Diseases caused by nuclear genes affecting mtDNA stability

Suomalainen, Anu; Kaukonen, Jyrki

doi:10.1002/ajmg.1379

Cited by 96 publications

(59 citation statements)

References 89 publications

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“…Interestingly, adPEO is characterized by the presence of multiple mtDNA deletions, and the disorder has also been linked to mutations in DNA polymerase ␥ (12,13). Taken together, these data demonstrate a functional relationship between TWINKLE and the DNA polymerase and suggest that TWINKLE may be a DNA helicase active in mammalian mitochondrial DNA replication.…”

mentioning

confidence: 76%

TWINKLE Has 5′ → 3′ DNA Helicase Activity and Is Specifically Stimulated by Mitochondrial Single-stranded DNA-binding Protein

Korhonen

Gaspari

Falkenberg

2003

Journal of Biological Chemistry

255

261

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Mutations in TWINKLE cause autosomal dominant progressive external ophthalmoplegia, a human disorder associated with multiple deletions in the mitochondrial DNA. TWINKLE displays primary sequence similarity to the phage T7 gene 4 primase-helicase, but no specific enzyme activity has been assigned to the protein. We have purified recombinant TWINKLE to near homogeneity and demonstrate here that TWINKLE is a DNA helicase with 5 to 3 directionality and distinct substrate requirements. The protein needs a stretch of 10 nucleotides of single-stranded DNA on the 5-side of the duplex to unwind duplex DNA. In addition, helicase activity is not observed unless a short single-stranded 3-tail is present. The helicase activity has an absolute requirement for hydrolysis of a nucleoside 5-triphosphate, with UTP being the optimal substrate. DNA unwinding by TWINKLE is specifically stimulated by the mitochondrial single-stranded DNA-binding protein.Our enzymatic characterization strongly supports the notion that TWINKLE is the helicase at the mitochondrial DNA replication fork and provides evidence for a close relationship of the DNA replication machinery in bacteriophages and mammalian mitochondria.The molecular mechanisms by which mtDNA is replicated in mammalian cells are of fundamental biological interest. Saccharomyces cerevisiae has served as a model system for studies of mammalian mtDNA replication, but there are significant differences between yeast and mammalian cells (1). Replication of the S. cerevisiae mtDNA is initiated from multiple sites of the ϳ86-kb genome, and the mtDNA molecules frequently undergo recombination. In contrast, the smaller mammalian mtDNAs (ϳ16 kb) initiate DNA replication from two specific origins of replication, oriH and oriL, and recombination is a rare or possibly even non-existent phenomenon (2).Mammalian mtDNA contains two major promoters, the light and heavy strand promoters, which produce near genomic length transcripts that, after RNA processing, release individual mRNAs, tRNAs, and rRNAs. A separate transcription unit for the rRNA genes in mammalian mitochondria has also been reported (3). Transcription from light strand promoters is not only necessary for gene expression but also produces the RNA primers required for initiation of mtDNA replication at oriH (1, 4). DNA synthesis from oriH is unidirectional and proceeds to displace the parental heavy strand. The nascent H strands frequently terminate 700 bp downstream of oriH, giving rise to 7 S DNA (D-loop strand). This termination event produces a characteristic triple-stranded structure, called the D-loop (5). The function of the D-loops is unknown, but they presumably play a role in regulating mtDNA replication.The mitochondrial DNA polymerase ␥ is a heterodimer comprising catalytic (A) and accessory (B) subunits of 140 and 54 kDa, respectively. The accessory subunit, polymerase ␥ B, which is not present in yeast, has been characterized as a processivity factor for the polymerase (6, 7). Polymerase ␥ B increases the affinity of the ...

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mentioning

confidence: 76%

TWINKLE Has 5′ → 3′ DNA Helicase Activity and Is Specifically Stimulated by Mitochondrial Single-stranded DNA-binding Protein

Korhonen

Gaspari

Falkenberg

2003

Journal of Biological Chemistry

255

261

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“…Ϫ/Ϫ mice was assessed by Southern blotting using a 2-kb EcoRI fragment of a mouse mitochondrial genome as a probe (43). Total RNA was isolated using Trizol reagent (Invitrogen, Carlsbad, CA).…”

Section: Iqgap2mentioning

confidence: 99%

Development of Hepatocellular Carcinoma in Iqgap2-Deficient Mice Is IQGAP1 Dependent

