H. Reuveni et al., Reversal of the Ras-induced transformed phenotype by HR12, a novel Ras farnesylation inhibitor, is mediated by the Mek/Erk pathway, J CELL BIOL, 151(6), 2000, pp. 1179-1192
We have used the selective farnesylation inhibitor HR12 [cysteine-N(methyl)
valine-N(cyclohexyl) glycine-methionine-O-methyl-ester] to study the role o
f oncogenic Ras in cytoskeletal reorganization in Ha-ras(V12)- transformed
Rat1 cells (Rat1/ras). Application of HR12 resulted in complete restoration
of the cytoskeleton and associated cell adhesions disrupted by oncogenic R
as. This included an increase in the number and size of focal adhesions, ac
companied by massive stress fiber formation and enhanced tyrosine phosphory
lation. Furthermore, HR12 induced assembly of adherens junctions and dramat
ically elevated the level of the junctional components, cadherin and beta -
catenin. HR12 was unable to restore the nontransformed phenotype in cells e
xpressing farnesylation-independent, myristylated Ras. Examination of the m
ain Ras-regulated signaling pathways revealed that HR12 induced a dose- and
time-dependent decline in Erk1&2 activation (t(1/2) similar to 6 h), which
correlated with the accumulation of nonfarnesylated oncogenic-Ras. Inhibit
ion of the Mek/Erk pathway in Rat1/ ras cells, using the Mek inhibitor, PD9
8059, resulted in complete cytoskeletal recovery, indistinguishable from th
at induced by HR12. Moreover, a constitutively active Mek mimicked the effe
ct of ras transformation in Rat1 cells, and prevented HR12-induced cytoskel
etal effects in Rat1/ras cells. No such effects were observed after treatme
nt of Rat1/ras cells with the phosphatidylinositol 3-kinase inhibitor LY294
002. These findings establish the Mek/Erk pathway as the dominant pathway i
nvolved in conferring the cytoskeletal and junctional manifestations of the
Ras-induced transformed phenotype.