We have designed a genetic screen to identify human genes that alter iron homeostasis when expressed in yeast. Human genes for the iron-storage protein ferritin have been expressed in yeast, and although the proteins are stable and assemble into the proper 24-subunit oligomer, only a small amount of iron is deposited within the ferritin core. We hypothesize that cytosolic iron chaperones that facilitate iron loading into ferritin may be expressed in human cells, but not in yeast, which do not synthesize ferritin. We have isolated multiple human cDNAs which, when expressed in a yeast cell that contains human ferritin, increase the transfer of cytosolic iron into ferritin. Using siRNA in cultured human cell lines, we have also determined that depletion of poly-C binding protein 1 (PCBP1) results in a defect in ferritin iron loading. Co-immunoprecipitation experiments indicate that PCBP1 binds to ferritin in vivo, but only in the presence of reduced iron. PCBP1 binds ferrous iron in vitro with micromolar affinity and can donate iron to ferritin in vitro. We propose that PCBP1 can function in yeast and human cells as an iron chaperone, and enhance the loading of iron into ferritin. PCBP1 is an iron chaperone for ferritin, and we investigated whether other PCBP family members also act as ferritin iron chaperones. PCBP1 is a member of a family of four homologous RNA binding proteins42, and both PCBP1 and 2 are expressed at high levels in most cell types. Preliminary data indicate that PCBP2 also binds iron and can donate iron to ferritin in yeast. Current efforts indicate that additional iron-dependent enzymes require PCBPs for iron delivery and activation in vivo.

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Philpott, Caroline C (2018) The flux of iron through ferritin in erythrocyte development. Curr Opin Hematol 25:183-188
Ryu, Moon-Suhn; Duck, Kari A; Philpott, Caroline C (2018) Ferritin iron regulators, PCBP1 and NCOA4, respond to cellular iron status in developing red cells. Blood Cells Mol Dis 69:75-81
Philpott, Caroline C; Ryu, Moon-Suhn; Frey, Avery et al. (2017) Cytosolic iron chaperones: Proteins delivering iron cofactors in the cytosol of mammalian cells. J Biol Chem 292:12764-12771
Ryu, Moon-Suhn; Zhang, Deliang; Protchenko, Olga et al. (2017) PCBP1 and NCOA4 regulate erythroid iron storage and heme biosynthesis. J Clin Invest 127:1786-1797
Frey, Avery G; Palenchar, Daniel J; Wildemann, Justin D et al. (2016) A Glutaredoxin-BolA Complex Serves as an Iron-Sulfur Cluster Chaperone for the Cytosolic Cluster Assembly Machinery. J Biol Chem :
Yabe-Wada, Toshiki; Matsuba, Shintaro; Takeda, Kazuya et al. (2016) TLR signals posttranscriptionally regulate the cytokine trafficking mediator sortilin. Sci Rep 6:26566
Li, Fengmin; Bullough, Kimberly Z; Vashisht, Ajay A et al. (2016) Poly(rC)-Binding Protein 2 Regulates Hippo Signaling To Control Growth in Breast Epithelial Cells. Mol Cell Biol 36:2121-31
Philpott, Caroline C; Protchenko, Olga (2016) Fungal physiology: Robbing the bank of haem iron. Nat Microbiol 1:16179
Frey, Avery G; Nandal, Anjali; Park, Jong Hwan et al. (2014) Iron chaperones PCBP1 and PCBP2 mediate the metallation of the dinuclear iron enzyme deoxyhypusine hydroxylase. Proc Natl Acad Sci U S A 111:8031-6
Philpott, Caroline C; Ryu, Moon-Suhn (2014) Special delivery: distributing iron in the cytosol of mammalian cells. Front Pharmacol 5:173

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