Transferrin receptor induction by hypoxia. HIF-1-mediated transcriptional activation and cell-specific post-transcriptional regulation.
The tight relationship between oxygen and iron prompted us to investigate whether the expression of transferrin receptor (TfR), which mediates cellular iron uptake, is regulated by hypoxia. In Hep3B human hepatoma cells incubated in 1% O(2) or treated with CoCl(2), which mimics hypoxia, we detected a 3-fold increase of TfR mRNA despite a decrease of iron regulatory proteins activity. Increased expression resulted from a 4-fold stimulation of the nuclear transcription rate of the TfR gene by both hypoxia and CoCl(2). A role for hypoxia-inducible factor (HIF-1), which activates transcription by binding to hypoxia-responsive elements in the activation of TfR, stems from the following observations. (a) Hypoxia and CoCl(2)-dependent expression of luciferase reporter gene in transiently transfected Hep3B cells was mediated by a fragment of the human TfR promoter containing a putative hypoxia-responsive element sequence, (b) mutation of this sequence prevented hypoxic stimulation of luciferase activity, (c) binding to this sequence of HIF-1alpha, identified by competition experiments and supershift assays, was induced in Hep3B cells by hypoxia and CoCl(2). In erythroid K562 cells, the same treatments did not affect iron regulatory proteins activity, thus resulting in a stimulation of TfR gene expression higher than in hepatoma cells.
Tacchini
L
L
Istituto di Patologia Generale, Università di Milano e Centro di Studio sulla Patologia Cellulare, Consiglio Nazionale delle Ricerche, via Mangiagalli 31, 20133 Milano, Italy.
Bianchi
L
L
Bernelli-Zazzera
A
A
Cairo
G
G
D015687:Cell Hypoxia; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins / Q000032:analysis; D009687:Nuclear Proteins / Q000502:physiology*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D016601:RNA-Binding Proteins / Q000032:analysis; D011990:Receptors, Transferrin / Q000235:genetics*; D014157:Transcription Factors; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D035925:Iron-Regulatory Proteins; D007506:Iron-Sulfur Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011990:Receptors, Transferrin; D014157:Transcription Factors; D004247:DNA