RT Journal Article
SR Electronic
T1 The G<sub>12</sub> Family of G Proteins as a Reporter of Thromboxane A<sub>2</sub> Receptor Activity
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 1433
OP 1440
DO 10.1124/mol.105.019703
VO 69
IS 4
A1 Li Zhang
A1 Cherisse DiLizio
A1 David Kim
A1 Emer M. Smyth
A1 David R. Manning
YR 2006
UL http://molpharm.aspetjournals.org/content/69/4/1433.abstract
AB Despite advances in the understanding of pathways regulated by the G12 family of heterotrimeric G proteins, much regarding the engagement of this family by receptors remains unclear. We explore here, using the thromboxane A2 receptor TPα, the ability of G12 and G13 to report differences in the potency and efficacy of receptor ligands. We were interested especially in the potential of the isoprostane 8-iso-prostaglandin F (8-iso-PGF2α), among other ligands examined, to activate G12 and G13 through TPα explicitly. We were also interested in the functionality of TPα-Gα fusion proteins germane to G12 and G13. Using fusion proteins in Spodoptera frugiperda (Sf9) cells and independently expressed proteins in human embryonic kidney 293 cells, and using guanosine 5′-O-(3-[35S]thio)triphosphate binding to evaluate Gα activation directly, we found for Gα that no ligand tested, including 8-iso-prostaglandin F (8-iso-PGF2α and a purported antagonist (pinane thromboxane A2), was silent. The activity of agonists was especially pronounced when evaluated for TPα-Gα13 and in the context of receptor reserve. Agonist activity for 8-iso-PGF2 was diminished and that for pinane thromboxane A nonexistent when Gα12 was the reporter. These data establish that G12 and G13 can report differentially potency and efficacy and underscore the relevance of receptor and G protein context.