Calcineurin inhibitors such as cyclosporin A (CsA) are widely used to treat organ transplantation-associated complications. However, CsA use is limited due to renal dysfunction. This study attempts to characterize the mechanism of CsA-induced nephrotoxicity using a human embryonic kidney cell line (HK-2). We performed microarray-based whole-genome expression analysis in HK-2 cells. CsA treatment induced the expression of endoplasmic reticulum (ER) stress-related and apoptosis-inducing genes at 6 and 24 h, respectively, indicating that ER-stress predisposed the cells to apoptosis. G1 phase cell-cycle arrest was also observed via ER stress in CsA-treated cells. Furthermore, we found an inverse relationship between activating transcription factor 3 (ATF3), a stress-inducible protein, and C/EBP homologous protein (CHOP), an apoptosis-inducing protein. Moreover, when ATF3 knockdown cells were exposed to CsA, a prompt induction of CHOP was observed, which stimulated ROS production and induced cell death-related genes as compared to wild type. Taken together, our data demonstrate that ATF3 plays a pivotal role in the attenuation of CsA-induced nephrotoxicity by downregulating CHOP and ROS production mediated by ER stress. (C) 2014 Elsevier Inc. All rights reserved.