title: Membrane-associated RING-CH (MARCH) 8 mediates the ubiquitination and lysosomal degradation of the transferrin receptor.
abstract: The transferrin receptor (TfR) mediates the uptake of transferrin (Tf)-bound iron from the plasma into the cells of peripheral tissues. The TfR continuously recycles between the plasma membrane and early/recycling endosomes. TfR expression is tightly controlled by the intracellular iron concentration through the regulation of TfR mRNA stability. However, much less is known about the mechanism by which TfR is degraded in cells. Previously, we reported a correlation between TfR ubiquitination and its iron-induced lysosomal degradation. The identification and characterization of a specific ubiquitin ligase for TfR is important in understanding the mechanism of iron homeostasis. Here, we show that membrane-associated RING-CH (MARCH) 8 ubiquitinates TfR and promotes its lysosomal degradation. Similar to other RING-type ubiquitin ligases, the RING-CH domain of MARCH8, which is located in the N-terminal cytoplasmic domain, is essential for the ubiquitination and downregulation of TfR. MARCH8 specifically recognizes the transmembrane domain of TfR and mediates ubiquitination of its cytoplasmic domain. In addition, the six-amino-acid sequence located in the C-terminal domain of MARCH8, which is highly conserved among different species, is required for the downregulation of TfR. Finally, and most importantly, TfR expression was markedly increased by siRNA-mediated knockdown of endogenous MARCH8. These findings demonstrate that the endogenous level of MARCH8 regulates TfR protein turnover through the downregulation and ubiquitination of TfR.
authors.affiliation: Division of Pharmaceutical Cell Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. fujita@niu.ac.jp
authors.forename: Hideaki
authors.initials: H
authors.lastname: Fujita
authors.forename: Yukie
authors.initials: Y
authors.lastname: Iwabu
authors.forename: Kenzo
authors.initials: K
authors.lastname: Tokunaga
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Tanaka
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002462:Cell Membrane / Q000378:metabolism*; D002522:Chlorocebus aethiops; D004705:Endocytosis; D006801:Humans; D007501:Iron / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D011990:Receptors, Transferrin / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D034741:RNA, Small Interfering; D011990:Receptors, Transferrin; D025801:Ubiquitin; D007501:Iron; C568898:MARCHF8 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: Endocytosis; Iron metabolism; Lysosome; Multivesicular body; Transferrin receptor; Ubiquitin ligase