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PubMed1999

CD45 regulates tyrosine phosphorylation of CD22 and its association with the protein tyrosine phosphatase SHP-1.

Cross-linking of CD45 induced capping and physical sequestration from CD22 leading to an increase in tyrosine phosphorylation of CD22 and SHP-1 recruitment. Additionally, CD22 isolated from a CD45-deficient B cell line exhibited increased basal/inducible tyrosine phosphorylation and enhanced recruitment of SHP-1 compared with CD22 isolated from CD45-positive parental cells. Subsequent experiments were performed to determine whether enhanced SHP-1 recruitment to CD22 is responsible for attenuation of receptor-mediated Ca2+ responses in CD45-deficient cells. Catalytically inactive SHP-1 expressed in CD45-deficient cells interacted with CD22 and decreased phosphatase activity in CD22 immunoprecipitates to levels that were comparable to those in CD45-positive cells. Expression of catalytically inactive SHP-1 restored intracellular mobilization of Ca2+ in response to MHC class II cross-linking, but did not affect B cell Ag receptor- or class II-mediated Ca2+ influx from the extracellular space. These results indicate that CD45 regulates tyrosine phosphorylation of CD22 and binding of SHP-1. The data further indicate that enhanced recruitment and activation of SHP-1 in CD45-deficient cells affect intracellular mobilization of Ca2+, but are not responsible for abrogation of receptor-mediated Ca2+ influx from the extracellular space.

Animals↗
PubMed1999

Cutting edge: the tyrosine phosphatase SHP-1 regulates thymocyte positive selection.

The binding kinetics of the TCR for its interacting ligand and the nature of the resulting signal transduction event determine the fate of a developing thymocyte. The intracellular tyrosine phosphatase SHP-1 is a potential regulator of the TCR signal transduction cascade and may affect thymocyte development. To assess the role of SHP-1 in thymocyte development, we generated T cell-transgenic mice that express a putative dominant negative form of SHP-1, in which a critical cysteine is mutated to serine (SHP-1 C453S). SHP-1 C453S mice that express the 3.L2 TCR transgene are increased in CD4 single positive cells in the thymus and are increased in cells that express the clonotypic TCR. These data suggest that the expression of SHP-1 C453S results in increased positive selection in 3.L2 TCR-transgenic mice and support a role for SHP-1 thymocyte development.

Animals↗
PubMed2006

Phosphopeptide ligands of the SHP-1 N-SH2 domain: effects on binding and stimulation of phosphatase activity.

Src homology 2 (SH2)-domain-mediated interactions with phosphotyrosine (pY)-containing ligands are critical for the regulation of SHP-1 phosphatase activity. Peptides based on a binding site from receptor tyrosine kinase Ros (EGLN-pY2267-MVL, 1) have recently been shown to bind to the SHP-1 N-terminal SH2 domain (N-SH2) with considerably high affinity. In addition, two peptides cyclized between positions -1 and +2 relative to pY (EGLc[K(COCH(2)NH)pYMX]L-NH(2), 2: X=D, 3: X=E) bound to the N-SH2 domain, but did not activate the enzyme and even partially prevented stimulation of SHP-1 activity by the physiological ligand 1. These findings prompted us to further examine the determinants for optimal binding to the N-SH2 domain and for the stimulation and inhibition of SHP-1 activity. Herein we demonstrate that combining the preferred residues in both pY+1 (such as Phe or norleucine, Nle) and pY+3 (such as homophenylalanine, Hfe) leads to highly efficient activating ligands of SHP-1. Particularly in the context of the cyclic peptides 7 (EGLc[K(COCH(2)NH)pYFD]Hfe-NH(2)) and 8 (EGLc[K(COCH(2)NH)pYNleD]HfeL-NH(2)), the incorporation of these residues resulted in high-affinity ligands with a significantly increased ability to stimulate SHP-1 activity. We suggest that different binding modes (according to consensus sequences class I and II) are responsible for obtaining either activating (7 and 8) or nonactivating (2 and 3) ligands. Peptides such as 7 and 8 that bind in the extended fashion of the type II mode activate the phosphatase through complete filling of the cavity for pY+3. In contrast, peptides such as 2 and 3 that bind in the class I mode do not activate the enzyme because they allow more conformational space at pY+3. Therefore, their binding does not force the conformational transition necessary to trigger the dissociation of N-SH2 and the catalytic domain.

