Essentiality of intron control in the induction of c-fos by glucose and glucoincretin peptides in INS-1 beta-cells.
Glucose controls long-term processes in the pancreatic beta-cell such as metabolic enzymes gene expression, cell growth, and apoptosis. Such control is likely mediated via the expression of immediate-early response genes since several of these genes including c-fos are strongly induced by glucose in the beta-cell line INS-1, provided costimulation with cAMP-raising glucoincretin hormones. This study addresses the mechanism of c-fos gene activation by glucose. Glucose in the presence of chlorophenylthio-cAMP generated a low threefold induction of the c-fos/basic luciferase reporter gene, which includes only the c-fos promoter. In contrast, the c-fos/intron construct containing the first intron in addition to promoter elements showed a pronounced 16-fold induction, comparable to the increased c-fos mRNA accumulation. Similar observations were made with glucose in combination with the glucoincretins glucagon-like peptide 1, glucose-dependent insulinotropic polypeptide, and pituitary adenylyl cyclase-activating peptide 38. Deletion of a 119 bp region in intron 1 that includes a transcriptional arrest site did not affect the inductive process. In contrast, a 534 bp deletion comprising a major part of the intron reduced the induction by 75%. At the promoter level, mutating the cAMP response element reduced by more than 60% the transcriptional activation whereas mutating the serum response element had no effect. Inhibitors of protein kinase A and Ca(2+)/calmodulin-dependent protein kinases each reduced by 50% the reporter gene activation and together fully prevented the glucose-glucoincretin effect. In conclusion, the strong induction of c-fos by glucose and glucoincretins results from Ca(2+) and cAMP signaling pathways addressing both the CRE in the promoter and essential response element(s) in the first intron that are unrelated to the transcription arrest site.
Susini
S
S
Fondation pour Recherches Médicales, University of Geneva, 1211 Geneva, Switzerland.
Van Haasteren
G
G
Li
S
S
Prentki
M
M
Schlegel
W
W
D001483:Base Sequence; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000502:physiology; D017931:DNA Primers; D017930:Genes, Reporter; D016762:Genes, fos; D005934:Glucagon / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D007438:Introns; D007515:Islets of Langerhans / Q000201:enzymology / Q000378:metabolism*; D009154:Mutation; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D015533:Transcriptional Activation / Q000502:physiology
D017931:DNA Primers; D005934:Glucagon; D000242:Cyclic AMP; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D005947:Glucose