title: Synergistic increase in c-fos expression by simultaneous activation of the ras/raf/map kinase- and protein kinase A signaling pathways is mediated by the c-fos AP-1 and SRE sites.
abstract: Expression of the c-fos proto-oncogene is induced by numerous stimuli some of which are transmitted through the Ras/Raf/MAP kinase or the cAMP-dependent protein kinase (PKA) pathways. The effect of cell-specific interactions between these pathways on c-fos expression was investigated by exposing quiescent NIH3T3 cells to serum, forskolin, or a combination. Co-stimulation with serum and forskolin resulted in a more than additive increase in c-fos transcription. Synergistic increase in c-fos promoter activity was also observed in transient transfection studies after co-stimulation with serum plus forskolin or co-transfection with c-Raf and PKA expression plasmids. Analysis of the cAMP signaling pathway revealed that the synergy was neither due to an increase in PKA activity nor to Ser-133 phosphorylation/activation of CREB. The activation status of the MAP kinases ERK1 and ERK2 in co-treated cells was comparable to that in serum-treated cells. Co-stimulation with forskolin did not alter the phosphorylation state of Elk-1 compared to serum-induced phosphorylation of Elk-1. Deletion of c-fos promoter elements previously shown to be important for regulation of c-fos expression in response to mitogens indicates a role for SRE and FAP-1 elements.
authors.affiliation: Department of Gene Biology, University of Tromsø, Norway.
authors.forename: O M
authors.initials: OM
authors.lastname: Seternes
authors.forename: R
authors.initials: R
authors.lastname: Sørensen
authors.forename: B
authors.initials: B
authors.lastname: Johansen
authors.forename: T
authors.initials: T
authors.lastname: Loennechen
authors.forename: J
authors.initials: J
authors.lastname: Aarbakke
authors.forename: U
authors.initials: U
authors.lastname: Moens
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D015500:Chloramphenicol O-Acetyltransferase / Q000096:biosynthesis; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D016762:Genes, fos; D007700:Kinetics; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D017362:Cyclic AMP Response Element-Binding Protein; D017931:DNA Primers; D004268:DNA-Binding Proteins; D016760:Proto-Oncogene Proteins c-fos; D011993:Recombinant Fusion Proteins; D018808:Transcription Factor AP-1; D005576:Colforsin; D000242:Cyclic AMP; D015500:Chloramphenicol O-Acetyltransferase; D019908:Proto-Oncogene Proteins c-raf; D017868:Cyclic AMP-Dependent Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins