Regulation of GTP-binding protein αq (Gαq) signaling by the ezrin-radixin-moesin-binding phosphoprotein-50 (EBP50)

Abstract

Although ezrin-radixin-moesin-binding phosphoprotein 50 (EBP50) is a PDZ domain-containing protein known to bind to various channels, receptors, cytoskeletal elements, and cytoplasmic proteins, there is still very little evidence for a role of EBP50 in the regulation of receptor signal transduction. In this report, we show that EBP50 inhibits the phospholipase C (PLC)-β-mediated inositol phosphate production of a Gαq-coupled receptor as well as PLC-β activation by the constitutively active Gαq-R183C mutant. Coimmunoprecipitation experiments revealed that EBP50 interacts with Gαq and to a greater extent with Gαq-R183C. Agonist stimulation of the thromboxane A2 receptor (TP receptor) resulted in an increased interaction between EBP50 and Gαq, suggesting that EBP50 preferentially interacts with activated Gαq. We also demonstrate that EBP50 inhibits Gαq signaling by preventing the interaction between Gαq and the TP receptor and between activated Gαq and PLC-β1. Investigation of the EBP50 regions involved in Gαq binding indicated that its two PDZ domains are responsible for this interaction. This study constitutes the first demonstration of an interaction between a G protein α subunit and another protein through a PDZ domain, with broad implications in the regulation of diverse physiological systems.