Cells were crosslinked in 1% formaldehyde at room temperature for 10 minutes and then quenched with 125 mmol/L glycine. Samples were then lysed, sonicated, and chromatin was immunoprecipitated by overnight incubation at 4C with ER antibodies prebound with Protein G magnetic dynabeads (Invitrogen). Samples were then washed vigorously with RIPA buffer and reversed crosslinked by an overnight incubation in elution buffer at 65C. DNA was digested with RNase and Proteinase K, purify precipitated with phenol chloroform and eluted in Tris-HCl pH 8.0.