(C-E) MCF-7 transfected with YFP-p27 or YFP-p27T198A mutant (C, D) or cotransfected with YFP-p27 and an empty RFP vector in a 5:1 (YFP-p27: RFP) ratio (E) were treated with (+) or without (−) MG132 (10 μM) for 12 h before western blot analysis (C) and fluorescence microscopy (D, E). 