title: Tumour necrosis factor alpha downregulates human hemojuvelin expression via a novel response element within its promoter.
abstract: BACKGROUND
  Iron homeostasis is chiefly regulated by hepcidin whose expression is tightly controlled by inflammation, iron stores, and hypoxia. Hemojuvelin (HJV) is a bone morphogenetic protein co-receptor that has been identified as a main upstream regulator of hepcidin expression; HJV mutations are associated with a severe form of iron overload (Juvenile haemochromatosis). Currently however, there is no information on how HJV is regulated by inflammation.
  
  
  METHODS
  To study the regulation of Hjv expression by inflammation and whether Hfe has a role in that regulation, control and LPS-injected wild type and Hfe KO mice were used. Moreover, human hepatoma cells (HuH7) were used to study the effect of IL-6 and TNF-α on HJV mRNA expression.
  
  
  RESULTS
  Here we show that LPS repressed hepatic Hjv and BMPs, while it induced hepcidin 1 expression in wild-type and Hfe KO mice with no effect on hepatic pSMAD 1, 5, 8 protein levels. In addition, exogenous TNF-α (20 ng/mL) decreased HJV mRNA and protein expression to 40% of control with no effect on hepcidin mRNA expression in 24 hours. On the other hand, IL-6 induced hepcidin mRNA and protein expression with no effect on HJV mRNA expression levels. Moreover, using the HJV promoter-luciferase reporter fusion construct (HJVP1.2-luc), we showed that the basal luciferase activity of HJVP1.2-luc was inhibited by 33% following TNF-α treatment of HuH7 transfected cells suggesting that the TNF-α down-regulation is exerted at the transcriptional level. Additionally, mutation of a canonical TNF- alpha responsive element (TNFRE) within HJVP1.2-luc abolished TNF-α response suggesting that this TNFRE is functional.
  
  
  CONCLUSIONS
  From these results, we conclude that TNF-α suppresses HJV transcription possibly via a novel TNFRE within the HJV promoter. In addition, the results suggest that the proposed link between inflammation and BMP-SMAD signalling is independent of HJV and BMP ligands.
authors.affiliation: Department of Structural and Molecular Biology, Division of Biosciences, University College London, Gower Street, London WC1E 6BT, UK. mohamed.salama@uclmail.net
authors.forename: Mohamed Fouda
authors.initials: MF
authors.lastname: Salama
authors.forename: Henry K
authors.initials: HK
authors.lastname: Bayele
authors.forename: Surjit S K
authors.initials: SS
authors.lastname: Srai
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D058851:GPI-Linked Proteins; D005786:Gene Expression Regulation / Q000187:drug effects; D006432:Hemochromatosis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism; D000071020:Hemochromatosis Protein; D064451:Hepcidins; D006801:Humans; D007249:Inflammation / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism / Q000494:pharmacology; D007501:Iron / Q000378:metabolism; D008024:Ligands; D008070:Lipopolysaccharides / Q000633:toxicity; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D020218:Response Elements / Q000235:genetics; D051785:Smad Proteins / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology
chemical_list: D023181:Antimicrobial Cationic Peptides; D058851:GPI-Linked Proteins; C578702:HAMP protein, human; C504414:HJV protein, mouse; C579599:Hamp protein, mouse; D000071020:Hemochromatosis Protein; D064451:Hepcidins; D015850:Interleukin-6; D008024:Ligands; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D051785:Smad Proteins; D014409:Tumor Necrosis Factor-alpha; D007501:Iron