Specificity protein, Sp1-mediated increased expression of Prdx6 as a curcumin-induced antioxidant defense in lens epithelial cells against oxidative stress

Peroxiredoxin 6 (Prdx6) is a pleiotropic oxidative stress-response protein that defends cells against reactive oxygen species (ROS)-induced damage. Curcumin, a naturally occurring agent, has diversified beneficial roles including cytoprotection. Using human lens epithelial cells (hLECs) and Prdx6-deficient cells, we show the evidence that curcumin protects cells by upregulating Prdx6 transcription via invoking specificity protein 1 (Sp1) activity against proapoptotic stimuli. Curcumin enhanced Sp1 and Prdx6 mRNA and protein expression in a concentration-dependent manner, as evidenced by western and real-time PCR analyses, and thereby negatively regulated ROS-mediated apoptosis by blunting ROS expression and lipid peroxidation. Bioinformatic analysis and DNA-protein binding assays disclosed three active Sp1 sites (-19/27, -61/69 and -82/89) in Prdx6 promoter. Co-transfection experiments with Sp1 and Prdx6 promoter-chloramphenicol acetyltransferase (CAT) constructs showed that CAT activity was dramatically increased in LECs or Sp1-deficient cells (SL2). Curcumin treatment of LECs enhanced Sp1 binding to its sites, consistent with curcumin-dependent stimulation of Prdx6 promoter with Sp1 sites and cytoprotection. Notably, disruption of Sp1 sites by point mutagenesis abolished curcumin transactivation of Prdx6. Also, curcumin failed to activate Prdx6 expression in the presence of Sp1 inhibitors, demonstrating that curcumin-mediated increased expression of Prdx6 was dependent on Sp1 activity. Collectively, the study may provide a foundation for developing transcription-based inductive therapy to reinforce endogenous antioxidant defense by using dietary supplements.