Tyrosine kinase A but not phosphacan/protein tyrosine phosphatase-ζ/β immunoreactivity and protein level changes in neurons and astrocytes in the gerbil hippocampus proper after transient forebrain ischemia

In the present study, ischemia-related changes in tyrosine kinase A (trkA) and phosphacan/protein tyrosine phosphatase-zeta/beta (PTP-zeta/beta) immunoreactivities and protein contents were examined in the hippocampus proper after transient forebrain ischemia for 5 min in a gerbil model. Our investigations showed that ischemia-induced changes occurred in trkA immunoreactivity in the hippocampal CA1 region, but not in the CA2/3 region of the hippocampus proper. In the sham-operated group, trkA immunoreactivity was barely detectable. trkA immunoreactivity increased from 30 min after ischemia and peaked at 12 h. Four days after ischemic insult, trkA immunoreactivity was observed in GFAP-immunoreactive astrocytes in the strata oriens and radiatum. In addition, we found that ischemia-related changes in trkA protein content were similar to immunohistochemical changes. On the other hand, PTP-zeta/beta immunoreactivities in the hippocampus proper were unaltered by forebrain ischemia. These results suggest that chronological changes of trkA after transient forebrain ischemia may be associated with an ischemic damage compensatory mechanism in CA1 pyramidal cells.

The extracellular matrix glycoprotein Tenascin-C is expressed by oligodendrocyte precursor cells and required for the regulation of maturation rate, survival and responsiveness to platelet-derived growth factor

Analysis of Tenascin-C (TN-C) knockout mice revealed novel roles for this extracellular matrix (ECM) protein in regulation of the developmental programme of oligodendrocyte precursor cells (OPCs), their maturation into myelinating oligodendrocytes and sensitivity to growth factors. A major component of the ECM of developing nervous tissue, TN-C was expressed in zones of proliferation, migration and morphogenesis. Examination of TN-C knockout mice showed roles for TN-C in control of OPC proliferation and migration towards zones of myelination [E. Garcion et al. (2001) Development, 128, 2485-2496]. Extending our studies of TN-C effects on OPC development we found that OPCs can endogenously express TN-C protein. This expression covered the whole range of possible TN-C isoforms and could be strongly up-regulated by leukaemia inhibitory factor and ciliary neurotrophic factor, cytokines known to modulate OPC proliferation and survival. Comparative analysis of TN-C knockout OPCs with wild-type OPCs reveals an accelerated rate of maturation in the absence of TN-C, with earlier morphological differentiation and precocious expression of myelin basic protein. TN-C knockout OPCs plated on poly-lysine displayed higher levels of apoptosis than wild-type OPCs and there was also an earlier loss of responsiveness to the protective effects of platelet-derived growth factor (PDGF), indicating that TN-C has anti-apoptotic effects that may be associated with PDGF signalling. The existence of mechanisms to compensate for the absence of TN-C in the knockout is indicated by the development of oligodendrocytes derived from TN-C knockout neurospheres. These were present in equivalent proportions to those found in wild-type neurospheres but displayed enhanced myelin membrane formation.

Receptor protein tyrosine phosphatase ζ as a therapeutic target for glioblastoma therapy

Astrocytomas are the most frequent brain tumour type in adults. The most common astrocytoma is the glioblastoma (GBM), which is also the most malignant and refractory to treatment--ultimately leading to the patient's death within a year of diagnosis. Neither the classical nor more experimental therapeutic approaches have significantly improved the clinical outcome of this disease. Expression profile analysis of primary tumours has provided recent insight into the identification of new GBM therapeutic targets. These proteins serve as excellent candidates to either inhibit the target molecule's functions (e.g., angiogenesis, migration or proliferation) or, coupled with a toxin or radionucleotide, to bind and exterminate the tumour cells. The receptor protein tyrosine phosphatase zeta (RPTPzeta) and one of its main ligands, pleiotropin (Ptn), are overexpressed in GBMs, thus making them potentially very good targets for the development of new immunotherapeutics. This review will summarise recent advances in GBM therapies focusing on RPTPzeta as a target for immunotherapeutics.

