THE CAAX PEPTIDOMIMETIC COMPOUND B581 SPECIFICALLY BLOCKS FARNESYLATED, BUT NOT GERANYLGERANYLATED OR MYRISTYLATED, ONCOGENIC RAS SIGNALINGAND TRANSFORMATION

Recently developed CAAX peptidomimetic compounds have been shown to be potent and specific inhibitors of farnesyl protein transferase activi ty and to block the growth of Ras-transformed eels. However whether th is growth inhibitory action is specifically a consequence of blocking oncogenic Ras signaling has not been determined. To address this quest ion, we have utilized mutants of the normally farnesylated oncogenic R as protein (Ras-F) that are modified by alternative lipids, a geranylg eranyl isoprenoid (Ras-GG) or the fatty acid myristate (Myr-Ras), to d etermine the specificity of the CAAX peptidomimetic compound, B581. Li ke Ras-F, both Ras-GG and Myr-Ras are membrane-associated and transfor ming. Unexpectedly, MH 3T3 cells transformed by each of the three Ras mutants underwent morphological alteration to a less transformed, but not normal, morphology. However, B581 inhibited the ability of only Ra s-F-transformed cells, but not Ras-GG- or Myr-Ras(or Raf-) transformed cells, to grow in soft agar. Furthermore, although all three lipid-mo dified versions of Ras stimulated mitogen-activated protein kinase act ivation, and both Jun and Elk-1 transcriptional activity, B581 inhibit ed only farnesylated Ras activation of these three downstream componen ts of Ras signaling. Therefore, B581 prevents the growth of Ras-transf ormed cells by specifically antagonizing Ras-mediated signaling.