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B G Neel

Publications and source records attributed to B G Neel.

At least 55 records · Page 3Linked to original sources
PubMed1997

Protein tyrosine phosphatases in signal transduction.

Protein-tyrosyl phosphorylation, regulated by protein tyrosine kinases and protein tyrosine phosphatases (PTPs), is a key cellular control mechanism. Until recently, little was known about PTPs. However, the past two years have witnessed an explosion of information about PTP structure, regulation and function. Crystal structures of several PTPs have provided insights into enzymatic mechanisms and regulation and suggested the design of 'substrate-trapping' mutants. Candidate homophilic and heterophilic ligands for transmembrane PTPs have been identified, and roles for transmembrane PTPs in regulating cell-cell interactions have been suggested. Finally, progress has been made in understanding signaling by Src homology 2 domain containing PTPs and PTPs controlling yeast osmoregulatory pathways.

Animals↗
PubMed1996

Lack of SHPTP1 results in src-family kinase hyperactivation and thymocyte hyperresponsiveness.

Protein tyrosine phosphorylation and dephosphorylation are key regulatory events in T-cell receptor (TCR) signaling. We investigated the role of the tyrosine phosphatase SHPTP1 in TCR signaling by analysis of TCR signal transduction in motheaten (me/me) mice, which lack SHPTP1 expression. As revealed by flow cytometric analysis, thymocyte development was normal in me/me mice. However, me/me thymocytes hyperproliferated (3-to 5-fold) in response to TCR stimulation, whereas their response to interleukin 2 stimulation was unchanged compared with normal thymocytes. TCR-induced hyperproliferation of me/me thymocytes was reproduced in purified single-positive thymocytes. Moreover, me/me thymocytes produced increased amounts of interleukin 2 production upon TCR stimulation. Biochemical analysis revealed that, in response to TCR or TCR/CD4 stimulation, thymocytes lacking SHPTP1 showed increased tyrosyl phosphorylation of several cellular substrates, which correlated with increased activation of the src-family kinases Lck and Fyn. Taken together, our data suggest that SHPTP1 is an important negative regulator of TCR signaling, acting at least in part to inactivate Lck and Fyn.

Animals↗
PubMed1996

Genetic analysis reveals cell type-specific regulation of receptor tyrosine kinase c-Kit by the protein tyrosine phosphatase SHP1.

Receptor protein tyrosine kinases (RTKs) transmit downstream signals via interactions with secondary signaling molecules containing SH2 domains. Although many SH2-phosphotyrosyl interactions have been defined in vitro, little is known about the physiological significance of specific RTK/SH2 interactions in vivo. Also, little is known about the mechanisms by which specific RTKs interact with and/or are regulated by specific protein tyrosine phosphatases (PTPs). To address such issue, we carried out a genetic analysis of the previously reported biochemical interaction between the RTK c-Kit, encoded at the W locus, and the SH2-containing non-transmembrane PTP SHP1, encoded at the motheaten (me) locus (1). Mice carrying a kinase-defective allele of c-Kit (Wv/+) were crossed with me/+ mice, which carry one effectively null allele of SHP1, and then backcrossed to generate all possible allelic combinations. Our results indicate strong intergenic complementation between these loci in hematopoietic progenitor cells. Compared to progenitors purified from normal mice, bone marrow progenitor cells (lin-) from me/me mice markedly hyper-proliferated in response to Kit ligand (KL). stimulation. Superimposition of the me/me genotype increased the number of one marrow-derived CFU-E from Wv/+ mice. Conversely, the presence of one or two copies of Wv decreased the number of macrophages and granulocytes in me/me lung, skin, peripheral blood and bone marrow, thereby decreasing the severity of the me/me phenotype. The decrease in dermal mast cells in Wv/Wv mice was rescued to levels found in Wv/+mice by superimposition of the me/me genotype. Surprisingly, however, the presence or absence of SHP1 had no effect on the proliferative response of bone marrow-derived cultured mast cells to KL or IL3 ex vivo. Nevertheless, the immediate-early response to KL stimulation, as measured by KL-induced tyrosyl phosphorylation, was substantially increased in mast cells from Wv/+:me/me compared to Wv/ +:+/+ mice, strongly suggesting that SHP1 directly dephosphorylates and regulates c-Kit. Taken together, our results establish that SHP1 negatively regulates signaling from c-Kit in vivo, but in a cell type-specific manner.

