Inhibition of growth of early passage normal rat liver epithelial cell lines by epidermal growth factor

The proliferation of newly derived or early passage nonparenchymal rat liver epithelial cell lines in serum-containing medium was inhibited consistently by epidermal growth factor (EGF). Inhibition of proliferation by EGF was a dominant effect which could not be overcome by insulin, phorbol ester or substances which raised the intracytoplasmic concentration of cyclic-AMP (cholera toxin and dibutyryl cyclic-AMP). EGF has a heterogeneous effect on colony formation by individual cells of early passage cell lines. Whereas the colony-forming ability of a majority of these cells was inhibited by EGF, a small fraction of the cells resisted this effect and formed colonies in the presence of EGF. Clonal strains of EGF-inhibited and EGF-stimulated cells were isolated. Measurement of 125I-EGF binding capacity of these cell strains revealed no significant differences between the EGF-inhibited and EGF-stimulated cells. In general, EGF-stimulated cell strains demonstrated faster growth rates and higher colony-forming efficiencies than EGF-inhibited strains. EGF-induced growth inhibition however, was an unstable phenotype that might be diminished or lost after multiple passages, especially when cells were allowed to remain confluent for many days between passages. These observations may explain the consistent findings that in late passage, rat liver epithelial cell lines in which the conditions for culture and times of subcultures have not been controlled rigorously, the inhibitory effect of EGF usually is not observed.