The catenin proteins contribute to the biology of all animal cells and tissues, displaying essential embryonic and adult functions within differing sub-cellular compartments. For example, in addition to binding the inner (cytoplasmic) domain of cadherin trans-membrane cell-cell adhesion molecules, beta-catenin is well known to play an essential role in Wnt developmental signaling where within the nucleus it regulates transcription from specific gene targets. These gene targets are not only important for normal embryogenesis but also for the progression of human diseases including colon carcinoma and melanoma. In this renewal application, we focus upon the roles of less understood members of the catenin family of proteins, specifically members of the p120-catenin sub-family (p120- catenin; ARVCF-catenin; delta-catenin). A major interest is how upstream Wnt- pathway signals produce a network of p120 sub-family responses in addition to those better known for beta-catenin.
Our aims i nclude elucidating the biochemical mechanisms by which Wnt signals act upon p120 sub-family members. Evidence gathered for p120-catenin itself suggests that such regulation involves kinase activity and modulation of p120-catenin protein stability. Preliminary evidence relating to ARVCF and delta-catenin likewise leaves open the possibility of Wnt-pathway responsiveness, with for example, identification of two novel delta-catenin protein complexes involving known Wnt- pathway components. Overall, our work is aimed at expanding the scope of our understanding of catenin biology, with particular regard to the novel roles of p120-subF proteins in Wnt signaling. For our studies, we will predominantly employ Xenopus laevis (frog) embryos. This vertebrate system offers facile introduction (micro-injection) of exogenous constructs/ reagents, rapid external development and many biochemical and molecular advantages. For functional analysis, we will utilize knock-down (morpholino oligonucleotide), exogenous expression and rescue approaches in conjunction with the study of developmental phenotypes and biochemical and molecular tests of protein complex formation or target gene activity. To complement our work in developing amphibian embryos, we will employ select mammalian cell lines, for example, Wnt-responsive HEK293T cells. Project narrative: The Wnt signaling pathway is required for the development of all animals, while it's proper later regulation remains important in maintaining health. For example, the progression of >90% of human colon carcinomas and melanomas involves pathological activation of the Wnt pathway. Our proposal examines the functions of a group of proteins belonging to the p120-catenin sub-family, that we have evidence and hypothesize participates in Wnt signaling, and whose study will assist in understanding of both normal development and human disease. ? ? ?
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