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

Vitamin D receptor interacting protein (DRIP150) coactivates estrogen receptor α (ERα)-mediated transactivation in breast cancer cell lines transfected with a construct (pERE3) containing three estrogen responsive elements (EREs). In this study, we show that DRIP150 also coactivates ERα/Sp1-mediated transactivation in ZR-75, MCF-7, and MDA-MB-231 breast cancer cells transfected with a construct (pSp13) containing three consensus GC-rich motifs. Studies on coactivation of wild-type and variant ERα/Sp1 by DRIP150 indicates that the DNA-binding domain and helix 12 in the ligand binding domain of ERα 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 ERα/Sp1 by wild-type and mutant DRIP150 expression plasmids show that coactivation of ERα/Sp1 by DRIP150 is independent of the NR-boxes. Deletion analysis of DRIP150 demonstrates that coactivation requires an α-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 ERα by DRIP150. Thus, although different domains of ERα are required for hormone-dependent activation of ERα and ERα/Sp1, coactivation of these transcription factors by DRIP150 requires the α-helical amino acids 795–804. This is the first report of a coactivator that enhances ERα/Sp1-mediated transactivation in breast cancer cells.