Involvement of receptor-like protein tyrosine phosphatase zeta/RPTPbeta and its ligand pleiotrophin/heparin-binding growth-associated molecule (HB-GAM) in neuronal migration

Developmental patterns of extracellular matrix molecules in the embryonic and postnatal mouse hindbrain

Normal brain development requires continuous communication between developing neurons and their environment filled by a complex network referred to as extracellular matrix (ECM). The ECM is divided into distinct families of molecules including hyaluronic acid, proteoglycans, glycoproteins such as tenascins, and link proteins. In this study, we characterize the temporal and spatial distribution of the extracellular matrix molecules in the embryonic and postnatal mouse hindbrain by using antibodies and lectin histochemistry. In the embryo, hyaluronan and neurocan were found in high amounts until the time of birth whereas versican and tenascin-R were detected in lower intensities during the whole embryonic period. After birth, both hyaluronic acid and neurocan still produced intense staining in almost all areas of the hindbrain, while tenascin-R labeling showed a continuous increase during postnatal development. The reaction with WFA and aggrecan was revealed first 4th postnatal day (P4) with low staining intensities, while HAPLN was detected two weeks after birth (P14). The perineuronal net appeared first around the facial and vestibular neurons at P4 with hyaluronic acid cytochemistry. One week after birth aggrecan, neurocan, tenascin-R, and WFA were also accumulated around the neurons located in several hindbrain nuclei, but HAPLN1 was detected on the second postnatal week. Our results provide further evidence that many extracellular macromolecules that will be incorporated into the perineuronal net are already expressed at embryonic and early postnatal stages of development to control differentiation, migration, and synaptogenesis of neurons. In late postnatal period, the experience-driven neuronal activity induces formation of perineuronal net to stabilize synaptic connections.

Pleiotrophin and the Expression of Its Receptors during Development of the Human Cerebellar Cortex

During embryonic and fetal development, the cerebellum undergoes several histological changes that require a specific microenvironment. Pleiotrophin (PTN) has been related to cerebral and cerebellar cortex ontogenesis in different species. PTN signaling includes PTPRZ1, ALK, and NRP-1 receptors, which are implicated in cell differentiation, migration, and proliferation. However, its involvement in human cerebellar development has not been described so far. Therefore, we investigated whether PTN and its receptors were expressed in the human cerebellar cortex during fetal and early neonatal development. The expression profile of PTN and its receptors was analyzed using an immunohistochemical method. PTN, PTPRZ1, and NRP-1 were expressed from week 17 to the postnatal stage, with variable expression among granule cell precursors, glial cells, and Purkinje cells. ALK was only expressed during week 31. These results suggest that, in the fetal and neonatal human cerebellum, PTN is involved in cell communication through granule cell precursors, Bergmann glia, and Purkinje cells via PTPRZ1, NRP-1, and ALK signaling. This communication could be involved in cell proliferation and cellular migration. Overall, the present study represents the first characterization of PTN, PTPRZ1, ALK, and NRP-1 expression in human tissues, suggesting their involvement in cerebellar cortex development.

Protein Tyrosine Phosphatase Receptor Zeta 1 as a Potential Target in Cancer Therapy and Diagnosis

Protein tyrosine phosphatase receptor zeta 1 (PTPRZ1) is a type V transmembrane tyrosine phosphatase that is highly expressed during embryonic development, while its expression during adulthood is limited. PTPRZ1 is highly detected in the central nervous system, affecting oligodendrocytes' survival and maturation. In gliomas, PTPRZ1 expression is significantly upregulated and is being studied as a potential cancer driver and as a target for therapy. PTPRZ1 expression is also increased in other cancer types, but there are no data on the potential functional significance of this finding. On the other hand, low PTPRZ1 expression seems to be related to a worse prognosis in some cancer types, suggesting that in some cases, it may act as a tumor-suppressor gene. These discrepancies may be due to our limited understanding of PTPRZ1 signaling and tumor microenvironments. In this review, we present evidence on the role of PTPRZ1 in angiogenesis and cancer and discuss the phenomenal differences among the different types of cancer, depending on the regulation of its tyrosine phosphatase activity or ligand binding. Clarifying the involved signaling pathways will lead to its efficient exploitation as a novel therapeutic target or as a biomarker, and the development of proper therapeutic approaches.

Neural Signaling in Cancer

Nervous system activity regulates development, homeostasis, and plasticity of the brain as well as other organs in the body. These mechanisms are subverted in cancer to propel malignant growth. In turn, cancers modulate neural structure and function to augment growth-promoting neural signaling in the tumor microenvironment. Approaching cancer biology from a neuroscience perspective will elucidate new therapeutic strategies for presently lethal forms of cancer. In this review, we highlight the neural signaling mechanisms recapitulated in primary brain tumors, brain metastases, and solid tumors throughout the body that regulate cancer progression. Expected final online publication date for the Annual Review of Neuroscience, Volume 45 is July 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

On the road to the brain-on-a-chip: a review on strategies, methods, and applications

The brain is the most complex organ of our body. Such a complexity spans from the single-cell morphology up to the intricate connections that hundreds of thousands of neurons establish to create dense neuronal networks. All these components are involved in the genesis of the rich patterns of electrophysiological activity that characterize the brain. Over the years, researchers coming from different disciplines developedin vitrosimplified experimental models to investigate in a more controllable and observable way how neuronal ensembles generate peculiar firing rhythms, code external stimulations, or respond to chemical drugs. Nowadays, suchin vitromodels are namedbrain-on-a-chippointing out the relevance of the technological counterpart as artificial tool to interact with the brain: multi-electrode arrays are well-used devices to record and stimulate large-scale developing neuronal networks originated from dissociated cultures, brain slices, up to brain organoids. In this review, we will discuss the state of the art of the brain-on-a-chip, highlighting which structural and biological features a realisticin vitrobrain should embed (and how to achieve them). In particular, we identified two topological features, namely modular and three-dimensional connectivity, and a biological one (heterogeneity) that takes into account the huge number of neuronal types existing in the brain. At the end of this travel, we will show how 'far' we are from the goal and how interconnected-brain-regions-on-a-chip is the most appropriate wording to indicate the current state of the art.

The Role of Chondroitin Sulfate Proteoglycans in Nervous System Development

The orderly development of the nervous system is characterized by phases of cell proliferation and differentiation, neural migration, axonal outgrowth and synapse formation, and stabilization. Each of these processes is a result of the modulation of genetic programs by extracellular cues. In particular, chondroitin sulfate proteoglycans (CSPGs) have been found to be involved in almost every aspect of this well-orchestrated yet delicate process. The evidence of their involvement is complex, often contradictory, and lacking in mechanistic clarity; however, it remains obvious that CSPGs are key cogs in building a functional brain. This review focuses on current knowledge of the role of CSPGs in each of the major stages of neural development with emphasis on areas requiring further investigation.

