Estrogen receptor (ER) and progesterone receptor (PgR) expression in MCF-7 cells exposed to ibandronate (Iban) and/or 17β-estradiol (E2) as assessed by western blot. (a) For ER determination, MCF-7 cells were incubated for 24 hours with 10-4 M Iban and/or 10-9 M E2 or vehicle (control) in steroid-free medium. Equal quantities of proteins (20 μg) were subjected to SDS-PAGE and electrotransferred onto nitrocellulose membranes. Immunodetection was performed with anti-human ER antibody raised against its F domain. (b) For PgR measurement, cells were incubated for 72 hours in the same experimental conditions. Equal amounts of proteins (40 μg) were loaded onto SDS-PAGE and immunoblot was revealed using anti-human PgR antibody raised against A/B isoforms of the receptor. Blots show representative experiments performed at least twice. Data were obtained from densitometric analyses and are presented as mean percentages of control values. Asterisks indicate ANOVA p < 0.01 versus control, Tukey post hoc test. NS, not significant.