Ape1 regulates WNT/β-catenin signaling through its redox functional domain in pancreatic cancer cells

Apurinic/apyrimidinic endonuclease 1/redox factor-1 (Apel/Ref-1, Apel) is a multifunctional protein that is upregulated in human pancreatic cancer. Apel redox domain plays an essential role in regulating the effects of reactive oxygen species (ROS) generated during physiological metabolism and pathological stress. In the present study, we explored whether Apel and ROS affect WNT/beta-catenin signaling. We used E3330, a small molecule inhibitor of the redox activity of Apel, and a siRNA approach to knock down Apel, in two human pancreatic cancer cell lines. Inhibition of Apel resulted in growth suppression of pancreatic cancer cells, increased ROS levels, upregulation of beta-catenin and c-myc and downregulation of cyclin D1. Consistent with these data, overexpression of Apel in pancreatic cancer cells reduced ROS and c-myc levels and increased cyclin D1 levels. Moreover, treatment of pancreatic cancer cells with H2O2 to induce oxidative stress resulted in upregulated ROS levels, decreased Apel at both the mRNA and protein level, and alterations in WNT/beta-catenin pathway components. Finally, treatment of pancreatic cancer cells with the WNT/beta-catenin inhibitor IWR-1 resulted in growth inhibition, which was greatly enhanced when combined with E3330 treatment. In summary, our results demonstrate that ROS is an important intracellular messenger that can modulate WNT/beta-catenin signaling. The present study provides interesting new insight into crosstalk between the redox function of Apel and WNT/beta-catenin signaling in cancer cells. Furthermore, our data show that the combination of Apel and WNT inhibitors enhanced the inhibition of pancreatic cell proliferation. These results provide a promising novel therapeutic strategy for treating pancreatic cancer in future.