Research report
Identification and characterization of RPTPρ, a novel RPTPμ/κ-like receptor protein tyrosine phosphatase whose expression is restricted to the central nervous system

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Abstract

We describe the cloning, chromosomal localization and characterization of RPTPρ, a new member of the RPTPμ/κ phosphatase subfamily. Receptor tyrosine phosphatases in this subfamily are comprised of a MAM domain near the N-terminal, an immunoglobulin-like domain, four fibronectin type III repeats, a single transmembrane domain, and a large juxtamembrane segment followed by two intracellular phosphatase domains. An alternatively spliced mini-exon was identified in the extracellular segment of RPTPρ, between the fourth fibronectin type III repeat and the transmembrane domain. The RPTRρ gene was mapped to human chromosome 20 and mouse chromosome 2. Northern blot analysis demonstrated that RPTPρ expression was restricted to the central nervous system, and in situ hybridization studies showed that the RPTPρ transcript was distributed throughout the murine brain and spinal cord. Exceptionally high levels of the transcript were present in the cortex and olfactory bulbs during perinatal development, but were down-regulated during postnatal week two. The motifs found in the extracellular segment of type II receptor protein tyrosine phosphatases are commonly found in neural cell adhesion molecules, suggesting that RPTPρ may be involved in both signal transduction and cellular adhesion in the central nervous system.

Introduction

Protein tyrosine phosphorylation is a reversible, dynamic process which has been linked to the regulation of diverse cellular functions including signal transduction, growth, differentiation, axon guidance and cell–cell contact [35]. These cellular processes are, to a large extent, controlled by a balance between the actions of protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) 7, 34, 35, 47, 60, 61. Protein tyrosine phosphatases are categorized as either transmembrane receptor-like, or intracellular, molecules. The overall structure of receptor-like PTPs (RPTPs) is similar to that of receptor-like PTKs; both contain an extracellular region, a single transmembrane segment, and an intracellular catalytic domain. In the majority of RPTPs, the catalytic region contains two highly conserved phosphatase domains of approximately 230 AA residues. The structural features of transmembrane RPTPs suggest the potential to bind ligands and convert extracellular signals into intracellular responses.

Receptor protein tyrosine phosphatases have been subdivided into several classes based on the structure of their extracellular segments 19, 60. The extracellular segment of type II RPTPs contains a combination of immunoglobulin (Ig)-like and fibronectin (FN) type III repeats. These motifs are found in neural cell adhesion molecules [14]where they are involved in homophilic binding [45]. A subset of the type II class, RPTPμ [22], RPTPκ [27], PCP-2 [63], RPTPπ [13]and RPTPψ [Banville et al., Genbank #U60289], share considerable amino acid similarity and contain a MAM domain near the N-terminal. The high degree of similarity in the nucleotide sequences of PCP-2, RPTPπ and RPTPψ suggest that they represent the same gene. Both RPTPμ 5, 24and RPTPκ [49]have been shown to mediate cell–cell aggregation by homophilic binding.

Several RPTPs have been shown to play critical roles in neural development 10, 15, 46, 47, 54, 62. Transfection of PTPα into embryonic stem cells induces differentiation into functional neurons [15]. PTPNE3/PTPσ is highly expressed in the olfactory epithelium where it is likely to play a role in neuronal proliferation or migration 46, 62, 65. RPTPs containing carbonic anhydrase domains have been shown to be chondroitin sulfate proteoglycans [1]. One such molecule, RPTPζ/β, specifically binds contactin, a glycosylphosphatidylinositol-anchored neuronal recognition molecule [42], and the domain responsible for this binding acts as a substrate for neuronal adhesion and induction of neurite outgrowth. RPTPζ/β is expressed in glial cells in the developing central nervous system [10]where it may act as a signal transducer as neurons migrate along glial pathways. Phosphacan, an RPTPζ/β splice variant, has been shown to bind N-CAM, Ng-CAM and tenascin, again suggesting a role for RPTPs in the regulation of neuronal cell adhesion [33]. Furthermore, analysis of RPTP mutations in Drosophila provide strong evidence that PTP69D, PTP99A, and DLAR are involved in motor axon guidance 16, 29: Mutants lacking these RPTPs display `bypass', `detour', or `stall' phenotypes, indicating an impaired ability to execute correct axonal pathfinding decisions.

Here we describe the cDNA cloning, characterization, chromosomal mapping and expression of RPTPρ, a new member of the RPTPμ/κ subfamily of receptor protein tyrosine phosphatases. Unlike the majority of RPTPs, the expression of the RPTPρ transcript is entirely restricted to the brain and spinal cord of adult and developing animals.

Section snippets

Identification of RPTPρ

Primers originally designed to amplify the dystroglycan gene [26]between 1090–1371 bp, amplified a portion of RPTPρ cDNA. Total RNA from human frontal cortex [12]was reverse transcribed and used as a template for RT-PCR. The reaction contained 125 nM of each primer (5′GAATTCGGGAAGCCCACGGTCACCACTCGG3′ and 5′GTCGACTCCTGGGTGTCCGTGGCTTCTTGGT3′), 2.5 mM MgCl2, 200 μM each dNTP, 1× Taq DNA polymerase buffer, and 0.5 U Taq DNA polymerase (Gibco BRL) and was run for 35 cycles of 94°C for 30 s, 55°C for

Identification of RPTPρ

Analysis of RT-PCR products amplified from frontal cortex cDNA with a dystroglycan primer set revealed the expected portion of dystroglycan and an additional 650 bp product. Sequence analysis of the latter product revealed a high degree of amino acid identity with RPTPμ and RPTPκ, members of the type II class of receptor-like protein tyrosine phosphatases. The RPTPρ cDNA fragment was used to screen cDNA libraries to obtain overlapping phage clones.

