Biased suppression of TP homodimerization and signaling through disruption of a TM GxxxGxxxL helical interaction motif

• Published in: Journal of lipid research Vol. 54; no. 6; pp. 1678 - 1690
• Main Authors: Frey, Alexander J., Ibrahim, Salam, Gleim, Scott, Hwa, John, Smyth, Emer M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.06.2013; The American Society for Biochemistry and Molecular Biology; Elsevier
• Subjects: Amino Acid Motifs; biased antagonism; Cyclic AMP - genetics; Cyclic AMP - metabolism; dimerization; G protein-coupled receptor; GTP-Binding Protein alpha Subunits, Gq-G11 - genetics; GTP-Binding Protein alpha Subunits, Gq-G11 - metabolism; HEK293 Cells; Humans; Protein Multimerization - physiology; Protein Structure, Tertiary; Receptors, Epoprostenol; Receptors, Prostaglandin - genetics; Receptors, Prostaglandin - metabolism; Receptors, Thromboxane - genetics; Receptors, Thromboxane - metabolism; Second Messenger Systems - physiology; thromboxane A2 receptor; transmembrane; transmembrane domain; G protein-coupled receptor; biased antagonism; dimerization; thromboxane A2 receptor; transmembrane; transmembrane domain
• ISSN: 0022-2275; 1539-7262
• DOI: 10.1194/jlr.M036673

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.