Analysis of the Pygopus/Legless signalling complex

The goal of this project is to analyse the function and structure of specific protein complexes that are involved in the Wingless/Wnt-pathway. The Wnt-pathway is an important cellular regulation pathway, which is evolutionary conserved and is often deregulated in human cancers. Specifically, complexes from the gene products of legless and pygopus should be characterised, which regulate the activity of the Wnt-pathway in Drosophila, and whose human counterparts, according to our model, also impinge on the Wnt-pathway in humans. Proteins involved in the Wnt-pathway are powerful regulators of cell proliferation and differentiation, and their signalling pathway involves proteins that directly participate in both gene transcription and cell adhesion. Quite recently a new protein complex involved in this Wnt-pathway has been identified, consisting of two proteins termed Pygopus and Legless. These have been shown to interact with ß-catenin which in turn interacts with the T cell factor/lymphoid enhancer factor (TCF/LEF), thereby activating TCF responsive target genes, like c-MYC and CyclinD1. The function of Pygopus and Legless appears to be the targeting of ß-catenin to the nucleus during signalling. Furthermore they are considered to act as a transcriptional co-activator together with the TCF/ß-catenin complex. But the function and the interaction of Legless with Pygopus has so far not been characterised in depth. In this project we plan to analyse this protein-interaction by use of X-ray crystallography and/or NMR. Furthermore, we will analyse how Pygopus is able to promote ß-catenin-mediated transcription. These questions are of intrinsic mechanistic interest, and the expected results should also contribute to an improved understanding of cancer development.