Fig. 1.

Suppression of AIB1 by RNAi leads to ERα protein stabilization in the presence of E2. (A) Suppression of AIB1 inhibits E2-induced ERα degradation. MCF-7 cells were seeded in hormone-free condition before siRNA transfection. Forty-eight hours posttransfection, cells were treated with either vehicle (–) or 100 nM E2 (+) for 16 h. The ERα protein expression was analyzed by Western blotting (Left). The expression of calnexin protein was included as a loading control. (Right) Quantitative analyses of the ERα expression relative to the calnexin level in three independent experiments are represented. (B) siRNA specific to each of the p160 coactivators leads to efficient inhibition of the target protein. siRNA targeting the luciferase gene was used as a negative control. (C) The carboxyl-terminal region of AIB1 is necessary to mediate the ERα degradation by E2. (Top) Schematic diagram of AIB1, SRC-1, and the HA-tagged SRC-1/AIB1 is shown; the site in AIB1 targeted by siAIB1 is indicated by an asterisk. (Middle and Bottom) Western blots.