A novel SHP-1/Grb2–dependent mechanism of negative regulation of cytokine-receptor signaling: contribution of SHP-1 C-terminal tyrosines in cytokine signaling

Blood ◽  
2004 ◽  
Vol 103 (4) ◽  
pp. 1398-1407 ◽  
Author(s):  
Parham Minoo ◽  
Maryam Mohsen Zadeh ◽  
Robert Rottapel ◽  
Jean-Jacques Lebrun ◽  
Suhad Ali
Keyword(s):  
Adaptor Protein ◽  
Sh2 Domain ◽  
Janus Kinase ◽  
Cytokine Receptor ◽  
Negative Regulator ◽  
Cytokine Signaling ◽  
Binding Motif ◽  
Receptor Signaling ◽  
Tyrosine Residues ◽  
Receptor Complexes

Abstract SHP-1, an src homology 2 (SH2) domain containing protein tyrosine phosphatase, functions as a negative regulator of signaling downstream of cytokine receptors, receptor tyrosine kinases and receptor complexes of the immune system. Dephosphorylation of receptors and/or receptor-associated kinases has been described as the mechanism for the function of SHP-1. Here we demonstrate a novel mechanism by which SHP-1 down-regulates the Janus kinase–2 (Jak2)/signal transducer and activator of transcription-5 (Stat5) pathway downstream of the prolactin receptor (PRLR) and the erythropoietin receptor (EPOR) in a catalytic activity–independent manner. Structural/functional analysis of SHP-1 defined the C-terminal tyrosine residues (Y278, Y303, Y538, Y566) within growth factor receptor–bound protein 2 (Grb-2) binding motif to be responsible for delivering the inhibitory effects. Our results further indicate that these tyrosine residues, via recruitment of the adaptor protein Grb-2, are required for targeting the inhibitory protein suppressor of cytokine signaling–1 (SOCS-1) to Jak2 kinase. Finally, loss of SOCS-1 expression in SOCS-1–/– mouse embryonic fibroblast (MEF) cells led to attenuation in SHP-1 function to down-regulate PRL-induced Stat5 activation. All together, our results indicate that SHP-1 inhibits PRLR and EPOR signaling by recruitment and targeting of SOCS-1 to Jak2, highlighting a new mechanism of SHP-1 regulation of cytokine-receptor signaling.

scholarly journals Adaptor Protein Lnk Binds to and Inhibits Normal and Leukemic FLT3

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 1312-1312
Author(s):  
Dechen Lin ◽  
Tong Yin ◽  
Maya koren-Michowitz ◽  
Ling-Wen Ding ◽  
Saskia Gueller ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Signaling Pathways ◽  
Hematopoietic Cells ◽  
Adaptor Protein ◽  
Sh2 Domain ◽  
Janus Kinase ◽  
Negative Regulator ◽  
Hematopoietic Progenitor Cell ◽  
Cytokine Signaling ◽  
Direct Binding

Abstract Abstract 1312 Background The production and lineage commitment of hematopoietic cells is controlled by the actions of a complex network of signaling pathways. Mutations and translocations of tyrosine kinases within these pathways lead to constitutive signaling and enhanced proliferation. Classic examples are BCR-ABL in CML, Janus kinase 2 (JAK2) mutations in MPN, Fms-like tyrosine kinase 3 (FLT3) and c-KIT mutations in AML. FLT3 is a receptor tyrosine kinase with important roles in hematopoietic progenitor cell survival and proliferation. It is mutated in about 1/3 of AML patients, mostly by internal tandem duplications (ITD). Adaptor protein Lnk is expressed in hematopoietic cells and is an important negative regulator in cytokine signaling and hematopoiesis. Previously, we and others have shown that Lnk interacts with the JXM domain of c-KIT, PDGFRA, PDGFRB and FMS, all of which share a similar sequence in this domain. The fact that FLT3 harbors a conserved JXM domain prompted us to investigate whether Lnk interacts with FLT3. Methods and Results Co-immunoprecipitation and GST-pulldown assay showed that Lnk physically interacts with both wild-type FLT3 (FLT3-WT) and FLT3-ITD through its SH2 domain in multiple types of hematopoietic cells. Through affinity fishing assay with immobilized peptides, we identified the tyrosine residues 572, 591 and 919 of FLT3 as phosphorylation sites involved in direct binding to Lnk. Importantly, Lnk itself was tyrosine-phosphorylated by both FLT3 ligand (FL)-activated FLT3-WT and constitutively activated FLT3-ITD. Functionally, both shRNA-mediated depletion and ectopic expression of Lnk demonstrated that activation signals emanating from both forms of FLT3 are under negative regulation by Lnk. Consequently, Lnk inhibited 32D cell proliferation driven by different FLT3 oncogenic variants. Moreover, analysis of primary bone marrow cells from Lnk−/−mice showed that Lnk suppresses the expansion of FL-stimulated hematopoietic progenitors, including lymphoid-primed multipotent progenitors, mainly through inhibiting MAPK-ERK activation by FL. Conclusions This study reveals that through direct binding to FLT3-WT and FLT3-ITD, Lnk constrains FLT3-WT/ITD-dependent signaling pathways involved in the proliferation and expansion of hematopoietic cells as well as related leukemic cells. Modulation of Lnk expression levels may provide a unique therapeutic approach for FLT3-ITD-associated hematopoietic diseases. Disclosures: No relevant conflicts of interest to declare.

