Abstract LB-271: The biological role of the transcription factor Kaiso in breast tumorigenesis

Abstract Introduction: The canonical Wnt signalling pathway regulates various cellular processes (e.g. proliferation, differentiation, apoptosis) and leads to tumorigenesis when aberrantly activated. -catenin, the key downstream effector in Wnt signalling, translocates to the nucleus upon Wnt pathway activation, and activates target genes involved in tumorigenesis. The transcription factor Kaiso is a novel BTB/POZ (Broad complex, Tramtrak, Bric à brac/Pox virus and zinc finger) zinc finger (POZ-ZF) protein that specifically interacts with the cell adhesion cofactor p120ctn. Recent studies from our lab and others have revealed that Kaiso negatively regulates the canonical Wnt pathway by repressing activation of Wnt/ -catenin target genes. Some studies implicate Kaiso as a tumor suppressor (decreased expression in breast, ovarian and colon tumors), and others implicate Kaiso in tumor initiation (Kaiso-deficient mice are resistant to intestinal cancer). The goal of this study is to elucidate the biological role of Kaiso in breast tumorigenesis using various cellular assays. Methods: To assess Kaiso's role in breast cancer, Kaiso was misexpressed in MCF7 (human breast adenocarcinoma) cell lines. Stable Kaiso overexpressing and depleted cell lines were generated and assessed for cell proliferation and cell migration using focus formation, wound healing and matrigel invasion assays. Western blot analysis was performed to assess the effects of Kaiso misexpression on p120 and E-cadherin as well as epithelial-mesenchymal transition markers such as N-cadherin, Snail, Twist and Vimentin. The subcellular localization of Kaiso and its putative target genes in vivo was examined using immunohistochemistry (IHC) analysis of matched pairs of human normal and tumor breast tissue. Results: Focus formation assays revealed increased transformation by cells over-expressing Kaiso, suggesting an oncogenic role for Kaiso in cell culture. Preliminary wound healing and matrigel assays show increased cell motility and migration respectively in Kaiso over-expressing cells compared to parental control cells, thereby suggesting a role for Kaiso in the epithelial-mesenchymal transition. IHC analysis revealed predominant nuclear Kaiso expression in lobular and ductal breast carcinomas in breast tissues. These data support Kaiso's potential role as an oncogene in human breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-271.