Krebswissenschaft und -therapie

CD24 Induces the Activation of β-Catenin in Intestinal Tumorigenesis

Abstract

Fokra Ahmad, Kazanov Dina, Bedny Faina, Brazowski Eli, Varol Chen, Kraus Sarah, Arber Nadir and Shapira Shiran

Background: CD24 is a glycosylphosphatidylinositol-linked protein that functions as an adhesion molecule and is overexpressed at an early stage of CRC. The Wnt/β-catenin signaling pathway plays an important role in the CRC carcinogenesis process. We have previously shown that CD24 could affect the tumorigenesis process in ApcMin/+ mice.
Methods: CD24-inducible 293T-RExTM cells previously developed in our lab, HT29 and SW480 CRC cells were used to study this interaction in vitro. ApcMin/+ and CD24 knockout (KO) mice, both on a C57BL/6J genetic background, were crossed to generate double KO transgenic mice. Large bowel polyps were counted macroscopically and small bowel polyps were verified microscopically.
Results: In vitro Western blotting analyses showed that induced expression of CD24 led to the activation of β-catenin. Co-immunoprecipitation studies of CD24 and β-catenin indicated that these two proteins might be interacting. Cytoplasmic/nuclear fractionation showed that more active β-catenin enters the nucleus in cells that express CD24 compared to control cells. In addition, TOP/FOP luciferase reporter assay showed a significant increase in luciferase activity upon CD24 expression induction.Conversely, down-regulation of CD24 by mAbs and siRNA caused a decrease in the levels of active β-catenin. Depletion of CD24 alleles in ApcMin/+ mice led to a significant reduction in the number of polyps in the small and large intestine. The ApcMin/+mice displayed severe splenomegaly compared to ApcMin/+/CD24+/- mice and double KO mice were similar to WT mice with normal spleen size. HGB and RBC levels were significantly lower than in the double KO mice.
Conclusions: CD24 plays a major role in intestinal tumorigenesis. It interacts with the Wnt pathway by activating β-catenin. Down regulation of CD24 reduces the polyp burden in mice and therefore it might serve as an important target in the therapy of CRC.