Expression and Function of Fibroblast Growth Factor 9 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is closely linked to hepatic fibrosis. The activation of hepatic stellate cells (HSC) is the key event of liver fibrosis and activated HSC are major players in hepatocarcinogenesis. Following activation, HSC produce fibroblast growth factors (FGFs) to promote liver regeneration. FGF signaling plays a major role in development, differentiation and wound healing. The FGF family comprises 22 proteins that can be classified into paracrine, intracrine and endocrine factors. FGFs signal through transmembrane tyrosine kinase FGF receptors (FGFRs). Overexpression of FGFRs contributes to HCC development and progression. However, the expression and tumorigenic effects of FGFR-ligands in HCC are largely unknown.

The aim of this study was to elucidate the role of paracrine FGFs in the HSC-HCC crosstalk with focus on FGF9.

Methods and Results:

Expression analysis of the fifteen paracrine FGFs revealed that FGF9 was expressed by activated human HSC while no FGF9 expression was detectable in human HCC cell lines (Hep3B, HepG2, Huh7, PLC). Immunofluorescence stainings of human HCC tissues showed co-localization of FGF9 and alpha-smooth muscle actin (alpha-sma), a characteristic marker of activated HSC. Fitting to this, FGF9 expression significantly correlated with alpha-sma expression in human HCC tissues indicating activated HSC as cellular FGF9 sources. Importantly, high expression levels of FGF9 significantly correlated with poor patient survival. Stimulation with recombinant FGF9 (rFGF9) induced ERK- and JNK-phosphorylation in HCC cells. In functional in vitro analysis, rFGF9 significantly increased proliferation, colony formation and migration of HCC cells. Furthermore, stimulation with rFGF9 significantly reduced the efficacy of sorafenib to inhibit proliferation and to induce apoptosis in HCC cells. Protumorigenic effects of FGF9 on HCC cells were almost completely blunted by the FGFR1/2/3 inhibitor BGJ398, while the selective FGFR4 inhibitor BLU9931 had no significant effect.

Summary and conclusion:

Stroma-derived FGF9 enhances the tumorigenicity and sorafenib resistance of HCC cells and FGF9 overexpression correlates with poor prognosis in HCC patients. Herewith, FGF9 appears as potential prognostic marker and novel therapeutic target in HCC.