Receptor protein tyrosine phosphatases are expressed by cycling retinal progenitor cells and involved in neuronal development of mouse retina.

Receptor protein tyrosine phosphatases (RPTPs) appear to coordinate many aspects of neural development, including cell proliferation, migration and differentiation. Here we investigated potential roles of RPTPs in the developing mouse retina. Using a degenerate oligonucleotide-based reverse transcription polymerase chain reaction approach, we identified 11 different RPTPs in the retina at embryonic stage 13 (E13). Subsequently, the expression patterns of RPTPkappa, RPTPJ, RPTPRR, RPTPsigma, RPTPepsilon and RPTPgamma in the retina from embryonic stages to adult were analyzed in detail using quantitative real-time-PCR, in situ hybridization, immunohistochemistry and Western blotting. At E13, all six RPTPs are expressed in actively cycling retinal progenitor cells and postmitotic newborn retinal neurons. With ongoing maturation, RPTPkappa, RPTPJ, RPTPRR, RPTPsigma, RPTPepsilon and RPTPgamma display a different spatiotemporal regulation of mRNAs and proteins in the pre- and postnatal retina. Finally, in adulthood these six RPTPs localize to distinct cellular compartments of multiple retinal neurons. Additional studies in RPTPgamma(-/-) and RPTPbeta/zeta(-/-) (also known as PTPRZ1, RPTPbeta or RPTPzeta) mice at postnatal stage P1 reveal no apparent differences in retinal laminar organization or in the expression pattern of specific retinal cell-type markers when compared with wild type. However, in RPTPbeta/zeta(-/-) retinas, immunoreactivity of vimentin, a marker of Müller glial cells, is selectively reduced and the morphology of vimentin-immunoreactive radial processes of Müller cells is considerably disturbed. Our results suggest distinct roles of RPTPs in cell proliferation and establishing phenotypes of different retinal cells during retinogenesis as well as later in the maintenance of mature retina.

The protein tyrosine phosphatase Rptpzeta is expressed in differentiated osteoblasts and affects bone formation in mice.

Tyrosine phosphorylation of intracellular substrates is one mechanism to regulate cellular proliferation and differentiation. Protein tyrosine phosphatases (PTPs) act by dephosphorylation of substrates and thereby counteract the activity of tyrosine kinases. Few PTPs have been suggested to play a role in bone remodeling, one of them being Rptpzeta, since it has been shown to be suppressed by pleiotrophin, a heparin-binding molecule affecting bone formation, when over-expressed in transgenic mice. In a genome-wide expression analysis approach we found that Ptprz1, the gene encoding Rptpzeta, is strongly induced upon terminal differentiation of murine primary calvarial osteoblasts. Using RT-PCR and Western Blotting we further demonstrated that differentiated osteoblasts, in contrast to neuronal cells, specifically express the short transmembrane isoform of Rptpzeta. To uncover a potential role of Rptpzeta in bone remodeling we next analyzed the skeletal phenotype of a Rptpzeta-deficient mouse model using non-decalcified histology and histomorphometry. Compared to wildtype littermates, the Rptpzeta-deficient mice display a decreased trabecular bone volume at the age of 50 weeks, caused by a reduced bone formation rate. Likewise, Rptpzeta-deficient calvarial osteoblasts analyzed ex vivo display decreased expression of osteoblast markers, indicating a cell-autonomous defect. This was confirmed by the finding that Rptpzeta-deficient osteoblasts had a diminished potential to form osteocyte-like cellular extensions on Matrigel-coated surfaces. Taken together, these data provide the first evidence for a physiological role of Rptpzeta in bone remodeling, and thus identify Rptpzeta as the first PTP regulating bone formation in vivo.

Molecular dissection of NRG1-ERBB4 signaling implicates PTPRZ1 as a potential schizophrenia susceptibility gene.

