Forced expression of hepatocyte-specific fibroblast growth factor 21 delays initiation of chemically induced hepatocarcinogenesis.
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abstract
Inappropriate fibroblast growth factor (FGF) signaling is involved in most tissue-specific pathologies including cancer. Previously we showed that inappropriate expression and chronic activity of FGF receptor (FGFR) 1 in hepatocytes accelerated diethylnitrosamine (DEN)-initiated hepatocarcinogenesis. Here we showed that although widely expressed FGF1 and FGF2 are frequently upregulated in hepatocellular carcinoma (HCC), germline deletion of both FGF1 and FGF2 had no effect on DEN-initiated hepatocarcinogenesis. Thus overexpression of FGF1 or FGF2 may be a consequence rather than contributor to hepatoma progression. FGF21 is the first of 22 homologues whose expression has been reported to be preferentially in the liver. We showed that similar to FGF1 and FGF2, FGF21 mRNA was upregulated in neoplastic and regenerating liver after partial hepatectomy (PH) and CCl4 administration. In situ hybridization analysis confirmed that in contrast to FGF1 and FGF2, expression of FGF21 mRNA was limited to hepatocytes. Forced overexpression of FGF21 in hepatocytes by gene targeting had no apparent impact on normal liver development and compensatory response to injury. Surprisingly, overexpression of FGF21 delayed the appearance of DEN-induced liver tumors. At 8 and 10 mo, only 10% and 30% of transgenic mice, respectively, developed adenomas compared to 50% (all adenomas) and 80% (60% adenoma/20% HCC) in the wild-type (WT) mice. However, the incidence and burden of HCC at 10 mo and later was equal in the FGF21 transgenic and WT mice. We propose that FGF21 may delay development of adenomas through activation of resident hepatocyte FGFR4 at early times, but counteracts the delay by acceleration of progression to HCC through interaction with ectopic FGFR1 once it appears in hepatoma cells. This indicates a dual function of FGF21 that may reflect changes in FGFR isotype during progression of differentiated hepatoma cells.
