Possible implication for an indirect interaction between basic fibroblast growth factor and (Na,K)ATPase

FGF2 modulates the voltage-dependent K+ current and changes excitability of rat dentate gyrus granule cells

Fibroblast growth factor 2 (FGF2) is involved in hippocampus-dependent learning. In this study, the effects of FGF2 on the excitability were investigated in granule cells of rat dentate gyrus. Hippocampal slices were used to perform patch clamp recordings in granule cells. Extracellularly applied FGF2 early quenched the depolarization-induced repetitive firing, suggesting a decreased excitability under these conditions. Consistently, transient and sustained voltage-gated K(+) currents decreased in a dose-dependent manner, repolarization phase of action potential was slowed down, afterhyperpolarization was reduced, and membrane resistance was decreased. These effects were not mediated by tyrosine kinase FGF2 receptors. Moreover, an involvement of G protein signaling was ruled out, as well as an intracellular action of FGF2. Considering the relationship between FGF2 and hippocampal functions, the modulation of neuron excitability by activity-driven FGF2 release may be regarded as a part of a homeostatic mechanism of self-regulation of hippocampal activity.

Inhibition of export of fibroblast growth factor-2 (FGF-2) from the prostate cancer cell lines PC3 and DU145 by Anvirzel and its cardiac glycoside component, oleandrin

Anvirzel is an extract of Nerium oleander currently undergoing Phase I clinical evaluation as a potential treatment for cancer. Two of the active components of Anvirzel are the cardiac glycosides oleandrin and oleandrigenin. Previous studies have demonstrated that, in vitro, cardiac glycosides may inhibit fibroblast growth factor-2 (FGF-2) export through membrane interaction with the Na(+),K(+)-ATPase pump. In continuing research on the antitumor activity of this novel plant extract, the relative abilities of oleandrin and oleandrigenin to inhibit FGF-2 export from two human prostate cancer cell lines, DU145 and PC3, were examined. An ELISA assay was utilized to determine the FGF-2 concentration in the cell culture medium before and after exposure to cardiac glycosides or the parent extract material Anvirzel. Both cell lines were exposed to non-cytotoxic concentrations of oleandrin (0.05 and 0.1 ng/mL) for up to 72 hr. Studies also were conducted with Anvirzel and ouabain. Oleandrin (0.1 ng/mL) produced a 45.7% inhibition of FGF-2 release from PC3 cells and a 49.9% inhibition from DU145 cells. Non-cytotoxic concentrations (100 ng/mL) of Anvirzel produced a 51.9 and 30.8% inhibition of FGF-2 release, respectively, in the two cell lines. The decrease in FGF-2 release from cells required continuous incubation for 48--72 hr; shorter incubation times were not effective. These results demonstrate that Anvirzel, like oleandrin, inhibited FGF-2 export in vitro from PC3 and DU145 prostate cancer cells in a concentration- and time-dependent fashion and may, therefore, contribute to the antitumor activity of this novel treatment for cancer.