Truncated APC is required for cell proliferation and DNA replication

Abstract The tumour suppressor APC is truncated in most colon cancers, which leads to the stabilization of β‐catenin and to the constitutive activation of Wnt signalling. However, it is not clear why colon cancer cells retain the truncated APC fragment. Here, we show that a decrease of APC levels achieved by RNA interference impairs cell proliferation and DNA replication, not only in 293 cells that express a wild‐type protein, but also in SW480 colon cancer cells that express exclusively a truncated APC fragment. This correlates with a reduction of the levels of cyclin A, cyclin A‐dependent kinase activity, p27 kip1 and the catalytic subunit of DNA polymerase δ. Thus, our data suggest that colon cancer cells retain a truncated APC fragment because it is essential for cell proliferation. © 2006 Wiley‐Liss, Inc.