Neuregulin and the neuregulin receptor ERBB4 have been genetically and functionally implicated in schizophrenia. In this study, we used the yeast two-hybrid system to identify proteins that interact with ERBB4, to identify genes and pathways that might contribute to schizophrenia susceptibility. We identified the MAGI scaffolding proteins as ERBB4-binding proteins. After validating the interaction of MAGI proteins with ERBB4 in mammalian cells, we demonstrated that ERBB4 expression, alone or in combination with ERBB2 or ERBB3, led to the tyrosine phosphorylation of MAGI proteins, and that this could be further enhanced with receptor activation by neuregulin. As MAGI proteins were previously shown to interact with receptor phosphotyrosine phosphatase beta/zeta (RPTPbeta), we postulated that simultaneous binding of MAGI proteins to RPTPbeta and ERBB4 forms a phosphotyrosine kinase/phosphotyrosine phosphatase complex. Studies in cultured cells confirmed both a spatial and functional association between ERBB4, MAGI and RPTPbeta. Given the evidence for this functional association, we examined the genes coding for MAGI and RPTPbeta for genetic association with schizophrenia in a Caucasian United Kingdom case-control cohort (n= approximately 1400). PTPRZ1, which codes for RPTPbeta, showed significant, gene-wide and hypothesis-wide association with schizophrenia in our study (best individual single-nucleotide polymorphism allelic P=0.0003; gene-wide P=0.0064; hypothesis-wide P=0.026). The data provide evidence for a role of PTPRZ1, and for RPTPbeta signaling abnormalities, in the etiology of schizophrenia. Furthermore, the data indicate a role for RPTPbeta in the modulation of ERBB4 signaling that may in turn provide further support for an important role of neuregulin/ERBB4 signaling in the molecular basis of schizophrenia.

Monoclonal antibody Cat-315 detects a glycoform of receptor protein tyrosine phosphatase beta/phosphacan early in CNS development that localizes to extrasynaptic sites prior to synapse formation.

Perineuronal nets (PNs) are lattice-like condensations of the extracellular matrix (ECM) that envelop synapses and decorate the surface of subsets of neurons in the CNS. Previous work has suggested that, despite the fact that PNs themselves are not visualized until later in development, some PN component molecules are expressed in the rodent CNS even before synaptogenesis. In the adult mammalian brain, monoclonal antibody Cat-315 recognizes a glycoform of aggrecan, a major component of PNs. In primary cortical cultures, a Cat-315-reactive chondroitin sulfate proteoglycan (CSPG) is also expressed on neuronal surfaces and is secreted into culture media as early as 24 h after plating. In this study, we show that in primary cortical cultures, the Cat-315 CSPG detected in early neural development is expressed in extrasynaptic sites prior to synapse formation. This suggests that ECM components in the CNS, as in the neuromuscular junction (NMJ), may prepattern neuronal surfaces prior to innervation. We further show that while the Cat-315-reactive carbohydrate decorates aggrecan in the adult, it decorates a different CSPG in the developing CNS. Using receptor protein tyrosine phosphatase beta (RPTPbeta/protein tyrosine phosphatase zeta) knock-out mice and immunoprecipitation techniques, we demonstrate here that in the developing rodent brain Cat-315 recognizes RPTPbeta isoforms. Our further examination of the Cat-315 epitope suggests that it is an O-mannose linked epitope in the HNK-1 family. The presence of the Cat-315 reactive carbohydrate on different PN components--RPTPbeta and aggrecan--at different stages of synapse development suggests a potential role for this neuron-specific carbohydrate motif in synaptogenesis.

BACE (beta-secretase) modulates the processing of APLP2 in vivo.

BACE is an aspartyl protease that cleaves the amyloid precursor protein (APP) at the beta-secretase cleavage site and is involved in Alzheimer's disease. The aim of our study was to determine whether BACE affects the processing of the APP homolog APLP2. To this end, we developed BACE knockout mice with a targeted insertion of the gene for beta-galactosidase. BACE appeared to be exclusively expressed in neurons as determined by differential staining. BACE was expressed in specific areas in the cortex, hippocampus, cerebellum, pons, and spinal cord. APP processing was altered in the BACE knockouts with Abeta levels decreasing. The levels of APLP2 proteolytic products were decreased in BACE KO mice, but increased in BACE transgenic mice. Overexpression of BACE in cultured cells led to increased APLP2 processing. Our results strongly suggest that BACE is a neuronal protein that modulates the processing of both APP and APLP2.

Pyk2 regulates multiple signaling events crucial for macrophage morphology and migration.

