HGF induces fibronectin matrix synthesis in melanoma cells through MAP kinase-dependent signaling pathway and induction of Egr-1 Ce´dric Gaggioli 1 , Marcel Deckert 2 , Guillaume Robert 1 , Patricia Abbe 1 , Michelle Batoz 2 , Markus U Ehrengruber 3,4 , Jean-Paul Ortonne 1 , Robert Ballotti 1 and Sophie Tartare-Deckert* ,1 1 INSERM Unite´597, Biologie et Pathologies des Cellules Me´lanocytaires, ‘e´quipe labellise´e la Ligue 2001’, IFR 50, 06107 Nice Ce´dex 2, France; 2 INSERM Unite´576, Hoˆpital de l’Archet, 06202 Nice, France; 3 Brain Research Institute, University of Zurich, CH-8057 Zurich, Switzerland The matrix fibronectin protein is a multifunctional adhesive molecule that promotes migration and invasive- ness of many tumors including melanomas. Increased fibronectin synthesis has been associated with the meta- static potential of melanoma cells; however, the molecular mechanisms underlying fibronectin overexpression during melanoma development are poorly understood. We report that hepatocyte growth factor/scatter factor (HGF) induces fibronectin expression and its extracellular assembly on the surface of melanoma cells through activation of mitogen-activated protein (MAP) kinase pathway, and induction and transcriptional activation of Early growth response-1 (Egr-1). Inhibition of B-RAF/ MAP kinase pathway by dominant-negative mutants and by U0126-abrogated HGF-induced Egr-1, and chromatin immunoprecipitation showed that Egr-1 is bound to the fibronectin promoter in response to HGF. Exogenously expressed Egr-1 increased fibronectin levels, while block- age of Egr-1 activation by expression of the Egr-1 corepressor NAB2 interfered with the upregulation of fibronectin synthesis induced by HGF, indicating that Egr-1 exerts a significant role in fibronectin expression in response to HGF. Finally, analysis of the expression pattern of fibronectin in melanoma cells demonstrated that fibronectin levels are correlated with constitutive MAP kinase signaling. Our data define a novel mechanism that might have important implications in regulation of melanoma progression by autocrine HGF signaling or by constitutive activation of MAP kinase pathway. Oncogene (2005) 24, 1423–1433. doi:10.1038/sj.onc.1208318 Published online 20 December 2004 Keywords: melanoma; fibronectin; HGF; B-RAF; Egr-1; signaling Introduction Malignant transformation is associated with alterations in cell–extracellular matrix (ECM) interactions that lead to major changes in adhesion and migration processes, and aberrant adhesion-mediated signaling (Sage, 2001). Fibronectin, a major constituent of ECMs, plays an important role during embryogenesis, wound healing and cancer invasion by promoting cell adhesion, motility, cell cycle progression and cell survival (Hynes and Yamada, 1982; Humphries et al., 1989; Frisch and Ruoslahti, 1997). Fibronectin serves as a ligand for integrin family of cell adhesion receptors (Giancotti and Ruoslahti, 1999). It is generally accepted that modulat- ing levels of fibronectin in the tumor environment may influence tumor cell behavior. Reduction or loss of fibronectin expression has been observed in many transformed cells in culture (Ruoslahti and Giancotti, 1989). However, overexpression of fibronectin is asso- ciated with various human tumor cells including color- ectal cancer, breast carcinoma, head and neck squamous carcinoma and metastatic melanoma (Zhang et al., 1997; Bittner et al., 2000; Al Moustafa et al., 2002; Jiang et al., 2002). Cutaneous melanoma is a malignant tumor deriving from the transformation of pigments producing mela- nocytes (Goding, 2000). Its incidence is increasing at a dramatic rate. Melanoma has a high capability of invasion and rapid metastasis to other organs (Goding, 2000). Increased fibronectin production has been corre- lated with the acquisition of metastatic potential of melanoma and higher invasive capacity (Bittner et al., 2000; Ridley, 2000). Highly metastatic melanoma tumors, derived from parental tumor cell lines by in vivo passage, show high levels of fibronectin transcript (Clark et al., 2000). Further, interfering with integrin signaling on melanoma cells by cell-binding fibronectin peptides (RGD-peptides) inhibits experimental metas- tasis of melanoma cells (Humphries et al., 1986). These studies suggest that melanoma cells are induced to produce their promigratory matrix, and that interaction of tumor cells with fibronectin contributes to the invasive and metastatic behavior of melanoma cells. Hepatocyte growth factor/scatter factor (HGF) is a mesenchymally derived cytokine that elicits mitogenic, Received 29 July 2004; revised 4 October 2004; accepted 22 October 2004; published online 20 December 2004 *Correspondence: S Tartare-Deckert; INSERM Unite´ 597, Faculte´ de Me´decine, 28 avenue de Valombrose, 06107 Nice Ce´dex 2, France E-mail: tartare@unice.fr 4 Current address: Kantonsschule Hohe Promenade, Promenadengasse 11, CH-8001 Zurich, Switzerland Oncogene (2005) 24, 1423–1433 & 2005 Nature Publishing Group All rights reserved 0950-9232/05 $30.00 www.nature.com/onc