Dual mode of signal transduction by externally added acidic fibroblast growth factor.

Acidic fibroblast growth factor (aFGF), fused to diphtheria toxin and translocated into cells, stimulated DNA synthesis in toxin-resistant cells lacking functional aFGF receptors while having a high number of diphtheria toxin receptors. In NIH 3T3 cells that lack diphtheria toxin receptors, but have receptors for aFGF, both aFGF and the fusion protein induced tyrosine phosphorylation, but only aFGF as such entered the nuclei and stimulated DNA synthesis. The results indicate that signaling occurs partly through cell surface receptors and partly by transport of the growth factor into the cell.