Animals↗
PubMed1996

A family of transmembrane proteins with homology to the MET-hepatocyte growth factor receptor.

In hunting for unknown genes on the human X chromosome, we identified a cDNA in Xq28 encoding a transmembrane protein (SEX) of 1871 amino acids. SEX shares significant homology with the extracellular domain of the receptors encoded by the oncogenes MET, RON, and SEA [hepatocyte growth factor (HGF) receptor family]. Further screenings of cDNA libraries identified three additional sequences closely related to SEX: these were named SEP, OCT, and NOV and were located on human chromosomes 3p, 1, and 3q, respectively. The proteins encoded by these genes contain large cytoplasmic domains characterized by a distinctive highly conserved sequence (SEX domain). Northern blot analysis revealed different expression of the SEX family of genes in fetal tissues, with SEX, OCT, and NOV predominantly expressed in brain, and SEP expressed at highest levels in kidney. In situ hybridization analysis revealed that SEX has a distinctive pattern of expression in the developing nervous system of the mouse, where it is found in postmitotic neurons from the first stages of neuronal differentiation (9.5 day postcoitus). The SEX protein (220 kDa) is glycosylated and exposed at the cell surface. Unlike the receptors of the HGF family, p220SEX, a MET-SEX chimera or a constitutively dimerized TPR-SEX does not show tyrosine kinase activity. These data define a gene family (SEX family) involved in the development of neural and epithelial tissues, which encodes putative receptors with unexpected enzymatic or binding properties.

Amino Acid Sequence↗
PubMed1996

Multiple requirements for SHPTP2 in epidermal growth factor-mediated cell cycle progression.

Using transient overexpression and microinjection approaches, we examined SHPTP2's function in growth factor signaling. Overexpression of catalytically inactive SHPTP2 (PTP2CS) but not catalytically inactive SHPTP1, inhibited mitogen-activated protein (MAP) kinase activation and Elk-1 transactivation following epidermal growth factor (EGF) stimulation of 293 cells. An SHPTP2 mutant with both C-terminal tyrosyl phosphorylation sites converted to phenylalanine (PTP2YF) was also without effect; moreover, PTP2YF rescued PTP2CS-induced inhibition of EGF-induced Elk-1 transactivation. PTP2CS did not inhibit transactivation by activated Ras, suggesting that SHPTP2 acts upstream of or parallel to Ras. Neither PTP2CS nor PTP2YF inhibited platelet-derived growth factor (PDGF)-induced Elk-1 transactivation. Thus, protein-tyrosine phosphatase activity, but not tyrosyl phosphorylation of SHPTP2, is required for the immediate-early responses to EGF but not to PDGF. To determine whether SHPTP2 is required later in the cell cycle, we assessed S-phase entry in NIH 3T3 cells microinjected with anti-SHPTP2 antibodies or with a glutathione S-transferase (GST) fusion protein encoding both SH2 domains (GST-SH2). Microinjection of anti-SHPTP2 antibodies prior to stimulation inhibited EGF- but no PDGF- or serum-induced S-phase entry. Anti-SHPTP2 antibodies or GST-SH2 fusion protein could inhibit EGF-induced S-phase entry for up to 8 h after EGF addition. Although MAP kinase activation was detected shortly after EGF stimulation, no MAP kinase activation was detected around the restriction point. Therefore, SHPTP2 is absolutely required for immediate-early and late events induced by some, but not all, growth factors, and the immediate-early and late signal transduction pathways regulated by SHPTP2 are distinguishable.

