Isolation and Characterization of A-431 Cells That Retain High Epidermal Growth Factor Binding Capacity and Respond to Epidermal Growth Factor by Growth Stimulation¹

A-431 cells, which exhibit large numbers of epidermal growth factor (EGF) receptors and respond to EGF by growth inhibition, are widely used to study EGF receptors and the effects of EGF. In this report, we describe the isolation and characterization of variant A-431 cells that respond to EGF by growth stimulation. One variant, which is referred to as A-431R-1, has been characterized in detail. EGF stimulates both monolayer and soft agar growth of A-431R-1 cells cultured in serum-free medium. In contrast to the original A-431 cells, growth of A-431R-1 cells is not inhibited by EGF, even at high concentrations. Scatchard analysis of EGF binding to A-431R-1 cells and A-431 cells indicates that both cell populations exhibit approximately 1.8 × 10⁶ EGF receptors per cell. Thus, unlike other variants of A-431 cells that are not inhibited by EGF, A-431R-1 cells exhibit as many EGF receptors as the parental A-431 cells. It was also determined that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate reduces EGF binding to the high affinity receptors of A-431R-1 cells; whereas, transforming growth factor type β did not significantly affect EGF binding. Our results suggest that A-431R-1 cells should be useful for studying the biochemical effects of EGF and for examining why some cells are inhibited by EGF, whereas others are stimulated by EGF.