Mirk/Dyrk1B controls ventral spinal cord development via Shh pathway

Cross-talk between Mirk/Dyrk1B kinase and Sonic hedgehog (Shh)/Gli pathway affects physiology and pathology. Here, we reveal a novel role for Dyrk1B in regulating ventral progenitor and neuron subtypes in the embryonic chick spinal cord (SC) via the Shh pathway. Using in ovo gain-and-loss-of-function approaches at E2, we report that Dyrk1B affects the proliferation and differentiation of neuronal progenitors at E4 and impacts on apoptosis specifically in the motor neuron (MN) domain. Especially, Dyrk1B overexpression decreases the numbers of ventral progenitors, MNs, and V2a interneurons, while the pharmacological inhibition of endogenous Dyrk1B kinase activity by AZ191 administration increases the numbers of ventral progenitors and MNs. Mechanistically, Dyrk1B overexpression suppresses Shh, Gli2 and Gli3 mRNA levels, while conversely, Shh, Gli2 and Gli3 transcription is increased in the presence of Dyrk1B inhibitor AZ191 or Smoothened agonist SAG. Most importantly, in phenotype rescue experiments, SAG restores the Dyrk1B-mediated dysregulation of ventral progenitors. Further at E6, Dyrk1B affects selectively the medial lateral motor neuron column (LMCm), consistent with the expression of Shh in this region. Collectively, these observations reveal a novel regulatory function of Dyrk1B kinase in suppressing the Shh/Gli pathway and thus affecting ventral subtypes in the developing spinal cord. These data render Dyrk1B a possible therapeutic target for motor neuron diseases.

Schwann cell transplantation for CNS repair

Demyelination occurs in several central nervous system (CNS) disorders, including multiple sclerosis, viral infection and spinal cord injury and can result in severe functional impairment. Therefore there is great interest in developing therapies promoting repair in CNS demyelinating diseases and trauma. Cell replacement therapy is an attractive approach for myelin repair, and experimental transplantation has provided convincing evidence of the repair potential of grafted myelin-forming cells. Schwann cells (SCs), oligodendrocyte progenitors, olfactory ensheathing cells and embryonic and neural stem cells have been shown to form myelin after transplantation into the demyelinated CNS. SCs are among the most promising candidates for autologous grafting. They can remyelinate spinal cord lesions after experimental demyelination, leading in some cases to functional recovery in rodent and primate models. However, SCs do not normally enter the CNS, and migration of SCs transplanted in CNS white matter is inhibited by astrocytes. As SC migration and myelination is mediated by interactions of sets of extracellular matrix molecules with cell surface molecules, genetic engineering of SCs to alter aspects of these interactions is a possible way forward. Thus efforts towards the development of SC-based therapies are focused in enhancing their migration and functional integration into the lesioned CNS. In addition, efforts are being made to use these cells as gene delivery vehicles for an array of molecules with repair potential. In this review we summarize data from the recent literature regarding the use of SCs in CNS repair and discuss the prospects for future therapeutic applications.

Soluble forms of NCAM and F3 neuronal cell adhesion molecules promote Schwann cell migration: identification of protein tyrosine phosphatases zeta/beta as the putative F3 receptors on Schwann cells

Neural cell adhesion molecule (NCAM) and F3 are both axonal adhesion molecules which display homophilic (NCAM) or heterophilic (NCAM, F3) binding activities and participate in bidirectional exchange of information between neurones and glial cells. Engineered Fc chimeric molecules are fusion proteins that contain the extracellular part of NCAM or F3 and the Fc region of human IgG1. Here, we investigated the effect of NCAM-Fc and F3-Fc chimeras on Schwann cell (SC) migration. Binding sites were identified at the surface of cultured SCs by chimera coated fluorospheres. The functional effect of NCAM-Fc and F3-Fc binding was studied in two different SC migration models. In the first, migration is monitored at specific time intervals inside a 1-mm gap produced in a monolayer culture of SCs. In the second, SCs from a dorsal root ganglion explant migrate on a sciatic nerve cryosection. In both systems addition of the chimeras significantly increased the extent of SC migration and this effect could be prevented by the corresponding anti-NCAM or anti-F3 blocking antibodies. Furthermore, antiproteoglycan-type protein tyrosine phosphatase zeta/beta (RPTPzeta/beta) antibodies identified the presence of RPTPzeta/beta on SCs and prevented the enhancing effect of soluble F3 on SC motility by 95%. The F3-Fc coated Sepharose beads precipitated RPTPzeta/beta from SC lysates. Altogether these data point to RPTPzeta/beta is the putative F3 receptor on SCs. These results identify F3 and NCAM receptors on SC as potential mediators of signalling occurring between axons and glial cells during peripheral nerve development and regeneration.

Cloning, expression and localization of human BM88 shows that it maps to chromosome 11p15.5, a region implicated in Beckwith-Wiedemann syndrome and tumorigenesis

Porcine BM88 is a neuron-specific protein that enhances neuroblastoma cell differentiation in vitro and may be involved in neuronal differentiation in vivo. Here we report the identification, by Western blotting, of homologous proteins in human and mouse brain and the isolation of their respective cDNAs. Several human and mouse clones were identified in the EST database using porcine BM88 cDNA as a query. A human and a mouse EST clone were chosen for sequencing and were found both to predict a protein of 149 amino acids, with 79.9% reciprocal identity, and 76.4% and 70.7% identities to the porcine protein, respectively. This indicated that the clones corresponded to the human and mouse BM88 homologues. In vitro expression in a cell-free system as well as transient expression in COS7 cells yielded polypeptide products that were recognized by anti-BM88 antibodies and were identical in size to the native BM88 protein. Northern-blot analysis showed a wide distribution of the gene in human brain whereas immunohistochemistry on human brain sections demonstrated that the expression of BM88 is confined to neurons. The initial mapping assignment of human BM88 to chromosome 11p15.5, a region implicated in Beckwith-Wiedemann syndrome and tumorigenesis, was retrieved from the UniGene database maintained at the National Centre for Biotechnology Information (NCBI, Bethesda, MD, U.S.A.). We confirmed this localization by performing fluorescence in situ hybridization on BM88-positive cosmid clones isolated from a human genomic library. These results suggest that BM88 may be a candidate gene for genetic disorders associated with alterations at 11p15.5.

