(A-D). Primary FoxO3+/+ and FoxO3-/- MEFs were treated with 75μM H2O2. At days 3, 10 and 17-post treatment, cells were analyzed for: A, SA-β-gal activity; and B, BrdU incorporation. Primary FoxO3+/+ and FoxO3-/- MEFs were infected with retrovirus expressing H-Rasv12. At days 3, 10 and 17 post selection, cells were analyzed for: C, SA-β-gal activity; and D, BrdU incorporation. All data represent the mean ± S.E.M. of at least three independent experiments. *,** p<0.05, 0.01 vs. FOXO3+/+; #, ##, ### p<0.05, 0.01, 0.001 vs. Day 3. E. Activated Akt induces premature senescence of MEFs. Primary wild-type MEFs were infected with retrovirus expressing inducible myristoylated Akt (mAkt-ER). After selection, cells were either untreated or treated with 4-OHT. At days 3, 12 and 20-post incubation with 4-OHT, cells were analyzed for SA-β-gal activity. Data represent the mean ± S.E.M. of at least three independent experiments. **, *** p<0.01, 0.001 vs. vehicle control; #,##, ### p<0.05, 0.01, 0.001 vs. Day 3.