Invaders Exposed: Understanding and Targeting Tumor Cell Invasion in Diffuse Intrinsic Pontine Glioma

Diffuse Intrinsic Pontine Glioma (DIPG) is a rare, highly aggressive pediatric brain tumor that originates in the pons. DIPG is untreatable and universally fatal, with a median life expectancy of less than a year. Resection is not an option, due to the anatomical location of the tumor, radiotherapy has limited effect and no chemotherapeutic or targeted treatment approach has proven to be successful. This poor prognosis is partly attributed to the tumor's highly infiltrative diffuse and invasive spread. Thus, targeting the invasive behavior of DIPG has the potential to be of therapeutic value. In order to target DIPG invasion successfully, detailed mechanistic knowledge on the underlying drivers is required. Here, we review both DIPG tumor cell's intrinsic molecular processes and extrinsic environmental factors contributing to DIPG invasion. Importantly, DIPG represents a heterogenous disease and through advances in whole-genome sequencing, different subtypes of disease based on underlying driver mutations are now being recognized. Recent evidence also demonstrates intra-tumor heterogeneity in terms of invasiveness and implies that highly infiltrative tumor subclones can enhance the migratory behavior of neighboring cells. This might partially be mediated by “tumor microtubes,” long membranous extensions through which tumor cells connect and communicate, as well as through the secretion of extracellular vesicles. Some of the described processes involved in invasion are already being targeted in clinical trials. However, more research into the mechanisms of DIPG invasion is urgently needed and might result in the development of an effective therapy for children suffering from this devastating disease. We discuss the implications of newly discovered invasive mechanisms for therapeutic targeting and the challenges therapy development face in light of disease in the developing brain.

Search for Nutritional Fitness Traits in a Biological Pest Control Agent Harmonia axyridis Using Comparative Transcriptomics

Harmonia axyridis is an important natural predator used in the biological control of insect pests. Vitellogenin (Vg) supplementation to artificial diet can improve fecundity of H. axyridis, however, the effects of Vg on physiology of H. axyridis at the molecular level is unclear. This study investigated the effects of Vg on the physiology (digestive enzyme activities) and transcriptome patterns by feeding H. axyridis adults with treatment (artificial diet with Vg supplement) and control (artificial diet supplemented with bovine serum albumin (BSA). The transcriptome sequencing yielded 43.94 Gb of clean data, and 3,946 differentially expressed genes (DEGs) - including 93 upregulated and 3,853 downregulated genes between the treatment and control. Six DEGs related to development and digestive enzyme were chosen for quantitative real-time PCR (qRT-PCR) to validate the accuracy of the RNA-seq results and confirmed that the transcriptome analysis yielded reliable results. The Vg supplement has increased activities of digestive enzymes and related genes expression in H. axyridis. The transcript level of digestive enzyme genes (apolipoprotein D and phosphoenolpyruvate carboxykinase) were much higher in adults fed on diet supplemented with Vg compared with that of the control.

Pleiotrophin increases neurite length and number of spiral ganglion neurons in vitro

Acoustic trauma, aging, genetic defects or ototoxic drugs are causes for sensorineural hearing loss involving sensory hair cell death and secondary degeneration of spiral ganglion neurons. Auditory implants are the only available therapy for severe to profound sensorineural hearing loss when hearing aids do not provide a sufficient speech discrimination anymore. Neurotrophic factors represent potential therapeutic candidates to improve the performance of cochlear implants (CIs) by the support of spiral ganglion neurons (SGNs). Here, we investigated the effect of pleiotrophin (PTN), a well-described neurotrophic factor for different types of neurons that is expressed in the postnatal mouse cochlea. PTN knockout mice exhibit severe deficits in auditory brainstem responses, which indicates the importance of PTN in inner ear development and function and makes it a promising candidate to support SGNs. Using organotypic explants and dissociated SGN cultures, we investigated the influence of PTN on the number of neurons, neurite number and neurite length. PTN significantly increased the number and neurite length of dissociated SGNs. We further verified the expression of important PTN-associated receptors in the SG. mRNA of anaplastic lymphoma kinase, α_v integrin, β₃ integrin, receptor protein tyrosine phosphatase β/ζ, neuroglycan C, low-density lipoprotein receptor-related protein 1 and syndecan 3 was detected in the inner ear. These results suggest that PTN may be a novel candidate to improve sensorineural hearing loss treatment in the future.

Overlapping migratory mechanisms between neural progenitor cells and brain tumor stem cells

Neural stem cells present in the subventricular zone (SVZ), the largest neurogenic niche of the mammalian brain, are able to self-renew as well as generate neural progenitor cells (NPCs). NPCs are highly migratory and traverse the rostral migratory stream (RMS) to the olfactory bulb, where they terminally differentiate into mature interneurons. NPCs from the SVZ are some of the few cells in the CNS that migrate long distances during adulthood. The migratory process of NPCs is highly regulated by intracellular pathway activation and signaling from the surrounding microenvironment. It involves modulation of cell volume, cytoskeletal rearrangement, and isolation from compact extracellular matrix. In malignant brain tumors including high-grade gliomas, there are cells called brain tumor stem cells (BTSCs) with similar stem cell characteristics to NPCs but with uncontrolled cell proliferation and contribute to tumor initiation capacity, tumor progression, invasion, and tumor maintenance. These BTSCs are resistant to chemotherapy and radiotherapy, and their presence is believed to lead to tumor recurrence at distal sites from the original tumor location, principally due to their high migratory capacity. BTSCs are able to invade the brain parenchyma by utilizing many of the migratory mechanisms used by NPCs. However, they have an increased ability to infiltrate the tight brain parenchyma and utilize brain structures such as myelin tracts and blood vessels as migratory paths. In this article, we summarize recent findings on the mechanisms of cellular migration that overlap between NPCs and BTSCs. A better understanding of the intersection between NPCs and BTSCs will to provide a better comprehension of the BTSCs' invasive capacity and the molecular mechanisms that govern their migration and eventually lead to the development of new therapies to improve the prognosis of patients with malignant gliomas.

Demystifying the extracellular matrix and its proteolytic remodeling in the brain: structural and functional insights

The extracellular matrix (ECM) plays diverse roles in several physiological and pathological conditions. In the brain, the ECM is unique both in its composition and in functions. Furthermore, almost all the cells in the central nervous system contribute to different aspects of this intricate structure. Brain ECM, enriched with proteoglycans and other small proteins, aggregate into distinct structures around neurons and oligodendrocytes. These special structures have cardinal functions in the normal functioning of the brain, such as learning, memory, and synapse regulation. In this review, we have compiled the current knowledge about the structure and function of important ECM molecules in the brain and their proteolytic remodeling by matrix metalloproteinases and other enzymes, highlighting the special structures they form. In particular, the proteoglycans in brain ECM, which are essential for several vital functions, are emphasized in detail.

Expression of the heparin-binding growth factors Midkine and pleiotrophin during ocular development

Midkine (MDK) and Pleiotrophin (PTN) belong to a group of heparin-binding growth factors that has been shown to have pleiotropic functions in various biological processes during development and disease. Development of the vertebrate eye is a multistep process that involves coordinated interactions between neuronal and non-neuronal cells, but very little is known about the potential function of MDK and PTN in these processes. In this study, we demonstrate by section in situ hybridization, the spatiotemporal expression of MDK and PTN during ocular development in chick and mouse. We show that MDK and PTN are expressed in dynamic patterns that overlap in a few non-neuronal tissues in the anterior eye and in neuronal cell layers of the posterior eye. We show that the expression patterns of MDK and PTN are only conserved in a few tissues in chick and mouse but they overlap with the expression of some of their receptors LRP1, RPTPZ, ALK, NOTCH2, ITGβ1, SDC1, and SDC3. The dynamic expression patterns of MDK, PTN and their receptors suggest that they function together during the multistep process of ocular development and they may play important roles in cell proliferation, adhesion, and migration of neuronal and non-neuronal cells.