Animals↗
PubMed1996

Regulation of colony-stimulating factor 1 receptor signaling by the SH2 domain-containing tyrosine phosphatase SHPTP1.

SHPTP1 (PTP1C, HCP, SHP) is an SH2 domain-containing tyrosine phosphatase expressed predominantly in hematopoietic cells. A frameshift mutation in the SHPTP1 gene causes the motheaten (me/me) mouse. These mice are essentially SHPTP1 null and display multiple hematopoietic abnormalities, most prominently hyperproliferation and inappropriate activation of granulocytes and macrophages. The me/me phenotype suggests that SHPTP1 negatively regulates macrophage proliferative pathways. Using primary bone marrow-derived macrophages from me/me mice and normal littermates, we examined the role of SHPTP1 in regulating signaling by the major macrophage mitogen colony-stimulating factor 1 (CSF-1) (also known as macrophage colony-stimulating factor). Macrophages from me/me mice hyperproliferate in response to CSF-1. In the absence of SHPTP1, the CSF-1 receptor (CSF-1R) is hyperphosphorylated upon CSF-1 stimulation, suggesting that SHPTP1 dephosphorylates the CSF-1R. At least some CSF-1R-associated proteins also are hyperactivated. SHPTP1 is associated constitutively, via its SH2 domains, with an unidentified 130-kDa phosphotyrosyl protein (P130). P130 and SHPTP1 are further tyrosyl phosphorylated upon CSF-1 stimulation. Tyrosyl-phosphorylated SHPTP1 binds to Grb2 via the Grb2 SH2 domain. Moreover, in me/me macrophages, Grb2 is associated, via its SH3 domains, with several tyrosyl phosphoproteins. These proteins are hyperphosphorylated on tyrosyl residues in me/me macrophages, suggesting that Grb2 may recruit substrates for SHPTP1. Our results indicate that SHPTP1 is a critical negative regulator of CSF-1 signaling in vivo and suggest a potential new function for Grb2.

Animals↗
PubMed1995

Different signaling roles of SHPTP2 in insulin-induced GLUT1 expression and GLUT4 translocation.

Insulin activates hexose transport via at least two mechanisms: a p21ras-dependent pathway, leading to an increase in the amount of cell surface GLUT1; and a metabolic, p21ras-independent pathway, leading to translocation of the insulin-responsive transporter GLUT4 to the cell surface. Following insulin stimulation, SHPTP2, a non-transmembrane protein-tyrosine phosphatase, associates with insulin receptor substrate 1 via its Src homology 2 (SH2) domains. Microinjection of a glutathione S-transferase fusion protein encoding the N- and C-terminal SH2 domains of SHPTP2 (GST-NC-SH2) or anti-SHPTP2 antibodies into NIH-3T3 fibroblasts overexpressing the insulin receptor blocks insulin-induced DNA synthesis. Microinjection of either GST-NC-SH2 or anti-SHPTP2 antibodies into 3T3-L1 adipocytes inhibited the insulin-stimulated increase in expression of GLUT1. In contrast, translocation of GLUT4 to the cell surface was unaffected by either GST-NC-SH2 or anti-SHPTP2 antibodies. These data confirm a role for SHPTP2 in insulin-stimulated mitogenesis and indicate that whereas SHPTP2 is necessary for insulin-stimulated expression of GLUT1, it is not required for activation of the metabolic pathway leading to GLUT4 translocation.

3T3 Cells↗
PubMed1995

Specific recruitment of SH-PTP1 to the erythropoietin receptor causes inactivation of JAK2 and termination of proliferative signals.

