Regulation of the human CHOP gene promoter by the stress response transcription factor ATF5 via the AARE1 site in human hepatoma HepG2 cells

Activating transcription factor (ATF) 5 is a member of the cAMP response element-binding protein (CREB)/ATF family of transcription factors. We have shown that ATF5 is a stress response transcription factor that responds to amino acid limitation, arsenite exposure, or cadmium exposure. In this study we investigated whether ATF5 is involved in the regulation of CCAAT/enhancer-binding protein (C/EBP) homologous protein ( CHOP) gene expression. We used a transient transfection system to express ATF5 and analyzed the regulation of CHOP gene promoter in human hepatoma, HepG2 cells. We also studied the effect of ATF5 knockdown on arsenite-induced CHOP protein expression and arsenite-induced cell death of HepG2 cells. We showed that ATF5 activates the CHOP gene promoter in HepG2 cells. Both deletion analysis and point mutations of the promoter revealed that amino acid response element (AARE) 1 is responsible for ATF5-dependent promoter activation. Furthermore, the existence of either AARE1 or activating protein-1 (AP-1) site is sufficient for transcriptional activation of the CHOP gene promoter by arsenite exposure, although complete induction requires the existence of both elements. We also demonstrated that knockdown of ATF5 reduced arsenite-induced CHOP protein expression and arsenite-induced cell death of HepG2 cells. These results suggested that the CHOP gene is a potential target for ATF5, and that ATF5 raises the arsenite-induced CHOP gene expression level via the AARE1 site in HepG2 cells.