Pygopus 2, also known as PYGO2, is a 406 amino acid protein that is the human homolog of the Drosophila pygopus protein. Localized to the nucleus, Pygopus 2 contains one PHD finger that interacts with the homology domain of the Wnt signaling protein Bcl-9. This interaction joins Pygopus 2 with the ∫-catenin/TCF complex (a crucial complex in Wnt signaling), thereby allowing ∫-catenin to transcriptionally activate Wnt target genes. Association of Pygopus 2 with proteins involved in the Wnt signaling pathway is thought to regulate proper signal transduction, as absence of the Pygopus 2/∫-catenin interaction may play a role in development of B-cell malignancies. In addition, Pygopus 2 expression is upregulated in and required for the growth of breast cancer cells, suggesting a crucial role in carcinogenesis.