The binding of erythropoietin (EPO) to its receptor (EPO-R) activates the protein tyrosine kinase JAK2. The mechanism of JAK2 inactivation has been unclear. We show that the hematopoietic protein tyrosine phosphatase SH-PTP1 (also called HCP and PTP1C) associates via its SH2 domains with the tyrosine-phosphorylated EPO-R. In vitro binding studies suggest that Y429 in the cytoplasmic domain of the EPO-R is the binding site for SH-PTP1. Mutant EPO-Rs lacking Y429 are unable to bind SH-PTP1; cells expressing such mutants are hypersensitive to EPO and display prolonged EPO-induced autophosphorylation of JAK2. Our results suggest that activation of SH-PTP1 by binding to the EPO-R plays a major role in terminating proliferative signals.

Animals↗
PubMed1995

The SH2-containing protein-tyrosine phosphatase SH-PTP2 is required upstream of MAP kinase for early Xenopus development.

SH-PTP2, the vertebrate homolog of Drosophila corkscrew, associates with several activated growth factor receptors, but its biological function is unknown. We assayed the effects of injection of wild-type and mutant SH-PTP2 RNAs on Xenopus embryogenesis. An internal phosphatase domain deletion (delta P) acts as a dominant negative mutant, causing severe posterior truncations. This phenotype is rescued by SH-PTP2, but not by the closely related SH-PTP1. In ectodermal explants, delta P blocks fibroblast growth factor (FGF)- and activin-mediated induction of mesoderm and FGF-induced mitogen-activated protein (MAP) kinase activation. Our results indicate that SH-PTP2 is required for early vertebrate development, acting as a positive component in FGF signaling downstream of the FGF receptor and upstream of MAP kinase.

Activins↗
PubMed1995

Differential regulation of the alpha/beta interferon-stimulated Jak/Stat pathway by the SH2 domain-containing tyrosine phosphatase SHPTP1.

Interferons (IFNs) induce early-response genes by stimulating Janus family (Jak) tyrosine kinases, leading to tyrosine phosphorylation of Stat transcription factors. Previous studies implicated protein-tyrosine phosphatase (PTP) activity in the control of IFN-regulated Jak/Stat signaling, but the specific PTPs responsible remained unidentified. We have found that SH2 domain-containing PTP1 (SHPTP1; also called PTP1C, HCP, or SHP) reversibly associates with the IFN-alpha receptor complex upon IFN addition. Compared with macrophages from normal littermate controls, macrophages from motheaten mice, which lack SHPTP1, show dramatically increased Jak1 and Stat1 alpha tyrosine phosphorylation, whereas Tyk2 and Stat2 activation is largely unaffected. These findings correlate with selectively increased complex formation on a gamma response element, but not an IFN-stimulated response element, in motheaten macrophages. Our results establish that SHPTP1 selectively regulates distinct components of Jak/Stat signal transduction pathways in vivo.

Animals↗
PubMed1995

Evidence for impaired retinoic acid receptor-thyroid hormone receptor AF-2 cofactor activity in human lung cancer.

Retinoic acid (RA) is required for normal airway epithelial cell growth and differentiation both in vivo and in vitro. One of the earliest events following the exposure of bronchial epithelial cells to RA is the strong induction of RA receptor beta (RAR beta) mRNA. Previous work established that many lung cancer cell lines and primary tumors display abnormal RAR beta mRNA expression, most often absence or weak expression of the RAR beta 2 isoform, even after RA treatment. Restoration of RAR beta 2 into RAR beta-negative lung cancer cell lines has been reported to inhibit tumorigenicity. Since RAR beta 2 inactivation may contribute to lung cancer, we have investigated the molecular mechanism of defective RAR beta 2 expression. Nuclear run-on assays and transient transfections with RAR beta 2 promoter constructs indicate the presence of trans-acting transcriptional defects in most lung cancer cell lines, which map to the RA response element (RARE). These defects cannot be complemented by RAR-retinoid X receptor cotransfection and can be separated into two types: (i) one affecting transcription from direct repeat RAREs, but not palindromic RAREs, and (ii) another affecting transcription from both types of RARE. Studies using chimeras between RAR alpha, TR alpha, and other transcription factors suggest the existence of novel RAR-thyroid hormone receptor AF-2-specific cofactors, which are necessary for high levels of transcription. Furthermore, these factors may be frequently inactivated in human lung cancer.

