Abstract 3075: Effect of reducing AXIN2 levels in CRC cells with APC mutation and activated WNT signaling

Regulation of the WNT/beta-catenin signaling pathway occurs by a negative feedback loop that keeps beta-catenin levels in check in normal cells. Dysregulation of this feedback mechanism due to APC mutation is well known. However, the role of AXIN2, another component of this negative feedback loop is less known, particularly in APC mutant tissues. Our goal is to study how AXIN2 functions as part of the negative WNT/beta-catenin signaling feedback loop and understand of how it contributes to CRC development. Our bioinformatics analysis suggests that CRC cells carrying APC-truncating mutations still retain residual function of the destruction complex, but there are significant changes between AXIN2 and APC expression levels. Therefore, we hypothesize that the interaction between truncated-APC and AXIN2 is responsible for the dysregulation of the feedback loop. We found, using a TCF/LEF reporter assay, that siRNA-mediated knockdown of AXIN2 leads to increased WNT/beta-catenin signaling. This result confirmed the functional integrity of the downstream part of the WNT pathway from destruction complex to transcription activation by TCF/beta-catenin complex. It also narrowed down the dysregulated component(s) to within the destruction complex. Protein analysis further demonstrated that AXIN2 siRNA-mediated knockdown changed expression of several WNT/beta-catenin target genes. Surprisingly, siRNA-mediated knockdown led to decreased cell proliferation of HT29 cells. We surmise that AXIN2 knockdown in the setting of mutant APC leads to a high level of WNT signaling that reduces the self-renewal capacity of colonic cancer stem cells and lowers the rate of cell proliferation. Overall, our results indicate that it is important to understand how WNT signaling levels play a role in SC self-renewal and stemness. We conjecture that if WNT signaling is not strictly controlled in CSCs, high WNT levels can be detrimental to CSC proliferation and/or survival, which could have important clinical implications. Citation Format: Chi Zhang, Caroline O. Facey, Katherine Funk, Lynn M. Opdenaker, Bruce M. Boman. Effect of reducing AXIN2 levels in CRC cells with APC mutation and activated WNT signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3075.