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Aaron A Cook, Wei Deng, Jinqi Ren, Renhao Li, John Sondek, Wolfgang Bergmeier
Platelets are recruited to sites of vascular injury, where they are activated and aggregate to form a hemostatic plug. This process requires the activation of the small GTPase Rap1B by its cognate guanine nucleotide exchange factor CalDAG-GEFI. Studies on platelet function suggest that CalDAG-GEFI activity is regulated by changes in cytosolic calcium, but the exact molecular mechanism is poorly understood. Here we show that purified CalDAG-GEFI is autoinhibited and directly regulated by calcium. Substitutions of putative calcium-binding residues within the canonical EF hands of CalDAG-GEFI diminish its capacity to activate Rap1B...
June 1, 2018: Journal of Biological Chemistry
Teresa Sevivas, José María Bastida, David S Paul, Eva Caparros, Verónica Palma-Barqueros, Margarida Coucelo, Dalila Marques, Francisca Ferrer-Marín, José Ramón González-Porras, Vicente Vicente, Jesús María Hernández-Rivas, Steve P Watson, María Luisa Lozano, Wolfgang Bergmeier, José Rivera
The RASGRP2 gene encodes the Ca2+ and DAG-regulated guanine nucleotide exchange factor I (CalDAG-GEFI), which plays a key role in integrin activation in platelets and neutrophils. We here report two new RASGRP2 variants associated with platelet dysfunction and bleeding in patients. The homozygous patients had normal platelet and neutrophil counts and morphology. Platelet phenotyping showed: prolonged PFA-100 closure times; normal expression of major glycoprotein receptors; severely reduced platelet aggregation response to ADP and collagen (both patients); aggregation response to PAR1 and arachidonic acid markedly impaired in one patient; PMA-induced aggregation unaffected; platelet secretion, clot retraction, and spreading minimally affected...
March 2018: Platelets
Emilse Bermejo, Maria F Alberto, David S Paul, Aaron A Cook, Paquita Nurden, Analia Sanchez Luceros, Alan T Nurden, Wolfgang Bergmeier
Congenital platelet function disorders are often the result of defects in critical signal transduction pathways required for platelet adhesion and clot formation. Mutations affecting RASGRP2, the gene encoding the Rap GTPase activator, CalDAG-GEFI, give rise to a novel, and rare, group of platelet signal transduction abnormalities. We here report platelet function studies for two brothers (P1 and P2) expressing a novel variant of RASGRP2, CalDAG-GEFI(p.Gly305Asp). P1 and P2 have a lifelong history of bleeding with severe epistaxis successfully treated with platelet transfusions or rFVIIa...
January 2018: Platelets
Jana Niemz, Stefanie Kliche, Marina C Pils, Eliot Morrison, Annika Manns, Christian Freund, Jill R Crittenden, Ann M Graybiel, Melanie Galla, Lothar Jänsch, Jochen Huehn
Using quantitative phosphopeptide sequencing of unstimulated versus stimulated primary murine Foxp3(+) regulatory and Foxp3(-) conventional T cells (Tregs and Tconv, respectively), we detected a novel and differentially regulated tyrosine phosphorylation site within the C1 domain of the guanine-nucleotide exchange factor CalDAG GEFI. We hypothesized that the Treg-specific and activation-dependent reduced phosphorylation at Y523 allows binding of CalDAG GEFI to diacylglycerol, thereby impacting the formation of a Treg-specific immunological synapse...
June 2017: European Journal of Microbiology & Immunology
Sarah K Westbury, Matthias Canault, Daniel Greene, Emilse Bermejo, Katharine Hanlon, Michele P Lambert, Carolyn M Millar, Paquita Nurden, Samya G Obaji, Shoshana Revel-Vilk, Chris Van Geet, Kate Downes, Sofia Papadia, Salih Tuna, Christopher Watt, Kathleen Freson, Michael A Laffan, Willem H Ouwehand, Marie-Christine Alessi, Ernest Turro, Andrew D Mumford
Heritable platelet function disorders (PFDs) are genetically heterogeneous and poorly characterized. Pathogenic variants in RASGRP2 , which encodes calcium and diacylglycerol-regulated guanine exchange factor I (CalDAG-GEFI), have been reported previously in 3 pedigrees with bleeding and reduced platelet aggregation responses. To better define the phenotype associated with pathogenic RASGRP2 variants, we compared high-throughput sequencing and phenotype data from 2042 cases in pedigrees with unexplained bleeding or platelet disorders to data from 5422 controls...
