Iron Chelation by Deferoxamine Induces Autophagy

Deferoxamine (DFO) is a high affinity Fe (III) chelator produced by Streptomyces pilosus that is used clinically to remove systemic iron in secondary iron overload disorders. DFO cannot be absorbed through the intestine and must be injected. As shown previously, De Domenico et al. EMBO J (2006), expression of Ferroportin (Fpn), the only mammalian iron exporter, can deplete cells of ferritin by lowering cytosolic iron and by exporting iron from cells. Fpn-mediated iron loss induces ferritin degradation by the proteosome. In this study we show that permeable iron chelators, desferirax or deferriprone also induce the proteosomal degradation of ferritin. In contrast, DFO-mediated iron chelation at clinically useful concentrations, leads to ferritin degradation in lysosomes. Immunochemical analysis revealed that DFO-treated cells show increased levels of LC3B, a protein required for autophagy, suggesting that DFO induces autophagy. Treatment of cells with desferasirox or deferriprone did not lead to accumulation of LC3B. Studies using high molecular weight conjugates of DFO or inhibitors of endocytosis showed that the presence of DFO in lysosomes was responsible for the induction of autophagy. Incubation of DFO-treated cells with 3-methyladenine, an autophagy inhibitor, does not, however, prevent ferritin loss suggesting there may be an alternate route for ferritin degradation. This hypothesis was confirmed by examining the effect of the proteosome inhibitor, MG132, on DFOinduced autophagy in cells treated with DFO and 3-methyladenine. Addition of MG132 to 3-methyladenine treated cells prevents ferritin degradation. These results indicate that ferritin degradation occurs by two routes: a DFO-induced entry of ferritin into lysosomes and a cytosolic route in which iron is extracted from ferritin prior to degradation by the proteosome.