In many cell types, increased intracellular calcium gives rise to a robust induction of c-fos gene expression. Here we show that in mouse Ltk(-) fibroblasts, calcium ionophore acts in synergy with either cAMP or PMA to strongly induce the endogenous c-fos gene. Run-on analysis shows that this corresponds to a substantial increase in active polymerases on downstream gene sequences, i.e. relief of an elongation block by calcium. Correspondingly a chimeric gene, in which the human metallothionein promoter is fused to the fos gene, is strongly induced by ionophore alone, unlike a c-fos promoter/beta-globin coding unit chimeric construct. Internal deletions in the hMT-fos reporter localize the intragenic calcium regulatory element to the 5′ portion of intron 1, thereby confirming and extending previous in vitro mapping data. Ionophore induced cAMP response element-binding protein phosphorylation on Ser(133) without affecting the extracellular signal-regulated kinase cascade. Surprisingly, induction involved neither CaM-Ks nor calcineurin, while the calmodulin antagonist W7 activated c-fos transcription on its own. These data suggest that a novel calcium signaling pathway mediates intragenic regulation of c-fos expression via suppression of a transcriptional pause site.
A novel calcium signaling pathway targets the c-fos intragenic transcriptional pausing site
Coulon, V.; Veyrune, J. L.; Tourkine, N.; Vie, A.; Hipskind, R. A.; Blanchard, J. M.
J Biol Chem
1999-10-22 / vol 274 / pages 30439-46
Humans; Animals; Mice; Calcineurin/metabolism; *Transcription, Genetic; Phosphorylation; Promoter Regions (Genetics); L Cells (Cell Line); Signal Transduction/*physiology; *Genes, fos; Genes, Reporter; Calcimycin/pharmacology; Mitogen-Activated Protein Kinases/metabolism; Introns; Recombinant Fusion Proteins/biosynthesis; Tetradecanoylphorbol Acetate/pharmacology; 5' Untranslated Regions/genetics; *Gene Expression Regulation/drug effects; 1-Methyl-3-isobutylxanthine/pharmacology; 8-Bromo Cyclic Adenosine Monophosphate/pharmacology; Calcium/*metabolism; Calmodulin/antagonists & inhibitors; Cyclic AMP Response Element-Binding Protein/metabolism; Cyclic AMP/physiology; Metallothionein/genetics; Serine; Sulfonamides/pharmacology