Figure 4.

The 26S proteasome activity is important for ligand-dependent interaction of RARα with its coregulators. (A) Co-immunoprecipitation of endogenous RARα with SRC-1 was examined following 4 h of TTNPB induction (1 µM) in the presence or absence of MG132 (MG, 5 µM). The western blots were first probed with a RARα antibody, and then stripped and re-probed for SRC-1. Lane 1 is a negative immunoprecipitation control. 10% of the input extracts were also subject to western analysis as internal controls. Shown are the representatives of three independent experiments. (B) Co-immunoprecipitation of endogenous RARα with p300 following the same treatments. Western blots were first probed with a RARα antibody and then re-probed for p300. (C) Co-immunoprecipitation of endogenous RARα with RXRα was also examined following the same treatment. The western blots were first probed with a RARα antibody then re-probed for RXRα.