title: H-Ferritin Is Preferentially Incorporated by Human Erythroid Cells through Transferrin Receptor 1 in a Threshold-Dependent Manner.
abstract: Ferritin is an iron-storage protein composed of different ratios of 24 light (L) and heavy (H) subunits. The serum level of ferritin is a clinical marker of the body's iron level. Transferrin receptor (TFR)1 is the receptor not only for transferrin but also for H-ferritin, but how it binds two different ligands and the blood cell types that preferentially incorporate H-ferritin remain unknown. To address these questions, we investigated hematopoietic cell-specific ferritin uptake by flow cytometry. Alexa Fluor 488-labeled H-ferritin was preferentially incorporated by erythroid cells among various hematopoietic cell lines examined, and was almost exclusively incorporated by bone marrow erythroblasts among human primary hematopoietic cells of various lineages. H-ferritin uptake by erythroid cells was strongly inhibited by unlabeled H-ferritin but was only partially inhibited by a large excess of holo-transferrin. On the other hand, internalization of labeled holo-transferrin by these cells was not inhibited by H-ferritin. Chinese hamster ovary cells lacking functional endogenous TFR1 but expressing human TFR1 with a mutated RGD sequence, which is required for transferrin binding, efficiently incorporated H-ferritin, indicating that TFR1 has distinct binding sites for H-ferritin and holo-transferrin. H-ferritin uptake by these cells required a threshold level of cell surface TFR1 expression, whereas there was no threshold for holo-transferrin uptake. The requirement for a threshold level of TFR1 expression can explain why among primary human hematopoietic cells, only erythroblasts efficiently take up H-ferritin.
authors.affiliation: Department of Hematology and Oncology, Graduate School of Medicine, Kyoto University, Kyoto, Japan; Department of Hematology, Japanese Red Cross Takatsuki Hospital, Takatsuki, Japan.
authors.forename: Soichiro
authors.initials: S
authors.lastname: Sakamoto
authors.affiliation: Department of Hematology and Oncology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kawabata
authors.affiliation: Laboratory of Food Quality Design and Development, Division of Agronomy and Horticultural Science, Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Masuda
authors.affiliation: Department of Hematology and Oncology, Graduate School of Medicine, Kyoto University, Kyoto, Japan; Department of Hematology and Immunology, Japanese Red Cross Otsu Hospital, Otsu, Japan.
authors.forename: Tatsuki
authors.initials: T
authors.lastname: Uchiyama
authors.affiliation: Department of Hematology and Immunology, Japanese Red Cross Otsu Hospital, Otsu, Japan.
authors.forename: Chisaki
authors.initials: C
authors.lastname: Mizumoto
authors.affiliation: Department of Clinical Laboratory, Kyoto University Hospital, Kyoto, Japan.
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Ohmori
authors.affiliation: Division of Hematology and Oncology, Cedars-Sinai Medical Center, University of California Los Angeles, School of Medicine, Los Angeles, California, United States of America; National University of Singapore, Singapore, Singapore.
authors.forename: H Phillip
authors.initials: HP
authors.lastname: Koeffler
authors.affiliation: Division of Endocrinology and Metabolism, Hematology, Rheumatology and Respiratory Medicine, Department of Internal Medicine, Graduate School of Medicine, Kagawa University, Takamatsu, Japan.
authors.forename: Norimitsu
authors.initials: N
authors.lastname: Kadowaki
authors.affiliation: Department of Hematology and Oncology, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors.forename: Akifumi
authors.initials: A
authors.lastname: Takaori-Kondo
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000378:metabolism*; D001052:Apoferritins / Q000378:metabolism*; D001692:Biological Transport; D016466:CHO Cells; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D041905:Erythroid Cells / Q000378:metabolism*; D005293:Ferritins / Q000378:metabolism; D006801:Humans; D011990:Receptors, Transferrin / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; C068126:CD71 antigen; D011990:Receptors, Transferrin; D005293:Ferritins; D001052:Apoferritins