The biological role of the protein tyrosine kinase, Pyk2, was explored by targeting the Pyk2 gene by homologous recombination. Pyk2-/- mice are viable and fertile, without overt impairment in development or behavior. However, the morphology and behavior of Pyk2-/- macrophages were impaired. Macrophages isolated from mutant mice failed to become polarized, to undergo membrane ruffling, and to migrate in response to chemokine stimulation. Moreover, the contractile activity in the lamellipodia of Pyk2-/- macrophages was impaired, as revealed by measuring the rearward movement toward the nucleus of fibronectin-coated beads on the lamellipodia in opposition to an immobilizing force generated by optical tweezers. Consistently, the infiltration of macrophages into a carageenan-induced inflammatory region was strongly inhibited in Pyk2-/- mice. In addition, chemokine stimulation of inositol (1, 4, 5) triphosphate production and Ca2+ release, as well as integrin-induced activation of Rho and phosphatidyl inositol 3 kinase, were compromised in Pyk2-/- macrophages. These experiments reveal a role for Pyk2 in cell signaling in macrophages essential for cell migration and function.

No obvious abnormality in mice deficient in receptor protein tyrosine phosphatase beta.

The development of neurons and glia is governed by a multitude of extracellular signals that control protein tyrosine phosphorylation, a process regulated by the action of protein tyrosine kinases and protein tyrosine phosphatases (PTPs). Receptor PTPbeta (RPTPbeta; also known as PTPzeta) is expressed predominantly in the nervous system and exhibits structural features common to cell adhesion proteins, suggesting that this phosphatase participates in cell-cell communication. It has been proposed that the three isoforms of RPTPbeta play a role in regulation of neuronal migration, neurite outgrowth, and gliogenesis. To investigate the biological functions of this PTP, we have generated mice deficient in RPTPbeta. RPTPbeta-deficient mice are viable, are fertile, and showed no gross anatomical alterations in the nervous system or other organs. In contrast to results of in vitro experiments, our study demonstrates that RPTPbeta is not essential for neurite outgrowth and node formation in mice. The ultrastructure of nerves of the central nervous system in RPTPbeta-deficient mice suggests a fragility of myelin. However, conduction velocity was not altered in RPTPbeta-deficient mice. The normal development of neurons and glia in RPTPbeta-deficient mice demonstrates that RPTPbeta function is not necessary for these processes in vivo or that loss of RPTPbeta can be compensated for by other PTPs expressed in the nervous system.

Unmasking by soluble IL-6 receptor of IL-6 effect on metastatic melanoma: growth inhibition and differentiation of B16-F10.9 tumor cells.

Interleukin-6 (IL-6) inhibits the growth of melanocytes and of early stage melanoma cells, but not that of advanced melanoma cells. The in vitro IL-6 response can be restored in the highly metastatic melanoma B16-F10.9 by addition of recombinant soluble IL-6 receptor alpha-chain (sIL-6R). The F10.9 cells then undergo irreversible growth-arrest and show increased adherence with changes from epithelioid to spindleoid morphology. The sIL-6R is required for IL-6 to induce a sustained activation of the various Stat transcription factors which bind to specific IL-6 inducible enhancers. The sIL-6R and IL-6 combination causes an increase in the level of the anti-oncogenic transcription factor IRF-1 protein and DNA-binding, which remain elevated for 24 h. The promoter activity of the anti-oncogenic p21/Waf-1/Cip-1 gene is induced and accumulation of the p21 protein is observed. These results illustrate the potent agonist activity of sIL-6R on molecular pathways which could mediate the growth-arrest and differentiation of the metastatic melanoma cells. Previously observed antimetastatic effects of IL-6 therapy in mice bearing F10.9 tumors may be at least partly due to direct growth inhibition and differentiation elicited by sIL-6R present in biological fluids.

5' upstream sequences of MyD88, an IL-6 primary response gene in M1 cells: detection of functional IRF-1 and Stat factors binding sites.

