Negative regulation of mitochondrial transcription by mitochondrial topoisomerase I

Abstract

Mitochondrial topoisomerase I is a genetically distinct mitochondria-dedicated enzyme with a crucial but so far unknown role in the homeostasis of mitochondrial DNA metabolism. Here, we present data suggesting a negative regulatory function in mitochondrial transcription or transcript stability. Deficiency or depletion of mitochondrial topoisomerase I increased mitochondrial transcripts, whereas overexpression lowered mitochondrial transcripts, depleted respiratory complexes I, III and IV, decreased cell respiration and raised superoxide levels. Acute depletion of mitochondrial topoisomerase I triggered neither a nuclear mito-biogenic stress response nor compensatory topoisomerase IIβ upregulation, suggesting the concomitant increase in mitochondrial transcripts was due to release of a local inhibitory effect. Mitochondrial topoisomerase I was co-immunoprecipitated with mitochondrial RNA polymerase. It selectively accumulated and rapidly exchanged at a subset of nucleoids distinguished by the presence of newly synthesized RNA and/or mitochondrial RNA polymerase. The inactive Y559F-mutant behaved similarly without affecting mitochondrial transcripts. In conclusion, mitochondrial topoisomerase I dampens mitochondrial transcription and thereby alters respiratory capacity. The mechanism involves selective association of the active enzyme with transcriptionally active nucleoids and a direct interaction with mitochondrial RNA polymerase. The inhibitory role of topoisomerase I in mitochondrial transcription is strikingly different from the stimulatory role of topoisomerase I in nuclear transcription.

Why chloroplasts and mitochondria retain their own genomes and genetic systems: Colocation for redox regulation of gene expression

“…Mitochondria from mammalian fibroblasts contain a specific DNA topoisomerase, topoisomerase I. Sobek et al (52) report increased transcription of respiratory chain mitochondrial genes when DNA topoisomerase I is either deficient or depleted. It is concluded that topoisomerase I inhibits mitochondrial DNA transcription and that release of transcriptional inhibition is accompanied by increased respiratory rate and superoxide production (52).…”

“…It is concluded that topoisomerase I inhibits mitochondrial DNA transcription and that release of transcriptional inhibition is accompanied by increased respiratory rate and superoxide production (52). DNA topoisomerase is also implicated in redox control of transcription of mitochondrial DNA in plant tissue (53).…”

Poisoning of Mitochondrial Topoisomerase I by Lamellarin D

“…Some drugs have been reported to deplete mitochondrial DNA by interfering with mitochondrial DNA polymerase gamma activity (Rowe et al, 2001;Neuzil et al, 2013). Top1mt is also important for mitochondrial homeostasis (Douarre et al, 2012), mtDNA replication (Zhang and Pommier, 2008), mtDNA transcription (Sobek et al, 2013), and mtDNA integrity (Medikayala et al, 2011). Yet, there are no drugs known to specifically target Top1mt.…”

“…Unlike TOP2Β (Low et al, 2003) and TOP3Α, TOP1mt is the only topoisomerase gene coding for a single polypeptide solely targeted to mitochondria (Zhang et al, 2001;Chinnery and Hudson, 2013). In addition to studying Top1mt's roles in regulating mtDNA replication (Zhang and Pommier, 2008), transcription (Sobek et al, 2013), and mtDNA integrity (Medikayala et al, 2011), it has become possible to examine Top1mt functions genetically. Murine embryonic fibroblasts generated from TOP1mt knockout mice exhibit mitochondrial defects with marked increase in reactive oxygen species production, calcium signaling, hyperpolarization of mitochondrial membranes, and increased mitophagy (Douarre et al, 2012).…”

A balanced perspective on animal welfare for improved meat and meat products

“…The rate-limiting enzyme in catecholamine synthesis, which is TH, indicates a selective increase in TH mRNA (mitochondria ribosomal nuclear atom). This is normally accompanied by a corresponding response in immune reactive TH protein owing to various stressors in the environment (Blanchard et al, 2001;Sobek et al, 2013;Janska & Kwasniak, 2014).…”