Differential proteome analysis of Smad4 re-expressing and negative SW480 cells. A) A representative example of the 2D-DIGE analyses is shown. Differentially expressed proteins are labeled by an arrow. The protein spot signals derived from the nuclear lysates of Smad4 negative cells are shown in green and those from Smad4 re-expressing cells in red. The protein names corresponding to each numbered spot are given in table 1. Spot numbers 10 and 11 mark the KRT23 spots. B) and C) Expression levels of the two KRT23 spots relative to the protein standard according to the dye swop experiment (neg., Smad4 negative SW480 cells; pos., Smad4 re-expressing SW480 cells) D) Expression of KRT23 analyzed by Northern blotting.