Hypertrophic agonists induce the binding of c-Fos to an AP-1 site in cardiac myocytes: implications for the expression of GLUT1.
OBJECTIVE
Serum is among the agents known to induce hypertrophy of cardiac myocytes, which occurs concomitant with an increase in AP-1-mediated transcription. We have examined if this effect correlates with changes in the relative abundance of particular AP-1 heterodimers, as their exact composition under these conditions is unknown. Furthermore, we obtained insight on the specific role of c-Fos from studying the induction of the glucose transporter GLUT1 by serum in fibroblasts.


METHODS
We characterised the AP-1 heterodimers expressed in neonatal cardiac myocytes by supershift electrophoretic mobility shift assay (EMSA) analysis. Quantitative changes in transcription were measured using a luciferase reporter vector, and we examined the expression of the glucose transporter GLUT1 in cardiac myocytes and a c-Fos knockout-derived fibroblast cell line by western blotting.


RESULTS
Transcriptionally active AP-1 in combinations of c-Jun, JunD and JunB with Fra1, Fra2 and possibly FosB, are expressed in cardiac myocytes. Hypertrophic stimuli transiently induced AP-1 dimers containing c-Fos, and this was dependent on the ERK mitogen-activated protein kinase pathway and coincided with the activation of AP-1-mediated transcription and the induction of GLUT1 in cardiac myocytes. In fibroblasts, the induction of GLUT1 by serum required the specific expression of c-Fos.


CONCLUSIONS
Our data suggest that induction of c-Fos containing AP-1 heterodimers may partly activate AP-1-mediated transcription in cardiac myocytes treated with hypertrophic agonists under conditions known to induce GLUT1. Data obtained in fibroblasts treated with serum lead us to hypothesise that c-Fos might play a major role in the regulation of GLUT1 expression.
D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western / Q000379:methods; D002460:Cell Line; D002478:Cells, Cultured; D024202:Electrophoretic Mobility Shift Assay / Q000379:methods; D004789:Enzyme Activation; D005347:Fibroblasts; D005419:Flavonoids / Q000494:pharmacology; D017353:Gene Deletion; D051272:Glucose Transporter Type 1; D007093:Imidazoles / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D011485:Protein Binding; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D018808:Transcription Factor AP-1 / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
D005419:Flavonoids; D051272:Glucose Transporter Type 1; D007093:Imidazoles; D009004:Monosaccharide Transport Proteins; D016760:Proto-Oncogene Proteins c-fos; D011725:Pyridines; C495678:Slc2a1 protein, mouse; C495679:Slc2a1 protein, rat; D018808:Transcription Factor AP-1; D020928:Mitogen-Activated Protein Kinases; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one