Abstract 3694: TonEBP promotes chemoresistance and recurrence of hepatocellular carcinoma via DNA repair of cancer stem cells

Hepatocellular carcinoma (HCC) is common cancer with a high rate of recurrence and mortality. In addition to diverse etiological agents and wide heterogeneity in individual tumors, inherent resistance to chemotherapeutic agents and a very high rate of recurrence are the major contributing factors to HCC-related death. Cancer stem cells (CSCs) are believed to play a major role in these pathological properties due to its highly efficient DNA damage responses. However, mechanistic understanding of liver CSCs is still lacking, unlike other cancers. Tonicity-responsive enhancer binding protein (TonEBP), also known as NFAT5, is a central component of the pro-inflammatory enhanceosome in which TonEBP bridges activated transcription factors to histone acetyltransferase p300 on gene promoters. Although inflammation is intimately associated with the pathogenesis of HCC, the role of TonEBP is unknown. We aimed to identify a function of TonEBP in HCC and liver CSCs. We previously reported that TonEBP promotes hepatocellular carcinogenesis and expression of TonEBP predicts recurrence, metastasis, and death of patients with HCC. Three common sites of TonEBP action in response to diverse etiological agents leading to tumorigenesis and tumor growth were found: cell injury and inflammation, induction by oxidative stress, and stimulation of the COX-2 promoter. The goal of the following study was to understand how TonEBP mediates recurrence and metastasis of HCC. In HCC cells, TonEBP was required for self-renewal and tumorigenic potential of liver CSCs. In addition, TonEBP knockdown reduced the maintenance of liver CSCs. TonEBP mediated DNA repair of the CSCs caused by cisplatin, UV, and mitomycin C - both inter- and intra-strand crosslinks. Chemoresistance by highly activated DNA repair is contributed by TonEBP. We found that TonEBP-mediated DNA repair was carried out by ERCC1/XPF dimer. TonEBP interacted with ERCC1/XPF dimer through rel-homology domain (RHD) and was required for DNA recruitment of the dimer. RHD is required for TonEBP-mediated self-renewal of liver CSCs. TonEBP-ERCC1/XPF complex activated ATM serine/threonine kinase in response to DNA damage leading to activation of NF-κB, STAT3, and expression of pro-inflammatory cytokines, which stimulate the self-renewal of CSCs. Of note, in a cohort of 296 patients with HCC, expression of ERCC1-XPF predicted recurrence, metastasis, and death with high significance in multivariate analyses in TonEBP dependent manner. We conclude that TonEBP-ERCC1/XPF plays a pivotal role in DNA repair-associated chemoresistance and recurrence via liver CSCs. As such, the TonEBP-ERCC1/XPF complex is an attractive target for the prevention of recurrence and effective chemotherapy in HCC. Citation Format: Jun Ho Lee, Jae Hee Suh, Soo Youn Choi, Hyun Je Kang, Orlando D. Scharer, Neung Hwa Park, Hyug Moo Kwon. TonEBP promotes chemoresistance and recurrence of hepatocellular carcinoma via DNA repair of cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3694.