ATF2 knockdown reinforces oxidative stress‐induced apoptosis in TE7 cancer cells

Cancer cells showing low apoptotic effects following oxidative stress‐induced DNA damage are mainly affected by growth arrest. Thus, recent studies focus on improving anti‐cancer therapies by increasing apoptosis sensitivity. We aimed at identifying a universal molecule as potential target to enhance oxidative stress‐based anti‐cancer therapy through a switch from cell cycle arrest to apoptosis. A cDNA microarray was performed with hydrogen peroxide‐treated oesophageal squamous epithelial cancer cells TE 7. This cell line showed checkpoint activation via p21 WAF1 , but low apoptotic response following DNA damage. The potential target molecule was chosen depended on the following demands: it should regulate DNA damage response, cell cycle and apoptosis. As the transcription factor ATF 2 is implicated in all these processes, we focused on this protein. We investigated checkpoint activation via ATF 2. Indeed, ATF 2 knockdown revealed ATF 2‐triggered p21 WAF1 protein expression, suggesting p21 WAF1 transactivation through ATF 2. Using chromatin immunoprecipitation ( ChIP ), we identified a hitherto unknown ATF 2‐binding sequence in the p21 WAF1 promoter. p‐ ATF 2 was found to interact with p‐c‐Jun, creating the AP ‐1 complex. Moreover, ATF 2 knockdown led to c‐Jun downregulation. This suggests ATF 2‐driven induction of c‐Jun expression, thereby enhancing ATF 2 transcriptional activity via c‐Jun‐ ATF 2 heterodimerization. Notably, downregulation of ATF 2 caused a switch from cell cycle arrest to reinforced apoptosis, presumably via p21 WAF1 downregulation, confirming the importance of ATF 2 in the establishment of cell cycle arrest. 1‐Chloro‐2,4‐dinitrobenzene also led to ATF 2‐dependent G2/M arrest, suggesting that this is a general feature induced by oxidative stress. As ATF 2 knockdown also increased apoptosis, we propose ATF 2 as a target for combined oxidative stress‐based anti‐cancer therapies.