A nonhomologous end-joining pathway is required for protein phosphatase 2A promotion of DNA double-strand break repair.
Protein phosphatase 2A (PP2A) functions as a potent tumor suppressor, but its mechanism(s) remains enigmatic. Specific disruption of PP2A by either expression of SV40 small tumor antigen or depletion of endogenous PP2A/C by RNA interference inhibits Ku DNA binding and DNA-PK activities, which results in suppression of DNA double-strand break (DSB) repair and DNA end-joining in association with increased genetic instability (i.e., chromosomal and chromatid breaks). Overexpression of the PP2A catalytic subunit (PP2A/C) enhances Ku and DNA-PK activities with accelerated DSB repair. Camptothecin-induced DSBs promote PP2A to associate with Ku 70 and Ku 86. PP2A directly dephosphorylates Ku as well as the DNA-PK catalytic subunit (DNA-PKcs) in vitro and in vivo, which enhances the formation of a functional Ku/DNA-PKcs complex. Intriguingly, PP2A promotes DSB repair in wild type mouse embryonic fibroblast (MEF) cells but has no such effect in Ku-deficient MEF cells, suggesting that the Ku 70/86 heterodimer is required for PP2A promotion of DSB repair. Thus, PP2A promotion of DSB repair may occur in a novel mechanism by activating the nonhomologous end-joining pathway through direct dephosphorylation of Ku and DNA-PKcs, which may contribute to maintenance of genetic stability.
UF Shands Cancer Center, Division of Hematology/Oncology, Department of Medicine and Department of Anatomy & Cell Biology, University of Florida, Gainesville, FL 32610-3633, USA.
Qinhong
Q
Wang
Fengqin
F
Gao
Ton
T
Wang
Tammy
T
Flagg
Xingming
X
Deng
D000818:Animals; D034961:Antigens, Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017209:Apoptosis; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002470:Cell Survival; D002478:Cells, Cultured; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016521:Electrophoresis, Gel, Pulsed-Field; D004622:Embryo, Mammalian / Q000166:cytology; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D000072200:Ku Autoantigen; D051379:Mice; D018345:Mice, Knockout; D010766:Phosphorylation; D055503:Protein Multimerization; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D011995:Recombination, Genetic; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D054648:Protein Phosphatase 2; C000606509:Xrcc6 protein, human; C000606510:Xrcc6 protein, mouse; D000072200:Ku Autoantigen