Activation of an enhancer on the syndecan-1 gene is restricted to fibroblast growth factor family members in mesenchymal cells.

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Fibroblast growth factors (FGFs) induce a variety of biological effects on different cell types. They activate a number of genes, including immediate-early genes, such as the transcription factors Fos and Jun, which are also common targets for other tyrosine kinase receptor-activating growth factors. Here we describe a secondary far-upstream enhancer on the syndecan-1 gene that is activated only by members of the FGF family in NIH 3T3 cells, not by other receptor tyrosine kinase-activating growth factors (e.g., epidermal growth factor, platelet-derived growth factor, insulin-like growth factor, or serum). This FGF-inducible response element (FiRE) consists of a 170-bp array of five DNA motifs which bind two FGF-inducible Fos-Jun heterodimers, one inducible AP-2-related protein, a constitutively expressed upstream stimulatory factor, and one constitutive 46-kDa transcription factor. Mutational analysis showed that both AP-1 binding motifs are required, but not sufficient, for FiRE activation. Moreover, agents such as 12-O-tetradecanoylphorbol-13-acetate, okadaic acid, or forskolin, which are known to activate AP-1 complexes and AP-1-driven promoters, fail to activate FiRE. However, FiRE can be activated by the tyrosine kinase phosphatase inhibitor orthovanadate. Taken together, this data implies a differential activation of growth factor-initiated signaling on AP-1-driven regulatory elements.

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