Fig 2: Suppression of hepatic GCN5 phosphorylation at Ser275 ameliorates diabetes.(a) Analysis of GCN5 phosphorylated at Ser275 in the liver of db/db or db/m (control) mice or of C57BL/6J mice fed NC or a HFD. All mice were deprived of food for 16 h before analysis. Liver extracts were subjected to IP with antibodies to Ser275-phosphorylated GCN5 followed by immunoblot analysis with antibodies to GCN5. (b,c) Effects of expression of GCN5(WT), GCN5(S275A) or GCN5(S275D) in the liver of db/db mice on plasma glucose concentration under fed or fasted (24 h) conditions (b) as well as on hepatic expression of G6pc and Pck1 under the fasted (24 h) condition (c). (d) Effect of CITED2 depletion on GCN5 phosphorylation at Ser275 in the liver of db/db mice deprived of food for 24 h. All quantitative data are means±s.e.m. (n=7 (b,c)). *P<0.05, **P<0.01 (ANOVA with Bonferroni's post hoc test). Data in a,d are representative of at least three independent experiments. Adenoviral vectors were used for these experiments. ANOVA, analysis of variance; NC, normal chow.

Fig 3: GCN5 phosphorylation at Ser275 drives its substrate switch.(a) AML12 cells expressing FLAG-tagged GCN5(WT) or GCN5(S275A) were exposed to pCPT-cAMP with or without H89 for 30 min and then subjected to IP with antibodies to phosphorylated PKA substrates followed by immunoblot analysis with antibodies to FLAG. (b) Effect of the S275A mutation of FLAG-GCN5 on in vitro acetylation of histone H3 in AML12 cells treated with pCPT-cAMP (1 h). (c) Acetylation of FLAG–PGC-1a in AML12 cells expressing GCN5(WT) or GCN5(S275A) with or without HA-CITED2. (d) Effects of the S275D mutation of GCN5 on histone H3 and PGC-1a acetyltransferase activities in AML12 cells. (e) Effect of the S275D mutation of FLAG-GCN5 on interaction with V5-tagged PGC-1a in AML12 cells. (f) Effects of the S275A and S275D mutations of FLAG-GCN5 on interaction with HA-CITED2 in AML12 cells. (g) The S275A mutation of GCN5 blocks the pCPT-cAMP-induced dissociation of HA-CITED2 from FLAG-GCN5 in AML12 cells. All data are representative of at least three independent experiments. Adenoviral vectors were used for these experiments.

Fig 4: GCN5 depletion suppresses hepatic gluconeogenesis in vivo and in vitro.(a,b) Effects of shRNA-mediated knockdown (KD) of GCN5 in the liver of C57BL/6J mice on hepatic gluconeogenic gene expression under the fasted (24 h) condition (a) or on plasma glycemia either under fasted (6 or 24 h) or fed conditions (a) or after pyruvate administration (b). (c) IP and immunoblot analysis of acetylated (Ac) PGC-1a in the liver of C57BL/6J mice injected with an adenovirus for GCN5 shRNA and deprived of food for 24 h. (d) Effects of shRNA-mediated depletion of GCN5 on gluconeogenic gene expression and glucose production in primary mouse hepatocytes exposed (or not) to pCPT-cAMP for 16 h. (e) IP and immunoblot analysis of acetylated PGC-1a in primary hepatocytes expressing FLAG–PGC-1a with or without GCN5 depletion and incubated in the absence or presence of pCPT-cAMP for 6 h. (f) Effects of GCN5 depletion on CITED2-dependent enhancement of gluconeogenic gene expression induced by pCPT-cAMP (100 µM, 6 h) in primary hepatocytes. (g) Effects of GCN5 knockdown on PGC-1a-induced gluconeogenic gene expression with or without CITED2 overexpression in primary hepatocytes. All quantitative data are means±s.e.m. (n=7 (a,b) or 3 (d,f,g)). Statistical analysis was performed with the unpaired Student's t-test (a) or ANOVA followed by Bonferroni's post hoc test (b,d,f,g). *P<0.05, **P<0.01 compared with control or as indicated. Data in c,e are representative of at least three independent experiments. Adenoviral vectors encoding GCN5 shRNA, FLAG–PGC-1a or CITED2 were used for these experiments. ANOVA, analysis of variance.

Fig 5: Phosphorylation of GCN5 at Ser275 promotes gluconeogenesis.(a) Effects of forced expression of GCN5(WT) or GCN5(S275A) together with CITED2 on gluconeogenic gene expression in primary hepatocytes exposed (or not) to pCPT-cAMP (6 h). (b,c) Effects of forced expression of GCN5(S275D) on gluconeogenic gene expression (b) and glucose production (c) in primary hepatocytes exposed (or not) to pCPT-cAMP (16 h). (d) qRT-PCR analysis of G6pc and Pck1 expression in primary mouse hepatocytes infected with adenoviruses encoding CITED2 shRNA or GCN5(S275D) and exposed (or not) to pCPT-cAMP for 6 h. (e,f) Effects of GCN5(S275D) expression in the liver of C57BL/6J mice on gluconeogenic gene expression (e) and plasma glycemia (f) under the fasted (24 h) condition. All data are means±s.e.m. (n=3 (a–d) or 7 (e,f)). *P<0.05, **P<0.01 versus control or as indicated (ANOVA with Bonferroni's post hoc test (a–d) or unpaired Student's t-test (e,f)). Adenoviral vectors were used for these experiments. RT–PCR, PCR with reverse transcription. ANOVA, analysis of variance.