AZATYROSINE IS INCORPORATED INTO PROTEINS INSTEAD OF TYROSINE RESIDUES, WITH THE RESULTANT CONVERSION OF TRANSFORMED-CELLS TO CELLS WITH A NORMAL PHENOTYPE

We reported recently that azatyrosine inhibits the growth of c-Ha-ras, c-raf or c-erbB-2-transformed NIH3T3 cells and converts the transform ed cells to cells with a normal phenotype. To analyze the mode of acti on of azatyrosine, we examined the effects of azatyrosine on the synth esis of macromolecules. Azatyrosine had no obvious inhibitory effects on the synthesis of DNA, RNA and protein in c-erbB-2-transformed cells . Furthermore, azatyrosine inhibited cell growth but did not interrupt the cell cycle at any specific stage. Thus, the mode of action of aza tyrosine appeared to be different from that of typical anticancer drug s. Moreover, we found that azatyrosine was incorporated into proteins instead of tyrosine. The simultaneous presence of a high concentration of tyrosine inhibited the conversion to a normal phenotype of transfo rmed cells by azatyrosine. These results strongly suggest that incorpo ration of azatyrosine into proteins might convert the transformed cell s to cells with a normal phenotype. The analysis of azatyrosine-contai ning proteins by two-dimensional electrophoresis revealed that the mob ilities of some proteins differed from those of the corresponding tyro sine-containing proteins. An alteration in molecular structure of the proteins that include azatyrosine residues might be associated with th e ability of azatyrosine to convert transformed cells to cells with a normal phenotype.