title: Sequential actions of ERK1/2 on the AP-1 transcription factor allow temporal integration of metabolic signals in pancreatic beta cells.
abstract: The AP-1 transcription factor composed of fos and jun gene products mediates transcriptional responses to hormonal and metabolic stimulations of pancreatic beta cells. Here, we investigated the mechanisms that dynamically control expression of AP-1 subunit proteins. In MIN6 cells, glucose and GLP-1 raised c-FOS protein with biphasic kinetics, an initial peak being followed by a plateau that persisted as long as stimuli were maintained. ERK1/2 activation paralleled c-FOS expression. Whereas initial induction of c-FOS protein required ERK1/2-dependent activation of c-fos transcription and de novo protein synthesis, persistent accumulation of c-FOS under sustained stimulation did not. Indeed, dependent on ERK1/2 activation, c-FOS accumulated in its hyperphosphorylated form protected from degradation through the proteasome pathway. The implication of ERK1/2 in the accumulation of c-FOS protein was confirmed in rat primary beta cells, and the functional consequences of this mechanism were demonstrated with DNA-binding and reporter assays. Altogether these findings reveal a sequential regulation of AP-1 by ERK1/2, which initially increases transcription of c-fos and, if stimulation persists, stabilizes freshly synthesized c-FOS protein to efficiently activate the transcription of AP-1-regulated genes. This ERK1/2-AP-1 module can function as a temporal integrator converting metabolic stimuli of different durations into differential transcriptional outputs.
authors.affiliation: Fondation pour Recherches Médicales, University of Geneva, Switzerland.
authors.forename: Dominique A
authors.initials: DA
authors.lastname: Glauser
authors.forename: Werner
authors.initials: W
authors.lastname: Schlegel
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D052216:Glucagon-Like Peptide 1 / Q000235:genetics / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006801:Humans; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000502:physiology*; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism; D008297:Male; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000502:physiology*; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D021122:Protein Subunits; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D052216:Glucagon-Like Peptide 1; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D005947:Glucose