TY - JOUR A1 - Dietz, Mariana S. A1 - Hasse, Daniel A1 - Ferraris, Davide M. A1 - Göhler, Antonia A1 - Niemann, Hartmut H. A1 - Heilemann, Mike T1 - Single-molecule photobleaching reveals increased MET receptor dimerization upon ligand binding in intact cells JF - BMC Biophysics N2 - Background: The human receptor tyrosine kinase MET and its ligand hepatocyte growth factor/scatter factor are essential during embryonic development and play an important role during cancer metastasis and tissue regeneration. In addition, it was found that MET is also relevant for infectious diseases and is the target of different bacteria, amongst them Listeria monocytogenes that induces bacterial uptake through the surface protein internalin B. Binding of ligand to the MET receptor is proposed to lead to receptor dimerization. However, it is also discussed whether preformed MET dimers exist on the cell membrane. Results: To address these issues we used single-molecule fluorescence microscopy techniques. Our photobleaching experiments show that MET exists in dimers on the membrane of cells in the absence of ligand and that the proportion of MET dimers increases significantly upon ligand binding. Conclusions: Our results indicate that partially preformed MET dimers may play a role in ligand binding or MET signaling. The addition of the bacterial ligand internalin B leads to an increase of MET dimers which is in agreement with the model of ligand-induced dimerization of receptor tyrosine kinases. KW - single-molecule photobleaching KW - fluorescence correlation spectroscopy KW - fluorescence KW - EGF receptor KW - rat hepatocytes KW - structural insights KW - Scatter factor KW - SEMA domain KW - hepatocyte-growth-factor KW - invasion protein-INLB KW - listeria-monocytogenes KW - tyrosine kinase KW - living cells KW - dimerization KW - MET receptor KW - Signal transduction Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121835 SN - 2046-1682 VL - 6 IS - 6 ER - TY - THES A1 - Gupta, Rohini T1 - Intracellular self-activation of the TrkB kinase domain causes FAK phosphorylation and disrupts actin filopodia dynamics T1 - Intrazelluläre Selbst-aktivierung der TrkB Kinase induziert FAK Phosphorylierung und verändert die Dynamik von Aktinfilopodien N2 - The tropomysin receptor kinase B (TrkB), the receptor for the neurotrophin brain-derived neurotrophic factor (BDNF), plays an important role in neuronal survival, neuronal differentiation, and cellular plasticity. Conventionally, TrkB activation is induced by binding of BDNF at extracellular sites and subsequent dimerization of receptor monomers. Classical Trk signaling concepts have failed to explain ligand-independent signaling of intracellular TrkB or oncogenic NTRK-fusion proteins. The intracellular activation domain of TrkB consists of a tyrosine kinase core, with three tyrosine (Y) residues at positions 701, 705 and 706, that catalyzes the phosphorylation reaction between ATPγ and tyrosine. The release of cisautoinhibition of the kinase domain activates the kinase domain and tyrosine residues outside of the catalytic domain become phosphorylated. The aim of this study was to find out how ligand-independent activation of TrkB is brought about. With the help of phosphorylation mutants of TrkB, it has been found that a high, local abundance of the receptor is sufficient to activate TrkB in a ligand-independent manner. This self-activation of TrkB was blocked when either the ATP-binding site or Y705 in the core domain was mutated. The vast majority of this self-active TrkB was found at intracellular locations and was preferentially seen in roundish cells, lacking filopodia. Live cell imaging of actin dynamics showed that self-active TrkB changed the cellular morphology by reducing actin filopodia formation. Signaling cascade analysis confirmed that self-active TrkB is a powerful activator of focal adhesion kinase (FAK). This might be the reason why self-active TrkB is able to disrupt actin filopodia formation. The signaling axis from Y705 to FAK could be mimicked by expression of the soluble, cytosolic TrkB kinase domain. However, the