Aberrant localization of the neuronal class III beta-tubulin in astrocytomas

BACKGROUND

The class III beta-tubulin isotype (betaIII) is widely regarded as a neuronal marker in development and neoplasia. In previous work, we have shown that the expression of betaIII in neuronal/neuroblastic tumors is differentiation dependent. In contrast, the aberrant localization of this isotype in certain nonneuronal neoplasms, such as epithelial neuroendocrine lung tumors, is associated with anaplastic potential.

OBJECTIVE

To test the generality of this observation, we investigated the immunoreactivity profile of betaIII in astrocytomas.

DESIGN

Sixty archival, surgically excised astrocytomas (8 pilocytic astrocytomas, WHO grade 1; 18 diffuse fibrillary astrocytomas, WHO grade 2; 4 anaplastic astrocytomas, WHO grade 3; and 30 glioblastomas, WHO grade 4), were studied by immunohistochemistry using anti-betaIII monoclonal (TuJ1) and polyclonal antibodies. A monoclonal antibody to Ki-67 nuclear antigen (NC-MM1) was used as a marker for cell proliferation. Antibodies to glial fibrillary acidic protein (GFAP) and BM89 synaptic vesicle antigen/synaptophysin were used as glial and neuronal markers, respectively.

RESULTS

The betaIII immunoreactivity was significantly greater in high-grade astrocytomas (anaplastic astrocytomas and glioblastomas; median labeling index [MLI], 35%; interquartile range [IQR], 20%-47%) as compared with diffuse fibrillary astrocytomas (MLI, 4%; IQR, 0.2%-21%) (P <.0001) and was rarely detectable in pilocytic astrocytomas (MLI, 0%; IQR, 0%-0.5%) (P <.0001 vs high-grade astrocytomas; P <.01 vs diffuse fibrillary astrocytomas). A highly significant, grade-dependent relationship was observed between betaIII and Ki-67 labeling and malignancy, but this association was stronger for Ki-67 than for betaIII (betaIII, P <.006; Ki-67, P <.0001). There was co-localization of betaIII and GFAP in neoplastic astrocytes, but no BM89 synaptic vesicle antigen/synaptophysin staining was detected.

CONCLUSIONS

In the context of astrocytic gliomas, betaIII immunoreactivity is associated with an ascending gradient of malignancy and thus may be a useful ancillary diagnostic marker. However, the significance of betaIII-positive phenotypes in diffuse fibrillary astrocytomas with respect to prognostic and predictive value requires further evaluation. Under certain neoplastic conditions, betaIII expression is not neuron specific, calling for a cautious interpretation of betaIII-positive phenotypes in brain tumors.

The neuron-glia signal beta-neuregulin promotes Schwann cell motility via the MAPK pathway

Neuregulins constitute a family of related growth factors that play important roles in Schwann cell development and maturation. We investigated the involvement of beta-neuregulin in Schwann cell migration, using a simple in vitro bioassay. Pure Schwann cells were prepared from the sciatic nerves of 5-day-old rats and were grown in defined medium, with or without serum, until a monolayer of confluent cells was formed. A cell-free area was then generated by inflicting a scratch resulting in a 1-mm-wide gap. Schwann cell migration within the gap was monitored microscopically at given time intervals and was quantified using an image analysis system. The extent of cell proliferation was estimated by BrdU incorporation, and cell migration was quantified both in the absence and presence of cytosine arabinoside. We found that, in the absence of serum, beta-neuregulin at a dose submaximal for proliferation increased the rate of Schwann cell migration by 84%. A more moderate effect was observed when beta-neuregulin was applied in the presence of serum which, however, is by itself responsible for increased Schwann cell motility. To assess the signal transduction pathways involved in this procedure we used one inhibitor of MAPK, PD098059, two inhibitors of PI-3-kinase, wortmannin, and LY0294002, and three different PKC inhibitors. Of these PD098059 inhibited the neuregulin-induced enhancement in Schwann cell migration by 40%, the two PI-3-kinase inhibitors yielded an approximately 20% inhibition while the PKC inhibitors were ineffective. Our data indicate that the action of beta-neuregulin on Schwann cell motility is primarily mediated via the MAPK pathway.

Isolation of a mouse brain cDNA expressed in developing neuroblasts and mature neurons

A previously uncharacterized 4.5-kb mouse cDNA clone, designated mc7, was isolated and found to be predominantly expressed in brain. This cDNA predicts a 1035-bp open reading frame that encodes for a 345-amino acid polypeptide especially rich in glutamic acid residues located in the region from residues 80 to 174. Computational analysis revealed among other features, putative zinc-finger motifs and coiled-coil regions. The corresponding mc7 gene is detected in mouse, rat, pig and human genomes. In mouse the mc7 mRNA is expressed predominantly in brain and to a much lesser extent in kidney, lung and spleen. In brain it is detectable as early as embryonic day 14 while it is retained in the adult. In situ hybridization studies revealed that mc7 mRNA is widely, albeit unevenly, expressed in neurons throughout the adult brain. Developmental in situ hybridization studies in the cerebellar cortex demonstrated that at postnatal day 5 mc7 mRNA is mainly expressed in neuroblasts of the external granular layer and in developing neurons of the internal granular layer. Some staining is also present in purkinje cells becoming particularly pronounced at postnatal day 10, the time of arborarization of their dendritic tree. In the adult cerebellar cortex expression is mainly confined in purkinje cells and to a lesser extent in granule neurons. The early expression of mc7 in neuroblasts and developing neurons as well as its retention in a wide variety of mature neurons suggest that it may play a role in the process of differentiation and maturation of these cells in the brain.

