The long non-coding RNA H19 suppresses carcinogenesis and chemoresistance in hepatocellular carcinoma

Abstract

The long non-coding RNA (lncRNA) <i>H19</i> represents a maternally expressed and epigenetically regulated imprinted gene product and is discussed to have either tumor-promoting or tumor-suppressive actions. Recently, <i>H19</i> was shown to be regulated under inflammatory conditions. Therefore, aim of this study was to determine the function of <i>H19</i> in hepatocellular carcinoma (HCC), an inflammation-associated type of tumor. In four different human HCC patient cohorts <i>H19</i> was distinctly downregulated in tumor tissue compared to normal or non-tumorous adjacent tissue. We therefore determined the action of <i>H19</i> in three different human hepatoma cell lines (HepG2, Plc/Prf5, and Huh7). Clonogenicity and proliferation assays showed that <i>H19</i> overexpression could suppress tumor cell survival and proliferation after treatment with either sorafenib or doxorubicin, suggesting chemosensitizing actions of <i>H19</i>. Since HCC displays a highly chemoresistant tumor entity, cell lines resistant to doxorubicin or sorafenib were established. In all six chemoresistant cell lines <i>H19</i> expression was significantly downregulated. The promoter methylation of the <i>H19</i> gene was significantly different in chemoresistant cell lines compared to their sensitive counterparts. Chemoresistant cells were sensitized after <i>H19</i> overexpression by either increasing the cytotoxic action of doxorubicin or decreasing cell proliferation upon sorafenib treatment. An <i>H19</i> knockout mouse model (<i>H19</i>Δ3) showed increased tumor development and tumor cell proliferation after treatment with the carcinogen diethylnitrosamine (DEN) independent of the reciprocally imprinted insulin-like growth factor 2 (IGF2). In conclusion, <i>H19</i> suppresses hepatocarcinogenesis, hepatoma cell growth, and HCC chemoresistance. Thus, mimicking <i>H19</i> action might be a potential target to overcome chemoresistance in future HCC therapy.