signaling pathway was inactive, when the TrkB kinase domain was targeted to the plasmamembrane with the help of artificial myristoylation membrane anchors. A cancer-related intracellular NTRK2-fusion protein (SQSTM1-NTRK2) also underwent constitutive kinase activation. In glioblastoma-like U87MG cells, self-active TrkB kinase reduced cell migration. These constitutive signaling pathways could be fully blocked within minutes by clinically approved, anti-tumorigenic Trk inhibitors. Moreover, this study found evidences for constitutively active, intracellular TrkB in tissue of human grade IV glioblastoma. In conclusion, the data provide an explanation and biological function for selfactive, constitutive TrkB kinase domain signaling, in the absence of a ligand. N2 - Die Rezeptortyrosinkinase TrkB, der Rezeptor für das Neurotrophin brain-derived neurotrophic factor (BDNF), spielt eine wichtige Rolle für das neuronale Überleben, die neuronale Differenzierung und die zelluläre Plastizität. Üblicherweise wird TrkB bei der Bindung von BDNF an extrazellulären Domänen durch Dimerisierung von Rezeptormonomeren aktiviert. Klassische Konzepte der Trk Signalübertragung können jedoch die Liganden-unabhängige Signalübertragung von intrazellulären TrkB- oder Onkogen-aktiven NTRK-Fusionsproteinen nicht erklären. Die intrazelluläre Aktivierungsdomäne von TrkB besitzt eine Tyrosinkinasedomäne mit drei Tyrosin (Y)-Resten an den Positionen 701, 705 und 706. Diese katalysieren die Phosphorylierungsreaktion zwischen ATPγ und Tyrosin. Durch die Enthemmung der cis-Autoinhibition wird die Kinase-Domäne aktiv und Tyrosinreste außerhalb der katalytischen Domäne werden phosphoryliert. Ziel dieser Arbeit war herauszufinden, wie es zur Liganden-unabhängigen Aktivierung von TrkB kommen kann. Mit Hilfe von TrkB-Phosphorylierungsmutanten wurde gefunden, dass eine hohe, lokale Abundanz des Rezeptors ausreicht, um TrkB Liganden-unabhängig zu aktivieren. Diese Selbstaktivierung von TrkB konnte blockiert werden, wenn entweder die ATP-bindende Domäne oder Y705 in der Kinasedomäne mutiert wurden. Die überwiegende Mehrheit dieses selbstaktivierenden TrkB wurde intrazellulär, in rundlichen Zellen ohne Filopodien, gefunden. Live-Zellbildgebung der Aktindynamik zeigte zudem, dass selbstaktives TrkB die Zellmorphologie veränderte, indem es die Bildung von Aktin-Filopodien reduzierte. Die Analyse von Signalkaskaden bestätigte, dass selbstaktives TrkB ein starker Aktivator der Focal Adhesion Kinase (FAK) ist. Dies kann der Grund sein, warum selbstaktives TrkB die Bildung von Aktin-Filopodien zerstört. Die Signalkaskade von Y705 bis FAK konnte durch Expression der löslichen, zytosolischen TrkB-Kinase-Domäne imitiert werden. Der Signalweg war jedoch inaktiv, wenn die TrkB-Kinase-Domäne durch künstliche Myristoylierung an die Plasmamembran gebunden wurde. Ein intrazelluläres NTRK2-Fusionsprotein (SQSTM1-NTRK) zeigte ebenfalls konstitutive Kinaseaktivierung. In Glioblastom-ähnlichen U87MG-Zellen reduzierte die selbstaktive TrkB-Kinase sogar die Zellwanderung. Die konstitutiven Signalwege konnten durch klinisch zugelassene, anti-tumorale Trk-Inhibitoren innerhalb von Minuten vollständig blockiert werden. Darüber hinaus zeigt diese Studie Beweise für konstitutiv-aktives, intrazelluläres TrkB im Gewebe von humanem Glioblastom Grad IV. Die Daten dieser Arbeit geben somit eine Erklärung und eine biologische Funktion für die selbst-aktive, konstitutive Signalübertragung der TrkB-Kinase-Domäne, in Abwesenheit eines Liganden. KW - TrkB KW - self-activation KW - NTRK fusions KW - tyrosine kinase KW - BDNF KW - phosphorylation KW - cancer Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-233829 ER - TY - JOUR A1 - Perrella, Gina A1 - Montague, Samantha J. A1 - Brown, Helena C. A1 - Garcia Quintanilla, Lourdes A1 - Slater, Alexandre A1 - Stegner, David A1 - Thomas, Mark A1 - Heemskerk, Johan W. M. A1 - Watson, Steve P. T1 - Role of tyrosine kinase Syk in thrombus stabilisation at high shear JF - International Journal of Molecular Sciences N2 - Understanding the pathways involved in the formation and