Keratan sulfate (KS)-proteoglycans and neuronal regulation in health and disease: the importance of KS-glycodynamics and interactive capability with neuroregulatory ligands

Compared to the other classes of glycosaminoglycans (GAGs), that is, chondroitin/dermatan sulfate, heparin/heparan sulfate and hyaluronan, keratan sulfate (KS), have the least known of its interactive properties. In the human body, the cornea and the brain are the two most abundant tissue sources of KS. Embryonic KS is synthesized as a linear poly-N-acetyllactosamine chain of d-galactose-GlcNAc repeat disaccharides which become progressively sulfated with development, sulfation of GlcNAc is more predominant than galactose. KS contains multi-sulfated high-charge density, monosulfated and non-sulfated poly-N-acetyllactosamine regions and thus is a heterogeneous molecule in terms of chain length and charge distribution. A recent proteomics study on corneal KS demonstrated its interactivity with members of the Slit-Robbo and Ephrin-Ephrin receptor families and proteins which regulate Rho GTPase signaling and actin polymerization/depolymerization in neural development and differentiation. KS decorates a number of peripheral nervous system/CNS proteoglycan (PG) core proteins. The astrocyte KS-PG abakan defines functional margins of the brain and is up-regulated following trauma. The chondroitin sulfate/KS PG aggrecan forms perineuronal nets which are dynamic neuroprotective structures with anti-oxidant properties and roles in neural differentiation, development and synaptic plasticity. Brain phosphacan a chondroitin sulfate, KS, HNK-1 PG have roles in neural development and repair. The intracellular microtubule and synaptic vesicle KS-PGs MAP1B and SV2 have roles in metabolite transport, storage, and export of neurotransmitters and cytoskeletal assembly. MAP1B has binding sites for tubulin and actin through which it promotes cytoskeletal development in growth cones and is highly expressed during neurite extension. The interactive capability of KS with neuroregulatory ligands indicate varied roles for KS-PGs in development and regenerative neural processes.

Contactin-1/F3 Regulates Neuronal Migration and Morphogenesis Through Modulating RhoA Activity

During neocortical development, newborn neurons migrate along radial fibers from the germinal ventricular zone (VZ) toward the cortical plate (CP) to populate the cerebral cortex. This radial migration requires adhesion activities between neurons and radial fibers; however, past research has identified only a limited number of adhesion molecules involved in this process. Contactin-1/F3 (Cntn1), a cell adhesion molecule expressed in the developing nervous system is essential for many key developmental events including neural cell adhesion, neurite outgrowth, axon guidance and myelination. However, the potential role of Cntn1 in neuronal migration during cortical development has not been investigated. Here we used in utero electroporation to introduce short hairpin RNA (shRNA) to knock down (KD) Cntn1 in neural stem cells in vivo. We found that Cntn1 KD led to a delay in neuronal migration. The arrested cells presented abnormal morphology in their leading process and more multipolar cells were observed in the deep layers of the brain, suggestive of dysregulation in process formation. Intriguingly, Cntn1 KD also resulted in upregulation of RhoA, a negative regulator for neuronal migration. Interference of RhoA by expression of the dominant-negative RhoA^N19 partially rescued the neuronal migration defects caused by Cntn1 KD. Our results showed that Cntn1 is a novel adhesion protein that is essential for neuronal migration and regulates process formation of newborn cortical neurons through modulating RhoA signaling pathway.

Proteoglycans in brain development and pathogenesis

Proteoglycans are diverse, complex extracellular/cell surface macromolecules composed of a central core protein with covalently linked glycosaminoglycan (GAG) chains; both of these components contribute to the growing list of important bio-active functions attributed to proteoglycans. Increasingly, attention has been paid to the roles of proteoglycans in nervous tissue development due to their highly regulated spatio/temporal expression patterns, whereby they promote/inhibit neurite outgrowth, participate in specification and maturation of various precursor cell types, and regulate cell behaviors like migration, axonal pathfinding, synaptogenesis and plasticity. These functions emanate from both the environments proteoglycans create around cells by retaining ions and water or serving as scaffolds for cell shaping or motility, and from dynamic interactions that modulate signaling fields for cytokines, growth factors and morphogens, which may bind to either the protein or GAG portions. Also, genetic abnormalities impacting proteoglycan synthesis during critical steps of brain development and response to environmental insults and injuries, as well as changes in microenvironment interactions leading to tumors in the central nervous system, all suggest roles for proteoglycans in behavioral and intellectual disorders and malignancies.

Regulation of Cortical Dendrite Morphology and Spine Organization by Secreted Semaphorins: A Primary Culture Approach

Primary tissue culture is an invaluable technique in cell biology and has a long history in demonstrating its versatility in characterizing cellular morphology, function, and behavior. Here, we describe a modified, low density, long-term, primary neuron culture system to characterize dendritic morphology and synaptic spine organization in developing mouse cortical neurons. While this method can be applied to investigate the signaling pathways of a range of extracellular cues' effect on neuronal development, we focus on how distinct secreted semaphorins regulate dendritic elaboration and spine morphogenesis in deep layer cortical neurons.

Diverse roles for glycosaminoglycans in neural patterning

The nervous system coordinates the functions of most multicellular organisms and their response to the surrounding environment. Its development involves concerted cellular interactions, including migration, axon guidance, and synapse formation. These processes depend on the molecular constituents and structure of the extracellular matrices (ECM). An essential component of ECMs are proteoglycans, i.e., proteins containing unbranched glycan chains known as glycosaminoglycans (GAGs). A defining characteristic of GAGs is their enormous molecular diversity, created by extensive modifications of the glycans during their biosynthesis. GAGs are widely expressed, and their loss can lead to catastrophic neuronal defects. Despite their importance, we are just beginning to understand the function and mechanisms of GAGs in neuronal development. In this review, we discuss recent evidence suggesting GAGs have specific roles in neuronal patterning and synaptogenesis. We examine the function played by the complex modifications present on GAG glycans and their roles in regulating different aspects of neuronal patterning. Moreover, the review considers the function of proteoglycan core proteins in these processes, stressing their likely role as co-receptors of different signaling pathways in a redundant and context-dependent manner. We conclude by discussing challenges and future directions toward a better understanding of these fascinating molecules during neuronal development. Developmental Dynamics 247:54-74, 2018. © 2017 Wiley Periodicals, Inc.

Pleiotrophin, a target of miR-384, promotes proliferation, metastasis and lipogenesis in HBV-related hepatocellular carcinoma

Hepatitis B virus (HBV) infection plays a crucial role and is a major cause of hepatocellular carcinoma (HCC) in China. microRNAs (miRNAs) have emerged as key players in hepatic steatosis and carcinogenesis. We found that down-regulation of miR-384 expression was a common event in HCC, especially HBV-related HCC. However, the possible function of miR-384 in HBV-related HCC remains unclear. The oncogene pleiotrophin (PTN) was a target of miR-384. HBx inhibited miR-384, increasing PTN expression. The PTN receptor N-syndecan was highly expressed in HCC. PTN induced by HBx acted as a growth factor via N-syndecan on hepatocytes and further promoted cell proliferation, metastasis and lipogenesis. PTN up-regulated sterol regulatory element-binding protein 1c (SREBP-1c) through the N-syndecan/PI3K/Akt/mTORC1 pathway and the expression of lipogenic genes, including fatty acid synthesis (FAS). PTN-mediated de novo lipid synthesis played an important role in HCC proliferation and metastasis. PI3K/AKT and an mTORC1 inhibitor diminished PTN-induced proliferation, metastasis and lipogenesis. Taken together, these data strongly suggest that the dysregulation of miR-384 could play a crucial role in HBV related to HCC, and the target gene of miR-384, PTN, represents a new potential therapeutic target for the prevention of hepatic steatosis and further progression to HCC after chronic HBV infection.

