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The GCN5-CITED2-PKA signalling module controls hepatic glucose metabolism through a cAMP-induced substrate switch

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ABSTRACT

Hepatic gluconeogenesis during fasting results from gluconeogenic gene activation via the glucagon–cAMP–protein kinase A (PKA) pathway, a process whose dysregulation underlies fasting hyperglycemia in diabetes. Such transcriptional activation requires epigenetic changes at promoters by mechanisms that have remained unclear. Here we show that GCN5 functions both as a histone acetyltransferase (HAT) to activate fasting gluconeogenesis and as an acetyltransferase for the transcriptional co-activator PGC-1α to inhibit gluconeogenesis in the fed state. During fasting, PKA phosphorylates GCN5 in a manner dependent on the transcriptional coregulator CITED2, thereby increasing its acetyltransferase activity for histone and attenuating that for PGC-1α. This substrate switch concomitantly promotes both epigenetic changes associated with transcriptional activation and PGC-1α–mediated coactivation, thereby triggering gluconeogenesis. The GCN5-CITED2-PKA signalling module and associated GCN5 substrate switch thus serve as a key driver of gluconeogenesis. Disruption of this module ameliorates hyperglycemia in obese diabetic animals, offering a potential therapeutic strategy for such conditions.

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GCN5 promotes gluconeogenesis in an acetyltransferase- and CITED2-dependent manner.(a) Quantitative RT-PCR analysis of Gcn5 and gluconeogenic gene expression in primary hepatocytes infected with adenoviruses for WT or ΔAT mutant forms of GCN5 and exposed to pCPT-cAMP for 6 h. (b) Effects of forced expression of WT or ΔAT forms of GCN5 together with CITED2 on pCPT-cAMP-induced gluconeogenic gene expression in primary hepatocytes. (c–e) Effects of GCN5 overexpression with or without that of CITED2 in the liver of C57BL/6J mice on glycemia under the fasted (6 h) condition (c) or after pyruvate administration (e) as well as on hepatic gluconeogenic gene expression under the fasted (24 h) condition (d). All data are means±s.e.m. (n=3 (a,b), 10 (c) or 8 (d,e)). Statistical analysis was performed with ANOVA followed by Bonferroni's post hoc test. *P<0.05, **P<0.01 compared with control or as indicated; †P<0.05, ††P<0.01 versus CITED2. Adenoviral vectors encoding GCN5(WT), GCN5(ΔAT) or CITED2 were used for these experiments. ANOVA, analysis of variance; RT–PCR, PCR with reverse transcription.
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f3: GCN5 promotes gluconeogenesis in an acetyltransferase- and CITED2-dependent manner.(a) Quantitative RT-PCR analysis of Gcn5 and gluconeogenic gene expression in primary hepatocytes infected with adenoviruses for WT or ΔAT mutant forms of GCN5 and exposed to pCPT-cAMP for 6 h. (b) Effects of forced expression of WT or ΔAT forms of GCN5 together with CITED2 on pCPT-cAMP-induced gluconeogenic gene expression in primary hepatocytes. (c–e) Effects of GCN5 overexpression with or without that of CITED2 in the liver of C57BL/6J mice on glycemia under the fasted (6 h) condition (c) or after pyruvate administration (e) as well as on hepatic gluconeogenic gene expression under the fasted (24 h) condition (d). All data are means±s.e.m. (n=3 (a,b), 10 (c) or 8 (d,e)). Statistical analysis was performed with ANOVA followed by Bonferroni's post hoc test. *P<0.05, **P<0.01 compared with control or as indicated; †P<0.05, ††P<0.01 versus CITED2. Adenoviral vectors encoding GCN5(WT), GCN5(ΔAT) or CITED2 were used for these experiments. ANOVA, analysis of variance; RT–PCR, PCR with reverse transcription.

Mentions: Overexpression of wild-type (WT) GCN5 suppressed gluconeogenic gene induction by cAMP in primary hepatocytes (Fig. 3a), consistent with the previously observed suppression of PGC-1α–induced gluconeogenic gene expression by GCN5 overexpression in Fao hepatoma cells17. This effect was also observed with a mutant (ΔAT) of GCN5 that lacks acetyltransferase activity21 toward both histone H3 and PGC-1α (Fig. 3a and Supplementary Fig. 2a,b), however, indicating that GCN5 suppresses gluconeogenic gene expression independently of its enzymatic activity in this setting.