Adenovirus E1A Proteins↗
PubMed1995

Specific modulation of ectodermal cell fates in Xenopus embryos by glycogen synthase kinase.

Shaggy is a downstream component of the wingless and Notch signaling pathways which operate during Drosophila development. To address the role of glycogen synthase kinase 3 beta (GSK3 beta), a mammalian homologue of Shaggy, in vertebrate embryogenesis, it was overexpressed in Xenopus embryos. Microinjection of rat GSK3 beta mRNA into animal ventral blastomeres of 8-cell-stage embryos triggered development of ectopic cement glands with an adjacent anterior neural tissue as evidenced by in situ hybridization with Xotx2, a fore/midbrain marker, and NCAM, a pan-neural marker. In contrast, animal dorsal injection of the same dose of GSK3 beta mRNA caused eye deficiencies, whereas vegetal injections had no pronounced effects on normal development. Using several mutated forms of rat GSK3 beta, we demonstrate that the observed phenotypes are dose-dependent and tightly correlate with GSK3 beta enzymatic activity. Lineage tracing experiments showed that the effects of GSK3 beta are cell autonomous and that ectopic cement glands and eye deficiencies arose directly from cells containing GSK3 beta mRNA. Molecular marker analysis of ectodermal explants overexpressing GSK3 beta has revealed activation of Xotx2 and of cement gland marker XAG-1, but expression of NCAM and XIF-3 was not detected. Phenotypic effects of mRNA encoding a Xenopus homologue of GSK3 beta were identical to those of rat GSK3 beta mRNA. We hypothesize that GSK3 beta mediates the initial steps of neural tissue specification and modulates anteroposterior ectodermal patterning via activation of Otx2 transcription. Our observations implicate GSK3 beta in signaling pathways operating during neural tissue development and during specification of anterior ectodermal cell fates.

Animals↗
PubMed1994

Intramolecular regulation of protein tyrosine phosphatase SH-PTP1: a new function for Src homology 2 domains.

The steady-state kinetic properties of SH-PTP1 (PTP1C, SHP, HCP), a Src homology 2 (SH2) domain-containing protein tyrosine phosphatase (PTPase), were assessed and compared with those of three truncation mutants, using p-nitrophenyl phosphate, phosphotyrosyl (pY) peptides, and reduced, carboxyamido-methylated, maleylated, and tyrosyl-phosphorylated lysozyme as substrates. At physiological pH (7.4), truncation of the two N-terminal SH2 domains [SH-PTP1(delta SH2)] or the last 35 amino acids of the C-terminus [SH-PTP1(delta C35)] activated the phosphatase activity by 30-fold and 20-34-fold relative to the wild-type enzyme, respectively. Truncation of the last 60 amino acids resulted in a mutant [SH-PTP1(delta C60)] with wild-type activity. SH-PTP1 and SH-PTP1(delta C60) displayed apparent saturation kinetics toward pNPP only at acidic pH (pH < or = 5.4); as pH increased above 5.5, their apparent KM values increased dramatically. In contrast, SH-PTP1(delta SH2) obeyed normal Michaelis-Menten kinetics at all pH values tested (pH 5.1-7.4) with a constant KM (10-14 mM). Furthermore, two synthetic pY peptides corresponding to known and potential phosphorylation sites on the erythropoietin (EPOR pY429) and interleukin-3 (IL-3R pY628) receptors bound specifically to the N-terminal SH2 domain of SH-PTP1 (KD = 1.8-10 microM) and activated the catalytic activity of SH-PTP1 and SH-PTP1(delta C60) but not SH-PTP1(delta SH2), in a concentration-dependent manner. Maximal activation (25-30-fold) of SH-PTP1 was achieved at 70 microM EPOR pY429, and the maximally activated enzyme approached the activity of SH-PTP1(delta SH2). Addition of EPOR pY429 peptide, which corresponds to the recently identified in vivo binding site for SH-PTP1, at 40 microM also completely restored the saturation kinetic behavior of SH-PTP1 (at pH 7.4) toward pNPP, with catalytic parameters (KM = 12.8 mM, kcat = 3.2 s-1) similar to those of SH-PTP1(delta SH2). These data suggest that the SH2 domains of SH-PTP1 serve to autoinhibit the phosphatase activity of the PTPase domain. A model is proposed in which the SH2 domains interact with the PTPase domain in a pY-independent fashion and drive the PTPase domain into an inactive conformation.