Adaptor Protein Lnk Negatively Regulates Mutant MPL and JAK2 Alleles Associated with Myeloproliferative Disorders

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 1531-1531
Author(s):  
Sigal Gery ◽  
Saskia Gueller ◽  
Julia Sohn ◽  
Shayne Nabavinouri ◽  
Amanda Leiter ◽  
...  
Keyword(s):  
Signaling Pathways ◽  
Molecular Mechanisms ◽  
Bone Marrow Cells ◽  
Adaptor Protein ◽  
Myeloproliferative Disorders ◽  
Sh2 Domain ◽  
Cytokine Receptor ◽  
Negative Regulator ◽  
Activating Mutations ◽  
Signaling Axis

Abstract Activating mutations in the cytokine receptor/JAK2 signaling axis are found at high frequency in myeloproliferative disorders (MPD). Lnk, an SH2-containing adaptor protein, is a negative regulator of several hematopoietic cytokine receptors including MPL and EpoR. Here, we assessed whether Lnk can attenuate the activity of mutant MPLW515L, JAK2V617F and JAK2K539L found in MPD patients. Lnk overexpression in Ba/F3-MPLW515L cells inhibited cytokine-independent growth, while suppression of Lnk in UT7-MPLW515L cells enhanced proliferation. Lnk-mediated growth inhibition was associated with downregulation of JAK/STAT, MAPK and PI3K signaling pathways. Similarly, Lnk inhibited cytokine-independent growth conferred by JAK2V617F and JAK2K539L in Ba/F3-EpoR cells. Following thrombopoietin stimulation, Lnk became tyrosyl-phosphorylated and associated with activated wild-type (WT) MPL and MPLW515L at the plasma membrane of Ba/F3 cells. An SH2 mutant Lnk (R392E) failed to bind and inhibit WT MPL and MPLW515L, demonstrating that the SH2 domain is essential for Lnk down-modulation of the receptors. The Lnk-MPL interaction was also detected with endogenously expressed proteins from cultured bone marrow cells. A series of C-terminally truncated Lnk constructs were used to determine which Lnk regions are required for Lnk inhibition of JAK2. Experiments in 293T cells indicated that Lnk SH2 domain binds to phosphorylated JAK2. In addition, other Lnk regions associated with non-phosphorylated JAK2, and these interactions were critical for Lnk inhibition of JAK2V617F and JAK2K539L constitutive activation. Our data suggest a model wherein Lnk downregulation of the receptor/JAK2 signaling involves two mechanisms; one is inhibition of the cytokine receptor utilizing JAK2, the second is direct suppression of JAK2 kinase activity. Furthermore, while the receptor mediated inhibition requires the SH2 domain, direct inhibition of JAK2 mutants, V617F and K539L, relies on other Lnk domains. Further elucidating the molecular mechanisms underlying Lnk inhibition of signaling pathways abnormally activated by oncogenic alleles, will provide insight into the pathogenesis of MPD and may have therapeutic value.

