Abstract PR004: Mechanistic Basis for TGF-β-induced Fibrogenic EMTs in Metastasis

Abstract The cytokine TGF-β is a central regulator of tissue homeostasis and regeneration through multiple coordinated effects on epithelial, immune, and mesenchymal stromal systems. Malfunctions of TGF-β signaling cause fibrosis, immune dysfunction, and cancer. As part of its multifunctional program, TGF-β induces epithelial-mesenchymal transitions (EMTs). Carcinoma cells use TGF-β to undergo EMT and adopt a highly plastic phenotype that facilitates tumor growth and metastasis. Notably, TGF-β-induced EMTs in epithelial progenitor cells are accompanied by the expression of fibrogenic factors that activate fibroblasts to produce and remodel the extracellular matrix. This not only occurs during wound healing but also in lung adenocarcinoma (LUAD) and pancreatic adenocarcinoma (PDAC) cells, suggesting that EMT and fibrogenesis are parts of an orchestrated program. We recently showed that the transcription factor RAS-Responsive Element-Binding Protein 1 (RREB1) activated by RAS-MAPK signaling synergizes with SMADs to coordinately activate the expression of EMT transcription factor Snai1 and fibrogenic genes in carcinoma progenitors (Su et al Nature 2020). Using metastasis transplantation models, we have now found that both arms of the RREB1-dependent TGF-β responses are important for metastasis. Knockout of individual fibrogenic genes in cancer cells inhibited metastasis without altering the induction of EMT by TGF-β. To address why these TGF-β target genes specifically require KRAS-activated RREB1 for transcriptional induction, we employed proteomics approaches coupled with a CRISPR-based genetic screen. With this approach we identified DXH9 and INO80 as RREB1-interacting factors essential for TGF-β activation of fibrogenic EMT programs in PDAC and LUAD cells. DXH9 and INO80 are helicases that interact and SMAD3 and RREB1 in response to TGF-β. Knockout of Dhx9 or Ino80 abolished the induction of Snai1 and fibrogenic genes by TGF-β, inhibited the LUAD metastasis, and decreased intratumoral fibrosis, thus phenocopying the knockout of Rreb1. The helicase domain of DHX9 is required for TGF-β gene responses and metastasis. Our evidence indicates that RREB1, DXH9, and INO80 function to remodel the chromatin at specific loci that constitute a TGF-β-dependent fibrogenic EMT program. This work illuminates a previously unknown cooperation between TGF-β and RAS-MAPK pathways during epithelial tissue regeneration and its cooption in carcinoma metastasis. Citation Format: Jun Ho Lee, Harihar Basnet, Francisco Sánchez-Rivera, Zhenghan Wang, Liangji Li, Joan Massagué. Mechanistic basis for TGF-β-induced fibrogenic EMTs in metastasis [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr PR004.