Enhancer of rudimentary homolog regulates DNA damage response in hepatocellular carcinoma

We previously demonstrated that the enhancer of rudimentary homolog (ERH) gene is required for the expression of multiple cell cycle and DNA damage response (DDR) genes. The present study investigated the role of ERH and its target DNA damage repair genes in hepatocellular carcinoma cells. We observed positive correlation between ERH and ataxia telangiectasia and Rad3 related (ATR) expression in liver tissues. Expression of ERH, ATR as well as checkpoint kinase 1 (CHK1) were higher in HCCs than in normal liver tissues. Knocking-down ERH augmented ultraviolet light induced DNA damage in HepG2 cells. ATR protein level is reduced upon ERH depletion as a result of defect in the splicing of ATR mRNA. Consequently, the ATR effector kinase Chk1 failed to be phosphorylated upon ultraviolet light or hydroxyurea treatment in ERH knocked-down HepG2 cells. Finally, we observed Chk1 inhibitor AZD7762 enhanced the effect of doxorubicin on inhibiting growth of HCC cells in vitro and in vivo. This study suggested that ERH regulates the splicing of the DNA damage response proteins ATR in HCC cells, and targeting DNA damage response by Chk1 inhibitor augments chemotherapy to treat HCC cells.