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 c ells lacking functional aFGF receptors while having a high number of d iphtheria toxin receptors. In NIH 3T3 cells that lack diphtheria toxin receptors, but have receptors for aFGF, both aFGF and the fusion prot ein induced tyrosine phosphorylation, but only aFGF as such entered th e nuclei and stimulated DNA synthesis. The results indicate that signa ling occurs partly through cell surface receptors and partly by transp ort of the growth factor into the cell.