Insulin regulation of hepatic gluconeogenesis through phosphorylation of CREB-binding protein

Abstract

Hepatic gluconeogenesis is essential for maintenance of normal blood glucose concentrations and is regulated by opposing stimulatory (cyclic adenosine monophosphate, cAMP) and inhibitory (insulin) signaling pathways. The cAMP signaling pathway leads to phosphorylation of cAMP response element-binding (CREB) protein, resulting in recruitment of the coactivators CREB-binding protein (CBP) and p300 and subsequent activation of gluconeogenesis. Insulin signaling leads to phosphorylation of CBP at serine 436, a residue near its CREB-interacting domain, but it is unknown whether this event modulates cAMP signaling. Here, we show in vitro and in 'knock-in' mice that a mutant CBP (S436A) is aberrantly recruited to CREB protein, resulting in inappropriate activation of gluconeogenesis in the fed state and glucose intolerance resulting from increased hepatic glucose production. We propose that insulin signaling may directly regulate many cAMP signaling pathways at the transcriptional level by controlling CBP recruitment.

Transcriptional Co-activator p300 Maintains Basal Hepatic Gluconeogenesis

“…We and others (7,19,20) have shown that CREB co-activators play critical roles in maintaining fasting blood levels (Fig. 1).…”

“…Plasmids and Adenoviruses-The expression vectors for wild type (WT) CBP, CBP mutants, and PKA were described previ-ously (19). The p300(G422S) expression vector was generated using site-directed mutagenesis (Stratagene).…”

Potential biomarker of metformin action

“…We and other investigators have shown that the CREB co-activators CBP and p300 are important in regulating HGP (He et al 2009, 2012, Zhou et al 2004, Liu et al 2008. CBP and p300 are highly related proteins and share extensive homology at the amino acid level (~60%) and harbor several conserved domains such as the histidine rich domains (CH1-3), the CREB binding domain (KIX domain), the bromodomain, the HAT (histone acetyltransferase) domain, and the SID (steroid receptor co-activator interacting domain) domain (Goodman 2000).…”

“…Our previous studies showed that insulin mediated the phosphorylation of CBP at S436 in the liver (Zhou et al 2004, He et al 2009), whereas activation of the cAMP-PKA pathway antagonized CBP phosphorylation by insulin (He et al 2009). These results suggest that CBP phosphorylation status might change in fasted and fed states in the liver.…”

“…1B) (Wilcock & Bailey 1994). We have previously reported that a germline-mutation of this CBP phosphorylation site (S436A) in mice leads to inappropriate activation of gluconeogenesis and metformin resistance (He et al 2012, Zhou et al 2004). Primary hepatocytes from CBPS436A mutant mouse produced significantly more glucose in basal condition and after cAMP stimulation than hepatocytes from WT littermate mice ( Fig.…”