Transcription regulatory elements have been analyzed in upstream sequences of an Interleukin-6 (Il-6) primary response gene, MyD88. MyD88 2.3 kb mRNA is strongly and persistently induced in the course of myeloleukemic M1 cells differentiation with Il-6. MyD88 cDNA sequences were found in a region of 12 kb of mouse genomic DNA. Using Il-6 treated M1 cell RNAs, two transcription start sites have been localized, approximately 100 bp upstream from the 5' end of the cloned cDNA. We sequenced 1.4 kb of 5' genomic DNA including the first exon. In 5' of mRNA transcription start site, MyD88 nucleotidic sequence is 85% identical to 5' complementary sequences of the rat 3'-ketoacetyl CoA thiolase gene, over 1.2 kb. A DNA element conferring Il-6-inducible transcription to reporter genes, and localized 30 bp upstream of MyD88 first RNA start site, contains overlapping binding sites for cytokine activated transcription factors Stat and for the Interferon Regulatory Factor-1 and -2 (IRF-1 and IRF-2). In vitro binding assays showed that attachment of Stat factors to this element early in Il-6 treatment requires tyrosine kinase activation. IRF1, an activator of transcription, is also induced to bind to this sequence at later times. A model of persistent activation of MyD88 gene through these two types of factors is proposed.

Antagonism of interferon beta on interferon gamma: inhibition of signal transduction in vitro and reduction of serum levels in multiple sclerosis patients.

Interferon gamma (IFN-gamma acts as a mediator of multiple sclerosis (MS) exacerbations through a number of biological effects, such as induction of major histocompatibility class II complexes (MHC-II), macrophage activation and potentiation of tumor necrosis factor (TNF-alpha). The clinical efficacy of interferon beta (IFN-beta) therapy in reducing exacerbations of relapsing-remitting MS has been related to antagonistic effects on various activities of IFN-gamma, including MHC-II gene induction. However, there is no model to explain such antagonistic effects of IFN-beta and IFN-gamma, and the two cytokines are also known to act synergistically against viruses and in the induction of MHC-I. We show that IFN-beta does inhibit an immediate molecular event of IFN-gamma, namely activation and DNA binding of the transcription factor Stat1. We propose a model of direct interference of the IFN-gamma and IFN-alpha,beta signal transduction pathways accounting for antagonistic effects on some genes, which in turn activate MHC-II transcription, as well as for synergistic effects on other genes. In addition, study of MS patients treated with natural IFN-beta shows that IFN-beta significantly reduces serum levels of IFN-gamma while increasing IL-4, strongly suggesting that IFN-beta also controls the relative activation of TH1- and TH2-type T lymphocytes.

Differential tyrosine phosphorylation of the IFNAR chain of the type I interferon receptor and of an associated surface protein in response to IFN-alpha and IFN-beta.

The human interferon alpha-receptor (IFNAR gene product) is a transmembranal protein of 557 amino acids with an intracytoplasmic domain of 100 amino acids containing four tyrosines. Antibodies to a C-terminal peptide (residues 521-536) were developed which efficiently immunoprecipitate the 105 kDa IFNAR protein from detergent extracts of human cells. We show that the IFNAR protein becomes tyrosine phosphorylated within 5 min after treatment of human myeloma U266 cells with IFN-alpha 2, IFN-alpha 8 or IFN-beta. The IFNAR chain interacts with both IFN-alpha 2 and IFN-beta, as demonstrated by cross-linking. Among elements involved in signal transduction by type I IFNs, the tyrosine kinase Tyk2 but not Jak1, and the ISGF3 transcription factor subunit Stat2 (p113) but not Stat1 (p91), are found associated with the IFNAR protein. After IFN-beta treatment for 5 min, a tyrosine-phosphorylated protein of approximately 95 kDa (beta-PTyr) is found bound to IFNAR, but can be dissociated by denaturation. The beta-PTyr protein is present on the cell surface, like IFNAR, as shown by extracellular biotin tagging. The ratio of beta-PTyr to IFNAR tyrosine phosphorylation is much higher with IFN-beta than with IFN-alpha 2 or 8. Both are IFN dependent and abrogated by a monoclonal antibody which blocks IFNAR action. The beta-PTyr component may represent an important difference in the action of IFN-beta as compared with IFN-alpha in their shared receptor system.

Interleukin-6 signaling via four transcription factors binding palindromic enhancers of different genes.