The receptor protein tyrosine phosphatase PTPRB negatively regulates FGF2-dependent branching morphogenesis

PTPRB is a transmembrane protein tyrosine phosphatase known to regulate blood vessel remodelling and angiogenesis. Here, we demonstrate that PTPRB negatively regulates branching morphogenesis in the mouse mammary epithelium. We show that Ptprb is highly expressed in adult mammary stem cells and also, although at lower levels, in oestrogen receptor-positive luminal cells. During mammary development, Ptprb expression is downregulated during puberty, a period of extensive ductal outgrowth and branching. In vivo shRNA knockdown of Ptprb in the cleared mammary fat pad transplant assay resulted in smaller epithelial outgrowths with an increased branching density and also increased branching in an in vitro organoid assay. Organoid branching was dependent on stimulation by FGF2, and Ptprb knockdown in mammary epithelial cells resulted in a higher level of fibroblast growth factor receptor (FGFR) activation and ERK1/2 phosphorylation, both at baseline and following FGF2 stimulation. Therefore, PTPRB regulates branching morphogenesis in the mammary epithelium by modulating the response of the FGFR signalling pathway to FGF stimulation. Considering the importance of branching morphogenesis in multiple taxa, our findings have general importance outside mammary developmental biology.

Neural Precursor-Derived Pleiotrophin Mediates Subventricular Zone Invasion by Glioma

The lateral ventricle subventricular zone (SVZ) is a frequent and consequential site of pediatric and adult glioma spread, but the cellular and molecular mechanisms mediating this are poorly understood. We demonstrate that neural precursor cell (NPC):glioma cell communication underpins this propensity of glioma to colonize the SVZ through secretion of chemoattractant signals toward which glioma cells home. Biochemical, proteomic, and functional analyses of SVZ NPC-secreted factors revealed the neurite outgrowth-promoting factor pleiotrophin, along with required binding partners SPARC/SPARCL1 and HSP90B, as key mediators of this chemoattractant effect. Pleiotrophin expression is strongly enriched in the SVZ, and pleiotrophin knock down starkly reduced glioma invasion of the SVZ in the murine brain. Pleiotrophin, in complex with the binding partners, activated glioma Rho/ROCK signaling, and ROCK inhibition decreased invasion toward SVZ NPC-secreted factors. These findings demonstrate a pathogenic role for NPC:glioma interactions and potential therapeutic targets to limit glioma invasion. PAPERCLIP.

Chondroitin sulfates and their binding molecules in the central nervous system

Chondroitin sulfate (CS) is the most abundant glycosaminoglycan (GAG) in the central nervous system (CNS) matrix. Its sulfation and epimerization patterns give rise to different forms of CS, which enables it to interact specifically and with a significant affinity with various signalling molecules in the matrix including growth factors, receptors and guidance molecules. These interactions control numerous biological and pathological processes, during development and in adulthood. In this review, we describe the specific interactions of different families of proteins involved in various physiological and cognitive mechanisms with CSs in CNS matrix. A better understanding of these interactions could promote a development of inhibitors to treat neurodegenerative diseases.

Uronyl 2-O sulfotransferase potentiates Fgf2-induced cell migration

Fibroblast growth factor 2 (Fgf2) is involved in several biological functions. Fgf2 requires glycosaminoglycans, like chondroitin and dermatan sulfates (hereafter denoted CS/DS) as co-receptors. CS/DS are linear polysaccharides composed of repeating disaccharide units [-4GlcUAb1-3-GalNAc-b1-] and [-4IdoUAa1-3-GalNAc-b1-],which can be sulfated. Uronyl 2-O-sulfotransferase (Ust)introduces sulfation at the C2 of IdoUA and GlcUA resulting inover-sulfated units. Here, we investigated the role of Ust-mediated CS/DS 2-O sulfation in Fgf2-induced cell migration. We found that CHO-K1 cells overexpressing Ust contain significantly more CS/DS2-O sulfated units, whereas Ust knockdown abolished CS/DS 2-O sulfation. These structural differences in CS/DS resulted in altered Fgf2 binding and increased phosphorylation of ERK1/2 (also known as MAPK3 and MAPK1, respectively). As a functional consequence of CS/DS 2-O sulfation and altered Fgf2 binding, cell migration and paxillin activation were increased. Inhibition of sulfation, knockdown of Ust and inhibition of FgfR resulted in reduced migration. Similarly, in 3T3 cells Fgf2 treatment increased migration, which was abolished by Ust knockdown. The proteoglycan controlling the CHO migration was syndecan 1. Knockdown of Sdc1 in CHO-K1 cells overexpressing Ust abolished cell migration.We conclude that the presence of distinctly sulfated CS/DS can tune the Fgf2 effect on cell migration.

Small-molecule inhibition of PTPRZ reduces tumor growth in a rat model of glioblastoma

Protein tyrosine phosphatase receptor-type Z (PTPRZ) is aberrantly over-expressed in glioblastoma and a causative factor for its malignancy. However, small molecules that selectively inhibit the catalytic activity of PTPRZ have not been discovered. We herein performed an in vitro screening of a chemical library, and identified SCB4380 as the first potent inhibitor for PTPRZ. The stoichiometric binding of SCB4380 to the catalytic pocket was demonstrated by biochemical and mass spectrometric analyses. We determined the crystal structure of the catalytic domain of PTPRZ, and the structural basis of the binding of SCB4380 elucidated by a molecular docking method was validated by site-directed mutagenesis studies. The intracellular delivery of SCB4380 by liposome carriers inhibited PTPRZ activity in C6 glioblastoma cells, and thereby suppressed their migration and proliferation in vitro and tumor growth in a rat allograft model. Therefore, selective inhibition of PTPRZ represents a promising approach for glioma therapy.

Sugar-dependent modulation of neuronal development, regeneration, and plasticity by chondroitin sulfate proteoglycans

Chondroitin sulfate proteoglycans (CSPGs) play important roles in the developing and mature nervous system, where they guide axons, maintain stable connections, restrict synaptic plasticity, and prevent axon regeneration following CNS injury. The chondroitin sulfate glycosaminoglycan (CS GAG) chains that decorate CSPGs are essential for their functions. Through these sugar chains, CSPGs are able to bind and regulate the activity of a diverse range of proteins. CSPGs have been found both to promote and inhibit neuronal growth. They can promote neurite outgrowth by binding to various growth factors such as midkine (MK), pleiotrophin (PTN), brain-derived neurotrophic factor (BDNF) and other neurotrophin family members. CSPGs can also inhibit neuronal growth and limit plasticity by interacting with transmembrane receptors such as protein tyrosine phosphatase σ (PTPσ), leukocyte common antigen-related (LAR) receptor protein tyrosine phosphatase, and the Nogo receptors 1 and 3 (NgR1 and NgR3). These CS-protein interactions depend on specific sulfation patterns within the CS GAG chains, and accordingly, particular CS sulfation motifs are upregulated during development, in the mature nervous system, and in response to CNS injury. Thus, spatiotemporal regulation of CS GAG biosynthesis may provide an important mechanism to control the functions of CSPGs and to modulate intracellular signaling pathways. Here, we will discuss these sulfation-dependent processes and highlight how the CS sugars on CSPGs contribute to neuronal growth, axon guidance, and plasticity in the nervous system.

Fell-Muir Lecture: Heparan sulphate and the art of cell regulation: a polymer chain conducts the protein orchestra

Heparan sulphate (HS) sits at the interface of the cell and the extracellular matrix. It is a member of the glycosaminoglycan family of anionic polysaccharides with unique structural features designed for protein interaction and regulation. Its client proteins include soluble effectors (e.g. growth factors, morphogens, chemokines), membrane receptors and cell adhesion proteins such as fibronectin, fibrillin and various types of collagen. The protein-binding properties of HS, together with its strategic positioning in the pericellular domain, are indicative of key roles in mediating the flow of regulatory signals between cells and their microenvironment. The control of transmembrane signalling is a fundamental element in the complex biology of HS. It seems likely that, in some way, HS orchestrates diverse signalling pathways to facilitate information processing inside the cell. A dictionary definition of an orchestra is 'a large group of musicians who play together on various instruments …' to paraphrase, the HS orchestra is 'a large group of proteins that play together on various receptors'. HS conducts this orchestra to ensure that proteins hit the right notes on their receptors but, in the manner of a true conductor, does it also set 'the musical pulse' and create rhythm and harmony attractive to the cell? This is too big a question to answer but fun to think about as you read this review.

