Mutation in PNPT1 , which Encodes a Polyribonucleotide Nucleotidyltransferase, Impairs RNA Import into Mitochondria and Causes Respiratory-Chain Deficiency

Abstract

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.

Exome sequencing in 32 patients with anophthalmia/microphthalmia and developmental eye defects

“…2F) that was paternally inherited. Although eye manifestations have not been described in patients with PNPT1 gene mutations, the remaining phenotypic features were consistent with the clinical presentations seen in other patients 18,19 and as both sequence variants were predicted to be deleterious, we consider them to be disease-causing.…”

Identification of Genes Potentially Regulated by Human Polynucleotide Phosphorylase (hPNPaseold-35) Using Melanoma as a Model

“…The exact mechanism of how hPNPase old-35 regulates these genes remains to be elucidated and the possibilities may be numerous ranging from RNA degradation, miRNA regulation or RNA import. Moreover, recently mutations in hPNPase old-35 have also been identified that impair respiratory-chain activity [44]. The ETC genes identified in this study identify the specific genes affected by hPNPase old-35 that maybe causative for mitochondrial dysfunction.…”

Biallelic Mutations in MRPS34 Lead to Instability of the Small Mitoribosomal Subunit and Leigh Syndrome

“…Variants were annotated and filtered using in-house software PolyWeb as described elsewhere. 31 RNA and DNA Analyses DNA was extracted from primary skin fibroblasts as described previously. 22 For cDNA studies of subject 1, cultured fibroblasts were grown with and without cycloheximide treatment, as described previously.…”