Differential upregulation of extracellular matrix molecules associated with the appearance of granule cell dispersion and mossy fiber sprouting during epileptogenesis in a murine model of temporal lobe epilepsy

We have investigated changes in the extracellular matrix of the hippocampus associated with the early progression of epileptogenesis in a murine model of temporal lobe epilepsy using immunohistochemistry. In the first week following intrahippocampal injection of the glutamate agonist, domoate, there is a latent period at the end of which begins a sequential upregulation of extracellular matrix (ECM) molecules in the granule cell layer of the dentate gyrus, beginning with neurocan and tenascin-C. This expression precedes the characteristic dispersion of the granule cell layer which is evident at 14 days post-injection when the first recurrent seizures can be recorded. At this stage, an upregulation of the chondroitin sulfate proteoglycan, phosphacan, the DSD-1 chondroitin sulfate motif, and the HNK-1 oligosaccharide are also observed. The expression of these molecules is localized differentially in the epileptogenic dentate gyrus, especially in the sprouting molecular layer, where a strong upregulation of phosphacan, tenascin-C, and HNK-1 is observed but there is no expression of the proteoglycan, neurocan, nor of the DSD-1 chondroitin sulfate motif. Hence, it appears that granule cell layer dispersion is accompanied by a general increase in the ECM, while mossy fiber sprouting in the molecular layer is associated with a more restricted repertoire. In contrast to these changes, the expression of the ECM glycoproteins, laminin and fibronectin, both of which are frequently implicated in tissue remodelling events, showed no changes associated with either granule cell dispersion or mossy fiber sprouting, indicating that the epileptogenic plasticity of the hippocampus is accompanied by ECM interactions that are characteristic of the CNS.

Growth factor and cytokine regulation of chondroitin sulfate proteoglycans by astrocytes

After injury to the adult central nervous system (CNS), numerous cytokines and growth factors are released that contribute to reactive gliosis and extracellular matrix production. In vitro examination of these cytokines revealed that the presence of transforming growth factor-beta1 (TGF-beta1) and epidermal growth factor (EGF) greatly increased the production of several chondroitin sulfate proteoglycans (CSPG) by astrocytes. Treatment of astrocytes with other EGF-receptor (ErbB1) ligands, such as TGF-alpha and HB-EGF, produced increases in CSPG production similar to those observed with EGF. Treatment of astrocytes, however, with heregulin, which signals through other members of the EGF-receptor family (ErbB2, ErbB3, ErbB4), did not induce CSPG upregulation. The specificity of activation through the ErbB1 receptor was further verified by using a selective antagonist (AG1478) to this tyrosine kinase receptor. Western blot analysis of astrocyte supernatant pre-digested with chondroitinase ABC indicated the presence of multiple core proteins containing 4-sulfated or 6-sulfated chondroitin. To identify some of these CSPGs, Western blots were screened using antibodies to several known CSPG core proteins. These analyses showed that treatment of astrocytes with EGF increased phosphacan expression, whereas treatment with TGF-beta1 increased neurocan expression. Reverse transcription-polymerase chain reaction (RT-PCR) was used to examine the expression of these molecules in vivo, which result in increased expression of TGF-beta1, EGF-receptor, neurocan, and phosphacan after injury to the brain. These data begin to elucidate some of the injury-induced growth factors that regulate the expression of CSPGs which could be targeted in the future to modulate CSPG production after injury to the central nervous system.

Intracellular VacA is a valuable marker to predict whether Helicobacter pylori induces progressive atrophic gastritis that is associated with the development of gastric cancer

VacA was histochemically stained in biopsy specimen and was intracellularly and mainly located in fundic gland area. It is recognized gastric atrophy was observed in the H. pylori-positive patients with intracellular VacA compared with others. The aim of study is to understand the relationship between intracellular VacA and the progression of gastric atrophy that is associated with gastric cancer. Biopsy specimens and sera were obtained from 364 people in their 50s and 60s without gastric cancer diagnosed at first endoscopy undergoing diagnostic endoscopy, for H. pylori infection, histology, and the histochemical status of intracellular VacA using anti-VacA Ab during the follow-up period (mean, 7.3 years). Three hundred eleven of 364 enrolled patients were H. pylori positive and 53 patients were H. pylori negative at first endoscopy. VacA was intracellularly stained with vacuolation and cell destruction in the fundic gland in 98 of 311 H. pylori-positive patients and not stained in another 213 H. pylori-positive patients plus 53 H. pylori-negative patients at first endoscopy. Gastric atrophy has significantly progressed in the H. pylori-positive patints with intracellular VacA with gastric ulcers compared with the others and six gastric cancers have developed in this group during the follow-up period (mean, 7.3 years). Intracellular VacA is a valuable marker to predict whether Helicobacter pylori induces progressive atrophic gastritis that is associated with the development of gastric cancer.

