Expression of a binding protein for FGF is associated with epithelial development and skin carcinogenesis Andreas Kurtz 1 , Huey-Lin Wang 1 , Nadine Darwiche 2 , Violaine Harris 1 and Anton Wellstein 1 1 Vincent T Lombardi Cancer Center and Departments of Pharmacology and Neurosurgery, Georgetown University, 3970 Reservoir Road, Washington DC 20007; 2 Laboratory of Cellular Carcinogenesis and Tumor Promotion, National Cancer Institute, NIH, 9000 Rockville Park, Bethesda, Maryland 20892, USA Fibroblast growth factors (FGF)-1 and -2 are found in most embryonic and adult normal and tumor tissues, where they are immobilized in the extracellular matrix (EM). Mobilization of these FGFs is part of a tightly controlled process resulting in the activation of high- anity receptors. Recently, we have shown that a novel human FGF-binding protein (FGF-BP) mediates the release of immobilized FGF-2 from the EM. Here we isolated genomic and cDNA clones of the mouse FGF- BP homologue and studied its expression during embryonic development and skin carcinogenesis. The murine gene contains two exons that generate a 1.2 kb mRNA and predicts an 18 kDa secreted protein that is 63% identical to its human homologue. FGF-BP mRNA expression during embryogenesis is restricted to skin, intestine and lung. In the developing skin, FGF-BP expression starts at embryonic day 9, reaches peak levels perinatally and is downregulated during postnatal development. Develepment regulation in the intestine is similar, but in lungs and ovaries high expression was also observed in the adult. FGF-BP mRNA expression in the adult skin is dramatically increased during early stages of carcinogen-induced transformation in vivo and by ras- activation in vitro. Finally, mouse FGF-BP binds to FGF-2 and can function as a modulator of FGF in FGF- responsive cells. Our results suggest a potential function of FGF-BP during development and tumorigenesis. Keywords: FGF-binding protein; gene; skin; carcino- genesis; development; expression Introduction Fibroblast growth factors (FGFs) constitute a family of structurally homologous proteins which play important inductive roles during embryogenesis, are potent angiogenic factors in vivo and are regulators of proliferation and dierentiation for a number of cell types (reviewed e.g. in Brem and Klagsbrun, 1993; Mason, 1994). FGF-1 and -2 (acidic and basic FGF, respectively), in contrast to most other members of the FGF-family, do not contain a signal peptide. Still, both are found complexed to low anity proteogly- can receptors of the extracellular matrix (EM), and both are widely distributed in embryonic, adult and tumor tissues. Mobilization of the dormant FGF-1 and -2 leads to their activation and facilitates binding to high anity tyrosine kinase receptors (Aviezer et al., 1994; Brem and Klagsbrun, 1993; Schlessinger et al., 1995). FGF-1 and -2 are expressed in a number of tumors (Esch et al., 1985; Moscatelli et al., 1986; Shing et al., 1984) but the significance of this expression remains unclear since both are also found in the EM of many normal cells (Moscatelli et al., 1986; Vlodavsky et al., 1987). A proposed function for FGF-2 in tumors might be to support tumor growth by stimulating blood vessel growth. However, there are conflicting reports on the correlation of FGF-2 expression with vascular- ity in squamous cell carcinomas (SCC) of the head and neck. FGF-2 expression has been correlated with increased vascularization in some SCC (Huang et al., 1993; Schultz-Hector and Haghayegh, 1993). Other studies reported a correlation of FGF-2 expression with enhanced dierentiation of these tumors but not with vascularization (Janot et al., 1995). This ambiguous correlation of FGF-2 levels to vascularity and the wide distribution of FGF-1 and -2 in embryonic as well as adult tissues and tumors suggests secondary regulatory mechanisms for their mobilization and activation. One established mobilizing mechanism involves extracellular heparitinases and proteases which attack heparansulfate chains and the proteoglycan-backbone, respectively, thereby releasing FGFs (Bashkin et al., 1989; Moscatelli, 1992; Vlodavsky et al., 1988, 1991). A recently proposed novel pathway for FGF release from the EM involves its binding to a secreted binding protein, FGF-BP (Czubayko et al., 1994). FGF-BP (=HBp 17) is a secreted, heparin binding protein of 17 kD molecular mass that was originally isolated from A431 human epidermoid carcinoma cells. FGF-BP binds FGF-1 and -2 in a non-covalent, reversible manner. In addition, binding of FGF-BP to FGF-2 prevents its degradation and retains its biological activity (Wu et al., 1991). Human FGF-BP is expressed in keratinocytes in vitro, a number of SCC-derived cell lines and in SCC tumor samples from patients (Czubayko et al., 1994; Wu et al., 1991). Previously, we have shown that transfection of a human FGF-BP cDNA into the FGF-2 positive, anchorage dependent, non tumorigenic cell line SW-13 allows these cells to grow in soft agar and to form highly vascularized tumors in athymic nude mice (Czubayko et al., 1994). A current working model proposes that this eect is due to FGF-BP- mediated mobilization of the dormant FGF-2 that is Correspondence: A Kurtz Received 26 June 1996; revised 28 February 1997; accepted 28 February 1997 Oncogene (1997) 14, 2671 – 2681  1997 Stockton Press All rights reserved 0950 – 9232/97 $12.00