3-Hydroxybutyrate dehydrogenase-2 and ferritin-H synergistically regulate intracellular iron.

Siderophores are best known as small iron-binding molecules that facilitate iron uptake in bacteria and fungi. In our previous study, we demonstrated that eukaryotes also produce siderophore-like molecules via a remarkably conserved biosynthetic pathway. A member of the short-chain dehydrogenase family of reductases, 3-hydroxybutyrate dehydrogenase-2, catalyzes a rate-limiting step in the biogenesis of the mammalian siderophore. Physiologically, depletion of the mammalian siderophore by inhibiting expression of the 3-hydroxybutyrate dehydrogenase-2 gene (Bdh2) results in abnormal accumulation of intracellular iron, increased oxidative stress, and mitochondrial iron deficiency. Thus, the mammalian siderophore is an important regulator of cellular iron homeostasis. The cellular iron storage protein ferritin also regulates iron metabolism and protects cells from oxidative stress. Depletion of ferritin results in intracellular iron accumulation, predisposes to oxidative stress, and confers a growth advantage to cells. We therefore hypothesize that the siderophore and ferritin coregulate cellular iron metabolism/homeostasis in eukaryotes. We tested this prediction by depleting both the siderophore and ferritin. This resulted in a marked accumulation of cellular iron, and caused increased sensitivity to oxidants. Interestingly, cells lacking both the siderophore and ferritin proliferated at a higher rate than cells lacking either of these components alone. Taken together, our findings suggest that the siderophore and ferritin synergistically regulate cellular iron levels.