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. 2008 May;19(5):2014–2025. doi: 10.1091/mbc.E07-08-0811

Figure 5.

Figure 5.

An interplay of AKT and JNK onto FOXO activity. (A) Expression of a constitutively active (CA) form of AKT resulted in abrogation of cell death by H2O2 even in the absence of IGF-I (right-hand bars). Cotransfection of GFP, WTFOXO3 and CA-AKT expressing vectors inhibits neuronal death after H2O2 compared with cultures cotransfected with control vector, GFP- and WTFOXO3-expressing vectors. Live neurons are expressed as percentage of GFP+ cells at time 0. **p < 0.01, n = 2. (B) Transcriptional activity of FOXO is robustly modulated by AKT. Cotransfection of CA-AKT with WTFOXO3 results in markedly reduced FOXO activity after H2O2 regardless of IGF-I. In contrast, cotransfection of CA-AKT with an AKT-insensitive mutant (M) FOXO3 results in preservation of enhanced FOXO activity after H2O2. **p < 0.01 and ***p < 0.001 versus indicated groups; n = 4. (C) Transcriptional activity of FOXO is enhanced by MEKK, which in turn counteracts the inhibitory action of IGF-I. *p < 0.05 and **p < 0.01 versus indicated groups; n = 3. (D) Antagonistic regulation of FOXO activity by MEKK and AKT, respectively. AKT was able to counteract the stimulatory effect of MEKK onto FOXO in a dose-dependent way. Neuronal cultures were cotransfected with various amounts of the respective vectors, and FOXO activity was determined with a luciferase gene-reporter system. ***p < 0.001 versus CA-AKT–cotransfected cultures; n = 3. (E) Expression of MEKK in neuronal cultures resulted in increased cell death as determined by the number of GFP+ cells. Cultures were cotransfected with GFP- and CA-MEKK– or GFP-expressing vectors only (controls) with or without IGF-I, and the number of cells was scored 24 h later. *p < 0.05 versus IGF-I–treated cultures; n = 3. (F) Partial abrogation of H2O2-induced FOXO activity by expression of CA-AKT (1 μg) was not modified by addition of the JNK inhibitor Sp600125. Note that inhibition of FOXO activity was similar by either inhibition of JNK or stimulation of AKT (p < 0.01 vs. H2O2-treated cultures (dotted bar); n = 3).