Amino Acid Sequence↗
PubMed1994

Protein-tyrosine-phosphatase SHPTP2 couples platelet-derived growth factor receptor beta to Ras.

Protein-tyrosine-phosphatase SHPTP2 (Syp/PTP-1D/PTP2C) is the homologue of the Drosophila corkscrew (csw) gene product, which transmits positive signals from receptor tyrosine kinases. Likewise, SHPTP2 has been implicated in positive signaling from platelet-derived growth factor receptor beta (PDGFR). Upon PDGF stimulation, SHPTP2 binds to the PDGFR and becomes tyrosine-phosphorylated. We have identified tyrosine-542 (pY542TNI) as the major in vivo site of SHPTP2 tyrosine phosphorylation. The pY542TNI sequence conforms to the consensus binding site for the SH2 domain of Grb2, which, by association with Sos1, couples some growth factor receptors to Ras. Following PDGF stimulation, Grb2 binds tyrosine-phosphorylated SHPTP2. Moreover, a mutant PDGFR lacking its SHPTP2 binding site displays markedly reduced Grb2 binding. These data indicate that phosphorylation of SHPTP2 couples Grb2 to PDGFR in vivo, providing a mechanism for Ras activation by PDGFR and for positive signaling via SHPTP2 and Csw.

3T3 Cells↗
PubMed1994

Activation of the SH2-containing protein tyrosine phosphatase, SH-PTP2, by phosphotyrosine-containing peptides derived from insulin receptor substrate-1.

The cytoplasmic insulin receptor substrate-1 (IRS-1), which is multiply phosphorylated in vivo on tyrosine residues, is a known binding protein for the tandem src homology 2 (SH2) domain-containing protein tyrosine phosphatase, SH-PTP2. Eleven phosphotyrosyl (pY) peptides from IRS-1 were screened for allosteric activation of SH-PTP2 phosphatase activity toward phosphorylated, reduced, carboxyamidomethylated, and maleylated-lysozyme. Peptides IRS-1pY895, IRS-1pY1172, and IRS-1pY1222 showed up to 50-fold acceleration of dephosphorylation. Analyses of Arg to Lys mutants in either or both SH2 domains indicate that both the N-terminal (N-SH2) and C-terminal (C-SH2) domains function in allosteric activation. Direct determination by surface plasmon resonance of the dissociation constants between pY peptides and glutathione S-transferase fusions to N-SH2 and C-SH2 domains reveals a 240-fold preference of the N-SH2 domain (compared with the C-SH2 domain) for IRS-1pY1172. The N-SH2 domain prefers IRS-1pY1172 > IRS-1pY895 > IRS-1pY1222, whereas C-SH2 domain prefers IRS-1pY1222 > IRS-1pY895 > IRS-1pY1172. These data suggest that each SH2 domain can bind to a distinct pY sequence of multiply phosphorylated protein substrates such as IRS-1, while activating hydrolysis at a third pY sequence bound in the SH-PTP2 active site. In addition, proteolysis and truncation studies reveal an autoregulatory function for the C-terminal region of SH-PTP2. Limited tryptic cleavage within the C-terminus results in 27-fold activation of protein tyrosine phosphatase activity. The activated tryptic fragment cannot be further activated by pY peptide binding to the SH2 domains indicating that autoregulatory functions of the SH2 domains are dependent on the C-terminal region. These data suggest that multiple levels for control of SH-PTP2 enzymatic activity may exist in vitro and in vivo.

