scholarly journals CpG-induced tyrosine phosphorylation occurs via a TLR9-independent mechanism and is required for cytokine secretion

2006 ◽  
Vol 172 (7) ◽  
pp. 1057-1068 ◽  
Author(s):  
Miguel A. Sanjuan ◽  
Navin Rao ◽  
Kuei-Tai A. Lai ◽  
Yin Gu ◽  
Siquan Sun ◽  
...  
Keyword(s):  
Tyrosine Phosphorylation ◽  
Actin Polymerization ◽  
Kinase Inhibitors ◽  
Adaptor Protein ◽  
Cytokine Secretion ◽  
Src Family Kinase ◽  
Kinase Activation ◽  
Cpg Oligonucleotides ◽  
Molecular Patterns ◽  
Kinase Expression

Toll-like receptors (TLRs) recognize molecular patterns preferentially expressed by pathogens. In endosomes, TLR9 is activated by unmethylated bacterial DNA, resulting in proinflammatory cytokine secretion via the adaptor protein MyD88. We demonstrate that CpG oligonucleotides activate a TLR9-independent pathway initiated by two Src family kinases, Hck and Lyn, which trigger a tyrosine phosphorylation–mediated signaling cascade. This cascade induces actin cytoskeleton reorganization, resulting in cell spreading, adhesion, and motility. CpG-induced actin polymerization originates at the plasma membrane, rather than in endosomes. Chloroquine, an inhibitor of CpG-triggered cytokine secretion, blocked TLR9/MyD88-dependent cytokine secretion as expected but failed to inhibit CpG-induced Src family kinase activation and its dependent cellular responses. Knock down of Src family kinase expression or the use of specific kinase inhibitors blocked MyD88-dependent signaling and cytokine secretion, providing evidence that tyrosine phosphorylation is both CpG induced and an upstream requirement for the engagement of TLR9. The Src family pathway intersects the TLR9–MyD88 pathway by promoting the tyrosine phosphorylation of TLR9 and the recruitment of Syk to this receptor.

scholarly journals Hierarchical Disabled-1 Tyrosine Phosphorylation in Src family Kinase Activation and Neurite Formation

2007 ◽  
Vol 368 (2) ◽  
pp. 349-364 ◽  
Author(s):  
Sachin Katyal ◽  
Zhihua Gao ◽  
Elizabeth Monckton ◽  
Darryl Glubrecht ◽  
Roseline Godbout
Keyword(s):  
Tyrosine Phosphorylation ◽  
Src Family Kinase ◽  
Kinase Activation ◽  
Neurite Formation

The Cytokine Signal Inhibitor Lnk Promotes αIIbβ3 Integrin Outside-In Signaling through β3 Tyrosine Phosphorylation in Platelets.

Blood ◽  
2007 ◽  
Vol 110 (11) ◽  
pp. 3651-3651
Author(s):  
Koji Eto ◽  
Hitoshi Takizawa ◽  
Satoshi Takaki ◽  
Hidekazu Nishikii ◽  
Atsushi Oda ◽  
...  
Keyword(s):  
Tyrosine Phosphorylation ◽  
Tyrosine Kinases ◽  
Adaptor Protein ◽  
Sh2 Domain ◽  
Cytokine Signaling ◽  
Adapter Protein ◽  
Clot Retraction ◽  
Hematopoietic Stem ◽  
Kinase Activation ◽  
C Terminus

Abstract Lnk is an SH2 domain-containing adapter protein that inhibits cytokine signaling. Lnk−/− mice exhibit a marked increase in numbers of hematopoietic stem cells, megakaryocytes and platelets, presumably due to the lack of negative regulation in thrombopoietin-mediated signals by Lnk. We previously reported that Lnk might play an unanticipated role in platelet integrin αIIbβ3 outside-in signaling. Lnk−/− platelets exhibited defects in full spreading on fibrinogen, clot retraction and formation of thrombi on collagen under flow conditions while they showed normal inside-out signaling (Blood, 106 (11):115a, 2005). However the mechanism(s) in which Lnk participates in αIIbβ3 outside-in signaling had not been elucidated. Here we report that in normal platelets Lnk forms a complex with c-Src, Syk, Fyn and adhesion and degranulation promoting adaptor protein (ADAP) but not SLP-76 in a manner dependent on αIIbβ3 ligation and Src kinase activation. c-Src-, but not Syk-, mediated tyrosine phosphorylation of C-terminus in Lnk appeared to be indispensable for the complex formation and Lnk-mediated function. Furthermore we have shown that Lnk is required for the association of Fyn to αIIbβ3 and for β3 subunit tyrosine phosphorylation while activation of non-receptor tyrosine kinases (c-Src and Syk) in proximity to αIIbβ3 is independent of Lnk. Thus, these results provide new insights into Lnk function and the mechanism by which Lnk contributes to integrin signaling in the adhesion responses of platelets.

