Proteomic screen with the proto-oncogene beta-catenin identifies interaction with Golgi coatomer complex I.

Beta-catenin is well-known as a key effector of Wnt signalling and aberrant expression is associated with several human cancers. Stabilisation of and atypical subcellular localisation of beta-catenin, regulated in part through specific protein-protein interactions has been linked to cancer development, however the mechanisms behind these pathologies is yet to be fully elucidated. Affinity purification and mass spectrometry were used to identify potential β-catenin interacting proteins in SW480 colon cancer cells. Recombinant β-catenin constructs were used to co-isolate interacting proteins from stable isotope labelled cells followed by detection using mass spectrometry. Several known and new putative interactors were observed. In particular, we identified interaction with a set of coatomer complex I subunits implicated in retrograde transport at the Golgi, and confirmed endogenous interaction of β-catenin with coatomer subunit COPB using immunoprecipitation assays and immunofluorescence microscopy. These observations suggest a hitherto unrecognised role for β-catenin in the secretory pathway and warrant further functional studies to unravel its activity at this cellular location.