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Thrombin Receptor (thrombin + receptor)
Selected AbstractsRegulation of gene expression in melanoma: New approaches for treatmentJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 1 2005Michael C. Leslie Abstract The molecular changes associated with the transition of melanoma cells from radial growth phase (RGP) to vertical growth phase (VGP, metastatic phenotype) are not yet well defined. We have demonstrated that the progression of human melanoma is associated with loss of expression of the transcription factor AP-2. In metastatic melanoma cells, this loss resulted in overexpression of MCAM/MUC18, MMP-2, the thrombin receptor (PAR-1), and lack of c-KIT expression. The transition from RGP to VGP is also associated with overexpression of the angiogenic factor IL-8. Additionally, the transition of melanoma cells from RGP to VGP is associated with overexpression of the transcription factors CREB and ATF-1, both of which may act as survival factors for human melanoma cells. Inactivation of CREB/ATF-1 activities in metastatic melanoma cells by dominant-negative CREB or by anti-ATF-1 single chain antibody fragment (ScFv), resulted in deregulation of MMP-2 and MCAM/MUC18, increased the sensitivity of melanoma cells to apoptosis, and inhibition of their tumorigenicity and metastatic potential in vivo. In this prospect article, we summarize our data on the role of AP-2 and CREB/ATF-1 in the progression of human melanoma and report on the development of new fully human antibodies anti-MCAM/MUC18 and anti-IL-8 which could serve as new modalities for the treatment of melanoma. © 2004 Wiley-Liss, Inc. [source] Thrombin and PAR-1 acitvating peptide increase iNOS expression in cytokine-stimulated C6 glioma cellsJOURNAL OF NEUROCHEMISTRY, Issue 3 2001Rosaria Meli Thrombin (THR) plays a key role in the brain under physiological and pathological conditions. Several of the biological activities of thrombin have been shown to be mainly driven through activation of protease-activated receptor-1 (PAR-1)-type thrombin receptor. Here we have studied the effect of THR and PAR-1-activating peptide (PAR1-AP), SFLLRN, on cytokine-induced expression of inducible nitric oxide (iNOS), a prominent marker of astroglial activation using the rat C6 glioma cells. In this cell line, THR (1,10 U/mL) and PAR1-AP (1,100 µm) induced a significant concentration-dependent increase both of IFN-,- (250 U/mL) or TNF-,- (500 U/mL) induced NO release. The observed increase of NO production was related to an enhancement of iNOS expression as measured in cell lysates prepared from different treatments by using SDS,PAGE followed by western blot analysis. The effect of THR, but not that of PAR1-AP, was significantly inhibited by hirulogTM (60 µg/mL), a specific and stochiometric THR inhibitor or by cathepsin-G (40 mU/mL), an inhibitor of PAR-1. In conclusion our data suggest a role for THR through activation of PAR-1 in the induction of astroglial iNOS, and further support the hypothesis that THR may function as an important pathophysiological modulator of the inflammatory response. [source] Thrombin induces neoangiogenesis in the chick chorioallantoic membraneJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2003M. Caunt Summary., Most tumors have constitutively active tissue factor on their surface, capable of generating thrombin in the surrounding environment, and thrombosis is associated with cancer. Thrombin is known to induce a malignant phenotype by enhancing tissue adhesion and cell growth in vitro and in vivo in mice. Because tumors require angiogenesis for growth, we examined whether thrombin induces neoangiogenesis in a physiologically intact in vivo model. Thrombin (0.1 U mL,1) induced neoangiogenesis in the chick chorioallantoic membrane over a 24,72-h period by approximately 2,3-fold. This was inhibited by the potent thrombin inhibitor, hirudin and shown to have its mode of action by ligation of the thrombin protease-activated receptor, PAR-1. The thrombin receptor activation peptide, SFLLRNPNDKYEPF (200 µm) also enhanced neoangiogenesis c. 2,3-fold. Thrombin-induced neoangiogenesis was accompanied by the induction of vascular endothelial growth factor (VEGF) and angiopoietin-2 (Ang-2) mRNA at 24,48 h (approximately 2-fold) as determined by semi-quantitative reverse transcriptase-polymerase chain reaction. Thrombin-induced neoangiogenesis was inhibited to baseline level by the specific angiogenesis receptor inhibitors KDR-Fc (vs. VEGF) and Tie-2-Fc (vs. Ang-1 and Ang-2), as well as the non-specific angiogenesis inhibitor thrombospondin-1. Thrombin-induced neoangiogenesis was also inhibited to baseline level by agents known to inhibit thrombin receptor signaling in other cells: G-coupled protein receptor inhibitor, pertussis toxin (40 pg per egg), protein kinase C inhibitor, bisindolylmaleimide (1 µm per egg), MAP kinase inhibitor, PD980598 (10 µm per egg) and PI3 kinase inhibitor, LY294002 (0.25 µm per egg). Thus angiogenesis is stimulated by thrombosis, which could