title: Integrin-dependent translocation of phosphoinositide 3-kinase to the cytoskeleton of thrombin-activated platelets involves specific interactions of p85 alpha with actin filaments and focal adhesion kinase.
abstract: Thrombin-induced accumulation of phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P2) but not of PtdIns(3,4,5,)P3 is strongly correlated with the relocation to the cytoskeleton of 29% of the p85 alpha regulatory subunit of phosphoinositide 3-kinase (PtdIns 3-kinase) and is accompanied by a significant increase in PtdIns 3-kinase activity in this subcellular fraction. Actually, PtdIns(3,4)P2 accumulation and PtdIns 3-kinase, pp60c-src, and p125FAK translocations as well as aggregation were concomitant events occurring with a distinct lag after actin polymerization. The accumulation of PtdIns(3,4)P2 and the relocalization of PtdIns 3-kinase to the cytoskeleton were both dependent on tyrosine phosphorylation, integrin signaling, and aggregation. Furthermore, although p85 alpha was detected in anti-phosphotyrosine immunoprecipitates obtained from the cytoskeleton of thrombin-activated platelets, we failed to demonstrate tyrosine phosphorylation of cytoskeletal p85 alpha. Tyrphostin treatment clearly reduced its presence in this subcellular fraction, suggesting a physical interaction of p85 alpha with a phosphotyrosyl protein. These data led us to investigate the proteins that are able to interact with PtdIns 3-kinase in the cytoskeleton. We found an association of this enzyme with actin filaments: this interaction was spontaneously restored after one cycle of actin depolymerization-repolymerization in vitro. This association with F-actin appeared to be at least partly indirect, since we demonstrated a thrombin-dependent interaction of p85 alpha with a proline-rich sequence of the tyrosine-phosphorylated cytoskeletal focal adhesion kinase, p125FAK. In addition, we show that PtdIns 3-kinase is significantly activated by the p125FAK proline-rich sequence binding to the src homology 3 domain of p85 alpha subunit. This interaction may represent a new mechanism for PtdIns 3-kinase activation at very specific areas of the cell and indicates that the focal contact-like areas linked to the actin filaments play a critical role in signaling events that occur upon ligand engagement of alpha IIb/beta 3 integrin and platelet aggregation evoked by thrombin.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale, Unité 326, Hôpital Purpan, Toulouse, France.
authors.forename: C
authors.initials: C
authors.lastname: Guinebault
authors.forename: B
authors.initials: B
authors.lastname: Payrastre
authors.forename: C
authors.initials: C
authors.lastname: Racaud-Sultan
authors.forename: H
authors.initials: H
authors.lastname: Mazarguil
authors.forename: M
authors.initials: M
authors.lastname: Breton
authors.forename: G
authors.initials: G
authors.lastname: Mauco
authors.forename: M
authors.initials: M
authors.lastname: Plantavid
authors.forename: H
authors.initials: H
authors.lastname: Chap
mesh_terms: D008841:Actin Cytoskeleton / Q000502:physiology; D000199:Actins / Q000378:metabolism; D030161:Avian Proteins; D001692:Biological Transport; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002451:Cell Compartmentation; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003599:Cytoskeleton / Q000502:physiology*; D004789:Enzyme Activation; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D016023:Integrins / Q000378:metabolism; D009097:Multienzyme Complexes / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D015539:Platelet Activation / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D013917:Thrombin / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
chemical_list: D000199:Actins; D030161:Avian Proteins; D015815:Cell Adhesion Molecules; D003598:Cytoskeletal Proteins; D016023:Integrins; D009097:Multienzyme Complexes; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C071033:cytoskeletal p85 protein, chicken; D014443:Tyrosine; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D016392:Proto-Oncogene Proteins pp60(c-src); D013917:Thrombin