Abstract
Despite having long telomeres, mouse embryo fibroblasts (MEFs) senesce more rapidly than human diploid fibroblasts because of the accumulation of oxidative DNA damage. The CUX1 homeodomain protein was recently found to prevent senescence in RAS-driven cancer cells that produce elevated levels of reactive-oxygen species. Here we show that Cux1-/- MEFs are unable to proliferate in atmospheric (20%) oxygen although they can proliferate normally in physiological (3%) oxygen levels. CUX1 contains three domains called Cut repeats. Structure/function analysis established that a single Cut repeat domain can stimulate the DNA binding, Schiff-base formation, glycosylase and AP-lyase activities of 8-oxoguanine DNA glycosylase 1, OGG1. Strikingly and in contrast to previous reports, OGG1 exhibits efficient AP-lyase activity in the presence of a Cut repeat. Repair of oxidative DNA damage and proliferation in 20% oxygen were both rescued in Cux1-/- MEFs by ectopic expression of CUX1 or of a recombinant Cut repeat protein that stimulates OGG1 but is devoid of transcription activation potential. These findings reinforce the causal link between oxidative DNA damage and cellular senescence and suggest that the role of CUX1 as an accessory factor in DNA repair will be critical in physiological situations that generate higher levels of reactive oxygen species.
Highlights
The presence of senescent cells is associated with, and is believed to contribute to, many age-related pathologies [1, 2]
RNAi-mediated knockdown and gene inactivation demonstrated that CUX1 is required for efficient repair of oxidative DNA damage, while base excision repair assays established that Cut repeat domains can increase the binding of OGG1 to 8-oxoG-containing DNA and stimulate both its glycosylase and AP-lyase activities (Figures 1, 3, 5 and 6)
We propose that the p200 CUX1 protein serves as an accessory factor in the sub-pathway of base excision repair that removes oxidized purines
Summary
The presence of senescent cells is associated with, and is believed to contribute to, many age-related pathologies [1, 2]. Cellular senescence is triggered by many types of genomic damage, including telomere shortening and oxidative DNA damage [3]. MEFs have long telomeres and express telomerase but senesce more rapidly than human diploid fibroblasts because of the accumulation of oxidative DNA damage [4]. MEFs become senescent after 4 to 5 weeks when cultured in 20% oxygen, but proliferate indefinitely when maintained in 3% oxygen [4]. Oxidative purine lesions are removed by 8-oxoguanine DNA glycosylase 1, OGG1, whereas oxidative pyrimidine lesions are removed by NTH1, NEIL1, or NEIL2 (reviewed in [6]). DNA glycosylases for oxidized bases are bifunctional. These enzymes hydrolyze the N-glycosidic bond to generate an apurinic/apyridinic (AP) site and generate a single-strand nick 3’ to the www.impactjournals.com/oncotarget
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
