title: Differential regulation of integrin-mediated proplatelet formation and megakaryocyte spreading.
abstract: Guinea pig bone marrow megakaryocytes were cultured on a type I rat tail collagen gel which stimulated proplatelet formation. Proplatelet formation was inhibited by monoclonal antibody LM609 to the alpha v beta 3 integrin (VnR), but not by monoclonal antibodies to the alpha 5, alpha 6, beta 1, or IIb beta 3(GPIIb-IIIa) integrin proteins. Megakaryocytes cultured on a plastic surface and stimulated with thrombin undergo a spreading and an adhesion reaction. This reaction is blocked in a dose-dependent manner by the tetrapeptide RGDS and by the monoclonal antibody PG2 to the GPIIb-IIIa integrin, but not by the monoclonal antibody LM609 to the VnR. Immunoprecipitation and affinity chromatography experiments demonstrate that guinea pig megakaryocytes have distinct GPIIb-IIIa and VnR integrins with similar electrophoretic mobility. Spreading was significantly inhibited in a dose-dependent fashion by drugs which elevate cellular cyclic AMP, including forskolin, dibutyryl cAMP, and isobutylmethylxanthine. In contrast to spreading, megakaryocyte proplatelet formation was stimulated by these agents in a dose-dependent manner. Megakaryocyte spreading was stimulated by the protein kinase C (PKC) activator phorbol myristate acetate (PMA) and inhibited by the PKC inhibitors Calphostin C and K5720 in a dose-dependent manner. PKC inhibitors did not inhibit megakaryocyte proplatelet formation. These results demonstrate that the closely related VnR and GPIIb-IIIa integrins regulate different aspects of megakaryocyte morphological change and appear to be associated with different second messenger systems.
authors.affiliation: Department of Anatomy, Rush-Presbyterian-St. Lukes Medical Center, Chicago, Illinois 60612, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Leven
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology; D001792:Blood Platelets / Q000166:cytology*; D002455:Cell Division; D002478:Cells, Cultured; D006168:Guinea Pigs; D016023:Integrins / Q000276:immunology / Q000302:isolation & purification / Q000502:physiology*; D008297:Male; D008533:Megakaryocytes / Q000737:chemistry / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D016024:Receptors, Cytoadhesin / Q000302:isolation & purification; D019030:Receptors, Vitronectin; D013234:Stem Cells / Q000166:cytology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000906:Antibodies; D016023:Integrins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D016024:Receptors, Cytoadhesin; D019030:Receptors, Vitronectin; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate