Stimulation of the expression of rhoB contributes to the ability of azatyrosine to convert c-erbB-2-transformed cells to a normal morphology.

We have reported recently that azatyrosine inhibits the growth of ras-, raf-, or c-erbB-2 transformed NIH3T3 cells and converts the transformed cells to cells with normal morphology. We show in this study that treatment of c-evbB-2-transformed cells with azatyrosine restore the capacity for the formation of actin stress fibers, which is closely associated with the phenotype of normal cells. Azatyrosine also restored the expression of the rhoB gene, the product of which regulates the formation of actin stress fibers. To investigate the roll of expression of rhoB in the morphological reversion, c-erbB-2 transformed cells were transfected with a rhoB expression vector. The cells that overexpressed rhoB were flatter than the parental transformed cells and the formation of actin stress fibers was observed in these flatter cells. Furthermore, the growth rate of these cells was lower than that of parental cells, although the flatter cells were still able to grow anchorage-independently. These results suggest that expression of rhoB is involved in the conversion of c-erbB-2-transformed cells to a normal phenotype that is induced by azatyrosine, but such expression is insufficient by itself for complete reversion.