Early expression of the BM88 antigen during neuronal differentiation of P19 embryonal carcinoma cells

Previous studies have shown that the BM88 antigen, a neuron-specific molecule, promotes the differentiation of mouse neuroblastoma cells [23] (Mamalaki A., Boutou E., Hurel C., Patsavoudi E., Tzartos S. and Matsas R. (1995) The BM88 antigen, a novel neuron-specific molecule, enhances the differentiation of mouse neuroblastoma cells. J. Biol. Chem. 270, 14201-14208). In particular, stably transfected with the BM88 cDNA, Neuro 2a cells over-expressing the BM88 antigen are morphologically distinct from their non-transfected counterparts; they exhibit enhanced process outgrowth and a slower rate of division. Moreover, they respond differentially to growth factors [10] (Gomez J., Boutou E., Hurel C., Mamalaki A., Kentroti S. , Vernadakis A. and Matsas R. (1998) Overexpression of the neuron-specific molecule BM88 in mouse neuroblastoma cells: Altered responsiveness to growth factors. J. Neurosci. Res. 51, 119-128). In order to further elucidate the role of the BM88 antigen in the differentiation of developing neurons we used the in vitro system of differentiating P19 cells which closely resembles early murine development in vivo. In this study, P19 cells were driven to the neuronal pathway with retinoic acid. We examined by immunofluorescence studies the expression of the BM88 antigen in these cells and we found that it correlates well with the expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) which characterizes early differentiating post-mitotic neurons. In contrast, very few of the BM88 antigen-positive/PSA-NCAM-positive cells expressed neurofilament protein, a marker of more mature neurons. Our findings, in accordance with previously reported data, strongly suggest that the BM88 antigen is involved in the early stages of differentiation of neuronal cells.

Overexpression of the neuron-specific molecule BM88 in mouse neuroblastoma cells: altered responsiveness to growth factors

Previous studies have shown that the BM88 antigen, a novel neuron-specific molecule, promotes the differentiation of mouse neuroblastoma (Neuro 2a) cells. In particular, stably transfected, with the BM88 cDNA, Neuro 2a cells overexpressing the BM88 antigen (Neuro2a-BM88 cells) are morphologically distinct from the nontransfected Neuro 2a cells; they exhibit enhanced process outgrowth and a slower rate of division. In this study we used Neuro2a and the morphologically differentiated Neuro 2a-BM88 cells to compare their responsiveness to growth factors. The growth factors we used were nerve growth factor (NGF), basic-fibroblast growth factor (b-FGF), and glial cell-line derived neurotrophic factor (GDNF). In addition, we used glial conditioned medium derived from either newborn mouse cerebral cortex (NBCC) or aged mouse cerebral hemispheres (MACH), as a source of normal glial factors. Because these cells express the cholinergic phenotype, we used choline acetyltransferase (ChAT) activity as a biochemical marker for comparison. A differential responsiveness to these factors was observed between Neuro 2a and Neuro 2a-BM88. The presence of NGF, 25 ng/ml, in the culture medium did not affect ChAT activity in either cell type. In contrast to NGF, in the presence of b-FGF, 5 ng/ml, the transfected cells, Neuro 2a-BM88, responded with a marked increase in ChAT activity. On the other hand, with GDNF, 1 ng/ml, only Neuro 2a cells showed an increase in ChAT activity. Finally, we found no response to the glial conditioned media, although these media contain several growth factors, including b-FGF. In conclusion, our findings show that overexpression of the neuron-specific antigen BM88 in neuroblastoma cells modifies their properties with respect to growth factor sensitivity, and, hence, the Neuro 2a and Neuro 2a-BM88 are suitable cell models to examine the role of growth factors in neuronal differentiation.

Purification and cDNA cloning of mouse BM89 antigen shows that it is identical with the synaptic vesicle protein synaptophysin

The BM89 antigen, first identified in porcine brain by means of a monoclonal antibody, is a neuron-specific molecule widely distributed in the mammalian central and peripheral nervous system (Merkouri and Matsas: Neuroscience 50:53-68, 1992). Here we describe the purification of BM89 antigen from porcine and mouse brain by immunoaffinity chromatography using, respectively, the previously described BM89 monoclonal antibody which belongs to the IgM class and a specific polyclonal antibody generated in the present study. This antibody was also used for the cDNA cloning of the BM89 antigen from mouse brain. cDNA sequencing revealed that the mouse BM89 antigen is identical with the synaptic vesicle protein synaptophysin which is implicated in the control of regulated exocytosis and neurotransmitter release. Mouse BM89 antigen/synaptophysin exhibits, except for one extra amino acid, 100% identity with rat synaptophysin and substantial sequence identity with bovine (92.5% identity) and human (94.8% identity) synaptophysin, but only 59.8% identity with Torpedo synaptophysin. Northern and Western blot analyses confirmed that the mouse BM89 antigen/synaptophysin is expressed only in neural tissues.

Antigenicity and conformational analysis of the Zn(2+)-binding sites of two Zn(2+)-metalloproteases: Leishmania gp63 and mammalian endopeptidase-24.11

The antigenic properties of the Zn(2+)-binding region of two Zn(2+)-metalloproteases, Leishmania surface protease gp63 and mammalian endopeptidase-24.11 (E-24.11), possessing in their active site the characteristic amino acid sequence HEXXH, were investigated by using oligoclonal antibodies raised against two synthetic peptides, V1VTHEMAHALG11 (pepgp63) and V1IGHEITHGFD11 (pepE-24.11), containing the respective Zn(2+)-binding sites of the cognate protein. The affinity-purified antibodies, tested on synthetic peptides modelled from the active sites of ten different Zn(2+)-metalloproteases, showed high selectivity for their respective peptides. However, cross-reactivity was revealed when the antibodies were tested against the gp63 and E-24.11 molecules. A panel of synthetic peptide analogues and peptides of various size was synthesized and used for the fine antigenic characterization of pepgp63 and pepE-24.11. The shortest peptides capable of significant antibody binding were the pentapeptides V1VTHE5 and E5ITHG9 for pepgp63 and pepE-24.11 respectively. His4 and Glu5 were found to be indispensable for anti-pepgp63 binding to pepgp63, whereas in the case of pepE-24.11, Glu5 and His8 were found to be critical. The conformational characteristics of the two peptides correlate well with the observed differences in their antigenicity. 1H-NMR studies showed that pepgp63 adopts a folded structure whereas pepE-24.11 takes up a rather flexible conformation. Moreover, the antigenically critical His4 of pepgp63 contributes to the structural stabilization of the peptide. Similarly, the antigenically critical His8 of pepE-24.11 is involved in partial structural stabilization of its C-terminal region. The generated antibodies may be useful tools for identifying and classifying proteins possessing similar Zn(2+)-binding motifs and/or environments.

