Coactivation of estrogen receptor α (ERα)/Sp1 by vitamin D receptor interacting protein 150 (DRIP150)

Vitamin D receptor interacting protein (DRIP150) coactivates estrogen receptor alpha (ER alpha)-mediated transactivation in breast cancer cell lines transfected with a construct (pERE(3)) containing three estrogen responsive elements (EREs). In this study, we show that DRIP150 also coactivates ER alpha/Sp1-mediated transactivation in ZR-75, MCF-7, and MDA-MB-231 breast cancer cells transfected with a construct (pSp1(3)) containing three consensus GC-rich motifs. Studies on coactivation of wild-type and variant ER alpha/Sp1 by DRIP150 indicates that the DNA-binding domain and helix 12 in the ligand binding domain of ER alpha are required and the coactivation response is squelched by overexpressing an NR-box peptide that contains two LXXLL motifs from GRIP2. In contrast, coactivation of ER alpha/Sp1 by wild-type and mutant DRIP150 expression plasmids show that coactivation of ER alpha/Sp1 by DRIP150 is independent of the NR-boxes. Deletion analysis of DRIP150 demonstrates that coactivation requires an alpha-helical NIFSEVRVYN (amino acids 795-804) motif within 23 amino acid sequence (789-811) in the central region of DRIP150 and similar results were obtained for coactivation of ER alpha by DRIP150. Thus, although different domains of ER alpha are required for hormone-dependent activation of ER alpha and ER alpha/Sp1, coactivation of these transcription factors by DRIP150 requires the alpha-helical amino acids 795-804. This is the first report of a coactivator that enhances ER alpha/Sp1-mediated transactivation in breast cancer cells. (C) 2007 Elsevier Inc. All rights reserved.