title: Targeting of type I protein kinase A to lipid rafts is required for platelet inhibition by the 3',5'-cyclic adenosine monophosphate-signaling pathway.
abstract: BACKGROUND
  Platelet adhesion to von Willebrand factor (VWF) is modulated by 3',5'-cyclic adenosine monophosphate (cAMP) signaling through protein kinase A (PKA)-mediated phosphorylation of glycoprotein (GP)Ibβ. A-kinase anchoring proteins (AKAPs) are proposed to control the localization and substrate specificity of individual PKA isoforms. However, the role of PKA isoforms in regulating the phosphorylation of GPIbβ and platelet response to VWF is unknown.
  
  
  OBJECTIVE
  We wished to determine the role of PKA isoforms in the phosphorylation of GPIbβ and platelet activation by VWF as a model for exploring the selective partitioning of cAMP signaling in platelets.
  
  
  RESULTS
  The two isoforms of PKA in platelets, type I (PKA-I) and type II (PKA-II), were differentially localized, with a small pool of PKA-I found in lipid rafts. Using a combination of Far Western blotting, immunoprecipitation, proximity ligation assay and cAMP pull-down we identified moesin as an AKAP that potentially localizes PKA-I to rafts. Introduction of cell-permeable anchoring disruptor peptide, RI anchoring disruptor (RIAD-Arg11 ), to block PKA-I/AKAP interactions, uncoupled PKA-RI from moesin, displaced PKA-RI from rafts and reduced kinase activity in rafts. Examination of GPIbβ demonstrated that it was phosphorylated in response to low concentrations of PGI2 in a PKA-dependent manner and occurred primarily in lipid raft fractions. RIAD-Arg11 caused a significant reduction in raft-localized phosphoGPIbβ and diminished the ability of PGI2 to regulate VWF-mediated aggregation and thrombus formation in vitro.
  
  
  CONCLUSIONS
  We propose that PKA-I-specific AKAPs in platelets, including moesin, organize a selective localization of PKA-I required for phosphorylation of GPIbβ and contribute to inhibition of platelet VWF interactions.
authors.affiliation: Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, UK.
authors.forename: Z
authors.initials: Z
authors.lastname: Raslan
authors.affiliation: Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, UK.
authors.forename: S
authors.initials: S
authors.lastname: Magwenzi
authors.affiliation: Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, UK.
authors.forename: A
authors.initials: A
authors.lastname: Aburima
authors.affiliation: Biotechnology Centre of Oslo, University of Oslo, Oslo, Norway.|K.G. Jebsen Inflammation Research Centre, University of Oslo, Oslo, Norway.|Centre for Molecular Medicine Norway, Nordic EMBL Partnership, University of Oslo and Oslo University Hospital, Oslo, Norway.|Department of Infectious Diseases, Oslo University Hospital, Oslo, Norway.
authors.forename: K
authors.initials: K
authors.lastname: Taskén
authors.affiliation: Centre for Cardiovascular and Metabolic Research, Hull York Medical School, University of Hull, Hull, UK.
authors.forename: K M
authors.initials: KM
authors.lastname: Naseem
mesh_terms: D054758:A Kinase Anchor Proteins / Q000097:blood* / Q000502:physiology; D000595:Amino Acid Sequence; D000242:Cyclic AMP / Q000502:physiology*; D054743:Cyclic AMP-Dependent Protein Kinase Type I / Q000037:antagonists & inhibitors / Q000097:blood*; D011464:Epoprostenol / Q000494:pharmacology; D006801:Humans; D021962:Membrane Microdomains / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000494:pharmacology; D010766:Phosphorylation; D010973:Platelet Adhesiveness / Q000502:physiology*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms / Q000097:blood; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D015290:Second Messenger Systems / Q000502:physiology*; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D054758:A Kinase Anchor Proteins; D008840:Microfilament Proteins; D010446:Peptide Fragments; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; D020033:Protein Isoforms; D047428:Protein Kinase Inhibitors; D014841:von Willebrand Factor; C028254:von Willebrand factor receptor; C071058:moesin; D011464:Epoprostenol; D000242:Cyclic AMP; D054743:Cyclic AMP-Dependent Protein Kinase Type I
keywords: A-kinase anchor proteins; blood platelets; cyclic AMP; glycoprotein Ib-IX complex; signal transduction