Epidermal growth factor induces G protein-coupled receptor 30 expression in estrogen receptor-negative breast cancer cells

Different cellular receptors mediate the biological effects induced by estrogens. In addition to the classical nuclear estrogen receptors (ERs)-alpha and -beta, estrogen also signals throughthe seven-transmembrane G-protein-coupled receptor (GPR)-30. Using as a model system SkBr3 and BT20 breast cancer cells lacking the classical ER, the regulation of GPR30 expressionby 17beta-estradiol, the selective GPR30 ligand G-1, IGF-I,and epidermal growth factor (EGF) was evaluated. Transient transfections with an expression plasmid encoding a short 5'-flanking sequence of the GPR30 gene revealed that an activatorprotein-1 site located within this region is required forthe activating potential exhibited only by EGF. Accordingly,EGF up-regulated GPR30 protein levels, which accumulated predominantly in the intracellular compartment. The stimulatoryrole elicited by EGF on GPR30 expression was triggeredthrough rapid ERK phosphorylation and c-fos induction,which was strongly recruited to the activator protein-1 site found in the short 5'-flanking sequence of the GPR30 gene. Of note, EGF activating the EGF receptor-MAPK transduction pathway stimulated a regulatory loop that subsequently engaged estrogen through GPR30 to boost the proliferation of SkBr3 and BT20 breast tumor cells. The up-regulation of GPR30 by ligand-activated EGF receptor-MAPK signaling provides new insight into the well-known estrogen and EGF cross talk, which, as largely reported,contributes to breast cancer progression. On the basis of our results, the action of EGF may include the up-regulation of GPR30 in facilitating a stimulatory role of estrogen,even in ER-negative breast tumor cells.