Cross-talk between Stat5b and estrogen receptor- and - in mammary epithelial cells

Both 17 -estradiol and prolactin play important roles in the mammary gland, raising the possibility of functional cross-talk between the two signaling pathways. Here, we demonstrate that estrogen receptor(ER ) and (ER ) are both able to potentiate transcription from a Stat5-responsive promoter when activated by prolactin. Potentiation was observed not only in the presence of 17 estradiol, but also in the presence of anti-estrogens such as tamoxifen and ICI 182,780. The magnitude of the response was dependent on cell-type: in the HC11 mouse mammary epithelial cell line ER potentiates transcription efficiently whereas ER showed low activity. Conversely, in COS-7 cells, both estrogen receptors were active. We show that activation domains in the N-terminus (AF-1) and the C-terminus (AF-2) of the ERs are dispensable for potentiation. The effects are dependent on the presence of an intact DNA-binding/hinge domain, which we show is capable of interacting with Stat5b in vitro and in HC11 cell extracts. We conclude that ER and ER act as coactivators for Stat5b through a mechanism which is independent of AF-1 and AF-2. Journal of Molecular Endocrinology (2001) 27, 93–106