Estrogen Receptor-α Mediates the Epidermal Growth Factor-Stimulated Prolactin Expression and Release in Lactotrophs

Epidermal growth factor (EGF) is a potent regulator of cell function in many cell types. EGF-receptor (EGFR/ErbB1)-activated Erk1/2 has been reported to activate estrogen receptor (ER) in an estrogen (E2)-independent manner. In the pituitary lactotrophs, both EGF and E2 stimulate prolactin (PRL) release, but the nature of interactions between ErbB and ER alpha signaling is unknown. Our objectives were to 1) characterize EGF-induced PRL release, 2) determine whether this effect requires ER alpha, and 3) determine the molecular basis for cross talk between ErbB and ER alpha signaling pathways. Using GH3 cells, a rat lactotroph cell line, we report that EGF stimulates PRL gene expression and release in a dose- and time-dependent manner. EGF caused a rapid and robust activation of Erk1/2 via ErbB1 and induced phosphorylation of S118 on ER alpha in an Erk1/2-dependent manner. The global antiestrogen ICI 182780 and the ER alpha-specific antagonist 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylet hoxy) phenol]-1H-pyrazole dihydrochloride (MPP), but not the ER alpha-specific antagonist 4-[2-Phenyl-5,7-bis(trifluoromethyl) pyrazolo[1,5-a]pyrimidin-3-yl]phenol (PHTPP), blocked the EGF-induced PRL release, indicating an ER alpha requirement. This was further supported by using ER alpha knockdown by small interfering RNA. Because the antiestrogens did not block EGF-induced Mek-1 or Erk1/2 phosphorylation, ER alpha is placed downstream from the ErbB1-activated Erk1/2. These results provide the first evidence that ErbB1-induced PRL release is ER alpha dependent. (Endocrinology 150: 795-802, 2009)