title: Genetic evidence for a predominant role of PI3Kbeta catalytic activity in ITAM- and integrin-mediated signaling in platelets.
abstract: Phosphatidylinositol 3-kinase (PI3K) isoforms PI3Kbeta and PI3Kgamma are implicated in platelet adhesion, activation, and aggregation, but their relative contribution is still unclear or controversial. Here, we report the first comparative functional analysis of platelets from mice expressing a catalytically inactive form of PI3Kbeta or PI3Kgamma. We demonstrate that both isoforms were similarly required for maximal activation of the small GTPase Rap1b and for complete platelet aggregation upon stimulation of G protein-coupled receptors for adenosine 5'-diphosphate (ADP) or U46619. Their contribution to these events, however, was largely redundant and dispensable. However, PI3Kbeta, but not PI3Kgamma, enzymatic activity was absolutely required for Akt phosphorylation, Rap1 activation, and platelet aggregation downstream of the immunoreceptor tyrosine-based activation motif (ITAM)-bearing receptor glycoprotein VI (GPVI). Moreover, PI3Kbeta was a major essential regulator of platelet adhesion to fibrinogen and of integrin alpha(IIb)beta(3)-mediated spreading. These results provide genetic evidence for a crucial and selective role of PI3Kbeta in signaling through GPVI and integrin alpha(IIb)beta(3).
authors.affiliation: Department of Biochemistry, University of Pavia, via Bassi 21, Pavia, Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Canobbio
authors.forename: Lucia
authors.initials: L
authors.lastname: Stefanini
authors.forename: Lina
authors.initials: L
authors.lastname: Cipolla
authors.forename: Elisa
authors.initials: E
authors.lastname: Ciraolo
authors.forename: Cristian
authors.initials: C
authors.lastname: Gruppi
authors.forename: Cesare
authors.initials: C
authors.lastname: Balduini
authors.forename: Emilio
authors.initials: E
authors.lastname: Hirsch
authors.forename: Mauro
authors.initials: M
authors.lastname: Torti
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D020816:Amino Acid Motifs / Q000235:genetics; D000818:Animals; D001792:Blood Platelets / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D005340:Fibrinogen / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D010973:Platelet Adhesiveness / Q000187:drug effects / Q000502:physiology; D010974:Platelet Aggregation / Q000187:drug effects / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D020668:rap GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D007527:Isoenzymes; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D010980:Platelet Membrane Glycoproteins; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D014662:Vasoconstrictor Agents; C098341:platelet membrane glycoprotein VI; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D005340:Fibrinogen; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; C492136:Rap1b protein, mouse; D020668:rap GTP-Binding Proteins