Amino Acid Sequence↗
PubMed2006

Inverse regulation of inducible nitric oxide synthase (iNOS) and arginase I by the protein tyrosine phosphatase SHP-1 in CNS glia.

We have previously shown that the SH2 domain-containing protein tyrosine phosphatase SHP-1 plays a critical role in controlling virus infection in CNS glia in vivo and in vitro. The present study addressed whether increased virus replication in SHP-1-deficient glia in vitro may be a result of altered expression of inducible nitric oxide synthase (iNOS/NOS2). First, we observed a profound reduction in iNOS protein expression and production of nitric oxide (NO) in response to the viral mimic double-stranded RNA (dsRNA), despite the induction of high levels of iNOS mRNA, in SHP-1-deficient motheaten mouse compared to wild type littermate mouse glia. Because both iNOS expression and NO production are suppressed by multiple pathways involving arginase I activity, it was important that we observed abnormally high constitutive expression of arginase I in cultured glia of SHP-1-deficient compared to wild type mice. Further, both constitutive and IL-4/IL-10-induced expression of arginase I correlated with elevated STAT6 nuclear binding activity, decreased NO production, and increased virus replication in motheaten compared to wild type astrocytes. These findings provide the first evidence of an inverse relationship between NO and arginase I activity regulated by SHP-1 in CNS glia that is relevant to modulation of innate anti-viral responses. Thus, we propose that SHP-1 is a critical regulator of innate immunity to virus infections in CNS cells.

Animals↗
PubMed2006

Tyrosine phosphatase SHP-2 regulates IL-1 signaling in fibroblasts through focal adhesions.

Interleukin-1beta (IL-1beta) mediates destruction of matrix collagens in diverse inflammatory diseases including arthritis, periodontitis, and pulmonary fibrosis by activating fibroblasts, cells that interact with matrix proteins through integrin-based adhesions. In vitro, IL-1beta signaling is modulated by focal adhesions, supramolecular protein complexes that are enriched with tyrosine kinases and phosphatases. We assessed the importance of tyrosine phosphatases in regulating cell-matrix interactions and IL-1beta signaling. In human gingival fibroblasts plated on fibronectin, IL-1beta enhanced the maturation of focal adhesions as defined by morphology and enrichment with paxillin and alpha-actinin. IL-1beta also induced activation of ERK and recruitment of phospho-ERK to focal complexes/adhesions. Treatment with the potent tyrosine phosphatase inhibitor pervanadate, in the absence of IL-1beta, recapitulated many of these responses indicating the importance of tyrosine phosphatases. Immunoblotting of collagen bead-associated complexes revealed that the tyrosine phosphatase, SHP-2, was also enriched in focal complexes/adhesions. Depletion of SHP-2 by siRNA or by homologous recombination markedly altered IL-1beta-induced ERK activation and maturation of focal adhesions. IL-1beta-induced tyrosine phosphorylation of SHP-2 on residue Y542 promoted focal adhesion maturation. Association of Gab1 with SHP-2 in focal adhesions correlated temporally with activation of ERK and was abrogated in cells expressing mutant (Y542F) SHP-2. We conclude that IL-1beta mediated maturation of focal adhesions is dependent on tyrosine phosphorylation of SHP-2 at Y542, leading to recruitment of Gab1, a process that may influence the downstream activation of ERK.

Actinin↗
PubMed2006

Motheaten (me/me) mice deficient in SHP-1 are less susceptible to focal cerebral ischemia.

We have demonstrated previously that the protein tyrosine phosphatase SHP-1 seems to play a role in glial development and is upregulated in non-dividing astrocytes after injury. The present study examines the effect of loss of SHP-1 on the CNS response to permanent focal ischemia. SHP-1 deficient (me/me) mice and wild-type littermates received a permanent middle cerebral artery occlusion (MCAO). At 1, 3, and 7 days after MCAO, infarct volume, neuronal survival and cell death, gliosis, and inflammatory cytokine levels were quantified. SHP-1 deficient me/me mice display smaller infarct volumes at 7 days post-MCAO, increased neuronal survival within the ischemic penumbra, and decreased numbers of cleaved caspase 3+ cells within the ischemic core compared with wild-type mice. In addition, me/me mice exhibit increases in GFAP+ reactive astrocytes, F4-80+ microglia, and a concomitant increase in the level of interleukin 12 (IL-12) over baseline compared with wild-type. Taken together, these results demonstrate that loss of SHP-1 results in greater healing of the infarct due to less apoptosis and more neuronal survival in the ischemic core and suggests that pharmacologic inactivation of SHP-1 may have potential therapeutic value in limiting CNS degeneration after ischemic stroke.

