Immunohistochemical localization of basic fibroblast growth factor in A431 human epidermoid carcinoma cells

The intracellular location of basic fibroblast growth factor (bFGF) was determined in A431 human epidermoid carcinoma cells both on immunofluorescence and on immunoelectron microscopy using a monoclonal anti-bFGF antibody. The immunofluorescence was located in the cytoplasm in quiescent cells. Following the addition of FCS to the culture medium of quiescent sparse cells the growth factor was translocated to and accumulated in the nucleolus. Immunogold particles were dense near the ribosomes, but were not recognized in the cytoplasmic structures concerned with the usual secretory pathway such as the rough endoplasmic reticulum, the Golgi apparatus, and secretory granules. These results suggest that endogenous bFGF undergoes intracellular sorting and enters the nucleoli in A431 cells according to an extracellular growth signal.