Molecular cloning of RPTPρ

Four overlapping cDNA clones containing the

Discussion

The present studies describe the structure, chromosomal localization and expression pattern of RPTPρ, a new member of the type II family of receptor-like protein tyrosine phosphatases. Like other members of this group, the RPTPρ molecule is comprised of an extracellular region, a single transmembrane segment, and an intracellular catalytic region containing two phosphatase domains. The presence of a MAM domain in the extracellular segment further classifies RPTPρ as a member of a smaller group

Acknowledgements

Supported by AR40015 (AB), MH57415 (AR) and NS32276 (AF) from the National Institutes of Health, the Muscular Dystrophy Association (AB), and the Paul Patton Memorial Trust (RAW). The authors would like to thank G. Grumbling, S. Ingraham, J. Evans, and S. Han for their assistance, and L. Rowe and M. Barter of the Jackson Laboratory for analyzing the linkage data.

References (68)

  • M.F.B.G Gebbink et al.

    Cell–cell adhesion mediated by a receptor-like protein tyrosine phosphatase

    J. Biol. Chem.

    (1993)
  • N.X Krueger et al.

    The transmembrane tyrosine phosphatase DLAR controls motor axon guidance in Drosophila

    Cell

    (1996)
  • J.B Levy et al.

    The cloning of a receptor-type protein tyrosine phosphatase in the central nervous system

    J. Biol. Chem.

    (1993)
  • S McLaughlin et al.

    Alternative splicing gives rise to a nuclear protein tyrosine phosphatase in Drosophila

    J. Biol. Chem.

    (1993)
  • R.J Mourey et al.

    Protein tyrosine phosphatases: characterization of extracellular and intracellular domains

    Curr. Opin. Genet. Dev.

    (1994)
  • B.G Neel et al.

    Protein tyrosine phosphatases in signal transduction

    Curr. Opin. Cell Biol.

    (1997)
  • M Ogata et al.

    cDNA cloning and characterization of a novel receptor-type protein tyrosine phosphatase expressed predominantly in the brain

    J. Cell. Biol.

    (1995)
  • P O'Grady et al.

    Genomic organization of human LAR protein tyrosine phosphatase gene and alternative splicing in the extracellular fibronectin type-III domains

    J. Biol. Chem.

    (1994)
  • S.H Oon et al.

    Alternative splicing in a novel tyrosine phosphatase gene (DPTP4E) of Drosophila melanogaster generates two large receptor-like proteins which differ in their carboxyl termini

    J. Biol. Chem.

    (1993)
  • M.-G Pan et al.

    Cloning and expression of two structurally distinct receptor-linked protein tyrosine phosphatases generated by RNA processing from a single gene

    J. Biol. Chem.

    (1993)
  • L Patthy

    Homology of a domain of the growth hormone/prolactin receptor family with type III modules of fibronectin

    Cell

    (1990)
  • E Peles et al.

    The carbonic anhydrase domain of receptor tyrosine phosphatase β is a functional ligand for the axonal recognition molecule contactin

    Cell

    (1995)
  • T.N Stitt et al.

    The anticoagulation factor protein s and its relative, gas 6, are ligands for the tyro 3/axl family of receptor protein kinases

    Cell

    (1995)
  • A.W Stoker

    Isoforms of a novel cell adhesion molecule-like protein tyrosine phosphatase are implicated in neuronal development

    Mech. Dev.

    (1994)
  • S Takagi et al.

    The A5 antigen, a candidate for the neuronal recognition molecule, has homologies to complement components and coagulation factors

    Neuron

    (1991)
  • X Tan et al.

    Demonstration of protein tyrosine phosphatase activity in the second of two homologous domains of CD45

    J. Biol. Chem.

    (1993)
  • K.M Walton et al.

    A novel receptor-type protein tyrosine phosphatase is expressed during neurogenesis in the olfactory neuroepithelium

    Neuron

    (1993)
  • H Yan et al.

    A novel receptor tyrosine phosphatase-σ that is highly expressed in the nervous system

    J. Biol. Chem.

    (1993)
  • G.C.M Zondag et al.

    Homophilic interactions mediated by receptor tyrosine phosphatases μ and κ

    J. Biol. Chem.

    (1995)
  • G Beckman et al.

    An adhesive domain detected in functionally diverse receptors

    Trends Biochem. Sci.

    (1993)
  • P Bellosta et al.

    The receptor tyrosine kinase Ark mediates cell aggregation by homophilic binding

    Mol. Cell Biol.

    (1995)
  • S.M Brady-Kalnay et al.

    Homophilic binding of PTPμ, a receptor-type protein tyrosine phosphatase, can mediate cell–cell aggregation

    J. Cell Biol.

    (1993)
  • S.M Brady-Kalnay et al.

    Receptor protein tyrosine phosphatase PTPμ associates with cadherins and catenins in vivo

    J. Cell Biol.

    (1995)
  • J.M Chirgwin et al.

    Isolation of biologically active ribonucleic acid from sources enriched in ribonuclease

    Biochem.

    (1979)
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