The BM88 antigen, a novel neuron-specific molecule, enhances the differentiation of mouse neuroblastoma cells

The BM88 antigen is a neuron-specific molecule widely distributed in the mammalian nervous system. It is a 22-kDa, apparently not glycosylated, integral membrane protein, which appears early during brain development and remains at high levels in the mature animal. Here, we describe the cDNA cloning of the porcine BM88 antigen and present evidence that this protein is involved in neuroblastoma cell differentiation. The deduced protein is a novel molecule consisting of 140 amino acids and bears a putative transmembrane domain at the COOH-terminal region. The mRNA of this protein is expressed only in neural tissues, where it is restricted to neurons. Stably transfected Neuro-2a cells overexpressing the BM88 antigen exhibited a significant change in morphology, reflected by enhanced process outgrowth, and a slower rate of division. Moreover, in the presence of differentiation agents, such as sucrose and retinoic acid, an accelerated differentiation of the transfected Neuro-2a cells was observed. Especially in the presence of sucrose, the consequent overexpression of the BM88 antigen in the transfected cells resulted in their enhanced morphological differentiation accompanied by the induction of neurofilament protein expression. Our results suggest that the BM88 antigen plays a role in the differentiation of neuroblastoma cells.

Expression of endopeptidase-24.11 (common acute lymphoblastic leukaemia antigen CD10) in the sciatic nerve of the adult rat after lesion and during regeneration

Endopeptidase-24.11, which is identical with the common acute lymphoblastic leukaemia antigen CD10 (CALLA), is a cell surface Zn2+ metalloprotease that regulates peptide-induced responses in different tissues, including the nervous and immune systems. In the peripheral nervous system, high levels of the enzyme are present in all neonatal and early postnatal Schwann cells, while as myelination proceeds it is gradually suppressed in the majority of cells that form myelin but retained in non-myelin-forming cells in the adult animal. In the present study we have investigated the effects of transection, crush and regeneration of the adult rat sciatic nerve on the expression of the endopeptidase by Schwann cells in situ. Endopeptidase-24.11 was monitored by immunocytochemistry using the monoclonal anti-endopeptidase antibody 23B11. For comparison, a parallel study was carried out with a monoclonal antibody directed against the rat nerve growth factor receptor. We found that (i) all Schwann cells of the distal segment re-expressed endopeptidase-24.11 as early as 4 days after axotomy, the level of immunostaining reaching a maximum after 2 weeks, (ii) axonal regeneration repressed Schwann cell expression of endopeptidase-24.11, and (iii) the induction of the nerve growth factor receptor followed a similar pattern to that of endopeptidase-24.11 in the transected and crushed nerve. Enzymatic amplification of endopeptidase-24.11 cDNA from normal and axotomized adult rat sciatic nerve confirmed the expression of endopeptidase-24.11 in these tissues. Our results show that the expression of endopeptidase-24.11 in Schwann cells, as is the case with the nerve growth factor receptor, is induced by the loss of the normal axon-Schwann cell contact. The significant increase in the expression of endopeptidase-24.11 by Schwann cells after axonal damage suggests that the enzyme could play a role in axonal regeneration.

Characterization and localization of the BM88 antigen in the developing and adult rat brain

Monoclonal antibody BM88 identifies a neuron-specific antigen (BM88 antigen) present in the central and peripheral nervous system of the pig (Patsavoudi et al.: Neuroscience 30:463-478, 1989; J Neurochem 56:782-788, 1991). We have previously shown that the antigen is also expressed by cultured neurons derived from newborn rat brain. In the present study we have used the monoclonal antibody BM88 and a specific polyclonal antibody in order to identify the nature of the cross-reactive antigen in rat brain and to investigate its expression and cellular localization in the developing and adult rat nervous system. Western blot analysis and immunocytochemistry revealed that the rat BM88 antigen displays very similar biochemical properties with its porcine homologue. It is a neuron-specific integral membrane protein, apparently not glycosylated, consisting of two 23 kD polypeptide chains. Immunoperoxidase staining demonstrated that the BM88 antigen is widely distributed in the brain of 19-day-old rat embryos. At this stage, immunoreactivity was particularly prominent in differentiated cellular areas and developing fiber tracts of the embryonic rat brain, but was also present in the neuroepithelium. A similar wide distribution of the BM88 antigen was observed in the adult rat brain. Here, immunoreactivity was detected in the neuropil and neuronal perikarya. Immunocytochemical analysis of the expression of the BM88 antigen during postnatal development of the cerebellar cortex showed that this molecule is particularly concentrated in the Purkinje cells between postnatal days 10 to 15; their somata and developing dendrites were distinctly immunopositive during this period. An age-dependent increase in the expression of the BM88 antigen both in brain and in the cerebellum was noted. Electron microscopy confirmed the presence of the BM88 reaction product within the perikarya, axons and dendrites of labeled neurons in the adult brain. The BM88 reaction product was preferentially associated with the limiting membrane of mitochondria, endoplasmic reticulum and small electron-lucent vesicles, but was also present in the plasma membrane, especially at the level of synaptic densities. Our results show that the BM88 antigen participates in an activity common to all or most neurons, and demonstrate that the expression of this antigen is elevated upon neuronal differentiation and maturation.