Animals↗
PubMed2000

Tyrosine phosphatase SHP-2 binding to CTLA-4: absence of direct YVKM/YFIP motif recognition.

CTLA-4 is well documented in its negative regulation of T-cell proliferation. However, little is known regarding the signaling mechanisms induced by CTLA-4. CTLA-4 associates with the phosphatidylinositol 3-kinase, the phosphatase SHP-2 and the clathrin adaptor complexes AP-1 and AP-2. SHP-2 SH2 domain binding to CTLA-4 is unusual given the absence of a I/VxYxxI/V/L motif. Here, we demonstrate that the phosphorylation of CTLA-4 tyrosines (YVKM and YFIP) fails to allow for single or tandem SHP-2 SH2 domain binding. This was observed using wild-type and inactive SHP-2 as well as a construct with the isolated two SH2 domains. The phosphorylated YVKM and YFIP motifs therefore do not appear to represent novel binding motifs for SHP-2 SH2 domains. At the same time, we could confirm that SHP-2 can associate with CTLA-4 in murine T-cells indicating that the interaction between the phosphatase and CTLA-4 is an indirect event, possibly mediated by PI 3-kinase/SHP-2 binding.

Abatacept↗
PubMed2000

Roles of the SHP-1 tyrosine phosphatase in the negative regulation of cell signalling.

The critical role for the SH2 domain-containing SHP-1 tyrosine phosphatase in regulating haemopoietic cell behaviour was initially revealed by data linking SHP-1 deficiency to the systemic autoimmunity and severe inflammation exhibited by motheaten mice. This discovery laid the groundwork for the identification of SHP-1 as an inhibitor of activation-promoting signalling cascades and for the coincident demonstration that protein tyrosine phosphatases (PTPs) such as SHP-1 show considerable specificity with respect to the mechanisms whereby they modulate the biochemical and biological sequelae of extracellular simulation. As outlined in this review, SHP-1 has now been implicated in the regulation of a myriad of signalling cascades and cell functions. As a result, the cumulative data generated from studies of this PTP have elucidated not only the functional relevance of SHP-1, but also a number of novel paradigms as to the molecular mechanisms whereby signalling cascades are regulated so as to either augment or abrogate specific cell behaviours.

Animals↗
PubMed2006

SHP-2-Erk signaling regulates concanavalin A-dependent production of TIMP-2.

To search for the signaling critical for the production of tissue inhibitor of metalloproteinase-2 (TIMP-2), we investigated the role of SHP-2 in TIMP-2 production with Concanavalin A (Con A)-treated cells. In wild-type fibroblasts, Con A-treatment dramatically activated TIMP-2 production. In contrast, production of TIMP-2 in response to Con A-treatment was severely impaired in cells expressing mutant SHP-2 whose 65 amino acids in the SH2-N domain were deleted. Con A-treatment activated dual signaling pathways, Erk and p38, in a SHP-2-dependent manner. Pretreatment of wild-type cells with U0126, a potent inhibitor of MEK1, significantly inhibited the production of TIMP-2, whereas SB203580, a specific inhibitor for p38, could not. Finally, expression of exogenous wild-type SHP-2 in SHP-2 mutant cells clearly rescued Erk activation and TIMP-2 production in response to Con A-treatment. Taken together, our results strongly suggest that SHP-2 plays a critical role as a positive modulator for the production of TIMP-2 via MEK1-Erk signaling in fibroblasts.

Cells, Cultured↗
PubMed2005

Role of SHP-1, Kv.1.2, and cGMP in nitric oxide-induced ERK1/2 MAP kinase dephosphorylation in rat vascular smooth muscle cells.

