title: Alterations to the expression level of mitochondrial transcription factor A, TFAM, modify the mode of mitochondrial DNA replication in cultured human cells.
abstract: Mitochondrial transcription factor A (TFAM) is an abundant mitochondrial protein of the HMG superfamily, with various putative roles in mitochondrial DNA (mtDNA) metabolism. In this study we have investigated the effects on mtDNA replication of manipulating TFAM expression in cultured human cells. Mammalian mtDNA replication intermediates (RIs) fall into two classes, whose mechanistic relationship is not properly understood. One class is characterized by extensive RNA incorporation on the lagging strand, whereas the other has the structure of products of conventional, strand-coupled replication. TFAM overexpression increased the overall abundance of RIs and shifted them substantially towards those of the conventional, strand-coupled type. The shift was most pronounced in the rDNA region and at various replication pause sites and was accompanied by a drop in the relative amount of replication-termination intermediates, a substantial reduction in mitochondrial transcripts, mtDNA decatenation and progressive copy number depletion. TFAM overexpression could be partially phenocopied by treatment of cells with dideoxycytidine, suggesting that its effects are partially attributable to a decreased rate of fork progression. TFAM knockdown also resulted in mtDNA depletion, but RIs remained mainly of the ribosubstituted type, although termination intermediates were enhanced. We propose that TFAM influences the mode of mtDNA replication via its combined effects on different aspects of mtDNA metabolism.
authors.affiliation: Institute of Medical Technology and Tampere University Hospital, FI-33014, University of Tampere, Finland.
authors.forename: Jaakko L O
authors.initials: JL
authors.lastname: Pohjoismäki
authors.forename: Sjoerd
authors.initials: S
authors.lastname: Wanrooij
authors.forename: Anne K
authors.initials: AK
authors.lastname: Hyvärinen
authors.forename: Steffi
authors.initials: S
authors.lastname: Goffart
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Holt
authors.forename: Johannes N
authors.initials: JN
authors.lastname: Spelbrink
authors.forename: Howard T
authors.initials: HT
authors.lastname: Jacobs
mesh_terms: D002460:Cell Line; D004261:DNA Replication / Q000187:drug effects; D004272:DNA, Mitochondrial / Q000096:biosynthesis* / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D024101:Mitochondrial Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D016047:Zalcitabine / Q000494:pharmacology
chemical_list: D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D024101:Mitochondrial Proteins; C499631:TFAM protein, human; D014157:Transcription Factors; D016047:Zalcitabine