Several lines of evidence suggest that accumulation of cytoplasmic β-catenin transduces an
oncogenic signal. We show that β-catenin is ubiquitinated and degraded by the proteosome
and that β-catenin stability is regulated by a diacylglycerol-independent protein kinase C-
like kinase activity, which is required for β-catenin ubiquitination. We also define a six-amino
acid sequence found in both β-catenin and the NF-κB regulatory protein IκBα, which, upon
phosphorylation, targets both proteins for ubiquitination. Mutation of a single serine within …