title: Expression of human Hemojuvelin (HJV) is tightly regulated by two upstream open reading frames in HJV mRNA that respond to iron overload in hepatic cells.
abstract: The gene encoding human hemojuvelin (HJV) is one of the genes that, when mutated, can cause juvenile hemochromatosis, an early-onset inherited disorder associated with iron overload. The 5' untranslated region of the human HJV mRNA has two upstream open reading frames (uORFs), with 28 and 19 codons formed by two upstream AUGs (uAUGs) sharing the same in-frame stop codon. Here we show that these uORFs decrease the translational efficiency of the downstream main ORF in HeLa and HepG2 cells. Indeed, ribosomal access to the main AUG is conditioned by the strong uAUG context, which results in the first uORF being translated most frequently. The reach of the main ORF is then achieved by ribosomes that resume scanning after uORF translation. Furthermore, the amino acid sequences of the uORF-encoded peptides also reinforce the translational repression of the main ORF. Interestingly, when iron levels increase, translational repression is relieved specifically in hepatic cells. The upregulation of protein levels occurs along with phosphorylation of the eukaryotic initiation factor 2α. Nevertheless, our results support a model in which the increasing recognition of the main AUG is mediated by a tissue-specific factor that promotes uORF bypass. These results support a tight HJV translational regulation involved in iron homeostasis.
authors: Departamento de Genética Humana, Instituto Nacional de Saúde Doutor Ricardo Jorge, Lisbon, Portugal Biosystems & Integrative Sciences Institute (BioISI), Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal.
authors: Cláudia
authors: C
authors: Onofre
authors: Departamento de Genética Humana, Instituto Nacional de Saúde Doutor Ricardo Jorge, Lisbon, Portugal.
authors: Filipa
authors: F
authors: Tomé
authors: Departamento de Genética Humana, Instituto Nacional de Saúde Doutor Ricardo Jorge, Lisbon, Portugal Biosystems & Integrative Sciences Institute (BioISI), Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal.
authors: Cristina
authors: C
authors: Barbosa
authors: Departamento de Genética Humana, Instituto Nacional de Saúde Doutor Ricardo Jorge, Lisbon, Portugal.
authors: Ana Luísa
authors: AL
authors: Silva
authors: Departamento de Genética Humana, Instituto Nacional de Saúde Doutor Ricardo Jorge, Lisbon, Portugal Biosystems & Integrative Sciences Institute (BioISI), Faculdade de Ciências, Universidade de Lisboa, Lisbon, Portugal luisa.romao@insa.min-saude.pt.
authors: Luísa
authors: L
authors: Romão
mesh_terms: D020121:5' Untranslated Regions; D000595:Amino Acid Sequence; D058851:GPI-Linked Proteins / Q000737:chemistry / Q000235:genetics*; D005786:Gene Expression Regulation; D006367:HeLa Cells; D000071020:Hemochromatosis Protein; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D019190:Iron Overload / Q000235:genetics*; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics*
chemical_list: D020121:5' Untranslated Regions; D058851:GPI-Linked Proteins; C481006:HJV protein, human; D000071020:Hemochromatosis Protein; D012333:RNA, Messenger