The Iron Regulatory Protein/Iron Responsive Element (IRP/IRE) system: functional studies of new target mRNAs and pathological implications for novel IRE mutations

• Autores: Sara Luscieti
• Directores de la Tesis: M. Carmen Sanchez Fernández de Sentle (dir. tes.), Rafael Oliva Virgili (tut. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2016
• Idioma: español
• Tribunal Calificador de la Tesis: Jordi Tamarit Sumalla (presid.), Fátima Gebauer Hernández (secret.), Maura Poli (voc.)
• Programa de doctorado: Programa de Doctorado en Biomedicina por la Universidad de Barcelona
• Materias:
  • Química
    • Bioquímica
      • Biología molecular
      • Proteínas
  • Ciencias de la vida
    • Biología celular
      • Cultivo celular
• Enlaces
  • Tesis en acceso abierto en:  Dipòsit Digital de la UB  TDX 
• Resumen

  • Iron is an essential micronutrient required for many cellular reactions and a tight regulation of its metabolism is therefore crucial for health. Cellular iron homeostasis relies on the coordination of iron uptake, storage and mobilization. These processes are controlled post-transcriptionally by the IRP/IRE regulatory system. The Iron Regulatory Proteins (IRP1 and IRP2) can recognize cis-regulatory mRNA motifs termed IREs (Iron Responsive Elements), conserved RNA elements located in the untranslated regions (UTR) of mRNAs that encode for proteins involved in iron metabolism. IRP/IRE interactions regulate the expression of mRNAs encoding for proteins for iron acquisition, storage, utilization and export in response to cellular iron level itself being the interaction of the IRPs with IRE motifs promoted under iron-deficient conditions and abolished in iron-replete conditions. Depending on the location of the IRE, IRPs binding regulates gene expression differentially: IRPs inhibit translation initiation when bound to IREs at the 5’ UTR, while IRPs association with 3’ IREs stabilizes and protects the mRNA from degradation.

    The lack of control of expression of IRE-containing mRNAs is associated in humans with pathological conditions showing the importance of components of the IRP/IRE regulatory system.

    In the last decades, significant progress has been made in the iron metabolism field, however, post-transcriptional regulation of gene expression by the IRP/IRE regulatory system has been limited to a small subset of known genes. A genome-wide study carried out by our group to characterize the whole repertoire of mRNAs that can interact with the IRPs, identified 35 novel IRP1 and IRP2 candidate target-genes.

    This work focused on the validation and functional characterization of one of this candidates: Profilin2 (Pfn2). Pfn2 is an actin-binding protein involved in the control of cytoskeletal dynamics. We identified a conserved IRE in the 3’ UTR of Pfn2 mRNA which is functional in in vitro binding studies with IRP1 and IRP2.

    Pfn2 mRNA showed preferentially downregulation under iron-excess condition in cell lines and we demonstrated to be regulated by IRPs-mediated stabilization in vivo, since Pfn2 mRNA levels are reduced in a mouse model with Irp1 and Irp2 gene inactivation.

    Moreover, the reduction of cellular free iron levels by Pfn2 overexpression experiments in cell lines, as well as, the misregulation of iron distribution observed in mice knockout for Pfn2 gene, revealed Pfn2 as a previously unrecognized player in iron metabolism.

    In addition, we also contributed to the identification of a functional 3’ IRE in human BDH2 mRNA, a protein involved in lipocalin-siderophores iron-trafficking, as well as, in the identification and characterization of two novel L-ferritin IRE mutations (Heidelberg +52G>C and Badalona+36C>U) causative of Hereditary Hyperferritinemia Cataract Syndrome and a novel mutation in ALAS2 IRE demonstrated to be a modifier of clinical severity in a family with Erythropoietic Protoporphyria.