Therapeutic potential of proteasome inhibitors in congenital erythropoietic porphyria

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 45; pp. 18238 - 18243
• Main Authors: Blouin, Jean-Marc, Duchartre, Yann, Costet, Pierre, Lalanne, Magalie, Ged, Cécile, Lain, Ana, Millet, Oscar, de Verneuil, Hubert, Richard, Emmanuel
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 05.11.2013; NATIONAL ACADEMY OF SCIENCES; National Acad Sciences
• Subjects: Animals; Biological Sciences; Blotting, Western; Boronic Acids - pharmacology; Boronic Acids - therapeutic use; Bortezomib; Circular Dichroism; Congenital diseases; DNA Primers - genetics; Enzyme kinetics; Enzymes; Erythroid cells; Erythroid Cells - metabolism; Erythropoietic porphyria; Gene expression; Genetic mutation; Humans; K562 cells; Medical treatment; Mice; Models, Molecular; Mutation; Mutation, Missense - genetics; Pharmacology; Photosensitivity; Porphyria, Erythropoietic - drug therapy; Porphyria, Erythropoietic - genetics; Porphyrins; Porphyrins - blood; Porphyrins - urine; Proteasome Inhibitors - therapeutic use; Protein Folding; Proteins; Pyrazines - pharmacology; Pyrazines - therapeutic use; Real-Time Polymerase Chain Reaction; Rodents; Spectrometry, Fluorescence; Thermodynamics; Uroporphyrinogen III Synthetase - chemistry; Uroporphyrinogen III Synthetase - genetics; Uroporphyrinogen III Synthetase - metabolism; pharmacological therapy; enzyme instability; Günther's disease; protein misfolding; heme biosynthetic pathway
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1314177110

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.