title: Therapeutic potential of proteasome inhibitors in congenital erythropoietic porphyria.
abstract: Congenital erythropoietic porphyria (CEP) is a rare autosomal recessive disorder characterized by uroporphyrinogen III synthase (UROS) deficiency resulting in massive porphyrin accumulation in blood cells, which is responsible for hemolytic anemia and skin photosensitivity. Among the missense mutations actually described up to now in CEP patients, the C73R and the P248Q mutations lead to a profound UROS deficiency and are usually associated with a severe clinical phenotype. We previously demonstrated that the UROS(C73R) mutant protein conserves intrinsic enzymatic activity but triggers premature degradation in cellular systems that could be prevented by proteasome inhibitors. We show evidence that the reduced kinetic stability of the UROS(P248Q) mutant is also responsible for increased protein turnover in human erythroid cells. Through the analysis of EGFP-tagged versions of UROS enzyme, we demonstrate that both UROS(C73R) and UROS(P248Q) are equally destabilized in mammalian cells and targeted to the proteasomal pathway for degradation. We show that a treatment with proteasomal inhibitors, but not with lysosomal inhibitors, could rescue the expression of both EGFP-UROS mutants. Finally, in CEP mice (Uros(P248Q/P248Q)) treated with bortezomib (Velcade), a clinically approved proteasome inhibitor, we observed reduced porphyrin accumulation in circulating RBCs and urine, as well as reversion of skin photosensitivity on bortezomib treatment. These results of medical importance pave the way for pharmacologic treatment of CEP disease by preventing certain enzymatically active UROS mutants from early degradation by using proteasome inhibitors or chemical chaperones.
authors.affiliation: Biothérapies des Maladies Génétiques et Cancers, Institut National de la Santé et de la Recherche Médicale U1035, Université Victor Segalen Bordeaux, F-33000 Bordeaux, France.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Blouin
authors.forename: Yann
authors.initials: Y
authors.lastname: Duchartre
authors.forename: Pierre
authors.initials: P
authors.lastname: Costet
authors.forename: Magalie
authors.initials: M
authors.lastname: Lalanne
authors.forename: Cécile
authors.initials: C
authors.lastname: Ged
authors.forename: Ana
authors.initials: A
authors.lastname: Lain
authors.forename: Oscar
authors.initials: O
authors.lastname: Millet
authors.forename: Hubert
authors.initials: H
authors.lastname: de Verneuil
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Richard
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001897:Boronic Acids / Q000494:pharmacology / Q000627:therapeutic use; D000069286:Bortezomib; D002942:Circular Dichroism; D017931:DNA Primers / Q000235:genetics; D041905:Erythroid Cells / Q000378:metabolism; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D020125:Mutation, Missense / Q000235:genetics; D017092:Porphyria, Erythropoietic / Q000188:drug therapy* / Q000235:genetics; D011166:Porphyrins / Q000097:blood / Q000652:urine; D061988:Proteasome Inhibitors / Q000627:therapeutic use*; D017510:Protein Folding; D011719:Pyrazines / Q000494:pharmacology / Q000627:therapeutic use; D060888:Real-Time Polymerase Chain Reaction; D013050:Spectrometry, Fluorescence; D014576:Uroporphyrinogen III Synthetase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
chemical_list: D001897:Boronic Acids; D017931:DNA Primers; D011166:Porphyrins; D061988:Proteasome Inhibitors; D011719:Pyrazines; D000069286:Bortezomib; D014576:Uroporphyrinogen III Synthetase
keywords: Günther's disease; enzyme instability; heme biosynthetic pathway; pharmacological therapy; protein misfolding