title: Impaired thromboxane receptor dimerization reduces signaling efficiency: A potential mechanism for reduced platelet function in vivo.
abstract: Thromboxane A2is a potent mediator of inflammation and platelet aggregation exerting its effects through the activation of a G protein-coupled receptor (GPCR), termed TP. Although the existence of dimers/oligomers in Class A GPCRs is widely accepted, their functional significance still remains controversial. Recently, we have shown that TPα and TPβ homo-/hetero-dimers interact through an interface of residues in transmembrane domain 1 (TM1) whose disruption impairs dimer formation. Here, biochemical and pharmacological characterization of this dimer deficient mutant (DDM) in living cells indicates a significant impairment in its response to agonists. Interestingly, two single loss-of-function TPα variants, namely W29C and N42S recently identified in two heterozygous patients affected by bleeding disorders, match some of the residues mutated in our DDM. These two naturally occurring variants display a reduced potency to TP agonists and are characterized by impaired dimer formation in transfected HEK-293T cells. These findings provide proofs that lack of homo-dimer formation is a crucial process for reduced TPα function in vivo, and might represent one molecular mechanism through which platelet TPα receptor dysfunction affects the patient(s) carrying these mutations.
authors.affiliation: Department of Pharmacological and Biomolecular Sciences, University of Milan, Milano, Italy; Department of Health Science, University of Milan, Milano, Italy. Electronic address: Valerie.Capra@unimi.it.
authors.forename: Valérie
authors.initials: V
authors.lastname: Capra
authors.affiliation: Department of Medicine and Surgery, University of Milano-Bicocca, Monza, Italy. Electronic address: mario.mauri@unimib.it.
authors.forename: Mario
authors.initials: M
authors.lastname: Mauri
authors.affiliation: Department of Medicine and Surgery, University of Milano-Bicocca, Monza, Italy. Electronic address: francesca.guzzi@unimib.it.
authors.forename: Francesca
authors.initials: F
authors.lastname: Guzzi
authors.affiliation: CNR, Institute of Neuroscience, University of Milan, Milan, Italy; Department of Medical Biotechnology and Translational Medicine, University of Milan, Milan, Italy. Electronic address: m.busnelli@in.cnr.com.
authors.forename: Marta
authors.initials: M
authors.lastname: Busnelli
authors.affiliation: Department of Pharmacological and Biomolecular Sciences, University of Milan, Milano, Italy. Electronic address: Maria.Accomazzo@unimi.it.
authors.forename: Maria Rosa
authors.initials: MR
authors.lastname: Accomazzo
authors.affiliation: Inserm UMR-S1140, Faculte' de Pharmacie, Université Paris Descartes, Sorbonne Paris Cité, Paris and AP-HP, Hopital Européen Georges Pompidou, Service d'Hématologie Biologique, Paris, France. Electronic address: pascale.gaussem@univ-paris5.fr.
authors.forename: Pascale
authors.initials: P
authors.lastname: Gaussem
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol BS8 1TD, UK. Electronic address: shaista.nisar@bristol.ac.uk.
authors.forename: Shaista P
authors.initials: SP
authors.lastname: Nisar
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol BS8 1TD, UK. Electronic address: s.j.mundell@bristol.ac.uk.
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Mundell
authors.affiliation: Department of Medicine and Surgery, University of Milano-Bicocca, Monza, Italy. Electronic address: marco.parenti@unimib.it.
authors.forename: Marco
authors.initials: M
authors.lastname: Parenti
authors.affiliation: Department of Pharmacological and Biomolecular Sciences, University of Milan, Milano, Italy. Electronic address: Genrico.Rovati@unimi.it.
authors.forename: G Enrico
authors.initials: GE
authors.lastname: Rovati
mesh_terms: D001792:Blood Platelets / Q000502:physiology*; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006801:Humans; D008024:Ligands; D009154:Mutation; D017482:Receptors, Thromboxane / Q000819:agonists / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D008024:Ligands; D017482:Receptors, Thromboxane
keywords: (Z)-7-[(1R,2R,3R,4S)-3-[[2-(phenylcarbamoyl)hydrazinyl]methyl]-7-oxabicyclo[2.2.1]heptan-2-yl]hept-5-enoic acid; (Z)-7-[(1S,2S,3R,4R)-3-[(E,3S)-3-hydroxyoct-1-enyl]-5-oxabicyclo[2.2.1]heptan-2-yl]hept-5-enoic acid; (Z)-7-[(1S,2S,3S,4R)-3-[(E,3R)-3-hydroxy-4-(4-iodophenoxy)but-1-enyl]-7-oxabicyclo[2.2.1]heptan-2-yl]hept-5-enoic acid; (Z)-7-[(1S,3R,4R,5S)-3-[(E,3R)-3-hydroxyoct-1-enyl]-6,6-dimethyl-4-bicyclo[3.1.1]heptanyl]hept-5-enoic acid; 3-[(3R)-3-[(4-fluorophenyl)sulfonylamino]-1,2,3,4-tetrahydrocarbazol-9-yl]propanoic acid; Eicosanoids; G protein coupled receptors; I-BOP (PubChem CID: 51015454); Pinane Thromboxane A2 (PTA2) (PubChem CID: 25834471); Platelets; Ramatroban (PubChem CID: 123879); Receptor dimer; SQ29,548 (PubChem CID: 6437074); Signal transduction; Thromboxane A(2); U46619 (PubChem CID: 5311493)