Inhibition of Estrogen Receptor Action by the Orphan Receptors, SHP and DAX-1

摘要

The estrogen receptor is a critical diagnostic marker and therapeutic target for a large number of breast cancers. In support of DoD grant number DAMD17- 99-1-9163, we present our findings regarding the mechanisms by which two orphan nuclear receptors, SHP and DAX-1 inhibit the actions of ER-alpha and ER-beta action. Consistent with prior studies of Shp, we show that Dax-1 binds directly to ER-a and ER-beta in an agonist dependent manner. Additionally, our data suggest that this interaction is sufficient to disrupt transcriptional activation of estrogen responsive reporters by ER-alpha and ER-beta in a dose dependent manner. Mutational analysis revealed that a 90 amino acid region of DAX-1 was sufficient to interact with agonist bound ER-alpha and ER-beta. This region contains two LXXML motifs similar to the LXXLL motifs found in ligand- dependent co-activators of the SRC-1 family. Consistent with this, a peptide containing LHRLL from the second NR Box of GRIP-1 was able to compete away the interaction between ER-alpha and this 90 amino acid fragment. Therefore, the mechanism by which DAX-1 interacts with ER-alpha and ER-beta is similar to the interaction of agonist bound ER and the SRC-1 family of nuclear receptor co- activators. Additionally, over-expression of SRC-1 was sufficient to override DAX-1-mediated repression of ER activity.