title: Regulation of muscle GLUT4 enhancer factor and myocyte enhancer factor 2 by AMP-activated protein kinase.
abstract: As the primary glucose transporter in skeletal muscle, GLUT4 is an important factor in the regulation of blood glucose. We previously reported that stimulation of AMP-activated protein kinase (AMPK) with 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) increased GLUT4 expression in muscle. GLUT4 enhancer factor (GEF) and myocyte enhancer factor 2 (MEF2) have been shown to be important for normal GLUT4 expression because deletion or truncation of the consensus sequences on the promoter causes depressed GLUT4 mRNA expression. This led to the current study to investigate possible roles for GEF and MEF2 in mediating the activation of GLUT4 gene transcription in response to AMPK. Here we show that, although AMPK does not appear to phosphorylate MEF2A, AMPK directly phosphorylates the GEF protein in vitro. MEF2 and GEF are activated in response to AMPK as we observed translocation of both to the nucleus after AICAR treatment. Nuclear MEF2 protein content was increased after 2 h, and GEF protein was increased in the nucleus 1 and 2 h post-AICAR treatment. Last, GEF and MEF2 increase in binding to the GLUT4 promoter within 2 h after AICAR treatment. Thus we conclude that GEF and MEF2 mediate the AMPK-induced increase in transcription of skeletal muscle GLUT4. AMPK can phosphorylate GEF and in response to AICAR, GEF, and MEF2 translocate to the nucleus and have increased binding to the GLUT4 promoter.
authors.affiliation: Department of Exercise and Sport Science, Human Performance Laboratory, Brody School of Medicine, East Carolina University, Greenville, NC, USA. bfh0530@arizona.edu
authors.forename: Burton F
authors.initials: BF
authors.lastname: Holmes
authors.forename: David P
authors.initials: DP
authors.lastname: Sparling
authors.forename: Ann Louise
authors.initials: AL
authors.lastname: Olson
authors.forename: William W
authors.initials: WW
authors.lastname: Winder
authors.forename: G Lynis
authors.initials: GL
authors.lastname: Dohm
mesh_terms: D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D051275:Glucose Transporter Type 4 / Q000235:genetics*; D006801:Humans; D064326:MEF2 Transcription Factors; D009097:Multienzyme Complexes / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000648:ultrastructure; D018006:Myogenic Regulatory Factors / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012265:Ribonucleotides / Q000494:pharmacology; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics* / Q000502:physiology
chemical_list: D004268:DNA-Binding Proteins; C506347:GLUT4 enhancer factor, rat; D051275:Glucose Transporter Type 4; D064326:MEF2 Transcription Factors; D009097:Multienzyme Complexes; D018006:Myogenic Regulatory Factors; D012333:RNA, Messenger; D011994:Recombinant Proteins; D012265:Ribonucleotides; C495692:SLC2A4 protein, human; D014157:Transcription Factors; D000620:Aminoimidazole Carboxamide; D004247:DNA; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide