scholarly journals Receptor-Like Protein Tyrosine Phosphatase α Homodimerizes on the Cell Surface

2000 ◽  
Vol 20 (16) ◽  
pp. 5917-5929 ◽  
Author(s):  
Guoqiang Jiang ◽  
Jeroen den Hertog ◽  
Tony Hunter
Keyword(s):  
Biological Activity ◽  
Cell Surface ◽  
Protein Tyrosine Phosphatase ◽  
Intracellular Signaling ◽  
Catalytic Domain ◽  
Transmembrane Domain ◽  
Tyrosine Phosphatase ◽  
Receptor Protein ◽  
Dependent Manner ◽  
Protein Tyrosine

ABSTRACT We reported previously that the N-terminal D1 catalytic domain of receptor protein-tyrosine phosphatase α (RPTPα) forms a symmetrical, inhibited dimer in a crystal structure, in which a helix-turn-helix wedge element from one monomer is inserted into the catalytic cleft of the other monomer. Previous functional studies also suggested that dimerization inhibits the biological activity of a CD45 chimeric RPTP and the catalytic activity of an isolated RPTPς D1 catalytic domain. Most recently, we have also shown that enforced dimerization inhibits the biological activity of full-length RPTPα in a wedge-dependent manner. The physiological significance of such inhibition is unknown, due to a lack of understanding of how RPTPα dimerization is regulated in vivo. In this study, we show that transiently expressed cell surface RPTPα exists predominantly as homodimers, suggesting that dimerization-mediated inhibition of RPTPα biological activity is likely to be physiologically relevant. Consistent with our published and unpublished crystallographic data, we show that mutations in the wedge region of D1 catalytic domain and deletion of the entire D2 catalytic domain independently reduced but did not abolish RPTPα homodimerization, suggesting that both domains are critically involved but that neither is essential for homodimerization. Finally, we also provide evidence that both the RPTPα extracellular domain and the transmembrane domain were independently able to homodimerize. These results lead us to propose a zipper model in which inactive RPTPα dimers are stabilized by multiple, relatively weak dimerization interfaces. Dimerization in this manner would provide a potential mechanism for negative regulation of RPTPα. Such RPTPα dimers could be activated by extracellular ligands or intracellular binding proteins that induce monomerization or by intracellular signaling events that induce an open conformation of the dimer.

scholarly journals The Cell-Specific Phenotype of the Polymorphic vacA Midregion Is Independent of the Appearance of the Cell Surface Receptor Protein Tyrosine Phosphatase β

2006 ◽  
Vol 74 (1) ◽  
pp. 49-55 ◽  
Author(s):  
David A. G. Skibinski ◽  
Christophe Genisset ◽  
Silvia Barone ◽  
John L. Telford
Keyword(s):  
Cell Surface ◽  
Cell Lines ◽  
Protein Tyrosine Phosphatase ◽  
Tyrosine Phosphatase ◽  
Cell Surface Receptor ◽  
Receptor Protein ◽  
Protein Tyrosine ◽  
Amino Acid Region ◽  
Receptor Protein Tyrosine Phosphatase ◽  
Surface Receptor

ABSTRACT There are two alleles, m1 and m2, of the midregion of the vacuolating cytotoxin gene (vacA) of Helicobacter pylori which code for toxins with different cell specificities. Here we describe the construction of five chimeric strains in which regions of vacA were exchanged between the two genotypes. By analyzing the toxicity of these strains for HeLa and RK13 cells we have confirmed that a 148-amino-acid region determines the phenotypic differences between the two forms of the protein and that this entire region is important for cytotoxicity. Furthermore, we have used our chimeric strains to investigate whether variations in the midregion of VacA have an effect on phorbol 12-myristate 13-acetate (PMA)-induced VacA sensitivity in HL-60 cells. The PMA-induced VacA sensitivity of HL-60 cells has been previously associated with the appearance of the cell surface receptor protein tyrosine phosphatase beta (RPTPβ). Our data indicate that both the m1 and m2 forms of VacA are able to utilize RPTPβ, and the cell-specific phenotype of the midregion is independent of the presence of RPTPβ. It appears that another as-yet-unidentified receptor exists in HL-60 cells that accounts for the m2 phenotype in this cell line. Also, by studying the effect of PMA on levels of RPTPβ in other cell lines and toxicity of VacA in these cell lines we have shown that RPTPβ does not play a major role in the vacuolation of HeLa cells.

scholarly journals Cell surface expression of receptor protein tyrosine phosphatase RPTP mu is regulated by cell-cell contact.

