FOXO3a upregulates DNA repair activities by transcriptional activation of target genes and provides the resistance to gamma radiation and the extension of lifespan in mouse.

To verify whether DNA repair is regulated by FOXO3a, a tet-on flag-h-FOXO3a transgenic mice were used. RT-q-PCR and western blot analysis showed that the mRNA and protein levels of flag-h-FOXO3a, XRCC4, XPC, APE1 and MSH2 increased dose dependently by doxycycline. DNA repair activities like non-homologous end joining (NHEJ), nucleotide excision repair (NER), base excision repair (BER), mismatch repair (MMR) also increased in a doxycycline dose dependent manner. MEF (mouse embryonic fibroblast) cells of the transgenic mouse were transfected with human XRCC4/XPC/APE1/MSH2 promoter-pGL3 basic vectors. Promoter assay and ChIP (chromatin immunoprecipitation) assay showed increased promoter activity and interactions of FOXO3a to FOXO consensus sites. The results indicate that XRCC4, XPC, APE1, and MSH2 are transcriptional target genes of FOXO3a and activities of NHEJ, NER, BER and MMR are regulated probably via transcriptional activation of XRCC4, XPC, APE1 and MSH2 by FOXO3a. FOXO3a overexpression in MEF cells and tet-on flag-h-FOXO3a transgenic mouse exhibited high resistance to gamma radiation. Small intestine showed less damage and apoptosis in doxycycline-treated mice. The median and maximum lifespan of the doxycycline-treated transgenic mice increased by about 30%. The results suggest that FOXO3a overexpression provide protection against gamma radiation and lifespan extension possibly via activation of DNA repair.