Stimulating the GPR30 Estrogen Receptor with a Novel Tamoxifen Analogue Activates SF-1 and Promotes Endometrial Cell Proliferation

Abstract

Estrogens and selective estrogen receptor (ER) modulators such as tamoxifen are known to increase uterine cell proliferation. Mounting evidence suggests that estrogen signaling is mediated not only by ERA and ERB nuclear receptors, but also by GPR30 (GPER), a seven transmembrane (7TM) receptor. Here, we report that primary human endometriotic H-38 cells express high levels of GPR30 with no detectable ERA or ERB. Using a novel tamoxifen analogue, STX, which activates GPR30 but not ERs, significant stimulation of the phosphatidylinositol 3-kinase (PI3K) and mitogenactivated protein kinase (MAPK) pathways was observed in H-38 cells and in Ishikawa endometrial cancer cells expressing GPR30; a similar effect was observed in JEG3 choriocarcinoma cells. STX treatment also increased cellular pools of phosphatidylinositol (3,4,5) triphosphate, a proposed ligand for the nuclear hormone receptor SF-1 (NR5A1). Consistent with these findings, STX, tamoxifen, and the phytoestrogen genistein were able to increase SF-1 transcription, promote Ishikawa cell proliferation, and induce the SF-1 target gene aromatase in a GPR30-dependent manner. Our findings suggest a novel signaling paradigm that is initiated by estrogen activation of the 7TM receptor GPR30, with signal transduction cascades (PI3K and MAPK) converging on nuclear hormone receptors (SF-1/LRH-1) to modulate their transcriptional output. We propose that this novel GPR30/ SF-1 pathway increases local concentrations of estrogen, and together with classic ER signaling, mediate the proliferative effects of synthetic estrogens such as tamoxifen, in promoting endometriosis and endometrial cancers. [Cancer Res 2009;69(13):5415-23]

The signaling phospholipid PIP 3 creates a new interaction surface on the nuclear receptor SF-1

“…Given that each position on the inositol head group has unique stereochemistry (33), one might imagine that the flipped orientations of the exposed PIP 2 and PIP 3 head groups differentially recruit stereo-specific coregulators. This hypothesis is consistent with our previous data showing that, at least on a subset of SF-1 target genes, PIP 3 but not PIP 2 is required for maximal SF-1 activity (13,15).…”

“…The ability of NR5As to interact with PIP n is well-conserved with the Caenorhabditis elegans ortholog nhr-25 able to bind both PIP 2 and PIP 3 (14). That phosphoinositides might serve as endogenous NR5A ligands is suggested by the fact that elevating cellular pools of PIP 3 increases SF-1 activity (15) and that impairing PIP 3 uptake decreases SF-1 activity (12). Further, when purified from mammalian cells, the phosphoinositide PIP 2 is found associated with SF-1 and can be modified by the lipid kinase, IPMK, as well as the lipid phosphatase, PTEN (13).…”

Follicular assembly: mechanisms of action

“…GPR30 is thought to be coupled to Ga s (Thomas et al 2005) and estrogen acting through GPR30 activates MAPK and PI3K signaling (Maggiolini & Picard 2010). Another mER agonist, STX (diphenyl acrylamide), selectively targets a Ga q -associated protein and also activates MAPK and PI3K signaling (Qiu et al 2006, Lin et al 2009). It is unclear whether STX is a GPR30 agonist or whether it signals via another unidentified mER (Lin et al 2009).…”

“…Another mER agonist, STX (diphenyl acrylamide), selectively targets a Ga q -associated protein and also activates MAPK and PI3K signaling (Qiu et al 2006, Lin et al 2009). It is unclear whether STX is a GPR30 agonist or whether it signals via another unidentified mER (Lin et al 2009). Evidence for other estrogenresponsive G protein-coupled receptors exists but they have not yet been well characterized (Hasbi et al 2005).…”

Extent of Vascular Remodeling Is Dependent on the Balance Between Estrogen Receptor α and G-Protein–Coupled Estrogen Receptor

“…11 GPER has been suggested to be important in rapid, nonclassic, estrogen-induced growth regulation in some tissues. [12][13][14][15][16][17][18][19] GPER's growth-regulating effects have been extensively studied, 13,18,[20][21][22][23][24][25][26] primarily in reproductive tissues and in cancer cells. Notably, GPER activation has also been shown to attenuate adverse cardiac ventricular remodeling in mRen2 Lewis rats.…”