Changes in the amounts of chondroitin sulfate proteoglycans in rat brain after neonatal hypoxia-ischemia

Chondroitin sulfate proteoglycans have been shown to participate in the pathogenesis of neuronal damages in the injured adult central nervous system (CNS). Upregulated expression of chondroitin sulfate proteoglycans has been reported around the injured sites and depletion of these chondroitin sulfate proteoglycans brings about increased axonal regeneration in the injured adult CNS. To examine if chondroitin sulfate proteoglycans are also involved in the pathologic process of hypoxia-ischemia in the neonatal brain, expressions of three chondroitin sulfate proteoglycans, neurocan, phosphacan, and neuroglycan C, were examined in rat brains after neonatal hypoxia-ischemia. Hypoxic-ischemic rats were produced by ligating the right carotid artery of 7-day-old rats, followed by 8% oxygen exposure. Western blot analysis revealed that in contrast to injured adult CNS, the amount of neurocan was reduced 24 hr after hypoxia in the neonatal hypoxic-ischemic cerebral hemisphere. The amounts of phosphacan and neuroglycan C were also reduced significantly 24 hr after hypoxia at the right injured cortex compared to those at the left cortex. Surprisingly, the immunohistologic staining for phosphacan was conversely intensified both at 24 hr and 8 days after hypoxia at the infarcted area. In addition, the habenula and fascicules retroflexus in the right cerebral hemisphere degenerated and became intensely immunostained with the anti-phosphacan antibody shortly after hypoxia. Hypoxic-ischemic insult may unmask phosphacan epitopes at the injured sites, resulting in intensified immunostaining. Because intensified immunostaining for neurocan and neuroglycan C was not observed, unmasking seems to be specific to phosphacan among these three chondroitin sulfate proteoglycans.

alpha4beta1- and alpha6beta1-integrins are functional receptors for midkine, a heparin-binding growth factor

Midkine is a heparin-binding growth factor that promotes the growth, survival, migration and differentiation of various target cells. So far, receptor-type protein tyrosine phosphatase zeta, low-density-lipoprotein-receptor-related protein and anaplastic lymphoma kinase have been identified as receptors for midkine. We found beta1 integrin in midkine-binding proteins from 13-day-old mouse embryos. beta1-Integrin bound to a midkine-agarose column and was eluted mostly with EDTA. Further study revealed that the alpha-subunits capable of binding to midkine were alpha4 and alpha6. Purified alpha4beta1- and alpha6beta1-integrins bound midkine. Anti-alpha4 antibody inhibited the midkine-dependent migration of osteoblastic cells, and anti-alpha6 antibody inhibited the midkine-dependent neurite outgrowth of embryonic neurons. After midkine treatment, tyrosine phosphorylation of paxillin, an integrin-associated molecule, was transiently increased in osteoblastic cells. Therefore, we concluded that alpha4beta1- and alpha6beta1-integrins are functional receptors for midkine. We observed that the low-density-lipoprotein-receptor-related-protein-6 ectodomain was immunoprecipitated with alpha6beta1-integrin and alpha4beta1-integrin. The low-density-lipoprotein-receptor-related-protein-6 ectodomain was also immunoprecipitated with receptor-type protein tyrosine phosphatase zeta. alpha4beta1- and alpha6beta1-Integrins are expected to co-operate with other midkine receptors, possibly in a multimolecular complex that contains other midkine receptors.

Activity-dependent regulation of a chondroitin sulfate proteoglycan 6B4 phosphacan/RPTPbeta in the hypothalamic supraoptic nucleus