OBJECTIVE: Nitric oxide (NO) elicits relaxation in vascular smooth muscle cells (VSMC) that is associated with guanylate cyclase (GC) and K(+) channel activation. In this study we determined the mechanisms that lead to ERK1/2 MAP kinase dephosphorylation in response to NO. METHODS: VSMC were treated with the NO donor SNAP or sodium nitroprusside (SNP), and ERK1/2, Src homology (SH) 1 domain-containing protein tyrosine phosphatase (SHP-1), and Kv.1.2 phosphorylation were assessed by immunoprecipitation and Western blot analysis. RESULTS: NO decreased basal ERK1/2 phosphorylation in a dose- and time-dependent manner. NO-induced ERK1/2 dephosphorylation was detected at 1 min and sustained for 30 min. Pre-treatment with the GC inhibitor ODQ or the protein tyrosine phosphatase inhibitor I prevented ERK1/2 dephosphorylation induced by SNAP. The inhibition of protein phosphatase 1A/2A had no effect on ERK1/2 dephosphorylation induced by SNAP. Treatment with cromakalim A, a nonspecific K(+) channel activator, also induced ERK1/2 dephosphorylation, while blockade of Kv.1.2 K(+) channels (AM92016 hydrochloride) prevented NO-induced ERK1/2 dephosphorylation. In addition, SNAP induced SHP-1 phosphorylation, and the Kv.1.2 dephosphorylation increase and SHP-1 phosphorylation was blocked by ODQ or AM92016. The basal interaction between ERK1/2 and SHP-1 was decreased in response to SNAP stimulation. SHP-1 also interacted with Kv.1.2 under basal conditions and participates in Kv.1.2 activation. Using the mouse mesenteric resistance artery, we found that ERK1/2 MAP kinase is involved in regulation of myogenic tone. CONCLUSION: Thus, our study provides the first evidence that NO controls basal ERK1/2 phosphorylation by a signaling cascade that involves a dynamic signaling complex between cGMP, Kv.1.2 and SHP-1.

Animals↗
PubMed2004

Characterization of the B2 receptor and activity of bradykinin analogs in SHP-77 cell line by Cytosensor microphysiometer.

The Cytosensor microphysiometer device (Molecular Devices, Sunnyvale, CA) is capable of measuring the rate at which cells acidify their environment in response to ligand-receptor binding. By measuring the extracellular acidification response (ECAR) we characterized some aspects of ligand-B2 receptor interaction in SHP-77 cell line. SHP-77 cells maximally acidified their environment within 30 s after the exposure to bradykinin (BK) or the BK agonist, B9972, with the maximum effect seen at a ligands concentration of 1 microM. Fetal bovine serum (FBS) modulated the binding of BK or B9972, showing that B9972 is a partial agonist. In addition, the binding of BK agonist or antagonist to the B2 receptor showed different ECAR and different interaction with other intracellular and plasma membrane proteins. Our microphysiometrical results showed that two parameters, antagonist binding affinity (pD2) and antagonist potency (pIC50) are required to characterize BK antagonist activity for the B2 receptor in the SHP-77 cell line. The previously used parameter of B2 antagonist activity, pA2, had high variation and poor correlation with the inhibition of SHP-77 cell growth in vitro and suppression of tumor growth when SHP-77 cells were injected to mice. Our results permit us to conclude that BK agonists and antagonists differ in their interactions with the B2 receptor and consequently elicit different cell responses. Based on our results, we have developed a new microphysiometrical assay for analyzing the activity of BK agonists and antagonist in SHP-77 cells, which may facilitate the discovery of new potent anticancer drugs.

Amino Acid Sequence↗
PubMed2004

SHP-1 regulates STAT6 phosphorylation and IL-4-mediated function in a cell type-specific manner.

SHP-1 has been shown to play positive and negative regulatory roles in IL-4-induced STAT6 phosphorylation and in IL-4-mediated functions. To determine whether SHP-1 can regulate STAT6 phosphorylation and IL-4-mediated functions in a cell type-specific manner in the immune system, we examined the IL-4 receptor (IL-4R) expression, STAT6 phosphorylation, and IL-4-mediated functions in CD4+ and CD8+ T cells of viable motheaten (me(v)/me(v)) and littermate control (+/-) mice. CD4+ T cells as well as CD8+ T cells from the lymph node of me(v)/me(v) and +/- mice expressed comparable levels of IL-4R. In CD4+ T cells, the loss of SHP-1 activity did not affect IL-4-induced STAT6 phosphorylation or IL-4-mediated function. In contrast, SHP-1-deficient CD8+ T cells from me(v)/me(v) mice failed to develop into IL-4-producing type-2 cytotoxic T cells (Tc2) in the presence of IL-4 despite that they showed comparable levels of STAT6 phosphorylation to that of +/- CD8+ T cells. Loss of SHP-1 activity also abolished IL-4-mediated inhibition of c-kit expression in bone marrow-derived mast cell (BMMC). Thus, our data suggest that SHP-1 may regulate IL-4-induced STAT6 phosphorylation and IL-4-mediated functions in a cell type-specific manner.

