Mutations in the Estrogen Receptor DNA-binding Domain Discriminate between the Classical Mechanism of Action and Cross-talk with Stat5b and Activating Protein 1 (AP-1)

Estrogen receptors (ERs) efficiently potentiate the transcriptional activity of prolactin-activated Stat5b through a mechanism that involves the ER DNA-binding domain (DBD) and the hinge domain. We have identified residues within the DBD of ER that are critical for the functional interaction of ER with Stat5b. We show that disruption of the second zinc finger structure abrogated cross-talk between ER and Stat5b, while the structure of the first zinc finger was not important. Furthermore, we confirm that intact DNA binding activity was not required for potentiation of Stat5b activity and that the dimerization of ER did not seem to be involved. Ligand-bound ERs also modulated activating protein 1-dependent transcription, and our data demonstrate that both zinc finger structures of the ER DBD are important for an intact response. We show that introduction of various point mutations within the DBD altered the response of the receptor to 17beta-estradiol and to the estrogen antagonists 4-hydroxytamoxifen and ICI 182,870 on the collagenase promoter. These findings provide new insights into the mechanisms by which ERs act in cross-talk with non-related transcription factors.