Sugar glues for broken neurons

Proteoglycans (PGs) regulate diverse functions in the central nervous system (CNS) by interacting with a number of growth factors, matrix proteins, and cell surface molecules. Heparan sulfate (HS) and chondroitin sulfate (CS) are two major glycosaminoglycans present in the PGs of the CNS. The functionality of these PGs is to a large extent dictated by the fine sulfation patterns present on their glycosaminoglycan (GAG) chains. In the past 15 years, there has been a significant expansion in our knowledge on the role of HS and CS chains in various neurological processes, such as neuronal growth, regeneration, plasticity, and pathfinding. However, defining the relation between distinct sulfation patterns of the GAGs and their functionality has thus far been difficult. With the emergence of novel tools for the synthesis of defined GAG structures, and techniques for their characterization, we are now in a better position to explore the structure-function relation of GAGs in the context of their sulfation patterns. In this review, we discuss the importance of GAGs on CNS development, injury, and disorders with an emphasis on their sulfation patterns. Finally, we outline several GAG-based therapeutic strategies to exploit GAG chains for ameliorating various CNS disorders.

Regulation of Pleiotrophin, Midkine, Receptor Protein Tyrosine Phosphatase β/ζ, and Their Intracellular Signaling Cascades in the Nucleus Accumbens During Opiate Administration

BACKGROUND

Most classes of addictive substances alter the function and structural plasticity of the brain reward circuitry. Midkine (MK) and pleiotrophin (PTN) are growth/differentiation cytokines which, similarly to neurotrophins, play an important role in repair, neurite outgrowth, and cell differentiation. PTN or MK signaling through receptor protein tyrosine phosphatase β/ζ (RPTPβ/ζ), leads to the activation of extracellular signal-regulated kinases and thymoma viral proto-oncogene. This activation induces morphological changes and modulates addictive behaviors. Besides, there is increasing evidence that during the development of drug addiction, astrocytes contribute to the synaptic plasticity by synthesizing and releasing substances such as cytokines.

METHODS

In the present work we studied the effect of acute morphine administration, chronic morphine administration, and morphine withdrawal on PTN, MK, and RPTPβ/ζ expression and on their signaling pathways in the nucleus accumbens.

RESULTS

Present results indicated that PTN, MK, and RPTPβ/ζ levels increased after acute morphine injection, returned to basal levels during chronic opioid treatment, and were up-regulated again during morphine withdrawal. We also observed an activation of astrocytes after acute morphine injection and during opiate dependence and withdrawal. In addition, immunofluorescence analysis revealed that PTN, but not MK, was overexpressed in astrocytes and that dopaminoceptive neurons expressed RPTPβ/ζ.

CONCLUSIONS

All these observations suggest that the neurotrophic and behavioral adaptations that occur during opiate addiction could be, at least partly, mediated by cytokines.

Proteoglycans and neuronal migration in the cerebral cortex during development and disease

Chondroitin sulfate proteoglycans and heparan sulfate proteoglycans are major constituents of the extracellular matrix and the cell surface in the brain. Proteoglycans bind with many proteins including growth factors, chemokines, axon guidance molecules, and cell adhesion molecules through both the glycosaminoglycan and the core protein portions. The functions of proteoglycans are flexibly regulated due to the structural variability of glycosaminoglycans, which are generated by multiple glycosaminoglycan synthesis and modifying enzymes. Neuronal cell surface proteoglycans such as PTPζ, neuroglycan C and syndecan-3 function as direct receptors for heparin-binding growth factors that induce neuronal migration. The lectican family, secreted chondroitin sulfate proteoglycans, forms large aggregates with hyaluronic acid and tenascins, in which many signaling molecules and enzymes including matrix proteases are preserved. In the developing cerebrum, secreted chondroitin sulfate proteoglycans such as neurocan, versican and phosphacan are richly expressed in the areas that are strategically important for neuronal migration such as the striatum, marginal zone, subplate and subventricular zone in the neocortex. These proteoglycans may anchor various attractive and/or repulsive cues, regulating the migration routes of inhibitory neurons. Recent studies demonstrated that the genes encoding proteoglycan core proteins and glycosaminoglycan synthesis and modifying enzymes are associated with various psychiatric and intellectual disorders, which may be related to the defects of neuronal migration.

Specific dephosphorylation at tyr-554 of git1 by ptprz promotes its association with paxillin and hic-5

G protein-coupled receptor kinase-interactor 1 (Git1) is involved in cell motility control by serving as an adaptor that links signaling proteins such as Pix and PAK to focal adhesion proteins. We previously demonstrated that Git1 was a multiply tyrosine-phosphorylated protein, its primary phosphorylation site was Tyr-554 in the vicinity of the focal adhesion targeting-homology (FAH) domain, and this site was selectively dephosphorylated by protein tyrosine phosphatase receptor type Z (Ptprz). In the present study, we showed that Tyr-554 phosphorylation reduced the association of Git1 with the FAH-domain-binding proteins, paxillin and Hic-5, based on immunoprecipitation experiments using the Tyr-554 mutants of Git1. The Tyr-554 phosphorylation of Git1 was higher, and its binding to paxillin was consistently lower in the brains of Ptprz-deficient mice than in those of wild-type mice. We then investigated the role of Tyr-554 phosphorylation in cell motility control using three different methods: random cell motility, wound healing, and Boyden chamber assays. The shRNA-mediated knockdown of endogenous Git1 impaired cell motility in A7r5 smooth muscle cells. The motility defect was rescued by the exogenous expression of wild-type Git1 and a Git1 mutant, which only retained Tyr-554 among the multiple potential tyrosine phosphorylation sites, but not by the Tyr-554 phosphorylation-defective or phosphorylation-state mimic Git1 mutant. Our results suggested that cyclic phosphorylation-dephosphorylation at Tyr-554 of Git1 was crucial for dynamic interactions between Git1 and paxillin/Hic-5 in order to ensure coordinated cell motility.

Elevated expression of pleiotrophin in pilocarpine-induced seizures of immature rats and in pentylenetetrazole-induced hippocampal astrocytes in vitro

Pleiotrophin (PTN) is a secreted extracellular matrix (ECM)-associated cytokine that has emerged as an important neuromodulator with multiple neuronal functions. In the present study, we detected and compared the dynamic expression of PTN in the hippocampus and adjacent cortex of immature rats with pilocarpine-induced epilepsy. Moreover, we also confirmed the results by examining PTN expression in hippocampal astrocytes cultured in the presence of pentylenetetrazole (PTZ). Immunohistochemistry showed faint immunostaining of PTN in the control hippocampus and adjacent cortex. Notably, PTN immunoreactivity began to increase in relatively small cells in the hippocampus and adjacent cortex at 2h and 3 weeks after seizures, and the labeling intensity reached the maximum level in the hippocampus and adjacent cortex at 8 weeks after seizures. Furthermore, we also found that PTZ treatment significantly reduced astrocytic viability in a dose-dependent manner and time-dependently increased expression levels of PTN in hippocampal astrocytes. In conclusion, our data suggest that increased expression of PTN in the brain tissues may be involved in epileptogenesis.

