Protein-protein interaction networks paint a structural and functional picture of all living cells by providing a framework for both how cellular signalling occurs and where. The cell polarity protein, Scribble, is a hub for numerous interactions and subsequently regulates key pathways and processes through localising and tethering signalling components to specific regions within the cell. Scribble is a multi-domain protein with 16 leucine-rich repeats and four PDZ domains that are responsible for its membrane-bound localisation and extensive protein interaction network. Importantly, aberrant localisation of Scribble is implicated in the development of aggressive epithelial cancers and lethal neural tube closure defects in human patients; however, the exact mechanism by which Scribble mislocalisation contributes to disease remains unclear. I hypothesise that alterations in the spatiotemporal protein-protein interaction network of mislocalised Scribble is responsible for its pathological properties.
To begin mapping this differential interaction network, I have utilised a proximity-labelling based approach, APEX, as well as pulldown assays with recombinant Scribble protein-interaction domains. Subsequently, multiple known and novel proteins have been identified as potential Scribble-interacting partners. Many of these novel interactors contain known PDZ-binding domains and are involved in Scribble-related processes, including cell differentiation, tissue growth, cell migration and apoptosis. Moreover, alterations in these proteins have been implicated in human cancer progression and developmental defects similar to those associated with mislocalised Scribble. Using the above proteomics approaches together with complementary cellular structure function studies of mislocalised Scribble alleles, a detailed portrait of Scribble’s role as a spatial organiser of signalling and its contribution to cancer and development can be defined through the careful functional characterisation of its differential surrounding protein network.