Characterization and tissue distribution of opioid-binding cell adhesion molecule (OBCAM) using monoclonal antibodies

Neuronal Wiring Receptors Dprs and DIPs Are GPI Anchored and This Modification Contributes to Their Cell Surface Organization

The Drosophila Dpr and DIP proteins belong to the immunoglobulin superfamily of cell surface proteins (CSPs). Their hetero- and homophilic interactions have been implicated in a variety of neuronal functions, including synaptic connectivity, cell survival, and axon fasciculation. However, the signaling pathways underlying these diverse functions are unknown. To gain insight into Dpr-DIP signaling, we sought to examine how these CSPs are associated with the membrane. Specifically, we asked whether Dprs and DIPs are integral membrane proteins or membrane anchored through the addition of glycosylphosphatidylinositol (GPI) linkage. We demonstrate that most Dprs and DIPs are GPI anchored to the membrane of insect cells and validate these findings for some family members in vivo using Drosophila larvae, where GPI anchor cleavage results in loss of surface labeling. Additionally, we show that GPI cleavage abrogates aggregation of insect cells expressing cognate Dpr-DIP partners. To test if the GPI anchor affects Dpr and DIP localization, we replaced it with a transmembrane domain and observed perturbation of subcellular localization on motor neurons and muscles. These data suggest that membrane anchoring of Dprs and DIPs through GPI linkage is required for localization and that Dpr-DIP intracellular signaling likely requires transmembrane coreceptors.

The Role of IgLON Cell Adhesion Molecules in Neurodegenerative Diseases

In the brain, cell adhesion molecules (CAMs) are critical for neurite outgrowth, axonal fasciculation, neuronal survival and migration, and synapse formation and maintenance. Among CAMs, the IgLON family comprises five members: Opioid Binding Protein/Cell Adhesion Molecule Like (OPCML or OBCAM), Limbic System Associated Membrane Protein (LSAMP), neurotrimin (NTM), Neuronal Growth Regulator 1 (NEGR1), and IgLON5. IgLONs exhibit three N-terminal C2 immunoglobulin domains; several glycosylation sites; and a glycosylphosphatidylinositol anchoring to the membrane. Interactions as homo- or heterodimers in cis and in trans, as well as binding to other molecules, appear critical for their functions. Shedding by metalloproteases generates soluble factors interacting with cellular receptors and activating signal transduction. The aim of this review was to analyse the available data implicating a role for IgLONs in neuropsychiatric disorders. Starting from the identification of a pathological role for antibodies against IgLON5 in an autoimmune neurodegenerative disease with a poorly understood mechanism of action, accumulating evidence links IgLONs to neuropsychiatric disorders, albeit with still undefined mechanisms which will require future thorough investigations.

Glycosylphosphatidylinositol-Anchored Immunoglobulin Superfamily Cell Adhesion Molecules and Their Role in Neuronal Development and Synapse Regulation

Immunoglobulin superfamily (IgSF) cell adhesion molecules (CAMs) are cell surface glycoproteins that not only mediate interactions between neurons but also between neurons and other cells in the nervous system. While typical IgSF CAMs are transmembrane molecules, this superfamily also includes CAMs, which do not possess transmembrane and intracellular domains and are instead attached to the plasma membrane via a glycosylphosphatidylinositol (GPI) anchor. In this review, we focus on the role GPI-anchored IgSF CAMs have as signal transducers and ligands in neurons, and discuss their functions in regulation of neuronal development, synapse formation, synaptic plasticity, learning, and behavior. We also review the links between GPI-anchored IgSF CAMs and brain disorders.

