Mitochondrial regulation by c-Myc and hypoxia-inducible factor-1α controls sensitivity to econazole

Econazole is an azole antifungal with anticancer activity that blocks Ca2+ influx and stimulates endoplasmic reticulum (ER) Ca2+ release through the generation of mitochondrial reactive oxygen species (ROS), resulting in sustained depletion of ER Ca2+ stores, protein synthesis inhibition, and cell death. c-Myc, a commonly activated oncogene, also promotes apoptosis in response to growth factor withdrawal and a variety of chemotherapeutic agents. We have investigated the role of c-myc in regulating sensitivity to econazole. Here, we show that c-myc-negative cells are profoundly resistant to econazole. c-Myc-negative rat fibroblasts failed to generate mitochondrial ROS in response to econazole and consequently failed to deplete the ER of Ca2+. HL60 cells knocked down for c-myc expression also displayed decreased ROS generation and decreased econazole sensitivity. Addition of H2O2 restored sensitivity to econazole in both c-myc-negative rat fibroblasts and c-myc knocked-down HL60 cells, supporting a role for ROS in cell death induction. c-Myc-negative cells and HL60 cells knocked down for c-myc have reduced mitochondrial content compared with c-myc-positive cells. The hypoxia sensor, hypoxia-inducible factor-1 alpha (HIF-1 alpha), interacts antagonistically with c-myc and also regulates mitochondrial biogenesis. Knockdown of HIF-1 alpha in c-myc-negative cells increased mitochondrial content restored ROS generation in response to econazole and increased sensitivity to the drug. Taken together, these results show that c-myc and HIF-1 alpha regulate sensitivity to econazole by modulating the ability of the drug to generate mitochondrial ROS.