Abstract LB-147: Characterization of a Kaiso overexpressing transgenic mouse model

Abstract Introduction: The WNT signaling pathway plays critical roles during embryogenesis and maintaining homeostasis of adult tissues. However constitutive WNT signaling leads to tumorigenesis. Upon activation of the WNT pathway, the main downstream effector of the WNT pathway, ß-catenin, stabilizes and translocates to the nucleus where it activates transcription of WNT target genes. Recently, our lab along with others identified the novel transcription factor Kaiso as a negative regulator of WNT target genes in mammalian cell lines and Xenopus models. However a study using a Kaiso depleted mouse model implicated Kaiso as a positive regulator of WNT signaling. Kaiso is a member of the BTB/POZ (broad-complex, tramtrack and bric-à-brac/poxvirus and zinc finger) protein family. The goal of this study is to elucidate the role of Kaiso in WNT signaling using the ApcMin/+ mouse model of intestinal cancer. Methodology: To assess the role of Kaiso in colon cancer in vivo, Kaiso overexpressing transgenic mice were created (KaisoTg). Targeted overexpression of Kaiso in KaisoTg mice was obtained by pronuclear injection of Kaiso cDNA under the control of the intestine-specific villin promoter. Reverse transcription PCR (RT-PCR) and Western Blot analyses were used to determine tissue specific Kaiso overexpression in KaisoTg mice. Immunohistochemisty (IHC) was performed on mouse intestinal tissues to examine the subcellular localization of Kaiso and assess developmental defects. KaisoTg mice were then mated with APCMin/+ mice models of intestinal cancer that develop polyps in the small intestine due to constitutively active -catenin. KaisoTg-APCMin/+ mice were examined for gross morphological phenotypes and IHC was performed on mouse intestinal tissues for Kaiso and other WNT target genes (e.g. cyclin D1) to elucidate the effects of Kaiso on the WNT pathway. Results: Western Blot analysis revealed high, moderate and low levels of Kaiso overexpression in three founder lines of the KaisoTg mice. RT-PCR analysis showed Kaiso overexpression limited to villin positive tissues including kidney, small and large intestines. IHC analysis of KaisoTg tissues showed no gross morphological differences compared to non-transgenic mice. However KaisoTg-APCMin/+ displayed decreased body size and weight, and had decreased life span when compared to the parentals (i.e. KaisoTg and APCmin/+). IHC analysis of KaisoTg-APCMin/+ mouse intestines revealed increased polyp numbers with Kaiso staining concentrated near the basal surface of the polyps. These data support Kaiso's potential role as an oncogene in mouse intestinal tissues. 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-147.