Additive loss-of-function proteasome subunit mutations in CANDLE/PRAAS patients promote type I IFN production
Anja Brehm, … , Ivona Aksentijevich, Raphaela Goldbach-Mansky
Anja Brehm, … , Ivona Aksentijevich, Raphaela Goldbach-Mansky
Published October 20, 2015
Citation Information: J Clin Invest. 2015;125(11):4196-4211. https://doi.org/10.1172/JCI81260.
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Research Article Immunology

Additive loss-of-function proteasome subunit mutations in CANDLE/PRAAS patients promote type I IFN production

Abstract

Autosomal recessive mutations in proteasome subunit β 8 (PSMB8), which encodes the inducible proteasome subunit β5i, cause the immune-dysregulatory disease chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature (CANDLE), which is classified as a proteasome-associated autoinflammatory syndrome (PRAAS). Here, we identified 8 mutations in 4 proteasome genes, PSMA3 (encodes α7), PSMB4 (encodes β7), PSMB9 (encodes β1i), and proteasome maturation protein (POMP), that have not been previously associated with disease and 1 mutation in PSMB8 that has not been previously reported. One patient was compound heterozygous for PSMB4 mutations, 6 patients from 4 families were heterozygous for a missense mutation in 1 inducible proteasome subunit and a mutation in a constitutive proteasome subunit, and 1 patient was heterozygous for a POMP mutation, thus establishing a digenic and autosomal dominant inheritance pattern of PRAAS. Function evaluation revealed that these mutations variably affect transcription, protein expression, protein folding, proteasome assembly, and, ultimately, proteasome activity. Moreover, defects in proteasome formation and function were recapitulated by siRNA-mediated knockdown of the respective subunits in primary fibroblasts from healthy individuals. Patient-isolated hematopoietic and nonhematopoietic cells exhibited a strong IFN gene-expression signature, irrespective of genotype. Additionally, chemical proteasome inhibition or progressive depletion of proteasome subunit gene transcription with siRNA induced transcription of type I IFN genes in healthy control cells. Our results provide further insight into CANDLE genetics and link global proteasome dysfunction to increased type I IFN production.

Authors

Anja Brehm, Yin Liu, Afzal Sheikh, Bernadette Marrero, Ebun Omoyinmi, Qing Zhou, Gina Montealegre, Angelique Biancotto, Adam Reinhardt, Adriana Almeida de Jesus, Martin Pelletier, Wanxia L. Tsai, Elaine F. Remmers, Lela Kardava, Suvimol Hill, Hanna Kim, Helen J. Lachmann, Andre Megarbane, Jae Jin Chae, Jilian Brady, Rhina D. Castillo, Diane Brown, Angel Vera Casano, Ling Gao, Dawn Chapelle, Yan Huang, Deborah Stone, Yongqing Chen, Franziska Sotzny, Chyi-Chia Richard Lee, Daniel L. Kastner, Antonio Torrelo, Abraham Zlotogorski, Susan Moir, Massimo Gadina, Phil McCoy, Robert Wesley, Kristina I. Rother, Peter W. Hildebrand, Paul Brogan, Elke Krüger, Ivona Aksentijevich, Raphaela Goldbach-Mansky

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Figure 1

Clinical findings and CANDLE/PRAAS-associated mutations in 4 proteasome-encoding genes and in silico modeling.

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Clinical findings and CANDLE/PRAAS-associated mutations in 4 proteasome-...
(A) Marked facial edema during flare. (B) Lipoatrophy later in life. (C) CANDLE rash during acute flare. (D) Abdominal protrusion due to intraabdominal fat deposition. (E) Pedigrees and identified genotypes of patients and their direct relatives. Underline in red indicates maternal, in blue, paternal, and in green, de novo inheritance of mutant allele. (F) Schematic organization of PSMB4, PSMA3, PSMB9, and PSMB8 genes (exon-intron structure, black rectangles represent coding sequences, white rectangles represent UTRs) with positions of the identified mutations. (G) Species conservation of mutated aa (yellow). Hs, Homo sapiens; Pt, Pan troglodytes (chimpanzee); Mm, Mus musculus (mouse); Oc, Oryctolagus cuniculus (rabbit); Bt, Bos tauris (cattle); Clp, Canis lupus familiaris (dog); Xl, Xenopus laevis (frog), Dr, Danio rerio (zebrafish). Alignment was performed with ClustalW. (H) PSMB8 and PSMB9 mutations were modeled based on the x-ray structure of the mouse immunoproteasome (PDB entry code: 3UNH) (46), and the mutations in PSMA3 and PSMB4 were based on the bovine 20S proteasome (PDB entry code: 1IRU) (19). Mutated subunits α7 (orange), β7 (cyan), and β1i (purple) are located at the opposite side of the 20S particle compared with β5i (red). (I) Top view of α ring. Subunit α7 (orange) with mutant residue R233 (balls) highlighted. (J) Detailed perspectives of ribbon models of mutant proteins. Mutated residues are depicted in yellow with relevant interaction aa side chains shown with stick models. Novel mutations are highlighted in yellow rectangles. Catalytic active sites in β1i and β5i are marked with asterisks. H, heterozygous, NM, nonmutant.