Epidermal growth factor and 12-tetradecanoyl phorbol 13-acetate induction of urokinase in A431 cells

The signal transduction pathways of urokinase (u-PA) in A431 cells, a human epidermoid carcinoma cell line, were studied using the inducers EGF and TPA. Based on the following observations, we conclude that the two pathways are different: (1) The effects are additive; (2) EGF induction of u-PA was not compromised either by down-regulation of PKC or selective inhibition of the same by H7; (3) 8-Br-cAMP has no effect by itself; however, it inhibits the EGF effect and doubles the TPA induction of u-PA; (4) after EGF-induced tyrosine phosphorylations are completed, addition of TPA can still induce u-PA, an effect that can be blocked by the addition of the tyrosine phosphorylation inhibitor, genistein, indicating that the two agents induce different tyrosine phosphorylation; (5) in 2-dimensional electrophoresis of 32P-labeled cell lysates, inducer-specific differences in the intensity of spots can be observed. Some of the spots weakened by genistein (tyrosine phosphorylations) are different, depending on the inducer used.