title: Differential HFE gene expression is regulated by alternative splicing in human tissues.
abstract: BACKGROUND
  The pathophysiology of HFE-derived Hereditary Hemochromatosis and the function of HFE protein in iron homeostasis remain uncertain. Also, the role of alternative splicing in HFE gene expression regulation and the possible function of the corresponding protein isoforms are still unknown. The aim of this study was to gain insights into the physiological significance of these alternative HFE variants.
  
  
  RESULTS
  Alternatively spliced HFE transcripts in diverse human tissues were identified by RT-PCR, cloning and sequencing. Total HFE transcripts, as well as two alternative splicing transcripts were quantified using a real-time PCR methodology. Intracellular localization, trafficking and protein association of GFP-tagged HFE protein variants were analysed in transiently transfected HepG2 cells by immunoprecipitation and immunofluorescence assays. Alternatively spliced HFE transcripts present both level- and tissue-specificity. Concerning the exon 2 skipping and intron 4 inclusion transcripts, the liver presents the lowest relative level, while duodenum presents one of the highest amounts. The protein resulting from exon 2 skipping transcript is unable to associate with β2M and TfR1 and reveals an ER retention. Conversely, the intron 4 inclusion transcript gives rise to a truncated, soluble protein (sHFE) that is mostly secreted by cells to the medium in association with β2M.
  
  
  CONCLUSIONS
  HFE gene post-transcriptional regulation is clearly affected by a tissue-dependent alternative splicing mechanism. Among the corresponding proteins, a sHFE isoform stands out, which upon being secreted into the bloodstream, may act in remote tissues. It could be either an agonist or antagonist of the full length HFE, through hepcidin expression regulation in the liver or by controlling dietary iron absorption in the duodenum.
authors.affiliation: Departamento de Genética, Instituto Nacional de Saúde Dr. Ricardo Jorge, Lisboa, Portugal.
authors.forename: Rute
authors.initials: R
authors.lastname: Martins
authors.forename: Bruno
authors.initials: B
authors.lastname: Silva
authors.forename: Daniela
authors.initials: D
authors.lastname: Proença
authors.forename: Paula
authors.initials: P
authors.lastname: Faustino
mesh_terms: D017398:Alternative Splicing / Q000235:genetics*; D005091:Exons / Q000235:genetics; D005455:Fluorescent Antibody Technique; D000071020:Hemochromatosis Protein; D056945:Hep G2 Cells; D015395:Histocompatibility Antigens Class I / Q000235:genetics*; D006801:Humans; D047468:Immunoprecipitation; D007438:Introns / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D009928:Organ Specificity / Q000235:genetics*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012995:Solubility; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: C103673:HFE protein, human; D000071020:Hemochromatosis Protein; D015395:Histocompatibility Antigens Class I; D008565:Membrane Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger