Twenty four hours later, DMEM with 25 g/mL puromycin (Sigma, St. Finally, knockdown Theobromine (3,7-Dimethylxanthine) of in cells resulted in FoxO3a-dependent gene expression patterns and increased radiosensitivity that partially mimicked those found in cells. Taken together, our data suggest a role for FoxO3a in the maintenance of genome integrity in response to DNA damage that is mediated by H2AX via yet unknown mechanisms. and genotype in humans is also strongly associated with longevity [14,15,16]. Recent evidence suggested that the mechanism by which FoxO3 activates the transcription of its target genes is mediated by the chromatin remodeling complex Rabbit Polyclonal to IL18R SWItch/Sucrose Non-Fermentable (SWI/SNF) that relaxes the chromatin to initiate transcription . There is a link between aging/longevity and genomic instability. Both H2AX and FoxO3a play important roles in these processes. Importantly, FoxO3a has been shown, Theobromine (3,7-Dimethylxanthine) in addition to its well known transcriptional regulation of stress response genes, to directly interact with ATM to trigger all downstream canonical DNA damage signaling including phosphorylation of H2AX [17,18]. H2AX is known to exert a positive feedback effect on maintaining and amplifying ATM activity via MDC1 . Would it be sensible to assume that H2AX or its phosphorylated form may also impact FoxO3a in a similar feedback manner? This question becomes even more appropriate given the fact that the regulation of longevity in worms by chromatin modifications was dependent on Foxo . Therefore, in this study we examined whether H2AX may play a role in the transcription of genes regulated by FoxO3a. Additionally, we studied the transcriptional responses of these genes to ionizing radiation in comprehensive dose-response and time-course experiments in the context of the presence or absence of histone H2AX. We show that both baseline and radiation-modulated expression of several genes is affected by the H2AX status. Results of experiments examining direct FoxO3a transcriptional activity, FoxO3a post-translational modification and intracellular FoxO3a localization all show that FoxO3a behavior is substantially changed in the compared to cells. Finally, we show that these differences were accompanied by increased genomic instability and radiosensitivity and that knockdown of in cells resulted in the effects similar to those observed in cells, providing a potential link between H2AX and FoxO3a in relation to the maintenance of genome integrity. 2. Results 2.1. Characterization of the Experimental Model of H2AX+/+ and H2AX?/? Cells We first characterized the genetically matched pair of mouse embryonic fibroblasts (MEF) and MEF cell lines in terms of (a) growth rate; (b) gene and protein levels; (c) ability to exert proper DNA damage response. Overall, the growth rate was slightly higher for cells; however, the difference was minimal in the first two days (Figure 1A). Cell cycle distribution was also not different between the two cell lines under control conditions and within 6 h after irradiation, followed by an accumulation of G2 cells in cells, indicating an aberrant cell cycle checkpoint signaling in the H2AX deficient cells (Figure S1). We confirmed that cells had negligible gene expression level (Figure 1B) and no H2AX protein was detected using Western blot in whole cell lysates (Figure 1C). Using immunofluorescence microscopy, we observed numerous and bright H2AX foci in cells 1 h after 2 Gy irradiation, with only few foci were present in untreated cells (Figure 1D). No H2AX signal was detected in cells (Figure 1D). H2AX protein was not detected in untreated or irradiated with up to 10 Gy cells using immunoblotting, whereas in cells H2AX protein levels were induced by irradiation in an expected dose-dependent manner (Figure 1E). Interestingly, the Theobromine (3,7-Dimethylxanthine) activation of the ATM protein by its auto-phosphorylation at Ser 1981, which is one of the earliest molecular responses to DNA damage, was not affected in MEFs (Figure 1E). Since H2AX is the main direct target for activated ATM in response to DNA damage, this observation further confirms that the lack of H2AX induction seen is not due to an inability to phosphorylate histone H2AX, but rather to the lack of H2AX. Altogether, this data validated the usefulness of this cell model to examine a potential role of H2AX in FoxO3a-regulated cellular stress responses. Open in a separate window Figure 1 Characterization of mouse embryonic fibroblasts (MEF) and cells. (A) Growth curves of untreated MEF and cells; (B) basal gene expression in MEF compared to cells measured by RT-qPCR; (C) Western blot showing lack.