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...

AMP-activated protein kinase (AMP-kinase) modulates many metabolic processes in response to fluctuations in cellular energy status. Although most of its known targets are metabolic enzymes, it has been proposed that AMPkinase might also regulate gene expression. Here we demonstrate that the transcriptional coactivator p300 is a substrate of AMP-kinase. Phosphorylation of p300 at serine 89 by AMP-kinase dramatically reduced its interaction, in vitro and in vivo, with the nuclear receptors peroxisome proliferator-activated receptor ␥, thyroid receptor, retinoic acid receptor, and retinoid X receptor, but did not affect its interaction with the non-nuclear receptor transcription factors E1a, p53, or GATA4. These findings indicate that the AMP-kinase signaling pathway selectively modulates a subset of p300 activities and represent the first example of a transcriptional component regulated by AMP-kinase. Our results suggest a direct link between cellular energy metabolism and gene expression. AMP-activated protein kinase (AMP-kinase)1 plays a key role in the modulation of cellular energy metabolism by phosphorylating key metabolic enzymes in response to increased AMP levels (1). AMP levels rise during states of low energy charge (i.e. reduced ATP/AMP ratios) that occur in a variety of normal processes like exercise and possibly also in some pathological states such as diabetes. Activated AMP-kinase phosphorylates key enzymes in both biosynthetic and oxidative pathways and differentially modulates their activities to promote a reestablishment of normal ATP/AMP ratios. In addition, AMP-kinase regulates key enzymes in lipid and glucose metabolism and has been proposed to play a role in glucose homeostasis (2). It has been proposed that AMP-kinase might also play a direct role in the regulation of gene expression. This possibility is supported by the observation that the yeast homologue of AMP-kinase, the SNF1 complex, mediates the regulation of genes involved in energy metabolism (1, 3). However, no component of the mammalian transcriptional machinery has yet been identified as a target of AMP-kinase.In searching for potential AMP-kinase substrates among transcriptional components, we initially considered the possibility that the PPAR family of nuclear receptor transcription factors might be regulated by this signaling pathway. The PPARs modulate the expression of genes involved in many of the same metabolic pathways that are regulated by AMPkinase. For example, PPAR␣ regulates genes involved in fatty acid oxidation, while PPAR␥ is clearly involved in glucose homeostasis (4 -6). These potentially overlapping roles of PPARs and AMP-kinase in the regulation of cellular energy metabolism initially prompted us to ask if these transcription factors or their cofactors might be targets for regulation by AMPkinase. Here we report that p300, a transcriptional coactivator that mediates the activity of many nuclear receptors including the PPARs, is a substrate of AMP-kinase in vitro and in vivo. In addition, we show that phosphory...