RECQL4 and p53 potentiate the activity of polymerase γ and maintain the integrity of the human mitochondrial genome.
Germline mutations in RECQL4 and p53 lead to cancer predisposition syndromes, Rothmund-Thomson syndrome (RTS) and Li-Fraumeni syndrome (LFS), respectively. RECQL4 is essential for the transport of p53 to the mitochondria under unstressed conditions. Here, we show that both RECQL4 and p53 interact with mitochondrial polymerase (PolγA/B2) and regulate its binding to the mitochondrial DNA (mtDNA) control region (D-loop). Both RECQL4 and p53 bind to the exonuclease and polymerase domains of PolγA. Kinetic constants for interactions between PolγA-RECQL4, PolγA-p53 and PolγB-p53 indicate that RECQL4 and p53 are accessory factors for PolγA-PolγB and PolγA-DNA interactions. RECQL4 enhances the binding of PolγA to DNA, thereby potentiating the exonuclease and polymerization activities of PolγA/B2. To investigate whether lack of RECQL4 and p53 results in increased mitochondrial genome instability, resequencing of the entire mitochondrial genome was undertaken from multiple RTS and LFS patient fibroblasts. We found multiple somatic mutations and polymorphisms in both RTS and LFS patient cells. A significant number of mutations and polymorphisms were common between RTS and LFS patients. These changes are associated with either aging and/or cancer, thereby indicating that the phenotypes associated with these syndromes may be due to deregulation of mitochondrial genome stability caused by the lack of RECQL4 and p53.


CONCLUSIONS
The biochemical mechanisms by which RECQL4 and p53 affect mtDNA replication have been elucidated. Resequencing of RTS and LFS patients' mitochondrial genome reveals common mutations indicating similar mechanisms of regulation by RECQL4 and p53.
National Institute of Immunology, Aruna Asaf Ali Marg, New Delhi 110067, India and.
Shruti
S
Gupta
Siddharth
S
De
Vivek
V
Srivastava
Mansoor
M
Hussain
Jyoti
J
Kumari
K
K
Muniyappa
Sagar
S
Sengupta
D004258:DNA Polymerase III / Q000235:genetics / Q000378:metabolism; D019951:DNA Polymerase beta / Q000235:genetics / Q000378:metabolism; D000074002:DNA Polymerase gamma; D004272:DNA, Mitochondrial / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts; D015894:Genome, Human; D054629:Genome, Mitochondrial / Q000502:physiology*; D042822:Genomic Instability; D006801:Humans; D016864:Li-Fraumeni Syndrome / Q000235:genetics*; D009154:Mutation; D011110:Polymorphism, Genetic; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism*; D011038:Rothmund-Thomson Syndrome / Q000235:genetics*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*
D004272:DNA, Mitochondrial; D016159:Tumor Suppressor Protein p53; C065639:DNA polymerase A; C415367:DNA polymerase beta2; D004258:DNA Polymerase III; D019951:DNA Polymerase beta; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase; C506731:RECQL4 protein, human; D053484:RecQ Helicases