August 24, 2017: Blood
Florian Beck, Jörg Geiger, Stepan Gambaryan, Fiorella A Solari, Margherita Dell'Aica, Stefan Loroch, Nadine J Mattheij, Igor Mindukshev, Oliver Pötz, Kerstin Jurk, Julia M Burkhart, Christian Fufezan, Johan W M Heemskerk, Ulrich Walter, René P Zahedi, Albert Sickmann
Adenosine diphosphate (ADP) enhances platelet activation by virtually any other stimulant to complete aggregation. It binds specifically to the G-protein-coupled membrane receptors P2Y1 and P2Y12, stimulating intracellular signaling cascades, leading to integrin αIIbβ3 activation, a process antagonized by endothelial prostacyclin. P2Y12 inhibitors are among the most successful antiplatelet drugs, however, show remarkable variability in efficacy. We reasoned whether a more detailed molecular understanding of ADP-induced protein phosphorylation could identify (1) critical hubs in platelet signaling toward aggregation and (2) novel molecular targets for antiplatelet treatment strategies...
January 12, 2017: Blood
Hisashi Kato, Yozo Nakazawa, Yumi Kurokawa, Hirokazu Kashiwagi, Yoichiro Morikawa, Daisuke Morita, Fumiaki Banno, Shigenori Honda, Yuzuru Kanakura, Yoshiaki Tomiyama
Affinity regulation of integrin αIIbβ3 for fibrinogen by inside-out signaling plays a critical role in hemostasis. Calcium and diacylglycerol (DAG)-regulated guanine nucleotide exchange factor I (CalDAG-GEFI) was identified as a Rap1-activating molecule, and its role in inside-out αIIbβ3 activation was established in CalDAG-GEFI-deficient mice. However, little information regarding CalDAG-GEFI in human platelets is available. Here, we report a 16-year-old girl with CalDAG-GEFI deficiency who has been suffering from severe bleeding tendency...
December 8, 2016: Blood
Marco Cattaneo
No abstract text is available yet for this article.
September 1, 2016: Blood
Raymond Piatt, David S Paul, Robert H Lee, Steven E McKenzie, Leslie V Parise, Dale O Cowley, Brian C Cooley, Wolfgang Bergmeier
OBJECTIVE: The tight regulation of platelet adhesiveness, mediated by the αIIbβ3 integrin, is critical for hemostasis and prevention of thrombosis. We recently demonstrated that integrin affinity in platelets is controlled by the guanine nucleotide exchange factor, CalDAG-GEFI (CD-GEFI), and its target, RAP1. In this study, we investigated whether low-level expression of CD-GEFI leads to protection from thrombosis without pathological bleeding in mice. APPROACH AND RESULTS: Cdg1(low) mice were generated by knockin of human CD-GEFI cDNA into the mouse Cdg1 locus...
September 2016: Arteriosclerosis, Thrombosis, and Vascular Biology
Annette Artz, Stefan Butz, Dietmar Vestweber
Growth differentiation factor 15 (GDF-15) is the first cytokine known to counteract chemokine-induced activation of leukocyte integrins. We showed recently that this activity dampens neutrophil recruitment into inflamed tissue and is required for survival of myocardial infarction in mice. The receptor responsible for this GDF-15-triggered anti-inflammatory mechanism on myeloid cells is not known. Here, we identify this receptor as transforming growth factor β receptor I (TGF-βRI) (activin receptor-like kinase 5 [ALK-5]) and TGF-β receptor II (TGF-βRII)...