scholarly journals Effect of sialylation on EGFR phosphorylation and resistance to tyrosine kinase inhibition

2015 ◽  
Vol 112 (22) ◽  
pp. 6955-6960 ◽  
Author(s):  
Hsin-Yung Yen ◽  
Ying-Chih Liu ◽  
Nai-Yu Chen ◽  
Chia-Feng Tsai ◽  
Yi-Ting Wang ◽  
...  
Keyword(s):  
Lung Cancer ◽  
Tyrosine Kinase ◽  
Tyrosine Phosphorylation ◽  
Cancer Progression ◽  
Conformational Changes ◽  
Kinase Inhibitors ◽  
Growth Factor Receptor ◽  
Kinase Activation ◽  
Downstream Signaling ◽  
Egfr Mutant

Epidermal growth factor receptor (EGFR) is a heavily glycosylated transmembrane receptor tyrosine kinase. Upon EGF-binding, EGFR undergoes conformational changes to dimerize, resulting in kinase activation and autophosphorylation and downstream signaling. Tyrosine kinase inhibitors (TKIs) have been used to treat lung cancer by inhibiting EGFR phosphorylation. Previously, we demonstrated that EGFR sialylation suppresses its dimerization and phosphorylation. In this report, we further investigated the effect of sialylation on the phosphorylation profile of EGFR in TKI-sensitive and TKI-resistant cells. Sialylation was induced in cancer progression to inhibit the association of EGFR with EGF and the subsequent autophosphorylation. In the absence of EGF the TKI-resistant EGFR mutant (L858R/T790M) had a higher degree of sialylation and phosphorylation at Y1068, Y1086, and Y1173 than the TKI-sensitive EGFR. In addition, although sialylation in the TKI-resistant mutants suppresses EGFR tyrosine phosphorylation, with the most significant effect on the Y1173 site, the sialylation effect is not strong enough to stop cancer progression by inhibiting the phosphorylation of these three sites. These findings were supported further by the observation that the L858R/T790M EGFR mutant, when treated with sialidase or sialyltransferase inhibitor, showed an increase in tyrosine phosphorylation, and the sensitivity of the corresponding resistant lung cancer cells to gefitinib was reduced by desialylation and was enhanced by sialylation.

scholarly journals Ectophosphorylation of CD36 Regulates Cytoadherence of Plasmodium falciparum to Microvascular Endothelium under Flow Conditions

2005 ◽  
Vol 73 (12) ◽  
pp. 8179-8187 ◽  
Author(s):  
May Ho ◽  
Holly L. Hoang ◽  
Kristine M. Lee ◽  
Naili Liu ◽  
Tara MacRae ◽  
...  
Keyword(s):  
Plasmodium Falciparum ◽  
Kinase Inhibitors ◽  
Critical Role ◽  
Wild Type ◽  
Flow Conditions ◽  
Src Family Kinase ◽  
Microvascular Endothelium ◽  
Kinase Activation ◽  
Amino Acid Peptide ◽  
Nih 3T3

ABSTRACT The adhesion of Plasmodium falciparum-infected erythrocytes (IRBCs) to human dermal microvascular endothelial cells (HDMECs) under flow conditions is regulated by a Src family kinase- and alkaline phosphatase (AP)-dependent mechanism. In this study, we showed that the target of the phosphatase activity is the ectodomain of CD36 at threonine-92 (Thr92). Mouse fibroblasts (NIH 3T3 cells) transfected with wild-type CD36 or a mutant protein in which Thr92 was substituted by Ala supported the rolling and adhesion of IRBCs. However, while the Src family kinase inhibitors PP1 and PP2 and the specific AP inhibitor levamisole significantly reduced IRBC adhesion to wild-type CD36 transfectants as with HDMECs, the inhibitors had no effect on IRBC adhesion to the mutant cells. Using a phosphospecific antibody directed at a 12-amino-acid peptide spanning Thr92, we demonstrated directly that CD36 was constitutively phosphorylated and could be dephosphorylated by exogenous AP. Endothelial CD36 was likewise constitutively phosphorylated. The phosphospecific antibody inhibited IRBC adhesion to HDMECs that could be reversed by preincubating the antibody with the phosphorylated but not the nonphosphorylated peptide. Pretreatment of HDMECs with AP abrogated the effect of PP1 on IRBC adhesion. Collectively, these results are consistent with a critical role for CD36 dephosphorylation through Src family kinase activation in regulating IRBC adhesion to vascular endothelium.

