Volume 272, Number 49, Issue of December 5, 1997 pp. 30852-30859
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.

Functional Components of Fibroblast Growth Factor (FGF) Signal Transduction in Pituitary Cells
IDENTIFICATION OF FGF RESPONSE ELEMENTS IN THE PROLACTIN GENE

(Received for publication, July 30, 1997, and in revised form, September 16, 1997)

Rebecca E. Schweppe , Ashley A. Frazer-Abel , Arthur Gutierrez-Hartmann ^§ and Andrew P. Bradford ^§

From the Departments of ^§ Medicine and of  Biochemistry and Molecular Genetics, Program in Molecular Biology, and the Colorado Cancer Center, University of Colorado Health Sciences Center, Denver, Colorado 80262

Fibroblast growth factors (FGFs) have been implicated in pituitary lactotroph tumorigenesis; however, little is known about the molecular mechanisms of FGF signal transduction. We used a transient transfection approach, in GH4 cells, to identify components of the FGF signaling pathway leading to activation of the rat prolactin (rPRL) promoter. Using dominant-negative constructs of p21^Ras, Raf-1 kinase, and mitogen-activated protein (MAP) kinase, we show that FGF activation of the rPRL promoter is independent of Ras and Raf-1 but requires MAP kinase. Furthermore, MAP kinase but not Raf-1 kinase catalytic activity is stimulated by FGFs. The rPRL promoter FGF response maps to two Ets binding sites, centered at 212 (FRE1) and 96 (FRE2), and co-transfection of dominant-negative Ets inhibits FGF activation. FRE1 co-localizes with a composite, Ets/GHF-1, Ras response element. However, overexpression of Ets-1 and GHF-1, which potentiate the Ras response, inhibits FGF stimulation of the rPRL promoter, implying that Ras and FGF signaling pathways target distinct factors to elicit their effects. These data suggest that Ets factors serve to sort and integrate MAP kinase-dependent growth factor signals, allowing highly specific transcriptional responses to be mediated via the interaction of distinct Ets proteins and cofactors at common response elements.

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