Midkine and cytoplasmic maturation of mammalian oocytes in the context of ovarian follicle physiology

Midkine (MK) was originally characterized as a member of a distinct family of neurotrophic factors functioning in the CNS. However, it was later discovered that MK is abundantly expressed in ovarian follicles. Since then, the physiological roles of this molecule in the ovary have been steadily investigated. During the in vitro maturation (IVM) of oocytes MK was shown to promote the cytoplasmic maturation of oocytes, as indicated by post-fertilization development. This effect of MK could be mediated via its pro-survival (anti-apoptotic) effects on the cumulus-granulosa cells that surround oocytes. The oocyte competence-promoting effects of MK are discussed in the context of the recently discovered involvement of MK in the full maturation of ovarian follicles. MK was at the frontline of a new paradigm for neurotrophic factors as oocytetrophic factors. MK may promote the developmental competence of oocytes via common signalling molecules with the other neurotrophic factor(s). Alternatively or concomitantly, MK may also interact with various transmembrane molecules on cumulus-granulosa cells, which are important for ovarian follicle growth, dominance and differentiation, and act as a unique pro-survival factor in ovarian follicles, such that MK promotes oocyte competence. MK, along with other ovarian neurotrophic factors, may contribute to the optimization of the IVM system.

LINKED ARTICLES

This article is part of a themed section on Midkine. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-4.

Receptor-type protein-tyrosine phosphatase ζ is a functional receptor for interleukin-34

Interleukin-34 (IL-34) is highly expressed in brain. IL-34 signaling via its cognate receptor, colony-stimulating factor-1 receptor (CSF-1R), is required for the development of microglia. However, the differential expression of IL-34 and the CSF-1R in brain suggests that IL-34 may signal via an alternate receptor. By IL-34 affinity chromatography of solubilized mouse brain membrane followed by mass spectrometric analysis, we identified receptor-type protein-tyrosine phosphatase ζ (PTP-ζ), a cell surface chondroitin sulfate (CS) proteoglycan, as a novel IL-34 receptor. PTP-ζ is primarily expressed on neural progenitors and glial cells and is highly expressed in human glioblastomas. IL-34 selectively bound PTP-ζ in CSF-1R-deficient U251 human glioblastoma cell lysates and inhibited the proliferation, clonogenicity, and motility of U251 cells in a PTP-ζ-dependent manner. These effects were correlated with an increase in tyrosine phosphorylation of the previously identified PTP-ζ downstream effectors focal adhesion kinase and paxillin. IL-34 binding to U251 cells was abrogated by chondroitinase ABC treatment, and CS competed with IL-34 for binding to the extracellular domain of PTP-ζ and to the cells, indicating a dependence of binding on PTP-ζ CS moieties. This study identifies an alternate receptor for IL-34 that may mediate its action on novel cellular targets.

The heparin-binding growth factor midkine: the biological activities and candidate receptors

The heparin-binding growth factor midkine (MK) comprises a family with pleiotrophin/heparin-binding growth-associated molecule. The biological phenomena in which MK is involved can be categorized into five areas: (i) cancer, (ii) inflammation/immunity, (iii) blood pressure, (iv) development and (v) tissue protection. The phenotypes are clear in vivo, but the mechanisms by which MK exerts these actions are not fully understood. Candidate receptors for MK include anaplastic lymphoma kinase, protein tyrosine phosphatase ζ, Notch2, LDL receptor-related protein 1, integrins and proteoglycans. Some physical associations between these candidate receptors are also known. Because of the striking in vivo phenotypes after manipulation of MK, MK could be an important molecular target for the treatment of various diseases. To this end, it will be important to pursue studies to fully understand the mechanisms of MK action.

Spatio-temporal characterization of the pleiotrophinergic system in mouse cerebellum: evidence for its key role during ontogenesis

The development of the central nervous system requires an appropriate micro-environment that is conditioned by a combination of various extracellular components. Most of the known signaling factors, such as neurotransmitters or neuropeptides, are soluble and diffuse into the extracellular matrix. However, other secreted molecules like proteoglycans or glycosaminoglycans anchor in the extracellular matrix to influence cerebral ontogenesis. As such, pleiotrophin (PTN), which binds the proteoglycans syndecan-3 (SDC3) and protein tyrosine phosphatase zeta (PTPζ), has been described as a pro-migratory and a pro-differentiating secreted cytokine on cortical neurons. In rat cerebellum, PTN is highly expressed during the first postnatal week, suggesting that this cytokine could participate to the development of the cerebellar cortex. According to this hypothesis, our spatio-temporal cartography of PTN, PTPζ and SDC3 indicated that, in mouse, the PTNergic system was present in the cerebellum at least from the first postnatal day (P0). Until P12, PTN was mainly expressed by granule cell precursors and located in the extracellular matrix, while SDC3 was expressed by Purkinje cells, Golgi cells and granule cell precursors, and PTPζ was present on Purkinje cells and Bergmann fibers. In vitro studies confirmed the presence of SDC3 on immature granule cells and demonstrated that PTN could stimulate directly their velocity in culture. In contrast, subarachnoidal injection of PTN in the cerebellum significantly reduced the rate of migration of granule cells, exacerbated their apoptosis and induced an atrophy of the Purkinje cell dendritic tree. Since differentiated granule cells did not express SDC3 or PTPζ, the PTN effect observed on migration and apoptosis may be indirectly mediated by Purkinje and/or Bergmann cells. From P21 to adulthood, the distribution of PTN, SDC3 and PTPζ changed and their expression dramatically decreased even if they were still detectable. PTN and SDC3 immunolabeling was restricted around Purkinje cell bodies and Golgi cells, whereas PTPζ was located around interneurons. These data suggested that, in the cerebellum of adult mice, PTN participates to the perineuronal nets that control neuronal plasticity. To conclude, the present work represents the first spatio-temporal characterization of the PTNergic system in the mouse cerebellum and indicates that PTN may contribute to cerebellum ontogenesis during the postnatal development as well as to neuronal plasticity at adulthood.

Roles of Integrins and Intracellular Molecules in the Migration and Neuritogenesis of Fetal Cortical Neurons: MEK Regulates Only the Neuritogenesis

The roles of integrin subunits and intracellular molecules in regulating the migration and neuritogenesis of neurons isolated from 16.5 gestation days rat fetal cortices were examined using in vitro assays. Results showed that laminin supported the migration of fetal cortical neurons better than fibronectin and that the fetal cortical neurons migrated on laminin using β1 and α3 integrin subunits which make up the α3β1 integrin receptor. On fibronectin, the migration was mediated by β1 integrin subunit. Perturbation of src kinase, phospholipase C, or protein kinase C activity, inhibition of IP3 receptor mediated calcium release, or chelation of intracellular calcium inhibited both migration and neuritogenesis, whereas inhibition of growth factor signaling via MEK inhibited only the neuritogenesis. The detection of α1 and α9 transcripts suggested that the migration of fetal cortical neurons may also be mediated by α1β1 and α9β1 integrin receptors. Results showed that calcium may regulate migration and neuritogenesis by maintaining optimum levels of microtubules in the fetal cortical neurons. It is concluded that the fetal cortical neurons are fully equipped with the integrin signaling cascade required for their migration and neuritogenesis, whereas crosstalk between the integrin and growth-factor signaling regulate only the neuritogenesis.

