E-cadherin is a transmembrane protein that mediates Ca 2؉ -dependent cell-cell adhesion and is implicated in a number of biologic processes, including cell growth and differentiation, cell recognition and cell sorting during development. We have previously demonstrated that both cell-cell adhesion and invasion are modulated by fibroblast growth factor (FGF)-1 and FGF-2 in a panel of pancreatic adenocarcinoma cell lines (BxPc3, T3M4 and HPAF). Here, we examine further the role of FGFs in the expression and activation of the E-cadherin/catenin system. We demonstrate that both FGF-1 and FGF-2 upregulate E-cadherin and -catenin at the protein level in the BxPc3 and HPAF cell lines and modestly in T3M4 cells. FGF-1 and FGF-2 facilitate the association of E-cadherin and ␣-catenin with the cytoskeleton, as demonstrated by the increase in the detergent-insoluble fraction of E-cadherin in BxPc3 and HPAF cells. Since the correct function of the E-cadherin/catenin complex requires its association with the cytoskeleton, our data suggest that FGF-1 and FGF-2 contribute to the integrity and thus the function of the complex. Furthermore, FGFs facilitate the assembly of the E-cadherin/catenin axis. The effect is associated with elevation of tyrosine phosphorylation of E-cadherin, ␣-catenin, -4051catenin and ␥-catenin, but not p120 ctn . These findings indicate that the E-cadherin/catenin system is a target of the FGF/FGFR system and that coordinated signals from both systems may determine the ultimate biologic responses. © 2001 Wiley-Liss, Inc.
Key words: E-cadherin; catenins; FGF; FGFR; pancreatic adenocarcinomaEvidence is compelling that a loss of function of E-cadherin and/or one or more of the associated catenins contributes to increased proliferation, invasion and metastasis in a wide variety of solid tumours. 1 Supporting observations include an inverse correlation between E-cadherin expression and increased invasiveness in vitro, 2 as well as an association between loss of E-cadherin expression and dedifferentiation, advanced tumour grade, metastasis and shortened survival. 3,4 The integrity of the entire E-cadherin-catenin-actin network is indispensable for E-cadherin-mediated cell-cell adhesion. Posttranslational modification such as tyrosine phosphorylation is widely recognised as the prevalent mechanism in regulating cadherin/catenin expression and/or function. 5 The catenins (-catenin, ␥-catenin and p120 ctn ) are the major targets of protein tyrosine kinases, which are heavily tyrosine phosphorylated in Src-transformed cells 6 and in response to growth factors such as EGF, 7,8 TGF-␣, PDGF 9,10 and HGF. 11 Furthermore, -catenin and ␥-catenin directly associate with at least two receptor tyrosine kinases: EGFR 7 and c-erbB-2. 12 There is mounting evidence that E-cadherin expression can be modulated, either positively or negatively, by growth factors and cytokines. However, the mechanism of regulation of expression remains largely speculative. For instance, TGF- induces dedifferentiation of normal mammary epithel...