AMP-activated Protein Kinase Regulates HNF4α Transcriptional Activity by Inhibiting Dimer Formation and Decreasing Protein Stability

Abstract

AMP-activated protein kinase (AMPK) is the central component of a cellular signaling system that regulates multiple metabolic enzymes and pathways in response to reduced intracellular energy levels. The transcription factor hepatic nuclear factor 4␣ (HNF4␣) is an orphan nuclear receptor that regulates the expression of genes involved in energy metabolism in the liver, intestine, and endocrine pancreas. Inheritance of a single null allele of HNF4␣ causes diabetes in humans. Here we demonstrate that AMPK directly phosphorylates HNF4␣ and represses its transcriptional activity. AMPK-mediated phosphorylation of HNF4␣ on serine 304 had a 2-fold effect, reducing the ability of the transcription factor to form homodimers and bind DNA and increasing its degradation rate in vivo. These results demonstrate that HNF4␣ is a downstream target of AMPK and raise the possibility that one of the effects of AMPK activation is reduced expression of HNF4␣ target genes.The transcription factor HNF4␣ 1 (NR2A1), a member of the nuclear receptor superfamily, plays a key role in regulating the expression of metabolic genes in multiple tissues including the liver, intestine, kidney, and endocrine pancreas (for review see Ref. 1). In humans, a nonsense mutation in a single allele of the HNF4␣ gene causes an inherited form of diabetes known as maturity onset diabetes of the young (MODY) (for a review see Ref. 2). This syndrome is characterized by insufficient insulin secretion (3, 4), indicating a significant defect in pancreatic function. Surprisingly, there is not a major deficit in liver function, despite the important role of HNF4␣ in hepatic gene expression (5). These observations suggest that HNF4␣ regulates pancreatic genes involved in glucose sensing and/or insulin production. This hypothesis is supported by experiments demonstrating that HNF4␣ regulates expression of genes encoding enzymes of glucose metabolism and insulin secretion (6 -8). Because MODY1 patients have a single null allele that does not produce a dominant-negative acting protein (9), the physiological abnormalities in these patients must be caused by a relatively mild (ϳ50%) decrease in the amount of HNF4␣ protein. Taken together, these observations raise the possibility that any modification of HNF4␣ that causes a reduction in its transcriptional activity could have significant effects on pancreatic function.HNF4␣ has also been shown recently to play an important role in the regulation of hepatic glucose output, a key component of the maintenance of plasma glucose levels. Yoon et al. (10) recently demonstrated that the transcriptional regulation of gene for the key gluconeogenic enzyme phosphoenolpyruvate carboxykinase by cAMP was mediated by the transcriptional co-activator PGC-1 acting through HNF4␣. These findings suggest that HNF4␣ may play a role in the transcriptional response of the liver to metabolic hormones and that factors regulating the activity of HNF4␣ could have an effect on hepatic glucose output.AMPK is the mammalian homolog of the yeast SNF1 pr...

Targeting the HDAC2/HNF-4A/miR-101b/AMPK Pathway Rescues Tauopathy and Dendritic Abnormalities in Alzheimer’s Disease

“…Moreover, HDAC2 overexpression induced greater phosphorylation of HNF-4A at the Ser304 epitope ( Figure 4F), which is phosphorylated by AMPK to inhibit its transcriptional activity. 20 Similar results were obtained from the hippocampus of 12-month-old 3xTg-AD mice www.moleculartherapy.org ( Figures 4G-4I). Therefore, the suppression of miR-101b by HDAC2 was further increased by activation of AMPK, which forms a strong regulatory feedback loop.…”

Identification of the Flavonoid Luteolin as a Repressor of the Transcription Factor Hepatocyte Nuclear Factor 4α

“…However, we cannot exclude the possibility that the receptor localized to the plasma membrane senses luteolin and that the addition of glucoside makes it inaccessible to the receptor. It has been reported that luteolin enhances the phosphorylation of AMP-activated protein kinase in HepG2 cells (38), and AMP-activated protein kinase directly phosphorylates HNF4␣ and represses its transcriptional activity (39). Thus, it is conceivable that luteolin indirectly suppressed HNF4␣ activity through the stimulation of AMP-activated protein kinase signaling in addition to direct binding to its LBD as an antagonist.…”

Regulation of Rat Hepatic L-Pyruvate Kinase Promoter Composition and Activity by Glucose, n-3 Polyunsaturated Fatty Acids, and Peroxisome Proliferator-activated Receptor-α Agonist

“…AMPK phosphorylation of ChREBP inhibits ChREBP translocation to the nucleus. AMPK phosphorylation of HNF-4␣ impairs HNF-4␣ dimer stability and DNA binding (42). Two groups have reported that fatty acids activate AMPK through phosphorylation of AMPK (24,43).…”