Glucagon regulates gluconeogenesis through KAT2B- and WDR5-mediated epigenetic effects
Kim Ravnskjaer, … , Jerrold Olefsky, Marc Montminy
Kim Ravnskjaer, … , Jerrold Olefsky, Marc Montminy
Published September 24, 2013
Citation Information: J Clin Invest. 2013;123(10):4318-4328. https://doi.org/10.1172/JCI69035.
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Glucagon regulates gluconeogenesis through KAT2B- and WDR5-mediated epigenetic effects

Abstract

Circulating pancreatic glucagon is increased during fasting and maintains glucose balance by stimulating hepatic gluconeogenesis. Glucagon triggering of the cAMP pathway upregulates the gluconeogenic program through the phosphorylation of cAMP response element–binding protein (CREB) and the dephosphorylation of the CREB coactivator CRTC2. Hormonal and nutrient signals are also thought to modulate gluconeogenic gene expression by promoting epigenetic changes that facilitate assembly of the transcriptional machinery. However, the nature of these modifications is unclear. Using mouse models and in vitro assays, we show that histone H3 acetylation at Lys 9 (H3K9Ac) was elevated over gluconeogenic genes and contributed to increased hepatic glucose production during fasting and in diabetes. Dephosphorylation of CRTC2 promoted increased H3K9Ac through recruitment of the lysine acetyltransferase 2B (KAT2B) and WD repeat–containing protein 5 (WDR5), a core subunit of histone methyltransferase (HMT) complexes. KAT2B and WDR5 stimulated the gluconeogenic program through a self-reinforcing cycle, whereby increases in H3K9Ac further potentiated CRTC2 occupancy at CREB binding sites. Depletion of KAT2B or WDR5 decreased gluconeogenic gene expression, consequently breaking the cycle. Administration of a small-molecule KAT2B antagonist lowered circulating blood glucose concentrations in insulin resistance, suggesting that this enzyme may be a useful target for diabetes treatment.

Authors

Kim Ravnskjaer, Meghan F. Hogan, Denise Lackey, Laszlo Tora, Sharon Y.R. Dent, Jerrold Olefsky, Marc Montminy

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Figure 4

CRTC2 mediates the recruitment of KAT2B to promoters of gluconeogenic genes in response to glucagon.

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CRTC2 mediates the recruitment of KAT2B to promoters of gluconeogenic ge...
(A and B) Immunoblots showing amounts of HA-KAT2A and HA-KAT2B recovered from IPs of FLAG epitope–tagged wild-type (WT) CRTC2 (aa 1–692), phosphorylation–defective CRTC2 (SA, S171A), or CRTC2 ΔTAD lacking the TAD (aa 1–632) in HEK293T cells exposed to FSK for 1 hour. (C) Transient assay of chromosomal GAL4-Luc reporter activity in HEK293T cells expressing GAL4-CRTC2 constructs containing the GAL4 DNA-binding domain fused to wild-type CRTC2, CRTC2 ΔTAD, or to the TAD alone (aa 624–692). Effects of GFP, KAT2B, or WDR5 overexpression on GAL4 CRTC2 activity are shown. Luciferase activity was normalized to β-gal activity. (D) Alignment of TADs in mouse and human CRTC1, 2, and 3. Conserved acidic residues in red (†conserved Glu665, important for mCRTC2 interaction with KAT2B). (E) Immunoblot of HA-KAT2B amounts recovered from IPs of FLAG-tagged wild-type or E665K mutant CRTC2 prepared from HEK293T cells. One-hour treatment with FSK is indicated. (F) Immunoblot of endogenous CRTC2 and KAT2B co-IP from primary mouse hepatocytes exposed to glucagon for 1 hour. C2, CRTC2; Ig, IgG control; IN, input; SUP, supernatant. (G and H) Effect of glucagon on H3K9Ac amounts and KAT2B occupancy (G) as well as RNA polymerase II recruitment and mRNA amounts (H) for gluconeogenic genes in wild-type and Crtc2–/– hepatocytes reconstituted with wild-type or E665K (EK) mutant CRCT2. Exposure to glucagon for 90 minutes is indicated (*P < 0.05 relative to glucagon-stimulated Crtc2+/+; n = 3).