Both fulvestrant and 17β-estradiol (E2) enhance proteasomal degradation of ERα protein in MCF-7 cells.

(A–C) Fulvestrant (A) and E2 (B) caused time-dependent reduction in ERα protein expression: Western blotting. Intensities of ERα protein bands were determined by densitometry (C, mean±SEM of three independent experiments. Asterisks indicate statistical significance, p<0.05 to vehicle control). (D, E) E2 dose-dependent reduction in ERα protein expression. Cells were exposed to varying concentrations of E2 for 6 hours and subjected to Western blotting analysis of ERα protein (D). Intensities of ERα protein bands were determined by densitometry (E, mean±SEM of three independent experiments. Asterisk indicates t-test significance p<0.05 to vehicle control). (F–H), Pre-exposure to MG132 dose-dependently prevented reduction in ERα protein expression caused by fulvestrant (F) and E2 (G). Con, vehicle control (0.1% ethanol). Cells were exposed to varying concentrations of MG132 for 30 minutes and then exposed additionally to fulvestrant or E2 for 6 hours. Intensities of ERα protein bands were determined by densitometry (H, mean±SEM of three independent experiments. Asterisks indicate statistical significance, p<0.05).