July 28, 2016: Blood
María Luisa Lozano, Aaron Cook, José María Bastida, David S Paul, Gemma Iruin, Ana Rosa Cid, Rosa Adan-Pedroso, José Ramón González-Porras, Jesús María Hernández-Rivas, Sarah J Fletcher, Ben Johnson, Neil Morgan, Francisca Ferrer-Marin, Vicente Vicente, John Sondek, Steve P Watson, Wolfgang Bergmeier, José Rivera
In addition to mutations in ITG2B or ITGB3 genes that cause defective αIIbβ3 expression and/or function in Glanzmann's thrombasthenia patients, platelet dysfunction can be a result of genetic variability in proteins that mediate inside-out activation of αIIbβ3 The RASGRP2 gene is strongly expressed in platelets and neutrophils, where its encoded protein CalDAG-GEFI facilitates the activation of Rap1 and subsequent activation of integrins. We used next-generation sequencing (NGS) and whole-exome sequencing (WES) to identify 2 novel function-disrupting mutations in RASGRP2 that account for bleeding diathesis and platelet dysfunction in 2 unrelated families...
September 1, 2016: Blood
Pete W Christopherson, Eric A Alexander, Kevin B King, Mary K Boudreaux
A 3-month-old female Basset Hound-Shar Pei mix puppy (Ba-Shar or Sharp Asset) presented with oral bleeding due to a cracked molar. On physical exam, an aural hematoma was also noted that the owner indicated was chronic. The puppy was hospitalized for over 24 h until the bleeding was brought under control. At 4 months of age, the puppy again presented with oral bleeding due to loss of deciduous teeth and was hospitalized until bleeding was controlled. Coagulation screening tests, platelet numbers, and von Willebrand Factor antigen levels were within reference limits...
June 2016: Veterinary Clinical Pathology
Yacine Boulaftali, A Phillip Owens, Ashley Beale, Raymond Piatt, Caterina Casari, Robert H Lee, Pamela B Conley, David S Paul, Nigel Mackman, Wolfgang Bergmeier
OBJECTIVE: Platelets are important for the development and progression of atherosclerotic lesions. However, relatively little is known about the contribution of platelet signaling to this pathological process. Our recent work identified 2 independent, yet synergistic, signaling pathways that lead to the activation of the small GTPase Rap1; one mediated by the guanine nucleotide exchange factor, CalDAG-GEFI (CDGI), the other by P2Y12, a platelet receptor for adenosine diphosphate and the target of antiplatelet drugs...
May 2016: Arteriosclerosis, Thrombosis, and Vascular Biology
Lucia Stefanini, Wolfgang Bergmeier
Platelets are critical for hemostasis, i.e., the body's ability to prevent blood loss at sites of vascular injury. They patrol the vasculature in a quiescent, non-adhesive state for approximately 10 days, after which they are removed from circulation by phagocytic cells of the reticulo-endothelial system. At sites of vascular injury, they promptly shift to an activated, adhesive state required for the formation of a hemostatic plug. The small GTPase RAP1 is a critical regulator of platelet adhesiveness. Our recent studies demonstrate that the antagonistic balance between the RAP1 regulators, CalDAG-GEFI and RASA3, is critical for the modulation of platelet adhesiveness, both in circulation and at sites of vascular injury...
January 2016: Journal of Molecular Medicine: Official Organ of the "Gesellschaft Deutscher Naturforscher und Ärzte"
Michele P Lambert
PURPOSE OF REVIEW: The inherited platelet disorders have witnessed a surge in our understanding of molecular mechanisms of disease in the past few years due in large to part to the introduction of next-generation sequencing for discovery of novel genes. The purpose of this review is to update the reader on the novel discoveries with regard to the inherited platelet disorders, with a particular focus on describing the novel disorders described most recently. RECENT FINDINGS: The description of novel mechanisms of disease including mutations in PRKACG, in a family with severe macrothrombocytopenia, RUNX1 and FLI1 mutations in patients with inherited mild platelet function disorders and CalDAG-GEFI resulting in a severe platelet bleeding phenotype show that there is still much to be learned from studying families and molecular sequencing of patients with well phenotyped platelet disorders...
