Abstract 5459: Regulation of IGF2 by TGF-β signaling in liver cancers and stem cell homeostasis

Development of hepatocellular carcinoma (HCC), which remains lethal, is associated with alterations in multiple factors including the transforming growth factor beta (TGF-β) signaling pathway. Previously we have uncovered a unique role for TGF-β signaling molecules, Smad3 and its adaptor β2SP, in suppressing stem cell transformation into cancer. Yet, while TGF-β plays a pleiotropic role including regulating stem cell differentiation, proliferation, and inflammation, mechanistic insight into the dichotomy of TGF-β, and its role in stem cell transformation remains poorly understood for these cancers. Here, we took an integrated approach to identify and validate effects of changes in this pathway in HCC and identify potential therapeutic targets such as IGF2. We extended our mechanistic studies associated with the regulation of insulin-like growth factor 2 (IGF2) in the context of the TGF-β-pathway, by utilizing both human liver cancer cell lines and TGF-β signaling-deficient mice (β2SP +/- and β2SP +/- /Smad3 +/- ) that develop liver cancers. We found the following: 1) IGF2 promotes stemness, overexpression leading to increased expression of stem cell genes that include SOX2 and ALDH1A1, and sphere formation in liver cancer cells; 2) A marked increase in IGF2 mRNA and protein in HepG2 cells and Huh7 cells with β2SP stable knockdown; 3) TGF-β signaling through β2SP/Smad3 significantly inhibits IGF2 transcription; ChIP assays validated binding of Smad3 at the human IGF2 promoter region between -859bp to -688bp upstream of the IGF2 transcriptional start site; 4) TCGA based integrated analyses identify specific HCC patient groups with altered TGF-β members and high expression of IGF2 that could be potentially targetable for IGF2; 5) TCGA analyses of 33 cancers also revealed that potentially “switching off” TGF-β-pathway (through decreased expression levels) leads to increased stemness validating findings of our TGF-β deficient mouse models that phenocopy a human cancer stem cell syndrome. In summary, TGF-β negatively regulates IGF2 transcription: loss of TGF-β signaling through β2SP/Smad3 leads to IGF2 activation, contributing to tumor progression. TGF-β-β2SP/Smad3 are important for IGF2 repression and maintaining stem cell homeostasis, which may result from TGF-β/β2SP/Smad3 and/or CTCF-dependent regulation of IGF2. Our studies provide a framework for new animal models of liver and gastrointestinal cancers and future new therapeutics. Citation Format: Shuyun Rao, Sobia Zaidi, Kazufumi Ohshiro, Jian Chen, Shoujun Gu, Wilma Jogunoori, Jon White, Bibhuti Mishra, Shulin Li, Rehan Akbani, Lopa Mishra. Regulation of IGF2 by TGF-β signaling in liver cancers and stem cell homeostasis [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 5459.