Dislogment and accelerated degradation of rats

Membrane anchorage of Ras oncoproteins, required for transforming activity, depends on their carboxy-terminal farnesylcysteine. We previously showed that S-trans,trans-farnesylthiosalicylic acid (FTS), a synthetic farnesylcysteine mimetic, inhibits growth of ErbB2- and Ras-transformed cells, but not of v-Raf-transformed cells, suggesting that FTS interferes specifically with Ras functions. Here we demonstrate that FTS disloges Ras from membranes of H-Ras-transformed (EJ) cells, facilitating its degradation and decreasing total cellular Ras. The disloged Ras that was transiently present in the cytosol was degraded relatively rapidly, causing a decrease of up to 80% in total cellular Ras. The half-life of Ras was 10 ± 4 h in FTS- treated EJ cells and 27 ± 4 h in controls. The dislogment of membrane Ras and decrease in total cellular Ras were dose-dependent: 50% of the effects occurred at 10-15 μM, comparable to concentrations (7-10 μM) required for 50% growth inhibition in EJ cells. Higher concentrations of FTS (25-50 μM) were required to dislodge Ras from Rat-1 cell membranes expressing normal Ras, suggesting some selectivity of FTS toward oncogenic Ras. Membrane localization of the prenylated Gβγ of heterotrimeric G proteins was not affected by FTS in EJ cells. an FTS-related compound, N-acetyl-S-farnesyl-L- cysteine, which does not inhibit EJ cell growth, did not affect Ras. FTS did not inhibit growth of Rat-1 cells transformed by N-myristylated H-Ras and did not reduced the total amount of this Ras isoform. The results suggest that FTS affects docking of Ras in the cell membrane in a rather specific manner, rendering the protein susceptible to proteolytic degradation.