Lnk Constrains Oncogenic JAK2-Induced Myeloproliferative Disease in Mice.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 1437-1437
Author(s):  
Alexey Bersenev ◽  
Chao Wu ◽  
Joanna Balcerek ◽  
Wei Tong
Keyword(s):  
Signaling Pathways ◽  
Conflicts Of Interest ◽  
Adaptor Protein ◽  
Janus Kinase ◽  
Negative Regulator ◽  
Myelogenous Leukemia ◽  
Cell Surface Receptor ◽  
Cytokine Signaling ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract Abstract 1437 Poster Board I-460 Hematopoietic stem cell (HSC) homeostasis and self-renewal are regulated by intrinsic cytokine signaling pathways. One important signaling axis for HSC is the cell surface receptor, Mpl, and its ligand, thrombopoietin (Tpo). Upon Tpo stimulation, Mpl activates Janus Kinase (JAK2), which in turn triggers a cascade of downstream signal transduction pathways that regulate key aspects of cell development. Mice that lack the inhibitory adaptor protein Lnk harbor a vastly expanded HSC pool with enhanced self-renewal. We previously demonstrated that Lnk controls HSC self-renewal predominantly through the Mpl/JAK2 pathway. Lnk binds directly to phosphorylated tyrosine 813 in JAK2 upon Tpo stimulation. Moreover, Lnk-deficient HSCs display potentiated JAK2 activation. Dysregulation of cytokine receptor signaling pathways frequently lead to hematological malignancies. Abnormal activation of JAK2 by a chromosomal translocation between the transcription factor Tel and JAK2 (Tel/JAK2) was shown to cause atypical Chronic Myelogenous Leukemia (aCML) in human patients. Moreover, the JAK2 V617F mutation has been observed at high frequency in several myeloproliferative diseases (MPDs). The JAK2V617F retains Lnk binding, suggesting that alterations in Lnk could influence MPD development. Indeed, we found that loss of Lnk accelerates and exacerbates oncogenic JAK2-induced MPD in mouse transplant models. Specifically, Lnk deficiency enhanced cytokine signaling, thereby augmenting the ability of oncogenic JAK2 to expand myeloid progenitors. To test whether the interaction between Lnk and JAK2V617F directly constrains MPD development in mice, we transplanted wild-type bone marrow cells expressing the JAK2V617F/Y813F double mutant that does not interact with Lnk (WT;JAK2VF/YF). WT;JAK2VF/YF engrafted mice exhibited increased myeloid expansion when compared to WT;JAK2VF mice, and conferred accelerated polycythemia vera development in secondary transplants. In summary, we identified Lnk as a physiological negative regulator of JAK2 in stem cells that may constrain leukemic transformation conferred by oncogenic JAK2. Disclosures No relevant conflicts of interest to declare.

scholarly journals Discovery of an exosite on the SOCS2-SH2 domain that enhances SH2 binding to phosphorylated ligands

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Edmond M. Linossi ◽  
Kunlun Li ◽  
Gianluca Veggiani ◽  
Cyrus Tan ◽  
Farhad Dehkhoda ◽  
...  
Keyword(s):  
Binding Affinity ◽  
Sh2 Domain ◽  
Janus Kinase ◽  
Negative Regulator ◽  
Cytokine Signaling ◽  
Signal Transducers ◽  
Src Homology 2 ◽  
Src Homology ◽  
Phosphorylated Peptide ◽  
Α Helix

AbstractSuppressor of cytokine signaling (SOCS)2 protein is a key negative regulator of the growth hormone (GH) and Janus kinase (JAK)-Signal Transducers and Activators of Transcription (STAT) signaling cascade. The central SOCS2-Src homology 2 (SH2) domain is characteristic of the SOCS family proteins and is an important module that facilitates recognition of targets bearing phosphorylated tyrosine (pTyr) residues. Here we identify an exosite on the SOCS2-SH2 domain which, when bound to a non-phosphorylated peptide (F3), enhances SH2 affinity for canonical phosphorylated ligands. Solution of the SOCS2/F3 crystal structure reveals F3 as an α-helix which binds on the opposite side of the SH2 domain to the phosphopeptide binding site. F3:exosite binding appears to stabilise the SOCS2-SH2 domain, resulting in slower dissociation of phosphorylated ligands and consequently, enhances binding affinity. This biophysical enhancement of SH2:pTyr binding affinity translates to increase SOCS2 inhibition of GH signaling.

scholarly journals Adaptor protein Lnk binds to and inhibits normal and leukemic FLT3

Blood ◽  
2012 ◽  
Vol 120 (16) ◽  
pp. 3310-3317 ◽  
Author(s):  
De-Chen Lin ◽  
Tong Yin ◽  
Maya Koren-Michowitz ◽  
Ling-Wen Ding ◽  
Saskia Gueller ◽  
...  
Keyword(s):  
Tyrosine Kinase ◽  
Adaptor Protein ◽  
Negative Regulator ◽  
Hematopoietic Progenitor Cell ◽  
Cytokine Signaling ◽  
Tyrosine Residues ◽  
Sh2 Domains ◽  
Multipotent Progenitors ◽  
Direct Binding ◽  
Tandem Duplications