Monoclonal antibody BM89 recognizes a novel cell surface glycoprotein of the L2/HNK-1 family in the developing mammalian nervous system

A monoclonal antibody, BM89, obtained with Triton X-114-treated pig synaptic membranes as an immunogen, recognizes a neuronal antigen in the newborn porcine nervous system. By immunohistochemistry, BM89 staining was observed within the neuropil of all areas of the forebrain and spinal cord tested. In addition, BM89 labeled the cell bodies and proximal dendrites of spinal cord neurons. In the peripheral nervous system, BM89 immunoreactivity was present in a subpopulation of dorsal root ganglion neurons and was predominantly associated with non-myelinated axons in peripheral nerves. Initial biochemical characterization of the antigen in pig brain showed that it is an integral membrane glycoprotein with a molecular weight of 41,000. Moreover, it cross-reacts with the L2/HNK-1 carbohydrate epitope expressed by members of a large family of glycoproteins. Homologous antigens with molecular weights of 41,000-43,000 were identified in the rat, rabbit and fetal human brain. Immunoblotting and immunohistochemistry revealed that the epitope recognized by BM89 is developmentally regulated in the rat nervous system. In cryostat sections from rat cerebellum, spinal cord and dorsal root ganglia, an age-dependent decline of BM89 immunoreactivity was observed during postnatal development. In the cerebellum, the BM89 epitope was very abundant in cells of the external and the internal granular layers between postnatal days 5 and 15. During this period some staining was also identified in the developing molecular layer and the prospective white matter. Subsequently, and in the adult, overall staining was greatly reduced and remaining immunoreactivity was associated only with the internal granular layer. In the spinal cord and dorsal root ganglia, staining was very prominent at postnatal day 5; it decreased considerably thereafter and was barely detectable in the adult. Immunostaining of rat brain and dorsal root ganglion cultures revealed that the BM89 antigen is a cell surface molecule expressed by a subpopulation of central and peripheral nervous system neurons. The biochemical properties in conjunction with the topographical location and the developmental profile of the antigen recognized by BM89 suggest that it may represent a developmentally important recognition molecule.

Endopeptidase-24.11 is suppressed in myelin-forming but not in non-myelin-forming Schwann cells during development of the rat sciatic nerve

Endopeptidase-24.11, which is identical with the common acute lymphoblastic leukemia antigen (CALLA), is a cell surface zinc metalloprotease that has the ability to hydrolyse a variety of physiologically active peptides. Interest in this enzyme is based on the view that it may play a role in the regulation of peptide signals in different tissues, including the nervous and immune systems. We have previously shown that endopeptidase-24.11 is present in Schwann cells in the peripheral nervous system of newborn pigs [Kioussi C. and Matsas R. (1991) J. Neurochem. 57, 431-440]. In the present study we have investigated the developmental expression of the endopeptidase by Schwann cells in the rat sciatic nerve, from embryonic day 16 to maturity. Endopeptidase-24.11 was monitored enzymatically as well as by immunoblotting and immunocytochemistry using the monoclonal anti-endopeptidase antibody 23B11. We found an age-dependent decline in both the enzyme activity and the levels of immunoreactive protein. Endopeptidase-24.11 was first detected at embryonic day 18 and was present in all neonatal and early postnatal Schwann cells. However, as myelination proceeded the endopeptidase was gradually suppressed in the majority of cells that form myelin but retained in non-myelin-forming cells in the adult animal. At this stage, only very few large diameter myelinated fibers expressed weakly endopeptidase-24.11. Schwann cells dissociated from postnatal day 5 nerves and cultured up to one week in the absence of axons expressed endopeptidase-24.11. These results show that the endopeptidase has a distinct developmental profile in the rat sciatic nerve, similar to that of a group of other Schwann cell surface antigens, including the cell adhesion molecules N-CAM and L1 and the nerve growth factor receptor. We suggest that, as is the case with these antigens, endopeptidase-24.11 may play a role in nerve development and/or regeneration. In addition, persistence of endopeptidase-24.11 in a minority of adult myelin-forming Schwann cells suggests a possible role for the enzyme in axon-myelin apposition and maintenance, especially of larger diameter axons.

Endopeptidase-24.11, a cell-surface peptidase of central nervous system neurons, is expressed by Schwann cells in the pig peripheral nervous system

Endopeptidase-24.11 is a 90-kDa surface glycoprotein with the ability to hydrolyze a variety of biologically active peptides. Interest in this enzyme is based on the consensus that it may play a role in the termination of peptide signals in the central nervous system. In the present study, we have investigated the distribution of endopeptidase-24.11 in two nerves of the peripheral nervous system of newborn pigs: the sciatic, composed of a mixture of myelinated and nonmyelinated axons, and cervical sympathetic trunk in which greater than 99% of the axons are nonmyelinated. The endopeptidase was monitored enzymatically, as well as by immunoblotting and immunocytochemistry using mono- and polyclonal anti-endopeptidase antibodies. Endopeptidase-24.11 was detected in both the sciatic nerve and the cervical sympathetic trunk. Membrane preparations from sciatic nerve hydrolyzed 125I-insulin B-chain, and more than 50% of the activity was inhibited by phosphoramidon with an IC50 concentration of 3.2 nM. Moreover, a 90-kDa polypeptide was detected by immunoblotting of sciatic nerve membranes. The type of cells expressing the endopeptidase was determined by immunohistochemistry. In teased nerve preparations, these cells were identified morphologically as myelin- and non-myelin-forming Schwann cells. Endopeptidase-24.11 was also expressed by cultured Schwann cells from sciatic nerve and cervical sympathetic trunk maintained for 3 h in vitro. The presence of endopeptidase-24.11 on the Schwann cell surface raises the possibility of a potential role for the enzyme in nerve development and/or regeneration.