Animals↗
PubMed1997

Deletion of SHIP or SHP-1 reveals two distinct pathways for inhibitory signaling.

Two signaling molecules have been implicated in the modulation of immune receptor activation by inhibitory coreceptors: an inositol polyphosphate 5'-phosphatase, SHIP, and a tyrosine phosphatase, SHP-1. To address the necessity, interaction, or redundancy of these signaling molecules, we have generated SHP-1- or SHIP-deficient B cell lines and determined their ability to mediate inhibitory signaling. Two distinct classes of inhibitory responses are defined, mediated by the selective recruitment of SHP-1 or SHIP. The Fc gammaRIIB class of inhibitory signaling is dependent on SHIP and not SHP-1; conversely, the KIR class requires SHP-1 and not SHIP. The consequence of this selective recruitment by inhibitory receptor engagement is seen in BCR-triggered apoptosis. SHP-1-mediated inhibitory signaling blocks apoptosis, while SHIP recruitment attenuates a proapoptotic signal initiated by Fc gammaRIIB.

Animals↗
PubMed1999

Defective expression of the SHP-1 phosphatase in polycythemia vera.

The SHP-1 phosphatase associates with the receptors for erythropoietin, stem cell factor, and interleukin-3, and negatively regulates the mitogenic signals generated during engagement by their respective ligands. The erythroid progenitors of patients with polycythemia vera are hypersensitive to the mitogenic effects of these growth factors despite the fact that the numbers and binding affinities for their receptors are not increased. To determine whether post-receptor signaling defects may account for growth factor-hypersensitivity in polycythemia vera, we determined the expression of SHP-1 in highly purified erythroid progenitors from polycythemia vera patients. Our data demonstrate that in approximately 60% of the patients, expression of SHP-1 in the colony forming unit-erythroid population is diminished. The decreased expression of the protein may result from a transcriptional defect, as suggested by the diminished SHP-1 mRNA expression in the erythroid progenitors of these patients. Studies to determine the level of maturation of polycythemia vera and normal cells indicated that there was no difference between the two at early colony forming unit-erythroid stage of differentiation although polycythemia vera cells showed retarded differentiation kinetics at late colony forming unit-erythroid stage of differentiation. Furthermore, SHP-1 expression in normal colony forming unit-erythroid demonstrated downregulation of mRNA and protein levels during terminal differentiation, suggesting that its function is required for growth control during the early stages of erythropoiesis. These results indicate an important role for SHP-1 in the regulation of normal human erythroid progenitors and suggest that defective expression of the protein may contribute to the pathogenesis of polycythemia vera.

Cell Differentiation↗
PubMed1998

The protein tyrosine phosphatase SHP-1 regulates integrin-mediated adhesion of macrophages.

The Src homology 2 domain phosphatase-1 (SHP-1) is a tyrosine phosphatase containing two amino-terminal SH2 domains and is expressed primarily by hematopoietic-derived cells [1]. The viable motheaten (Hcphme-v) mutant mice (mev) suffer from progressive inflammation due to a deficiency of SHP-1 enzyme activity [2,3] and die at 3-4 months of age from macrophage and neutrophil accumulation in the lung [4]. The mechanism by which SHP-1 deficiency leads to inflammation is unknown. We found that macrophages from mev mice adhered and spread to a greater extent than normal macrophages through alpha m beta 2 integrin-mediated contacts. Whereas macrophages deficient in the transmembrane tyrosine phosphatase CD45 (CD45-/-) spontaneously detached from alpha m beta 2 integrin contacts [5], cells deficient in both CD45 and SHP-1 did not. In SHP-1 deficient macrophages there was a 10-15-fold increase in D-3 phospholipid products of phosphatidylinositol (PI) 3-kinase. Concomitantly, there was a 2-5-fold increase in membrane-associated PI 3-kinase activity in mev macrophages relative to normal macrophages. Treatment of macrophages with the PI 3-kinase inhibitors wortmannin or LY294002 resulted in a dramatic detachment of cells, indicating that PI 3-kinase activity is required for adhesion. These data demonstrate that SHP-1 is necessary for detachment from alpha m beta 2 integrin-mediated contacts in primary macrophages and suggest that a defect in this pathway may contribute to inflammatory disease.

Animals↗
PubMed2003

SHP-1: a regulator of neutrophil apoptosis.

