What are the roles of vertebrate catenins in the nucleus, and how do they contribute to shared or distinct developmental or disease outcomes? In sharp contrast to the dominant focus upon beta-catenin in the existing literature, we will probe the nuclear roles of p120-catenin and plakophilin3-catenin. Each is poorly understood despite playing key roles in development and human pathology. We recently revealed that p120 and additional catenins are regulated via Wnt-pathway mechanisms known to act upon beta-catenin. We thus ask if Wnt (or other) signals may involve a larger catenin network whose nuclear activities have yet to be defined. Providing a strong entry point to the nuclear functions of these "other catenins", we recently discovered two novel complexes that respectively involve p120-catenin and plakophilin3-catenin. The first complex is of p120-catenin with REST/CoREST (Aim 1), and the second is of plakophilin3-catenin with ETV1 (Aim 2). Given the importance of REST/CoREST and ETV1 in stem cells, development and pathology, an understanding of these complexes will have an impact upon multiple scientific fields. Finally, to provide the scientific community with a much needed but currently absent overview of catenin nuclear functions, we will undertake the first genome-wide comparative evaluation of representative catenins from three distinct subfamilies (Aim 3). We will employ Xenopus embryos and mammalian cell lines for mechanistic and functional studies in Aims 1 and 2, and mouse embryo stem cells (mESCs) for our genome wide analysis of nuclear catenins in Aim 3. Our Hypothesis is that catenins of the p120- and plakophilin-subfamilies, in common with the much better known beta-catenin, act in networked nuclear capacities during vertebrate development and disease.
Aim 1. Reveal nuclear functions of the novel p120-catenin:REST/CoREST complex.
Aim 2. Reveal nuclear functions of the novel Pkp3-catenin:ETV1 complex.
Aim 3. Genome-wide analysis of p120-, plakophilin3-, and beta-catenin nuclear functions. The key nature of beta-catenin and canonical Wnt signaling in development and human disease is firmly established, yet the nuclear contributions of additional catenins, that likewise play key roles in human embryogenesis and disease, is in contrast poorly understood. By in-depth examination of the nuclear roles of two novel catenin complexes we have discovered (respectively involving p120- and Pkp3-catenin), as well as revealing these catenins'nuclear roles on a much wider whole-genome level, we will produce the first understanding of what we hypothesize is an integrated network of catenin functions needed to maintain health.
Through conducting focused experiments in a proven animal model (frog embryos) as well as mammalian cell lines (Aims 1&2), and then addressing broader questions at the whole-genome level (Aim 3), the work proposed in this Application will help reveal the nuclear roles of a key group of proteins named catenins. While beta-catenin is already convincingly established to be a critical player in animal development and disease progression, very little is known concerning the nuclear roles of related catenins such as p120-catenin and plakophilin3-catenin that likewise play vital developmental roles and are implicated in human disease. Based upon our preliminary evidence, we will test the hypothesis that p120 and plakophilin3 regulate important transcriptional regulators that we have revealed they bind, and on the wider whole-genome level, that these two catenins along with beta-catenin regulate shared as well as distinct genes central in development and pathology.