Inhibition of cell migration by 24-kDa fibroblast growth factor-2 is dependent upon the estrogen receptor

The single-copy gene for fibroblast growth factor-2 (FGF-2) encodes for mul tiple forms of the protein with molecular masses of 24, 22.5, 22, and 18 kD a, We reported previously that the 24-22-kDa FGF-2 forms inhibit the migrat ion of endothelial and MCF-7 cells by 50% and 70%, respectively. Here we sh ow that this inhibition of migration is mediated by the estrogen receptor ( ER). We have found that depletion of the receptor in either cell line abrog ates the inhibitory activity of 24-kDa FGF-2 while re-introduction of the E R into deficient cells once again promotes the inhibitory response. To dete rmine whether exposure to 24-kDa FGF-2 resulted in the activation of the es trogen receptor, 3T3 cells were cotransfected with estrogen receptor cDNA a nd an estrogen regulatory element-luciferase gene reporter construct and tr eated with 24- and 18-kDa FGF-2. The high molecular weight form stimulated luciferase activity 5-fold while 18-kDa FGF-2 at the same concentration had no effect, Treatment of ER-positive MCF-7 cells transfected with the repor ter construct only showed the same results. Inclusion of the pure estrogen antagonist ICI 182,780 blocked the increase in luciferase activity by 24-kD a FGF-8, further indicating that the response was estrogen receptor depende nt. Expression of dominant negative FGF receptor 1 inhibited ER activation, indicating that this was the cell surface receptor mediating the effect. A lthough growth factor-dependent activation of the ER was reported to requir e mitogen-activated protein kinase-induced phosphorylation at Ser(118) in C OS and HeLa cells, this mechanism is not involved with the activation by 24 -kDa FGF-8, These results suggest that the addition of 55 amino acids to th e amino-terminal end of 18-kDa FGF-2 by alternative translation alters FGF- 8 function and allows for the activation of a second signaling pathway invo lving the estrogen receptor.