help explain the enhancement of experimental tumorigenesis by thrombin. [source] The role of thrombin and thrombin receptors in ischemic, hemorrhagic and traumatic brain injury: deleterious or protective?JOURNAL OF NEUROCHEMISTRY, Issue 1 2003Guohua Xi Abstract In the last two decades it has become apparent that thrombin has many extravascular effects that are mediated by a family of protease-activated receptors (PARs). PAR-1, -3 and -4 are activated via cleavage by thrombin. The importance of extravascular thrombin in modulating ischemic, hemorrhagic and traumatic injury in brain has recently become clear. Thus, in vitro, thrombin at low concentration protects neurons and astrocytes from cell death caused by a number of different insults. In vivo, pretreating the brain with a low dose of thrombin (thrombin preconditioning), attenuates the brain injury induced by a large dose of thrombin, an intracerebral hemorrhage or by focal cerebral ischemia. Thrombin may also be an important mediator of ischemic preconditioning. In contrast, high doses of thrombin kill neurons and astrocytes in vitro and cause disruption of the blood,brain barrier, brain edema and seizures in vivo. This review examines the role of thrombin in brain injury and the molecular mechanisms and signaling cascades involved. [source] Thrombin induces GPIb-IX-mediated fibrin binding to ,IIb,3 in a reconstituted Chinese hamster ovary cell modelJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 10 2006D. PABÓN Summary.,Background: The interaction of thrombin with platelet glycoprotein (GP) Ib-IX-V has been recently suggested to induce fibrin-dependent platelet aggregation associated with signaling events. The approaches used to avoid the protease-activated receptor (PAR) thrombin receptors in platelets have provided controversial conclusions regarding the precise mechanism and molecules involved in the response. Objectives: In the present study, we developed a cellular model to investigate the functional consequences following the binding of thrombin to GPIb-IX. Methods: We used Chinese hamster ovary (CHO) cells stably expressing human ,IIb,3 and/or GPIb-IX complexes (CHO- ,IIb,3 -IbIX cells) to analyze the effect of thrombin on the binding of polymerizing fibrin by using fluorescein isothiocyanate-fibrinogen as precursor. Results: Thrombin induces, in a dose-dependent manner, the binding of polymerizing fibrin to CHO- ,IIb,3 -IbIX cells. This response is not observed in cells expressing only one of the receptors, and it can be blocked by monoclonal antibodies against ,IIb,3 and GPIb,. We show that the reaction is not due to simple cell trapping by the fibrin clot, and provide data supporting a role of a signaling pathway in which the 14-3-3, adaptor and calcium,calmodulin-dependent events are involved. Conclusions: The present data support a significant role of GPIb-IX and ,IIb,3 receptors in an alternative fibrin-mediated pathway of platelet activation induced by thrombin. [source] Megakaryocytes derived from human embryonic stem cells: a genetically tractable system to study megakaryocytopoiesis and integrin functionJOURNAL OF THROMBOSIS AND HAEMOSTASIS, Issue 2 2006M. GAUR Summary.,Background:,The platelet fibrinogen receptor, a heterodimer consisting of integrin subunits ,IIb and ,3, is required for platelet aggregation, spreading, and hemostasis. Platelet agonists such as thrombin and adenosine diphosphate (ADP) lead to the activation of ,IIb,3, thereby enhancing its affinity and avidity for binding fibrinogen (inside-out signaling). Furthermore, fibrinogen binding to ,IIb,3 triggers cytoskeletal changes and granule release (outside-in signaling).Aim:,Genetic approaches to characterize the molecular pathways involved in ,IIb,3 signaling are not possible with anucleate blood platelets. Therefore, we have established an OP9 stromal cell co-culture system to generate megakaryocytes from human embryonic stem cells (hESCs).Results:,,IIb,3 activation, measured by soluble fibrinogen binding to hESC-derived megakaryocytes, /GPIb,+ cells, is readily detectable following stimulation with known platelet agonists. Dose,response curves for peptide agonists specific for the two platelet thrombin receptors, protease-activated receptor 1 (PAR1) and PAR4, show a relative responsiveness that mirrors that of human platelets, and sub-maximal ADP responses are augmented by epinephrine. Moreover, hESC-derived megakaryocytes undergo lamellipodia formation, actin filament assembly, and vinculin localization at focal adhesions when plated on a fibrinogen-coated surface, characteristic of ,IIb,3 outside-in signaling. Undifferentiated hESCs genetically modified by lentiviral infection can be cloned and maintained in an undifferentiated state and then differentiated into megakaryocytes capable of ,IIb,3 activation.Conclusion:,Using hESCs, we have developed a renewable source of human megakaryocytes, and a genetically tractable system for studying megakaryocytopoiesis and ,IIb,3 signaling in the native cellular environment. [source] | ||||||||||