title: The small GTPase Rap1 is activated by turbulence and is involved in integrin [alpha]IIb[beta]3-mediated cell adhesion in human megakaryocytes.
abstract: The small GTPase Rap1, which is activated by a large variety of stimuli, functions in the control of integrin-mediated cell adhesion. Here we show that in human megakaryocytes and several other commonly used hematopoietic cell lines such as K562, Jurkat, and THP-1, stress induced by gentle tumbling of the samples resulted in rapid and strong activation of Rap1. This turbulence-induced activation could not be blocked by inhibitors previously shown to affect Rap1 activation in human platelets, such as the intracellular calcium chelator BAPTA-AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) and various protein kinase C inhibitors. Also inhibition of actin cytoskeleton dynamics did not influence this activation of Rap1, suggesting that this activation is mediated by cell surface receptors. Human platelets, however, were refractory to turbulence-induced activation of Rap1. To determine the consequences of Rap1 activation we measured adhesion of megakaryocytes to fibrinogen, which is mediated by the integrin alphaIIbbeta3, in the presence of inhibitors of Rap1 signaling. Introduction of both Rap1GAP and RalGDS-RBD in the megakaryoblastic cell line DAMI strongly reduced basal adhesion to immobilized fibrinogen. This inhibition was partially rescued by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate but not by alpha-thrombin. From these results we conclude that in megakaryocytes turbulence induces Rap1 activation that controls alphaIIbbeta3-mediated cell adhesion.
authors.affiliation: Department of Physiological Chemistry, University Medical Center, Utrecht, The Netherlands.
authors.forename: Kim M T
authors.initials: KM
authors.lastname: de Bruyn
authors.forename: Fried J T
authors.initials: FJ
authors.lastname: Zwartkruis
authors.forename: Johan
authors.initials: J
authors.lastname: de Rooij
authors.forename: Jan-Willem N
authors.initials: JW
authors.lastname: Akkerman
authors.forename: Johannes L
authors.initials: JL
authors.lastname: Bos
mesh_terms: D001792:Blood Platelets / Q000502:physiology*; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005340:Fibrinogen / Q000502:physiology*; D006801:Humans; D019169:Jurkat Cells; D020014:K562 Cells; D008533:Megakaryocytes / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000502:physiology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013314:Stress, Mechanical; D014162:Transfection; D014407:Tumor Cells, Cultured; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D002614:Chelating Agents; D004791:Enzyme Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011994:Recombinant Proteins; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D005340:Fibrinogen; D011493:Protein Kinase C; D020827:rap1 GTP-Binding Proteins