September 2015: Current Opinion in Hematology
A T Nurden, P Nurden
The gene variants responsible for the primary genotype of many platelet disorders have now been identified. Next-generation sequencing technology (NGST), mainly exome sequencing, has highlighted genes responsible for defects in platelet secretion (NBEAL2, gray platelet syndrome), procoagulant activity (STIM1, Stormorken syndrome), and activation pathways (RASGRP2, CalDAG-GEFI deficiency and integrin dysfunction; PRKACG, cyclic adenosine monophosphate-dependent protein kinase deficiency). Often disorders of platelet function are associated with a modified platelet production with changes in platelet number and size and can accompany malfunction of other organs or tissues...
June 2015: Journal of Thrombosis and Haemostasis: JTH
Lucia Stefanini, David S Paul, Raymond F Robledo, E Ricky Chan, Todd M Getz, Robert A Campbell, Daniel O Kechele, Caterina Casari, Raymond Piatt, Kathleen M Caron, Nigel Mackman, Andrew S Weyrich, Matthew C Parrott, Yacine Boulaftali, Mark D Adams, Luanne L Peters, Wolfgang Bergmeier
The small GTPase RAP1 is critical for platelet activation and thrombus formation. RAP1 activity in platelets is controlled by the GEF CalDAG-GEFI and an unknown regulator that operates downstream of the adenosine diphosphate (ADP) receptor, P2Y12, a target of antithrombotic therapy. Here, we provide evidence that the GAP, RASA3, inhibits platelet activation and provides a link between P2Y12 and activation of the RAP1 signaling pathway. In mice, reduced expression of RASA3 led to premature platelet activation and markedly reduced the life span of circulating platelets...
April 2015: Journal of Clinical Investigation
Chieh-Yu Liao, Chia-Lin Lee, Hui-Chun Wang, Shih-Shin Liang, Po-Hsiung Kung, Yang-Chang Wu, Fang-Rong Chang, Chin-Chung Wu
CalDAG-GEFI is a guanine nucleotide exchange factor, which actives small GTPase Rap1 and plays an important role in platelet aggregation. Our previous study has shown that CalDAG-GEFI contains redox-sensitive thiols, and its function can be inhibited by thiol modification. In the present study, the effect of CLL2-1, a 1,4-phenanthrenequinone, on CalDAG-GEFI and platelet functions was investigated. In human platelets, CLL2-1 prevented platelet aggregation caused by various stimulators. Flow cytometric analysis revealed that CLL2-1 inhibited GPIIb/IIIa activation and P-selectin secretion...
January 2015: Free Radical Biology & Medicine
A Amirkhosravi, Y Boulaftali, L Robles-Carrillo, T Meyer, S E McKenzie, J L Francis, W Bergmeier
INTRODUCTION: Platelet activation via the Fcγ receptor IIa (FcγRIIa) is implicated in the pathogenesis of immune complex (IC)-mediated thrombocytopenia and thrombosis (ITT). We previously showed that ICs composed of antigen and antibodies targeting CD40 ligand (CD40L) or β2 Glycoprotein I (β2GPI) induce ITT in mice transgenic for human FcγRIIa (hFcR) but not wild-type controls (which lack FcγRIIa). Here we evaluated the contribution of the guanine nucleotide exchange factor, CalDAG-GEFI, and P2Y12, key regulators of Rap1 signaling in platelets, to ITT induced by these clinically relevant ICs...
December 2014: Journal of Thrombosis and Haemostasis: JTH
John C Gomez, Mitsuhiro Yamada, Jessica R Martin, Hong Dang, W June Brickey, Wolfgang Bergmeier, Mary C Dinauer, Claire M Doerschuk
Bacterial pneumonia is a common public health problem associated with significant mortality, morbidity, and cost. Neutrophils are usually the earliest leukocytes to respond to bacteria in the lungs. Neutrophils rapidly sequester in the pulmonary microvasculature and migrate into the lung parenchyma and alveolar spaces, where they perform numerous effector functions for host defense. Previous studies showed that migrated neutrophils produce IFN-γ early during pneumonia induced by Streptococcus pneumoniae and that early production of IFN-γ regulates bacterial clearance...
March 2015: American Journal of Respiratory Cell and Molecular Biology
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