Purification and characterization of neuron-specific surface antigen defined by monoclonal antibody BM88

Monoclonal antibody BM88 recognizes a neurospecific surface antigen in the CNS and the PNS. In the present study, the antigen recognized by BM88 was immunopurified from pig brain and shown to be a 22-kDa polypeptide by reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Under nonreducing conditions a protein of 40 kDa was obtained, a result indicating that the antigen is composed of two polypeptide chains of equal molecular weight linked by disulfide bridges. Gel filtration of the purified antigen in the presence of Emulphogene suggested that it may be either a monomeric or a dimeric protein. However, in the presence of Triton X-100 a monomeric structure was implied. N-Glycanase digestion indicated that the protein is probably not glycosylated. The purified antigen was characterized as an integral membrane protein by hydrophobic chromatography and phase-separation experiments with Triton X-114. The antigen, or at least the antibody binding region of the molecule, is very susceptible to protease attack, as judged by protease digestion experiments on brain membranes. By using very low concentrations of papain combined with short incubation times, the antigen was converted to a 16.3-kDa membrane-associated polypeptide as assessed by immunoblotting. This polypeptide contained the BM88 binding epitope. Soluble BM88 immunoreactive polypeptides were not obtained. Bacillus cereus phospholipase C was also unable to solubilize the antigen from the membrane. Our results suggest that the molecule, possessing at least one small extramembranous domain, is attached to the membrane via a polypeptide chain.

Immunocytochemical localization of endopeptidase-24.11 in cultured neurons from pig striatum

Endopeptidase-24.11 ("enkephalinase") appears to play a key role in the metabolism of a number of neuropeptides at cell surfaces. It has been previously mapped in the central nervous system, but some doubt has been expressed concerning the identity of the cell type expressing this peptidase. Primary cell cultures derived from striata of new-born piglets were set up and cells were characterized by immunocytochemistry using antibodies to neurofilament protein, a glial fibrillary acidic protein and a neuronal antigen recognized by a monoclonal antibody BM88 and by histochemistry for acetylcholinesterase. Some cultures were set up in which neurons were selectively enriched. Cells which were thus morphologically defined as neurons were recognized by an affinity-purified polyclonal antibody to endopeptidase-24.11. The staining for the peptidase, which was punctate in appearance, was shown to be at the cell surface and extended to the perikaryon and all neurites. Compared with the number of neurofilament protein-positive cells, relatively few cells were positive for endopeptidase-24.11. No glial cells, immunochemically defined by glial fibrillary acidic protein, were stained by the antibody to endopeptidase-24.11. We conclude that endopeptidase-24.11 is expressed on the surface of a set of neurons derived from the striatum in primary culture and not by any glial cells in these cultures.

Neuron- and myelin-specific monoclonal antibodies recognizing cell-surface antigens of the central and peripheral nervous system

Immunohistochemical screening of monoclonal antibodies raised against Triton X-114-treated synaptic membranes revealed two monoclonal antibodies, namely BM88 and BM72, with characteristic binding specificities in the central and peripheral nervous systems of the pig. Monoclonal antibody BM88 was exclusively associated with neuronal elements while BM72 was myelin-specific. Thus, in the central nervous system, immunostaining with BM88 was observed throughout the gray matter of all regions of the forebrain and spinal cord tested. In the peripheral nervous system, BM88 strongly labelled the perikarya and processes of dorsal root ganglion neurons as well as the myelinated and unmyelinated neuronal processes of the dorsal roots; BM88 immunoreactivity was also detected in neuronal cell bodies and fibres of the enteric ganglia. In addition, BM88 immunolabelled the cell-surface of cultured neurons derived from brain. In mixed cultures the staining was uniformly distributed on the perikarya and along the neurites of these cells. However, in neuron-enriched cultures where 95% of the cells were immunochemically identified as neurons, the staining of the neuronal surface membrane was patchy. This phenomenon was independent of days in culture and suggested that the distribution of the BM88 antigen on the cell surface of neurons may be regulated by neuron glia interactions. By Western blotting, the antigen recognized by BM88 in brain membrane fractions which had undergone reducing sodium dodecyl sulphate/polyacrylamide gel electrophoresis was shown to be a 22,000 mol. wt polypeptide. When extracted with Triton X-114 this polypeptide partitioned into the detergent-rich phase, a property typical of an amphipathic membrane protein. In non-reducing conditions BM88 bound to a band with a molecular weight of 43,000. These results show that the BM88 antigen is composed of two polypeptide chains of equal molecular weight linked by disulphide bridges. Monoclonal antibody BM72 recognized a myelin-associated antigen in the central and peripheral nervous system. Immunohistochemical evidence suggested a cell-surface location for this antigen. By solid phase radioimmunoassay, monoclonal antibody BM88 was shown to cross-react with brain membrane fractions from pig, rabbit and rat while BM72 recognized only a pig membrane antigen. Both monoclonal antibodies BM88 and BM72 may be used as specific cellular markers in the nervous system.

Endopeptidase-24.11 is striosomally ordered in pig brain and, in contrast to aminopeptidase N and peptidyl dipeptidase A ('angiotensin converting enzyme'), is a marker for a set of striatal efferent fibres

Endopeptidase-24.11 (sometimes referred to as 'enkephalinase') is a key cell-surface enzyme in the metabolism of neuropeptides. A previous immunohistochemical study mapped the enzyme in pig brain and indicated a striosomal ordering of the enzyme within the striatum. This point has now been confirmed by staining adjacent sections for acetylcholinesterase (by histochemistry) and endopeptidase-24.11 (by an immunoperoxidase method). While there were some general similarities in the mapping of these two hydrolases, e.g. in the caudate-putamen, globus pallidus, olfactory tubercle, substantia nigra and striatonigral tract, there were differences in intensity and in the microscopic distribution, e.g. as in striosomes for which acetylcholinesterase was diminished. Two other membrane peptidases, peptidyl dipeptidase A ('angiotensin converting enzyme') and aminopeptidase N, were also mapped by the same immunohistochemical method. Peptidyl dipeptidase A had some similarities with endopeptidase-24.11, e.g. in its concentration within the striatal nuclei, but clear differences were also apparent, in particular the absence of staining of the former in the globus pallidus and olfactory tubercle. Immunostaining for aminopeptidase N, in contrast to the other peptidases, was observed as a diffuse staining throughout the gray matter. At the microscopic level, two important differences were that staining for aminopeptidase N and peptidyl dipeptidase A was very intense throughout the vasculature of the brain and that striatal efferent bundles of unmyelinated fibres staining positively for endopeptidase-24.11 were depleted of the other two peptidases. All three peptidases were identified in the pia mater. Thus, endopeptidase-24.11, unlike peptidyl dipeptidase A and aminopeptidase N, is a marker for a set of striatal efferent fibres in pig brain.

