The PTPμ Protein-tyrosine Phosphatase Binds and Recruits the Scaffolding Protein RACK1 to Cell-Cell Contacts

RPTP mu is a receptor-like protein tyrosine phosphatase that mediates homophilic cell-cell interactions. Surface expression of RPTP mu is restricted to cell-cell contacts and is upregulated with increasing cell density, suggesting a role for RPTP mu in contact-mediated signaling. It was recently reported (Brady-Kalnay, S.M., D.L. Rimm, and N.K. Tonks. 1995. J. Cell Biol. 130:977-986) that RPTP mu binds directly to cadherin/catenin complexes, and thus may regulate the tyrosine phosphorylation of such complexes. Here we report that this concept needs revision. Through reciprocal precipitations using a variety of antibodies against RPTP mu, cadherins, and catenins, we show that RPTP mu does not interact with cadherin/catenin complexes, even when assayed under very mild lysis conditions. We find that the anti-RPTP mu antiserum used by others precipitates cadherins in a nonspecific manner independent of RPTP mu. We conclude that, contrary to previous claims, RPTP mu does not interact with cadherin complexes and thus is unlikely to directly regulate cadherin/catenin function.

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Homophilic binding of PTP mu, a receptor-type protein tyrosine phosphatase, can mediate cell-cell aggregation

The Journal of Cell Biology ◽

10.1083/jcb.122.4.961 ◽

1993 ◽

Vol 122 (4) ◽

pp. 961-972 ◽

Cited By ~ 170

Author(s):

SM Brady-Kalnay ◽

AJ Flint ◽

NK Tonks

Keyword(s):

Fusion Protein ◽

Protein Tyrosine Phosphatase ◽

Tyrosine Phosphatase ◽

Recombinant Baculovirus ◽

Sf9 Cells ◽

Homophilic Binding ◽

Protein Tyrosine ◽

Baculovirus Infection ◽

Induced Aggregation ◽

Cell Cell

The receptor-like protein tyrosine phosphatase, PTPmu, displays structural similarity to cell-cell adhesion molecules of the immunoglobulin superfamily. We have investigated the ability of human PTPmu to function in such a capacity. Expression of PTPmu, with or without the PTPase domains, by recombinant baculovirus infection of Sf9 cells induced their aggregation. However, neither a chimeric form of PTPmu, containing the extracellular and transmembrane segments of the EGF receptor and the intracellular segment of PTPmu, nor the intracellular segment of PTPmu expressed as a soluble protein induced aggregation. PTPmu mediates aggregation via a homophilic mechanism, as judged by lack of incorporation of uninfected Sf9 cells into aggregates of PTPmu-expressing cells. Homophilic binding has been demonstrated between PTPmu-coated fluorescent beads (Covaspheres) and endogenously expressed PTPmu on MvLu cells. Additionally the PTPmu-coated beads specifically bound to a bacterially expressed glutathione-S-transferase fusion protein containing the extracellular segment of PTPmu (GST/PTPmu) adsorbed to petri dishes. Covaspheres coated with the GST/PTPmu fusion protein aggregated in vitro and also bound to PTPmu expressed endogenously on MvLu cells. These results suggest that the ligand for this transmembrane PTPase is another PTPmu molecule on an adjacent cell. Thus homophilic binding interactions may be an important component of the function of PTPmu in vivo.

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RPTPμ and protein tyrosine phosphorylation regulate K+channel mRNA expression in adult cardiac myocytes

AJP Cell Physiology ◽

10.1152/ajpcell.2000.278.2.c397 ◽

2000 ◽

Vol 278 (2) ◽

pp. C397-C403 ◽

Cited By ~ 3

Author(s):

Kenneth M. Hershman ◽

Edwin S. Levitan

Keyword(s):

Mrna Expression ◽

Tyrosine Phosphorylation ◽

Cardiac Myocytes ◽

Protein Tyrosine Phosphatase ◽

Cardiac Myocyte ◽

Tyrosine Phosphatase ◽

Receptor Protein ◽

Mrna Levels ◽

Protein Tyrosine ◽

Cell Cell

Previously, we reported that cell-cell contact regulates K+channel mRNA expression in cultured adult rat cardiac myocytes. Here we show that exposing cardiac myocytes to tyrosine kinase inhibitors (genistein, tyrphostin A25), but not inactive analogs, prevents downregulation of Kv1.5 mRNA and upregulation of Kv4.2 mRNA normally observed when they are cultured under low-density conditions. Furthermore, cardiac myocytes cocultured with cells that endogenously (Mv 1 Lu) or heterologously (Chinese hamster ovary cells) express the receptor-type protein tyrosine phosphatase μ (RPTPμ) display Kv1.5 mRNA levels paralleling that which was observed in myocytes cultured under high-density conditions and in intact tissue. In contrast, myocytes cocultured with control cells failed to produce this response. Finally, it is shown that Kv4.2 mRNA expression is unaffected by RPTPμ. These findings reveal that multiple tyrosine phosphorylation-dependent mechanisms control cardiac myocyte K+channel genes. Furthermore, we conclude that RPTPμ specifically regulates cardiac myocyte Kv1.5 mRNA expression. Thus this receptor protein tyrosine phosphatase may be important in responses to pathological conditions associated with the loss of cell-cell interactions in the heart.

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Rat testicular myotubularin, a protein tyrosine phosphatase expressed by Sertoli and germ cells, is a potential marker for studying cell-cell interactions in the rat testis

Journal of Cellular Physiology ◽

10.1002/1097-4652(200012)185:3<366::aid-jcp7>3.0.co;2-1 ◽

2000 ◽

Vol 185 (3) ◽

pp. 366-385 ◽

Cited By ~ 28

Author(s):

Jonathan C.H. Li ◽

Eileen T. Samy ◽

Josephine Grima ◽

Sanny S.W. Chung ◽

Dolores Mruk ◽

...

Keyword(s):

Germ Cells ◽

Protein Tyrosine Phosphatase ◽

Tyrosine Phosphatase ◽

Cell Interactions ◽

Protein Tyrosine ◽

Rat Testis ◽

Potential Marker ◽

Cell Cell

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

The Journal of Cell Biology ◽

10.1083/jcb.131.1.251 ◽

1995 ◽

Vol 131 (1) ◽

pp. 251-260 ◽

Cited By ~ 85

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.

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Mechanistic insights explain the transforming potential of the T507K substitution in the protein-tyrosine phosphatase SHP2

Journal of Biological Chemistry ◽

10.1074/jbc.ra119.010274 ◽

2020 ◽

Vol 295 (18) ◽

pp. 6187-6201 ◽

Cited By ~ 1

Author(s):

Ruo-Yu Zhang ◽

Zhi-Hong Yu ◽

Lan Chen ◽

Chad D. Walls ◽

Sheng Zhang ◽

...

Keyword(s):

Substrate Specificity ◽

Protein Tyrosine Phosphatase ◽

Cell Biology ◽

Tyrosine Phosphatase ◽

Negative Regulator ◽

Scaffolding Protein ◽

Ras Signaling ◽

Biochemical Basis ◽

Protein Tyrosine ◽

Transforming Activity

The protein-tyrosine phosphatase SHP2 is an allosteric enzyme critical for cellular events downstream of growth factor receptors. Mutations in the SHP2 gene have been linked to many different types of human diseases, including developmental disorders, leukemia, and solid tumors. Unlike most SHP2-activating mutations, the T507K substitution in SHP2 is unique in that it exhibits oncogenic Ras-like transforming activity. However, the biochemical basis of how the SHP2/T507K variant elicits transformation remains unclear. By combining kinetic and biophysical methods, X-ray crystallography, and molecular modeling, as well as using cell biology approaches, here we uncovered that the T507K substitution alters both SHP2 substrate specificity and its allosteric regulatory mechanism. We found that although SHP2/T507K exists in the closed, autoinhibited conformation similar to the WT enzyme, the interactions between its N-SH2 and protein-tyrosine phosphatase domains are weakened such that SHP2/T507K possesses a higher affinity for the scaffolding protein Grb2-associated binding protein 1 (Gab1). We also discovered that the T507K substitution alters the structure of the SHP2 active site, resulting in a change in SHP2 substrate preference for Sprouty1, a known negative regulator of Ras signaling and a potential tumor suppressor. Our results suggest that SHP2/T507K's shift in substrate specificity coupled with its preferential association of SHP2/T507K with Gab1 enable the mutant SHP2 to more efficiently dephosphorylate Sprouty1 at pTyr-53. This dephosphorylation hyperactivates Ras signaling, which is likely responsible for SHP2/T507K's Ras-like transforming activity.

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Elevated protein tyrosine phosphatase activity provokes Eph/ephrin-facilitated adhesion of pre-B leukemia cells

Blood ◽

10.1182/blood-2007-11-121681 ◽

2008 ◽

Vol 112 (3) ◽

pp. 721-732 ◽

Cited By ~ 37

Author(s):

Sabine H. Wimmer-Kleikamp ◽

Eva Nievergall ◽

Kristina Gegenbauer ◽

Samantha Adikari ◽

Mariam Mansour ◽

...

Keyword(s):

Protein Tyrosine Phosphatase ◽

Lymphoblastic Leukemia ◽

Tyrosine Phosphatase ◽

Cell Movement ◽

Leukemia Cells ◽

Cell Contact ◽

Eph Receptors ◽

Protein Tyrosine ◽

Phosphotyrosine Signaling ◽

Cell Cell

Abstract Signaling by Eph receptors and cell-surface ephrin ligands modulates adhesive cell properties and thereby coordinates cell movement and positioning in normal and oncogenic development. While cell contact–dependent Eph activation frequently leads to cell-cell repulsion, also the diametrically opposite response, cell-cell adhesion, is a probable outcome. However, the molecular principles regulating such disparate functions have remained controversial. We have examined cell-biologic mechanisms underlying this switch by analyzing ephrin-A5–induced cell-morphologic changes of EphA3-positive LK63 pre-B acute lymphoblastic leukemia cells. Their exposure to ephrin-A5 surfaces leads to a rapid conversion from a suspended/nonpolarized to an adherent/polarized cell type, a transition that relies on EphA3 functions operating in the absence of Eph-kinase signaling. Cell morphology change and adhesion of LK63 cells are effectively attenuated by endogenous protein tyrosine phosphatase (PTP) activity, whereby PTP inhibition and productive EphA3-phosphotyrosine signaling reverse the phenotype to nonadherent cells with a condensed cytoskeleton. Our findings suggest that Eph-associated PTP activities not only control receptor phosphorylation levels, but as a result switch the response to ephrin contact from repulsion to adhesion, which may play a role in the pathology of hematopoietic tumors.

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