G Protein-Coupled Receptor 30 Localizes to the Endoplasmic Reticulum and Is Not Activated by Estradiol

Abstract

The classical estrogen receptor (ER) mediates genomic as well as rapid nongenomic estradiol responses. In case of genomic responses, the ER acts as a ligand-dependent transcription factor that regulates gene expression in estrogen target tissues. In contrast, nongenomic effects are initiated at the plasma membrane and lead to rapid activation of cytoplasmic signal transduction pathways. Recently, an orphan G protein-coupled receptor, GPR30, has been claimed to bind to and to signal in response to estradiol. GPR30 therefore might mediate some of the nongenomic estradiol effects. The present study was performed to clarify the controversy about the subcellular localization of GPR30 and to gain insight into the in vivo function of this receptor. In transiently transfected cells as well as cells endogenously expressing GPR30, we confirmed that the receptor localized to the endoplasmic reticulum. However, using radioactive estradiol, we observed only saturable, specific binding to the classical ER but not to GPR30. Estradiol stimulation of cells expressing GPR30 had no impact on intracellular cAMP or calcium levels. To elucidate the physiological role of GPR30, we performed in vivo experiments with estradiol and G1, a compound that has been claimed to act as selective GPR30 agonist. In two classical estrogen target organs, the uterus and the mammary gland, G1 did not show any estrogenic effect. Taken together, we draw the conclusion that GPR30 is still an orphan receptor.

Estradiol Induces Export of Sphingosine 1-Phosphate from Breast Cancer Cells via ABCC1 and ABCG2

“…9) may contribute to nongenomic signaling of E 2 important for breast cancer pathophysiology. Furthermore, the S1P receptors may be the G protein-coupled receptors that mediate rapid nongenomic responses to E 2 rather than GPR30, which has been shown to be present in endoplasmic reticulum, not the plasma membrane (17,53). Our work, taken together with the criss-cross model for E 2 signaling proposed by Sukocheva et al (19), suggests that E 2 stimulates SphK1, increasing production of S1P in the vicinity of the ABC transporters, ABCC1 and ABCG2, at the plasma membrane, which facilitate its export (Fig.…”

Estrogen receptor (ER) expression and function in the pregnant human myometrium: estradiol via ERα activates ERK1/2 signaling in term myometrium

“…The discovery that GPR30 is a membrane-associated ER added a novel dimension to the complexity of estrogen signaling. Controversy exists, however, regarding whether GPR30 is truly an ER (Levin 2009, Langer et al 2010, with several studies showing that GPR30 directly binds E 2 (Revankar et al 2005, Thomas et al 2005, Thomas & Dong 2006 and another study showing that it does not (Otto et al 2008). It also remains unclear whether GPR30 localizes to the plasma membrane (Funakoshi et al 2006, Filardo et al 2007 or to the endoplasmic reticulum (Revankar et al 2005, Otto et al 2008.…”

“…Controversy exists, however, regarding whether GPR30 is truly an ER (Levin 2009, Langer et al 2010, with several studies showing that GPR30 directly binds E 2 (Revankar et al 2005, Thomas et al 2005, Thomas & Dong 2006 and another study showing that it does not (Otto et al 2008). It also remains unclear whether GPR30 localizes to the plasma membrane (Funakoshi et al 2006, Filardo et al 2007 or to the endoplasmic reticulum (Revankar et al 2005, Otto et al 2008. GPR30 clearly mediates components of estrogen signaling, as evidenced by multiple studies that confer estrogen responsiveness by inducing GPR30 expression or repress estrogen signaling via GPR30 knockdown or inhibition (reviewed in Prossnitz & Maggiolini (2009) and Maggiolini & Picard (2010)).…”

Hetero-oligomeric Complex between the G Protein-coupled Estrogen Receptor 1 and the Plasma Membrane Ca2+-ATPase 4b

“…Our initial task was to verify a parameter for GPER/GPR30 activity. Despite evidence that GPER/GPR30 was a G␣ s -associated GPCR (1), it has been shown that 17␤-estradiol failed to stimulate cAMP production in cells endogenously expressing GPER/GPR30 or heterologously overexpressing the receptor (37,38). More recently, it was shown that neither 17␤-estradiol nor GPER/GPR30 agonist G-1 stimulated cAMP production in cells overexpressing GPER/GPR30 and that GPER/GPR30 constitutively inhibits adenylyl cyclase-mediated cAMP production by interacting with the MAGUKs and AKAP5 (15).…”