title: Biased suppression of TP homodimerization and signaling through disruption of a TM GxxxGxxxL helical interaction motif.
abstract: Thromboxane A2 (TXA2) contributes to cardiovascular disease (CVD) by activating platelets and vascular constriction and proliferation. Despite their preclinical efficacy, pharmacological antagonists of the TXA2 receptor (TP), a G protein-coupled receptor, have not been clinically successful, raising interest in novel approaches to modifying TP function. We determined that disruption of a GxxxGxxxL helical interaction motif in the human TP's (α isoform) fifth transmembrane (TM) domain suppressed TP agonist-induced Gq signaling and TPα homodimerization, but not its cell surface expression, ligand affinity, or Gq association. Heterodimerization of TPα with the functionally opposing prostacyclin receptor (IP) shifts TPα to signal via the IP-Gs cascade contributing to prostacyclin's restraint of TXA2 function. Interestingly, disruption of the TPα-TM5 GxxxGxxxL motif did not modify either IP-TPα heterodimerization or its Gs-cAMP signaling. Our study indicates that distinct regions of the TPα receptor direct its homo- and heterodimerization and that homodimerization is necessary for normal TPα-Gq activation. Targeting the TPα-TM5 GxxxGxxxL domain may allow development of biased TPα homodimer antagonists that avoid suppression of IP-TPα heterodimer function. Such novel therapeutics may prove superior in CVD compared with nonselective suppression of all TP functions with TXA2 biosynthesis inhibitors or TP antagonists.
authors.affiliation: University of Pennsylvania Institute for Translational Medicine and Therapeutics, Smilow Center for Translational Research, Philadelphia, PA; and.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Frey
authors.affiliation: University of Pennsylvania Institute for Translational Medicine and Therapeutics, Smilow Center for Translational Research, Philadelphia, PA; and.
authors.forename: Salam
authors.initials: S
authors.lastname: Ibrahim
authors.affiliation: Yale University School of Medicine, Cardiovascular Research Center, Department of Internal Medicine, Section of Cardiovascular Medicine, New Haven, CT.
authors.forename: Scott
authors.initials: S
authors.lastname: Gleim
authors.affiliation: Yale University School of Medicine, Cardiovascular Research Center, Department of Internal Medicine, Section of Cardiovascular Medicine, New Haven, CT.
authors.forename: John
authors.initials: J
authors.lastname: Hwa
authors.affiliation: University of Pennsylvania Institute for Translational Medicine and Therapeutics, Smilow Center for Translational Research, Philadelphia, PA; and. Electronic address: emsmyth@mail.med.upenn.edu.
authors.forename: Emer M
authors.initials: EM
authors.lastname: Smyth
mesh_terms: D020816:Amino Acid Motifs; D000242:Cyclic AMP / Q000235:genetics / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D055503:Protein Multimerization / Q000502:physiology*; D017434:Protein Structure, Tertiary; D044006:Receptors, Epoprostenol; D011982:Receptors, Prostaglandin / Q000235:genetics / Q000378:metabolism*; D017482:Receptors, Thromboxane / Q000235:genetics / Q000378:metabolism*; D015290:Second Messenger Systems / Q000502:physiology*
chemical_list: C113936:PTGIR protein, human; D044006:Receptors, Epoprostenol; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D000242:Cyclic AMP; D043802:GTP-Binding Protein alpha Subunits, Gq-G11
keywords: G protein-coupled receptor; biased antagonism; dimerization; thromboxane A2 receptor; transmembrane; transmembrane domain