APC and mantle cell lymphoma: Western blot analysis demonstrated that cyclin B1 protein levels increased during mitotic arrest in all MCL and DLBCL human cell lines used, as indicated by phosphorylation of the APC/C subunit APC3 (also known as Cdc27).34 Skp2 protein levels remained mostly unchanged, except in the ABC–DLBCL cell line (Fig. 3a).