Expression of ovarian tumour suppressor OPCML in the female CD-1 mouse reproductive tract

Opioid binding protein/cell adhesion molecule-like gene (OPCML) is frequently inactivated in epithelial ovarian cancer, but the role of this membrane protein in normal reproductive function is unclear. The ovarian surface epithelium (OSE) is thought to be the cell of origin of most epithelial ovarian cancers, some of which arise after transformation of OSE cells lining ovarian inclusion cysts, formed during ovulation. We used immunohistochemistry, immunoblotting and quantitative RT-PCR (qRT-PCR) to investigate OPCML expression in the uteri and ovaries of cycling 3-month CD-1 mice, as well as in ovaries from older mice containing inclusion cysts derived from rete ovarii tubules. Immunoblotting showed OPCML bands in uterine, but not whole ovarian or muscle extracts. Strong OPCML immunoreactivity was observed in oviduct, rete ovarii and uterus, whereas in ovary more immunoreactivity was seen in granulosa cells than OSE. No staining was observed in OSE around ovulation sites, where OSE cells divide to cover the site. OPCML immunoreactivity was also weaker in more dysplastic cells lining large ovarian inclusion cysts, compared with normal rete ovarii. No significant changes in Opcml mRNA expression were observed in whole ovarian and uterine extracts at different stages of the cycle. We conclude that murine OPCML is more consistently expressed in cells lining the uterus, oviduct and rete ovarii than in ovary and is not expressed in OSE associated with ovulation sites. This observation supports the hypothesis that a proportion of epithelial ovarian cancers arise from ductal cells and other epithelia of the secondary Mullerian system, rather than the OSE.

Glycosylation analysis of IgLON family proteins in rat brain by liquid chromatography and multiple-stage mass spectrometry

IgLON family proteins, including limbic-associated membrane protein (LAMP), opioid-binding cell adhesion molecule (OBCAM), neurotrimin, and Kilon, are immunoglobulin (Ig) superfamily cell adhesion molecules. These molecules are composed of three Ig domains and a glycosylphosphatidylinositol (GPI) anchor and contain six or seven potential N-glycosylation sites. Although their glycosylations are supposed to be associated with the development of the central nervous system like other Ig superfamily proteins, they are still unknown because of difficulty in isolating individual proteins with a high degree of homology in performing carbohydrate analysis. In this study, we conducted simultaneous site-specific glycosylation analysis of rat brain IgLON proteins by liquid chromatography and multiple-stage mass spectrometry (LC-MS ( n )). The rat brain GPI-linked proteins were enriched and separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The four proteins were extracted from the gel, and subjected to LC-MS ( n ) after proteinase digestions. A set of glycopeptide MS data, including the mass spectrum, the mass spectrum in the selected ion monitoring mode, and the product ion spectra, was selected from all data based on carbohydrate-related ions in the MS/MS spectrum. The peptide portion and the carbohydrate structure were identified on the basis of peptide-related ion and carbohydrate-related ions, and the accurate mass. The site-specific glycosylations of four proteins were elucidated as follows. N-Glycans near the N-terminal were disialic acid-conjugated complex- and hybrid-type oligosaccharides. The first Ig domains were occupied by Man-5-9. Diverse oligosaccharides, including Lewis a/x-modified glycans, a brain-specific glycan known as BA-2, and Man-5, were found to be attached to the third Ig domain. Three common structures of glycans were found in the GPI moiety of LAMP, OBCAM, and neurotrimin.

Synaptic adhesion molecule OBCAM; synaptogenesis and dynamic internalization

Opioid-binding cell adhesion molecule (OBCAM) is the member of the IgLON family, a subgroup of the immunoglobulin superfamily. In the present study, the functions and dynamics of OBCAM were investigated in hippocampal neurons in vitro. Western blotting revealed that OBCAM expression was low at early stages of culture but it was increased as culture development. Double labeling immunofluorescence microscopy showed that OBCAM immunoreactivity was localized mainly at postsynaptic spines labeled with phalloidin and anti-PSD-95. The inhibition of OBCAM function with the specific antibody resulted in a significant decrease in the number of synapses on dendrites compared with control mouse IgG. The suppression of OBCAM expression using the antisense oligodeoxynucleotide also impaired the formation of synapses compared with control universal ones. The overexpression of OBCAM mRNA using a plasmid vector augmented the formation of synapses. Moreover, the internalization of OBCAM was promoted with increased neuronal activity by 4-aminopyridine. This internalization was reduced with the treatment of filipin, a sterol agent, indicating that this process is a raft-dependent pathway. These results indicate that OBCAM is a synaptic cell adhesion molecule concerning synaptogenesis and its surface localization is dynamically regulated in response to neuronal activity.

