The b isoform of Fibroblast Growth Factor Receptor 2 (FGFR2IIIb) is highly expressed
in hepatocytes and has been shown to play an important role in liver homeostasis and
regeneration. Here, we analyzed the expression and function of FGFR2IIIb in hepatocellular
carcinoma (HCC).
Methods and Results: FGFR2IIIb mRNA expression was downregulated in HCC cell lines compared to primary
human hepatocytes as determined by quantitative PCR. Similarly, HCC tissues from patients
and animal models (c-myc and IgEGF transgenic mice) showed reduced or lost FGFR2IIIb
mRNA expression compared to corresponding non-cancerous liver tissue. Immunohistochemical
analysis of HCC tissues applying a newly generated polyclonal antibody that specifically
recognizes the IIIb variant of the FGFR2 receptor confirmed these findings on the
protein level. The 5' region of the FGFR2 gene contains a CpG island, but 5-azacytidine
treatment did not affect FGFR2IIIb expression in HCC cells, excluding promotor methylation
as potential cause for the FGFR2IIIb downregulation. However, cell differentiation
induced by high cell density and confluence induced FGFR2IIIb mRNA and protein expression
in HCC cells in vitro. To gain insight into the functional role of FGFR2IIIb downregulation
in HCC, FGFR2IIIb was re-expressed in HCC cell lines by stable transfection, and the
generated cell clones were analyzed in vitro and in vivo. FGFR2IIIb clones exhibited
a higher basal apoptosis rate and a significantly reduced proliferation as compared
to mock transfected and control cells. In accordance, FGFR2IIIb clones grew significantly
slower in nude mice and Tunel staining of FGFR2IIIb tumors revealed higher apoptosis
rate compared to controls.
Summary and Conclusion: Data presented indicate FGFR2IIIb as tumor suppressor of HCC
and provide insight into the mechanisms of FGFR2IIIb tumor suppression. Identification
and therapeutic targeting of the molecular mechanisms responsible for FGFR2IIIb suppression
in HCC may be a viable method of inhibiting the progression of HCC.
