title: Phosphoinositide 3-kinases p110α and p110β have differential roles in insulin-like growth factor-1-mediated Akt phosphorylation and platelet priming.
abstract: OBJECTIVE
  Platelet hyperactivity is a contributing factor in the pathogenesis of cardiovascular disease and can be induced by elevated levels of circulating growth factors, such as insulin-like growth factor-1 (IGF-1). IGF-1 is a primer that cannot stimulate platelet activation by itself, but in combination with physiological stimuli can potentiate platelet functional responses via a phosphoinositide 3-kinase-dependent mechanism. In this study, we explored the role of the phosphoinositide 3-kinase p110α isoform in IGF-1-mediated enhancement of platelet function.
  
  
  RESULTS
  Using a platelet-specific p110α knockout murine model, we demonstrate that genetic deletion, similar to pharmacological inactivation of p110α, did not affect proteinase-activated receptor 4 signaling to Akt/protein kinase B but significantly reduced IGF-1-mediated Akt phosphorylation. The p110β inhibitor TGX-221 abolished IGF-1-induced Akt phosphorylation in p110α-deficient platelets, demonstrating that both p110α and p110β contribute to IGF-1-mediated Akt phosphorylation. Genetic deletion of p110α had no effect on IGF-1-mediated increases in thrombus formation on collagen and enhancement of proteinase-activated receptor 4-mediated integrin activation and α-granule secretion. In contrast, pharmacological inhibition of p110α blocked IGF-1-mediated potentiation of integrin activation and α-granule secretion. Functional enhancement by IGF-1 in p110α knockout samples was lost after TGX-221 treatment, suggesting that p110β drives priming in the absence of the p110α isoform.
  
  
  CONCLUSIONS
  Together, these results demonstrate that both p110α and p110β are involved in Akt signaling by IGF-1, but that it is the p110α isoform that is responsible for IGF-1-mediated potentiation of platelet function.
authors.affiliation: From the School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom (T.A.B., S.F.M., C.M.W., A.W.P., I.H.); and Research Department of Oncology, UCL Cancer Institute, University College London, London, United Kingdom (B.V.).
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Blair
authors.affiliation: From the School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom (T.A.B., S.F.M., C.M.W., A.W.P., I.H.); and Research Department of Oncology, UCL Cancer Institute, University College London, London, United Kingdom (B.V.).
authors.forename: Samantha F
authors.initials: SF
authors.lastname: Moore
authors.affiliation: From the School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom (T.A.B., S.F.M., C.M.W., A.W.P., I.H.); and Research Department of Oncology, UCL Cancer Institute, University College London, London, United Kingdom (B.V.).
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Williams
authors.affiliation: From the School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom (T.A.B., S.F.M., C.M.W., A.W.P., I.H.); and Research Department of Oncology, UCL Cancer Institute, University College London, London, United Kingdom (B.V.).
authors.forename: Alastair W
authors.initials: AW
authors.lastname: Poole
authors.affiliation: From the School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom (T.A.B., S.F.M., C.M.W., A.W.P., I.H.); and Research Department of Oncology, UCL Cancer Institute, University College London, London, United Kingdom (B.V.).
authors.forename: Bart
authors.initials: B
authors.lastname: Vanhaesebroeck
authors.affiliation: From the School of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom (T.A.B., S.F.M., C.M.W., A.W.P., I.H.); and Research Department of Oncology, UCL Cancer Institute, University College London, London, United Kingdom (B.V.). i.hers@bristol.ac.uk.
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Hers
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology*; D058534:Class I Phosphatidylinositol 3-Kinases; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D039421:Integrin alpha2 / Q000378:metabolism; D039661:Integrin beta3 / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D019869:Phosphatidylinositol 3-Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D015539:Platelet Activation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D018179:Receptors, Thrombin / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism; D015398:Signal Transduction; D013927:Thrombosis / Q000097:blood / Q000201:enzymology; D013997:Time Factors
chemical_list: D058534:Class I Phosphatidylinositol 3-Kinases; D007334:Insulin-Like Growth Factor I; D039421:Integrin alpha2; D039661:Integrin beta3; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D018179:Receptors, Thrombin; C546639:Pik3ca protein, mouse; C546640:Pik3cb protein, mouse; C112908:protease-activated receptor 4
keywords: blood platelets; insulin-like growth factor-1; mice; thrombosis