Tan Y, Low K G, Boccia C, Grossman J, Comb M J
Laboratory of Molecular Neurobiology, Massachusetts General Hospital, Charlestown 02129.
Mol Cell Biol. 1994 Nov;14(11):7546-56. doi: 10.1128/mcb.14.11.7546-7556.1994.
Growth factors and cyclic AMP (cAMP) are known to activate distinct intracellular signaling pathways. Fibroblast growth factor (FGF) activates ras-dependent kinase cascades, resulting in the activation of MAP kinases, whereas cAMP activates protein kinase A. In this study, we report that growth factors and cAMP act synergistically to stimulate proenkephalin gene expression. Positive synergy between growth factor- and cAMP-activated signaling pathways on gene expression has not been previously reported, and we suggest that these synergistic interactions represent a useful model for analyzing interactions between these pathways. Transfection and mutational studies indicate that both FGF-dependent gene activation and cAMP-dependent gene activation require cAMP response element 2 (CRE-2), a previously characterized cAMP-dependent regulatory element. Furthermore, multiple copies of this element are sufficient to confer FGF regulation upon a minimal promoter, indicating that FGF and cAMP signaling converge upon transcription factors acting at CRE-2. Among many different ATF/AP-1 factors tested, two factors, ATF-3 and c-Jun, stimulate proenkephalin transcription in an FGF- or Ras-dependent fashion. Finally, we show that ATF-3 and c-Jun form heterodimeric complexes in SK-N-MC cells and that the levels of both proteins are increased in response to FGF but not cAMP. Together, these results indicate that growth factor- and cAMP-dependent signaling pathways converge at CRE-2 to synergistically stimulate gene expression and that ATF-3 and c-Jun regulate proenkephalin transcription in response to both growth factor- and cAMP-dependent intracellular signaling pathways.
已知生长因子和环磷酸腺苷（cAMP）可激活不同的细胞内信号通路。成纤维细胞生长因子（FGF）激活依赖于ras的激酶级联反应，导致丝裂原活化蛋白激酶（MAP激酶）的激活，而cAMP则激活蛋白激酶A。在本研究中，我们报告生长因子和cAMP协同作用以刺激前脑啡肽基因表达。生长因子激活的信号通路和cAMP激活的信号通路在基因表达上的正向协同作用此前尚未见报道，我们认为这些协同相互作用代表了一个用于分析这些通路之间相互作用的有用模型。转染和突变研究表明，FGF依赖的基因激活和cAMP依赖的基因激活都需要cAMP反应元件2（CRE-2），这是一个先前已被表征的cAMP依赖的调控元件。此外，该元件的多个拷贝足以赋予最小启动子FGF调控，表明FGF和cAMP信号传导汇聚于作用于CRE-2的转录因子。在测试的许多不同的ATF/AP-1因子中，两个因子，即ATF-3和c-Jun，以FGF或Ras依赖的方式刺激前脑啡肽转录。最后，我们表明ATF-3和c-Jun在SK-N-MC细胞中形成异二聚体复合物，并且这两种蛋白质的水平在FGF刺激下升高，但在cAMP刺激下不升高。总之，这些结果表明生长因子依赖的信号通路和cAMP依赖的信号通路在CRE-2处汇聚以协同刺激基因表达，并且ATF-3和c-Jun响应生长因子依赖的和cAMP依赖的细胞内信号通路调节前脑啡肽转录。
