Iron Regulatory Protein 1 Suppresses Hypoxia-Induced Iron Uptake Proteins Expression and Decreases Iron Levels in HepG2 Cells.
Transferrin receptor (TfR1) and divalent metal transporter 1 (DMT1) are important proteins for cellular iron uptake, and both are regulated transcriptionally through the binding of hypoxia-inducible factor 1 (HIF-1) to hypoxia-responsive elements (HREs) under hypoxic conditions. These proteins are also regulated post-transcriptionally through the binding of iron regulatory protein 1 (IRP1) to iron-responsive elements (IREs) located in the mRNA untranslated region (UTR) to control cellular iron homeostasis. In iron-deficient cells, IRP1-IRE interactions stabilize TfR1 and DMT1 mRNAs, enhancing iron uptake. However, little is known about the impact of IRP1 on the regulation of cellular iron homeostasis under hypoxia. Thus, to investigate the role of IRP1 in hypoxic condition, overexpression and knockdown assays were performed using HepG2 cells. The overexpression of IRP1 suppressed the hypoxia-induced increase in TfR1 and DMT1 (+IRE) expression and reduced the stability of TfR1 and DMT1 (+IRE) mRNAs under hypoxia, whereas IRP1 knockdown further increased the hypoxia-induced expression of both proteins, preventing the decrease in IRE-dependent luciferase activity induced by hypoxia. Under hypoxic conditions, ferrous iron uptake, the labile iron pool (LIP), and total intracellular iron reduced when IRP1 was overexpressed and further increased when IRP1 was knocked down. IRP1 expression declined and TfR1/DMT1 (+IRE) expression increased with the time of hypoxia prolonged, whereas the binding of IRP1 to the IRE of TfR1/DMT1 mRNA maintained. In summary, IRP1 suppressed TfR1/DMT1 (+IRE) expression, limited the cellular iron content and decreased lactate dehydrogenase (LDH) release induced by hypoxia.
Department of Biochemistry, Institute for Nautical Medicine, Nantong University, Nantong, Jiangsu, 226001, PR China.
Chun-Ming
CM
Cheng
Department of Biochemistry, Institute for Nautical Medicine, Nantong University, Nantong, Jiangsu, 226001, PR China.
Dan
D
Wang
Department of Biochemistry, Institute for Nautical Medicine, Nantong University, Nantong, Jiangsu, 226001, PR China.
Xian
X
Cao
Department of Biochemistry, Institute for Nautical Medicine, Nantong University, Nantong, Jiangsu, 226001, PR China.
Qian-Qian
QQ
Luo
Department of Biochemistry, Institute for Nautical Medicine, Nantong University, Nantong, Jiangsu, 226001, PR China.
Ya-Peng
YP
Lu
Department of Biochemistry, Institute for Nautical Medicine, Nantong University, Nantong, Jiangsu, 226001, PR China.
Li
L
Zhu
D015703:Antigens, CD / Q000737:chemistry / Q000235:genetics*; D001665:Binding Sites; D015687:Cell Hypoxia; D015972:Gene Expression Regulation, Neoplastic; D056945:Hep G2 Cells; D006801:Humans; D007501:Iron / Q000737:chemistry / Q000378:metabolism*; D035941:Iron Regulatory Protein 1 / Q000235:genetics / Q000378:metabolism*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism; D011990:Receptors, Transferrin / Q000737:chemistry / Q000235:genetics*; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics*; D020506:Untranslated Regions
D015703:Antigens, CD; C068126:CD71 antigen; C110547:DMRT1 protein; D012333:RNA, Messenger; D011990:Receptors, Transferrin; D014157:Transcription Factors; D020506:Untranslated Regions; D007501:Iron; D007770:L-Lactate Dehydrogenase; C546175:ACO1 protein, human; D035941:Iron Regulatory Protein 1
DMT1; HIF-1; IRON METABOLISM; IRP1; TfR1