New Regulators of Wnt/β-Catenin Signaling Revealed by Integrative Molecular Screening

Integration of protein-protein interaction networks and human genome-wide RNAi screens produces mechanistic insight into Wnt/β-catenin signaling. Finding the Right Candidate A genome-wide RNAi screen in human colon cancer cells, followed by two additional validation steps, reveals new components of the Wnt pathway. Combining RNAi analysis with protein-protein interaction data provides a powerful approach that not only identifies new players in a signaling pathway, but also provides functional insight about the modulators, leading to the generation of testable hypotheses. The identification and characterization of previously unidentified signal transduction molecules has expanded our understanding of biological systems and facilitated the development of mechanism-based therapeutics. We present a highly validated small interfering RNA (siRNA) screen that functionally annotates the human genome for modulation of the Wnt/β-catenin signal transduction pathway. Merging these functional data with an extensive Wnt/β-catenin protein interaction network produces an integrated physical and functional map of the pathway. The power of this approach is illustrated by the positioning of siRNA screen hits into discrete physical complexes of proteins. Similarly, this approach allows one to filter discoveries made through protein-protein interaction screens for functional contribution to the phenotype of interest. Using this methodology, we characterized AGGF1 as a nuclear chromatin-associated protein that participates in β-catenin–mediated transcription in human colon cancer cells.