The Src homology domain 2 (SH2)-containing tyrosine phosphatase-1 (SHP-1) has been implicated in the regulation of differentiation, proliferation, and activation of hematopoietic cells. In this review, we discuss the potential role of SHP-1 in modulating apoptosis pathways in neutrophils. Low enzymatic SHP-1 was associated with increased neutrophil survival in vitro and SHP-1-deficient mice were reported to develop severe neutrophilic inflammatory responses. In contrast, high expression of this phosphatase was observed in neutropenic patients. Moreover, when neutrophils were exposed to Fas ligand, TNF-alpha, or TRAIL, the anti-apoptotic effects of granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), or IFN-gamma were blocked, most likely by SHP-1-mediated inactivation of anti-apoptotic signaling molecules. In summary, the current available data point to an important role of SHP-1 in the regulation of neutrophil apoptosis.

Animals↗
PubMed2003

Chemical dissection of the effects of tyrosine phosphorylation of SHP-2.

The regulation of the protein tyrosine phosphatase (PTPase) SHP-2 by tyrosine phosphorylation has been difficult to elucidate because of the intrinsic instability of the phosphoprotein. In the past, expressed protein ligation has been used to site-specifically incorporate the phosphotyrosine mimic Pmp (phosphonomethylene phenylalanine) into the two tyrosine phosphorylation sites (542, 580) of SHP-2 one at a time to analyze the effects on catalytic behavior. In this study, we have incorporated two Pmps into the phosphorylation sites simultaneously and examined the effects of double SHP-2 tyrosine phosphorylation. We have found that the Pmp groups show close to additive effects on PTPase stimulation, suggesting dual SH2 domain occupancy. The relative effects of the phosphotyrosine analogue difluoromethylene phosphonophenylalanine (F(2)Pmp) compared to those of Pmp were also examined. It was found that the F(2)Pmp analogue showed slightly enhanced PTPase stimulation compared with the Pmp analogue, consistent with its higher affinity for SH2 domains. Taken together with the bis-Pmp studies, these data suggest that double phosphorylation of the SHP-2 C-terminus could give rise to a 9-fold overall PTPase activation, 30-50% of the value associated with deletion of the SH2 domains. Catalytically inactive forms of phosphorylated SHP-2 proteins were also produced by expressed protein ligation. This allowed for a systematic analysis of intermolecular autodephosphorylation of SHP-2, which revealed how conformational plasticity can modulate phosphotyrosine stability.

Amino Acid Sequence↗
PubMed2003

Novel mesenchymal and haematopoietic cell isoforms of the SHP-2 docking receptor, PZR: identification, molecular cloning and effects on cell migration.

SHP-2 (Src homology phosphatase type-2) is essential for haematopoietic skeletal and vascular development. Thus the identification of its binding partners is critically important. In the present study, we describe a unique monoclonal antibody, WM78, which interacts with PZR, a SHP-2 binding partner. Furthermore, we identify two novel isoforms of PZR, PZRa and PZRb, derived by differential splicing from a single gene transcription unit on human chromosome 1q24. All are type 1 transmembrane glycoproteins with identical extracellular and transmembrane domains, but differ in their cytoplasmic tails. The PZR intracellular domain contains two SHP-2 binding immunoreceptor tyrosine-based inhibitory motifs (VIY(246)AQL and VVY(263)ADI) which are not present in PZRa and PZRb. Using the WM78 monoclonal antibody, which recognizes the common extracellular domain of the PZR isoforms, we demonstrate that the PZR molecules are expressed on mesenchymal and haematopoietic cells, being present on the majority of CD34(+)CD38(+) and early clonogenic progenitors, and at lower levels on CD34(+)CD38(-) cells and the hierarchically more primitive pre-colony forming units. Interestingly, we show by reverse transcriptase-PCR that the PZR isoforms are differentially expressed in haematopoietic, endothelial and mesenchymal cells. Both PZR and PZRb are present in CD133(+) precursors and endothelial cells, PZRb predominates in mesenchymal and committed myelomonocytic progenitor cells, and all three isoforms occur in erythroid precursor cell lines. Importantly, using SHP-2 mutant (Delta 46-110) and SHP-2 rescue of embryonic fibroblasts stably expressing the PZR isoforms, we demonstrate for the first time that PZR, but not PZRa or PZRb, facilitates fibronectin- dependent migration of cells expressing a competent SHP-2 molecule. These observations will be instrumental in determining the mechanisms whereby PZR isoforms regulate cell motility.

Amino Acid Motifs↗