Interferons (IFNs), as well as some interleukins, growth factors, and hormones, all induce tyrosine phosphorylation of STAT1 and additional transcription factors of similar sizes. These factors are activated to translocate to nucleus and bind to enhancers of consensus sequence TTnCnnnAA (gamma-IFN activated sequence-like enhancers). In mammary cells or hybridoma B9 cells, four distinct tyrosine-phosphorylated transcription complexes activated by interleukin-6 (IL-6) and IFN-beta were observed: pIRFA and complexes I, II, and III (of increasing electrophoretic mobility). The factors have unequal affinities for enhancers of different genes; they are activated with distinct kinetics and to different extents by IL-6 and IFNs. The pIRFA band isolated from IL-6-stimulated B9 hybridoma cells revealed three DNA-interacting components: two large subunits of 91 and 98 kDa, as well as a small component of 46 kDa not seen in other complexes analyzed. One of the large pIRFA subunits may be APRF/STAT3, since pIRFA reacted with anti-APRF antibodies as do complexes I and II. However, pIRFA did not react with antibodies to STAT1, indicating STAT1 is not the other large component of pIRFA. Complex II, which reacted to anti-acute phase response factor antibodies also reacted to anti-STAT1 antibodies, whereas complex III reacted only to anti-STAT1 and was the only complex resistant to N-ethylmaleimide. By its multimeric subunit structure and its cytokine and enhancer sequence specificities, the slowly migrating pIRFA band appears as a novel tyrosine-phosphorylated transcription complex acting on a subset of gamma-IFN activated sequence-like enhancers.

Induction by interleukin-6 of interferon regulatory factor 1 (IRF-1) gene expression through the palindromic interferon response element pIRE and cell type-dependent control of IRF-1 binding to DNA.

The effects of interleukin-6 (IL-6) on interferon regulatory factor 1 (IRF-1) gene expression were studied in B-hybridoma B9 cells which are growth-stimulated by IL-6 and breast carcinoma T47D cells which are growth-inhibited. IL-6 induced the production of IRF-1 mRNA and protein in both cell types, but IRF-1 binding activity to its target DNA sequence was induced only in T47D cells. With B9 cells, there was no IRF-1 binding but instead strong constitutive binding of the IRF-2 repressor, indicating that binding of IRF-1 to DNA is an important regulatory step. The IRF-1 gene promoter element, palindromic IFN-response element (pIRE), was found to respond to IL-6 with high efficiency as compared with IFN-gamma or IFN-beta. On this palindromic TTC...GAA sequence, two protein complexes (pIRE-a and pIRE-b) were induced within minutes by IL-6. pIRE-b is similar to the main complex induced by IFN-gamma and contains the Stat91 protein. pIRE-a predominantly induced by IL-6 is a slowly migrating complex which does not contain Stat91 and has low affinity for IFN-gamma activated sequence (GAS)-type sequences. Comparison of the relative effects of IL-6 and IFN-gamma shows that pIRE enhancers are differently regulated than GAS elements. Distinct transcription complexes, forming in ratios dependent on the inducer, help explain how various cytokines sharing effects through Stat91 on related enhancers can produce specific patterns of gene expression. Activation of the pIRE-a factors defines a novel transcriptional activity of IL-6 in epithelial and lymphoid cells.

Interleukin-6 activates and regulates transcription factors of the interferon regulatory factor family in M1 cells.

Activation of (2'-5') A synthetase gene expression in interleukin-6 (IL-6)-treated myeloleukemic M1 cells correlates with protein binding to the interferon response sequence enhancer (IRS). A new interferon response sequence complex, F6, is induced by IL-6 independently of interferon and is identified here as comprising the interferon regulatory factor-1 (IRF-1) and IRF-2, by use of specific antibodies in DNA mobility shift assays with probes containing IRF binding sites. IRF-1 and IRF-2 have, respectively, positive and negative transcriptional effects on interferon-beta and interferon-inducible genes. In the IL-6-treated M1or cells, IRF-1 binding is activated early and maximally at 1 h, whereas the onset of IRF-2 binding is delayed. In a cell variant M1res, where (2'-5') A synthetase is no more induced, IRF-2 binding is constitutive, and IRF-1 binding is not seen before or after IL-6 treatment. In sensitive M1or cells, IL-6 rapidly induces IRF-1 mRNA, but in M1res cells, IRF-1 mRNA is constitutively high and not changed by IL-6. IRF-2 mRNA levels are also constitutive and not inducible by IL-6 even in M1or cells. The dissociation between induction of mRNAs and of protein binding observed suggests that the activity of the IRF proteins is regulated by IL-6. Transcripts of a third member of the IRF gene family, ICSBP, encoding a protein known to act as repressor, were found to be strongly down-regulated by IL-6. The rapid activation of IRF-1 and the modulation of the other transcription factors of this family may play a role in the early phase of IL-6 action on the M1 cells.