Regulation of Amphiregulin gene expression by ß-catenin signaling in human Hepatocellular carcinoma cells: a novel crosstalk between FGF19 and the EGFR system

Hepatocellular carcinoma (HCC) is the most prevalent liver tumor and a deadly disease with limited therapeutic options.
Dysregulation of cell signaling pathways is a common denominator in tumorigenesis, including hepatocarcinogenesis. The epidermal growth factor receptor (EGFR) signaling system is commonly activated in HCC, and is currently being evaluated as a therapeutic target in combination therapies. We and others have identified a central role for the EGFR ligand amphiregulin (AR) in the proliferation, survival and drug resistance of HCC cells.ARexpression is frequently up-regulated in HCC tissues and cells through mechanisms not completely known. Here we identify the ß-catenin signaling pathway as a novel
mechanism leading to transcriptional activation of theARgene in human HCC cells. Activation of ß-catenin signaling, or expression of the T41A ß-catenin active mutant, led to the induction ofARexpression involving three specific ß-catenin-Tcf responsive elements in its proximal promoter. We demonstrate that HCC cells expressing the T41A ß-catenin active mutant show enhanced proliferation that is dependent in part onARexpression and EGFR signaling. We also demonstrate here a
novel cross-talk of the EGFR system with fibroblast growth factor 19 (FGF19).FGF19is a recently identified driver gene in hepatocarcinogenesis and an activator of ß-catenin signaling in HCC and colon cancer cells. We show that FGF19 inducedARgene expression through the ß-catenin pathway in human HCC cells. Importantly,ARup-regulation and EGFR signaling participated in the induction of cyclin D1 and cell proliferation elicited by FGF19. Finally, we demonstrate a positive correlation between FGF19 and AR expression in human HCC tissues, therefore supporting in clinical samples our experimental observations. These findings identify the AR/EGFR system as a key mediator of FGF19 responses in HCC cells involving ß-catenin signaling, and suggest that combined targeting of FGF19 and AR/EGFR may enhance therapeutic efficacy.