The roles of hypoxia-inducible Factor-1 and iron regulatory protein 1 in iron uptake induced by acute hypoxia

Background Information: Divalent metal transporter 1 (DMT1) and transferrin receptor (TfR1) are vital proteins for cellular iron uptake. These proteins have hypoxia-responsive elements (HREs) in their 5'-regulatory region, and they are regulated by hypoxia-inducible factor 1 alpha (HIF-1 alpha) transcriptionally under hypoxic condition. Besides, iron regulatory protein 1 (IRP1) regulates DMT1 and TfR1 by binding to iron-responsive elements (IREs) present in their mRNAs to control cellular iron homeostasis. Results: Here, we explored the effect of acute hypoxia on iron uptake. Ferrous iron uptake was elevated by DMT1(+IRE) and TfR1 under acute hypoxia. The luciferase activity analysis revealed that the functional HREs of DMT1 and TfR1 were increased. However, their IREs-dependent luciferase activities were reduced simultaneously. The mRNA stability of TfR1 and DMT1(+IRE) was suppressed under acute hypoxia. The mRNA levels of TfR1 and DMT1(+IRE) were restrain by silencing IRP1. In sharp contrast, HIF-1 alpha overexpression enhanced the mRNA levels of TfR1 and DMT1(+IRE), which reversed the inhibition of IRP1 on both. HIF-1 alpha konckdown suppressed the hypoxia-induced increase expression of TfR1 and DMT1(+IRE), whereas both proteins had little change when further decreased the IRP1 expression under hypoxia. Hypoxia upregulated the protein expression of Ferrtin-L in a time-dependent manner, yet there was no different when IRP1 silencing or overexperssion under hypoxia. The lactate dehydrogenase (LDH) release induced by hypoxia was increased by TfR1 siRNA silence. Conclusions: We propose that HIF-1/FIRE system might play a principal part in hypoxia induced iron uptake. (C) 2018 Elsevier Inc. All rights reserved.