Beta-Catenin Signaling Mediates Pathogenic Pro-Inflammatory Conversion Of Foxp3(+) T-Reg Cells Early During Colon Cancer Development

In the present study we provide a temporal and mechanistic explanation of how β-catenin signaling skews regulatory T cells (T reg ) into a pathogenic, pro-inflammatory phenotype that co-express the Th17 lineage transcription factor RORγt along with Foxp3 during colon cancer (CC) development. We previously described this distinct subset of T reg s in the peripheral blood (PB) of established CC patients that suppresses effector T cell functions but simultaneously maintains inflammation by failing to regulate mast cell degranulation and production of IL-17. Moreover, we showed in mice that RORγt expression correlates with elevated β-catenin levels in T cells and that RORγt is a transcriptional target of β-catenin interaction partners TCF-1 ( Tcf7 ) and HEB ( Tcf12 ). To elucidate how Wnt/β-catenin signaling orchestrates the induction of pathogenic properties in T reg s specifically we analyzed inflammatory bowel disease (IBD) patients9 tissue and PB. As IBD can progress to colon cancer, this disease presents a unique platform to study the temporal emergence of RORγt + /Foxp3 + T reg s during the course of the disease. To further mechanistically establish how activated β-catenin signaling facilitates re-programming of T reg s and acquisition of pro-inflammatory properties we over-expressed β-catenin specifically in T reg s and/or knocked out its interaction partners TCF-1 and HEB in a Foxp3-Cre mouse model. Indeed, in a specific sub-population of IBD patients we were able to detect RORγt + /Foxp3 + double positive T reg s in the patients9 blood and tissue, expressing high levels of β-catenin and producing IL-17 upon re-stimulation. Mice expressing β-catenin T reg -specifically showed striking X-linked immune pathology. Males died 4 weeks after birth of a severe scurfy-like phenotype, indicating failure of T reg function. β-catenin overexpressing T reg s in mice displayed a reduced suppressive capacity, higher rate of apoptosis and produced effector cytokines IL-17 and IFN-γ. Furthermore, the chromatin accessibility of bona fide T reg genes was drastically reduced, whereas accessibility in T cell activation and IL-17 signature genes increased compared to wild-type T reg s in ATACseq analysis. An additional T reg -specific knock-out of HEB or TCF-1 reduced or delayed auto-immunity, respectively, with increased survival in both cases and partial rescue of systemic T reg numbers. We herewith provide evidence that induction of β-catenin signaling is indeed responsible for the pathogenic, pro-inflammatory conversion of T reg s through activation of RORγt expression. Further transcriptome analysis will reveal how the epigenetic changes in the chromatin translate to gene expression. We anticipate, that this mechanistic insight into β-catenin mediated pathogenic conversion of T reg s will reveal novel targets for cancer immuno-therapy. Citation Format: Jasmin Quandt, Leila Haghi, Akinola O. Emmanuel, Khashayarsha Khazaie, Fotini Gounari. β-catenin signaling mediates pathogenic pro-inflammatory conversion of Foxp3 + T reg cells early during colon cancer development [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-281.