The goal of this project is to understand the mechanism of Wnt/?-catenin transactivation and its regulation by the adenomatous polyposis coli (APC), a tumor suppressor that is mutated in the majority of human colon cancers. Preliminary data show that the metastatic tumor suppressor ?-catenin, plays a direct role in the repression of Wnt/?-catenin-dependent genes through recruitment of the APC tumor suppressor, and repression-coupled exchange of coactivator and corepressor complexes, resulting in release of ?-catenin from DNA-bound LEF-1. Novel components of APC and ?-catenin nuclear complexes will be identified by robust and sensitive proteomics analyses and assessed for recruitment to Wnt regulatory loci by genomic ChIP-Seq analysis (Aim 1), the detailed mechanism of APC-mediated repression and coregulator exchange will be defined in HT29-APC colon cancer cells (Aim 2), and the role of ?-catenin in this process will be studied in prostate and colon cancer cells, as well as in a novel cell-free assay system developed to understand ?- catenin release from LEF-1. Together, these data will identify new proteins that control Wnt-dependent cancer cell growth and reveal previously unknown roles for the APC and alpha-catenin tumor suppressors in the nucleus.
We report here the identification of novel proteins and functions for two important tumor suppressor proteins, APC and alpha-catenin, and report that these proteins function directly to block the expression of genes that drive tumorigenesis and progression of colon, breast and prostate cancers. In this proposal, we will analyze how these two important tumor suppressors interact with each other and with newly-identified partner proteins to regulate gene expression in the nucleus in response to cues from the cell environment. The proteins that are targeted for inhibition by these tumor suppressors are indispensable for cancer cell growth, and therefore are excellent candidates for future therapeutic strategies to combat these human cancers.