The hypothalamic magnocellular neurons, synthesizing arginine vasopressin (AVP) and oxytocin, are well known to show structural plasticity during chronic physiological stimulation. We have previously reported that 6B4 phosphacan/receptor-type protein-tyrosine phosphatasebeta (RPTPbeta), a chondroitin sulfate proteoglycan is highly expressed in the supraoptic nucleus (SON) of adult hypothalamus. Here, we undertook to study the activity-dependent regulation of 6B4 phosphacan/RPTPbeta in this system. Double labeling confocal microscopy demonstrated in the SON that 6B4 phosphacan/RPTPbeta-immunoreactive perineuronal nets were seen around AVP-containing somata and dendrites and its distribution pattern was well coincided with that of TAG-1. Quantitative immunohistochemical and Western analyses showed that 1-week salt loading, known as the chronic physiological stimulation for inducing the structural changes such as synaptic remodeling and direct neuronal membrane apposition, decreased 6B4 phosphacan/RPTPbeta levels in the SON, but did not alter TAG-1 levels. The 6B4 phosphacan/RPTPbeta levels were returned to control basal values within 3 weeks after the cessation of the chronic stimulation. Activity-dependent decreases in 6B4 phosphacan/RPTPbeta levels of the SON were confirmed when Western and immunohistochemical samples were digested with chondroitinase ABC, indicating that the decrease in 6B4 phosphacan/RPTPbeta levels was due to disappearance of 6B4 phosphacan/RPTPbeta core protein rather than increase in chondroitin sulfate glycosaminoglycans. With electron microscopy, the electron-dense immunoproducts for 6B4 phosphacan/RPTPbeta were found on the membrane surface of axons and glial processes, but not at synaptic junctions in control SON, and its immunoreactivity was eliminated with the chronic salt loading. The present results indicate that the levels of 6B4 phosphacan/RPTPbeta are regulated with activity-dependent manner and may be concerned with the structural plasticity seen in the SON.

Essential domain of receptor tyrosine phosphatase beta (RPTPbeta) for interaction with Helicobacter pylori vacuolating cytotoxin

Helicobacter pylori produces a potent exotoxin, VacA, which causes progressive vacuolation as well as gastric injury. Although VacA was able to interact with two receptor-like protein tyrosine phosphatases, RPTPbeta and RPTPalpha, RPTPbeta was found to be responsible for gastric damage caused by VacA. To define the region of RPTPbeta involved in VacA binding, we made mutants of human cDNA RPTPbeta-B, a short receptor form of RPTPbeta. Immunoprecipitation experiments to assess VacA binding to RPTPbeta-B mutants indicated that five residues (QTTQP) at positions 747-751 of the extracellular domain of RPTPbeta-B (which is commonly retained in RPTPbeta-A, a long form of RPTPbeta) play a crucial role in its interaction with VacA, resulting in vacuolation as well as Git-1 phosphorylation. Transfected cells expressing deletion mutant Delta752, which lacks QTTQP, or the double point mutant Delta747 (T748A,T749A) had diminished vacuolation in response to VacA. Treatment of RPTPbeta-B and Delta747 (which have QTTQP at 747-751) with neuraminidase and O-glycosidase diminished their VacA binding, whereas chondroitinase ABC did not have an effect. No inhibitory effect of pleiotrophin, a natural RPTPbeta ligand, on VacA binding to RPTPbeta-B or Delta747 was observed, supporting the conclusion that the extracellular region of RPTPbeta-B responsible for VacA binding is different from that involved in binding pleiotrophin. These data define the region in the RPTPbeta extracellular domain critical for VacA binding, in particular the sequence QTTQP at positions 747-751 with crucial threonines at positions 748 and 749 and are consistent with a role for terminal sialic acids possibly because of threonine glycosylation.

Identification of pleiotrophin in conditioned medium secreted from neural stem cells by SELDI-TOF and SELDI-tandem mass spectrometry

Neural stem cells (NSCs) are multipotential progenitor cells that have self-renewal activity. Since the fates of the NSCs in situ depend on their niche containing growth factors and cytokines, we performed surface enhanced laser desorption/ionization time-of flight mass spectrometry (SELDI-TOF-MS) to screen for differentially secreted proteins in conditioned medium of neural stem cells and compared with that of NIH3T3 cells. A 15.3-kDa protein detected only in the conditioned medium of neural stem cells was determined as pleiotrophin (PTN) by SELDI-TOF-MS and ProteinChip-tandem MS systems. Identification of pleiotrophin was further confirmed by one-dimensional SDS gel electrophoresis and Edman degradation analysis. The mRNA transcripts of PTN and its receptors [receptor protein tyrosine phosphatase (RPTP) beta/zeta, N-syndecan and anaplastic lymphoma kinase (ALK)] were detected in neurosphere, suggesting that pleiotrophin signaling systems are present in the neural stem cells and are involved in the modulation of fate of neural stem cells.