ALK receptor activation, ligands and therapeutic targeting in glioblastoma and in other cancers

The intracellular anaplastic lymphoma kinase (ALK) fragment shows striking homology with members of the insulin receptor family and was initially identified as an oncogenic fusion protein resulting from a translocation in lymphoma and more recently in a range of cancers. The full-length ALK transmembrane receptor of ~220 kDa was identified based on this initial work. This tyrosine kinase receptor and its ligands, the growth factors pleiotrophin (PTN) and midkine (MK) are highly expressed during development of the nervous system and other organs. Each of these genes has been implicated in malignant progression of different tumor types and shown to alter phenotypes as well as signal transduction in cultured normal and tumor cells. Beyond its role in cancer, the ALK receptor pathway is thought to contribute to nervous system development, function, and repair, as well as metabolic homeostasis and the maintenance of tissue regeneration. ALK receptor activity in cancer can be up-regulated by amplification, overexpression, ligand binding, mutations in the intracellular domain of the receptor and by activity of the receptor tyrosine phosphatase PTPRz. Here we discuss the evidence for ligand control of ALK activity as well as the potential prognostic and therapeutic implications from gene expression and functional studies. An analysis of 18 published gene expression data sets from different cancers shows that overexpression of ALK, its smaller homolog LTK (leukocyte tyrosine kinase) and the ligands PTN and MK in cancer tissues from patients correlate significantly with worse course and outcome of the disease. This observation together with preclinical functional studies suggests that this pathway could be a valid therapeutic target for which complementary targeting strategies with small molecule kinase inhibitors as well as antibodies to ligands or the receptors may be used.

Protein tyrosine phosphatase receptor type z negatively regulates oligodendrocyte differentiation and myelination

Background

Fyn tyrosine kinase-mediated down-regulation of Rho activity through activation of p190RhoGAP is crucial for oligodendrocyte differentiation and myelination. Therefore, the loss of function of its counterpart protein tyrosine phosphatase (PTP) may enhance myelination during development and remyelination in demyelinating diseases. To test this hypothesis, we investigated whether Ptprz, a receptor-like PTP (RPTP) expressed abuntantly in oligodendrocyte lineage cells, is involved in this process, because we recently revealed that p190RhoGAP is a physiological substrate for Ptprz.

Methodology/Principal Findings

We found an early onset of the expression of myelin basic protein (MBP), a major protein of the myelin sheath, and early initiation of myelination in vivo during development of the Ptprz-deficient mouse, as compared with the wild-type. In addition, oligodendrocytes appeared earlier in primary cultures from Ptprz-deficient mice than wild-type mice. Furthermore, adult Ptprz-deficient mice were less susceptible to experimental autoimmune encephalomyelitis (EAE) induced by active immunization with myelin/oligodendrocyte glycoprotein (MOG) peptide than were wild-type mice. After EAE was induced, the tyrosine phosphorylation of p190RhoGAP increased significantly, and the EAE-induced loss of MBP was markedly suppressed in the white matter of the spinal cord in Ptprz-deficient mice. Here, the number of T-cells and macrophages/microglia infiltrating into the spinal cord did not differ between the two genotypes after MOG immunization. All these findings strongly support the validity of our hypothesis.

Conclusions/Significance

Ptprz plays a negative role in oligodendrocyte differentiation in early central nervous system (CNS) development and remyelination in demyelinating CNS diseases, through the dephosphorylation of substrates such as p190RhoGAP.

Loss of receptor protein tyrosine phosphatase β/ζ (RPTPβ/ζ) promotes prostate cancer metastasis

BACKGROUND

The role of pleiotrophin and its receptors RPTPβ/ζ and Syndecan-3 during tumor metastasis remains unknown.

RESULTS

RPTPβ/ζ knockdown initiates EMT, promotes pleiotrophin-mediated migration and attachment through Syndecan-3 and induces in vivo metastasis.

CONCLUSION

RPTPβ/ζ plays a suppressor-like role in prostate cancer metastasis.

SIGNIFICANCE

Boosting RPTPβ/ζ or attenuating Syndecan-3 signaling pathways may lead to more effective therapeutic strategies in treating prostate cancer metastasis. Pleiotrophin is a growth factor that induces carcinogenesis. Despite the fact that many published reports focused on the role of pleiotrophin and its receptors, receptor protein tyrosine phosphatase (RPTPβ/ζ), and syndecan-3 during tumor development, no information is available regarding their function in tumor metastasis. To investigate the mechanism through which pleiotrophin regulates tumor metastasis, we used two different prostate carcinoma cell lines, DU145 and PC3, in which the expression of RPTPβ/ζ or syndecan-3 was down-regulated by the RNAi technology. The loss of RPTPβ/ζ expression initiated epithelial-to-mesenchymal transition (EMT) and increased the ability of the cells to migrate and invade. Importantly, the loss of RPTPβ/ζ expression increased metastasis in nude mice in an experimental metastasis assay. We also demonstrate that RPTPβ/ζ counterbalanced the pleiotrophin-mediated syndecan-3 pathway. While the inhibition of syndecan-3 expression inhibited the pleiotrophin-mediated cell migration and attachment through the Src and Fak pathway, the inhibition of RPTPβ/ζ expression increased pleiotrophin-mediated migration and attachment through an interaction with Src and the subsequent activation of a signal transduction pathway involving Fak, Pten, and Erk1/2. Taken together, these results suggest that the loss of RPTPβ/ζ may contribute to the metastasis of prostate cancer cells by inducing EMT and promoting pleiotrophin activity through the syndecan-3 pathway.

Insulin-like growth factor (IGF) binding protein 2 functions coordinately with receptor protein tyrosine phosphatase β and the IGF-I receptor to regulate IGF-I-stimulated signaling

Insulin-like growth factor I (IGF-I) is a mitogen for vascular smooth muscle cells (VSMC) and has been implicated in the development and progression of atherosclerosis. IGF binding proteins (IGFBPs) modify IGF-I actions independently of IGF binding, but a receptor-based mechanism by which they function has not been elucidated. We investigated the role of IGFBP-2 and receptor protein tyrosine phosphatase β (RPTPβ) in regulating IGF-I signaling and cellular proliferation. IGFBP-2 bound RPTPβ, which led to its dimerization and inactivation. This enhanced PTEN tyrosine phosphorylation and inhibited PTEN activity. Utilization of substrate trapping and phosphatase-dead mutants showed that RPTPβ bound specifically to PTEN and dephosphorylated it. IGFBP-2 knockdown led to decreased PTEN tyrosine phosphorylation and decreased AKT Ser473 activation. IGFBP-2 enhanced IGF-I-stimulated VSMC migration and proliferation. Analysis of aortas obtained from IGFBP-2(-/-) mice showed that RPTPβ was activated, and this was associated with inhibition of IGF-I stimulated AKT Ser473 phosphorylation and VSMC proliferation. These changes were rescued following administration of IGFBP-2. These findings present a novel mechanism for coordinate regulation of IGFBP-2 and IGF-I signaling functions that lead to stimulation of VSMC proliferation. The results have important implications for understanding how IGFBPs modulate the cellular response to IGF-I.

Receptor type protein tyrosine phosphatases (RPTPs) - roles in signal transduction and human disease

Protein tyrosine phosphorylation is a fundamental regulatory mechanism controlling cell proliferation, differentiation, communication, and adhesion. Disruption of this key regulatory mechanism contributes to a variety of human diseases including cancer, diabetes, and auto-immune diseases. Net protein tyrosine phosphorylation is determined by the dynamic balance of the activity of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs). Mammals express many distinct PTKs and PTPs. Both of these families can be sub-divided into non-receptor and receptor subtypes. Receptor protein tyrosine kinases (RPTKs) comprise a large family of cell surface proteins that initiate intracellular tyrosine phosphorylation-dependent signal transduction in response to binding of extracellular ligands, such as growth factors and cytokines. Receptor-type protein tyrosine phosphatases (RPTPs) are enzymatic and functional counterparts of RPTKs. RPTPs are a family of integral cell surface proteins that possess intracellular PTP activity, and extracellular domains that have sequence homology to cell adhesion molecules. In comparison to extensively studied RPTKs, much less is known about RPTPs, especially regarding their substrate specificities, regulatory mechanisms, biological functions, and their roles in human diseases. Based on the structure of their extracellular domains, the RPTP family can be grouped into eight sub-families. This article will review one representative member from each RPTP sub-family.

