Parafibromin/Hyrax activates Wnt/Wg target gene transcription by direct association with beta-catenin/Armadillo.
The Wnt pathway controls cell fates, tissue homeostasis, and cancer. Its activation entails the association of beta-catenin with nuclear TCF/LEF proteins and results in transcriptional activation of target genes. The mechanism by which nuclear beta-catenin controls transcription is largely unknown. Here we genetically identify a novel Wnt/Wg pathway component that mediates the transcriptional outputs of beta-catenin/Armadillo. We show that Drosophila Hyrax and its human ortholog, Parafibromin, components of the Polymerase-Associated Factor 1 (PAF1) complex, are required for nuclear transduction of the Wnt/Wg signal and bind directly to the C-terminal region of beta-catenin/Armadillo. Moreover, we find that the transactivation potential of Parafibromin/Hyrax depends on the recruitment of Pygopus to beta-catenin/Armadillo. Our results assign to the tumor suppressor Parafibromin an unexpected role in Wnt signaling and provide a molecular mechanism for Wnt target gene control, in which the nuclear Wnt signaling complex directly engages the PAF1 complex, thereby controlling transcriptional initiation and elongation by RNA Polymerase II.
Pubmed ID: 16630820 RIS Download
Adaptor Proteins, Signal Transducing | Amino Acid Sequence | Animals | Axin Protein | Cell Line | Drosophila Proteins | Drosophila melanogaster | Gene Expression Regulation | Humans | Intracellular Signaling Peptides and Proteins | Molecular Sequence Data | Phylogeny | Sequence Alignment | Signal Transduction | Transcription, Genetic | Tumor Suppressor Proteins | Two-Hybrid System Techniques | Wing | Wnt Proteins | beta Catenin