INHIBITION OF EPIDERMAL GROWTH FACTOR-STIMULATED EGF RECEPTOR TYROSINE KINASE-ACTIVITY IN A431 HUMAN EPIDERMOID CARCINOMA-CELLS BY POLYAMINES

Polyamines-putrescine, spermidine, and spermine-are ubiquitous cellula r components that play an important role in cell growth and differenti ation. Using A431 cells, a cell line that overexpresses the epidermal growth factor (EGF) receptor, we found that polyamines modulate ECF-me diated growth inhibition. The natural polyamine, putrescine, was the m ost effective, followed by diamines containing lower and higher methyl ene bridging between the amino groups. To understand the mechanism, we examined the effects of polyamines on ECF-mediated signal transductio n in A431 cells. All three polyamines partially inhibited ECF-receptor tyrosine kinase activity in a dose-dependent manner. The maximal inhi bition was 75% with spermidine. Polyamine effects were exerted 12-16 h after treatment, although HPLC analysis revealed uptake of polyamines within 1 h. Homologues of putrescine had no significant effect on tyr osine kinase activity, indicating structural specificity of naturally occurring polyamines in this process. Amine oxidase inhibitors did not alter spermidine and spermine-mediated effects, suggesting that the i nhibition of tyrosine kinase activity was not a consequence of the oxi dative metabolism of polyamines. Difluoromethylornithine, a specific i nhibitor of polyamine biosynthesis, did not affect ECF receptor tyrosi ne kinase activity. Polyamines also had no effect on ECF receptor leve ls or ECF-EGF receptor high-affinity binding, indicating that they are not competitive inhibitors of the ECF receptor tyrosine kinase. Our r esults suggest that polyamine action in A431 cells involves modulation of ECF receptor signal transduction pathways.