AMP-activated protein kinase phosphorylates transcription factors of the CREB family

Abstract

AMP-activated protein kinase (AMPK) has been identified as a regulator of gene transcription, increasing mitochondrial proteins of oxidative metabolism as well as hexokinase expression in skeletal muscle. In mice, muscle-specific knockout of LKB1, a component of the upstream kinase of AMPK, prevents contraction- and 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR)-induced activation of AMPK in skeletal muscle, and the increase in hexokinase II protein that is normally observed with chronic AICAR activation of AMPK. Since previous reports show a cAMP response element in the promoter region of the hexokinase II gene, we hypothesized that the cAMP-response element (CRE) binding protein (CREB) family of transcription factors could be targets of AMPK. Using radioisotopic kinase assays, we found that recombinant and rat liver and muscle AMPK phosphorylated CREB1 at the same site as cAMP-dependent protein kinase (PKA). AMPK was also found to phosphorylate activating transcription factor 1 (ATF1), CRE modulator (CREM), and CREB-like 2 (CREBL2), but not ATF2. Treatment of HEK-293 cells stably transfected with a CREB-driven luciferase reporter with AICAR increased luciferase activity approximately threefold over a 24-h time course. This increase was blocked with compound C, an AMPK inhibitor. In addition, AICAR-induced activation of AMPK in incubated rat epitrochlearis muscles resulted in an increase in both phospho-acetyl-CoA carboxylase and phospho-CREB. We conclude that CREB and related proteins are direct downstream targets for AMPK and are therefore likely involved in mediating some effects of AMPK on expression of genes having a CRE in their promoters.

AMPKα is essential for acute exercise-induced gene responses but not for exercise training-induced adaptations in mouse skeletal muscle

“…Phosphorylation of histone deacetylase 5 (HDAC5) by AMPK increases HDAC5 binding to 14-3-3 protein, and the subsequent nuclear export of the complex allows transcription factor-mediated regulation of glucose transporter 4 (GLUT4) gene expression (41). The gene encoding the glucose-metabolizing protein hexokinase II (HKII) contains a cAMP response element in its promoter region (49), and AMPK regulates the activity of the transcription factor cAMP response element-binding protein through direct phosphorylation (53). Experiments performed in vitro and in cell culture have shown that AMPK phosphorylates peroxisome proliferator-activated receptor-␥ coactivator-1␣ (PGC-1␣) (23), which is known as a major transcriptional regulator of genes encoding oxidative proteins in skeletal muscle (36).…”

Heme and metformin coordinate human and murine macrophage heme oxygenase 1 expression with foam cell resistance partly via adenosine monophosphate kinase and activating transcription factor 1 (AMPK-ATF1)

“…Both CREB1 and ATF1 are phosphorylated on homologous motifs by cAMP-dependent protein kinase (protein kinase A, PKA) and 5'-AMPK-activated protein kinase (AMPK) 8,9 .…”

“…AMPK may modify transcription via phosphorylation of a large and growing number of transcription factors and chromatin proteins 13,[15][16][17][18][19][20][21] . Critically, these include ATF1 9 . Purified AMPK phosphorylated recombinant purified ATF1 in an in vitro kinase assay in a cell-free system, in a paper defining AMPK-mediated phosphorylation of CREB family proteins in vivo in skeletal muscle during exercise 22 .…”

“…Critically, these include ATF1 9 . Purified AMPK phosphorylated recombinant purified ATF1 in an in vitro kinase assay in a cell-free system, in a paper defining AMPK-mediated phosphorylation of CREB family proteins in vivo in skeletal muscle during exercise 22 . Moreover, AMPK activation in macrophages induces an anti-inflammatory response, with release of IL-10 23 .…”

Reactive oxygen species and endurance training-induced adaptations

“…For example, an increase in the intracellular free AMP/ATP ratio during exercise results in the activation of AMP-activated protein kinase (AMPK) 30) . Activated AMPK regulates PGC-1α via both the posttranslational phosphorylation of preexisting PGC-1α 31) and increased PGC-1α transcription by activating transcription factors targeted to their regulatory elements 7,32) . An oscillatory change in the intracellular calcium ion concentration during excitation-contraction coupling activates Ca 2+ activated enzymes calcium/calmodulin dependent protein kinase Ⅱ (CaMKⅡ) 33) .…”