Trabid, a new positive regulator of Wnt-induced transcription with preference for binding and cleaving K63-linked ubiquitin chains.
A key effector of the canonical Wnt pathway is beta-catenin, which binds to TCF/LEF factors to promote the transcription of Wnt target genes. In the absence of Wnt stimulation, beta-catenin is phosphorylated constitutively, and modified with K48-linked ubiquitin for subsequent proteasomal degradation. Here, we identify Trabid as a new positive regulator of Wnt signaling in mammalian and Drosophila cells. Trabid show a remarkable preference for binding to K63-linked ubiquitin chains with its three tandem NZF fingers (Npl4 zinc finger), and it cleaves these chains with its OTU (ovarian tumor) domain. These activities of Trabid are required for efficient TCF-mediated transcription in cells with high Wnt pathway activity, including colorectal cancer cell lines. We further show that Trabid can bind to and deubiquitylate the APC tumor suppressor protein, a negative regulator of Wnt-mediated transcription. Epistasis experiments indicate that Trabid acts below the stabilization of beta-catenin, and that it may affect the association or activity of the TCF-beta-catenin transcription complex. Our results indicate a role of K63-linked ubiquitin chains during Wnt-induced transcription.
Pubmed ID: 18281465 RIS Download
Animals | Blotting, Western | Cells, Cultured | Colorectal Neoplasms | Drosophila Proteins | Drosophila melanogaster | Genes, APC | Humans | Immunoprecipitation | Lymphoid Enhancer-Binding Factor 1 | NF-kappa B | Nuclear Proteins | Plasmids | Proto-Oncogene Proteins | RNA, Messenger | Reverse Transcriptase Polymerase Chain Reaction | Signal Transduction | TCF Transcription Factors | Transcription, Genetic | Two-Hybrid System Techniques | Ubiquitin | Ubiquitin-Specific Proteases | Wnt Proteins | Wnt1 Protein | beta Catenin