Expression of phosphacan and neurocan during early development of mouse retinofugal pathway

We have investigated whether the two major brain chondroitin sulfate (CS) proteoglycans (PGs), phosphacan and neurocan, are expressed in patterns that correlate to the axon order changes in the mouse retinofugal pathway. Expression of these proteoglycans was examined by polyclonal antibodies against phosphacan and N- and C-terminal fragments of neurocan. In E13-E15 mouse embryos, when most optic axons grow in the chiasm and the optic tract, phosphacan and neurocan were observed in the inner regions of the retina. In the chiasm and the tract, phosphacan but not neurocan was expressed prominently at the midline and in the deep parts of the tract. Both proteoglycans were observed on the chiasmatic neurons, which have been shown to regulate axon divergence at the chiasmatic midline and the chronotopic fiber ordering in the tract, but phosphacan appeared to be the predominant form that persists to later developmental stages. Intense staining of both proteoglycans was also observed in a strip of glial-like elements in lateral regions of the chiasm, partitioning axons in the stalk from those in the tract. We conclude that phosphacan but not neurocan is likely the major carrier of the CS glycosaminoglycans that play crucial functions in axon divergence and age-related axon ordering in the mouse optic pathway. Furthermore, localization of these carrier proteins in the optic pathway raises a possibility that these two proteoglycans regulate axon growth and patterning not only through the sulfated sugars but also by interactions of the protein parts with guidance molecules on the optic axons.

Neural precursors express multiple chondroitin sulfate proteoglycans, including the lectican family

Chondroitin sulfate proteoglycans (CSPGs) abnormally accumulate in cerebrospinal fluid (CSF) of both human neonates with preterm hydrocephalus, and P8 hydrocephalic mice. We hypothesized CSF CSPGs are synthesized by neural precursors, separated from ventricular CSF by ependyma, which is often disrupted in hydrocephalus. Western blotting demonstrates that neural precursors cultured as neurospheres secrete CSPGs (> 30 microg/ml) into their media which appear to be very similar to these CSF CSPGs. Some CSPGs bear the stage-specific embryonic antigen-1 (ssea-1), associated with embryonic/neural stem cells. Neurospheres transcribe many CSPG genes, including the entire aggrecan/lectican family, phosphacan, and tenascin. Phosphacan can be detected in media by Western blotting. Aggrecan can be detected in media after purification using hyaluronic acid affinity chromatography. During differentiation, neurospheres downregulate CSPGs. This is the first report to show that proliferating neural precursors synthesize lecticans, including aggrecan, which are downregulated with differentiation. These observations suggest novel links between CSPGs and CNS precursor biology.

Mutational analysis of the tyrosine phosphatome in colorectal cancers

Tyrosine phosphorylation, regulated by protein tyrosine phosphatases (PTPs) and kinases (PTKs), is important in signaling pathways underlying tumorigenesis. A mutational analysis of the tyrosine phosphatase gene superfamily in human cancers identified 83 somatic mutations in six PTPs (PTPRF, PTPRG, PTPRT, PTPN3, PTPN13, PTPN14), affecting 26% of colorectal cancers and a smaller fraction of lung, breast, and gastric cancers. Fifteen mutations were nonsense, frameshift, or splice-site alterations predicted to result in truncated proteins lacking phosphatase activity. Five missense mutations in the most commonly altered PTP (PTPRT) were biochemically examined and found to reduce phosphatase activity. Expression of wild-type but not a mutant PTPRT in human cancer cells inhibited cell growth. These observations suggest that the mutated tyrosine phosphatases are tumor suppressor genes, regulating cellular pathways that may be amenable to therapeutic intervention.

Decorin suppresses neurocan, brevican, phosphacan and NG2 expression and promotes axon growth across adult rat spinal cord injuries

The formation of misaligned scar tissue by a variety of cell types expressing multiple axon growth inhibitory proteoglycans presents a physical and molecular barrier to axon regeneration after adult spinal cord injuries. Decorin is a small, leucine-rich proteoglycan that has previously been shown to reduce astrogliosis and basal lamina formation in acute cerebral cortex stab injuries. We have therefore tested whether mini pump infusion of hr-decorin into acute stab injuries of the adult rat spinal cord can not only inhibit formation of an astroglial limitans but also deposition of the axon growth inhibitory proteoglycans neurocan, NG2, phosphacan and brevican. Combined immunohistochemical and quantitative Western blot analysis revealed major reductions in levels of core protein expression (>80% for 130-kDa neurocan, 145/80-kDa brevican, 300-kDa phosphacan) and immunoreactivity for all four chondroitin sulfate proteoglycans (CSPGs) within decorin-treated injuries compared with untreated controls. Astrogliosis within lesion margins and the accumulation of OX42+ macrophages/microglia within lesion centres were also significantly reduced. These decorin-induced changes in scar formation combined to promote the striking ability of axons from microtransplanted adult sensory neurons to enter, grow within and exit decorin-infused spinal cord injuries, in sharp contrast to the complete failure of axons to cross untreated, CSPG-rich lesions. Decorin pretreatment of meningial fibroblasts in vitro also resulted in a three-fold increase in neurite outgrowth from co-cultured adult sensory neurons and suppression of NG2 immunoreactivity. The ability of decorin to promote axon growth across acute spinal cord injuries via a coordinated suppression of inflammation, CSPG expression and astroglial scar formation make decorin treatment a promising component of future spinal cord regeneration strategies.