Postnatal expression profile of OBCAM implies its involvement in visual cortex development and plasticity

This study examined the expression of a neuron-specific cell adhesion molecule, OBCAM (opioid-binding cell adhesion molecule), at both the mRNA and protein levels in the cat primary visual cortex at various postnatal ages, using cDNA array analysis and immunocytochemistry. Results obtained using both methods showed that the expression level of OBCAM was high in young and low in older and adult visual cortex. OBCAM-immunoreactivities were associated predominantly with perikarya and dendrites of pyramidal neurons, and OBCAM-immunopositive neurons were present in all cortical layers. Immunostaining of OBCAM in adult visual cortex showed a reduced number of immunopositive neurons and neurites and relatively lower staining intensities as compared with younger animals. In addition, the number of OBCAM-immunopositive neurons was significantly higher in the visual cortex of 4-month-old animals dark-reared from birth than those in age-matched normally reared animals. These results suggest that OBCAM may play an important role in visual cortex development and plasticity.

Polarized targeting of IgLON cell adhesion molecule OBCAM to dendrites in cultured neurons

Opioid-binding cell adhesion molecule (OBCAM) belongs to the immunoglobulin superfamily CAMs and shows a dendritically polarized distribution in hypothalamic magnocellular neurons. In the present study, the cellular localization of OBCAM was monitored in cultured cortical and hippocampal neurons to examine its polarized distribution. Double labeling immunofluorescence microscopy after fixation showed only faint OBCAM immunoreactivity in the neuronal somata during the early stages of culture, whereas the immunoreactivity was strong in MAP2-positive somata and dendrites of fully polarized neurons after longer culture. Moreover, the immunoreactivity for OBCAM showed a punctate pattern in the dendrites similar to the immunostaining pattern of synapsin I. High resolution revealed close apposition with only a partial overlap of synapsin I and OBCAM immunoreactivities, suggesting the synaptic localization of OBCAM to the dendrites. When the fully polarized neurons were reacted with anti-OBCAM antibody before fixation, OBCAM immunoreactivity became stronger on the dendritic surface than the somatic surface. Extracellular immunoreactivity was eliminated with phosphatidylinositol-specific phospholipase C and this immunoreactivity resisted extraction with the nonionic detergent Triton X-100 at 4 degrees C, indicating that OBCAM is attached to the rafts via a glycosylphosphatidyl inositol anchor. These results indicate that OBCAM is efficiently targeted to the dendritic surface of fully polarized cortical and hippocampal neurons. OBCAM is, hence, concluded to be a dendrite-associated CAM in cortical and hippocampal neurons as in hypothalamic magnocellular neurons.

Biochemical and ultrastructural analyses of IgLON cell adhesion molecules, Kilon and OBCAM in the rat brain

Kilon (kindred of IgLON) and opioid-binding cell adhesion molecule belong to the IgLON subgroup of immunoglobulin superfamily together with the limbic system-associated membrane protein and neurotrimin. In the present study, we have analyzed biochemical and ultrastructural characterization of Kilon and opioid-binding cell adhesion molecule such as regional and developmental expression patterns, light and electron microscopic localization, and intermolecular interactions. Western blotting revealed a widespread distribution pattern of Kilon with high expression levels in the olfactory bulb, cerebral cortex, diencephalon, hippocampus, and cerebellum and low expression levels in the medulla oblongata and spinal cord. In contrast, opioid-binding cell adhesion molecule showed a regionally restricted expression pattern with high levels only in the cerebral cortex and hippocampus. Expression of Kilon and opioid-binding cell adhesion molecule was increased gradually during postnatal development and maintained until adulthood. Light microscopic immunohistochemistry demonstrated that the localization of opioid-binding cell adhesion molecule and Kilon coincided well with that of vesicle-associated membrane protein 2, a synaptic marker protein, in the cerebral cortex and hippocampus of adult brain. In the cerebellum, Kilon-immunoreactive puncta were observed to colocalize well with that of vesicle-associated membrane protein 2, while opioid-binding cell adhesion molecule immunoreactivity was observed only at part of synaptic glomeruli in the granular layer and rare in the molecular layer. Electron microscopic analysis revealed that Kilon and opioid-binding cell adhesion molecule immunoreactivity was observed mainly at postsynaptic sites of dendritic and somatic synapses in adult cerebral cortex and hippocampus. Only trace levels of Kilon and opioid-binding cell adhesion molecule were detected in the soluble fraction of a cortical homogenate, although a substantial amount of F3 was present in the soluble fraction. A binding analysis using a cross-linker and the immunoprecipitation technique demonstrated that Kilon and opioid-binding cell adhesion molecule interacted heterophilically and homophilically. These findings show that Kilon and opioid-binding cell adhesion molecule are clearly distinguishable from each other in regional expression and localization, and binding patterns. These differences possibly represent diverse functions of each IgLON molecule.

Gene expression patterns during enhanced periods of visual cortex plasticity

During a critical period in its postnatal development the mammalian visual cortex displays susceptibility to experience-dependent alterations of neuronal response properties. Plasticity represents an integrated set of developmental processes controlled by a transcriptional hierarchy that coordinates the action of many genes. To illuminate the expression of these critical genes, we examined gene expression patterns of 18371 non-redundant cDNAs in the visual cortex of cats at birth, at eye opening, at the peak of the critical period of eye dominance plasticity and in the adult cat using filter-based cDNA arrays and software-based hierarchical cluster analysis. We identified a small set of genes that were selectively expressed during the peak of the critical period for plasticity. We further examined the patterns of expression of these genes by analyzing the gene expression pattern of dark-reared chronologically older animals that are known to retain this ocular dominance plasticity beyond the chronologically defined critical period. This additional cluster assessment allowed us to separate age-related changes in the patterns of gene expression from plasticity-related changes, thus identifying a subset of genes that we define as plasticity candidate genes. Those plasticity candidate genes that have previously characterized functions include participants in second messenger systems, in cell adhesion, in transmitter recycling and cytokines, among others. Comparison of cDNA array quantitation with reverse transcription-polymerase chain reaction showed almost identical expression profiles for three genes that we examined. The expression pattern of one identified gene, opioid binding cell adhesion molecule, from the cDNA array analysis, is also in agreement with immunocytochemical results. We conclude that the approach of high-density cDNA array hybridization can be used as a useful tool for examining a complex phenomenon of developmental plasticity since it is amenable to multiple developmental stage gene expression comparisons.

Two members of the IgLON family are expressed in a restricted region of the developing chick brain and neural crest

The precise expression patterns of two IgLON genes, CEPU-1 and limbic system-associated membrane protein (LAMP), were studied during early embryogenesis. It was found that expression of both was localized to restricted regions of the brain and neural crest. In the developing neural tube, CEPU-1 was expressed in the isthmus and a restricted region of the hindbrain, whereas LAMP was expressed in the anterior midbrain. Most neural crest cells expressed LAMP, whereas CEPU-1 expression was limited to crest cells derived from the hindbrain. These results suggest that members of the IgLON family have important roles during embryogenesis, particularly in brain formation and differentiation.

Developmental expression of opioid-binding cell adhesion molecule (OBCAM) in rat brain

Opioid-binding cell adhesion molecule (OBCAM), a neuron-specific protein, consists of three immunoglobulin (Ig)-like domains anchored to the membrane through a glycosylphosphatidylinositol (GPI)-tail. OBCAM has been presumed to play a role as a cell adhesion/recognition molecule, but its function has not been fully elucidated. We investigated the developmental expression of OBCAM in rat brain by using a monoclonal anti-OBCAM peptide antibody (OBC53). OBCAM was clearly detectable on embryonic day 16 (E16) as assessed by immunoblotting. The expression level increased by the second postnatal week and was maintained at a constant level until week 17. During the early developmental period OBCAM was found to be expressed on postmitotic neurons and to be strongly expressed in at the fiber tracts containing expanding axons, in contrast to the adult brain, in which OBCAM is principally expressed in the gray matter. These findings suggest that the function of OBCAM involves axonal outgrowth.

