Summer Research Description: Wnt signaling is an evolutionarily conserved pathway critical for development and cell regulation, and is known to be misregulated in several diseases including cancer. β-catenin, a Wnt co-activator, is degraded in the cytoplasm by a macromolecular complex termed the destruction complex. Upon Wnt activation, the destruction complex is disassembled and β-catenin regulates transcription in the nucleus. Tankyrase is a poly- ADP-ribosylating (PARsylation) polymerase known to bind and promote ubiquitination of Axin, the rate limiting component of the β-catenin destruction complex. However, the precise mechanisms by which Tankyrase regulates PARsylation of Axin is largely unknown. Recombinant Tankyrase will be expressed and purified from Escherichia coli, and recombinant Axin will be purified utilizing a mammalian expression system. Using GST-WWE protein pull down experiments we will assess ADP-ribosylation of Axin in vitro. Surface plasma resonance will also be used to quantify the binding affinity of modified and unmodified axin to LRP6, a Wnt co-receptor. Tankyrase is an attractive therapeutic target for Wnt-related diseases because small molecule inhibitors of Tankyrase have been shown to stabilize Axin levels, and restore the destruction complex. Understanding the relationship between Tankyrase and Axin will be vital to utilizing these small molecule inhibitors as treatments.