The activation and composition of FiRE (an FGF-inducible response element) differ in a cell type- and growth factor-specific manner

Abstract

The expression of the heparan sulfate proteoglycan, syndecan-1, is induced both in keratinocytes and in ®broblasts during development and tissue regeneration. Here we report that in keratinocytes the syndecan-1 gene was stimulated by EGF but not by FGF-2. In ®broblasts it was stimulated by FGF-2 but not by EGF. Likewise, the recently discovered FGF-inducible response element (FiRE) on the gene of syndecan-1 was stimulated by FGF-2 in ®broblasts and by EGF in keratinocytes, but not vice versa. The FiRE has two binding sites for an activator protein-1 (AP-1), one for an FGF-inducible nuclear factor (FIN-1) and one for an upstream stimulatory factor-1 (USF-1). The growth factorstimulated binding of these transcription factors, as well as their requirement for FiRE activation, varied between the two cell types. First, although AP-1s were required for activation of FiRE in both cell types, the binding of AP-1 to FiRE was increased by growth factor-stimulation only in ®broblasts and not in keratinocytes. Secondly, FiRE did not bind FIN-1 nor needed the FIN-1 binding site for EGF-stimulated activation in keratinocytes, in contrast to the FGF-stimulated activation of FiRE in ®broblasts. Thirdly, EGF, which did not activate FiRE in ®broblasts, failed to activate FIN-1 in these cells. Finally, an USF-1 binding site that was necessary for activation of FiRE in keratinocytes was not needed in ®broblasts. These data suggest mechanisms by which members of the EGF-and FGF-families can di erentially stimulate transcription through AP-1 regulated elements in a cell type-speci®c manner.

Extracellular Matrix-dependent Activation of Syndecan-1 Expression in Keratinocyte Growth Factor-treated Keratinocytes

“…The most 3Ј-motif (motif 1) of the enhancer binds an uncharacterized 46-kDa protein constitutively expressed in 3T3 cells (21). The DNA binding activity of this protein was equally present in treated and control MCA-3D cells and was unchanged by extracellular matrix molecules (data not shown).…”

“…Finally, we have found that an enhancer for syndecan-1 gene (named FiRE for FGF-inducible response element) is activated in vivo in wound edge keratinocytes and that in cultured keratinocytes, FiRE can be activated by KGF and EGF (21,22). Interestingly, this enhancer element is not sufficient for the default expression in suprabasal cells: the only epidermal expression detected in the FiRE-LacZ mice occurs at the wound edge (22).…”

“…Collagen-We had previously seen that the enhancer for syndecan-1 gene (the FiRE) is activated in wound edge keratinocytes in vivo and that the FiRE can drive reporter gene expression after KGF or EGF treatment (21,22). At the wound edge, syndecan-1 induction is not uniform, however, as the leading front of migrating keratinocytes remain syndecan-1-negative (14).…”

“…The DNA binding activity of this protein was equally present in treated and control MCA-3D cells and was unchanged by extracellular matrix molecules (data not shown). Motif 2 contains an E-box that is bound by USF-1 in both cell lines (20,21). Fig.…”

“…We have previously characterized the enhancer by DNaseI footprinting and gel mobility shift assays (20,21). An overview of the enhancer is presented in the Fig.…”