Human Molecular Genetics Advance Access originally published online on June 29, 2009
Human Molecular Genetics 2009 18(18):3470-3483; doi:10.1093/hmg/ddp291
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Published by Oxford University Press 2009
Direct and indirect roles of RECQL4 in modulating base excision repair capacity
1 Laboratory of Molecular Gerontology and 2 Research Resources Branch, National Institute on Aging, NIH, 251 Bayview Blvd, Suite 100, Baltimore, MD 21224, USA, 3 Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a 02-106, Warszawa, Poland and 4 Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, 333 Cedar St., C130 Sterling Hall of Medicine, New Haven, CT 06520, USA
* To whom correspondence should be addressed at: Laboratory of Molecular Gerontology, National Institute on Aging, NIH, 251 Bayview Blvd, Suite 100, Rm 06B133, Baltimore, Maryland 21224, USA. Tel: +1 410 558 8162; Fax: +1 410 558 8157; Email: vbohr{at}nih.gov
Received March 7, 2009; Accepted June 16, 2009
RECQL4 is a human RecQ helicase which is mutated in approximately two-thirds of individuals with Rothmund–Thomson syndrome (RTS), a disease characterized at the cellular level by chromosomal instability. BLM and WRN are also human RecQ helicases, which are mutated in Bloom and Werner's syndrome, respectively, and associated with chromosomal instability as well as premature aging. Here we show that primary RTS and RECQL4 siRNA knockdown human fibroblasts accumulate more H2O2-induced DNA strand breaks than control cells, suggesting that RECQL4 may stimulate repair of H2O2-induced DNA damage. RTS primary fibroblasts also accumulate more XRCC1 foci than control cells in response to endogenous or induced oxidative stress and have a high basal level of endogenous formamidopyrimidines. In cells treated with H2O2, RECQL4 co-localizes with APE1, and FEN1, key participants in base excision repair. Biochemical experiments indicate that RECQL4 specifically stimulates the apurinic endonuclease activity of APE1, the DNA strand displacement activity of DNA polymerase β, and incision of a 1- or 10-nucleotide flap DNA substrate by Flap Endonuclease I. Additionally, RTS cells display an upregulation of BER pathway genes and fail to respond like normal cells to oxidative stress. The data herein support a model in which RECQL4 regulates both directly and indirectly base excision repair capacity.
Present address: Department of Radiation Oncology and Molecular Radiation Sciences, The Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.