1995 ◽  
Vol 131 (1) ◽  
pp. 251-260 ◽  
Author(s):  
M F Gebbink ◽  
G C Zondag ◽  
G M Koningstein ◽  
E Feiken ◽  
R W Wubbolts ◽  
...  
Keyword(s):  
Cell Surface ◽  
Protein Tyrosine Phosphatase ◽  
Tyrosine Phosphatase ◽  
Surface Expression ◽  
Lung Epithelial Cells ◽  
Receptor Protein ◽  
Cell Surface Expression ◽  
Cell Contact ◽  
Protein Tyrosine ◽  
Cell Cell

RPTP mu is a transmembrane protein tyrosine phosphatase with an adhesion molecule-like ectodomain. It has recently been shown that RPTP mu mediates homophilic interactions when expressed in insect cells. In this study, we have examined how RPTP mu may function as a cell contact receptor in mink lung epithelial cells, which express RPTPmu endogenously, as well as in transfected 3T3 cells. We find that RPTP mu has a relatively short half-life (3-4 hours) and undergoes posttranslational cleavage into two noncovalently associated subunits, with both cleaved and uncleaved molecules being present on the cell surface (roughly at a 1:1 ratio); shedding of the ectodomain subunit is observed in exponentially growing cells. Immunofluorescence analysis reveals that surface expression of RPTPmu is restricted to regions of tight cell-cell contact. RPTPmu surface expression increases significantly with increasing cell density. This density-induced upregulation of RPTP mu is independent of its catalytic activity and is also observed when transcription is driven by a constitutive promoter, indicating that modulation of RPTPmu surface expression occurs posttranscriptionally. Based on our results, we propose the following model of RPTP mu function: In the absence of cell-cell contact, newly synthesized RPTP mu molecules are rapidly cleared from the cell surface. Cell-cell contact causes RPTPmu to be trapped at the surface through homophilic binding, resulting in accumulation of RPTP mu at intercellular contact regions. This contact-induced clustering of RPTPmu may then lead to tyrosine dephosphorylation of intracellular substrates at cell-cell contacts.

scholarly journals Molecular cloning and characterization of PTPπ, a novel receptor-like protein-tyrosine phosphatase

1996 ◽  
Vol 319 (1) ◽  
pp. 249-254 ◽  
Author(s):  
Susan CROSSLAND ◽  
Paul D SMITH ◽  
Mark R CROMPTON
Keyword(s):  
Protein Tyrosine Phosphatase ◽  
Catalytic Domain ◽  
Transmembrane Domain ◽  
Tyrosine Phosphatase ◽  
Growth Factor Receptor ◽  
Predicted Amino Acid Sequence ◽  
Phosphatase Domain ◽  
Protein Tyrosine ◽  
Foetal Brain

Novel cDNAs encoding a receptor-like protein-tyrosine phosphatase (rPTP) have been isolated from human breast tumour cells and foetal brain. The predicted protein of ∼160 kDa, called PTPπ, comprises an extracellular portion with a MAM (meprin-A5 antigen-PTPµ) domain, an IgG-like domain and four fibronectin III-like repeats, a hydrophobic transmembrane domain and an intracellular portion consisting of two PTP catalytic units. The predicted amino acid sequence shows high identity with those of the two homophilic binding rPTPs, PTPµ and PTPκ. A variant of PTPπ potentially encoding a protein lacking three amino acids within the N-terminal tyrosine phosphatase domain has been identified. Reverse transcription-PCR has been used to confirm the expression of the variant in human foetal brain tissue. Expression analysis has shown that PTPπ is expressed in a variety of tissue types. Both forms of the N-terminal catalytic domain, the C-terminal catalytic domain and both catalytic domains in tandem were expressed in bacteria as fusion proteins. Intrinsic phosphatase activity was detected for all protein products with an artificial substrate. The fusion protein comprising both domains in tandem was also shown to dephosphorylate purified autophosphorylated epidermal growth factor receptor in vitro.

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