Serine/threonine kinase activation in human neutrophils: relationship to tyrosine phosphorylation

1994 ◽  
Vol 267 (6) ◽  
pp. C1574-C1581 ◽  
Author(s):  
J. H. Brumell ◽  
S. Grinstein
Keyword(s):  
Tyrosine Phosphorylation ◽  
Kinase Activity ◽  
Kinase Inhibitors ◽  
Human Neutrophils ◽  
Serine Threonine Kinase ◽  
Kinase Activation ◽  
Threonine Kinase ◽  
Phosphorylated Proteins ◽  
Chemotactic Peptides ◽  
Threonine Kinases

Tyrosine phosphorylation is among the earliest responses of neutrophils to chemotactic peptides. Tyrosine phosphorylated proteins comigrate with serine/threonine kinases of 65 and 72 kDa (PK65 and PK72), which are activated concomitantly by the chemoattractants. Studies were designed to test whether tyrosine phosphorylation is required for activation of PK65 and PK72. Pretreatment of cells with the tyrosine kinase inhibitors erbstatin or genistein prevented both phosphotyrosine accumulation and activation of PK65 and PK72. In nondenaturing lysates, PK65 and PK72 became spontaneously inactivated in parallel with rapid endogenous tyrosine dephosphorylation. Spontaneous dephosphorylation and inactivation of PK65 and PK72 were prevented in denatured lysates. Under these conditions, dephosphorylation could be induced by exogenous phosphotyrosine phosphatase 1B. PK65 and PK72 activation persisted despite virtually complete tyrosine dephosphorylation. Moreover, immunoprecipitation experiments indicated that PK65 and PK72 are not themselves tyrosine phosphorylated. We concluded that tyrosine phosphorylation is a necessary upstream event in the activation of the serine/threonine kinases. However, once the posttranslational modification that renders PK65 and PK72 active has occurred, tyrosine phosphorylation is no longer required for maintenance of their kinase activity.

scholarly journals Maternal Ethanol Exposure Acutely Elevates Src Family Kinase Activity in the Fetal Cortex

2021 ◽  
Author(s):  
Dandan Wang ◽  
Brian W. Howell ◽  
Eric C. Olson
Keyword(s):  
Tyrosine Phosphorylation ◽  
Cortical Neurons ◽  
Molecular Mechanisms ◽  
Fetal Brain ◽  
Ethanol Exposure ◽  
Src Family Kinase ◽  
Cortical Cells ◽  
Signaling Systems ◽  
Sustained Reduction ◽  
Reelin Signaling

AbstractFetal alcohol syndrome (FAS) is characterized by disrupted fetal brain development and postnatal cognitive impairment. The targets of alcohol are diverse, and it is not clear whether there are common underlying molecular mechanisms producing these disruptions. Prior work established that acute ethanol exposure causes a transient increase in tyrosine phosphorylation of multiple proteins in cultured embryonic cortical cells. In this study, we show that a similar tyrosine phosphorylation transient occurs in the fetal brain after maternal dosing with ethanol. Using phospho-specific antibodies and immunohistochemistry, we mapped regions of highest tyrosine phosphorylation in the fetal cerebral cortex and found that areas of dendritic and axonal growth showed elevated tyrosine phosphorylation 10 min after maternal ethanol exposure. These were also areas of Src expression and Src family kinase (SFK) activation loop phosphorylation (pY416) expression. Importantly, maternal pretreatment with the SFK inhibitor dasatinib completely prevents both the pY416 increase and the tyrosine phosphorylation response. The phosphorylation response was observed in the perisomatic region and neurites of immature migrating and differentiating primary neurons. Importantly, the initial phosphotyrosine transient (~ 30 min) targets both Src and Dab1, two critical elements in Reelin signaling, a pathway required for normal cortical development. This initial phosphorylation response is followed by sustained reduction in Ser3 phosphorylation of n-cofilin, a critical actin severing protein and an identified downstream effector of Reelin signaling. This biochemical disruption is associated with sustained reduction of F-actin content and disrupted Golgi apparatus morphology in developing cortical neurons. The finding outlines a model in which the initial activation of SFKs by ethanol has the potential to disrupt multiple developmentally important signaling systems for several hours after maternal exposure.

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