FIG. 2.

Protein phosphatases play an important role in the control of the steady-state level of p300. (A) Equal amounts (50 μg) of whole-cell extracts from HeLa cells were used for Western blot analysis of endogenous p300 after treatment with okadaic acid (OA) (0.4 μM [+] or 0.8 μM [++]). The treatment time (in hours) is indicated above the lanes. The blot was then stripped and reprobed with a p53 antibody. (B) The same experimental setup as in panel A, except the cells were treated with okadaic acid (OA) (0.2 μM) in the presence or absence of valproic acid (VPA) (2 mM) or sodium butyrate (NaB) (5 mM) for 16 h. (C) The same procedure as in panel B, except the blot was probed with p300 antibody, stripped, and reprobed with a RAR antibody. A protein band cross-reacting with the RAR antibody is shown as a control (Ctl).