Glutathionylation of UCP2 sensitizes drug resistant leukemia cells to chemotherapeutics.

Uncoupling protein-2 (UCP2) is used by cells to control reactive oxygen species (ROS) production by mitochondria. This ability depends on the glutathionylation state of UCP2. UCP2 is often overexpressed in drug resistant cancer cells and therein controls cell ROS levels and limits drug toxicity. With our recent observation that glutathionylation deactivates proton leak through UCP2, we decided to test if diamide, a glutathionylation catalyst, can sensitize drug resistant cells to chemotherapeutic agents. Using drug sensitive HL-60 cells and the drug resistant HL-60 subline, Mx2, we show that chemical induction of glutathionylation selectively deactivates proton leak through UCP2 in Mx2 cells. Chemical glutathionylation of UCP2 disables chemoresistance in the Mx2 cells. Exposure to 200μM diamide led to a significant increase in Mx2 cell death that was augmented when cells were exposed to either menadione or the anthracycline doxorubicin. Diamide also sensitized Mx2 cells to a number of other chemotherapeutics. Proton leak through UCP2 contributed significantly to the energetics of the Mx2 cells. Knockdown of UCP2 led to a significant decrease in both resting and state 4 (i.e., proton leak-dependent) respiration (~43% and 62%, respectively) in Mx2 cells. Similarly diamide inhibited proton leak-dependent respiration by ~64%. In contrast, diamide had very little effect on proton leak in HL-60 cells. Collectively, our observations indicate that manipulation of UCP2 glutathionylation status can serve as a therapeutic strategy for cancer treatment.