The GCN5-CITED2-PKA signalling module controls hepatic glucose metabolism through a cAMP-induced substrate switch
GCN5 promotes gluconeogenesis in an acetyltransferase- and CITED2-dependent manner.(a) Quantitative RT-PCR analysis of Gcn5 and gluconeogenic gene expression in primary hepatocytes infected with adenoviruses for WT or ΔAT mutant forms of GCN5 and exposed to pCPT-cAMP for 6 h. (b) Effects of forced expression of WT or ΔAT forms of GCN5 together with CITED2 on pCPT-cAMP-induced gluconeogenic gene expression in primary hepatocytes. (c–e) Effects of GCN5 overexpression with or without that of CITED2 in the liver of C57BL/6J mice on glycemia under the fasted (6 h) condition (c) or after pyruvate administration (e) as well as on hepatic gluconeogenic gene expression under the fasted (24 h) condition (d). All data are means±s.e.m. (n=3 (a,b), 10 (c) or 8 (d,e)). Statistical analysis was performed with ANOVA followed by Bonferroni's post hoc test. *P<0.05, **P<0.01 compared with control or as indicated; †P<0.05, ††P<0.01 versus CITED2. Adenoviral vectors encoding GCN5(WT), GCN5(ΔAT) or CITED2 were used for these experiments. ANOVA, analysis of variance; RT–PCR, PCR with reverse transcription.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5121418&req=5

f3: GCN5 promotes gluconeogenesis in an acetyltransferase- and CITED2-dependent manner.(a) Quantitative RT-PCR analysis of Gcn5 and gluconeogenic gene expression in primary hepatocytes infected with adenoviruses for WT or ΔAT mutant forms of GCN5 and exposed to pCPT-cAMP for 6 h. (b) Effects of forced expression of WT or ΔAT forms of GCN5 together with CITED2 on pCPT-cAMP-induced gluconeogenic gene expression in primary hepatocytes. (c–e) Effects of GCN5 overexpression with or without that of CITED2 in the liver of C57BL/6J mice on glycemia under the fasted (6 h) condition (c) or after pyruvate administration (e) as well as on hepatic gluconeogenic gene expression under the fasted (24 h) condition (d). All data are means±s.e.m. (n=3 (a,b), 10 (c) or 8 (d,e)). Statistical analysis was performed with ANOVA followed by Bonferroni's post hoc test. *P<0.05, **P<0.01 compared with control or as indicated; †P<0.05, ††P<0.01 versus CITED2. Adenoviral vectors encoding GCN5(WT), GCN5(ΔAT) or CITED2 were used for these experiments. ANOVA, analysis of variance; RT–PCR, PCR with reverse transcription.
Mentions: Overexpression of wild-type (WT) GCN5 suppressed gluconeogenic gene induction by cAMP in primary hepatocytes (Fig. 3a), consistent with the previously observed suppression of PGC-1α–induced gluconeogenic gene expression by GCN5 overexpression in Fao hepatoma cells17. This effect was also observed with a mutant (ΔAT) of GCN5 that lacks acetyltransferase activity21 toward both histone H3 and PGC-1α (Fig. 3a and Supplementary Fig. 2a,b), however, indicating that GCN5 suppresses gluconeogenic gene expression independently of its enzymatic activity in this setting.

View Article: PubMed Central - PubMed

ABSTRACT

Hepatic gluconeogenesis during fasting results from gluconeogenic gene activation via the glucagon&ndash;cAMP&ndash;protein kinase A (PKA) pathway, a process whose dysregulation underlies fasting hyperglycemia in diabetes. Such transcriptional activation requires epigenetic changes at promoters by mechanisms that have remained unclear. Here we show that GCN5 functions both as a histone acetyltransferase (HAT) to activate fasting gluconeogenesis and as an acetyltransferase for the transcriptional co-activator PGC-1&alpha; to inhibit gluconeogenesis in the fed state. During fasting, PKA phosphorylates GCN5 in a manner dependent on the transcriptional coregulator CITED2, thereby increasing its acetyltransferase activity for histone and attenuating that for PGC-1&alpha;. This substrate switch concomitantly promotes both epigenetic changes associated with transcriptional activation and PGC-1&alpha;&ndash;mediated coactivation, thereby triggering gluconeogenesis. The GCN5-CITED2-PKA signalling module and associated GCN5 substrate switch thus serve as a key driver of gluconeogenesis. Disruption of this module ameliorates hyperglycemia in obese diabetic animals, offering a potential therapeutic strategy for such conditions.

No MeSH data available.


Related in: MedlinePlus