A novel calcium signaling pathway targets the c-fos intragenic transcriptional pausing site.
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.
Coulon
V
V
Institut de Génétique Moléculaire, CNRS, UMR 5535, IFR24, 1919 route de Mende, 34293 Montpellier Cedex 5, France.
Veyrune
J L
JL
Tourkine
N
N
Vié
A
A
Hipskind
R A
RA
Blanchard
J M
JM
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D020121:5' Untranslated Regions / Q000235:genetics; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D019703:Calcineurin / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D000242:Cyclic AMP / Q000502:physiology; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D017930:Genes, Reporter; D016762:Genes, fos; D006801:Humans; D007438:Introns; D007739:L Cells; D008668:Metallothionein / Q000235:genetics; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012694:Serine; D015398:Signal Transduction / Q000502:physiology*; D013449:Sulfonamides / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic
D020121:5' Untranslated Regions; D002147:Calmodulin; D017362:Cyclic AMP Response Element-Binding Protein; D011993:Recombinant Fusion Proteins; D013449:Sulfonamides; D015124:8-Bromo Cyclic Adenosine Monophosphate; D000001:Calcimycin; D012694:Serine; C017967:W 7; D008668:Metallothionein; D000242:Cyclic AMP; D020928:Mitogen-Activated Protein Kinases; D019703:Calcineurin; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine