Transfection of NG108-15 cells with antisense opioid-binding cell adhesion molecule cDNA alters opioid receptor-G-protein interaction

Removal of polysialylated neural cell adhesion molecule increases morphine analgesia and interferes with tolerance in mice

Neurons that express high levels of polysialylated neural cell adhesion molecule (PSA-NCAM) in adult spinal substantia gelatinosa also express the μ-opioid receptor. While PSA removal from NCAM by spinal intrathecal injection of endoneuraminidase-N (endo-N) did not detectably change opioid receptor expression, morphine-induced analgesia was significantly increased. This analgesic strengthening was detected as early as 15 min after endo-N treatment and persisted for at least 7 days. In addition, the tolerance that develops with chronic morphine treatment was overcome in the absence of PSA. Interestingly, the same effects on analgesia and tolerance were also produced by selective deletion of the NCAM-180 isoform.

Co-localisation, heterophilic interactions and regulated expression of IgLON family proteins in the chick nervous system

The chick glycoprotein GP55 has been shown to inhibit the growth and adhesion of DRG and forebrain neurons. GP55 consists of several members of the IgLON family, a group of glycoproteins including LAMP, OBCAM, CEPU-1 (chick)/neurotrimin (rat) and neurotractin (chick)/kilon (rat) thought to play a role in the guidance of growing axons. IgLONs belong to the Ig superfamily and have three C2 domains and a glycosyl phosphatidylinositol anchor which tethers them to the neuronal plasma membrane. We have now completed the deduced amino acid sequence for two isoforms of chicken OBCAM and used recombinant LAMP, OBCAM and CEPU-1 to raise antisera specific to these three IgLONs. LAMP and CEPU-1 are co-expressed on DRG and sympathetic neurons, while both overlapping and distinct expression patterns for LAMP, OBCAM and CEPU-1 are observed in retina. Analysis of IgLON mRNA expression reveals that alternatively spliced forms of LAMP and CEPU-1 are developmentally regulated. In an attempt to understand how the IgLONs function, we have begun to characterise their molecular interactions. LAMP and CEPU-1 have already been shown to interact homophilically. We now confirm that OBCAM will bind homophilically and also that LAMP, OBCAM and CEPU-1 will interact heterophilically with each other. We propose that IgLON activity will depend on the complement of IgLONs expressed by each neuron.

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.

Perinatal exposure to morphine: reactive changes in the brain after 6-hydroxydopamine

The effects of neonatal 6-hydroxydopamine treatment on the brain of control rats and of rats perinatally exposed to morphine were examined. Noradrenaline levels were increased in the pons-medulla, mesencephalon and caudate of 8-week-old control rats lesioned with neonatal 6-hydroxydopamine; perinatal morphine treatment prevented such an increase. In the caudate, there was a loss of dopamine and an increase of serotonin following the neurotoxic lesion; exposure to perinatal morphine prevented the serotonin increase. Brain expression of synapsin I mRNA was particularly abundant in cerebral cortex, hippocampus, dentate gyrus and olfactory bulb. In perinatal morphine-treated rats, the expression of synapsin I mRNA was significantly reduced; interestingly, the neonatal treatment with 6-hydroxydopamine normalized its expression. Therefore, brain-reactive neurochemical changes triggered by 6-hydroxydopamine were suppressed by perinatal morphine exposure whereas the association of morphine exposure and 6-hydroxydopamine lesion promoted the normal mRNA expression of the synaptic marker synapsin I.

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

Monoclonal antibodies to opioid-binding cell adhesion molecule (OBCAM) were produced against a synthetic OBCAM peptide. Immunoblotting analysis revealed that the antibodies reacted with 58 and/or 51 kDa proteins in P2 membranes from bovine, rat, mouse, guinea pig and rabbit brains. In bovine brain, the 58 and 51 kDa proteins were present in the striatum and cerebral cortex at high levels, but not in the pituitary. OBCAM was also detected in the cerebellum mainly in the 51 kDa form. In other tissues, the proteins were found in the spleen at very low levels, but not at all in the liver or kidney of the rat. OBCAM was effectively solubilized from bovine P2 membranes by bacterial phosphatidylinositol specific-phospholipase C (PI-PLC), indicating that OBCAM is a glycosylphosphatidylinositol (GPI)-anchored protein. PI-PLC treatment, however, had little effect on the opioid binding activity of the residual P2 membranes. The molecular weight of the proteins (58 and 51 kDa) was reduced to 36 kDa following treatment with N-glycanase but not further reduced after subsequent treatment with neuraminidase and O-glycanase, suggesting that OBCAM has N-glycosylated carbohydrate chains and that its two isoforms are different, at least, in the degree of N-glycosylation. Taken together, these results suggest that OBCAM consists of 58/51 kDa GPI-anchored glycoproteins which are highly N-glycosylated and are expressed mainly in the nervous system.

Expression of OBCAM-related cDNA clones in Cos 1 cells: evidence for a phosphatidylinositol linkage to the cell membrane

Previously, our laboratory purified and isolated the cDNA for OBCAM (opioid binding cell adhesion molecule) from bovine brain, as well as highly homologous rat brain cDNA clones, SG13 and DUZ-1. Structural similarities with members of the immunoglobulin superfamily suggest a possible role for OBCAM in cell adhesion and recognition, while studies in our own laboratory suggest that OBCAM is important in the regulation of opioid binding and signal transduction. However, OBCAM lacks a putative transmembrane domain, and its possible mode of linkage to the cellular membrane has not been studied. Upon transfection of Cos 1 cells with SG13 and DUZ-1 cDNAs, the OBCAM-homologous proteins were expressed on the surface of the Cos 1 cells. These proteins were released from the membrane of the Cos 1 cells upon digestion with phosphatidylinositol-specific phospholipase C (PI-PLC), demonstrating that they are linked to the membrane via a phosphatidylinositol (PI) linkage. These results are consistent with a role for OBCAM in cell recognition and adhesion, as well as in cellular signaling.

Alteration of OBCAM conformation as a result of opioid receptor expression and opioid ligand treatment

Several lines of evidence link the opioid binding cell adhesion molecule (OBCAM) to opioid function. When delta-opioid receptor cDNA (DOR-1) was expressed in CHO cells, OBCAM immunoreactivity (OBCAM-ir) was detected. Transfected cell lines which displayed high opioid binding also expressed high cell surface OBCAM-ir, while untransfected CHO and vector control cells did not. The positive control, neural cell adhesion molecule (NCAM), a protein with structural homology to OBCAM, displayed the same levels of immunofluorescence in transfected and nontransfected cell lines. Membranes from CHO cells transfected with and expressing a variety of muscarinic and dopamine receptors were tested for immunoreactivity. No significant OBCAM-ir was detected in any of these cell membranes. When anti-OBCAM peptide antibodies were used for immunoblots of CHO cells, untransfected, non-binding transfected, and high binding transfected cells revealed the same banding patterns with approximately equal intensity. These observations suggest that in untransfected cells OBCAM is either not present on the extracellular side of the CHO cell membrane or that it exists in an altered conformation which changes upon transfection with opioid receptors to allow recognition of the non-denatured protein by anti-OBCAM antibodies.

An opioid binding protein is specifically down-regulated by chronic morphine treatment in dorsal root and trigeminal ganglia

Despite the recent cloning of mu, delta and kappa opioid receptors, a role in opioid receptor function for an opioid binding cell adhesion molecule is supported by several lines of evidence, including inhibition of opioid binding by opioid binding cell adhesion molecule antibodies, down-regulation of opioid binding cell adhesion molecule by chronic opioid agonist treatment of cultured NG108-15 cells, and reduction of opioid binding in NG108-15 cells by transfection of opioid binding cell adhesion molecule antisense cDNA. In the present study, we report that chronic in vivo treatment of mice with morphine results in down-regulation of opioid binding cell adhesion molecule immunoreactivity in primary afferent neurons in dorsal root and trigeminal ganglia as well as their axons. This effect was blocked by the opioid antagonist naloxone. Down-regulation of opioid binding cell adhesion molecule immunoreactivity was not observed in other areas of the central nervous system. Taken together, the previous studies which demonstrated the role played by opioid receptors in regulating release of transmitters from primary afferent neurons and the present findings of a specific regulation of opioid binding cell adhesion molecule expression by chronic exposure to morphine, provides evidence from an in vivo perspective which advances the notion that opioid binding cell adhesion molecule plays a role in the action of opioids.

Cloning, sequencing and localization to chromosome 11 of a cDNA encoding a human opioid-binding cell adhesion molecule (OBCAM)

Oligodeoxyribonucleotide (oligo) primers derived from rat opioid-binding cell adhesion molecule (OBCAM)-encoding cDNA sequence were used to amplify a 403-bp fragment from a human brain cDNA library using the polymerase chain reaction (PCR). The fragment was cloned, sequenced and used as a hybridization probe to screen the library. lambda plaque clones were isolated which contained a 1.5-kb cDNA fragment, including a complete open reading frame (ORF) of 1038 bp. Sequence analysis of the ORF revealed 93% identity to the rat OBCAM cDNA at the nucleotide level, and the deduced amino-acid sequences shared 98% identity. Percentages of identity between human and bovine OBCAM ORFs were within 2% of these values. OBCAM was mapped to human chromosome 11 by hybridizing the probe with a somatic cell hybrid panel.