Expression of the IgLON cell adhesion molecules Kilon and OBCAM in hypothalamic magnocellular neurons

The vasopressin (AVP) and oxytocin (OXT) magnocellular neurons in the hypothalamic supraoptic (SON) and paraventricular nuclei (PVN) display reversible structural plasticity of neurons and glial cells under different conditions of neuropeptide secretion. In the present study, we investigated the expression of two immunoglobulin superfamily (IgSF) proteins, Kilon and OBCAM, in the magnocellular neurons by using monoclonal antibodies. Anti-Kilon antibody reacted specifically with the bacterially expressed recombinant Kilon but not with the recombinant OBCAM, and similarly anti-OBCAM antibody specifically recognized the recombinant OBCAM. Western blotting analysis revealed the specific expression of Kilon and OBCAM in the SON homogenates. Although Kilon and OBCAM of the SON homogenates were present as the insoluble form, most Kilon was present in the Triton-insoluble fraction, and OBCAM was localized mainly in the Triton-soluble fraction. Immunocytochemistry revealed Kilon and OBCAM immunoreactivity in the magnocellular neurons of the SON and PVN of the rat hypothalamus compared with outside of the SON and PVN in the hypothalamus. The double-labeling study with confocal microscopy further demonstrated that Kilon immunoreactivity was observed mainly in the dendrites of AVP-secreting neurons and also occasionally OXT-secreting neurons. However, OBCAM immunoreactivity was exclusively seen in the dendrites of AVP-secreting magnocellular neurons. Chronic physiological stimulation by 2% NaCl had no effect on the expression levels of either IgLON protein in the SON. Our study thus demonstrated specific expression of Kilon and OBCAM in the hypothalamic magnocellular neurons, particularly in dendrites, suggesting that they confer on magnocellular neurons the ability to rearrange dendritic connectivity.

Developmentally regulated expression of Thy-1 in structures of the mouse sensory-motor system

Thy-1 is a cell-surface molecule of the immunoglobulin superfamily which is expressed at high levels in the mature nervous system. Thy-1 has been implicated in regulating axonal outgrowth and synaptic function, but little is known regarding its cellular localization and expression in the central nervous system (CNS) during development or in adulthood. In this study, Thy-1 gene expression and protein localization were examined in sensory-motor and related areas of the adult and postnatally developing mouse CNS. Thy-1 mRNA expression was restricted to neurons; immunoreactivity was densely distributed throughout the neuropil of all regions examined, often delineated the neuronal plasmalemma, and labeled axons in white matter tracts of the brain and spinal cord. In adulthood, immunolabeling was regionally widespread and was present relatively homogeneously throughout all cell-dense layers of sensory-motor cortex, throughout most thalamic nuclei, globus pallidus, and spinal cord. Developmentally, however, Thy-1 expression and localization exhibited a spatially and temporally staggered sequence leading to the adult pattern. In sensory-motor cortex, Thy-1 expression in layer V preceded expression in other layers; in the barrel field, labeling of barrel septa preceeded a gradually increasing intensity of immunolabeling of barrel centers; in the thalamus, Thy-1 exhibited a differential onset and temporal pattern of expression across different nuclei associated with motor, sensory, or limbic systems; in the caudate nucleus, Thy-1 expression was greatest during the first postnatal week of life before declining during subsequent development. Taken together, the adult distribution and developmental patterns leading to it form a unique profile in comparison with other structurally related glycosyl-phosphatidylinositol (GPI)-anchored neural cell adhesion molecules. The pattern and timing of Thy-1 expression across layers and nuclei during early postnatal development are more complex than previously recognized, thus perhaps reflecting varied roles for Thy-1 in aspects of structural or functional maturation which proceed independently of the timing of neurogenesis, migration, and dendritic and axonal growth.

