Alteration in growth, cell morphology, and cytoskeletal structures of KB cells induced by epidermal growth factor and transforming growth factor-β

Abstract

Long-term biological effects of epidermal growth factor (EGF), insulin, insulin-like growth factor-I (IGF-I), and transforming growth factor-β (TGF-β) were examined with human epidermoid carcinoma KB cells. EGF inhibited the growth of KB cells in both serum-containing and serum-free synthetic media by reducing the growth rate and by lowering the saturation density. The cells cultured with EGF showed relatively high motility and grew dispersely as single cells, whereas the cells cultured in the absence of EGF grew in clusters. Although TGF-β itself did not inhibit the growth of KB cells, it augmented the growth inhibition by EGF. TGF-β also affected the cell morphology. In the presence of TGF-β, the cells became flattened and actin stress fibers were well developed compared to those cultured in its absence. The effects of EGF on growth, cell motility, and cell morphology were reversible. Tyrosine phosphorylation of EGF receptors was continuously observed for at least 50 h in the presence of EGF. TGF-β did not increase the phosphorylation induced by EGF. These results suggested that signals continuously transmitted through EGF receptors caused the changes in cell growth and morphology and that TGF-β did not act on the cells by modulating binding of EGF to its receptors or activation of the receptor kinase. In contrast to EGF and TGF-β, neither insulin nor IGF-I affected cell morphology or growth, although KB cells express their receptors and the receptor kinases were also continuously activated during exposure of the cells to insulin or IGF-I.