Knockdown of p300 decreases acetylation and stability of ERα protein. (a) T47D cells were transfected with si-p300 or nonspecific siRNA (NS) and treated with 1 μM trichostatin A (TSA) for 3 hours. (b) HeLa cells were transiently transfected with 2 μg Myc-ERα together with si-p300 or NS and treated with 1 μM TSA for 3 hours. Then 500 μg whole-cell lysate was immunoprecipitated (IP) using anti-acetylated-lysine (Ac-Lys) or normal IgG antibodies, and probed using anti-ERα antibody. The expression of p300 and ERα was analyzed by western blot (WB) using anti-p300 or anti-Myc as input.