Abstract 1259: HMGA1: An epigenetic gatekeeper of Wnt signals during colon tumorigenesis and regeneration

Abstract Cancer cells undergo epigenetic reprogramming to co-opt stem cell networks and drive tumor progression, although how this occurs remains unclear. The High Mobility Group A1 (HMGA1) gene encodes an architectural transcription factor that binds to DNA at AT-rich sequences where it recruits chromatin complexes to modulate gene expression. HMGA1 is highly expressed during embryogenesis and in adult stem cells, but silenced in differentiated cells. HMGA1 becomes re-expressed in aggressive cancers where high levels portend adverse outcomes. In colorectal cancer (CRC), HMGA1 is among the genes most highly overexpressed compared to normal colon epithelium. We previously discovered that HMGA1 is required for oncogenic phenotypes in CRC cell lines by inducing genes involved in an epithelial-mesenchymal transition. Hmga1 transgenic mice also develop aberrant proliferation and polyposis of small intestinal epithelium where Hmga1 amplifies Wnt signals to enhance self-renewal. To determine how HMGA1 functions in colon epithelial homeostasis and tumorigenesis, we examined mouse models with overexpression or deficiency of Hmga1. Here, we uncover a previously unknown role for HMGA1 as an epigenetic gatekeeper of Wnt signals in colon epithelial cells, both during tumorigenesis driven by mutant APC or stress-induced tissue repair. Strikingly, loss of just a single Hmga1 allele within the colon epithelium disrupts tumorigenesis while prolonging survival in two models of colon tumorigenesis driven by APC mutation, including CDX2P-CreERTCApcfl/fl and APCMin mice inoculated with pro-carcinogenic, enterotoxigenic Bacteroides fragilis. Single cell RNA sequencing in Apc mutant crypt epithelial cells reveals that intact Hmga1 is required for expansion in the Lgr5+ stem cell pool, deep secretory cells, and tuft cells during tumorigenesis. Hmga1 deficiency impacts the stem cell pool the greatest, decreasing Lgr5+ stem cells with skewing to more proliferative, transit amplifying-like cells. Single cell transcriptomic analyses together with assays of single cell chromatin accessibility demonstrate that Hmga1 maintains accessible chromatin to activate gene loci involved in Wnt signals, including Ascl2, a stem cell master regulator, Wnt agonist receptors, and Wnt downstream effectors. Surprisingly, either depletion or overexpression of Hmga1 has no impact on colon epithelial regeneration under homeostatic conditions, although Hmga1 overexpression enhances tissue repair and survival following injury induced by inflammation or irradiation. Together, our results establish HMGA1 as an epigenetic gatekeeper of Wnt signals in colon stem cells during APC-driven tumorigenesis or injury, but not steady state homeostasis, highlighting its role as a promising therapeutic target for both cancer and regenerative medicine. Citation Format: Linda M. S. Resar, Li Z. Luo, Lingling Xian, Iliana Herrera, Shaoguang Wu, Jung-Hyun Kim, Ying Feng, Julian Calderon-Espinosa, Eric R. Fearon, Cynthia Sears. HMGA1: An epigenetic gatekeeper of Wnt signals during colon tumorigenesis and regeneration [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1259.