. The versican- and decorin-like molecules, substrate-coated alone or in a mixture with fibronectin or laminin, were at most slightly inhibitory to neurite outgrowth from PC12 phaeochromocytoma cells and neonatal dorsal root ganglion neurons. In a solid-phase ligand-binding assay the versican- and decorin-like molecules interacted with fibronectin, but not with laminin or collagen types I and IV. Binding of the versican-like molecule to fibronectin and inhibition of cell adhesion by this molecule was mediated via the heparin and cell-binding domains of fibronectin. These observations suggest that binding of the two proteoglycans to fibronectin is involved in the modulation of adhesion of cells to fibronectin.

Up-regulation of a chondroitin sulphate epitope during regeneration of mouse sciatic nerve: evidence that the immunoreactive molecules are related to the chondroitin sulphate proteoglycans decorin and versican

After transection of adult mouse sciatic nerve, the expression of a chondroitin sulphate epitope recognized by the monoclonal antibody 473-HD (mAb 473-HD) was found to be up-regulated. The epitope was localized immunocytochemically mainly in Schwann cell basal laminae and, more weakly, also in the endoneurium. In cultures of mouse dorsal root ganglion cells, Schwann cells expressed high levels but fibroblasts only low levels of the epitope. To identify the molecule(s) carrying this chondroitin sulphate epitope, human sciatic nerves were extracted with phosphate-buffered saline and shown to contain two chondroitin sulphate proteoglycans of apparent molecular weights of 130 and 900 kDa. The 900 kDa and, more weakly, the 130 kDa proteoglycan were reactive with mAb 473-HD, which was found to recognize chondroitin-6-sulphate as epitope. Following chondroitinase ABC treatment of the 130 kDa proteoglycan, a core protein of approximately 45 kDa was seen and shown to react with polyclonal antibodies against the chondroitin-dermatan sulphate proteoglycan decorin from human fibroblasts. Chondroitinase ABC treatment of the 900 kDa proteoglycan yielded a core protein with a molecular weight of approximately 400 kDa that was recognized by polyclonal antibodies against recombinantly expressed fusion proteins from human versican. After transection of adult mouse sciatic nerves, the distal nerve stumps showed up-regulation of the chondroitin-6-sulphate epitope of the 900 kDa proteoglycan, whereas the core protein of this proteoglycan did not show any detectable change in the level of expression. In contrast, the core protein of the 130 kDa proteoglycan was up-regulated in expression. These observations suggest that versican- and decorin-like molecules may contribute to successful regeneration in the peripheral nervous system of mammals.