Function analysis of estrogenically regulated protein tyrosine phosphatase gamma (PTPgamma) in human breast cancer cell line MCF-7

Protein tyrosine phosphatase gamma (PTPgamma) is a member of the receptor-like family of tyrosine phosphatases and has been implicated as a tumor suppressor gene in kidney and lung cancers. Based on our previous findings, we hypothesize that PTPgamma is a potential estrogen-regulated tumor suppressor gene in human breast cancer. To examine the effects of PTPgamma on growth of MCF-7 human breast cancer cells and compare the estrogenic responses of human breast cells with different PTPgamma expression levels, we established several stably transfected MCF-7 cell lines expressing different levels of PTPgamma, which were confirmed by RT-PCR and immunostaining. In our work, we used the antisense construct to breakdown endogenous PTPgamma level in MCF-7 cells. The results from doubling time assay suggested that PTPgamma is capable of inhibiting MCF-7 breast cancer cell growth. We further demonstrated that PTPgamma is able to inhibit anchorage-independent growth of breast cancer cells in soft agar and reduce the estrogenic responses of MCF-7 cell proliferation to estradiol-17beta (E(2)) and zeranol (Z, a nonsteroidal growth promoter with estrogenic activity). Our data suggest that PTPgamma may function as an important modulator in regulating the process of tumorigenesis in human breast.

Regulation of RPTPbeta/phosphacan expression and glycosaminoglycan epitopes in injured brain and cytokine-treated glia

Several chondroitin sulfate proteoglycans (CSPGs) are upregulated after CNS injury and are thought to limit axonal regeneration in the adult mammalian CNS. Therefore, we examined the expression of the CSPG, receptor protein tyrosine phosphatase beta (RPTPbeta)/phosphacan, after a knife lesion to the cerebral cortex and after treatment of glial cultures with regulatory factors. The three splice variants of this CSPG gene, the secreted isoform, phosphacan, and the two transmembrane isoforms, the long and short RPTPbeta, were examined. Western blot and immunostaining analysis of injured and uninjured tissue revealed a transient decrease of phosphacan protein levels, but not of short RPTPbeta, in the injured tissue from 1 to 7 days postlesion (dpl). By real time RT-PCR, we show that phosphacan and long RPTPbeta mRNA levels are transiently down-regulated at 2 dpl, unlike those of short RPTPbeta which increased after 4 dpl. In contrast to the core glycoprotein, the phosphacan chondroitin sulfate (CS) glycosaminoglycan epitope DSD-1 was up-regulated after 7 dpl. Phosphacan was expressed by cultivated astrocytes and oligodendrocyte precursors but was more glycanated in oligodendrocyte precursors, which produce more of DSD-1 epitope than astrocytes. Epidermal growth factor/transforming growth factor alpha strongly increased the astrocytic expression of long RPTPbeta and phosphacan and slightly the short RPTPbeta protein levels, while interferon gamma and tumor necrosis factor alpha reduced astrocytic levels of phosphacan, but not of the receptor forms. Examining the effects of phosphacan on axon growth from rat E17 cortical neurons, we found that phosphacan stimulates outgrowth in a largely CS dependent manner, while it blocks the outgrowth-promoting effects of laminin through an interaction that is not affected by removal of the CS chains. These results demonstrate complex injury-induced modifications in phosphacan expression and glycanation that may well influence axonal regeneration and repair processes in the damaged CNS.

