title: RecQL4 cytoplasmic localization: implications in mitochondrial DNA oxidative damage repair.
abstract: RecQL4, one of the five human RecQ helicases, is crucial for genomic stability and RecQL4 when mutated leads to premature aging phenotypes in humans. Unlike other human RecQ helicases, RecQL4 is found both in the nucleus and the cytoplasm. While the nuclear localization signal (NLS) and the retention domain at the N-terminus are responsible for the nuclear localization of RecQL4, the signal for its cytoplasmic localization is essentially unknown. In this study, two functional nuclear exporting signals (NESs; pNES2 and pNES3) were identified at the C-terminus of RecQL4. Deletion of pNES2 drastically diminished the cytoplasmic localization of RecQL4. Strikingly, addition of ubiquitination tail at the C-terminus of RecQL4 substantially enriched the cytoplasmic fraction of RecQL4 only in the presence of functional pNES2. Immunofluorescence studies revealed that the cytoplasmic RecQL4 was localized in mitochondria. Consistent with its mitochondrial localization, a regulatory role for RecQL4 in the maintenance of mitochondrial DNA (mtDNA) copy number was demonstrated. Elevation of ectopic expression of RecQL4 increased the mtDNA copy number in HEK293 cells while RecQL4 knock down markedly decreased the mtDNA copy number in U2OS cells. Additionally, a substantially increased level of mitochondrial superoxide production, and a markedly decreased repair capacity for oxidative DNA damage were observed in the mitochondria of both RecQL4 deficient human fibroblasts and RecQL4-suppressed cancer cells. These data strongly suggest a regulatory role for RecQL4 in mitochondrial stability and function. Collectively, our study demonstrates that NES-mediated RecQL4 export to the cytoplasm is essential for the maintenance of mitochondrial genome stability.
authors: Laboratory of Disease Genomics and Individualized Medicine, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100029, China.
authors: Zhenfen
authors: Z
authors: Chi
authors: Linghu
authors: L
authors: Nie
authors: Zhao
authors: Z
authors: Peng
authors: Qiong
authors: Q
authors: Yang
authors: Kuan
authors: K
authors: Yang
authors: Jiahai
authors: J
authors: Tao
authors: Yang
authors: Y
authors: Mi
authors: Xiangdong
authors: X
authors: Fang
authors: Adayabalam S
authors: AS
authors: Balajee
authors: Yongliang
authors: Y
authors: Zhao
mesh_terms: D000595:Amino Acid Sequence; D002460:Cell Line; D003593:Cytoplasm / Q000201:enzymology*; D004249:DNA Damage; D004260:DNA Repair; D004272:DNA, Mitochondrial / Q000378:metabolism*; D018628:Gene Dosage; D020868:Gene Silencing; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000378:metabolism; D053140:Organelle Shape; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D021381:Protein Transport; D017382:Reactive Oxygen Species / Q000378:metabolism; D053484:RecQ Helicases / Q000737:chemistry / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology
chemical_list: D004272:DNA, Mitochondrial; D019913:Nuclear Localization Signals; D017382:Reactive Oxygen Species; D049452:Green Fluorescent Proteins; C506731:RECQL4 protein, human; D053484:RecQ Helicases