The activation and composition of FiRE (an FGF-inducible response element) dier in a cell type- and growth factor-speci®c manner Panu Jaakkola 1 , Arto MaÈaÈttaÈ 1,2 and Markku Jalkanen 1 1 Turku Centre for Biotechnology, University of Turku and A Ê bo Akademi University, Tykisto Èkatu 6B, BioCity, FIN-20520 Turku, Finland 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 factor- stimulated 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-stimula- tion 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 activa- tion 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. Keywords: AP-1; EGF; FGF; FIN-1; KGF; Syndecan-1; transcription Introduction Members of the epidermal growth factor (EGF) and the ®broblast growth factor (FGF) families share many biological functions and frequently activate same signal transduction pathways in their target cells. However, the genes that these growth factors upregulate in a given cell type are not always identical. Both EGF and the basic ®broblast growth factor, FGF-2, act on epithelial cells and ®broblasts stimulating their migra- tion and cell proliferation (Basilico and Moscatelli, 1992; Bennet and Schultz, 1993; Tsuboi et al., 1993). There are also common pathways, such as the extracellular regulated kinase (ERK) pathway of MAP kinases, which transduce signals upon activation of both EGF and FGF receptors (Karin et al., 1997). Furthermore, EGF and FGF-2 are able to promote regeneration processes, such as wound healing (Andree et al., 1994; Brown et al., 1989; Davidson and Broadley, 1991). It is remarkable that although sharing all these activities, the gene expression pattern the growth factors induce in one cell type is only partially overlapping. This has been shown, for example, in neural cells where EGF and FGF can dierentially upregulate the expression of several proteins (Loret et al., 1989). Similarly, in ®broblasts FGF, but not EGF, upregulates the vinculin gene (Ben-Ze'ev et al., 1990). The induced expression of genes is mainly achieved by activating transcription through the activation of transcription factors. The transcription factors of the Fos ± family (c-Fos, FosB, Fra-1, Fra-2) and the Jun- family (c-Jun, JunB, JunD) form hetero- and homo- dimers called activator protein-1 (AP-1). AP-1 dimers bind to DNA at consensus sequences such as the classical TPA-responsive element (TRE) and the cAMP-responsive element (CRE) to activate transcrip- tion, but the binding site can vary depending on the composition of the AP-1 dimer. Furthermore, some other transcription factors adjacent to AP-1 are supposed to have an ability of modulating the transactivation induced by AP-1. A wide variety of genes are known to have an AP-1 site in their promoter. The Fos- and Jun-family members are mostly associated with proliferation and survival of cells and are induced by several mitogenic stimuli, including growth factors (Hill and Treisman, 1995; Karin et al., 1997). EGF and FGF-2 are known to induce the AP-1 transcription factor family members in numerous cells. EGF and FGF-2 also upregulate several AP-1 driven promoters (Felts et al., 1995; Han et al., 1992; Pestell et al., 1995; Tan et al., 1994). However, the signaling induced by EGF and FGF can not be identical. This can be seen in situations where in a single cell type one growth factor elicits expression of a gene, while the other one fails to do it. Furthermore, if this expression is dependent on an AP-1 regulated promoter, it is obvious that these growth factors can not equally regulate the transactivation capacity of AP- 1. The speci®city of growth factors to dierentially regulate transcription, also among the AP-1 driven promoters, is not well understood. Syndecan-1 is one example of a protein that is induced in a cell type-speci®c manner. It is a heparan sulfate proteoglycan expressed in keratinocytes and Correspondence: M Jalkanen 2 Current address: Keratinocyte Laboratory, Imperial Cancer Research Fund, 44 Lincoln's Inn Fields, London WC2A 3PX, UK Received 24 November 1997; revised 25 March 1998; accepted 25 March 1998 Oncogene (1998) 17, 1279 ± 1286  1998 Stockton Press All rights reserved 0950 ± 9232/98 $12.00 http://www.stockton-press.co.uk/onc