Cooperation of protein kinase A and Ras/ERK signaling pathways is required for AP-1-mediated activation of fibroblast growth factor-inducible response element (FiRE).
Recent studies suggest a crucial role for protein kinase A (PKA) in the regulation of growth factor signaling. However, the effect of PKA on the transcription of growth factor-responsive genes has drawn far less attention. Here we have investigated the signaling mechanisms involved in the activation of an activator protein-1 (AP-1)-driven, growth factor-specific enhancer element, fibroblast growth factor-inducible response element (FiRE). The activation was found to be mediated by three phorbol 12-O-tetradecanoate-13-acetate-response element-related DNA elements of FiRE, including motif 4 and two distinct elements of motif 5 (referred to as M5-1 and M5-2). All three elements were required for full FiRE activity. Stimulation of cells with fibroblast growth factor-2 (FGF-2) induced the binding of AP-1 to motif 4 and M5-2, whereas M5-1 did not show detectable binding. The FGF-2-induced FiRE activation appeared to require cooperational function of the Ras/ERK and PKA pathways. Inhibition of either of the pathways abolished the binding of AP-1 complexes to motif 4 and motif 5 and the subsequent FiRE activation. By contrast, costimulation of cells with FGF-2 and the PKA activator 8-bromo-cyclic AMP increased the binding of AP-1 to FiRE and potentiated the level of transcriptional activity. The cooperational function of these two pathways was confirmed by experiments with cell lines stably expressing 4-hydroxytamoxifen-inducible oncogenic Raf-1 (DeltaRaf-1:ER[DD]). Noticeably, the induction systems showed variations with respect to regulation of AP-1-driven activation of FiRE. These differences were likely to originate from the ability of these two systems to induce the differential activation pattern of the Ras/ERK pathway.
Pursiheimo
Juha-Pekka
JP
Turku Centre for Biotechnology, University of Turku, Finland. juha-pekka.pursiheimo@juvantia.com
Saari
Jussi
J
Jalkanen
Markku
M
Salmivirta
Markku
M
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D017931:DNA Primers; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D015398:Signal Transduction; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
D017931:DNA Primers; D018808:Transcription Factor AP-1; D005346:Fibroblast Growth Factors; D017868:Cyclic AMP-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins