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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.

Multiple reports implicated the function of G protein-coupled receptor (GPR)-30 with nongenomic effects of estrogen, suggesting that GPR30 might be a G-protein coupled estrogen receptor. However, the findings are controversial and the expression pattern of GPR30 on a cell type level as well as its function in vivo remains unclear. Therefore, the objective of this study was to identify cell types that express Gpr30 in vivo by analyzing a mutant mouse model that harbors a lacZ reporter (Gpr30-lacZ) in the Gpr30 locus leading to a partial deletion of the Gpr30 coding sequence. Using this strategy, we identified the following cell types expressing Gpr30: 1) an endothelial cell subpopulation in small arterial vessels of multiple tissues, 2) smooth muscle cells and pericytes in the brain, 3) gastric chief cells in the stomach, 4) neuronal subpopulations in the cortex as well as the polymorph layer of the dentate gyrus, 5) cell populations in the intermediate and anterior lobe of the pituitary gland, and 6) in the medulla of the adrenal gland. In further experiments, we aimed to decipher the function of Gpr30 by analyzing the phenotype of Gpr30-lacZ mice. The body weight as well as fat mass was unchanged in Gpr30-lacZ mice, even if fed with a high-fat diet. Flow cytometric analysis revealed lower frequencies of T cells in both sexes of Gpr30-lacZ mice. Within the T-cell cluster, the amount of CD62L-expressing cells was clearly reduced, suggesting an impaired production of T cells in the thymus of Gpr30-lacZ mice.