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

Abstract

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.

Rapid directional shift of mitochondrial DNA heteroplasmy in animal tissues by a mitochondrially targeted restriction endonuclease

“…Additional data from the literature support this concept. Using an inducible dominant negative DNA polymerase ␥, Jazayeri et al (27) showed that decreasing mtDNA levels by 99% resulted in a reduction of the activity of the respiratory complexes to 18-30% of controls (27). In mice with a brain-specific Tfam knockout, which leads to lack of mtDNA replication, there was a 1-to 2-mo interval between severe mtDNA depletion and the detection of a biochemical defect (28).…”

Mitochondrial pyrimidine nucleotide carrier (PNC1) regulates mitochondrial biogenesis and the invasive phenotype of cancer cells

“…HeLa clones stably expressing shRNA targeting PNC1 exhibited a 40% and 60% reduction in protein did not show reduced proliferation (Figure 6b). Previous studies of mtDNA suppression after ethidium bromide treatment or suppression of critical components of the mtDNA maintenance machinery have shown impaired proliferation only when a critical level of mtDNA (less than 25% of initial content) is reached, which suggests that a minimal level of mtDNA is sufficient for cell proliferation (Jazayeri et al, 2003;Jeng et al, 2008). Interestingly, the effects of PNC1 on cell size and ROS production were not as tightly correlated with the degree of PNC1 suppression (Floyd et al, 2007 and this study).…”

Depletion of mitochondria in mammalian cells through enforced mitophagy

“…Alternative methods to deplete mtDNA and generate ρ 0 cells include mitochondrial targeting of the restriction endonuclease EcoRI 18 or expression of a dominant negative form of Polγ, a gene that codes for the catalytic subunit of the mitochondrial DNA polymerase 19 . However, these solutions do not circumvent a major drawback, which is that ρ 0 cells still contain functional mitochondria.…”