Abstract Fms-like tyrosine kinase 3 (FLT3) is a receptor tyrosine kinase with important roles in hematopoietic progenitor cell survival and proliferation. It is mutated in approximately one-third of AML patients, mostly by internal tandem duplications (ITDs). Adaptor protein Lnk is a negative regulator of hematopoietic cytokine signaling. In the present study, we show that Lnk interacts physically with both wild-type FLT3 (FLT3-WT) and FLT3-ITD through the SH2 domains. We have identified the tyrosine residues 572, 591, and 919 of FLT3 as phosphorylation sites involved in direct binding to Lnk. Lnk itself was tyrosine phosphorylated by both FLT3 ligand (FL)–activated FLT3-WT and constitutively activated FLT3-ITD. Both shRNA-mediated depletion and forced overexpression of Lnk demonstrated that activation signals emanating from both forms of FLT3 are under negative regulation by Lnk. Moreover, Lnk inhibited 32D cell proliferation driven by different FLT3 variants. Analysis of primary BM cells from Lnk-knockout mice showed that Lnk suppresses the expansion of FL-stimulated hematopoietic progenitors, including lymphoid-primed multipotent progenitors. The results of the present study show that through direct binding to FLT3, Lnk suppresses FLT3-WT/ITD–dependent signaling pathways involved in the proliferation of hematopoietic cells. Therefore, modulation of Lnk expression levels may provide a unique therapeutic approach for FLT3-ITD–associated hematopoietic disease.

scholarly journals A Role of Suppressor of Cytokine Signaling 3 (SOCS3/CIS3/SSI3) in CD28-mediated Interleukin 2 Production

2003 ◽  
Vol 197 (4) ◽  
pp. 425-436 ◽  
Author(s):  
Akira Matsumoto ◽  
Yoh-ichi Seki ◽  
Ryosuke Watanabe ◽  
Katsuhiko Hayashi ◽  
James A. Johnston ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Interleukin 2 ◽  
Sh2 Domain ◽  
Janus Kinase ◽  
Expression Level ◽  
Cytokine Signaling ◽  
Suppressor Of Cytokine Signaling ◽  
Cd28 Costimulation

Suppressor of cytokine signaling (SOCS)3 has been characterized as a negative feedback regulator in cytokine-mediated Janus kinase signal transducer and activator of transcription signaling. However, this study shows that T cells from transgenic mice expressing SOCS3 exhibit a significant reduction in interleukin (IL)-2 production induced by T cell receptor cross-linking when T cells are costimulated with CD28. Decreased protein expression in SOCS3+/− mice enhanced CD28-mediated IL-2 production, clearly indicating the correlation between expression level of SOCS3 and IL-2 production ability. The SOCS3 protein interacted with phosphorylated CD28 through its SH2 domain but not the kinase inhibitory region. In addition, a point mutation in the SOCS3 SH2 domain attenuated the inhibition of CD28 function in IL-2 promoter activation. Committed T helper (Th)2 cells exclusively expressed SOCS3 and production of Th2 cytokines, such as IL-4 and IL-5, was much less dependent on CD28 costimulation compared with interferon γ and IL-2 production in Th1 cells. Consistent with this notion, the expression level of SOCS3 in early T cell activation influenced the ability of IL-2 production induced by CD28 costimulation. Therefore, the SOCS3 may play an alternative role in prohibiting excessive progression of CD28-mediated IL-2 production.

scholarly journals Characterization of JAK1 Pseudokinase Domain in Cytokine Signaling

Cancers ◽  
2019 ◽  
Vol 12 (1) ◽  
pp. 78 ◽  
Author(s):  
Juuli Raivola ◽  
Teemu Haikarainen ◽  
Olli Silvennoinen
Keyword(s):  
Biochemical Characterization ◽  
Myeloproliferative Neoplasms ◽  
Interleukin 2 ◽  
Binding Pocket ◽  
Janus Kinase ◽  
Regulatory Function ◽  
Cytokine Signaling ◽  
Interferon Α ◽  
Atp Binding ◽  
Receptor Complexes