Localization of opioid-binding cell adhesion molecule (OBCAM) in adult rat brain

We investigated the tissue distribution and brain localization of opioid-binding cell adhesion molecule (OBCAM) in the adult rats by immunoblotting and immunohistochemistry using a monoclonal anti-OBCAM peptide antibody that is specific for OBCAM. OBCAM was preferentially expressed in the central nervous system (CNS) and at a very low level in the spleen. Within the brain, OBCAM was distributed in almost all the gray matter, but little or no immunoreactive OBCAM was found in the white matter. Morphologically, the distribution pattern of OBCAM immunoreactivity was very similar to that of synaptophysin, suggesting a role in the synaptic machinery.

Characterization of a novel rat brain glycosylphosphatidylinositol-anchored protein (Kilon), a member of the IgLON cell adhesion molecule family

In the central nervous system, many cell adhesion molecules are known to participate in the establishment and remodeling of the neural circuit. Some of the cell adhesion molecules are known to be anchored to the membrane by the glycosylphosphatidylinositol (GPI) inserted to their C termini, and many GPI-anchored proteins are known to be localized in a Triton-insoluble membrane fraction of low density or so-called "raft." In this study, we surveyed the GPI-anchored proteins in the Triton-insoluble low density fraction from 2-week-old rat brain by solubilization with phosphatidylinositol-specific phospholipase C. By Western blotting and partial peptide sequencing after the deglycosylation with peptide N-glycosidase F, the presence of Thy-1, F3/contactin, and T-cadherin was shown. In addition, one of the major proteins, having an apparent molecular mass of 36 kDa after the peptide N-glycosidase F digestion, was found to be a novel protein. The result of cDNA cloning showed that the protein is an immunoglobulin superfamily member with three C2 domains and has six putative glycosylation sites. Since this protein shows high sequence similarity to IgLON family members including LAMP, OBCAM, neurotrimin, CEPU-1, AvGP50, and GP55, we termed this protein Kilon (a kindred of IgLON). Kilon-specific monoclonal antibodies were produced, and Western blotting analysis showed that expression of Kilon is restricted to brain, and Kilon has an apparent molecular mass of 46 kDa in SDS-polyacrylamide gel electrophoresis in its expressed form. In brain, the expression of Kilon is already detected in E16 stage, and its level gradually increases during development. Kilon immunostaining was observed in the cerebral cortex and hippocampus, in which the strongly stained puncta were observed on dendrites and soma of pyramidal neurons.

Opiate effects on in vitro human retroviral infection

The transmission and progression of the human retroviruses HIV-1 and HTLV-1/2 can be most likely influenced by a variety of "lifestyle cofactors" which includes the use of certain injected pharmaceuticals. Some investigations have suggested that HIV-1 infected individuals who are injecting drug users (IDUs) may undergo an accelerated rate of progression to AIDS. It is known that opioid receptors exist on cells pertinent to immune function, and that the activation or inhibition of these receptors may enhance or down-regulate some cell activities. The mechanisms for these effects have not yet been elucidated, nor have the effects of opioids on retroviral infection models been fully determined. While some work has been performed on the effects of opiates on infection by HIV-1 and SIV virtually no work has been done on the potential effects of this class of drugs on HTLV-1 and 2 infection. The potential effects of opiates on these retroviruses are important because of the higher incidence of infection in IDUs. Because IDUs compose one of the emerging high risk populations for infection with HIV-1 and more recently HTLV it is relevant to analyze the direct and indirect effects of opioids on the progression of retroviral infections. Our preliminary results from in vitro syncytia formation studies suggest a modulation by opioid-selective receptor agonists of in vitro infection by both HIV-1 and HTLV-I. These initial results underscore the necessity for further studies to define and elucidate the role of opiate abuse in the infection by human retroviruses as well as the associated pathogenesis.