Professor, Molecular Biosciences
University of Kansas
Structure function analysis of tumor suppressor APC Protein (2017-18)
Because loss of the tumor suppressor Adenomatous polyposis coli (APC) is thought to initiate over 80% of all colorectal cancers, APC protein is the central focus of this proposal. The best characterized APC binding partner is Wnt signaling protein beta-catenin. We have also identified topoisomerase II alpha (topo II) as an APC binding protein. Binding to each of these proteins is mediated by a central region of APC containing several 15- and 20-amino acid (aa) repeats. Most colon cancers with mutant APC express a truncated APC protein which retains this central region.
It remains to be determined why the 15-aa repeat region is so strongly selected as beneficial to cancer cells. However, the apparent selection raises the potential that unique interactions between this APC region and critical binding partners might serve as targets for future development of anti-cancer strategies. Further, we propose that the interaction between this central portion of APC with topo II might also result in the resistance to chemotherapeutic topoisomerase inhibitors that is observed for most colon cancers. The large extent of predicted disorder within the 15- and 20-aa repeat regions of APC has deterred structural studies and there is little published regarding resolved secondary features or precise binding mchanisms for any part of APC. As such, solution-based NMR is an attractive method to study structural features and residues that are important for the interaction of APC with partners such as beta-catenin and topo II.
Our objective in this application is to resolve structural features that facilitate interactions between truncated APC and binding partners beta-catenin and TopoII. We will define the domains of TopoII that bind to APC as well as the binding kinetics and stoichiometry of the various APC TopoII and beta-catenin interactions. It is expected that knowledge gained through successful completion of this research will lead to submission of a federal grant proposal aimed to expand analysis of this critical APC domain to further define regions potentially responsible for colorectal cancer resistance to topoII inhibitors, and also to determine why this region appears to be selected in APC truncations expressed in most colorectal cancers.