An immunohistochemical study of endopeptidase-24.11 ("enkephalinase") in the pig nervous system

Endopeptidase-24.11, a plasma membrane ectoenzyme with the ability to hydrolyse a variety of neuropeptides, has been localized in the pig nervous system by an immunoperoxidase technique. The endopeptidase was mapped in cryostat sections of the fore and mid-brain to the following structures: caudate-putamen, globus pallidus, olfactory tubercle, nucleus interpeduncularis and substantia nigra. Endopeptidase-24.11-like immunoreactivity was also found in the pia mater, choroid plexus and ependymal lining of the central canal. In the spinal cord, weak staining was observed in the dorsal horn, but strong staining was found in the dorsal root ganglia and nerve roots. Within the central nervous system, endopeptidase immunoreactivity was confined to gray matter and within the positive areas of the striatum densely staining areas, corresponding to striosomes, were discernible. These well-defined structures were exploited in serial sections to examine the alignment of the enzyme-rich patches of neuropil with correspondingly strong staining for other antigens. A consistent match was observed with a monoclonal antibody to neurofilament protein, but there was a poor correlation with a polyclonal antibody to glial fibrillary acidic protein. Substance P-like and [Leu]enkephalin-like immunoreactivity were also studied in sections adjacent to those stained for the endopeptidase. Good matching between enzyme-rich and peptide-rich areas was observed, but some enkephalin-rich areas did not align with enzyme staining and indeed endopeptidase-rich areas were not necessarily matched with areas rich in either peptide. These findings suggest a neuronal rather than an astrocytic location for endopeptidase-24.11 in the CNS and lend support to the view that it plays a central role in neuropeptide metabolism at membrane surfaces. In the peripheral nervous system, the endopeptidase was located in Schwann cell membranes surrounding dorsal root ganglion cells and nerve fibres, while in the pituitary the main concentration was in the adenohypophysis, where only a proportion of the endocrine cells were found to be immunoreactive.

The metabolism of neuropeptides. Phase separation of synaptic membrane preparations with Triton X-114 reveals the presence of aminopeptidase N

The property of solutions of Triton X-114 to separate into detergent-rich and detergent-poor phases at 30 degrees C has been exploited to investigate the identities of the aminopeptidases in synaptic membrane preparations from pig striatum. When titrated with an antiserum to aminopeptidase N (EC 3.4.11.2), synaptic membranes solubilized with Triton X-100 revealed that this enzyme apparently comprises no more than 5% of the activity releasing tyrosine from [Leu]enkephalin. When assayed in the presence of puromycin, this proportion increased to 20%. Three integral membrane proteins were fractionated by phase separation in Triton X-114. Aminopeptidase activity, endopeptidase-24.11 and peptidyl dipeptidase A partitioned predominantly into the detergent-rich phase when kidney microvillar membranes were so treated. However, only 5.5% of synaptic membrane aminopeptidase activity partitioned into this phase, although the other peptidases behaved predictably. About half of the aminopeptidase activity in the detergent-rich phase could now be titrated with the antiserum, showing that aminopeptidase N is an integral membrane protein of this preparation. Three aminopeptidase inhibitors were investigated for their ability to discriminate between the different activities revealed by these experiments. Although amastatin was the most potent (IC50 = 5 X 10(-7) M) it failed to discriminate between pure kidney aminopeptidase N, the total activity of solubilized synaptic membranes and that in the Triton X-114-rich phase. Bestatin was slightly more potent for total activity (IC50 = 6.3 X 10(-6) M) than for the other two forms (IC50 = 1.6 X 10(-5) M). Puromycin was a weak inhibitor, but was more selective. The activity of solubilized membranes was more sensitive (IC50 = 1.6 X 10(-5) M) than that of the pure enzyme or the Triton X-114-rich phase (IC50 = 4 X 10(-4) M). We suggest that the puromycin-sensitive aminopeptidase activity that predominates in crude synaptic membrane preparations may be a cytosolic contaminant or peripheral membrane protein rather than an integral membrane component. Aminopeptidase N may contribute to the extracellular metabolism of enkephalin and other susceptible neuropeptides in the brain.

The metabolism of neuropeptides. The hydrolysis of peptides, including enkephalins, tachykinins and their analogues, by endopeptidase-24.11

Endopeptidase-24.11 (EC 3.4.24.11), purified to homogeneity from pig kidney, was shown to hydrolyse a wide range of neuropeptides, including enkephalins, tachykinins, bradykinin, neurotensin, luliberin and cholecystokinin. The sites of hydrolysis of peptides were identified, indicating that the primary specificity is consistent with hydrolysis occurring at bonds involving the amino group of hydrophobic amino acid residues. Of the substrates tested, the amidated peptide substance P is hydrolysed the most efficiently (Km = 31.9 microM; kcat. = 5062 min-1). A free alpha-carboxy group at the C-terminus of a peptide substrate is therefore not essential for efficient hydrolysis by the endopeptidase. A large variation in kcat./Km values was observed among the peptide substrates studied, a finding that reflects a significant influence of amino acid residues, remote from the scissile bond, on the efficiency of hydrolysis. These subsite interactions between peptide substrate and enzyme thus confer some degree of functional specificity on the endopeptidase. The inhibition of endopeptidase-24.11 by several compounds was compared with that of pig kidney peptidyldipeptidase A (EC 3.4.15.1). Of the inhibitors examined, only N-[1(R,S)-carboxy-2-phenylethyl]-Phe-p-aminobenzoate inhibited endopeptidase-24.11 but not peptidyldipeptidase. Captopril (D-3-mercapto-2-methylpropanoyl-L-proline), Teprotide (pGlu-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro) and MK422 [N-[(S)-1-carboxy-3-phenylpropyl]-L-Ala-L-Pro] were highly selective as inhibitors of peptidyldipeptidase. Although not wholly specific, phosphoramidon was a more potent inhibitor of endopeptidase-24.11 than were any of the synthetic compounds tested.

Endopeptidase-24.11 and aminopeptidase activity in brain synaptic membranes are jointly responsible for the hydrolysis of cholecystokinin octapeptide (CCK-8)

Endopeptidase-24.11 (EC 3.4.24.11) from pig kidney hydrolysed CCK-8 (sulphated) at two distinct sites: Asp-Tyr(SO3H)-Met-Gly Trp-Met-Asp PheNH2. Under initial conditions, the splitting of the Asp7-Phe8NH2 bond proceeded 4-times more rapidly than the Gly4-Trp5 bond. Pig brain striatal synaptic membranes attacked this substrate at the same sites and this activity was inhibited by phosphoramidon. However, other products were detected even in the presence of phosphoramidon. One of these products was identified as free tryptophan. Since their formation was inhibited by bestatin, one or more membrane aminopeptidases is also implicated in the degradation of CCK-8.

Purification of endopeptidase-24.11 ('enkephalinase') from pig brain by immunoadsorbent chromatography

Membrane preparations from striatum of pig brain contain endopeptidase activity towards iodoinsulin B-chain. Only 50% of the hydrolysis of insulin B-chain is inhibitable by phosphoramidon, and DEAE-cellulose chromatography can resolve the phosphoramidon-sensitive and -insensitive activities. The former activity (now designated 'endopeptidase-24.11') is responsible for hydrolysis of [D-Ala2,Leu5]enkephalin and is identical with an enzyme in brain that has previously been referred to as 'enkephalinase'. Pig striatal endopeptidase-24.11 has now been purified to homogeneity in a single step by immunoadsorbent chromatography using a monoclonal antibody. The overall purification was 23 000-fold, with a yield of 30%. The brain enzyme appears to be identical with kidney endopeptidase-24.11 in amino acid composition as well as by immunological and kinetic criteria. However, it differs slightly in apparent subunit size (Mr = 87 000), attributable to differences in glycosylation.

A monoclonal antibody to kidney endopeptidase-24.11. Its application in immunoadsorbent purification of the enzyme and immunofluorescent microscopy of kidney and intestine

Hybridoma methodology has been used to produce a monoclonal antibody, GK 7C2, that binds specifically to microvillar endopeptidase-24.11 (EC 3.4.24.11). The antibody (an immunoglobulin G) was generated by fusion of mouse plasmacytoma cells with splenocytes from a Balb/c mouse immunized with pig kidney microvillar membranes. The identity of the antigen recognized by GK 7C2 was established by immuno-precipitation from detergent-solubilized pig kidney microvilli. The protein had an apparent Mr of 90 000 and contained endopeptidase activity sensitive to phosphoramidon. The identity was confirmed by immunoadsorbent purification of endopeptidase-24.11 by a column to which GK 7C2 had been attached. The endopeptidase, purified in a yield of 40%, was electrophoretically homogeneous and of specific activity comparable with that purified by other means. Fluorescence microscopy established that GK 7C2 bound specifically to the luminal membranes of kidney tubules and the intestinal mucosa. Thus endopeptidase-24.11 is located in the brush-border membranes of both cell types.

Substance P and [Leu]enkephalin are hydrolyzed by an enzyme in pig caudate synaptic membranes that is identical with the endopeptidase of kidney microvilli

The hydrolysis of [Leu]enkephalin and substance P by purified pig kidney endopeptidase (EC 3.4.24.11) and synaptic membranes prepared from pig caudate nuclei has been compared. The hydrolysis of an enkephalin analogue (Tyr-D-Ala-Gly-Phe-Leu) at the Gly-Phe bond was completely inhibited by phosphoramidon. The IC50 concentration (8 nM) was similar to that reported for [Leu]enkephalin hydrolysis by the purified endopeptidase [Fulcher, I. S., Matsas, R., Turner, A. J. & Kenny, A. J. (1982) Biochem. J. 203, 519-522]. Seven peptides were produced when substance P (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2) was hydrolyzed by the kidney endopeptidase. These were formed by cleavage at bonds Gln-Phe (positions 6 and 7), Phe-Phe (positions 7 and 8), and Gly-Leu (positions 9 and 10). Synaptic membranes generated peptides with the same HPLC retention times and hydrolysis of substance P by either preparation was inhibited completely by 10 microM phosphoramidon. The most susceptible bond appeared to be Gly-Leu (positions 9 and 10). A specific polyclonal antibody raised in rabbits to purified pig endopeptidase inhibited the hydrolysis of [Leu]enkephalin and substance P by detergent-solubilized kidney microvilli or synaptic membranes; the titration curves were essentially identical. We conclude that the endopeptidase, which we suggest should be designated "endopeptidase-24.11," is present in caudate synaptic membranes and could play an important role in the hydrolysis of neuropeptides.

Kidney neutral endopeptidase and the hydrolysis of enkephalin by synaptic membranes show similar sensitivity to inhibitors

Neutral endopeptidase (EC 3.4.24.11) from pig kidney hydrolyses [125I]iodo-insulin B-chain and leucine-enkephalin. Both activities were equally sensitive to inhibition by phosphoramidon [N-(alpha-L-rhamnopyranosyloxyhydroxyphosphinyl)-L-leucyl-L-tryptophan] and thiorphan [N-(DL-2-benzyl-3-mercaptopropionyl)glycine]. Thermolysin hydrolysis of insulin B-chain was also sensitive to both inhibitors. The hydrolysis of the Gly3-Phe4 bond of Leu-enkephalin by synaptic membranes prepared from pig brain was partially inhibited by phosphoramidon and thiorphan. Synaptic membranes appear to contain another endopeptidase activity that is insensitive to these reagents. These observations suggest that enzymes similar to the kidney endopeptidase may play a general role in neuropeptide metabolism.