The Janus kinase-signal transducer and activator of transcription protein (JAK-STAT) pathway mediates essential biological functions from immune responses to haematopoiesis. Deregulated JAK-STAT signaling causes myeloproliferative neoplasms, leukaemia, and lymphomas, as well as autoimmune diseases. Thereby JAKs have gained significant relevance as therapeutic targets. However, there is still a clinical need for better JAK inhibitors and novel strategies targeting regions outside the conserved kinase domain have gained interest. In-depth knowledge about the molecular details of JAK activation is required. For example, whether the function and regulation between receptors is conserved remains an open question. We used JAK-deficient cell-lines and structure-based mutagenesis to study the function of JAK1 and its pseudokinase domain (JH2) in cytokine signaling pathways that employ JAK1 with different JAK heterodimerization partner. In interleukin-2 (IL-2)-induced STAT5 activation JAK1 was dominant over JAK3 but in interferon-γ (IFNγ) and interferon-α (IFNα) signaling both JAK1 and heteromeric partner JAK2 or TYK2 were both indispensable for STAT1 activation. Moreover, IL-2 signaling was strictly dependent on both JAK1 JH1 and JH2 but in IFNγ signaling JAK1 JH2 rather than kinase activity was required for STAT1 activation. To investigate the regulatory function, we focused on two allosteric regions in JAK1 JH2, the ATP-binding pocket and the αC-helix. Mutating L633 at the αC reduced basal and cytokine induced activation of STAT in both JAK1 wild-type (WT) and constitutively activated mutant backgrounds. Moreover, biochemical characterization and comparison of JH2s let us depict differences in the JH2 ATP-binding and strengthen the hypothesis that de-stabilization of the domain disturbs the regulatory JH1-JH2 interaction. Collectively, our results bring mechanistic understanding about the function of JAK1 in different receptor complexes that likely have relevance for the design of specific JAK modulators.

Human SLP-65 isoforms contribute differently to activation and apoptosis of B lymphocytes

Blood ◽  
2006 ◽  
Vol 108 (12) ◽  
pp. 3761-3768 ◽  
Author(s):  
Annika Grabbe ◽  
Jürgen Wienands
Keyword(s):  
B Cell ◽  
Lymphoblastic Leukemia ◽  
Adaptor Protein ◽  
Sh2 Domain ◽  
Binding Motif ◽  
B Lymphopoiesis ◽  
Suppressor Activity ◽  
B Cell Signaling ◽  
Tumor Suppressor Activity ◽  
Mitogen Activated Protein

AbstractThe SH2 domain-containing leukocyte adaptor protein of 65 kDa (SLP-65) is the key effector for signaling downstream of the B-cell antigen receptor (BCR). SLP-65 controls not only B lymphopoiesis and humoral immunity but also possesses a yet poorly defined tumor suppressor activity that is lost in many cases of acute lymphoblastic leukemia. We found that the 2 isoforms of human SLP-65 are differentially involved in positive and negative B-cell signaling. Reconstitution experiments revealed that an atypical SH3 domain-binding motif, which is present in the long but not in the short SLP-65 isoform, mediates association to Grb2 and suppresses activation of mitogen-activated protein kinases p38 and JNK as well as up-regulation of c-Fos expression. In turn, the short isoform activates not only AP1-driven but also NF-κB–driven gene transcription more potently than the long isoform. Conversely, the long rather than the short SLP-65 isoform promotes BCR-induced B-cell apoptosis. Our data further delineate the structural requirements of positive and negative SLP-65 signal transduction in normal and neoplastic cells.

Adaptor Protein Lnk Binds to PDGFRA, PDGFRB and FIP1L1-PDGFRA, but Not to the TEL-PDGFRB Fusion Protein.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 2213-2213
Author(s):  
Saskia Gueller ◽  
Sigal Gery ◽  
H. Phillip Koeffler
Keyword(s):  
Fusion Protein ◽  
Western Blot ◽  
Adaptor Protein ◽  
Sh2 Domain ◽  
Negative Regulator ◽  
Pleckstrin Homology Domain ◽  
Wild Type ◽  
Nih3t3 Cells ◽  
Sh2 Domains ◽  
Juxtamembrane Region