stability of the core and shell regions of a platelet-rich arterial thrombus may result in new ways to treat arterial thrombosis. The distinguishing feature between these two regions is the absence of fibrin in the shell which indicates that in vitro flow-based assays over thrombogenic surfaces, in the absence of coagulation, can be used to resemble this region. In this study, we have investigated the contribution of Syk tyrosine kinase in the stability of platelet aggregates (or thrombi) formed on collagen or atherosclerotic plaque homogenate at arterial shear (1000 s\(^{−1}\)). We show that post-perfusion of the Syk inhibitor PRT-060318 over preformed thrombi on both surfaces enhances thrombus breakdown and platelet detachment. The resulting loss of thrombus stability led to a reduction in thrombus contractile score which could be detected as early as 3 min after perfusion of the Syk inhibitor. A similar loss of thrombus stability was observed with ticagrelor and indomethacin, inhibitors of platelet adenosine diphosphate (ADP) receptor and thromboxane A\(_2\) (TxA\(_2\)), respectively, and in the presence of the Src inhibitor, dasatinib. In contrast, the Btk inhibitor, ibrutinib, causes only a minor decrease in thrombus contractile score. Weak thrombus breakdown is also seen with the blocking GPVI nanobody, Nb21, which indicates, at best, a minor contribution of collagen to the stability of the platelet aggregate. These results show that Syk regulates thrombus stability in the absence of fibrin in human platelets under flow and provide evidence that this involves pathways additional to activation of GPVI by collagen. KW - disaggregation KW - platelet KW - Syk KW - thrombus KW - tyrosine kinase Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-284243 SN - 1422-0067 VL - 23 IS - 1 ER - TY - JOUR A1 - Pils, Stefan A1 - Kopp, Kathrin A1 - Peterson, Lisa A1 - Tascon, Julia Delgado A1 - Nyffenegger-Jann, Naja J. A1 - Hauck, Christof R. T1 - The Adaptor Molecule Nck Localizes the WAVE Complex to Promote Actin Polymerization during CEACAM3-Mediated Phagocytosis of Bacteria JF - PLoS One N2 - Background: CEACAM3 is a granulocyte receptor mediating the opsonin-independent recognition and phagocytosis of human-restricted CEACAM-binding bacteria. CEACAM3 function depends on an intracellular immunoreceptor tyrosine-based activation motif (ITAM)-like sequence that is tyrosine phosphorylated by Src family kinases upon receptor engagement. The phosphorylated ITAM-like sequence triggers GTP-loading of Rac by directly associating with the guanine nucleotide exchange factor (GEF) Vav. Rac stimulation in turn is critical for actin cytoskeleton rearrangements that generate lamellipodial protrusions and lead to bacterial uptake. Principal Findings: In our present study we provide biochemical and microscopic evidence that the adaptor proteins Nck1 and Nck2, but not CrkL, Grb2 or SLP-76, bind to tyrosine phosphorylated CEACAM3. The association is phosphorylation-dependent and requires the Nck SH2 domain. Overexpression of the isolated Nck1 SH2 domain, RNAi-mediated knock-down of Nck1, or genetic deletion of Nck1 and Nck2 interfere with CEACAM3-mediated bacterial internalization and with the formation of lamellipodial protrusions. Nck is constitutively associated with WAVE2 and directs the actin nucleation promoting WAVE complex to tyrosine phosphorylated CEACAM3. In turn, dominant-negative WAVE2 as well as shRNA-mediated knock-down of WAVE2 or the WAVE-complex component Nap1 reduce internalization of bacteria. Conclusions: Our results provide novel mechanistic insight into CEACAM3-initiated phagocytosis. We suggest that the CEACAM3 ITAM-like sequence is optimized to co-ordinate a minimal set of cellular factors needed to efficiently trigger actin-based lamellipodial protrusions and rapid pathogen engulfment. KW - activation KW - neisseria gonorrhoeae KW - human pathogens KW - T cell KW - signal transduction KW - escherichia coli KW - epithelial cells KW - tyrosine kinase KW - receptor KW - adhesion Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-131747 VL - 7 IS - 3 ER -