LAUSR

Colorectal cancer (CRC) originates from stem cell (SC) overpopulation, which is driven by constitutively activated WNT-signaling due to mutations in genes that encode components of the WNT-signaling pathway, particularly APC. WNT-signaling is regulated by the ꞵ-catenin destruction complex, which contains APC, AXIN1, AXIN2 and other proteins. Availability of AXIN1/2 proteins is the rate-limiting factor of destruction complex function. The Gap in Our Knowledge is how to target AXIN in order to restore destruction complex function in APC-mutant colon tissues. A growing body of scientific evidence shows both AXIN1 & AXIN2 promote ꞵ-catenin degradation and AXINs are hub proteins involved in regulation of multiple cellular pathways that play a role in tumor phenotype. While AXIN2 expression is up-regulated in CRC, the increased level of AXIN2 is incapable of deterring CRC progression. This evidence indicates that AXIN2 is in a key pivotal position to therapeutically target WNT signaling whereby the availability of AXIN2 can be used to fine-tune ꞵ-catenin levels. We HYPOTHESIZE that the intracellular level of AXIN2 and AXIN1 determines the degree of WNT-signaling activity in APC-mutant CRC cells and affects tumor cell phenotypic properties relevant to CRC progression. Accordingly, we have created siRNA-mediated AXIN2 knockdown and lentiviral-based AXIN2 overexpressing HT29 and SW480 cells to study the effect of modulating AXIN2 levels. The RESULTS show that decreasing AXIN2 leads to increased WNT-signaling and increasing AXIN2 leads to increased expression of WNT-target genes. Moreover, increasing AXIN2 leads to diminished tumor cell phenotype as shown by: 1) lower cell proliferation rate; 2) up-regulated expression of SC markers (ALDH & LGR5) and increased SC population size (ALDEFLUOR+ or LGR5+); 3) down-regulated cell cycle rate; 4) down-regulated apoptosis. Moreover, our bioinformatics analyses of the effect of tankyrase inhibitors (TIs), which prevent AXIN degradation, indicate that efficacy of TIs against CRC cells depends on the APC genotype. Thus, our findings indicate that AXIN2, by down-regulating WNT-signaling, reduces cancer stem cell phenotype including decreased SC population size. SIGNIFICANCE: discovering ways to target AXIN2-based mechanisms has vast clinical importance for developing new treatment against CRC. Citation Format: Chi Zhang, Caroline Facey, Lynn Opdenaker, Bruce Boman. A study of AXIN2-regulatory mechanisms and their role in the stem cell origin of human CRC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2452.