Evidence for a lack of a direct transcriptional suppression of the iron regulatory peptide hepcidin by hypoxia-inducible factors.
BACKGROUND
Hepcidin is a major regulator of iron metabolism and plays a key role in anemia of chronic disease, reducing intestinal iron uptake and release from body iron stores. Hypoxia and chemical stabilizers of the hypoxia-inducible transcription factor (HIF) have been shown to suppress hepcidin expression. We therefore investigated the role of HIF in hepcidin regulation.


RESULTS
Hepcidin mRNA was down-regulated in hepatoma cells by chemical HIF stabilizers and iron chelators, respectively. In contrast, the response to hypoxia was variable. The decrease in hepcidin mRNA was not reversed by HIF-1alpha or HIF-2alpha knock-down or by depletion of the HIF and iron regulatory protein (IRP) target transferrin receptor 1 (TfR1). However, the response of hepcidin to hypoxia and chemical HIF inducers paralleled the regulation of transferrin receptor 2 (TfR2), one of the genes critical to hepcidin expression. Hepcidin expression was also markedly and rapidly decreased by serum deprivation, independent of transferrin-bound iron, and by the phosphatidylinositol 3 (PI3) kinase inhibitor LY294002, indicating that growth factors are required for hepcidin expression in vitro. Hepcidin promoter constructs mirrored the response of mRNA levels to interleukin-6 and bone morphogenetic proteins, but not consistently to hypoxia or HIF stabilizers, and deletion of the putative HIF binding motifs did not alter the response to different hypoxic stimuli. In mice exposed to carbon monoxide, hypoxia or the chemical HIF inducer N-oxalylglycine, liver hepcidin 1 mRNA was elevated rather than decreased.


CONCLUSIONS
Taken together, these data indicate that hepcidin is neither a direct target of HIF, nor indirectly regulated by HIF through induction of TfR1 expression. Hepcidin mRNA expression in vitro is highly sensitive to the presence of serum factors and PI3 kinase inhibition and parallels TfR2 expression.
Volke
Melanie
M
Department of Nephrology and Hypertension, University Hospital Erlangen, University of Erlangen-Nuremberg, Erlangen, Germany.
Gale
Daniel P
DP
Maegdefrau
Ulrike
U
Schley
Gunnar
G
Klanke
Bernd
B
Bosserhoff
Anja-Katrin
AK
Maxwell
Patrick H
PH
Eckardt
Kai-Uwe
KU
Warnecke
Christina
C
D020816:Amino Acid Motifs; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D023181:Antimicrobial Cationic Peptides / Q000378:metabolism*; D001483:Base Sequence; D002867:Chromones / Q000494:pharmacology; D064451:Hepcidins; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism*; D015850:Interleukin-6 / Q000378:metabolism; D035925:Iron-Regulatory Proteins / Q000737:chemistry*; D051379:Mice; D008969:Molecular Sequence Data; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011990:Receptors, Transferrin / Q000378:metabolism
D015703:Antigens, CD; D023181:Antimicrobial Cationic Peptides; D002867:Chromones; D064451:Hepcidins; D051793:Hypoxia-Inducible Factor 1; D015850:Interleukin-6; D035925:Iron-Regulatory Proteins; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D011990:Receptors, Transferrin; C068126:CD71 antigen; C578702:HAMP protein, human; C579599:Hamp protein, mouse; C503640:TFR2 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one