Mutation in PNPT1, which encodes a polyribonucleotide nucleotidyltransferase, impairs RNA import into mitochondria and causes respiratory-chain deficiency.
Multiple-respiratory-chain deficiency represents an important cause of mitochondrial disorders. Hitherto, however, mutations in genes involved in mtDNA maintenance and translation machinery only account for a fraction of cases. Exome sequencing in two siblings, born to consanguineous parents, with severe encephalomyopathy, choreoathetotic movements, and combined respiratory-chain defects allowed us to identify a homozygous PNPT1 missense mutation (c.1160A>G) that encodes the mitochondrial polynucleotide phosphorylase (PNPase). Blue-native polyacrylamide gel electrophoresis showed that no PNPase complex could be detected in subject fibroblasts, confirming that the substitution encoded by c.1160A>G disrupts the trimerization of the protein. PNPase is predominantly localized in the mitochondrial intermembrane space and is implicated in RNA targeting to human mitochondria. Mammalian mitochondria import several small noncoding nuclear RNAs (5S rRNA, MRP RNA, some tRNAs, and miRNAs). By RNA hybridization experiments, we observed a significant decrease in 5S rRNA and MRP-related RNA import into mitochondria in fibroblasts of affected subject 1. Moreover, we found a reproducible decrease in the rate of mitochondrial translation in her fibroblasts. Finally, overexpression of the wild-type PNPT1 cDNA in fibroblasts of subject 1 induced an increase in 5S rRNA import in mitochondria and rescued the mitochondrial-translation deficiency. In conclusion, we report here abnormal RNA import into mitochondria as a cause of respiratory-chain deficiency.
Université Paris Descartes-Sorbonne Paris Cité, Institut Imagine and INSERM U781, Hôpital Necker-Enfants Malades, 149 rue de Sèvres, Paris, France.
Vanessa
V
Vedrenne
Ali
A
Gowher
Pascale
P
De Lonlay
Patrick
P
Nitschke
Valérie
V
Serre
Nathalie
N
Boddaert
Cecilia
C
Altuzarra
Anne-Marie
AM
Mager-Heckel
Florence
F
Chretien
Nina
N
Entelis
Arnold
A
Munnich
Ivan
I
Tarassov
Agnès
A
Rötig
D000293:Adolescent; D001921:Brain / Q000473:pathology; D002675:Child, Preschool; D004272:DNA, Mitochondrial / Q000235:genetics*; D005091:Exons; D005095:Exoribonucleases / Q000235:genetics* / Q000378:metabolism; D005260:Female; D056945:Hep G2 Cells; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D028361:Mitochondrial Diseases / Q000175:diagnosis / Q000235:genetics*; D009154:Mutation; D034622:RNA Interference; D034443:RNA Transport / Q000235:genetics*; D012335:RNA, Ribosomal / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism; D024101:Mitochondrial Proteins
D004272:DNA, Mitochondrial; D005095:Exoribonucleases; D012335:RNA, Ribosomal; D012343:RNA, Transfer; C476417:PNPT1 protein, human; D024101:Mitochondrial Proteins