The APC tumour suppressor protein contributes to several cellular processes including the regulation of β-catenin in Wnt signalling and in cell adhesion and migration. We have established that N-terminally phosphorylated β-catenin (N-P-β-cat) localises specifically to several subcellular sites including cell-cell contacts and the ends of cell protrusions in epithelial cells. N-P-β-cat associates with E-cadherin at adherens junctions and with APC in cell protrusions. We isolated protrusions from stimulated MDCK cells and detected APC β-catenin, GSK3β and CK1α, but not axin. The APC/ N-P-β-cat complex in cell protrusions appears to be distinct from the APC/axin/β-catenin destruction complex. This suggests that N-P-β-cat is not only targeted for degradation and that the regulation of β-catenin phosphorylation at specific adherens junctions and/or protrusions may contribute to the tumour suppressor activity of APC. APC localisation to cell protrusions is lost upon APC mutation: in colon cancer cells that contain only truncated APC protein, APC no longer accumulates at the ends of microtubules and appears instead to be distributed throughout the cytoplasm. We have isolated cell protrusions from SW480 colon cancer cells and SW480 cells with restored full-length APC (SW480APC). Immunofluorescent staining reveals a larger proportion of APC positive protrusions in SW480APC compared to SW480 control cells. Biochemical isolation of cell protrusions will allow us to identify proteins associated with cell protrusions and proteins complexed with protrusion-localised APC.