Abstract PDGFRA and PDGFRB (platelet derived growth factor receptors alpha and beta) are frequently expressed on malignant hematopoietic cells and regulate various cellular responses such as development, proliferation, differentiation, cell survival and cellular transformation. Stimulation by either autocrine loops or constitutional activation by chromosomal translocation (i.e. chronic myelomonocytic leukemia [CMML, TEL-PDGFRB] or chronic eosinophilic leukemia [CEL, FIP1L1-PDGFRA]) makes them important factors in development of hematopoietic disorders. Normally, interaction with the ligand PDGF, induces dimerization of two distinct receptor subunits, resulting in activation of the intracellular tyrosine kinase domain and phosphorylation of tyrosine residues, thereby creating binding sites for several molecules containing Src homology 2 (SH2) domains. We hypothesized that one such protein may be the adaptor Lnk, a negative regulator of several hematopoietic cytokine receptors including MPL, EpoR and c-Kit. Lnk belongs to a family of proteins sharing several structural motifs including a SH2 domain, a pleckstrin homology domain (PH) and a dimerization domain (DD). The SH2 domain is known to be essential for its inhibitory effect which can be abolished by the point mutation R392E. We investigated the ability of Lnk to bind to PDGFRA, PDGFRB, FIP1L1-PDGFRA and TEL-PDGFRB. To determine the domain of Lnk that is responsible for the binding, we constructed a series of V5-tagged Lnk mutants including: a mutation in the SH2 domain (R392E); deletion of the SH2 domain; deletion of the PH and SH2 domains and a construct only containing the DD domain. 293T cells were co-transfected with cDNAs encoding either PDGFRA, PDGFRB or one of the translocation products and either wild-type or mutant Lnk. Whole cell lysates were used to perform immunoprecipitation with either V5-tag or PDGFR antibodies. Binding of Lnk and PDGFR was detected by Western blot probed with PDGFR or V5-tag antibodies. NIH3T3 cells were transfected either with empty vector or Lnk cDNA, transfectants were selected for 5 days with G418, serum starved for 16 hours and induced with PDGF for 10 minutes. Phosphorylation of downstream targets of PDGFRA and PDGFRB was detected by Western blot. Our data showed that Lnk bound to PDGFRA and PDGFRB only after exposure of the cells to PDGF and to the FIP1L1-PDGFRA fusion protein independent of PDGF exposure. Mutation or deletion of the Lnk SH2 domain abolished binding completely in PDGFRA and FIP1L1-PDGFRA, but just partly in PDGFRB. Expression of Lnk in NIH3T3 cells inhibited phosphorylation of ERK after treatment with PDGF. In other experiments, we determined that Lnk bound the juxtamembrane region of this class of receptors. Interestingly, the TEL-PDGFRB fusion protein was unable to bind Lnk, although its breakpoint in PDGFRB is distal to the juxtamembrane domain and the whole intracellular region of PDGFRB is included in the fusion protein. Further exploration of the mechanisms by which Lnk affects wild-type or PDGFR fusion product will provide insight into the molecular pathophysiology of myeloid disorders and could help develop new treatments.

scholarly journals pp125FAK-dependent tyrosine phosphorylation of paxillin creates a high-affinity binding site for Crk.

1995 ◽  
Vol 15 (5) ◽  
pp. 2635-2645 ◽  
Author(s):  
M D Schaller ◽  
J T Parsons
Keyword(s):  
Tyrosine Phosphorylation ◽  
Focal Adhesion ◽  
Protein Tyrosine Kinase ◽  
Focal Adhesions ◽  
Sh2 Domain ◽  
Binding Motif ◽  
Adapter Protein ◽  
Tyrosine Residues ◽  
Sh2 Domains ◽  
High Affinity Binding Site

Paxillin, a focal-adhesion-associated protein, becomes phosphorylated in response to a number of stimuli which also induce the tyrosine phosphorylation of the focal-adhesion-associated protein tyrosine kinase pp125FAK. On the basis of their colocalization and coordinate phosphorylation, paxillin is a candidate for a substrate of pp125FAK. We describe here conditions under which the phosphorylation of paxillin on tyrosine is pp125FAK dependent, supporting the hypothesis that paxillin phosphorylation is regulated by pp125FAK. pp125FAK must localize to focal adhesions and become autophosphorylated to induce paxillin phosphorylation. Phosphorylation of paxillin on tyrosine creates binding sites for the SH2 domains of Crk, Csk, and Src. We identify two sites of phosphorylation as tyrosine residues 31 and 118, each of which conforms to the Crk SH2 domain binding motif, (P)YXXP. These observations suggest that paxillin serves as an adapter protein, similar to insulin receptor substrate 1, and that pp125FAK may regulate the formation of signaling complexes by directing the phosphorylation of paxillin on tyrosine.

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