The adenomatous polyposis coli tumor suppressor (APC) is a large multidomain protein that plays an integral role in intercellular adhesion and in the Wnt/Wingless signaling transduction pathway — key in a number of developmental processes and in tumorigenesis. APC is mutated in most colorectal cancers and binds to a guanine nucleotide exchange factor Asef — involved in actin cytoskeletal reorganization and cell morphology regulation — but the precise signaling pathways have been unclear. In an Advanced Online Publication in Nature Cell Biology, Yoshihiro Kawasaki and colleagues at the University of Tokyo, Japan, provide evidence that the APC-Asef complex promotes colorectal tumor cell migration and thus in tumor progression (Nature Cell Biology, DOI:10.1038/ncb937, February 24, 2003).