Abstract 4234: Identification of molecular targets for retinoid signaling to regulate human hepatocellular carcinoma development: contribution of OTUD7B, a negative regulator of NF-κB signaling, in antitumor effect of retinoic acid

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Abstract BACKGROUND & AIMS: The loss of retinoid content and diminished retinoid signaling and downstream gene function are closely associated with the progression of liver disease including hepatocellular carcinoma (HCC). We previously identified 26 retinoic acid (RA)-responsive genes through a gene screening based on genome-wide in silico analysis of RA response elements. To understand the clinical and biological significance of RA-responsive genes in HCC, we performed gene expression analysis using clinical HCC samples and functional analyses using HCC cell lines. METHODS: mRNA expressions of RA-responsive genes were investigated in tumor and non-tumor tissues of the liver from 171 HCC patients by qRT-PCR. The association of clinicopathological parameters and gene expression with survival time was evaluated using univariate and multivariate Cox regression modeling. Potential anti-tumor activity of the candidate genes were evaluated using siRNA-mediated knockdown and adenovirus-mediated overexpression experiments in HCC cells. Functional analyses of the genes in the regulation of intracellular signal pathways were performed using luciferase-based reporter assays. RESULTS: Among the 9 genes that showed ATRA responsiveness in HuH7 or HepG2 cells, 3 genes, OTU domain-containing 7B (OTUD7B), kinesin family member 21B (KIF21B), and odd-skipped related 1 (OSR1) were significantly upregulated in tumor tissue compared to non-tumor tissue, and 4 genes, colony stimulating factor 3 receptor (CSF3R), thioredoxin interacting protein (TXNIP), cytochrome P450 26A1 (CYP26A1), and olfactomedin-like 1 (OLFML1) were downregulated. Frizzled 4 (FZD4) mRNA level was not different between tumor and non-tumor tissue. In tumor tissue, low expression of OTUD7B gene, which was upregulated by ATRA, was significantly associated with a low cancer-specific survival of HCC patients. Functional analyses revealed that OTUD7B negatively regulates nuclear factor κB (NF-κB) signaling and decreased the cell viability by inducing apoptosis in HCC cells. Frizzled 4 (FZD4), which was downregulated by ATRA, was shown to positively regulate Wnt/β-catenin signaling and increased the cell viability in HCC cells. DISCUSSIONS AND CONCLUSION: Our results suggest that the downregulation of OTUD7B expression in tumors facilitates tumor growth and enhances the cancer phenotype, leading to malignancy and poor cancer-specific survival. Therefore, retinoid signaling, which upregulates OTUD7B, prevents tumor development by suppressing aberrant NF-κB signaling in HCC cells, being beneficial for antitumor therapy for HCC. Our results also suggested that Wnt/β-catenin signaling may be a potential target for retinoid signaling to regulate HCC development. Citation Format: Goshi Shiota, Keita Kanki. Identification of molecular targets for retinoid signaling to regulate human hepatocellular carcinoma development: contribution of OTUD7B, a negative regulator of NF-κB signaling, in antitumor effect of retinoic acid. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4234. doi:10.1158/1538-7445.AM2014-4234