title: Heterodimerization with the prostacyclin receptor triggers thromboxane receptor relocation to lipid rafts.
abstract: OBJECTIVE
  Prostacyclin and thromboxane mediate opposing cardiovascular actions through receptors termed IP and TP, respectively. When dimerized with IP, the TP shifts to IP-like function. IP localizes to cholesterol-enriched membrane rafts, but TP and IPTP heterodimer localization is not defined. We examined these receptors' membrane localization and the role of rafts in receptor function.
  
  
  RESULTS
  Microdomain distribution of IP, TP, and IPTP heterodimers was examined in COS-7 cells by measuring energy transfer from renilla luciferase-fused receptors to fluorescently labeled rafts. IP raft association was confirmed. TP was raft excluded, but redistributed to rafts upon dimerization with IP. Signaling of the IP and IPTP heterodimer, but not TP alone, was suppressed after raft disruption by cholesterol depletion. Cholesterol enrichment also selectively suppressed IP and IPTP function. Native IP and IPTP signaling in smooth muscle cells and macrophages were similarly sensitive to cholesterol manipulation, whereas macrophages from hypercholesterolemic mice displayed suppressed IP and IPTP function.
  
  
  CONCLUSIONS
  IP and TP function within distinct microdomains. Raft incorporation of TP in the IPTP heterodimer likely facilitates its signaling shift. We speculate that changes in IP and IPTP signaling after perturbation of membrane cholesterol may contribute to cardiovascular disease associated with hypercholesterolemia.
authors.affiliation: Institute for Translational Medicine, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Salam
authors.initials: S
authors.lastname: Ibrahim
authors.forename: Ann
authors.initials: A
authors.lastname: McCartney
authors.forename: Nune
authors.initials: N
authors.lastname: Markosyan
authors.forename: Emer M
authors.initials: EM
authors.lastname: Smyth
mesh_terms: D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D002784:Cholesterol / Q000172:deficiency; D000242:Cyclic AMP / Q000378:metabolism; D019281:Dimerization; D004195:Disease Models, Animal; D005260:Female; D031541:Fluorescence Resonance Energy Transfer; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D006801:Humans; D006937:Hypercholesterolemia / Q000378:metabolism; D049410:Luciferases, Renilla / Q000235:genetics / Q000378:metabolism; D017737:Macrophages, Peritoneal / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism*; D051379:Mice; D032389:Myocytes, Smooth Muscle / Q000378:metabolism; D021381:Protein Transport; D044006:Receptors, Epoprostenol; D011982:Receptors, Prostaglandin / Q000235:genetics / Q000378:metabolism*; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
chemical_list: C113936:PTGIR protein, human; D044006:Receptors, Epoprostenol; D011982:Receptors, Prostaglandin; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D011993:Recombinant Fusion Proteins; D002784:Cholesterol; D000242:Cyclic AMP; D049410:Luciferases, Renilla; D019205:GTP-Binding Protein alpha Subunits, Gs