Keratan sulfate proteoglycan phosphacan regulates mossy fiber outgrowth and regeneration

We have examined the role of chondroitin sulfate proteoglycans (CSPGs) and keratan sulfate proteoglycans (KSPGs) in directing mossy fiber (MF) outgrowth and regeneration in rat hippocampal slice cultures. MFs normally exhibit a very specific innervation pattern that is restricted to the stratum lucidum (SL). In addition, MFs in hippocampal slice cultures will regenerate this specific innervation pattern after transection. CSPGs are one of the best characterized inhibitory axon guidance molecules in the CNS and are widely expressed in all areas of the hippocampus except SL. KSPGs are also widely expressed in the hippocampus, but their role in axon outgrowth has not been extensively studied in the CNS where phosphacan is the only protein that appears to contain KS-GAGs. Cultured hippocampal slices were treated with either chondroitin ABC lyase or keratanases to reduce the inhibitory axon guidance properties of CS and KS proteoglycans, respectively. The ability of transected MFs to regenerate their normal innervation pattern after digestion of CS and KS-GAGS sugars with these enzymes was examined. Only keratanase treatment resulted in misrouting of MFs. Identifying the mechanism by which keratanase produced MF misrouting is complicated by the presence of splice variants of the phosphacan gene that include the extracellular form of phosphacan and the transmembrane receptor protein tyrosine phosphatase beta/zeta (RPTPbeta/zeta). Both forms of phosphacan are made by astrocytes, suggesting that keratanase alters MF outgrowth by modifying astrocyte function.

Receptor-like protein tyrosine phosphatase zeta/RPTP beta is expressed on tangentially aligned neurons in early mouse neocortex

Protein tyrosine phosphatase zeta (PTPzeta)/RPTPbeta is a chondroitin sulfate proteoglycan predominantly expressed in the brain. In this study, we examined immunohistochemical localisation of PTPzeta in the mouse telencephalon from embryonic day 9.5 (E9.5) to E15.5. During E10.5-E12.5, immunoreactivities for PTPzeta are specifically observed on the tangentially aligned neurons at the preplate (PP) of the neocortex, as well as on the neurons at the mantle layer (ML) of the ganglionic eminences (GEs). Likewise, neurons immunoreactive for CR50, a marker for Cajal-Retzius neurons, are aligned from the ML of the ganglionic eminences to the PP of the neocortex and co-express PTPzeta. During E13.5-E15.5, PTPzeta-positive neurons are present at the subplate (SP) as well as at the marginal zone (MZ) of the neocortex. These results indicate that PTPzeta is a useful marker for early-generated neocortical neurons in mice: Cajal-Retzius neurons as well as the subplate neurons.

Kainic acid-induced convulsions cause prolonged changes in the chondroitin sulfate proteoglycans neurocan and phosphacan in the limbic structures

Systemic administration of kainic acid induces repeated convulsive seizures (KA convulsions) that result in neuropathological changes similar to temporal lobe epilepsy and the appearance of spontaneous recurrent seizures (SRS). The appearance of SRS is considered a result of the remodeling of neuronal networks following neuronal degeneration. We investigated the changes in chondroitin sulfate proteoglycans (CSPGs) in the limbic structures after KA convulsions in the rat using monoclonal antibodies 1G2, which recognizes full-length neurocan and the C-terminal half of neurocan, neurocan C, and 6B4, which recognize phosphacan and protein tyrosine phosphatase zeta. After KA convulsions, full-length neurocan appeared by 24 h and reached a peak by 48 to 72 h, whereas phosphacan decreased within 24 h in the hippocampus. In immunohistochemistry, neurocan increased in the limbic structures coincident with the appearance of reactive astrocytes. Phosphacan decreased coincident with pyramidal cell loss in the hippocampus, and the number of phosphacan-positive perineuronal nets around parvalbumin neurons decreased, whereas parvalbumin neurons were relatively conserved. In contrast, phosphacan increased in the entorhinal and piriform cortices in correlation with the severity of neuronal loss. Both neurocan and phosphacan recovered to the control level by 8 weeks after KA convulsions in some rats, but the changes in neurocan and phosphacan described above still persisted in more than half the rats. The results indicate that KA convulsions induce prolonged changes in neurocan and phosphacan similar to those in the developing rat brain and suggest a role of these CSPGs in the remodeling of neuronal networks related to the establishment or enhancement of epileptogenesis.

