HIF-1-mediated activation of transferrin receptor gene transcription by iron chelation

Treatment with iron chelators mimics hypoxic induction of the hypoxia induc ible factor (HIF-1) which activates transcription by binding to hypoxia res ponsive elements (HRE), We investigated whether HIF-1 is involved in transc riptional activation of the transferrin receptor (TfR), a membrane protein which mediates cellular iron uptake, in response to iron deprivation, The t ranscription rate of the TfR gene in isolated nuclei was up-regulated by tr eatment of Hep3B human hepatoma cells with the iron chelator desferrioxamin e (DFO), The role of HIF-1 in the activation of TfR was indicated by the fo llowing observations: (i) DFO-dependent activation of a luciferase reporter gene in transfected Hep3B cells was mediated by a fragment of the human Tf R promoter containing a putative HRE sequence; (ii) mutation of this sequen ce prevented stimulation of luciferase activity; (iii) binding to this sequ ence of HIF-1 alpha identified by competition experiments and supershift as says, was induced by DFO, Furthermore, in mouse hepatoma cells unable to as semble functional HIF-1, inducibility of TfR transcription by DFO was lost and TfR mRNA up-regulation was reduced. These results, which show the role of HIF-1 in the control of TfR gene expression in conditions of iron deplet ion, give insights into the mechanisms of transcriptional regulation which concur with the well-characterized post-transcriptional control of TfR expr ession to expand the extent of response to iron deficiency.