Deficiency of DDI2 suppresses liver cancer progression by worsening cell survival conditions

The levels of reactive oxygen species (ROS) and the extent of ensuing DNA damage significantly influence cancer initiation and progression. Of crucial importance, the aspartate protease DDI2 has been proposed to play a pivotal role in monitoring intracellular ROS levels (to trigger oxidative eustress or distress), as well as in the oxidative DNA damage repair, through redox homeostasis-determining factor Nrf1 (encoded by NFE2L1 ). However, the specific role of DDI2 in the multi-step process resulting in the development and progression of liver cancer remains elusive to date. In the present study, we employed the CRISPR/Cas9 gene editing system to create two nuanced lines of DDI2 knockout (i.e., DDI2 ^−/− and DDI2 ^insG/− ) from liver cancer cells. Subsequent experiments indicate that the knockout of DDI2 leads to increased ROS levels in hepatoma cells by downregulating two major antioxidant transcription factors Nrf1 and Nrf2 (encoded by NFE2L2 ), exacerbating endogenous DNA damages caused by ROS and not-yet-identified factors, thereby inhibiting cell proliferation and promoting apoptosis, and ultimately hindering in vivo malignant growth of xenograft tumor cells. Conversely, the restoration of DDI2 expression reverses the accumulation of ROS and associated DNA damage caused by DDI2 knockout, eliminating the subsequent inhibitory effects of DDI2 deficiency on both in vitro and in vivo growth of liver cancer cells. Collectively, these findings demonstrate that DDI2 deficiency impedes liver tumor growth by disrupting its survival environment, suggesting that DDI2 may serve as a novel therapeutic target for anti-cancer strategies aimed at modulating ROS or DNA damage processes.