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Haematologica 2022 Volume 107(2):478-488
UBA6 and NDFIP1 regulate the degradation of ferroportin
Lisa Traeger,1 Steffen B. Wiegand,1 Andrew J. Sauer,1 Benjamin H.P. Corman,1 Kathryn M. Peneyra,1 Florian Wunderer,1,2 Anna Fischbach,1 Aranya Bagchi,1 Rajeev Malhotra,3 Warren M. Zapol1 and Donald B. Bloch1,4
1Anesthesia Center for Critical Care Research of the Department of Anesthesia, Critical Care and Pain Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA; 2Department of Anesthesiology, Intensive Care Medicine and Pain Therapy, University Hospital Frankfurt, Goethe University, Frankfurt, Germany; 3Cardiovascular Research Center and the Cardiology Division of the Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA and 4Division of Rheumatology, Allergy and Immunology of the Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
ABSTRACT
Hepcidin regulates iron homeostasis by controlling the level of fer- roportin, the only membrane channel that facilitates export of iron from within cells. Binding of hepcidin to ferroportin induces the ubiquitination of ferroportin at multiple lysine residues and subse- quently causes the internalization and degradation of the ligand-channel complex within lysosomes. The objective of this study was to identify components of the ubiquitin system that are involved in ferroportin degradation. A HepG2 cell line, which inducibly expresses ferroportin- green fluorescent protein (FPN-GFP), was established to test the ability of small interfering (siRNA) directed against components of the ubiquitin system to prevent BMP6- and exogenous hepcidin-induced ferroportin degradation. Of the 88 siRNA directed against components of the ubiq- uitin pathway that were tested, siRNA-mediated depletion of the alter- native E1 enzyme UBA6 as well as the adaptor protein NDFIP1 prevent- ed BMP6- and hepcidin-induced degradation of ferroportin in vitro. A third component of the ubiquitin pathway, ARIH1, indirectly inhibited ferroportin degradation by impairing BMP6-mediated induction of hep- cidin. In mice, the AAV-mediated silencing of Ndfip1 in the murine liver increased the level of hepatic ferroportin and increased circulating iron. The results suggest that the E1 enzyme UBA6 and the adaptor protein NDFIP1 are involved in iron homeostasis by regulating the degradation of ferroportin. These specific components of the ubiquitin system may be promising targets for the treatment of iron-related diseases, including iron overload and anemia of inflammation.
Introduction
Iron is an essential element that is required for a spectrum of cellular and biological processes including oxygen transport, DNA synthesis and the production of energy. High levels of iron, in the presence of oxygen, may catalyze the production of reac- tive oxygen species, which are free radicals that may damage cellular proteins and membranes. The level of iron in the body must be tightly regulated to provide suffi- cient levels to permit fundamental biological processes while preventing the damag- ing effects of excess iron.1,2
The hepatic hormone hepcidin is a critical regulator of systemic iron homeosta- sis.3–5 Hepcidin expression is controlled by at least three stimuli: i) increased serum and liver iron, which induce hepcidin via the bone morphogenetic protein (BMP) sig- naling pathway; ii) increased mediators of inflammation (IL-1b and IL-6), which increase hepcidin via the Jak/Stat pathway; and iii) the hormone erythroferrone, which inhibits BMP signaling by sequestering BMP6 in response to increased ery- thropoietic demand.6–9 Hepcidin regulates iron homeostasis by controlling the cell surface level of ferroportin, which is the only known membrane channel that facili- tates export of iron from within cells.10 Ferroportin is a member of the superfamily
Iron Metabolism & its Disorders
Correspondence:
DONALD B. BLOCH
dbloch@mgh.harvard.edu
LISA TRAEGER
email@lisatraeger.de
Received: February 6, 2021. Accepted: July 22, 2021. Pre-published: July 29, 2021
https://doi.org/10.3324/haematol.2021.278530 ©2022 Ferrata Storti Foundation
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