Benzodiazepine peptidomimetic BZA-5B interrupts the MAP kinase activation pathway in H-Ras-transformed rat-1 cells, but not in untransformed cells

A benzodiazepine peptidomimetic, BZA-5B, inhibits farnesylation of H-Ras and normalizes the morphology of Rat-1 cells transformed with H-Ras(V12) at concentrations that do not affect the growth of untransformed Rat-1 cells. In the current experiments, we show that BZA-5B decreases the active forms of enzymes in the mitogen-activated protein (MAP) kinase signaling cascade, including Raf, MAP kinase kinase (MEK), and MAP kinase, in cells transformed with H-Ras(V12). BZA-5B had no effect on these enzymes in cells transformed with H-Ras(V12,L189), which is geranylgeranylated rather than farnesylated. In cells transformed with H-Ras(V12), BZA-5B reduced the activities of enzymes in the MAP kinase pathway at concentrations that only partially blocked farnesylation of H-Ras(V12), suggesting that nonfarnesylated H- Ras(V12) is a dominant inhibitor of the action of farnesylated H-Ras(V12) in the BZA-5B treated cells. In untransformed Rat-1 cells, BZA-5B did not inhibit MAP kinase activity nor did it prevent the acute activation triggered by epidermal growth factor, even though farnesylated endogenous H-Ras was no longer detectable. These data raise the possibility that untransformed cells contain a form of Ras (K-Ras or N-Ras) whose prenylation is not inhibited by BZA-5B, thus allowing them to resist the effects of BZA-5B.