Molecular Cloning and Tissue‐Specific RNA Processing of a Murine Receptor‐Type Protein Tyrosine Phosphatase

Abstract

The molecular cloning of a murine receptor-type protein tyrosine phosphatase, termed PTP NU-3, with an extracellular cell-adhesion-molecule-like domain is reported. NU-3 was isolated from 11.5-day total mouse embryonic RNA by reverse-transcriptase PCR using degenerate oligonucleotides flanking the conserved protein tyrosine phosphatase catalytic domain. This produced a 280-bp DNA probe which was subsequently employed to screen a mouse embryonic kidney library. Several overlapping cDNA clones were isolated, collectively forming a cDNA of 6.0 kb that encodes a putative 211 -kDa protein. Northern-blot analysis of total RNA from adult and embryonic mouse tissues indicates the existence of two major PTP NU-3 transcripts of approximately 6 kb and 7 kb. Both messages are expressed predominantly in brain tissues and neuronal-derived cell lines, although detectable levels of the 7-kb message were found in other non-neuronal tissues. We have identified a unique 132-bp exon segment that is present in the 7-kb message but is completely absent in the 6-kb transcript, suggesting tissue-specific levels of expression and RNA processing. Analysis of the amino acid sequence encoded by the 132-bp segment reveals that it completes a partial fibronectin type-I11 element resulting in a protein with a total of nine such elements. Bacterial expression of the two catalytic domains demonstrated that only the first domain possesses enzymic activity towards a tyrosine phosphorylated substrate.The location, extent and timing of protein phosphorylation at tyrosine residues have been shown to be key processes in events such as cell homeostasis, growth and proliferation. This is evidenced by the identification of multiple oncogenes encoding protein tyrosine kinases (PTKs) and the correlation of an oncogenic state with tyrosine phosphorylation of specific proteins. Therefore, much attention is now focussed on enzymes which perform the reverse reaction, namely protein tyrosine phosphatase (PTPases; for a recent review, see Mourey and Dixon, 1994). Cloning efforts by many groups have led to the identification of two major classes of PTPases. The first class is specific to phosphorylated tyrosine residues and a second class, known as the VH1-type PTPases, can dephosphorylate phosphorylated tyrosine as well as serine and threonine residues. The former can be further subdivided into two major groups; the intracellular and the receptor-like enzymes. Intracellular PTPases are generally small proteins containing one highly conserved catalytic domain, whereas the receptor-type enzymes usually

The LAR/PTP delta/PTP sigma subfamily of transmembrane protein-tyrosine-phosphatases: multiple human LAR, PTP delta, and PTP sigma isoforms are expressed in a tissue-specific manner and associate with the LAR-interacting protein LIP.1.

“…1), suggesting the existence of multiple HPTPo-isoforms that are generated by alternative splicing. This suggestion is consistent with previous results demonstrating the existence of two or more isoforms for rodent PTPor (12,(26)(27)(28)(29), mouse and human PTPS (9,10), and human and rat LAR (30,33). To determine the extent to which the meA-meD and F4-F7 sequences were alternatively used by HPTPo-, HPTP6, and LAR, RT-PCR analysis using primers flanking the alternatively used sequences was followed by sequence 6 6.4kb…”

“…A cDNA clone thus isolated (clone 16, Fig. 1) encoded a peptide that was related to LAR and HPTP8, but was most similar to rodent PTPcr (11,12,(26)(27)(28)(29). This cDNA was termed HPTPo-cDNA.…”

“…For instance, deficiencies in the expression of the CD45 transmembrane PTPase abrogate lymphocyte maturation and activation (6). Several closely related transmembrane PT-Pases, including LAR, PTP8, PTPu, PTP,u, and PTPK, have extracellular regions comprising tandemly arranged Ig-like domains and fibronectin type III (FN III)-like domains (7)(8)(9)(10)(11)(12)(13)(14)(15). This extracellular-region architecture is also found in known cell adhesion molecules, including the neural cell adhesion…”

N-Cadherin Is an In Vivo Substrate for Protein Tyrosine Phosphatase Sigma (PTPσ) and Participates in PTPσ-Mediated Inhibition of Axon Growth

“…These results suggest that the elevated tyrosine phosphorylation of N-cadherin in the PTP ؊/؊ mice likely disrupted N-cadherin function, resulting in accelerated DRG nerve growth. We conclude that N-cadherin is a physiological substrate for PTP and that N-cadherin (and likely ␤-catenin) participates in PTP-mediated inhibition of axon growth.Protein tyrosine phosphatase sigma (PTP) (also known as LAR-PTP2, PTP-P1, CRYP␣, PTP-NU3, PTP-NE3, and CPTP1 [42,51,58,68,71,81,84]) belongs to the LAR family of receptor PTPs (class IIa) (3, 4, 13). In mammals, this family includes LAR, PTP, and PTP␦, whereas DLAR is the Drosophila melanogaster orthologue of all three family members (13,61,62).…”

The Second Catalytic Domain of Protein Tyrosine Phosphatase δ (PTPδ) Binds to and Inhibits the First Catalytic Domain of PTPς

“…PTPs, like PTKs, can be classified into cytosolic and receptortype PTPs (11,25). One subclass of receptor PTPs (RPTPs) is represented by the LAR family of phosphatases, which includes LAR and Drosophila DLAR (37, 39), PTP␦ (20,23,29), PTP (also known as LAR-PTP2, PTP-P1, CRYP␣, PTP-NU3, and CPTP1 [27,30,34,44,45,49,52] and referred to herein as PTP), and the three related phosphatases PTP, PTP, and PTP (6,12,16). These PTPs are characterized by an extracellular domain composed of multiple immunoglobulin (Ig)-like and fibronectin type III (FNIII) repeats, resembling cell adhesion molecules (CAM) such as N-CAM and L1 (7, 24) and several receptor PTKs.…”