Proteomics of Smad4 regulated transforming growth factor-beta signalling in colon cancer cells

TGF-beta signalling can play a paradoxical cell type specific role in cancer progression. Smad4 is a key mediator of the TGF-beta pathway, and is mutated and/or deleted in many cancers. To investigate Smad4 regulated TGF-beta signalling in colon cancer we conducted an iTRAQ mass spectrometry quantitative screen using wild type SW480 (Smad4 negative) colon carcinoma cells and stably restored Smad4 positive SW480 cells. In cells possessing a restored canonical TGF-beta signalling pathway, 48 h TGF-beta stimulation induced the expression of 15 proteins and repressed 1 protein, while in Smad4 wild type cells, TGF-beta induced 7 proteins and repressed 2 proteins. The expression of several S100 protein family members (A2, A4, A10, and A11), transgelin-2 and AKAP12, amongst others, were shown to be regulated by TGF-beta in a Smad4 dependent manner. We observed that S100 A4 could be repressed by TGF-beta, independently of Smad4 expression, while other Smad4 independent TGF-beta responses were restricted to induction of ribosomes and cytoskeletal proteins. Our proteomic screen has identified new Smad4 dependent and independent TGF-beta responses in colon carcinoma cells.