Azatyrosine inhibits the activation of c-Raf-1, c-Jun and AP1 but not the activation of Ras during signal transduction triggered by oncogenic c-ErbB-2.

Azatyrosine [L-beta-(5-hydroxy-2-pyridyl)alanine] is known to convert ras- or raf- transformed NIH3T3 cells to a normal phenotype. We report herein that azatyrosine also inhibits the growth of c-erbB-2-transformed cells and induces normal morphology. We attempted to identify the signal-transduction process triggered by oncogenic c-ErbB-2 that was inhibited by azatyrosine. Azatyrosine neither affected the phosphorylation of the introduced oncogenic c-ErbB-2 nor did it suppress activation of Ras induced by introduction of c-ErbB-2. Thus, azatyrosine did not inhibit the signal transduction from oncogenic c-ErbB-2 to Ras. However, azatyrosine inhibited increases in phosphorylation of c-Raf-1 and c-Jun induced by oncogenic c-ErbB-2. Furthermore, azatyrosine inhibited activation of the 12-O-tetradecanoylphorbol-13-acetate (TPA) response element in response to stimulation by oncogenic c-ErbB-2. These results suggest that azatyrosine acts downstream of Ras in signal transduction from oncogenic c-ErbB-2 to nuclear factors.