Amino Acid Sequence↗
PubMed1994

SH-PTP2/Syp SH2 domain binding specificity is defined by direct interactions with platelet-derived growth factor beta-receptor, epidermal growth factor receptor, and insulin receptor substrate-1-derived phosphopeptides.

Signaling by tyrosine kinases involves direct associations between proteins with Src homology 2 (SH2) domains and sites of tyrosine phosphorylation. Specificity in signaling pathways results in part from inherent selectivity in interactions between particular SH2 domains and phosphopeptide sequences. The cytoplasmic phosphotyrosine phosphatase SH-PTP2 (Syp, PTP 1D, PTP-2C) contains two SH2 domains (N and C) which mediate its association with and activation by the platelet-derived growth factor (PDGF) and epidermal growth factor receptors and IRS-1. We have developed a competitive phosphopeptide binding assay to analyze specificity of the SH-PTP2 N-SH2 domain for phosphorylation sites of these phosphoproteins. The sequence surrounding Tyr1009 bound with greatest affinity (ID50 = 14 microM) of eight PDGF receptor-derived phosphopeptides tested. No peptides corresponding to known epidermal growth factor receptor phosphorylation sites bound with high affinity. However, an alternative sequence surrounding Tyr954 bound tightly (ID50 = 21 microM). Of the 13 IRS-1-related peptides analyzed, sequences surrounding Tyr546, Tyr895, and Tyr1172 bound with highest affinity (ID50 = 11, 4, and 1 microM, respectively). Alternative phosphopeptides generally bound with much weaker affinity (ID50 > 150 microM). These findings are consistent with recent mutational analyses of the PDGF receptor and predict site-specific interactions between SH-PTP2 and each of these phosphoproteins. Comparisons between peptide sequences suggest that the N-terminal SH2 domain of SH-PTP2 binds with highest affinity to phosphotyrosine (pY) followed by a beta-branched residue (Val, Ile, Thr) at pY+1 and a hydrophobic residue (Val, Leu, Ile) at pY+3 positions. Peptide truncation studies also indicate that residues outside of the pY-1 to pY+4 motif are required for high affinity interactions.

Amino Acid Sequence↗
PubMed1994

Lck-dependent tyrosyl phosphorylation of the phosphotyrosine phosphatase SH-PTP1 in murine T cells.

The phosphorylation and dephosphorylation of proteins on tyrosyl residues are key regulatory mechanisms in T-cell signal transduction and are controlled by the opposing activities of protein tyrosine kinases and phosphotyrosyl phosphatases (PTPs). In T cells, several nontransmembrane protein tyrosine kinases are associated with receptors; for example, Lck is bound to the coreceptors CD4 and CD8 and becomes activated upon their stimulation. In comparison, little is known about the role of nontransmembrane PTPs in early T-cell signaling. SH-PTP1 (PTP1C, HCP, SHP) is a nontransmembrane PTP expressed primarily in hematopoietic cells, including T cells. We have found that SH-PTP1 is basally phosphorylated on serine in resting T cells. Upon stimulation of CD4 or CD8 either in a T-cell hybridoma cell line or in primary thymocytes, SH-PTP1 becomes tyrosyl phosphorylated. Moreover, SH-PTP1 is constitutively phosphorylated on tyrosine in the Lck-overexpressing lymphoma cell line LSTRA. SH-PTP1 is also a good substrate for recombinant Lck in vitro. Comparisons of the tryptic phosphopeptide maps of wild-type SH-PTP1 and deletion and point mutations establish that the two sites (Y-536 and Y-564) which are directly phosphorylated by Lck in vitro are also phosphorylated in vivo in LSTRA cells. One of these sites (Y-564) is phosphorylated in T cells in response to Lck activation. We conclude that SH-PTP1 undergoes Lck-dependent tyrosyl phosphorylation in T cells and likely plays a role in early T-cell signaling.

Amino Acid Sequence↗