Expression and Function of the Receptor Protein Tyrosine Phosphatase ζ and Its Ligand Pleiotrophin in Human Astrocytomas

Using subtractive cloning combined with cDNA array analysis, we previously identified the genes encoding for the protein tyrosine phosphatase zeta/receptor-type protein tyrosine phosphatase beta (PTPzeta/RPTPbeta) and its ligand pleiotrophin (PTN) as overexpressed in human glioblastomas compared to normal brain. Both molecules have been implicated in neuronal migration during central nervous system development, and PTN is known to be involved in tumor growth and angiogenesis. We confirm overexpression of both molecules at the protein level in astrocytic gliomas of different malignancy grades. PTPzeta/RPTPbeta immunoreactivity was associated with increasing malignancy grade and localized predominantly to the tumor cells. PTN immunoreactivity as determined by ELISA and immunohistochemistry analysis was increased in low-grade astrocytomas compared to normal brain. Further increase in malignant gliomas was marginal, and thus no correlation with malignancy grade or microvessel density was present. However, PTN levels were significantly associated with those of fibroblast growth factor-2, suggesting co-regulation of both factors. Functionally, PTN induced weak chemotactic and strong haptotactic migration of glioblastoma and cerebral microvascular endothelial cells. Haptotaxis of glioblastoma cells towards PTN was specifically inhibited by an anti-PTPzeta/RPTPbeta antibody. Our findings suggest that upregulated expression of PTN and PTPzeta/RPTPbeta in human astrocytic tumor cells can create an autocrine loop that is important for glioma cell migration. Although PTN is a secreted growth factor, it appears to exert its mitogenic effects mostly in a matrix-immobilized form, serving as a substrate for migrating tumor cells.

Receptor and nonreceptor protein tyrosine phosphatases in the nervous system

Protein tyrosine phosphatases (PTPs) have emerged as a new class of signaling molecules that play important roles in the development and function of the central nervous system. They include both tyrosine-specific and dual-specific phosphatases. Based on their cellular localization they are also classified as receptor-like or intracellular PTP. However, the intracellular mechanisms by which these PTPs regulate cellular signaling pathways are not well understood. Evidence gathered to date provides some insight into the physiological function of these PTPs in the nervous system. In this review, we outline what is currently known about the functional role of PTPs expressed in the brain.

Overexpression of receptor-type protein tyrosine phosphatase beta causes abnormal development of the cranial nerve in Xenopus embryos

Roles of receptor-type protein tyrosine phosphatase beta (RPTPbeta, also called PTPzeta) were investigated in the nervous system development of Xenopus embryos. We previously showed that Xenopus embryos express mRNAs for 11 receptor-type (XRPTPbeta.1-XRPTPbeta.11) and two secretory (sXRPTPbeta.1 and sXRPTPbeta.2) variants generated by alternative RNA splicing. Whole-mount in situ hybridization analyzes demonstrated central nervous system-specific gene transcription in tailbud embryos. Distributions of mRNAs for receptor-type and secretory variants partially differ in the hindbrain. Overexpression of XRPTPbeta.4 or sXRPTPbeta.2, which was brought about by microinjection of the recombinant plasmid vectors, caused abnormal development of the cranial nerve X. Deletion of the cytoplasmic segment from XRPTPbeta.4 did not affect the ability to cause the abnormality, but deletion of the extracellular segment abolished it. These results suggest that normal development of the cranial nerve X requires regulated expression of the XRPTPbeta gene products.

A role for receptor tyrosine phosphataseζ in glioma cell migration

Glioblastomas (GBM) are the most frequent and malignant human brain tumor type. Typically striking in adulthood, tumor progression is rapid, relentless, and ultimately leads to the patient's death within a year of diagnosis. The identification of transcriptionally regulated genes can lead to the discovery of targets for antibody or small-molecule-mediated therapy, as well as diagnostic markers. We prepared cDNA arrays that are specifically enriched for genes expressed in human brain tumors and profiled gene expression patterns in 14 individual tumor samples. Out of 25,000 clones arrayed, greater than 200 genes were found transcriptionally induced in glioblastomas compared to normal human brain tissue including the receptor tyrosine phosphatasezeta (RPTPzeta) and one of its ligands, pleiotrophin (Ptn). We confirmed by Northern blot analysis and immunohistochemistry that RPTPzeta is enriched in tumor samples. Knockdown of RPTPzeta by RNA interference studies established a functional role of RPTPzeta in cell migration. Our results suggest a novel function for RPTPzeta in regulating glioblastoma cell motility and point to the therapeutic utility of RPTPzeta as a target for antibody-mediated therapy of brain tumors.