Biological and clinical implications of retinoic acid-responsive genes in human hepatocellular carcinoma cells

Abstract

Background & aims: Accumulating data from epidemiological and experimental studies have suggested that retinoids, which are vitamin A derivatives, exert antitumor activity in various organs. We performed a gene screening based on in silico analysis of retinoic acid response elements (RAREs) to identify the genes facilitating the antitumor activity of retinoic acid (RA) and investigated their clinical significance in hepatocellular carcinoma (HCC).

Methods: In silico analysis of RAREs was performed in the 5-kb upstream region of EST clusters. Chromatin immunoprecipitation analysis of the retinoic acid receptors and gene expression analysis were performed in HuH7, HepG2, and MCF7 cells treated with all-trans RA (ATRA). mRNA expression of RA-responsive genes was investigated using tumor and non-tumor tissues of clinical HCC samples from 171 patients. The association between gene expression and survival of patients was examined by Cox regression analysis.

Results: We identified 201 candidate genes with promoter regions containing consensus RARE and finally selected 26 RA-responsive genes. Of these, downregulation of OTU domain-containing 7B (OTUD7B) gene, which was upregulated by ATRA, in tumor tissue was associated with a low cancer-specific survival of HCC patients. Functional analyses revealed that OTUD7B negatively regulates nuclear factor κB (NF-κB) signaling and decreases the survival of HCC cells.

Conclusions: We identified RA-responsive genes which are regulated by retinoid signal and found that low-OTUD7B mRNA expression is associated with a poor prognosis for HCC patients. OTUD7B-mediated inhibition of NF-κB signaling may be an effective target for antitumor therapy for HCC.

Keywords: ATRA; CYP26A1; ChIP; Chemoprevention; DR5; EST; HCC; Hepatocellular carcinoma; NF-κB; OTU domain-containing 7B; OTUD7B; RA; RAR; RARE; RT-PCR; RXR; Retinoid; TRRA; all-trans retinoic acid; chromatin immunoprecipitation; cytochrome P450 family 26A1; direct repeat 5; expression sequence tag; hepatocellular carcinoma; nuclear factor kappa B; retinoic acid; retinoic acid receptor; retinoic acid response element; retinoid X receptor; reverse transcription-polymerase chain reaction; siRNA; small-interfering RNA; target RNA of retinoic acid.