Mechanisms of neurotoxicity induced in the developing brain of mice and rats by DNA-damaging chemicals

It is not widely known how the developing brain responds to extrinsic damage, although the developing brain is considered to be sensitive to diverse environmental factors including DNA-damaging agents. This paper reviews the mechanisms of neurotoxicity induced in the developing brain of mice and rats by six chemicals (ethylnitrosourea, hydroxyurea, 5-azacytidine, cytosine arabinoside, 6-mercaptopurine and etoposide), which cause DNA damage in different ways, especially from the viewpoints of apoptosis and cell cycle arrest in neural progenitor cells. In addition, this paper also reviews the repair process following damage in the developing brain.

Chondroitin sulfate "wobble motifs" modulate maintenance and differentiation of neural stem cells and their progeny

Chondroitin sulfate/dermatan sulfate (CS/DS) proteoglycans, major components of the central nervous system, have the potential to interact with a wide range of growth factors and neurotrophic factors that influence neuronal migration, axon guidance pathways, and neurite outgrowth. Recent studies have also revealed the role of CS/DS chains in the orchestration of the neural stem/progenitor cell micromilieu. Individual functional proteins recognize a set of multiple overlapping oligosaccharide sequences decorated to give different sulfation patterns, which are termed here "wobble CS/DS oligosaccharide motifs," and induce signaling pathways essential for the proliferation, self-renewal, and cell lineage commitment of neural stem/progenitor cells.

The synthetic peptide P111-136 derived from the C-terminal domain of heparin affin regulatory peptide inhibits tumour growth of prostate cancer PC-3 cells

Background

Heparin affin regulatory peptide (HARP), also called pleiotrophin, is a heparin-binding, secreted factor that is overexpressed in several tumours and associated to tumour growth, angiogenesis and metastasis. The C-terminus part of HARP composed of amino acids 111 to 136 is particularly involved in its biological activities and we previously established that a synthetic peptide composed of the same amino acids (P111-136) was capable of inhibiting the biological activities of HARP. Here we evaluate the ability of P111-136 to inhibit in vitro and in vivo the growth of a human tumour cell line PC-3 which possess an HARP autocrine loop.

Methods

A total lysate of PC-3 cells was incubated with biotinylated P111-136 and pulled down for the presence of the HARP receptors in Western blot. In vitro, the P111-136 effect on HARP autocrine loop in PC-3 cells was determined by colony formation in soft agar. In vivo, PC-3 cells were inoculated in the flank of athymic nude mice. Animals were treated with P111-136 (5 mg/kg/day) for 25 days. Tumour volume was evaluated during the treatment. After the animal sacrifice, the tumour apoptosis and associated angiogenesis were evaluated by immunohistochemistry. In vivo anti-angiogenic effect was confirmed using a mouse Matrigel™ plug assay.

Results

Using pull down experiments, we identified the HARP receptors RPTPβ/ζ, ALK and nucleolin as P111-136 binding proteins. In vitro, P111-136 inhibits dose-dependently PC-3 cell colony formation. Treatment with P111-136 inhibits significantly the PC-3 tumour growth in the xenograft model as well as tumour angiogenesis. The angiostatic effect of P111-136 on HARP was also confirmed using an in vivo Matrigel™ plug assay in mice

Conclusions

Our results demonstrate that P111-136 strongly inhibits the mitogenic effect of HARP on in vitro and in vivo growth of PC-3 cells. This inhibition could be linked to a direct or indirect binding of this peptide to the HARP receptors (ALK, RPTPβ/ζ, nucleolin). In vivo, the P111-136 treatment significantly inhibits both the PC-3 tumour growth and the associated angiogenesis. Thus, P111-136 may be considered as an interesting pharmacological tool to interfere with tumour growth that has now to be evaluated in other cancer types.

Functions of chondroitin sulfate and heparan sulfate in the developing brain

Chondroitin sulfate and heparan sulfate proteoglycans are major components of the cell surface and extracellular matrix in the brain. Both chondroitin sulfate and heparan sulfate are unbranched highly sulfated polysaccharides composed of repeating disaccharide units of glucuronic acid and N-acetylgalactosamine, and glucuronic acid and N-acetylglucosamine, respectively. During their biosynthesis in the Golgi apparatus, these glycosaminoglycans are highly modified by sulfation and C5 epimerization of glucuronic acid, leading to diverse heterogeneity in structure. Their structures are strictly regulated in a cell type-specific manner during development partly by the expression control of various glycosaminoglycan-modifying enzymes. It has been considered that specific combinations of glycosaminoglycan-modifying enzymes generate specific functional microdomains in the glycosaminoglycan chains, which bind selectively with various growth factors, morphogens, axon guidance molecules and extracellular matrix proteins. Recent studies have begun to reveal that the molecular interactions mediated by such glycosaminoglycan microdomains play critical roles in the various signaling pathways essential for the development of the brain.

Increased trabecular bone formation in mice lacking the growth factor midkine

Midkine (Mdk) and pleiotrophin (Ptn) comprise a family of heparin-binding growth factors known primarily for their effects on neuronal cells. Since transgenic mice overexpressing Ptn have been reported to display increased bone density, we have previously analyzed Ptn-deficient mice but failed to detect any abnormality of skeletal development and remodeling. Together with the finding that Mdk expression increases in the course of primary osteoblast differentiation, we reasoned that Mdk, rather than Ptn, could play a physiologic role in bone formation. Here, we show that Mdk-deficient mice display an increased trabecular bone volume at 12 and 18 months of age, accompanied by cortical porosity. Histomorphometric quantification demonstrated an increased bone-formation rate compared with wild-type littermates, whereas bone resorption was differentially affected in trabecular and cortical bone of Mdk-deficient mice. To understand the effect of Mdk on bone formation at the molecular level, we performed a genome-wide expression analysis of primary osteoblasts and identified Ank and Enpp1 as Mdk-induced genes whose decreased expression in Mdk-deficient osteoblasts may explain, at least in part, the observed skeletal phenotype. Finally, we performed ovariectomy and observed bone loss only in wild-type but not in Mdk-deficient animals. Taken together, our data demonstrate that Mdk deficiency, at least in mice, results in an increased trabecular bone formation, thereby raising the possibility that Mdk-specific antagonists might prove beneficial in osteoporosis therapy.

Neuroglycan C, a brain-specific chondroitin sulfate proteoglycan, interacts with pleiotrophin, a heparin-binding growth factor

Neuroglycan C (NGC) is a transmembrane-type chondroitin sulfate proteoglycan that promotes neurite outgrowth. To identify the ligand of NGC, we applied a detergent-solubilized membrane fraction of fetal rat brains to an NGC-immobilized affinity column. Several proteins were eluted from the column including an 18 kDa-band protein recognized by an anti-pleiotrophin antibody. The binding of pleiotrophin (PTN) to NGC was confirmed by a quartz crystal microbalance method and had a Kd of 8.7 nM. PTN bound to the acidic amino acid cluster of the NGC extracellular domain. In addition, PTN bound to both chondroitin sulfate-bearing NGC and chondroitinase-treated NGC prepared from the neonatal rat brain. These results suggest that NGC interacts with PTN.