Ferritin is secreted via 2 distinct nonclassical vesicular pathways

Marianna Truman-Rosentsvit, Dina Berenbaum, Lior Spektor, Lyora A. Cohen, Shirly Belizowsky-Moshe, Lena Lifshitz, Jing Ma, Wei Li, Ellina Kesselman, Inbal Abutbul-Ionita, Dganit Danino, Lucia Gutierrez, Huihui Li, Kuanyu Li, Huifang Lou, Maria Regoni, Maura Poli, Fabian Glaser, Tracey A. Rouault, Esther G. Meyron-Holtz*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

53 Scopus citations

Abstract

Ferritin turnover plays a major role in tissue iron homeostasis, and ferritin malfunction is associated with impaired iron homeostasis and neurodegenerative diseases. In most eukaryotes, ferritin is considered an intracellular protein that stores iron in a nontoxic and bioavailable form. In insects, ferritin is a classically secreted protein and plays a major role in systemic iron distribution. Mammalian ferritin lacks the signal peptide for classical endoplasmic reticulum–Golgi secretion but is found in serum and is secreted via a nonclassical lysosomal secretion pathway. This study applied bioinformatics and biochemical tools, alongside a protein trafficking mouse models, to characterize the mechanisms of ferritin secretion. Ferritin trafficking via the classical secretion pathway was ruled out, and a 2:1 distribution of intracellular ferritin between membrane-bound compartments and the cytosol was observed, suggesting a role for ferritin in the vesicular compartments of the cell. Focusing on nonclassical secretion, we analyzed mouse models of impaired endolysosomal trafficking and found that ferritin secretion was decreased by a BLOC-1 mutation but increased by BLOC-2, BLOC-3, and Rab27A mutations of the cellular trafficking machinery, suggesting multiple export routes. A 13-amino-acid motif unique to ferritins that lack the secretion signal peptide was identified on the BC-loop of both subunits and plays a role in the regulation of ferritin secretion. Finally, we provide evidence that secretion of iron-rich ferritin was mediated via the multivesicular body–exosome pathway. These results enhance our understanding of the mechanism of ferritin secretion, which is an important piece in the puzzle of tissue iron homeostasis.

Original languageEnglish
Pages (from-to)342-352
Number of pages11
JournalBlood
Volume131
Issue number3
DOIs
StatePublished - 18 Jan 2018
Externally publishedYes

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