PR and AP-1 interaction involvement in endocrine therapy response. (A) Proliferation , c-Jun phosphorylation and cyclin D1 promoter activation were studied as described in Figures 1, 3 and 6. (B) c-Jun and PR recruitment to the cyclin D1promoter was analyzed by ChIP as in Figure 5. Data are expressed as n-fold chromatin enrichment over untreated cells. For b vs. a and c vs. b: P <0.001. (C) to (J) Tam effects in sensitive and resistant cells. (C) and (D) Cell variants were treated as shown and proliferation was studied as in Figure 6. (E) Protein levels were analyzed by WB. Signal intensities of PR-A and PR-B bands were analyzed by densitometry and normalized to β-tubulin. Densitometric analysis of PR-A and PR-B expression levels in HR and HR6 clones, relative to those in BT474 cells (set to 1), are shown in the right panel. (F) and (G) WB in BT474-HR (F) and BT474 cells (G) were performed with the indicated phospho-antibodies and filters were re-probed with the respective total antibody. Signal intensities of phospho-proteins were normalized to total protein bands. Significance of MPA and Tam effects on the regulation of protein phosphorylation was analyzed as described in Methods (P <0.001). (H) and (I) c-Jun, PR, and ER α recruitment to the cyclin D1 promoter was studied by ChIP. We set as 1 the value of the untreated sample for BT474-HR cells (H) and of the IgG for BT474 (I). For b vs. a and c vs. b: P <0.001. (J) Tam effects on cyclin D1 protein expression. WBs were performed as in Figure 3 using β tubulin as loading control. Experiments in A to J were repeated five times with similar results. See Additional file 1: Figures 4, 5 and 6. ChIP, chromatin immunoprecipitation; MPA, Medroxyprogesterone acetate; PR, Progesterone receptor; Tam, Tamoxifen WB, Western blot.