Figure 5. Mre11 deletion or inhibition in oncogene overexpressing cells reduces cellular survival.

(A) Inhibition of MRE11 nuclease activity by the small molecule inhibitor, mirin, reduces survival of cells overexpressing oncogenes. Mre11^cond/− and Mre11^cond/−Artemis^−/− MEFs were transduced with control retrovirus (empty vector, EV) or retroviruses expressing MYC or N-MYC, then treated with mirin or vehicle for 24h. Live cells were counted and survival (mirin/DMSO) relative to untransduced cells is plotted. Mean ± SEM of 3 or more independent experiments. *, p≤0.05. (B) MYC overexpressing human U2OS cells exhibit decreased survival upon treatment with mirin. U2OS-pBABE and U2OS-MYC-ER cells were treated with DMSO or 4-OHT for 72h, then with increasing concentrations of mirin for 24h. Cellular survival after 48h was determined relative to vehicle controls. Graph represents Mean ± SEM of 3 independent experiments. *p≤0.05. (C) Cells were treated as in B, and the percentages of annexin V positive cells were determined by flow cytometry. (D-E) U2OS-cMycER cells were treated as in C. Localization of 53BP1 (D) and NBS1 (E) to DNA repair foci was examined by immunofluorescence microscopy. Percentage of nuclei with indicated DNA repair foci is plotted. Mean + SEM of 3 independent experiments. *, p<0.05; paired t-test.