RECQL4 is essential for the transport of p53 to mitochondria in normal human cells in the absence of exogenous stress

Abstract

SummaryMutations in RECQL4 helicase are associated with Rothmund-Thomson syndrome (RTS). A subset of RTS patients is predisposed to cancer and is sensitive to DNA damaging agents. The enhanced sensitivity of cells from RTS patients correlates with the accumulation of transcriptionally active nuclear p53. We found that in untreated normal human cells these two nuclear proteins, p53 and RECQL4, instead colocalize in the mitochondrial nucleoids. RECQL4 accumulates in mitochondria in all phases of the cell cycle except S phase and physically interacts with p53 only in the absence of DNA damage. p53-RECQL4 binding leads to the masking of the nuclear localization signal of p53. The N-terminal 84 amino acids of RECQL4 contain a mitochondrial localization signal, which causes the localization of RECQL4-p53 complex to the mitochondria. RECQL4-p53 interaction is disrupted after stress, allowing p53 translocation to the nucleus. In untreated normal cells RECQL4 optimizes de novo replication of mtDNA, which is consequently decreased in fibroblasts from RTS patients. Wild-type RECQL4-complemented RTS cells show relocalization of both RECQL4 and p53 to the mitochondria, loss of p53 activation, restoration of de novo mtDNA replication and resistance to different types of DNA damage. In cells expressing D84 RECQL4, which cannot translocate to mitochondria, all the above functions are compromised. The recruitment of p53 to the sites of de novo mtDNA replication is also regulated by RECQL4. Thus these findings elucidate the mechanism by which p53 is regulated by RECQL4 in unstressed normal cells and also delineates the mitochondrial functions of the helicase.

Mitochondrial functions of RECQL4 are required for the prevention of aerobic glycolysis dependent cell invasion

“…Our recent results (De et al, 2012;Gupta et al, 2014) led to the question whether the lack of mitochondrial localization of RECQL4 in RTS patients affects the functioning of the mitochondria and, thereby, contributes to the neoplastic transformation process. To answer this question, two cellular models were employed: (i) hTERT immortalized normal human fibroblasts GM07532 and RTS patient fibroblast cell lines AG03587, AG05013, AG05139, L9552914-J, B1865425K, D8903644-K; (ii) an isogenic system, wherein either Aequorea coerulescens (Ac)GFP-tagged wild-type RECQL4 or RECQL4 without the mitochondrial localization signal, i.e.…”

“…The role of RECQL4 in the maintenance of both the nuclear and mitochondrial genomes might, thus, be due to the cell-cycle-specific subcellular localizations of the protein (De et al, 2012). The fact that not all initially cytosolic RECQL4 localizes to the mitochondria (Fig.…”

“…hTERT immortalized normal human fibroblasts GM07532 and RTS fibroblasts, isogenic cell lines AcGFP-N1-RECQL4 (1-1208) Clone 1, AcGFP-N1-RECQL4 (Δ84) Clone 5 and GM07532 shRECQL4 and GM07532 shControl have been described earlier (De et al, 2012). Protein levels of RECQL4 in GM07532, GM07532 shRECQL4 and RTS fibroblasts have been reported previously (De et al, 2012). AcGFP-N1 Clone 5 cells were created by lentiviral transduction followed by selection with puromycin (0.5 µg/ml).…”

“…RECQL4 also localizes to the mitochondria (Croteau et al, 2012a;De et al, 2012), mediated through a validated N-terminal mitochondrial localization signal (MLS) (De et al, 2012). RECQL4 is involved in enhancing the processivity and polymerization of mitochondrial DNA (mtDNA) replication.…”

Clinical utility gene card for: Rothmund–Thomson syndrome

“…Although some clinical signs and recent breakthroughs regarding the pathways compromised by RECQL4 defects 15 suggest precocious aging, the patient's lifespan is not altered, provided that the neoplastic disease is diagnosed and treated in time. Lifespan in the absence of malignancy is probably normal, although follow-up data in the literature are limited.…”