Schmidt

Chiariello

Capilla

et al. 2008

Molecular and Cellular Biology

115

124

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IQGAPs are multidomain scaffolding proteins that integrate Rho GTPase and Ca2؉ /calmodulin signals with cell adhesive and cytoskeletal reorganizational events. Targeted disruption of the murine Iqgap2 gene resulted in the age-dependent development of apoptosis and hepatocellular carcinoma (HCC), characterized by the overexpression of IQGAP1, the loss of membrane E-cadherin expression, the cytoplasmic translocation (and activation) of ␤-catenin, and the overexpression of a nuclear target of ␤-catenin, cyclin D1. In normal hepatocytes, IQGAP2 was found to exist as one component of a multifunctional scaffolding complex comprising IQGAP1, ␤-catenin, and E-cadherin, with no evidence for direct IQGAP1-IQGAP2 interactions. Interbreeding of Iqgap2 ؊/؊ mice into the Iqgap1 ؊/؊ background resulted in the phenotypic correction of the preexisting hepatopathy, decreases in the incidence and sizes of HCC tumors, and the normalization of overall survival rates compared to those of Iqgap2 ؊/؊ mice, suggesting that maximal penetrance of the Iqgap2 ؊/؊ HCC phenotype requires the coordinate expression of IQGAP1. These results identify Iqgap2 as a novel tumor suppressor gene specifically linked to the development of HCC and the activation of the Wnt/␤-catenin signaling pathway, while also suggesting that IQGAP1 and IQGAP2 retain functionally divergent roles in hepatocellular carcinogenesis.

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“…1 Because electron transport complexes are composed of both nuclear and mitochondrial encoded subunits, normal oxidative metabolism is dependent upon the integrity and coordinated expression of both genomes. Indeed, disease states are associated with mutations of the mtDNA (4 -8), as well as with nuclear genes that encode respiratory complex subunits (9,10). Determining whether a disease state is associated with respiratory chain dysfunction or is caused by a nuclear or mitochondrial mutation(s) can be challenging.…”

mentioning

confidence: 99%

Inducible Expression of a Dominant Negative DNA Polymerase-γ Depletes Mitochondrial DNA and Produces a ρ0Phenotype

Jazayeri¹,

Andreyev²,

Will³

et al. 2003

Journal of Biological Chemistry

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We report the inducible, stable expression of a dominant negative form of mitochondria-specific DNA polymerase-␥ to eliminate mitochondrial DNA (mtDNA) from human cells in culture. HEK293 cells were transfected with a plasmid encoding inactive DNA polymerase-␥ harboring a D1135A substitution (POLGdn). The cells rapidly lost mtDNA (t1 ⁄2 ‫؍‬ 2-3 days) when expression of the transgene was induced. Concurrent reduction of mitochondrial encoded mRNA and protein, decreased cellular growth rate, and compromised respiration and mitochondrial membrane potential were observed. mtDNA depletion was reversible, as demonstrated by restoration of mtDNA copy number to normal within 10 days when the expression of POLGdn was suppressed following a 3-day induction period. Long term (20 days) expression of POLGdn completely eliminated mtDNA from the cells, resulting in 0 cells that were respiration-deficient, lacked electron transport complex activities, and were auxotrophic for pyruvate and uridine. Fusion of the 0 cells with human platelets yielded clonal cybrid cell lines that were populated exclusively with donor-derived mtDNA. Respiratory function, mitochondrial membrane potential, and electron transport activities were restored to normal in the cybrid cells. Inducible expression of a dominant negative DNA polymerase-␥ can yield mtDNA-deficient cell lines, which can be used to study the impact of specific mtDNA mutations on cellular physiology, and to investigate mitochondrial genome function and regulation.

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Diseases caused by nuclear genes affecting mtDNA stability

Cited by 96 publications

References 89 publications

TWINKLE Has 5′ → 3′ DNA Helicase Activity and Is Specifically Stimulated by Mitochondrial Single-stranded DNA-binding Protein

TWINKLE Has 5′ → 3′ DNA Helicase Activity and Is Specifically Stimulated by Mitochondrial Single-stranded DNA-binding Protein

Development of Hepatocellular Carcinoma in Iqgap2-Deficient Mice Is IQGAP1 Dependent

Inducible Expression of a Dominant Negative DNA Polymerase-γ Depletes Mitochondrial DNA and Produces a ρ0Phenotype

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